USER’S HANDBOOK

A Guide to Using Roller Cone

Rock Bits in Mining

Table of Contents

Chapter 1 - Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Minerals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Rocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Drillability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Chapter 2 - Roller Cone Rock Bit Familiarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-18

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Circulating System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Hole Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Bearing Cooling and Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Chapter 3 - Bore Hole Economics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

When to take a bit out of service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Chapter 4 - Drill Bit Selection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Chapter 5 - Dull Bit Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Chapter 6 - How a Roller Cone Bit Drills Rock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Chapter 7 - Changing Nozzles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32, 33

Appendix A: IADC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

Appendix B: Bit Record Card . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Appendix C: Conversion Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Appendix D: Compressed Air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Appendix E: Rotary Shoulder Make-Up Torque. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Appendix F: Old Timer’s Drilling Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Geology

Any discussion about roller cone drilling should begin

with an overview of geology so that we have a better

understanding of why we must select different bit types

for differing conditions. It is fair to say that geological and

mechanical properties of rock are interrelated, and both

must be taken into consideration when choosing a bit and

when interpreting drilling performance. Rock character-

istics are determined primarily by origin, formation, and

mineral composition.

4

Figure 1

Sandstone

Quartzite

CorallineLimestone

Ocean Deposits

Clay / Shale

Igneous Intrusion

Rock Types

-Granite

-Diabase

-Basalt

Metamorphic

-Gneiss

-Amphibolite

-Marble

Magma or Glacial Deposits

Alluvial Deposits

Geologically speaking, the earth is in a constant state of

fl ux where both rocks and minerals are constantly be-

ing formed and altered. The Earth’s crust is made up

of three main rock classifi cations based on origin: igne-

ous, sedimentary, and metamorphic rocks. The above

schematic (fi gure 1) provides a pictorial of the rock and

mineral formation.

Figures 2 and 3 (below and next page) on the “rock cycle” illustrate the process by which rock is altered and

transformed.

5

Schematic illustration of mineral deposits in the earth’s crust

Seabed: calcite

Ore veins: lead sulphide, zinc sulphide, copper py-

rites, sulphur pyrites

Weathered clay-shales: china clay, bauxite

Weathered sandstone: quartz

Weathered ore veins: azurite, malachite, cuprite,

lead vitriol, zinc carbonate

River valleys: alluvial sediments (gold, platinum,

diamonds, tin ore, magnetite, titaniferous iron)

•

•

•

•

•

•

Figure 2

Volcanic rock: feldspar, quartz, olivine, hornblende,

magnetite mica

Metamorphic sandstone: quartz

Metamorphic limestone: calcite, dolomite

Metamorphic clay shales: granite, mica, feldspar

Contact zones: granite, hornblende, sulphides

•

•

•

•

•

Igneous

Magma is essentially a hot silicate melt (600 - 1200 Cel-

sius) and is the parent material of igneous rocks. Mag-

mas and the formation of igneous rocks can be observed

in volcanic regions.

Although igneous rocks can be formed within, on, or

close to the surface of the Earth’s crust, they are usually

formed within the crust. Igneous rocks that are formed

when magma cools and solidifi es within the crust are

classifi ed as intrusive (plutonic and hypabyssal). Since

the Earth’s temperature is greater at depth, the magma

cools slowly and allows for growth of large crystals, which

gives igneous rocks formed in these conditions a coarse

grain texture. These intrusive igneous rocks are later ex-

posed at the surface due to erosion or earth movements

such as uplifts caused by plate tectonics. When igneous

rocks are formed on or close to the earth’s surface, they

are called extrusive (volcanic) igneous rocks. Because

the magma is deposited where the ambient temperature

is cooler, the cooling rate is relatively fast and results in

the development of small crystals, or in some cases, no

crystal structure develops at all. This results in a fi ne

grain rock. Igneous rocks are subdivided by composition

into acidic, intermediate, basic (mafi c), and ultrabasic

(ultramafi c) rocks, depending on the amount of silica they

contain. Table 1 captures some of the more common

rocks for each subclassifi cation:

6

Minerals

All rocks are formed with an aggregate of minerals. The

proportion of each mineral in the rock, together with the

rock’s granular structure, texture, and origin serves as a

basis for geological classifi cation.

A mineral is homogeneous, meaning it is the same all

the way through; whereas rock is not homogeneous as it

is a mixture of different minerals. For instance, the rock

granite is comprised of three minerals: mica, feldspar,

and quartz. A mineral may be defi ned as an inorganic

substance that has consistent physical properties and a

fi xed chemical composition. With the exception of some

carbon forms, sulfur, and a few metals, all minerals are

chemical compounds, each containing two or more ele-

ments in fi xed proportion by weight. Some elements are

present in many minerals, the most common being oxy-

gen and silicon, while others, including most precious and

base metals, form an insignifi cant proportion of the rocks

within the earth’s crust.

Rocks

As mentioned earlier, the three (3) main rock classifi ca-

tions are igneous, sedimentary, and metamorphic and all

are classifi ed according to their origin. In this section, we

will discuss these three classifi cations and some of their

subclassifi cations.

Figure 3

NOTES:

Magma type refers to color of extrusive rocks (light to

dark) with increasing SiO2 % (silica).

The terms acidic and basic, when used in this context,

have NOTHING to do with pH.

This table does NOT contain all possible igneous rock

types; it is a general guide to help you equate SiO2 %

(silica) with common rock names.

Sedimentary

Sedimentation is the result of atmospheric and hydro-

spheric (air and water) interaction on the earth’s crust.

The processes that produce sedimentary rocks include:

weathering, erosion, transportation, deposition, and

lithifi cation. Igneous rocks remain relatively stable when

they remain in the ambient temperature and pressure

conditions from which they formed. However, when they

are removed from the environment from which they were

formed, they become unstable and are transformed by

exposure to air and water. This process of transforma-

tion is called weathering. Physical and chemical weath-

ering are the two categories of weathering recognized

by geologists. Silicates vary considerably in chemical

stability. Minerals that are stable under pressure, tem-

perature, H2O (water) and higher O

2 (oxygen) conditions

near the Earth’s surface are listed below (from most to

least stable):

SiO2 (wt.%) (silica) <45 45 - 52 52 - 57 57 - 63 63 - 68 >68

Compositional or

Chemical

Equivalent

Ultrabasic BasicBasic to

IntermediateIntermediate

Intermediate to

Acidic or Silicic

Acidic or

Silicic

Magma Type Ultramafi c Mafi cMafi c to

IntermediateIntermediate

Intermediate to

FelsicFelsic

Extrusive Rock Name Komatiite BasaltBasaltic

AndesiteAndesite Dacite Rhyolite

Intrusive Rock Name Peridotite Gabbro Diorite

Diorite or

Quartz

Diorite

Granodiorite Granite

Liquidus

Temperature

Mafi c Mineral Content

Water Content

Magnesium / Iron

Calcium Sodium or

Calcium Potassium

IGNEOUS COMPOSITIONAL NAMES AND MAGMA TYPES

7

Table 1

Iron Oxides, Aluminum Oxides (such as hematite iron

ore - Fe2O

3)

Quartz

Clay Minerals

Muscovite

Alkali Feldspar

Biotite

Amphiboles

Pyroxenes

Calcium-rich Plagioclase

Olivine

The weathering process creates sediments that are trans-

ported by wind, water, and glaciers which are eventually

deposited in low areas on dry land or under water. Sedi-

mentary rocks are then formed, lithifi ed by the burial/com-

paction, and cemented.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Sedimentary rocks can be subdivided into three main

groups according to whether they were formed mechani-

cally, from organic remains, or chemically. Although 95%

of the Earth’s crust is made up of igneous rocks, about

75% of its surface is covered with sedimentary rocks;

sandstone, limestone, or shale account for 95% of all

sedimentary rocks. Based on these numbers, it is easy

to see how important understanding sedimentary rock is

to the drilling process. There are two major classifi ca-

tions of sedimentary rocks, clastic and chemical-organic.

Clastic rocks are classifi ed according to grain size and

then by composition. Chemical precipitates are classi-

fi ed on the basis of composition with subdivisions based

on texture or other dominant features. Some common

clastic sedimentary rocks are: conglomerate, breccia,

quartz sandstone, and siltstone. Some common chemi-

cal precipitates are: cyrstalline limestone, oolitic lime-

stone, fossiliferous limestone, chalk, dolomite, chert, and

gypsum.

Metamorphic

Metamorphic rocks are rocks that were originally igneous,

sedimentary, or even metamorphic, Meta is the Greek

word for change and morph is the Greek word for form,

so a metamorphic rock is a rock that has changed form

(structurally and minerally). Most of the crust, below the

thin layer of sediments and sedimentary rock that cov-

ers most of the Earth’s surface, is comprised of igneous

rocks with most of the balance made of metamorphic

rocks. Rocks change form by three processes/forces:

Temperature, Pressure, and Chemical.

Temperature: To be classifi ed as a metamorphic rock,

the temperature that the rock is subjected to has to be

above 200 Celsius and below the temperature that the

rock liquifi es. If the rock turns to liquid, it is classifi ed

as magma, and therefore, is classifi ed as an igneous

rock once it has cooled and crystallized. Temperature

increases can be caused by layers of sediments being

buried deeper and deeper under the Earth’s surface. The

deeper they are buried, the hotter they become (estimat-

ed to increase in temperature about 25 degrees for every

kilometer in depth). The greater the depth, the greater

the pressure, and as the pressure increases, so does the

temperature. In addition, metamorphic rock is formed

when rocks are subjected to heat generated from two

tectonic plates sliding by each other or subduction (one

plate sliding over or under another plate) causing shear-

ing forces and the resultant heat generated from friction.

Furthermore, the heat that causes rock to change form

can be introduced via magma. There are two subcatego-

ries of thermal metamorphism:

Regional metamorphism: the large scale heating and

modifi cation of existing rock through the creation of

plutons (magma) at tectonic zones of subduction. It

involves large areas and large volumes of rocks.

Contact metamorphism: The small scale heating and

alteration of rock by way of localized igneous intru-

sion (for example, volcanic dykes or sills).

1.

2.

Pressure: There are three factors that cause increased

pressure which subsequently creates metamorphic rocks:

Weight generated from overlying sediments

Stresses caused by plates colliding in the process of

mountain building

Stresses caused by plates sliding past each other

When rocks change form because of pressure, scien-

tist call this process dynamic metamorphism. Dynamic

metamorphism does not result in chemical changes to

the mineral. Rather, it results in structural changes to the

rock. Metamorphic rock can be foliated or banded (the

alignment of minerals from being squeezed) or it can be

structureless (nonfoliated) except for evidences of defor-

mation of constituent mineral grains.

Chemical: Scientists call this process metasomatic metamorphism. When liquid gases permeate into the

bedrock (or are captured in the rock during formation)

and are heated, it can result in chemical replacement of

elements in the rock minerals, which is believed by scien-

tists to take place over a long period of time.

Metamorphic rocks are almost always harder than

sedimentary rocks. They are generally as hard as, and

sometimes harder than, igneous rocks. Because meta-

morphic rocks are typically formed by being subjected to

pressure, they are usually denser than most other rocks.

Table 2 on the next page is provided as an aid to identify-

ing and classifying metamorphic rocks.

Structure

Rocks can be further classifi ed according to their struc-

ture. For instance, if the mineral grains are mixed into

a homogenous mass, the rock is said to be massive.

Granite is an example of a massive rock. When the min-

eral grains in rock are arranged in layers, they are called

stratifi ed rocks.

1.

2.

3.

8

Drillability:

The ability to drill rock is dependent on many things. As

discussed in the “Mineral and Rock Types” section, rocks

are made up of several different mineral constituents;

they vary in grain sizes and silica content and have dif-

ferent structures. All of these attributes create signifi cant

variability in drillability. The variability is not only evident

between rock types, it is also evident within given rock

types. In this section, we will discuss, on a macro level,

the rock characteristics that have the greatest effect on

drillability and bit wear. In addition, we will briefl y discuss

the different measurement methods used to classify rock

strength and hardness. The one thing we will not do is

provide you with a formula for predicting ROP (rate of

penetration). The subject of drillability is far too complex

to relegate to a simple formula. Any attempt to do so will

ultimately result in an erroneous conclusion when com-

pared to actual drill bit performance.

Grain Size

A coarse grained rock is easier to drill and causes less

wear than a fi ne grained rock. A rock with similar mineral

content can have a variety of grain sizes, which is depen-

dent on how rapidly they cool, whether or not they are

exposed to pressure, and if so, how much. Let’s take two

examples: Quartz and Granite. The grain size in quartz

can range from fi ne grained (0.5 to 1.0 mm) to dense

grained (up to 0.05mm). The grain size of granite can

range from coarse grained (>2.0mm) to medium grained

(1.0 to 2.0mm) to fi ne grained (<1.0mm) to very fi ne or

glassy (grains cannot be seen with the naked eye).

Hardness

Quartz is the most common mineral found on the Earth

and can be found in nearly every rock type. Quartz (Sili-

con Dioxide) is very hard and abrasive. Therefore, rocks

with high quartz content are diffi cult to drill and cause

high rates of wear to the TCI (Tungsten Carbide Inserts)

on the drill bit. Conversely, rock that is high in calcite (low

in quartz) is relatively easy to drill by comparison, and

results in less wear to the TCI and the bit.

TEXTUREGRAIN

SIZECOMPOSITION

TYPE OF

METAMORPHISMCOMMENTS ROCK NAME

FO

LIA

TE

D

MIN

ER

AL

AL

IGN

ME

NT FINE

MIC

ARegional

(Heat and pressure

increase with depth)

Low-grade

metamorphism

of shale

Slate

FINE TO

MEDIUM

QU

AR

TZ

FE

LD

SPA

R

AM

PH

IBO

LE

GA

RN

ET

Foliated surfaces

shiny from mi-

croscopic mica

crystals

Phylite

BA

ND

ING

MEDIUM

TO

COARSE

Platy mica

crystals visible

from metamor-

phism of clay or

feldspars

Schist

PY

RO

XE

NE

High-grade

metamorphism;

some mica

changed to feld-

spar, segregated

by mineral into

bands

Gneiss

NO

NF

OL

IAT

ED

FINE VARIABLE Contact (Heat)

Various rocks

changed by heat

from nearby

magmalava

Hornfeis

FINE TO

COARSE

QUARTZ

Regional or Contact

Metamorphism

of quartz sand-

stone

Quartzite

CALCITE AND/OR DOLOMITE

Metamorphism

of limestone to

dolostone

Marble

COARSEVARIOUS MINERALS IN

PARTICLES AND MATRIX

Pebbles may

be distorted or

stretched

Metaconglomerate

9

Table 2

Measurements of Hardness and Strength

There are several ways to measure hardness and

strength of rock and hardness of minerals.

Mohs’ Scale

The standard for measuring mineral hardness is the

Mohs scale. The Mohs scale was devised by Friedrich

Mohs in 1812 and has been a valuable aid to identifying

minerals ever since. This scale is strictly a relative scale

that uses the following minerals that are ranked from 1 to

10 (softest to hardest):

Talc

Gypsum

Calcite

Fluorite

Apatite

Feldspar

Quartz

Topaz

Corundum

Diamond

The scale is used by testing your unknown mineral

against one of these standard minerals. Whichever one

scratches the other is harder, and if both scratch each

other, they are both the same hardness. Because the

Mohs’ scale is not a precise absolute scale, the Mohs’

scale can use half-numbers. For instance, the hardness

of dolomite, which scratches calcite but not fl uorite, has

a Mohs’ hardness of 3 1/2 or 3.5. A knife or a piece of

glass has a hardness of 6.5, so if the unknown mineral

does not scratch these items, you know it is not as hard.

A hardened metal fi le has a Mohs’ scale hardness of

6.5, so if the unknown mineral marks the fi le, we know

that it is harder than 6.5. In terms of absolute hardness,

diamond (hardness 10) is actually four (4) times harder

than corundum (hardness 9) and six (6) times harder than

topaz (hardness 8).

As we discussed in the geology section of this manual,

rocks are made up of two or more minerals, whereas min-

erals are homogeneous. Because we are drilling rock,

the Mohs’ scale is not a good indicator of rock drillability.

Compressive Strength / Young’s Modulus

Compressive strength is a measurement of maximum

compressive stress that a volume of rock sample can

be subjected to before failure. The Young’s modulus is

a measurement of the elasticity of rock. It is the ratio of

stress to strain (stress/strain) a rock sample can with-

stand before it yields (ductile deformation). The different

compressive strength rock tests are uni-axial, unconfi ned

or confi ned, or tri-axial. As the name implies, the con-

fi ned compressive strength test places a rock sample in

a cell that subjects the sample to both confi ning pressure

and axial pressure. The amount of confi ning pressure

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

and strain as it relates to UCS:

Many people use compressive strength as a measure-

ment to indicate rock drillability. It is only an indicator

and should not be used on its own because the strength

of rock depends on physical and chemical composition,

as well as other factors such as mineralogy, porosity,

cementation, degree of weathering, grain size, elastic-

ity, density, lamination/foliation, and dip. Compressive

strength and Young’s Modulus are nothing more than a

barometer of rock drillability. Again, this is a volumetric

test of rock strength and does not necessarily represent

the conditions that the drill bit cutting teeth are exposed

Alternative Method of Determining Drillability:

As mentioned previously, Mohs’ scale is a relative

scale for measuring mineral hardness and compressive

strength measurements are volumetric tests. Neither one

of these tests represent what a drill bit typically confronts.

When drilling, a rock bit is trying to overcome surface

strength not volumetric strength. To quote the Sandvik

Tamrock “Rock Excavation Handbook for civil engineer-

ing”:

“most mechanical tools (including rock bits) break rock by indenting the surface. Rock crushing, macro-fracture propagation and chip formation occur under a loaded indention tool,” and goes on to say, “. . . the indention process is a combination of the following failure modes:

Initial tool indention of rock surface with crushing and compacting of the rock material underneath the tool tipDevelopment of macro-fracture propagation patterns resulting in rock chip formation, chip loosening and stress releaseMultiple pass cutting if the chip loosening does not occur for every tool pass or load cycleEffi cient chip and fi nes removal so as to avoid recut-ting and recompacting of broken material in the tool path.”

•

•

•

•

10

can be varied from low to beyond the maximum anticipat-

ed in-situ pressure. Chart 1 characterizes typical stress

Chart 1

“Rock cutting or drilling is therefore the art of maximizing chip formation and rock material removal as cuttings. It is not the development of extensive macro-fracture propa-gation patterns under the tool. The infl uence of rock mass discontinuities on rock mass cuttability is generally on a larger scale than on individual tools. It typically af-fects several tools simultaneously and the cutting perfor-mance of the cutter head as a whole.”

When considering the process described above, a better

indicator of drillability would be to measure rock surface

hardness. One possible test that may be a better predic-

tor of drillability would be the Vickers hardness test modi-

fi ed to measure rock hardness. VHNR (Vickers Hardness

Number Rock), or the “surface hardness” of the rock,

is an aggregate value based on the weighted hardness

values of its mineral constituents.

Table 3, taken from the Sandvik “Rock Excavation Hand-

book,” captures some mean values for the Vickers hard-

ness number rock test for a selection of common rocks:

11

Table 2.4-3Vickers Hardness Number Rock (VHNR) for some com-

mon rock types

Rock Type VHNR Rock Type VHNR

Amphibolite 500. . . 750 Marble 125. . . 250

Andesite 550. . . 775 Metadiabase 500. . . 750

Anortosite 600. . . 800 Metagabbro 450. . . 775

Basalt 450. . . 750 Micagneiss 500. . . 825

Black shale 300. . . 525 Micaschist 375. . . 750

Chromite 400. . . 610 Nickel ores 300. . . 550

Copper ores 350. . . 775 Norite 575. . . 725

Diabase/do-

lorite525. . . 825 Porphyrite 550. . . 850

Diorite 525. . . 775 Pyrite ores 500. . . 1450

Epidotite 800. . . 850 Phyllite 400. . . 700

Gabbro 525. . . 775 Quartzite 900. . . 1060

Gneiss 650. . . 925 Rhyolite 775. . . 925

Granite/Granite

gneiss725. . .925 Sandstone 550. . . 1060

Granodiorite 725. . .925 Serpentinite 100. . . 300

Granulite/lep-

tite725. . .925

Shale and

silstone200. . . 750

Green schist 625. . .750 Skarn 450. . . 750

Greenstone 525. . .625 Sphalite ores 200. . . 850

Hornfels 600. . .825 Tonalite 725. . . 925

Limestone 125. . .350 Tuffi te 150. . . 850

Table 3

Table 4

Comparison between MPA, Psi, and Protodjakonov

Psi Mpa Protodjakonov Psi Mpa Protodjakonov

1,000 7 1 28,000 193 15

2,000 14 2 29,000 200 16

3,000 21 3 30,000 207 16

4,000 28 4 31,000 214 16

5,000 34 4 32,000 221 17

6,000 41 5 33,000 228 17

7,000 48 6 34,000 234 17

8,000 55 6 35,000 241 18

9,000 62 7 36,000 248 18

10,000 69 7 37,000 255 18

11,000 76 8 38,000 262 19

12,000 83 8 39,000 269 19

13,000 90 9 40,000 276 19

14,000 97 9 41,000 283 20

15,000 103 10 42,000 290 20

16,000 110 10 43,000 297 20

17,000 117 11 44,000 303 *21

18,000 124 11 45,000 310 *21

19,000 131 12 46,000 317 *21

20,000 138 12 47,000 324 *22

21,000 145 12 48,000 331 *22

22,000 152 13 49,000 338 *22

23,000 159 13 50,000 345 *23

24,000 166 14 51,000 352 *23

25,000 172 14 52,000 359 *23

26,000 179 14 53,000 366 *24

27,000 186 15

These numbers can be used as a guide, but until VHNR

measurement or another one like it becomes an industry

standard, we will need to use the VHNR and the previ-

ously mentioned measurements along with historical

data as our guide to rock drillability. The following table

compares MPA, Protodjakonov Scale, and PSI. Please

keep in mind that the Protodjakonov Scale only goes to

20. In the table below, the fi gures from 21 to 24 have

been mathematically calculated.

Values with an astrick (*) have been

mathematically calculated.

The drillability of a certain rock type depends largely on factors such as mineral content, grain size, and structure.

Here, we have compared the drillability and wear factors associated with a number of common rock types.

12

Limestone and shale are often easy to drill and non-abrasive, giving high penetration and little wear. Sandstone, on

the other hand (also a sedimentary rock type), causes heavy wear, owing to its quartz content.

Photo 1 Photo 2 Photo 3

Photo 6Photo 5Photo 4

Granite Basalt Diorite

Limestone Shale Sandstone

Basalt and diorite are two other types of igneous rock. They often cause

less wear to the drill steel and bit and can be easier to drill.

Comparisons are made with ordinary

granite, which we consider to have

“normal” wear and drillability charac-

teristics.

As the name implies, quartzite

contains a great deal of quartz, and

therefore, causes heavy wear.

13

Photo 9Photo 7 Photo 8 QuartziteAmphibolite Gneiss

Seldom does one rock type exist at a

specifi c location. This makes it diffi cult to

predict whether the rock will be easy or dif-

fi cult to drill. In reality, the exact answer to

the question is known only after drilling has

taken place.

Limestone is normally easy to drill and

causes little wear. However, if it looks like

this, it can be diffi cult to drill. In soft and

friable rock, one always runs the parallel

risks of hole deviation, jamming of the bit,

and even getting stuck in the hole. In such

conditions careful drilling is essential.

Photo 10 Photo 11

Above:

Since metamorphous (transformed) rock can be transformed to different de-

grees, its drillability and wear characteristics vary widely. Take for example

gneiss and amphibolite, both of which are comparatively diffi cult to drill. Gneiss

causes heavy wear, owing to its high quartz content, whereas amphibolite is

less abrasive. However, since it is fi ne-grained, amphibolite is more diffi cult to

drill.

bit leg

shirttail

protection

heel rowgage

row

cone

air tube

nozzle

Main air to bearing

passage

ball plug

outer roller

bearing

ball bearing

secondary axial thrust bearing

inner roller bearing

primary axial thrust button

Roller Cone Rock Bit Introduction

A roller bit consists of 3 main component groups: the

cones (or cutters), the bearings, and the bit body (or leg).

The cones make up the actual tool that breaks up the

rock. All tungsten carbide insert bits (Fig. 4a) have tung-

sten carbide inserts pressed into them. These inserts

are arranged in a pattern of rows which allow the inserts

to effi ciently cut the rock. Milled tooth bits (Fig. 4b) have

cones that have teeth milled into them. The milled teeth

cut the rock. Generally speaking, milled tooth bits are

used for very soft formations and tungsten carbide bits

are used for most other formations. Figure 4 illustrates

the common nomenclature.

All Sandvik Smith roller bits are designed to give the

highest possible penetration rate and long service life. In

order to achieve both high cutting rates and longevity, the

correct bit must be selected.

A typical roller cone bit for soft-rock is equipped with long,

sparsely placed, sharp teeth (fi gure 5). The soft-rock bit

is also designed with a skidding action so that the teeth

14

Rock Bit Nomenclature

Figure 4

Tungsten Carbide Insert

(TCI) BitMilled Tooth Bit

Figure 6 - Least

aggressive cutting

structure for hard rock

formations

Figure 5 - Most

aggressive cutting

structure for soft rock

formations

perform a scraping action when in contact with the bottom

of the hole. This means that the rock is broken up by

means of both crushing and scraping (or “digging”).

Typically, a roller cone bit for hard-rock is equipped with

short, densely placed blunt or even spherical teeth (fi gure

6. The hard-rock bit is designed to break up the rock by

means of crushing only. The skidding effect is kept to a

minimum in order to reduce wear to the teeth. This kind

of bit is generally used with a higher feed force compared

to the soft-rock bit. For this reason, the bearings in the

hard-rock bit are usually more robust than those in soft-

rock bits. The concept of a soft formation bit cutting by

a skidding action and a hard formation bit cutting by a

crushing action is best illustrated in the following con-

tinuum (Figure 7):

Figure 4a

Figure 4b

Milled Tooth Bit Medium TCI

Soft TCI Bit Hard TCI Bit

100%

Skidding

100%

Crushing

Figure 7

Most mining bits used today utilize Tungsten Carbide

Inserts (TCI) of various shapes to cut the rock. Tungsten

carbide inserts are comprised of Tungsten and Cobalt;

the wear resistance and toughness of an insert is deter-

mined by the grain size of the tungsten and the % cobalt.

An insert comprised of a certain grain structure and %

cobalt is classifi ed as a grade. Because different grades

have different characteristics, insert grade selection is

another important criterion for selecting the right bit. As

in selecting a drill bit, selecting the correct carbide shape

and grade is often times a compromise between wear re-

sistance and toughness. This is best illustrated in fi gure

8. Your bit representative can assist you in selecting the

best grade of insert for your application.

In either confi guration, most of the radial forces are car-

ried by the large roller bearing, with some help from the

small inner roller bearing, or friction bearing.

There are two axial bearing surfaces in a rock bit. The

primary axial bearing is the thrust button system, which is

located in the pilot pin of the leg journal, and the mating

surface located in the cone bore. The secondary axial

bearing is the contact area between the cone and journal

thrust fl ange. As the primary thrust bearing wears, the

secondary axial bearing engages to help share the load.

Circulating System

The purpose of the circulation system (sometimes re-

ferred to as “Flushing”) is to clean the hole by transport-

ing the cuttings from the bottom of the hole to the surface

and to effectively cool and clean the drill bit bearings.

The two most common methods for cleaning the hole of

drill cuttings are air and mud. Air, because it is a gas and

light weight by nature, requires high volume and velocity

to transport the cuttings out of the hole. Mud, because it

is dense, requires volume and enough bottom hole pres-

sure to lift the cuttings out of the hole. For the purpose of

this manual, we are only going to discuss air circulation.

The following section describes the guidelines for air

circulation systems with respect to hole cleaning, bearing

cleaning, and nozzle selection.

Hole Cleaning

Cleaning the hole requires suffi cient air velocity to lift

the cuttings out of the hole (Figures 11 and 12 - next two

pages). Both volume, (spoken of as CFM - Cubic Feet

per Minute) and pressure are regulated by increasing

or decreasing the drill bit nozzle sizes. The compressor

rating for pressure and CFM can usually be found on the

data plate that is affi xed to the compressor.

15

Figure 8

From left to right: Gage, Conical, Chisel, Semi-round

top

Radial forces

5-5/6

5-5/7

Axial forces

Radial forces

Axial forces

Figure 9

Figure

10

To achieve long life, the bearings must be designed to

withstand the high axial and radial forces that are used

in the drilling process. Roller cone bits use fi ve different

bearings that work together as a system. The balanc-

ing of these bearings is one of the most critical factors

that a designer must consider when developing a new bit

design.

In Sandvik Smith open and air cooled bearing roller bits,

two bearing confi gurations are used: the RBR (roller-ball-

roller) (Fig. 9) in larger drill bits, and the RBF (roller-ball-

friction) (Fig. 10) in smaller drill bits.

To calculate the volume rate of air fl ow (measured in

m3/min {cfm}), one of the following two formulas can be

used:

Formula 1 - Metric units

Q = V(DH2 - DP2)47m3/min

Formula 2 = English units

Q = V(DH2 -DP2)cfm

183.33

Where:

V = Desired air velocity (meters/second or feet/minute)

DH = Hole diameter (bit diameter)

DP = Pipe diameter

Q = Air fl ow

AO = Actual output (either cfm or m3/min)

183.3 = Constant for English units

47 = Constant for Metric units

16

d

P = W o rk in g P re s s u re

Q = R a te d F lo wÊ

Please remember that the volume of air that a compres-

sor generates is reduced if the compressor is worn or if it

is working at high elevation. Please see the appendix for

more information on the effects that altitude and tem-

perature have on compressed air. Consult your drill bit

representative for more information on this subject.Air volume to clean the hole is referred to as BV (Bailing

Velocity) and has a direct impact on penetration rates and

bit life. Generally speaking, the higher the bailing veloc-

ity, the better the hole is cleaned and the higher the pen-

etration rates and bit life. Bailing velocity is determined

by the relationship between the annulus (hole diameter

less the drill pipe diameter) and fl ow rate (m3/min or cfm)

that the compressor generates. As a rule of thumb, pipe

diameter should be about 80% of the bit diamter. The

formula used to calculate BV is as follows:

Example:

V = 35 m/s (7000 ft/min)

DH = 251 mm = 0.251 m or 9 7/8” = 09.875

DP = 197 mm = 0.197 m or 7 3/4” = 07.750

Stated in metric:

Q = 35 x (0.2512 - 0.1972) x 47 = 40 m3/min

or stated in English units:

Q = 7000 x (9.8752 - 7.7502) = 1430 cfm

183.33

The following formula can be used to calculate the cur-

rent bailing velocity:

Formula 1 - English units:

V = 183.3 x AO

DH2 - DP2

Formula 2 - Metric units:

V = Q(m3/m)

47(DH2 - DP2)

Rocks have different mineral content, densities, and

structures resulting in differences in chip weights and

sizes. As a result, a different BV may be required for the

differing geological conditions. Determining the optimum

BV can be further complicated by the presence of natural-

ly occuring water that adds to the density of the cuttings.

The following recommendations are considered to be the

minimum standards for BV. However, drilling tests, dull

bit conditions, or previous experiences in the local condi-

tions may be a better indicator of the optimum BV for your

operation.

Fine drill cutting and light weight minerals require a

BV of approximately V = 25 m/s (5,000 ft/min)

Coarse drill cuttings and heavy minerals require a

fl ushing velocity of approximately V = 35 m/s (7,000

ft/min)

Coarse drill cuttings with high water content may

require a BV of up to V = 50 m/s (10,000 ft/min)

Sometimes fi ne drill cuttings are mistakenly attributed

to geological conditions, when if fact, they are actually

a symptom of poor bailing velocity. Poor bailing veloc-

ity can cause cuttings to recirculate in the hole until they

become fi ne enough to be carried out of the hole.

1.

2.

3.

Figure 11 (Air

Flow)

All Sandvik Smith roller cone bits larger than 6 1/4” use

the jet nozzle system. Most bits under 6” use a full center

hole. A jet nozzle circulation system has jets that are

an extension of the bit body and are located near the

outside diameter of the bit body and positioned between

the cones. The jet nozzle system uses easy to remove

orifi ces so that the circulation system maintains proper

backpressures. Sandvik Smith nozzles are retained in

one of two ways: Spring pin or Nail-in nozzle systems

(see page 31 and 32).

In addition, most 6 3/4” and larger air bearing bits are

equipped with BFV’s (back fl ow valves) (Fig. 15). BFV’s

are used as a check value to prevent water and cuttings,

that are suspended in the annulas, from entering the bit

when the bit air is turned off (Fig. 12).

5-5/17

5-5/95-5/11

17

Figure 13 Figure 14

Figure 15

Bearing Cooling and Cleaning

Cooling and cleaning the bearing requires back pres-

sure to force air through the bearing and to pressurize

the bearing cavity. The pressurization of the bearing

cavity acts to prevent cuttings from entering the bearing.

Drill cuttings and other foreign debris will reduce bearing

life. In addition, air is used to cool the bearings. This

is accomplished by the transfer of heat from the bear-

ing to the compressed air. In essence, the air travels

through the air tube, into the bearing cavity, and out of

the air exhaust slot that is located between the cone and

the leg (the air tube is designed to fi lter out debris that

could, if it entered the bearing cavity, restrict air fl ow and

cause the bearing to overheat and fail prematurly). As

the air travels through the bearing cavity, it picks up the

heat generated in the bearing and carries the heat to the

annulus of the hole. Air is forced through the bearings

by creating pressure inside the bit. As mentioned earlier,

the amount of internal pressure is regulated by the nozzle

size. Increase the size of the nozzle and pressure will be

reduced. Conversely, if the nozzle size is decreased, the

pressure inside the bit will increase. A limited amount of

air can fl ow through the bearings; therefore, we recom-

mend that the internal bit pressure be set at between 30

and 36 psi (2.1 to 2.5 bar).

Drill bits have to be ported so that the drilling fl uid can exit

the bit to clean the hole bottom and bail the cuttings out

of the hole. Roller cone bits are typically ported with one

of two confi gurations, a center hole (Fig. 13) or three jet

nozzles (Fig. 14). Both confi gurations direct the bailing

media to the hole bottom.

Figure 12

Bore Hole Economics

An economic evaluation is the best means to determine

the best bit for your operation.

The two most common ways to measure drilling cost are

PDC (Partial Drilling Cost) and TDC (Total Drilling Cost).

Partial Drilling Cost is the bit purchase price divided by

the distance it drills. PDC expressed as a formula:

PDC = Purchase Price

Distance drilled (ft or mtrs)

TDC expands on PDC by including productivity in the

equation. TDC includes bit cost, drill rig hourly rate, feet

or meters per hour and distance drilled. The TDC for-

mula is commonly expressed in one of the two following

equations:

TDC = Bit Cost + [(Hourly rate)(Hours)]

Feet (meters) drilled

or

Bit Cost + Hourly Rig Rate

Feet (mtrs) drilled Rate of Penetration (ROP)

If you are not drill constrained, PDC is probaby the best

way to measure bit performance. However, if you are

drill constrained and are willing to manage your drill fl eet

based on productivity, TDC could be a good measure to

use. Let’s look at a couple of hypothetical examples:

Mine has 5 drills and the following bit statisitcs (Table 4):

Bit Type A Bit Type B

Bit Price $3,000.00 $3,600.00

Meters (feet) 2,000 2,100

Hours 100 100

ROP 20/hour 21/hour

Hourly Drill rate/hour $200.00 $200.00

Partial Drilling Costs: $1.50 $1.71

Total Drilling Costs: $11.50 $11.24

As demonstrated in the above statistics, bit type B’s

purchase price is 20% higher and it penetrated 5% faster

than bit type A and drills at a lower TDC, but at a higher

PDC. So, what is the best bit to use? To determine this,

you must answer the following questions:

Is drilling a constrained resource?

Can I manage the drill fl eet to take advantage of the

reduction in TDC?

Is the TDC savings merely a paper savings?

Can I increase ROP enough to remove a drill from

service?

•

•

•

•

When to take a bit out of service:

There is only one reason to take a bit out of service and

that is when the bit is no longer economical to use. This

usually happens when a bearing locks up or when the

cutting structure fails. In either one of these conditions,

it is no longer economical to use the bit because it quits

If drilling is not a constraining resource, if the increase in

pentration does not result in the retiring of a drill or does

not forestall the purchase of a new drill, or if the savings

is only on paper, a 5% increase in productivity may not

have a signifi cant economic impact on drilling costs.

Is there a better way to measure and compare perfor-

mance? For reasons mentioned above, we propose that

a modifi ed burden rate may be the best measurement.

In fact, some cost accountants have suggested that the

TDC measurement method is an appropriate method

to use for AFE’s (Authorizations for Expenditure) when

justifying the purchasing of a new drill, but it’s not a good

method for paying for and comparing drill bits. This is be-

cause the bit only has a limited impact on drilling produc-

tivity. Management, maintenance, and policies have a

far greater impact on productivity than drill bits. Because

of the aforementioned, a better way to measure perfor-

mance is by using a MTDC (Modifi ed Total Drilling Cost).

The MTDC uses a drill operating rate per hour that only

includes labor, maintenance, and fuel. It excludes depre-

ciation, overhead, etc. The MTDC formula is expressed

as follows:

MTDC = Bit Cost + [(Mod. hourly rate)(Hours)]

Feet (meters) drilled

or

Bit Cost + Mod. houry rig rate

Feet (meters) drilled Rate of Penetration (ROP)

Now let’s apply the MTDC to the hypothetical example

detailed above (Table 5):

Bit Type A Bit Type B

Bit Price $3.000.00 $3,600.00

Meters (feet) 2,000 2,100

Hours 100 100

ROP 20/hour 21/hour

Mod Hrly Drill Rate/Hour $75.00 $75.00

Partial Drilling Costs: $1.50 $1.71

Total Drilling Costs: $5.25 $5.29

In the above example, Bit Type A is the lowest cost bit to

use, where as in the previous example, Bit Type B was

the least expensive bit to use. The circumstances at the

mine will dictate what economic evaluation method you

need to use.

Table 5

Table 4

18

Unless a bit quits drilling, the answer to when to pull a bit

out of service depends on what measurement you use,

whether or not your drill resources are constrained, and if

the change in productivity is manageable.

drilling or is extremely slow. There is a less subtle reason

for taking a bit out of service - the gradual wearing of

the cutting structure that causes a gradual reduction in

penetration rates. As demonstrated in Chart 2, a reduc-

tion in penetration rate eventually results in an increase in

both TDC and MTDC. However, when using a MTDC the

impact of lower penetration rates is not a consequence

until later in its life. When comparing TDC and MTDC,

you will note that PDC never increases.

Chart 2

Chart 3

Chart 3 is the same

bit and performance

data as Chart 2

except that we have

used the MTDC

formula:

19

20

Drill Bit Selection

Choosing the correct drill bit is of fundamental importance

to successful and economical drilling. Important factors

to consider include the surface strength, compressive

strength, abrasiveness, massiveness and homogeneity of

the rock, the desired penetration rate, the capabilities and

characteristics of the drill rig, and previous drilling experi-

ence at the mine (see page 37 - Mining Bit Records).

Sandvik Smith makes a wide range of drill bits that meet

most requirements. The range includes both TCI (Tung-

sten Carbide Insert) bits and milled tooth bits.

Rock Hardness / Strength

The fi rst step in selecting the correct bit for your operation

is to know the rock strength and hardness so that you

can select the bits that best match these characteristics.

Selecting a bit based solely on rock hardness is often

diffi cult since the working ranges of bits overlap. With

the help of your Sandvik Smith representative, you will be

able to choose the bits that have the greatest potential to

lower your drilling costs.

Abrasion

The next consideration is determining the abrasiveness of

the rock. However, selecting an abrasion resistant hard

formation bit, just to be safe, is often a mistake because

it could limit both penetration rates and bit life. There

is an old saying, “drill with a hard formation bit and the

formation will drill hard.” To drill effi ciently and economi-

cally, we need to match the correct bit type to the forma-

tion being drilled. An abrasive fromation will require a

bit equipped with abrassion resistant carbide grades

and shapes. Therefore, a very abrasive formation may

require a slightly harder formation bit than a non-abrasive

formation. This is because a harder formation bit gener-

ally has insert shapes that are more condusive to this

type of formation.

Homogeneity and Massiveness of rock

When selecting the correct bit for the drilling operation,

we must take into consideration homogeneity and mas-

siveness. If a rock is not homogeneous, a tougher bit

may be required than if you were drilling a massive and

homogeneous rock. In addition, the use of a tougher bit

may be required if you are drilling through highly fractured

rock or deep collars.

History as a guide

If roller cone drilling has been conducted at the mine

before, a good place to start is by examining the historical

performance data to identify the top performing product

(manufacturer, brand, type, IADC code (see page 36),

and possibly the manufacturer’s part number). This

information will aid you in selecting the best product

to benchmark and will aid the drill bit manufacturers in

selecting comparable bits. If there is no historical infor-

mation available, please provide your bit supplier with the

following geological data:

Rock strength

Abrasiveness

Homogeneity

Rock type(s) to be drilled

This information is necessary for them to select the best

bit(s) for your application.

After selecting the best bits for your application and drill-

ing commences, it is important not to overdrill the bit. It is

recommended that no more than 90% of the insert exten-

sion be penetrated into the rock being drilled.

One method that you can use to determine if you are

overdrilling is to measure the millimeters per cone

revolution (or inches per cone revolution). The following

formula can be used to make this calculation:

MM/Rev = ROP X 1000

RPM x 60

or: Penetration rate times 1000 divided by RPM times

60.

Where:

MM = Millimeter

REV = Revolution of drill pipe

ROP = Rate of Penetration in m/hr

RPM = Rev Per Minute drill pipe

English units:

IN/Rev = ROP x 12

RPM x 60

Where:

IN = Inches

REV = Revolution of drill pipe

ROP = Rate of Penetration in ft/hr

RPM = Rev Per Minute drill pipe

If the resultant of the above formula is greater than 90%

of the insert extension times 1.2 (cone revolutions per

one drill pipe revolution), then you are overdrilling the bit.

Stated as a formula: IN/REV > (90% of insert exten-

sion)(1.2).

Final Considerations

After we have narrowed down the bit choices, the best

way to determine the most economical bit for your

operation is to conduct a drill test under controlled and

measureable conditions. Because drilling conditions

vary greatly, even over short distances, it is important to

collect information and evaluate these differences when

making your selection. Choosing a bit is often a compro-

mise, but it is critical to your drilling performance.

•

•

•

•

21

Dull Bit Analysis

In this section, we will look at the most common causes of premature drill bit failure. The reason that we study dull bits

is to improve the effi ciency and economics of the drilling operation and to aid in product development.

Dull bits are indicative of:

Drill conditions

Driller competency

Compressor and compressor line condition

Operating parameters (if they are suited for the drilling conditions)

Drill string conditions

By studying dull bits, you can save money.

All bits fail. So, the questions we have to ask are: why did the bit fail and has it failed prematurely? Usually, drill bits

fail prematurely from mis-application; however, they can also fail because they are designed or manufactured improp-

erly. Accordingly, we classify failures in the following categories: “As Applied,” “As Designed,” and “As Manufactured.”

In this section of the “User’s Manual,” we are going to study premature “As Applied” failures. This section is not

intended to cover all the “As Applied” failures, just some of the most common ones. We will use the symptom > cause

> remedy methodology for evaluating dull bits. By using this methodology, we can identify root cause and then imple-

ment the appropriate remedy.

•

•

•

•

•

Broken Teeth - Inner (BT):

Symptom:

Tungsten Carbide inserts break fl ush to cone steel in the

inner rows.

Cause:

Too high of WOB

Broken ground formation either while drilling or collar-

ing the hole

Wrong TCI grade inserts

Remedy:

Review drilling practice and reduce WOB

Reduce WOB and slow down rotation speed

Select bit that has a tougher insert grade

•

•

•

•

•

•

Tracking (TR) - Photo 13:

Symptom:

Inserts are worn predominately on one side. This results

in bit vibration and poor cutting effi ciency.

Cause:

Usually caused by improper WOB (weight on bit) and

rotation speed. This results in inserts striking the

sidewalls of craters cut by another insert.

Improper bit selection

Remedy:

Adjust WOB and rotation so that proper spall weights

and dwell times are achieved

Select bit better suited for the application or bit with

skip pitch changes.

•

•

•

•

Photo 12

Photo 13

22

Broken Teeth - Gage (BT) - Photo 12:

Symptom:

Broken inserts on gage

Cause:

Too high of rotation speed

Broken ground formation either while drilling or collar-

ing the hole

Improper bit selection due to changing conditions

Remedy:

Reduce rotary speed

Drill these intervals with reduced weight and rotation

speeds

Select bit that is more appropirate for dirlling condi-

tionss

•

•

•

•

•

•

Photo 14

Cone Interference (CI) - Photo 16

Symptom:

Bearing wear results in the teeth (inserts) from one cone

to interfere (hit) another cone. Often results in intermit-

tant cone locking and skidding and/or tooth breakage

Cause:

Too much WOB resulting in exaggerated bending

moment of journals

Plugged air to bearing passage resulting in one of the

bearings being starved of coolant

Outer or inner roller bearing letdown, excessive thrust

or eccentric drilling caused by bent steel, x-threading

or bad deckbushing causing ball fl ange to break

Exceed useful service life of air bearing

Running a bit down an undersized hole

Remedy:

Reduce WOB

Review drilling practices to assure that bit is cleaned

properly between uses

Review drilling practices and inspect drill string and

deck bushing for effectiveness

Use a sealed bearing bit

•

•

•

•

•

•

•

•

•

Cracked Cone (CC) - Photo 15:

Symptom:

Cone cracks either axial or circumferentially

Cause:

Cone steel fatigue

Out-thrusting causing the cone thrust fl ange to heat

and generate cracks

OB let down resulting in cone mouth riding on shirt-

tail, thus generating heat and cracking

High speed impact with hole bottom

Remedy:

Can be normal for long life bit runs

Reduce WOB

Review drilling practices to assure that bit tags the

hole bottom gently

•

•

•

•

•

•

•

Photo 15

Photo 16

23

Rounded Gage (RG) - Photo 17:

Symptom:

Gage inserts round in toward the center of the bit. Slow

penetration rates

Cause:

Too high of RPM’s

Too soft of carbide

Remedy:

Reduce RPM’s so that gage row has time to engage

the hole wall on bottom

Use bit with different carbide grade

Use bit with less offset and/or a higher journal angle

•

•

•

•

•

Heat Checking (HC) - Photo 18:

Symptom:

Snake skin surface appearing on carbide surface. Often

this results in insert breakage

Cause:

Improper tungsten carbide grade for formation drilled

Simultaneous heating and cooling of carbide from

water, either injected or ground water

Remedy:

Select bit with carbide less prone to heat checking

(lower cobalt content or larger tungsten grain size)

Slow rotation speeds down and use less water

•

•

•

•

Worn Teeth or Cutters (WT) - Photo 19:

Symptom:

Inserts wear blunt resulting in reduced productivity

Cause:

Inadequate WOB

Improper tungsten carbide grade

Ground conditions have changed

Too high of RPM’s

Remedy:

Review drilling parameters and increase WOB and/or

slow rotation speed

Select bit with carbide less prone to wear (harder

grade)

Select bit more suited for conditions

Reduce RPM’s to increase insert dwell time

•

•

•

•

•

•

•

•

Photo 17

Photo 18

Photo 19

24

Erosion (ER) - Photo 20:

Symptom:

Cone steel erodes away from inserts and results in insert

loss. Also, excessive leg erosion can cause ball hole

plug and shirttail failures

Cause:

Improper bit selection

Inadequate air volume

Wet (from either ground water or excessive water

injection), sticky, and abrasive formation

Air pressure is too high

Remedy:

Select bit that helps keep cutting structure off of the

hole bottom

Inspect air delivery system for leaks, plugged air

fi lters, and pinched hoses

If using water injection, reduce quantity. Insure bit is

nozzled properly

Check bailing velocity

Increase nozzle size to reduce air pressure

•

•

•

•

•

•

•

•

•

Broken Shirttail (BST) - Photo 22:

Symptom:

Breakage of the shirttail that protects the rollers and/or

seals

Cause:

Bearing out-thrusting causing shirttail tip to carry a

protection of the load

Eccentric drilling

Erosion reducing structural strength of the shirttail

Remedy:

Reduce WOB or select bit with a lower journal angle

Inspect drill string for bends and trueness, and bit sub

for evidence of x-threading and concentricity

Inspect drill string and compressor and air delivery

system and make necessary adjustments

•

•

•

•

•

•

Bent Steel (STL) / Pin Cross Threaded (PCT) - Photo

21:

Symptom:

Excessive wear on one or two of the leg assemblies (leg,

shirttail, and gage rows). Excessive gage row wear or

breakage. Uneven bearing wear (in-thrusting, out-thrust-

ing, and leg journal fl ange breakage).

Cause:

Drill pipe has been bent resulting in the bit rotating

eccentrically

Bit has been cross threaded

Remedy:

Inspect drill string for concentricity

Check and replace bit sub if threads are damaged

•

•

•

•

Photo 20

Photo 21

Photo 22

25

Lost Circulation (LCR) - Photo 24:

Symptom:

All three cones lock simultaneously

Cause:

Air compressor shuts down while drilling, allowing for-

mation to pack the bearing and/or overheat bearings

Bit air is prevented from reaching the bit because

blow hose is pinched, major air leak develops in the

system, or blow hose separates and stuffs bit dome

with debris

Remedy:

Inspect air system valves and coolant system and

make corrections

Inspect air delivery system for leaks, pinched and

kinked hoses, and for debris in bit dome

•

•

•

•

Plugged Nozzle (PLG) - Photo 23:

Symptom:

Obstructed nozzle that results in compressor discharging

air to atmosphere and resultant dirty hole drilling. Also, it

can manifest itself with excessive erosion on one part of

the bit.

Cause:

Air turned off prior to the bit exiting the hole allowing

cuttings to enter nozzles and bearing cavity

Over drilling (drilling faster than the cuttings are

evacuated)

Bit left in hole for maintenance of the drill head

Blow hole or shock-sub rubber element separating

Remedy:

Review drilling procedures and make corrections

Reduce penetration rates by reducing WOB and/or

RPM’s

Clean bit out after maintenance or use a used bit

Replace

•

•

•

•

•

•

•

•

Photo 23

Photo 24

Broken Leg(s) (BRL) - Photo 25:

Symptom:

The loss of leg(s). Often times this is the result of abuse

Cause:

Bit is dropped from top of hole to bottom of hole

Excessive upper leg erosion narrowing the leg cross-

section and weakening the leg

Remedy:

Insure that head is blocked and locked while parked

over a hole and while changing drill pipe

Review drilling process to assure that all available air

is delivered to the bit

Check condition of bit more frequently

•

•

•

•

•Photo 25

26

Pinched Bit (PB) - Photo 26:

Symptom:

All three gage rows are worn and the bit in-thrusts result-

ing in damage to the inner row TCI (tungsten carbide

inserts)

Cause:

Redrilling or cleaning out an existing hole with a new

or full diameter bit

Remedy:

Use a worn bit to redrill holes

Drill a new hole adjacent to old hole

Buy an undersized bit to clean out or redrill holes

•

•

•

•

Photo 26

Cored (CR) - Photo 27

Symptom:

The inner portion of the cones are lost, missing, or worn

Cause:

Too much WOB causing the cone to impinge on the

hole bottom

Using hard formation bit that causes the cone to

impinge on the hole bottom

Too much WOB resulting in borken inserts

Inadequate hole cleaning causing cone erosion

Remedy:

Reduce WOB

Select soft formation bit with greater extension

Evaluate compressor output and pipe diameter and

check to see if bit is nozzled properly

•

•

•

•

•

•

•

Photo 27

27

How a Roller Cone Bit Drills Rock

Penetration Rate:

This fi gure illustrates the effect that WOB (weight

on bit) has on the ROP (rate of penetration) while

the RPM’s (revloutions per minute) are fi xed.

After the rock has been “spalled” (Point A), ad-

ditional weight will only reduce the drilling rate.

Abrasion Phase of Rock Failure:

Figure 17 illustrates the fi rst phase of rock

failure. Because the WOB is not suffi cient

to overcome the surface strength of the

rock, the inserts wear the rock rather than

drill it. The cutting action is very similar

to sharpening a knife blade on a grinding

stone. The driller can easily identify this

phase because the cuttings coming out of

the hole are a very fi ne powder.

Figure 17

Figure 16

28

Fatigue Phase of Rock Failure:

In fi gure 18, the WOB has been increased while maintain-

ing the same RPM’s as in the previous example. As you

can see, by adding WOB, the inserts are now penetrat-

ing slightly into the rock. Even though the inserts are

being forced into the rock, rock failure has not occurred.

This phase is called the fatigue phase of rock failure.

The driller will recognize this phase because the cutting

returns will contain some small chips along with fi ne dust.

By subjecting the rock to many cycles, rock failure can

occur in this phase. Even though rock failure can occur,

ROP will be very slow and bit wear will be increased.

Spalling Phase of Rock Failure:

In the spalling phase of rock failure, while the RPM’s

remain constant, enough WOB has been applied to over-

come the surface strength of the rock. As you can see

in this illustration, the cone matrix is not impinging on the

rock formation.

Figure 18

Figure 19

29

Rock Failure / Spalling Phase:

In this example of the spalling phase, you can see that

proper WOB generates a spalling or chipping action. The

chips are circulated up and out of the hole by the circula-

tion fl uid, allowing the cutting structure to advance on a

clean hole bottom. When the drilling parameters cause

a drill bit to operate in this “zone”, the bit is drilling at a

maximum effi ciency. The driller will know when he has

achieved the spalling phase because the cutting returns

will be predominately chips with very little dust.

More is Better? Excess Weight:

The addition of more weight to the drill bit, after achieving

the spalling phase, is harmful to drilling effi ciency and the

drill bit life. As illustrated in fi gure 21, the cone matrix is

impinging on the rock formation and spalled chips are be-

ing trapped between the bit and the hole bottom, resulting

in a reduction of bit productivity and increased wear and

tear on the drill bit.

Figure 20

Figure 21

30

Maximizing Penetration:

Now that the drill bit is drilling in the spalling phase,

higher rates of penetration (drilling effi ciency) can be

achieved by increasing RPM’s, while the WOB remains

constant. The actual increase in effi ciency is dependent

on rock characteristics, and drill and driller capabilities.

As the curve in the above illustration indicates, if RPM’s

are increased beyond a certain point, effi ciency will dimin-

ish. The phenomenon is caused because the inserts are

not dwelling long enough on the hole bottom to effectively

transfer the energy into the rock.

Summary:

The preceding demonstrates that:

Once SPALLING WEIGHT is ACHIEVED, additional RO-

TATION SPEED improves PENETRATION RATE.

Thus, ideal drilling productivity and bit life is established

by:

Setting the spalling WOB, then INCREASING the RPM’s

to the level that PENETRATION RATES are MAXIMIZED.

Note: The preceding is true for brittle rock. The mechan-

ical characteristics of highly elastic rock might behave

more like the illustration on the fatigue phase instead of

the spalling phase.

Figure 22

31

CHANGING NOZZLES - (TWO SYSTEMS OF NOZZLE RETENTION)

ALWAYS USE SAFETY GLASSESALWAYS CHANGE ALL THREE NOZZLES TOGETHER

When required to change the nozzles of the drill bit, the following procedure is to be carried out:

CHANGING SPRING PIN RETENTION METHOD:

clean the area around the

spring pins and nozzles

drive the spring pin out using

a 5mm punch

•

•

remove nozzle from housing•

ensure nozzle housing is clean

insert nozzle into housing

ensuring that the groove on

the nozzle is aligned with the

pin hole

•

•replace spring pin with ham-

mer, ensuring that the head of

the spring pin is fl ush with the

bit surface

•

Figure 23 Figure 24

Figure 25 Figure 26

CHANGING NAIL-IN NOZZLES

remove the retaining

nail with the nozzle

hammer or pliers

• remove the nozzle with a

screwdrive

•

place the nozzle in the

nozzle bore and align the

groove with the nail hole

•

32

Figure 27 Figure 28

Figure 29 Figure 30

Figure 31 Figure 32

insert and drive the

retaining nail with the

nozzle hammer

•

Note: Concave side of nozzle is inserted into bit

Practical tips on how to drill with a Sandvik Smith roller bit

Choose the correct nozzle sizes. En-

sure that the minimum recommended

air pressure (30 psi, 2.1 bar) is main-

tained in the drill bit.

5-5/22

Switch on the air fl ushing before the bit starts to drill, and continue

fl ushing until the bit has been out of the hole for at least 10 seconds.

This will ensure that the bearings are blown clean, and that duct

blockage and jamming of the rollers is avoided. Check fl ushing air

through all 3 cones.

5-5/23

Check that there is no foreign matter

in the drill bit, and that none of the air

ducts is blocked. Check also that all

rollers rotate.

Use thread grease, and take care not

to damage the threads when coupling

the roller bit to the drill string.

Check the straightness of the drill

string. Straight tubes are a pre-condi-

tion for good results.

When using a new drill bit, drill the fi rst

hole with reduced feed and reduced

rotation speed.

Always use low feed force and a low

rotation speed when collaring a new

hole.ROCK DRILLING TOOLS

5-5/24

5-5/255-5/26

75%

33

> 10sec.

5-5/27

Always apply rotation to the drill

bit as it goes into or out of the

hole.

5-5/30

5-5/31

PSi

MAX

5-5/32

Always use a minimum amount of

water to reduce dusting.

Always use a used drill bit to

clean out a collapsed hole.

In order to avoid bearing prob-

lems, always use the highest pos-

sible air-pressure and fl ow rate in

holes that contain a lot of water.

To avoid water and mud to enter

drillstring and stabilizer a back

fl ow valve can be used.

34

Inspect the drill bit after drilling. All rollers

must rotate. Uneven cone temperature

after drilling indicates a blocked air duct.

45

5-5/33

Oil5-5/34

5-5/36

ROP

F

5-5/35

Used drill bits which are to be used again

must be blown clean until the rollers rotate

freely, and then lubricated with clean oil.

Store bit away from dust.

Calculate the penetration of the inserts (in mm or inches/

revolution). If less or more than 90% of the insert is

penetrating into the rock, the down pressure can be ad-

justed accordingly. (Note: if the bit has broken inserts or

if added weight on bit results in insert break, do not add

weight.) After weight on bit has been adjusted, review

RPM parameters per “How a Roller Cone Bit Drills Rock.”

35

36

Standard Roller Bearing Roller Bearing Air Cooled

Sealed Roller Bearing Sealed Friction Bearing

Ope

n B

earin

gsS

eale

d B

earin

gs

IADC xx1or xx3

IADC xx2or xx3

IADC xx6or xx7

IADC xx4or xx5

5-5/15

Appendix A - IADC

37

Ap

pen

dix

B -

Bit

Reco

rd C

ard

Measurement Conversion

DEPTH feet meters 0.3048

meters feet 3.2808

inches millimeters 25.4

millimeters inches 0.0394

WEIGHT ON BIT pounds decanewtons 0.4448

decanewtons pounds 2.2481

pounds tonne (metric) 0.0004536

tonne pounds 2205

pounds kilograms 0.4536

kilograms pounds 2.205

NOZZLE SIZE 32nds inch millimeters 0.7938

millimeters 32nds inch 1.2598

VOLUME barrels cubic meters 0.1590

cubic meters barrels 6.290

U.S. gallons cubic meters 0.003785

cubic meters U.S. gallons 264.2

U.S. gallons liters 3.7854

liters U.S. gallons 0.2642

CIRCULATION RATE barrels/min gallons/min 42

gallons/min barrels/min 0.02381

gallons/min liters/min 3.7854

liters/min gallons/min 0.2642

ANNULAR VELOCITY feet/min meters/min 0.3048

meters/min feet/min 3.2808

PRESSURE psi kilopascals 6.8947

kilopascals psi 0.14504

psi megapascals 0.006895

megapascals psi 145.038

psi atm 0.06804

atm psi 14.696

psi bars 0.06895

bars psi 14.5038

psi kilogram/sq cm 0.07031

kilogram/sq cm psi 14.2233

MUD WEIGHT ( Density) pound/gallon kilogram/cubic meter 119.829

kilogram/cubic meter pound/gallon 0.008345

pound/gallon specifi c gravity 0.119829

specifi c gravity pound/gallon 8.3452

pound/gallon psi/1000 ft. 51.948

psi/1000 ft. pound/gallon 0.01923

TORQUE foot pound newton meters 1.3558

newton meters foot pound 0.7376

AREA square inches square millimeters 645.16

square millimeters square inches 0.00155

To Convert INTO Multiply By

38

Appendix C - Conversion Table

Appendix D - Compressed Air

Defi nitions:

PSI: Pounds per Square Inch

PSIG: Pounds per Square Inch Gauge

PSIA: Pounds per Square Inch Absolute. This

is the gauge pressure plus atmospheric pressure.

For example, a gauge at sea level reads 100 psi, and

the atmospheric pressure is 14.6, then the PSIA is

equal to 114.6.

ACFM: Actual Cubic Feet per Minute. This is the

actual cubic feet per minute, inlet, at ambient condi-

tions. Changes in humidity, pressure, and tempera-

ture do not change these values. ACFM is a volu-

metric rating, irrespective of weight.

SCFM: Standard Cubic Feet per Minute. Air

compressors are rated in SCFM. Standard air varies

in volume if the local ambient conditions are different

than the standard conditions that it was rated. SCFM

is a measure of weight, not volume, and is always

.075 of a pound. It is important to recognize that

there are different defi nitions of SCFM. For example,

the SCFM standard adapted by the ASME (American

Society of Mechanical Engineers) is: 68° F (20° C), at

14.7 PSIA and a relative humidity of 36%. Where as,

the Compressed Air and Gas Institute and PNEUROP

have adopted the ISO standard, which is: 68° F (20°

C), at 14.5 PSIA (Pounds per Square Inch Absolute),

and 0% humidity.

Compressors are rated in fl ow rates. Their capacity is

measured in how many one foot (meter) cubes of fl uid

(air) they can move through the inlet every minute.

•

•

•

•

•

39

Let’s take a look at what happens to the volume when we

keep a constant weight at two different elevations using

the following for Ideal Gas:

P*V = R*T

Where:

P = Pressure

V = Volume

R = Gas Constant

PSIA * Feet3

Lbm * R(R = Temperature)

T = Temperature

A balloon containing 100 Feet3 at sea level would grow to

131 feet3 at 10,000 feet as the following illustrates:

Now let’s look at different atmospheric conditions caused

by variations in altitude and temperature. We will begin

by examining altitude. The atmospheric pressure of an

one inch column of air that extends from sea level to the

top of the troposphere is greater at sea level than it is

at 10,000 feet above sea level, because there is 10,000

more feet of air volume stacked above it. This causes the

air at sea level to be more dense (more molecules per

equivalent volume) than at 10,000 feet.

Now, we need to consider the weight or mass condition

of the same volume of air at different altitudes assuming

temperature and humidity are constant. As illustrated

below, the air at sea level has a higher mass weight:

1 ft

1 ft

1 ft

Sea Level

W = 0.075 lbs

10,000 feet

W = 0.056 lbs

1 ft

1 ft

1 ft

1 ft

1 ft

1 ft

100 feet3 @

sea level

131 feet3 @

10,000 feet above

sea level

In addition, the molecular density changes with altitude.

The following illustrates the differences in molecular den-

sity between sea level and 10,000 feet above sea level.

1 ft 1 ft

1 ft

1 ft

1 ft

1 ftSea level 10,000 ft

Because the air is less dense (fewer air molecules) at

10,000 feet, there will be a lower PSIG and PSIA. Con-

sequently, more CFM is required to generate the same

pressure as at standard conditions.

40

In addition, an ambient temperature that is different

than the temperature at standard condition changes the

density of air and its ability to hold water (humidity). This

is because cold air is denser than hot air and therefore, it

cannot hold as much water as hot air.

The accumulative affect of the change in pressure

caused by altitude and temperature result in a different

compression ratio than standard conditions. Because

of these variables, correction factors need to be used to

determine the ACFM that a SCFM of air will deliver in an

ambient condition. Conversely, correction factors can be

used to convert ACFM to SCFM so that you can compare

corrected SCFM to rated SCFM (see table at end of this

section).

Now, how does all of this impact compressor perfor-

mance and drill bit performance? Let’s start with ACFM.

As mentioned earlier, ambient pressure decreases as

altitude increases, causing an increase in the pressure

ratio across the compressor. For the following examples,

we are going to use 1,000 CFM at 100 PSI for the SCFM.

The compression raito at standard condition would be:

7.89:1 ((14.7+100)/14.7)

Now, if you relocate the same compressor to a loca-

tion that is 10,000 feet above sea level and all the other

standard conditions remaining constant, the atmospheric

pressure would be 10.1, which is signifi catly different than

14.7. The resultant compression ratio would be:

10.9:1 ((10.1+100)/10.1)

The higher the compression ratio causes the high pres-

sure air to leak back to the inlet and to re-expand. This

results in a slight reduction in volumetric effi ciency that

needs to be corrected.

Now, let’s take a look at SCFM. SCFM needs to be

corrected for both altitude and temperature, if they are

different than standard conditions. As the density of inlet

air is reduced with altitude, the amount of “pressure”

generated by the compressor is reduced correspondingly.

In addition, the temperature of air effects that amount of

“pressure” generated because it too affects the air density

at intake, in addition to the amount of moisture that the air

can hold. Because changes in altitude and temperature

impacts PSIG, the ability to cool the bearings, bail the

hole, will be less than at standard conditions. Reductions

in pressures at the bit can lead to lower bearing life (in air

cooled bearing bits), and a reduction in cleaning capacity

results in a dirty hole, which can lead to lower penetra-

tion rates, reduced bit life, and increased wear on the

drill string. Therefore, these factors need to be taken into

consideration when specifying compressors for drills.

To summarize, any change to ambient pressure, temper-

ature, and humidity changes the output of the compressor

in terms of ACFM and SCFM. The following correction

factor table is provided as a guide:

Correction Factors

For altitude and ambient temperature

Temperature Feet / Meter

C F 0 / 0 1000 /

304.8

2000 /

609.6

3000 /

914.4

4000 /

1219.2

5000 /

1524

6000 /

1828.8

7000 /

2133.6

8000 /

2438.4

9000 /

2743.2

10000 /

3048

11000 /

3352.8

12000 /

3657.6

13000 /

3962.4

14000 /

4267.2

15000 /

4572

-40 -40 .805 .835 .866 .898 .932 .968 1.004 1.043 1.084 1.127 1.170 1.217 1.266 1.317 1.371 1.426

-37.2 -35 .815 .845 .876 .909 .944 .980 1.016 1.056 1.097 1.141 1.184 1.232 1.282 1.333 1.387 1.443

-34.5 -30 .824 .855 .886 .920 .954 .991 1.028 1.068 1.110 1.154 1.198 1.246 1.297 1.349 1.403 1.460

-31.7 -25 .834 .865 .897 .931 .965 1.003 1.040 1.080 1.123 1.167 1.212 1.261 1.312 1.365 1.420 1.477

-28.9 -20 .844 .875 .907 .941 .976 1.014 1.052 1.092 1.136 1.180 1.226 1.275 1.327 1.380 1.436 1.494

-26.1 -15 .854 .885 .918 .952 .988 1.026 1.064 1.105 1.149 1.194 1.240 1.290 1.342 1.396 1.453 1.511

-23.3 -10 .863 .895 .928 .962 .999 1.037 1.076 1.117 1.161 1.207 1.254 1.304 1.357 1.411 1.469 1.528

-20.5 -5 .873 .905 .938 .973 1.010 1.049 1.088 1.130 1.174 1.221 1.268 1.319 1.372 1.427 1.485 1.545

-18.3 0 .882 .915 .948 .984 1.021 1.060 1.100 1.142 1.187 1.234 1.282 1.333 1.387 1.443 1.501 1.562

-15 5 .892 .925 .959 .995 1.032 1.072 1.112 1.155 1.200 1.248 1.296 1.348 1.402 1.459 1.518 1.579

-12.2 10 .901 .935 .969 1.005 1.043 1.083 1.123 1.167 1.213 1.261 1.310 1.362 1.417 1.474 1.534 1.596

-9.4 15 .911 .945 .980 1.016 1.054 1.095 1.135 1.180 1.226 1.275 1.324 1.377 1.432 1.490 1.550 1.613

-6.6 20 .920 .954 .990 1.026 1.065 1.106 1.147 1.192 1.239 1.288 1.338 1.391 1.447 1.506 1.566 1.630

-3.9 25 .930 .964 1.000 1.037 1.076 1.118 1.159 1.205 1.252 1.302 1.352 1.406 1.463 1.522 1.583 1.647

-1.1 30 .939 .974 1.010 1.048 1.087 1.129 1.171 1.217 1.265 1.315 1.365 1.420 1.478 1.537 1.599 1.664

1.7 35 .949 .984 1.021 1.059 1.009 1.141 1.183 1.229 1.278 1.328 1.379 1.435 1.493 1.553 1.616 1.681

4.5 40 .959 .994 1.031 1.069 1.110 1.152 1.195 1.241 1.290 1.341 1.393 1.449 1.508 1.568 1.632 1.698

7.2 45 .969 1.004 1.041 1.080 1.121 1.164 1.207 1.254 1.303 1.355 1.407 1.464 1.523 1.584 1.648 1.715

10 50 .978 1.014 1.051 1.091 1.132 1.175 1.219 1.266 1.316 1.368 1.421 1.478 1.538 1.600 1.664 1.732

12.8 55 .988 1.024 1.062 1.102 1.143 1.187 1.231 1.279 1.329 1.382 1.435 1.493 1.553 1.616 1.681 1.749

15.5 60 .997 1.034 1.072 1.112 1.154 1.198 1.243 1.291 1.342 1.395 1.449 1.507 1.568 1.631 1.697 1.766

18.3 65 1.007 1.044 1.083 1.123 1.165 1.210 1.255 1.304 1.355 1.409 1.463 1.522 1.583 1.647 1.714 1.783

21.1 70 1.016 1.054 1.093 1.133 1.176 1.221 1.267 1.316 1.368 1.422 1.477 1.536 1.598 1.662 1.730 1.800

23.9 75 1.026 1.064 1.103 1.144 1.187 1.233 1.279 1.329 1.381 1.436 1.491 1.551 1.613 1.678 1.746 1.817

26.7 80 1.035 1.074 1.113 1.155 1.198 1.244 1.291 1.341 1.394 1.449 1.505 1.565 1.628 1.694 1.762 1.834

29.5 85 1.045 1.084 1.124 1.166 1.210 1.256 1.303 1.353 1.407 1.462 1.519 1.580 1.643 1.710 1.779 1.851

32.2 90 1.055 1.094 1.134 1.176 1.221 1.267 1.315 1.365 1.419 1.475 1.533 1.594 1.658 1.725 1.795 1.868

35 95 1.065 1.104 1.144 1.187 1.232 1.279 1.327 1.378 1.432 1.489 1.547 1.609 1.674 1.741 1.812 1.885

37.8 100 1.074 1.114 1.154 1.198 1.243 1.290 1.339 1.390 1.445 1.502 1.560 1.623 1.689 1.756 1.828 1.902

40.6 105 1.084 1.124 1.165 1.209 1.254 1.302 1.351 1.403 1.458 1.516 1.574 1.638 1.704 1.770 1.844 1.919

43.3 110 1.093 1.137 1.175 1.219 1.265 1.313 1.363 1.415 1.471 1.529 1.588 1.652 1.719 1.783 1.860 1.936

46.1 115 1.103 1.143 1.186 1.230 1.276 1.325 1.375 1.428 1.484 1.543 1.602 1.667 1.734 1.797 1.876 1.953

48.9 120 1.112 1.153 1.196 1.240 1.287 1.336 1.386 1.440 1.497 1.556 1.615 1.681 1.749 1.810 1.892 1.970

Instructions:

Determine the altitude and typical ambient conditions that the compressor will be working. (It is best to use worse

case scenarios. Peak ambient temperatures and altitudes, and peak humidity.)

Find the nearest 1,000 feet and go down the column until it intersects with the row that contains the nearest typical

ambient temperature.

Multiply SCFM by the correction factor to obtain the ACFM required under the given conditions.

In the exmaple on page 17, we determined that a mine needed 1430 CFM (40 m3/min) to achieve a bailing velocity of

7,000 ft/min. How much air would be required if this drill was at 10,000 ft above sea level with a median temperature

of 40° F? The answer is calcuated as follows: 1430 x 1.449 = 2,072 ACFM.

1.

2.

3.

41

Discharge of air through an Orifi ce at 100 psi

Gauge

pressure

before

orifi ce in

psi

Diameter of Orifi ce

1/64 1/32 3/64 1/16 3/32 1/8 3/16 1/4 3/8 1/2 5/8 3/4 7/8 1 1 1/8 1 1/4 1 3/8 1 1/2 1 3/4 2

Discharge in cubic feet of free air per minute

2 .04 .158 .356 .633 1.43 2.53 5.7 10.1 22.8 40.5 63.3 91.2 124 162 205 253 307 364 496 648

5 .062 .248 .568 .993 2.23 3.97 8.93 15.9 35.7 63.5 99.3 143 195 254 321 397 482 572 780 1015

10 .077 .311 .712 1.24 2.8 4.98 11.2 19.9 44.7 79.6 124.5 179.2 244.2 318.2 402.5 498 604 716 972 1274

15 .105 .42 .944 1.68 3.78 6.72 15.2 26.9 60.5 108 168 242 329 430 544 672 816 968 1318 1720

20 .123 .491 1.1 1.96 4.41 7.86 17.65 31.4 70.7 126 196 283 385 503 637 784 954 1132 1540 2120

25 .14 .562 1.26 2.25 5.05 8.98 20.2 35.9 80.9 144 225 323 440 575 727 900 1091 1293 1760 2300

30 .158 .633 1.42 2.53 5.69 10.1 22.8 40.5 91.1 162 253 365 496 648 820 1019 1230 1460 1985 2594

35 .176 .703 1.58 2.81 6.31 11.3 25.2 45 101 180 281 405 551 720 910 1124 1367 1620 2205 2880

40 .194 .774 1.75 3.1 7 12.4 28 49.6 112 198 310 446 607 793 1004 1240 1505 1783 2429 3173

45 .211 .845 1.91 3.38 7.63 13.5 30.5 54.1 122 216 338 487 662 865 1094 1352 1643 1946 2650 3460

50 .229 .916 2.06 3.66 8.25 14.7 33 58.6 132 235 366 528 718 938 1187 1464 1780 2112 2875 3752

60 .267 1.06 2.38 4.23 9.50 16.9 38 67.6 152 271 423 609 828 1082 1370 1693 2054 2335 3310 4330

70 .3 1.2 2.7 4.79 10.8 19.2 43.2 76.7 173 307 479 690 939 1227 1552 1917 2330 2760 3755 4915

80 .335 1.34 3 5.36 12 21.4 48.3 85.7 193 343 536 771 1050 1371 1734 2144 2607 3081 4200 5480

90 .37 1.48 3.33 5.92 13.3 23.7 53.2 94.8 213 379 592 853 1162 1516 1918 2370 2880 3412 4643 6070

100 .406 1.62 3.66 6.49 14.6 26 58.5 104 234 415 649 934 1272 1661 2101 2596 3153 3734 5085 6650

125 .494 1.98 4.44 7.9 17.8 31.6 71 126 284 506 790 1138 1549 2023 2560 3160 3840 4550 6195 8100

150 .583 2.32 5.25 9.31 20.9 37.3 84 149.3 336 596 932 1340 1825 2385 3020 3725 4525 5360 7300 9540

Make-Up Torque

Bit Size Pin Connection Recommended Torque

(Inches) (Millimeters) (inches) (Millimeters) ft-lbs N-m

03 3/4” - 04 1/2” 95 - 114 02 3/8 Reg 60 3000 - 3500 4000 - 4800

04 5/8” - 05 1/2” 117 - 139 02 7/8 Reg 73 6000 - 7000 8000 - 9500

05 5/8” - 07 3/8” 143 - 187 03 1/2 Reg 89 7000 - 9000 9500 - 12000

07 7/8” - 09” 200 - 229 04 1/2 Reg 114 12000 - 16000 16000 - 22000

09 7/8” - 13 3/4” 251 - 349 06 5/8 Reg 168 28000 - 32000 38000 - 43000

15” - 17 1/2” 381 - 444 07 5/8 Reg 194 40000 - 60000 54000 - 81000

Appendix E - Rotary Shoulder Make-Up Torque

Notes:

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43

Appendix F - Old Timer’s Drilling Tips

Always make up and break out the bit carefully.

Use a good grade of thread grease and maintain con-

nections properly.

Always maintain as high a pressure drop as possible

across the bit air courses.

To collar or start new hole, reduce down pressure

and rotation.

Always open the air valves before the bit starts drill-

ing the hole and keep the air on until the bit is out of

the hole.

Re-establish bottom hole pattern with reduced down

pressure and rotation when drilling is interrupted.

Never fi nish an old hole with a new bit. This can

pinch the cones, damaging the bearings and gage

teeth.

Always break in a new bit by drilling at reduced

weight and rotation for a short period.

Guard against dropping the bit and drill steel.

Occasionally check the bit for uniform cone tempera-

ture.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Always maintain drilling air pressure at appropriate

levels.

Rotary speed should be decreased as down pressure

increases.

Do not use more water than is necessary to control

dust and maintain hole wall.

Maintain rotation while tripping into or out of a hole.

Near bit stabilization, deck centralizers, and shock

subs can help bit life and drill longevity.

Always clean a bit before an idle period by pass-

ing air through it while rotating the cones by hand.

A slight coating of oil will help prevent rust over an

extended idle period.

Before reusing a bit that has been idle, make sure all

cones turn freely by hand.

Bent steel will reduce drill bit life.

Follow the break-in procedures recommended by the

manufacturer.

11.

12.

13.

14.

15.

16.

17.

18.

19.

Sandvik Smith Inc. Ponca City, OK

Tel: 580-762-2481

Sandvik Smith Inc.Houston, TX

Tel: 281-443-3370

Sandvik Smith Inc.

Tucson, AZ

Tel: 520-882-5422

Sandvik Smith Chile S.A. Conchali, Santiago, Chile

Tel: 56-2-676-0290

Sandvik Smith Canada Inc.

Laval, Quebec, Canada

Tel: 450-688-7775

Sandvik Smith Australia Pty, Ltd.Brisbane, QLD, Australia

Tel: 61-7-3637-7400

Sandvik Smith South Africa Pty, Ltd.Gauteng, South Africa

Tel: 27-11-570-9736

Sandvik Smith Inc. (HDD)Houston, TX

Tel: 281-233-5798

Corporate Offi ce

Sandvik Smith ABKoping, Sweden

Tel: 46-221-27500

Copyright 2005 Sandvik Smith AB

All Rights Reserved