7 drilling brake

8/11/2019 7 Drilling Brake

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Davorin Matanovi

Drilling

BRAKE


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Mechanical brake

Mechanical brake is the essential part of thederrick.

Its purpose is to slow down and stop the downwardsmovement of the drill string.

It also serves to control the load on the bit.

The frictional brake consists basically of flexiblesteel bands that fit around the drum flanges, eachhaving one end anchored and the other free.. When the free end is pulled (by means of a brake lever,

the whole band tightens around the drum flange andslows or stops it by friction.


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Band frictional

brake

Construction

Drum flanges have wearresistant rims bolted to them.

They are gripped by the brakebands as they tighten.

The brake bands have a lining

of brake blocks. The blocks are composed of

asbestos fiber compoundedwith a bonding agentinterwoven with cooper wire.

The blocks are bolted to thebrake bands with brass boltscountersunk on the inside ofthe band circle.

One end (the dead end) of

each brake band is anchored;and the other end (the liveend) is attached to the manualbrake lever by means of acamshaft.


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Blocks bolting

API standard defines friction blocks

with four or six bores


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Blocks with six

bores Blocks with four

bores

API

No.A (mm) B (mm) C (mm)

1 152,4 31,8 88,9

2 177,8 38,1 101,6

3 203,2 44,5 114,3

4 228,6 50,8 127

5 254 57,2 139,7

6 279,4 63,5 152,4

7 304,8 69,9 165,1

The thickness of theblock is not defined, but

it is possible to use

several block thickness:

t*

(mm)15,9 19 22,2 25,4 28,6 31,8

(inch) 5/8 3/4 7/8 11

1/81 1/4

API

No.D (mm) E (mm) F (mm)

10 152,4 31,8 88,9

11 177,8 38,1 101,6

12 203,2 38,1 12713 228,6 38,1 152,4

14 254 38,1 177,8

t*(mm) 15,9 19 22,2 25,4(inch) 5/8 3/4 7/8 1


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Screw diameter

for blockfastening is 9,525mm (3/8") with

the flat -countersunk headwith angle of 120

and thread;16UNC-2A.

o

120


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Several factors affect breaking capacity: The first is the ratio between the diameter of

the brake flange and the diameter of the drumspool.

Another is a band width.

That is according tofriction area.

Third one is the angle of wrap, that means thedistance that the brake band wraps around

the flange. It can be from 270 to 330.


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330 wrapping 270 wrapping


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Equalizer

At the front of the hoist, the brake bands arefastened with heavy-duty pins or bolts to a dead

anchor firmly fastened to the draw works frame atthe center of the drum. This dead anchor is in the form of a yoke and acts as

an equalizer to ensure that each brake band will

receive an equal amount of tension. The equalizer also switches the full load to one band if

the other fails.

The brakes must be adjusted properly to make sure thelong lasting work. Some draw works have automaticequalizing devices.


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Cooling The brakes are cooled with clean fresh water

circulated through the drum shaft to the brakeflanges.

Cooling is necessary to help dissipate the heat that isgenerated by the friction of brake lining on flanges.

It is important for water to be fresh to prevent mineraldeposition that would affect the cooling system.

The water is pumped by the system that hasindependent power.

The great amount of generated heat must be

removed quickly to prevent poor braking actionand excessive wear on blocks and flanges.


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Frictional brake actsas it is shown on

picture.

The force on thelever that driller

must apply is

defined as:

( ) ( ) N

elRbM

lebQ

lbtF

ookkv

kbr

k

kbr

k

pk 490

1122 ..

=

==


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Where:

Fk the force the driller must apply on the lever, Ntp force in the free end of band, N

bk length of the short lever, m

lk length of the long lever, m

Qbr.

braking force on the flange, N

e natural logarithm base (2,718)

- coefficient of friction (0,5)

o wrap angle (from 270 to 330)

Rkv brake flange radius, m

Mbr. breaking moment that must be achieved,Nm

rkon final drum diameter, m

b drum efficiency (0,95)

Kbr.

factor due the dynamic forces (from 1,2 to2,5)

Dkv braking flange diameter, m (1,8 to 2,8)DbDb drum diameter, m

F force in the wire rope, N

kv

brbr

R

MQ

=2

..

.. brbkonbr KrFM =

( )

2

8,28,1

2

bkvkv

DtoDR

==


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Auxiliary brakes Auxiliary brakes are used in the hoisting

system to slow the rate of descent of the

traveling block with a heavy load. They ensure that a heavy load comes down slowly

and smoothly.

Care must be taken, to prevent the blocks fromfalling faster than they could be stopped by thefriction brake alone.

Auxiliary brake should be hydrodynamic

brake or electrodynamic brake.


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Hydrodynamic brake

Hydrodynamic brakeis often called as the

water-brake,

because it works bythe action of fluid;

normally water.


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The fluid is circulated by a moving rotor,and mechanical energy is converted intoheat within the fluid itself.

The amount of mechanical energy that canbe absorbed depends upon the quantity

and velocity of the fluid in the workingchamber.

It will be increased with revolving speed ofthe rotor.

To control the operating level, driller simplyopens or closes the valve that controls thelevel of the water in the brake.

So the main control should be in thecirculating system.

Maximum allowable brake outlettemperature must never exceed 77 C (180F).


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Electrodynamicbrake

An electrodynamic brakeconsists basically of a largesteel armature drum thatrotates in a magnetic fieldproduced by electromagnetsaround the drum. The combination of drum motion

(rotation) and magnetic fieldscauses electric currents (eddycurrents) to flow in the drum.

They react with the stationarymagnetic fields to resist the drummotion and produce a retardingor breaking action.

The amount of breaking action iscontrolled by adjusting thestrength of magnetic fields, bythe amount of direct current.

ROTOR

WATER

INLET

WATER OUTLET

ELECTRO

MAGNETS

7 drilling brake

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