wheel loader - cycle time

8/19/2019 Wheel Loader - Cycle Time

1/612-106 Edition 40

Wheel LoadersIntegrated Toolcarriers

SAE Loader RatingsMachine Selection● Cycle Time Factors

SAE BUCKET RATING

SAE Bucket CapacitiesStruck capacity is that volume contained in a

bucket after a load is leveled by drawing a straightedge resting on the cutting edge and the back of thebucket.

Heaped capacity is a struck capacity plus thatadditional material that would heap on the struckload at a 2:1 angle of repose with the struck lineparallel to the ground.

SAE J742 (FEB85) specifies that the addition of anyauxiliary spill guard to protect against spillage whichmight injure the operator will not be included in bucketcapacity ratings. Buckets with irregular shaped cut-ting edges (vee edge) the strike plane should be drawnat one-third the distance of the protruding portion of the cutting edge. Cat rock buckets are built with inte-gral see-through rock guards. Cat light materialbuckets come standard with bolt-on edges. These fea -

tures which add to actual bucket capacity are includedin published ratings.

Dump HeightSAE J732 JUN92 specifies that dump height is

the vertical distance from the ground to the lowestpoint of the cutting edge with the bucket hinge pinat maximum height and the bucket at a 45° dumpangle. Dump angle is the angle in degrees that thelongest flat section of the inside bottom of the bucketwill rotate below horizontal.

SELECTING A MACHINE

Steps in selecting the proper size loader:1. Determine production required or desired.2. Determine loader cycle time and cycles per hour.

A machine size must be assumed to select a basiccycle time.

3. Determine required payload per cycle in loosecubic yards and pounds (meters and kilograms).

4. Determine bucket size needed.5. Make machine selection using bucket size and pay-

load as criteria to meet production requirements.6. Compare the loader cycle time used in calculations

to the cycle time of the machine selected. If thereis a difference, rework the process beginning atstep 2.

1. Production RequiredThe production required of a wheel or track loader

should be slightly greater than the production capa-bility of the other critical units in the earth or mate-rial moving system. For example, if a hopper canhandle 300 tons per hour, a loader capable of slightlymore than 300 tons should be used. Required pro-duction should be carefully calculated so the propermachine and bucket selections are made.

2. Loader Cycle TimesWhen hauling loose granular material on a hard

smooth operating surface, a .45-.55 minute basiccycle time is considered reasonable for Cat articu-lated loaders with a competent operator. This includesload, dump, four reversals of direction, full cycle of hydraulics and minimum travel.

Material type, pile height, and other factors mayimprove or reduce production, and should be addedto or subtracted from the basic cycle time whenapplicable.

When hauls are involved, obtain the haul and returnportion of the cycle from the estimated travel chart (thissection). Add the haul and return times to the esti-mated basic cycle time to obtain total cycle time.

CYCLE TIME FACTORS A basic cycle time (Load, Dump, Maneuver) of

.45-.55 minutes is average for an articulated loader[the basic cycle for large loaders, 3 m 3 (4 yd 3) aup, can be slightly longer], but variations can beanticipated in the field. The following values formany variable elements are based on normal oper-

ations. Adding or subtracting any of the variabletimes will give the total basic cycle time.

STRUCK

HEAPED


2/6

Machine Selection● Truck Loading

● Bucket Fill Factors

Edition 40 12-10


Minutes added (+)or Subtracted (–)

From Basic Cycle Machine

— Material handler . . . . . . . . . . . . . –.05 Materials

— Mixed. . . . . . . . . . . . . . . . . . . . . . . +.02 — Up to 3 mm (1/8 in). . . . . . . . . . . . +.02 — 3 mm (1/8 in) to 20 mm

(3/4 in) . . . . . . . . . . . . . . . . . . . . . . –.02 — 20 mm (3/4 in) to 150 mm

(6 in) . . . . . . . . . . . . . . . . . . . . . . . – .00 — 150 mm (6 in) and over . . . . . . . . +.03 and Up — Bank or broken . . . . . . . . . . . . . . . +.04 and Up

Pile — Conveyor or Dozer piled 3 m

(10 ft) and up . . . . . . . . . . . . . . . . – .00 — Conveyor or Dozer piled 3 m(10 ft) or less . . . . . . . . . . . . . . . . . +.01

— Dumped by truck . . . . . . . . . . . . . +.02 Miscellaneous

— Common ownership of trucksand loaders . . . . . . . . . . . . . . . . . . Up to –.04

— Independently ownedtrucks . . . . . . . . . . . . . . . . . . . . . . Up to +.04

— Constant operation. . . . . . . . . . . . Up to –.04 — Inconsistent operation . . . . . . . . . Up to +.04 — Small target . . . . . . . . . . . . . . . . . Up to +.04 — Fragile target . . . . . . . . . . . . . . . . Up to +.05

Using actual job conditions and the above factors,total cycle time can be estimated. Convert total cycletime to cycles per hour.

Cycles per hour at 60 min100% Efficiency = Total Cycle Time

in MinutesJob efficiency is an important factor in machine

selection. Efficiency is the actual number of min-utes worked during an hour. Job efficiency accountsfor bathroom breaks and other work interruptions.Cycles per hourat 50 minutes Cycles per hour 50 min

per hour = at 100% actual work(83% efficiency) efficiency time

60 min hour

TRUCK LOADING Average loader cycle times914G-962H . . . . . . . . . . . . . . . . . . . . 0.45-0.50 min966H-980H . . . . . . . . . . . . . . . . . . . . 0.50-0.55 min988H-990H . . . . . . . . . . . . . . . . . . . . 0.55-0.60 min992K-994F. . . . . . . . . . . . . . . . . . . . . 0.60-0.70 min

3. Required Payload Per CycleRequired payload per cycle is determined by divid

ing required hourly production by the number of cycles per hour.

4. Bucket Selection After required payload per cycle has been calcu-

lated, the payload should be divided by the loose cubicyard (meter) material weight to determine numberof loose cubic yards (meters) required per cycle.

The bulk of material handled does not weigh1800 kg/m 3 (3000 lb/yd 3), so a reasonable knowledgeof material weight is necessary for accurate pro-duction estimates. The Tables Section has averageweight for certain materials when actual weightsare not known.

The percentage of rated capacity a bucket carriesin various materials is estimated below. The bucketsize required to handle the required volume per cycleis found with the aid of the percentage of rated bucketcapacity called “Bucket Fill Factor.’’

The bucket size needed is determined by dividingloose cubic meters (or yards) required per cycle bythe bucket fill factor.

Bucket size =Volume Required/Cycle

Bucket Fill Factor

BUCKET FILL FACTORS The following indicates the approximate amounts

of material as a percent of rated bucket capacitywhich will actually be delivered per bucket per cycle.This is known as “Bucket Fill Factor.’’

Loose Material Fill factorMixed moist aggregates. . . . . . . . . . . . . 95-100%Uniform aggregates up to 3 mm

(1/8 in). . . . . . . . . . . . . . . . . . . . . . . . . 95-1003 mm (1/8 in) to 9 mm (3/8 in) . . . . . . . . 90-9512 mm (1/2 in) to 20 mm (3/4 in) . . . . . . 85-9024 mm (1.0 in) and over . . . . . . . . . . . . . 85-90


3/612-108 Edition 40


Machine Selection● Bucket Fill Factors● Example Problem

Blasted RockWell blasted . . . . . . . . . . . . . . . . . . . . . 80-95%

Average. . . . . . . . . . . . . . . . . . . . . . . . . 75-90Poor. . . . . . . . . . . . . . . . . . . . . . . . . . . . 60-75

OtherRock dirt mixtures . . . . . . . . . . . . . . . . 100-120%Moist loam . . . . . . . . . . . . . . . . . . . . . . 100-110Soil, boulders, roots . . . . . . . . . . . . . . . 80-100Cemented materials. . . . . . . . . . . . . . . 85-95

NOTE: Fill factors on wheel loaders are affected bybucket penetration, breakout force, rackbackangle, bucket profile and ground engagingtools such as bucket teeth or bolt-on replace -able cutting edges.

Example:

12 mm (1/2 in) material and 3 m 3 (4 yd 3) bucket..90 3 m 3 = 2.75 Loose m 3 delivered per cycle..90 4 yd 3 = 3.6 Loose yd 3 delivered per cycle.

NOTE: Check the static tipping load on the specificmachine to determine if bucket load is infact a safe operating load.

Bucket SelectionTons Required/Hour

Tons Required/Cycle = CyclesHour

Kg (Pounds)Required/Cycle = Tons Required/Cycle

907 kg (2000 lb)

Volume Required/Cycle = kg (Pounds) Cycle

Material Weightkg/m 3 (lb/yd 3 )

Always select a machine with a greater capacitythan the calculated required operating capacity.For most applications, payload above recommendedand excessive counterweight can hinder machineperformance and reduce dynamic stability andmachine life.

For optimum performance in fast cycling situations

such as truck loading, operating loads should notexceed the recommended capacity. To provide extrastability, calcium chloride (CaCl 2) ballast may bedesired when operating at recommended operatingload, see SAE Loader rating pages in this section. Forspecific stability data and optional tire sizes, see the“Performance Data’’ pages in this section.

When selecting special application buckets, such asmulti-purpose and side dump the additional bucketweight must be deducted from recommended capacity.

Specific circumstances may involve other conditionswhich would also affect loader capacity. Because of the greatly varied applications and conditions, yourCat dealer should be contacted for guidance.

Example problem:

JOB CONDITIONS Application Truck loadingProduction Required 450 metric ton (496 Tons)

per hourMaterial 9 mm (3/8") gravel in 6 m

(20 ft) high stockpileDensity 1660 kg/m 3 (2800 lb/yd 3)

Trucks are 6-9 m 3 (8-12 yd 3) capacity and are ownedby three contractors. Loading is constant. Hard levelsurface for loader maneuvering.

1. PRODUCTION REQUIRED: Given

2. CYCLE TIME: Assume loader size between 914Gand 962H for initial choice of basic cycle.

(Refer to Cycle Time Factors in this section)Independent trucks .04 minBasic Cycle .50 minMaterial –.02 minIndependent trucks +.04 min

Constant operation –.02 minTotal Cycle .50 minNOTE: Load and carry times not required in total

cycle.Cycles/hr 50 min actualat 83% = 120 cycles/hr work timeefficiency 60 min per hr

= 100 cycles/h

3. VOLUME REQUIRED PER CYCLE (Density in tons)Density in this example was given. When notgiven, refer to Tables Section to obtain an esti-mated density for the material being handled.

1660 kg/m 3 Metric:

1000 kg/ton= 1.66 ton/m 3

2800 lb/yd 3English:

2000 lb/ton= 1.4 tons/yd 3


4/6Edition 40 12-10

Machine Selection● Example Problem

● Alternative Method


Production Rate Required450 tons/hr

Metric:1.66 tons/m 3

= 271 m 3/hr

496 tons/hrEnglish:

1.4 tons/yd 3= 354 yd 3/hr

Volume Required per Cycle271 m 3/hr

Metric:100 cycles/hr

= 2.71 m 3/cycle

354 yd 3/hrEnglish:

100 cycles/hr= 3.54 yd 3/cycle

4. DETERMINE BUCKET SIZE

BUCKET FILL FACTORThe volume of material required per cycle has

been determined. Because of varying material fillfactors, buckets do not always carry their ratedload, a larger capacity bucket may be needed tocarry the volume required. For fill factors, referto Bucket Fill Factor Chart in this section.

Rated Bucket Capacity Required (Heaped)

2.71 m 3/cycle= 2.85 m 3

.95 fill factor

3.54 yd 3/cycle= 3.73 yd 3

.95 fill factor A 2.9 m 3 (3.75 yd 3) bucket would provide therequired capacity.

5. MACHINE SELECTION The bucket size required and material density

lead to the choice of a 950H with a 2.9 m 3 (3.75 yd 3)General Purpose Bucket (see bucket selectionguide pages which follow.)

Finally, SAE payload criteria must be satis-fied as follows:

The required operating capacity must notexceed one-half of the full turn static tipping loadof the loader as equipped with a specific bucket.

The required operating capacity of the machineis determined by the volume the machine willcarry per load times the density.

2.9 m 3 1660 kg/m 3 = 4814 kg(3.75 yd 3 2800 lb/yd 3 = 10,500 lb)

One half of full turn static tipping load for the950H with a 2.9 m 3 (3.75 yd 3) General PurposeBucket is 5410 kg (11,925 lb). SAE criteria is satisfied.

● ● ●

An Alternative Method of Machine Selection Another method of selecting the right Wheel

Loader and bucket to meet production requirementsis by use of the nomographs on the following pages.The method is quicker and easier than the preced-ing example because it does not require as manycalculations, yet the accuracy is about the samewithin the normal limits of input data.

Be careful when entering and reading data fromthe nomographs because some scales increase from

bottom to top, while others are the reverse. Do not beoverly concerned with the precision as affected by pencil line width or reading to the hundredth of a m 3 (yRemember that bucket fill factor, material densityand cycle time are at best close estimates.

Example problem:

A Wheel Loader must produce 230 m 3 (300 yper hour in a truck loading application. Estimatedcycle time is .6 minutes, working 45 minutes perhour. Bucket fill factor is 95% and material densityis 1780 kg/m 3 (3000 lb/yd 3).

Determine bucket size and machine model.Solution:

At full efficiency, the Wheel Loader will cycle 100times per hour. Since only an average of 45 minutesare available, only 75 cycles will be completed.

Starting on Scale A at 75 cycles per hour draw astraight line intersecting 230 m 3/hr (300 yd 3/hr) Scale B and extending it on to Scale C giving3 m 3/cycle (4 yd 3/cycle) required payload. Followsolution steps 1-10.


5/612-110 Edition 40


Production and Machine Selection Nomograph● To find required bucket payload and bucket size

1. Enter required hourly production on Scale B230 m 3/hr (300 yd 3/hr).

2. Enter cycles per hour on Scale A (60 ÷ .6 = 100

.75 = 75 cycles/hr).3. Connect A through B to C. This shows a required

payload of 3 m 3 (4 yd 3) per cycle.

4. Enter estimated bucket fill factor on Scale D(0.95).

5. Connect C through Scale D to E for required bucket

size 3 m3

(4 yd3

).6. Transfer cycles per hour Scale A and required

payload Scale C to the following page.

m 3 /cycle yd 3 /cycle

m 3 /hr yd 3 /hr

m 3

A B C D ECycles Hourly Required Bucket Required

per hour Production Payload Fill BucketVolume Volume Factor


6/6Edition 40 12-11

Production and Machine Selection Nomograph● To find payload weight and tons per hour


7. Enter material density on Scale F 1780 kg/m 3(3000 lb/yd 3).

8. Connect C through Scale F to Scale G to give pay -

load weight per cycle 5300 kg (11,500 lb).9. Compare Scale G quantity 5300 kg (11,500 lb)

with recommended machine working rangelisted on the following bucket selection pages.

Operating capacity for the 950H with 3.1 m(4 yd 3) bucket is dependent on material densityand bucket capacity (see bucket selection pagesthat follow).

10. For hourly tonnage, draw a straight line fromScale G through Scale A to Scale I 400 metric tons(450 U.S. tons).

C F G A IRequired Material Bucket Cycles/hr Tons perPayload Density Payload HourVolume Weight per

cycle

kg/cycle

MetricTons

lb/cycle

U.S.Short Tons

m 3 /cycle yd 3 /cycle

kg/m 3 lb/yd 3

wheel loader - cycle time

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