Determining Correct Wheel Loader Size for High Production Job Demand: LOAD AND CARRY APPLICATION.

Wheel loaders are perceived as “go anywhere all-terrain multi-purpose utility workhorses”, but can be an expensive means to move earth if their application and concept basics are incorrectly job calculated and misapplied on site. Most of their installed power by concept design is used to overcome their own weight inertia and exert underfoot grip co-efficient, limiting bucket payload capacity potential. Barloworld Equipment markets an extensive renowned range of Caterpillar wheel loaders, from the Cat 914G (67 kW nett – 7,4 t – 1, 4 m3) up to the Cat 988G (354 kW nett – 51 t – 6,6 m3), and beyond with larger mining size machines (the Cat 990 – 992G & 994D). Kenn Smart , application and product manager, Barloworld Equipment, provides some insight, on a self teach basis, on how to assess and determine an appropriate size machine matched to a production orientated job, particularly in a LOAD AND CARRY situation: A common deficiency among users in southern Africa, he says, is that there is a distinct tendency to acquire wheel loaders that are too small in size and capacity for a specific high demand production job. Hence, owners/users are handicapped with under-performance and high unit cost from the outset, limiting or suppressing system output/throughput potential and incurring a higher extracted cost per tonne of material moved ; a lowered machine availability and longevity period (UEL = Useful Economic Life), and an increased operating and maintenance cost, coupled to problematic mechanical downtime. Basically, wheel loader unit size matched to an actual job assessment is more complex than is generally appreciated. The initial determination of appropriate work factors is often overlooked or not brought into the application scenario and perhaps this is where the deficiency lies. Over shorter haul distances from extraction face to dump zone (+/- up to 100m one way), wheel loaders are now used more frequently with good economics and effectiveness in LOAD AND CARRY prime productive applications: The objective is to lessen or avoid the capital investment and supporting logistics of acquiring an integral, and often unnecessary, dedicated haul truck fleet. But the key is to correctly size, spec. and configure the wheel loader from the outset.

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Prerequisite LOAD AND CARRY factors to fix or calculate correctly beforehand are: • Material to be handled: class type (C1 to C4) and fragmentation, lump

sizing/structure: pre-treatment/pre-loosen method if applicable and resistance to bucket penetration; heaping ability; loadability; in situ and loose density relevant to moisture content; swell factor; t.p.h. requirement vs number of work shifts, etc. All earthmoving machine buckets are rated in loose m3 volume.

• Bucket Choice: flat (for aggregate type materials, or softs), or curved bottom bucket for optimum digging force (for hard lumpy types); bucket shape; GET (Ground Engaging Tools) choice; wear protection and the effect on filling time and bucket fill factor/ability. Incorrect bucket technology and capacity sizing can have a dramatic negative effect on machine output performance and associated operating costs. An understanding of wheel loader static versus dynamic tipping load design restraint is required to exploit full capabilities.

• Underfoot Condition and Haul Route/s: preparation and maintenance of load and dump area surfaces, plus that of haul route/s underfoot (often a major on site failing = the performance, operating cost and longevity ability of mobile earthmoving equipment is directly proportional to the quality of the running surface maintained and on which it must operate); grade/s resistance/assistance to traverse; haul distance/s; rolling resistance/tyre penetration; tyre type suited to underfoot and grip co-efficient ability (L2 to L5); dust control; inclement weather, etc.

• Operator Proficiency and Supervision Expertise: Many a machine is blamed for under performance due to the lack of adequate personnel with on-the-job operating and supervision experience, planning vision and method expertise.

• Load Receiving Arrangement/Dimensions: hopper height/match (or truck) at discharge point; clearance area for dump and manoeuvre; eliminating time consuming switchbacks or inconveniences to attain high tramming speed; maintaining correct extraction face/bench height and arrangement at loading area, which influence bucket filling time and the fill factor, etc.

• System Lost Time Factors: assessing, controlling and minimising erosive lost time which penalises machine productive uptime and usage on the job = can be a prolific system time penalty if neglected, resulting in low overall job efficiency. Striving for a high minute/hour job efficiency by curtailing time losses should be a first rule on any site. Losses come in many forms: mechanical down time; servicing periods; re-fuelling; shift change; lack of planning and safety; outside interference/s; absenteeism; improper job set-up; lack of discipline, etc.

We examine below, for calculation by the reader, a typical exercise to CALCULATE WHEEL LOADER SIZE FOR A GIVEN JOB ASSESSMENT. [refer to the Caterpillar Performance Handbook No. 32 (latest edition) for more information on this selection process.] THE JOB : determine size of Wheel Loader (simplified, as a one machine requirement in this instance) to move by LOAD AND CARRY means 220 tph (every hour), of loose calcrete material from stockpile to hopper intake, over a one way haul distance of 50 metres. KNOWN JOB FACTORS to use/apply : (use only those shown)

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• Material: class 2 type, loose, more powdery than lumpy, non abrasive; slightly moist, but not wet or sticky; 1,6 t/m3 loose density; bucket fill factor and retention “on the run” = 90%.

• Bucket: curved bottom type, materials handling purpose, with teeth and segments. • Underfoot Conditions: well maintained hard, smooth, dirt running surface/s and

work area/s, watered frequently. • Haul Route/s: from stockpile level at face area, to discharge at hopper intake 50m

one way (use this as overall distance between load and discharge points) with a constant upgrade of 3%, up and onto a level landing at same horizontal with hopper top; return route is a mirror image of loaded haul description; rolling resistance = 3% (tyre grip co-efficient, radial type).

• Operator Proficiency: 90% constant. • Overall Job Efficiency: 45-minute hour. • Typical Wheel Loader Cycle Factors to use: fill bucket at stockpile face and

manoeuvre to turn = 25 seconds; dump into hopper and manoeuvre to turn = 10 seconds.

• Refer to the Caterpillar Performance Handbook No. 32, wheel loader speed graphs to calculate loaded and empty travel times.

ANSWER: holistically, you probably determined that a wheel loader with a bucket capacity of +/- 3,75m3 would suffice in this instance. This matches with a CAT 966G SERIES 2 model, weighing 23 t, with 184 kW nett installed power. For future job capacity reserve and machine component conservation, it might be prudent to step up one size and select the CAT 972G (>4,3m3 – 25 t – 198 kW nett.)

Caterpillar Series II medium wheel loaders The latest wheeled loaders in the Caterpillar range are the Series 2 machines which host a number of

features unique to Caterpillar

Variable shift control (VSC), standard in 950GII through to 980GII, provides an economy mode which

allows the machine to upshift at lower engine RPM versus the standard mode. Particularly good for load

and carry operations, the easier smoother shifting provides benefits in reduced fuel consumption and lower

sound levels. VSC allows the operator to match the machine’s shift pattern to the application.

Integrated braking system provides downshift and neutralizer logic to the left pedal, enabling downshifting

to next lower gear for downhill retarding as well as full brake and neutralizer operation. By providing

retarding through the powertrain, the system transfers energy away from the brakes resulting in lower axle

oil temperatures. With correct usage, it also reduces load times and therefore productivity can be increased

relative to a machine without this system.

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Electronic engine management allows for the engine to produce maximum power in the working range rather than at rated RPM. The combination of more available torque and maximum power in the entire working range improves response, provides greater rimpull and faster cycle times. Coupled to the engine management system is a temperature sensing on-demand fan which slows fan speed at low temperatures and increased speed when required. Lower average fan speeds contribute to lower fuel consumption, lower noise levels and reduced radiator plugging.