Conveyor vs Haul Truck

7/29/2019 Conveyor vs Haul Truck

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Basic Conveyor Design and Maintenance

Belt Conveyor Design Idler Life

Stockpile Segregation

Pulley Stress Contributors and Their Variables

Contact Superior Industries to order more printed literature.


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The landscape of the world continues to change inmany different facets in the aggregate and miningindustries. Aggregate reserves are becoming rarecommodities in many areas, transportation issuesare priorities because of rising costs and citizenconcerns, and industry requirements for specializedproducts are all factors in the discussion surrounding

this transformation. These factors continue to drivethe need for change in the way that aggregates aretransported, not only from the source of the aggre-gate and/or the production area, but also from theproduction site to the area of further processingor end-use.

The decision to get product from the aggregatereserve to the crusher or to the area of stockpilingby truck or by conveyor is made because of a num-ber of inputs that are analyzed. Cost benefit, prod-uct quality, topography, and environmental issuesare the areas that need to be analyzed in order to

make the right decision when choosing conveyors ortrucks to move product. Improvements in conveyormobility, function, design, and flexibility, as well asescalating costs for operating haul trucks show thedecision to use conveyors much more cost effective.

#OST"ENElTThe main benefits of using conveyors, not only over-land applications of short, medium or longer length,but radial stacking or telescoping conveyors forstockpiling where trucks have also been traditionallyused, are decreased operating expense, (see Figure1) limited inflationary effect, improved product qual-ity, continuous flow, environmental friendliness, andthe flexibility of design for conveyor systems.

Maintenance costs of conveyors are less as moredowntime is required to keep trucks and loaders run-ning efficiently. In addition, most conveyor replace-ment parts are available locally. Conveyor systems

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are also less labor intensive as trucks orloaders require one or sometimes two opera-tors. Conveyors will also operate at maximumefficiency every hour of operation. This candecrease workforce and training requirements.

While the big advantage of the haul truck con-tinues to be its flexibility, even bigger disadvan-tages are increased fuel prices, increased laborcosts to operate, maintenance costs, and theshortage of parts such as tires, with lead timesof over six months being reported.

Overland conveyors offer cost-effective mate-rial transport and a wide spectrum of capacitiesthat can vary from a trickle of material all theway up to 30,000 tons per hour. Furthermore,with a lifespan of more than twenty years, thebenefits of their high-capacity and low-cost

operation are realized long after the initialtruck fleet is retired. As an example, a Texas-based mining operation reports that their newlyinstalled 2-mile-long conveyor eliminates morethan 140,000 truck trips and 570,000 vehiclemiles on an annual basis. Added to the fuelsavings, this operation is significantly reducingcosts associated with labor, workers compen-sation costs, MSHA training, emissions,maintenance and engine depreciation.

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The above costs, and cycle-time considerationswhen truck hauling in urban traffic congestion, werealso factors in the recent Atlanta Airport projectwhere a 5-mile-long overland conveyor was chosenas the method to transport 40 million cubic yards offill material from several nearby quarries to the con-struction site of a fifth runway. This overland convey-or also allowed the proper blending of crushed rockand overburden material in desired percentages asit was fed onto the belt.

Limited inflationary effect is achieved because ris-ing fuel and energy prices have little effect on theoperating costs of conveyors, and are not sensitiveto fuel shortages. Electricity costs are fairly stablecompared to diesel prices and conveyors can be runat off peak energy times.

Improved product quality is seen because convey-ors eliminate multiple handlings of material, whichprevents compaction and contamination typicallycaused by trucks and/or loaders. Telescoping con-veyors eliminate segregation and material degrada-tion. Continuous flow is another advantage realizedbecause conveyors are not affected by weather,can be fully automated and operated at the touchof a button. Aside from initial capital cost, operat-ing expenses are the next major measured costsin aggregate operations. Initial comparative areasshow that conveyor systems have high capacity anda low cost of operation, while depending on dis-tance, the capital cost of a conveyor system can behigher than a haul truck. However, no matter whatthe distance, cost of operating a conveyor will beless. Long range costs show that conveyors havelimited inflationary effect and a long life span of atleast 20 years.

4OPOGRAPHY

Current conveyor technology can take on inclinesup to 35-degrees while truck efficiency is compro-mised in any inclined application (see Figure 2).There are also immovable issues such as the layof the land. Haul trucks are not designed to tacklegrades much above 6%. It is clear that more andmore operations are limiting truck transport to thearea between the working face and the pit crusher.That means that haul trucks are suitable mainlyfor level applications and truck efficiency iscompromised in any inclined application.


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However, bigger isnt necessarily better. A commonmisconception is that oversized equipment lastslonger and requires less maintenance. Conveyorsshould be sized according to the expected load yetallowing for a small capacity increase. For example,going with a 36-in belt when you only need a 30-inbelt will ultimately result in additional belt and idler

rolling resistance, and less energy efficiency. Also,overland conveyors do not need to be five miles longover rugged, mountainous terrain to be consideredas a legitimate option. Overland conveyor lengths asshort as 500 feet are shown to have significant costreductions over haul trucks. Payback of a systemfrom 1,000 feet to 3,000 feet have been shown tobe as short as 88 days to 182 days.

Electric motors consume 64 percent of the electric-ity produced in the United States, says a Northeastutilities provider whose report cites the example of a

100 HP AC induction motor that costs approximately$5,000, yet will use as much as $35,000 worth ofelectricity over its lifetime. With that said, its clearthat small improvements in efficiency can generatenotable energy savings. As such, todays conveyormanufacturers normally install new premium effi-ciency motors on each unit they build. Since thesemotors perform most efficiently near their designedpower rating, its recommended to run at between75 percent and near 100 percent of full load rating.If youre running at 50 percent of capacity or lower,

the efficiency of the motor drops dramatically.Motor size should be matched to the horsepowerrequirements of the load.

Again, some producers will oversize a motor think-ing that it will require less maintenance. But thinkagain the energy savings realized from a properlysized motor will outperform any maintenance sav-

ings derived from a larger model.

Monitoring and minimizing rolling resistance requirespaying close attention to the quality of your belt andidlers. Manufacturers are now designing belts withspecial covers that help to counter rolling resistance.As to idlers, they may look similar but they vary inperformance. Ask your conveyor manufacturer torecommend the right bearing and seal type for yourapplication. Proper idler spacing is also important.Consult with the Conveyor Equipment ManufacturersAssociation (CEMA) or your conveyor manufacturerfor idler spacing and rolling resistance formulas.

Systems must be designed and operated relative tothe maximum material lump size. This is particularlyapplicable to material conveyed from the primarycrusher. As the lump size increases, the potentialcapacity for a given belt width decreases. Someproducers may skimp on belt width, while runningat higher speeds or capacities. And while they maysize their belt according to lump size, they may berunning at a capacity that is not suitable to that lumpsize. A basic rule of thumb dictates that you shouldnever run at an excess of 80 percent of volumetriccapacity. Plus, when youre running material that isat maximum lump size, its best to remain under 80percent volumetric capacity to maintain standardedge distance and safe operation.

3AFETYAND-AINTENANCE

Obviously, safe conveyor maintenance does notallow for crawling under the unit to get to the otherside. A ground line or overland conveyor must be de-signed with crossover points (for pedestrian and/orvehicles) at convenient intervals, so that producers


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%NVIRONMENTAL)SSUES

But beyond costs-per-ton, there are other keydrivers in an emerging overland conveying trend.Consider the ever-tightening environmental regula-tions. Individual mobile haulage units emit and stir

pollution along the entire transfer path. As produc-tion sites expand and encroach upon suburbandevelopment, concerns arise over dust, noise andtraffic. As such, quarry owners are often involved indecade-long negotiations over leasing and permit-ting. For instance, when faced with government andcommunity opposition, a California-based aggregateoperation proposed the use of overland conveyorsover scrapers and trucks. They were armed withan environmental impact statement issued by theBureau of Land Management. It reported that theuse of overland conveyors over haul trucks wouldreduce estimated PM-10 (particulate matter larger

than 10 microns) emissions by mobile haulagefrom 211 lbs. per day to as little as 5.1 lbs. perday (see Figure 3). Additionally, community con-cerns could be eased by the fact that an overlandconveyor would offer quiet material transport,and when designed properly, could blend inwith the environment.

$ESIGN1UESTIONS

A system needs to be based in reality, and accordingto your specific site parameters. What is the lay ofthe land? What is the percentage of incline? Will

you need to cross roads or streams? What is thebest way to route the conveyor? What is your poweravailability? What are your horsepower requirements?Answering these questions will provide a clearerpicture of what conveyor system will not only work foryou, but will make your operation an environmentallyfriendly neighbor, reduce safety issues for yourassociates, and save you mountains of money.

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Conveyor vs Haul Truck