There are a number of factors that affect width. These include TPH feed, future considerations, lump size and the % of fines, cross section of how the material settles on the belt, and material weight.
Normally, portable conveyors are set-up to run at 350 feet per minute, as this is accepted as the best speed for the greatest number of types of material and optimum component life. When it is desirable to run at a different speed, this will usually be a factory decision based on the material and the capabilities requested by the customer. These variations are generally applicable on engineered systems.
Lump size and the % of fines can have a major affect on width selection. As a rule of thumb, for a 20-degree surcharge angle, with 10 percent lumps and 90 percent fines, the recommended maximum lump size is one third of the belt width (BW/3). With all lumps and no fines, the recommended maximum lump size is one fifth of the belt width (BW/5). For a 30-degree surcharge angle, with 10 percent lumps and 90 percent fines, the recommended maximum lump size is one sixth of the belt width (BW/6). With all lumps and no fines, the recommended maximum lump size is one tenth of the belt width (BW/10). Belts must be wide enough so any combination of lumps and fine material do not load the lumps too close to the edge of the belt.
The cross section of how the material settles on a moving belt can have a major affect on expected tonnage for a given width conveyor.
FACTORS AFFECTING THE CROSS SECTION ARE:
- The angle of repose of a material is the angle that the surface of a normal, freely formed pile, makes to the horizontal.
- The angle of surcharge of a material is the angle to the horizontal that the surface of the material assumes while the material is at rest on a moving conveyor belt. This angle usually is 5° to 15° less than the angle of repose, though in some materials it may be as much as 20° less.
- The flowability of a material, as measured by its angle of repose and angle of surcharge, determines the cross-section of the material load that safely can be carried on a belt. It also is an index of the safe angle of incline of the belt conveyor. The flowability is determined by such material characteristics as: size and shape of the fine particles and lumps, roughness or smoothness of the surface of the material particles, proportion of fines and lumps present, and moisture content of material.
The material weight affects the volume, which affects the width. Most aggregate weighs between 90-110 lbs. per cubic foot. When the weight varies significantly, it can have a dramatic effect on expected belt width needed to achieve a given tonnage.
The power required to operate a belt conveyor depends on the maximum tonnage handled, the length of the conveyor, the width of the conveyor and the vertical distance that the material is lifted. Factors X + Y + Z (from tables below) = Total HP Required at Head-shaft. The figures shown are based on average conditions with a uniform feed and at a normal operating speed. Additional factors such as pulley friction, skirtboard friction, material acceleration and auxiliary device frictions (mechanical feeder, tripper, etc.) may require an increase in horsepower.
Drive efficiency is taken into consideration to determine the motor horsepower required. This can be an additional 10-15% above the headshaft HP. The ability to start a loaded conveyor will also require an additional HP consideration.
Series 12: Portable, standard duty, lattice frame feed conveyors and surge bins. Series 11: 30″ or 36″ wide conveyors incorporate various hopper/feeder combinations.
- Gravity feed hoppers are used primarily in “free flowing” materials and are installed directly over the conveyor tail end and are used with top loading equipment.
- Feeder hoppers generally provide a more accurate metering of material than does a gravity hopper.
- Belt feeder/hopper – belt feeders are commonly used and recommended for handling sand and gravel and sticky materials, such as clay or topsoil that tend to build-up in other types of feeders. A hopper is mounted above the feeder for use with top loading equipment.
- Reciprocating plate feeders/hoppers – reciprocating plate feeders are used for free-flowing sand and gravel, to minimize impact directly to the conveyor belt. A hopper is mounted above the feeder for use with top loading equipment.
- Gravity feed dozer trap is used primarily for “free flowing” materials when push loading material with a dozer. Material feeds directly to conveyor belt.
- Belt feeder/dozer trap – includes belt feeder as described above with feed coming from a dozer, pushing material into the dozer trap.
- Plate feeder/dozer trap – includes plate feeder as described above with the feeder coming from a dozer pushing material into the dozer trap.
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