Components, such as idlers, motors and bearings are important in plant operations. There are many options for these types of components, depending upon the kind of equipment being used.

When it comes to idlers (right), choosing the proper one for your application can make the difference between efficient production and frequent shutdowns.

Load limits for idlers discussed in this chapter reflect CEMA methods. Basic calculations are based on L10 requirements at 500 rpm.

While the smaller cans will help with reduced build up, larger cans help with lower speed, revolutions per minute (rpm) and therefore the bearing, extending bearing life. For this reason, the suggested maximum belt speed for different can size exists.

If these suggested maximums are exceeded, then a decreased life of the idler bearing will be experienced. To overcome this may require a decreased rating, or an increase in CEMA class. For more detailed look at conveyor design and idler selection consult CEMA's book, "Belt Conveyors For Bulk Materials."

The following steps and tables will enable you to select belt speed and belt width for most applications. Idler manufacturers are available to assist if you have special requirements, including specific bearing-life expectations.

Getting Started

If you know your tensions, belt width and speed, skip to Step 5 on page 171.

What are you conveying? Do you know your material?

Note: Important information needed is the material density (weight per cu. ft.), and the Angle of Repose. To determine the Angle of Surcharge, look up Angle of Repose in Table 13, and apply it to Diagram 2.

Diagram 1

What is the Angle of Repose? There are two basic angles that describe the flow nature of material. One is the Angle of Repose (Ar); the other is the Angle of Surcharge (As). The Angle of Repose is the angle the material makes with the horizontal when dumped in a pile, such as a stockpile or a stationary belt. It is a direct measure of the static friction of the material.

Diagram 2

The Angle of Surcharge (As) is the angle the material makes with the horizontal when the material is bumped, or moving, such as on a moving conveyor belt. It is a direct measure of the kinetic friction. The higher the surcharge angle, the more material can be stacked on the belt for conveying. It is often the maximum incline of the conveyor. The surcharge angle is normally 5 degrees- to 15-degrees less than the Angle of Repose.

Step 1) Determine the material characteristics, lump size, Surcharge Angle of material being conveyed, the desired or preferred Trough Angle, and cu. wt.-per-ft. of material. The trough angle is the angle the wing roll of the trougher make with the horizontal. (See Table 13).

Note: If you are unsure use 35 degrees for standard troughers, use 20 degrees for CIT and unequal troughers.

Step 2) Calculate the Volumetric Capacity, C, required. This is calculated from the tons per hour (tph), using the following formula:

C (ft3/hr) = tph * 2000 / Material density (lbs/ft3)