Minimum run out of idler rollers for belt conveyor

Most of the drivers understand that proper wheel alignment for your vehicle is paramount to your safety and extends the life of your tires, provides better mileage and gives more comfortable ride. Similarly, proper alignment of the “scale area” is paramount to satisfactory operation of a belt conveyor scale. Most scale manufacturers have established strict guidelines for installing and aligning belt conveyor scales. Failure to follow these guidelines may result in less than favorable scale accuracies and repeatability.

The idler alignment must be completed prior to placing a belt conveyor scale into operation. This alignment includes idler spacing, centering the idlers on the conveyor frame and adjusting the idler backing height. All of these dimensions must be held to a maximum tolerance of 0.030. The height and centering dimensions of alignment are verified by use of several “string lines”. It is recommended that a minimum of five string lines be used and on wide conveyors (≥42”) as many as 7 string lines be used. These lines will ensure that the idlers are level with one another, aligned on the same conveyor centerline and that the wing roll angles match within ± 1o.

It is recommend the usage of idler specially manufactured for use with a belt conveyor scale. These idlers are known as scale duty or scale quality ensure. The minimum Total Indicated Runout (T.I.R) tolerance is 0.015” and that the idler trough angle is within ± 1o. T.I.R is a measurement of the variance of a cylindrical item as it is rotated. Here’s a sketch to illustrate the measurement using a dial indicator.

Some manufacturers build a scale quality idler that has an adjustable plate built into the end stand to enable fine alignment of the trough angle during installation. The use of existing idlers (non-scale quality) is not prohibited, it may result in additional time being required for the alignment. In extreme circumstances, it may be necessary to modify the trough angle to meet the 1 degree tolerance, as well as adding bracing to the cross member and adding gusset supports to the end stands.

These “extreme” measures of idler modification may seem time-consuming and costly, but they will aid in long-term accuracies from the belt conveyor scale system.

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