Most drivers understand that proper wheel alignment for your vehicle is paramount to your safety. It also extends the life of your tires, provides better gas mileage, and gives a 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.
As with any scale system, a solid, non-flexing support is required. Any deflection in the support will result in a change in idler alignment. 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” or more), as many as seven 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 +/- 1 degree.
I recommend that you use an idler specifically manufactured for use with a belt conveyor scale. These idlers, sold as either “scale duty” or “scale quality”, ensure, among other things, that the idler rolls meet the minimum Total Indicated Runout (T.I.R.) tolerance of .015” and that the idler trough angle is within +/- 1 degree. T.I.R. is 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. While 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 (and be) time-consuming and costly, but they will aid in long-term accuracies from the belt conveyor scale system.
For more maintenance tips, read Keeping your Bulk Material Handling Systems in Balance – Maintain Your Scales
To help you decide which belt scale system is best for your mining operation, we’ve outlined the options in an easy-to-read belt scale system selection guide so you can decide which belt scale system is right for you. Click on the image, take a look at the chart, and see if it helps you decide.