Did you know proper idler alignment is critical for your beltscale to run at its best?
Let’s review all the steps necessary to ensure that your alignment is performed correctly.
Be sure that your beltscale and idlers are properly installed as per the appropriate Beltscale Operating Instructions Manual
and the Siemens Beltscale Product Application Guidelines Manual.
The proper beltscale location, idler modification and installation are critical before performing the idler alignment.
If necessary, Siemens also has FAQs, forums and service requests giving you access to product experts to help from our Industry Online Support site.
The number or target idlers varies with the model of the Beltscale;
For single idler scales we consider a minimum of 2 idler before and 2 idlers after the beltscale.
For multi-idler scales we consider a minimum of 3 idler before and 3 idlers after the beltscale.
Idler alignment means that the target idlers are all the same make, model and shape and that they are all on the same plane.
This means if we were to place a long straight edge at any common point on the idlers that they would all come in contact with it.
It is not always practical to use a straight edge, so the easiest method to achieve a detailed idler alignment is the string line method.
The String can be any strong, fine line such as piano wire, masonry twine or fishing line less than 0.030” or 0.76 mm diameter.
This example is using fishing line.
Two runs of fishing line are used for flat idler applications with each string located 25 mm from the idler’s edge.
For a troughed idler application use 3 strings.
Two located 25 mm from the edge of each wing roller and one centered on the center roll.
To begin we raise or remove the conveyor belt to give us room to work.
Next, we run the strings, secure one end to the conveyor structure.
Then wrap around once on the first idler, the string is then stretched out over all the idlers until the last idler.
On the last idler, wrap the string around as you did on the first one and down to the frame of the conveyor.
Wrap the string around the frame one time to make it easy to cinch the string to a very tight state.
Once the string is tight enough that there is no sag in the line, tie it off to the frame.
Repeat this process for the other strings.
With the strings installed and tight we can now see if any of the idlers are sitting lower than the rest, but not if one or more of them are too high.
Now we add small pieces of “keystock” also known as machine keys, keyway stock or square mechanical steel bar.
These pieces are cut into 50mm or 2 inch lengths and ends are de-burred.
3 pieces of keystock are placed between the string and the roller on each of the first and last idlers, making sure they are at the highest point of the rollers.
Now the string is sitting up off the rollers by the thickness of the keystock.
We use another piece of the keystock to examine each of the rollers on all of the idlers in-between for alignment.
This method can tell us if the idlers are too high or low with respect to the first and last idlers, it also determines if the transverse (or side-to-side) alignment of the idlers is correct.
Shims can be added or removed to adjust the heights to achieve the target alignment.
Typical Motor Mount Shims in different thicknesses can be used to make these adjustments.
These shims, often made of stainless steel can be purchased at most Bearing Houses around the world.
They can be purchased in bulk by size and thickness or in a Shim Pack with an assortment of thicknesses in one convenient carrying case.
Alternatively Siemens offers a “Belt Scale Installation Kit”.
When placing the shims under an idler, use 2 shims of the same thickness under the mounting foot to ensure the idler is being raised straight up.
When shimming the scale we have a choice to raise the entire scale or to raise the scale mounted idler only.
During the alignment process is an excellent time to ensure that the idler spacing is all the same for a minimum of 2 spaces before and after the beltscale and that all of the idlers are parallel to one another and square to the frame of the conveyor.
The tolerance value for the vertical alignment is very tight because the deflection of a loadcell is very small.
The tolerance value for the vertical alignment is +/- 1/32nd of an inch for a single idler beltscale.
And +/- 1/64th of an inch for a multi-idler beltscale.
Poor idler alignment is the number 1 cause of non-repeatability and inaccuracy in beltscale applications, taking the time to do a detailed idler alignment right the first time will ensure that your system is delivering as expected.