AtRed Label Abrasives, we’re always educating customers on how to choose the right abrasive for their application. While abrasive selection is an important part of getting the best results, you also want to ensure that your belt sander is set at the correct parameters.
Abrasive belts are widely used in grinding and sanding equipment, and all of them require tension to operate.They should be tensioned just enough so that the belt does not slip on the drive wheel or track off the machine.
Belt tension is fixed on some sanding machines. Portable sanders, for example, have a factory-set loaded spring, which cannot be adjusted. There is, however, usually some type of tensioning device on most sanding machines. Weighing mechanisms, screw-type mechanisms, and pneumatic cylinders are some examples. This blog reviews how much tension a belt sander should have, along with how to achieve it.
Low vs. High Belt Tension
When the belt tension is not fixed, determining the optimal setting can be a case of trial and error. Below is an overview of the signs that your setting may be too low or too high.
Low Belt Tension
There are a variety of symptoms associated with low belt tension, including belt tracking problems. For example, tracking off in the same direction every time may indicate excessive wear on the tracking wheel or roll or a side-to-side variation in length. Other signs include:
When the belt folds over, it breaks. A combination of roll wear and low belt tension can also cause this problem.
Wear is evident on the printing on the back of the belt. It slips on the drive roll, which wears off the print on the back.
The parts being finished have skip marks. The marks may have been caused by the belt losing speed or stopping, which can occur when the belt slips on the drive roll. In high-load situations, this can be a typical problem.
When the head starts up or parts are processed, a short, high-pitched whining occurs. In this case, too, the belt may have slipped off the drive roll. The belt whines when it has even minimal tension.
Over time, low tension can reduce the working life of the belt. This is because less pressure is applied when the belt slips, and the abrasive does not have the chance to break down and sharpen like it’s supposed to.
High Belt Tension
Tracking cylinders are typically much smaller than tension ones, so high belt tension can overwhelm them. Bearings on the drive, tracking, and idler rolls of the head may also break down prematurely. On any type of grinding or sanding equipment, the higher the belt tension, the more wear there is on all related bearings.
Other signs that belt tension is too high include:
Thesanding belt breaks easily. When a belt is overtightened, it is less able to absorb high or fluctuating shock loads.
Wear occurs on all rolls within the head. The belt typically wears at the outside edges of the rolls where it tracks back and forth. As belt tension increases, such wear increases excessively.
For screw-adjusted tension devices, it can be difficult to determine the proper tensioning amount unless you have considerable experience with that machine. After the machine is turned off, the belt should rotate five or more times. The tension may be too high if the belt stops very quickly.
Measuring Belt Tension
Most belt sanders need certain conditions in place in order to function property. For example, if you are using steel or rubber contact roll heads with an 80 durometer, apply 20 to 25 lbs of pressure per linear inch of belt width. In the case of platen heads and combination heads, use 15 to 20 lbs.
A variety of tools are available for measuring belt tension, including special tools designed for the purpose. You can use an OEM-recommended belt tension gauge, but standard air regulators can also be converted into measurement tools.
There must be two output ports and one inlet port on the regulator. Attach an air plug to the inlet port that matches the coupler on the airline closest to the belt sander. Next, install a good air gauge at one of the outlet ports. The other should be fitted with the belt tension air gauge's threads.
Upon completion of the tool, thread the gauge into the outlet port and connect the air supply line to the regulator. To determine the accuracy of the readings, compare the correct gauge with the suspect one at various PSI settings.
Watch Out for Air Leaks
Abrasive belt tension problems can be caused by air leaks, which are common in plants that use compressed air. There can be leaks in the air supply system as well as in tension cylinder seals. Ensure that all leaks are repaired and that periodic air audits are conducted throughout your facility. A compressed air system that is more efficient can save you money.
Abrasive Belt Tension Formulas
Use the following formula to calculate the correct tension for your abrasive belt.
Tension Cylinder Area = π × Radius2
Abrasive Belt Tension = (Tension Cylinder Area × Gauge Pressure rin PSI) / Belt Width
Generally speaking, wood sanding applications such as mold sanding (using narrow cloth belts) require belt tensions of approximately 40 psi. There are, however, some exceptions. In planing operations, for example, belt tension is typically between 70 and 90 psi.
For intermediate wide belt sanding, a tension of 60 to 75 psi is usually used. (Intermediate usually refers to 60 to 220-grit abrasives.) Paper belts should be tensioned at about 20 to 25% less than cloth belts in these applications. This is because cloth belts stretch slightly during use, while paper belts do not. To determine specific air tension settings, consult the manufacturer of the wide belt machine.
In drawer sanders, which sand the inside lip of a drawer front, it is best to use the least amount of belt tension. If you turn off the machine, you should be able to rotate the belt by hand easily. If the belt has stretched after 10 minutes of use, increase the tension of the sander.
Question About Belt Tension? An Abrasive Manufacturer Can Help!
Correct belt tensioning can increase product life, provide the best possible finish, and extend the life of your belt sander. If you’re not sure of the proper parameters, an abrasive manufacturer can help. Our abrasive technicians take pride in offering both customer and technical support.
Red Label Abrasives has been manufacturing and selling super-quality and high-performance abrasive belts for over 35 years. Our products are used in a wide range of industries, from woodworking and metal fabrication to plastic and textile production. If you have questions about sanding beltsor would like to know more about our abrasives before placing your order, pleasecontact us by filling out a contact form or calling 844-824-1956.
David Kranker is a writer and creative maker who has been covering the abrasive and knife-making industries on the Red Label Abrasives Blog since 2020. David spends his time continually researching sanding and bladesmithing to provide readers with the latest and greatest information. In his free time, David utilizes abrasives for many different home and auto projects at his home in Delton, MI.