Lyn Fischels from Bertch Cabinets asks: Why do abrasive belts fold over or crease while running?

Lyn, there are several reasons why your abrasive belts may be folding over or creasing. The most common reason would be due to humidity levels in your facility. If you are experiencing  an unusual amount of humidity, the moisture will soak into your abrasive belts. Think of your abrasive belts as being like sponges. This usually is not an issue in the winter months as the humidity levels are much lower. When your humidity levels have increased, it is best to keep all of your abrasive belts in a controlled environment, and only remove the number of belts needed to operate your machine. If you do not have a controlled environment to store your belts in, another solution is to install the belts on the machine and allow the belts to run for 5-10 minutes prior to running any material through the machine. This will allow your abrasive belts to become acclimated to the environment better.

Another reason your abrasive belts could be folding or creasing is because either the sanding drum or idler roll have tapers worn in them and will need to be dressed, or turned, and balanced. Think of these drums being in the shape of a bowling pin instead of rolling pin. Now try to successfully wrap a sheet of paper tight around that bowling pin. What happens? The paper will wrinkle or fold over and eventually tear. This could be what’s happening with one of your sanding heads.

The last thing to check is the speed of the tracking for the abrasive belt. If your abrasive belt is tracking to fast, it could cause the belt to fold. You are looking for a smooth and consistent back and forth motion of your abrasive belt.

Our conveyor belt is slick and glazed over. Do we have to replace it? Brad @ Raytheon Aircraft

That depends. First, you need to determine the condition of the belt, are there tears or gouges in the surface, how much of the surface of the belt is left, and what condition is the seam of the belt in. If all of these factors are good, then you should be able to “dress” your conveyor belt with one of the sanding drums. However, you MUST make sure that your sanding drum is in good condition and has minimal wear to it. I would also verify the condition of your bed plates for wear. If any of these components have wear in them, you will transfer that wear pattern to your conveyor belt when “dressing” it.

If you have a “rough top” or “diamond” style conveyor belt, I would recommend using an 80 grit cloth abrasive belt to dress it. If you have a “smooth top” or “waffle pattern” style conveyor belt, I would recommend using a 60 grit cloth abrasive belt to dress it.

Graphite Covered Polishing Platen

The graphite covered polishing platen (polishing pad) of most wide belt sanders is made up of a steel or aluminum bar with either a felt or foam padding, followed by graphite material. The polishing platen is used to generate the final end finish of wide belt sanders and prepare your material for orbital sanding or a finish coat.

It is very important that the graphite pad be free of any grooves, low depressions, or worn areas. We recommended that this polishing pad be removed from the sander weekly and inspected for any surface defects. This will also ensure the mounting bar does not collect dust, allowing for easy removal and installation of polishing platen.

If a defect is found and it is shallow enough, hand sanding can be used to create a flat surface. We recommend using a block type sander with 120 or 150 grit abrasive to hand sand the graphite of the wide belt sander polishing platen assembly while blending in the affected area. After hand sanding is complete, use an air hose to blow off any loose graphite so as not to affect the inside of the abrasive belt or the surface of the rollers used in the polishing platen head. If the felt or foam material has been damaged, we recommend replacing it prior to applying new graphite.

Note: Remember that the polishing platen of most wide belt sanders is used to generate final finish, and has the capability of removing only .004 – .005 of material. With this in mind, it is very critical that the surface of this pad be as smooth and flat as possible.

Also you will increase your abrasive belt life by using paper abrasive belts versus cloth abrasive belts. The cloth backing generally is rougher than the paper backing and will wear your graphite out quicker.

Paper vs. Cloth Abrasive Belts 

The two most common abrasive belts used in the industry generally have either a cloth backing or a paper backing.

A cloth belt is recommended for heavy stock removal (1/32” or more). For abrasive belts of grade 100 and below (80-60-40-36-24) a cloth belt is preferred.

A paper belt is recommended for light stock removal (1/64” or less). For abrasive belts of grade 120 and higher (150-180-220-240-280-320) a paper belt is preferred. Paper abrasive belts generally provide a better quality finish compared to that of the same grade cloth belt. The paper backing is more uniform than cloth and allows the abrasive grit a flat surface for bonding. Thus, paper abrasive belts sand more uniformly. Paper abrasive belts are generally less expensive than cloth abrasive belts.

U.S. Graded vs. “P” Graded Abrasive Belts

Abrasive belts are marked on the inside with abrasive grit type and direction of proper rotation. Abrasive belts can be purchased in either a U.S. grade or a “P” grade. A “P” graded belt, such as P180 or P220, are finer in nature and produce a smoother finish than a 180 or 220 marked belt. When high-end finish or minimum cross grain scratches are desired, a “P” graded product is recommended.

Open Coat vs. Closed Coat Abrasive Belts

Abrasive belts can be purchased in either open coat or closed coat. An open coat abrasive belt has less abrasive grit per square inch and is used for heavier stock removal. When finish and light stock removal are desired, a closed coat abrasive belt is recommended. A closed coat abrasive belt, with more abrasive grit per square inch, is also used if minimum cross grain scratch pattern is desired.

Static Electricity Streaking
The conveyor belt and abrasive belt within a wide belt sander have a tendency to create static electricity, which can cause streaking. Static electricity streaking is seen as a raised line of a relatively short nature (3/4” – 1”), randomly throughout the wide belt sander.

These streaks often have a tendency to come and go during the course of the abrasive belt life, so it is recommended that all wide belt sanders be properly earth grounded. A copper wire of approximately 3/8” diameter should be attached to the conveyor bed assembly. Removing the paint from the conveyor bed assembly prior to the attachment of the copper wire will achieve the best ground. The grounding wire is then connected to a 6’ – 8’ copper rod that is driven into the ground to achieve an earth ground.

It is also recommended that proper humidity levels be maintained around a wide belt sander because they can often collect dust, which removes the air in and around the sander. This can often create a very dry condition so many facilities have installed humidification systems very close to the wide belt sanders.

Note: When making an earth ground, it is very important that there is only one ground. Having two or more grounds can create a loop effect, very much like that of a generator, not allowing the static electricity to leave the vicinity, but rather to build.

It has also been determined that electrical conduits and blow pipes are of a coated material and do not provide a proper earth ground for wide belt sanders.