Abrasive Grain

In selecting a coated abrasive belt, the user must choose from several abrasive grain types available. The coated abrasive grain has a direct relationship to product life and finish. At its most basic, this can be best described as shown below:
 Good - aluminum oxide
 Better - zirconia alumina
 Best - seeded gel ("SG") ceramic aluminum oxide
On applications where productivity and cost-effectiveness can be measured, nothing matches the productivity and finish quality consistency produced by using SG ceramic abrasives. The difference in abrasive performance can be traced to the way SG grain is manufactured. The abrasive is made using a process that creates ceramic aluminum oxide crystals containing billions of abrasive particles per grain. This "microstructure" allows each grain to remain sharp during sanding, continually exposing fresh, sharp cutting points.
When comparing belt life and finish consistency using SG versus standard aluminum oxide, productivity increases of 300 to 600 percent are common. For example, one major wood furniture manufacturer using SG abrasive belts found that the belts ran for six full production days on three wide belt-sanding machines. At another, SG belts running on a variety of wood species ran for an average of four production days, as compared to .75 days for competitive belts.
When specifying the grit size of the grain you've selected, don't choose a coarser grit size than is absolutely necessary to achieving your required finish. Coarse grit products create patterns that must be completely removed as finish upgrade approaches your required sanded surface.
Don't skip more than one grit size in a grit sequence when finish upgrading. Skipping two or more grits in a sequence can become very costly, because an excessive number of the finer grit belts must be used to remove the previous coarse grit pattern.

Backing

Belt selection also includes the choice between cloth-backed and paper- backed products. On sanding machines, cloth-backed belts are normally used on the primary contact roll heads because of the potential for breakage when thick and tapered parts are fed into the sander. Cloth-backed coated abrasive belts will better withstand the shock caused by these pieces.
Paper-backed belts are generally recommended for use on the platen finishing heads. When compared to cloth belts of the same grit size, paper belts are less costly and will typically produce a higher quality finish. And, with today's designs, paper belts can produce nearly equal belt life. In many applications, SG paper-backed belts have out-produced cloth belts by a factor of 3 to 1.
When testing paper vs. cloth on belt applications, it is advisable to decrease the belt tension gauge pressure by approximately 20 - 25 percent. The reason: cloth will stretch very slightly, while paper will not.
Both cloth- and paper-backed coated abrasives are now available with "anti-static" abrasive technology, which neutralizes the static charges of dust particles, allowing these particles to be exhausted more efficiently. In this way, anti-static technology minimizes dust on the work piece and sanding equipment, and prevents premature loading of the abrasive belts. Because the work piece stays cleaner, belt life and rate of cut are improved and a better overall finish results.

Cause and Effect

When approaching any sanding challenge, it's important to understand the "cause and effect" relationships in the sanding process. A machine adjustment may temporarily solve the problem at hand; however, it may create a different problem entirely. This is particularly true when making frequent adjustments on multi-head wide belt machines.
For example, feed through speed has a direct relationship to stock removal rate. Slower feed through speeds allow for greater stock removal, and vice versa. However, it's important to remember that slower feed through speeds can generate more heat.
Finish also has a direct relationship to feed through speed. Faster feed through speeds produce a finer finish with less heat. The opposite is true using slower speeds.
These examples, while hardly exhaustive, demonstrate how an understanding of the sanding and finishing process can help you to identify -- or better yet, avoid --sanding problems. To optimize your sanding results, work with your coated abrasives manufacturer to ensure proper product selection and usage.