February 19, 2013

Sanding Belts & Grinding Metal

Abrasive Resource can have sanding belts made up for you in any width or length you may need for grinding or polishing metal. We show the more popular sizes in an aluminum oxide material on our Sanding Belts page, but we can custom fabricate any size, grit or abrasive material you require in just a day or two!

Offhand grinding on metal is the most traditional way to use sanding belts and covers all the methods of abrading metal where the operator holds the workpiece in their hand and presents it to the abrasive belt (as opposed to the piece being held in a fixture.)

This type of grinding is done on a Backstand Sander—also called a polishing jack or belt grinder. These machines vary considerably in horsepower, ranging from one to 75 HP. Typically, units with 7-1/2 to 15 HP provide a good working power for most applications at speeds between 3500 and 7000 sfpm. All grinding should be below the center line of the contact wheel and the workpiece should be brought up to the belt.

Optimum belt speed depends mostly upon the material you are grinding. Testing indicates that as the belt speed increases, so does the amount of metal being removed. However—as belt speed increases, the amount of heat generated also increases which may result in premature dulling of the abrasive grains (glazing) and/or heat damage to your workpiece.  The optimal speed range in sfpm for grinding belts is shown in this table:

Next you need to factor in grinding pressure. Pressure is an important part of the grinding process as it causes the abrasive grain on the belt to fracture and create a continuing supply of fresh, sharp cutting edges. An operator will generate this pressure against the contact wheel in a range of 20-50 psi. On an average offhand operation of moderate stock removal, a 70-75 durometer rubber contact wheel is the most useful. For more information on contact wheels, refer to our 2005 Sandpaper Blog post “Contact Wheels for Abrasive Belts”.

Finally, remember to check that the abrasive belt, idler assembly and contact wheel are enclosed within a sheet metal hood when using a backstand grinder. The hood must confine flying sparks and fumes as well as protect the operator from a belt breakage.

Basic Sanders

The basic styles of portable sanders haven’t changed very much over the years. We have some old advertising posters from the Rockwell Manuf...