Introduction to Abrasive Finishing

Abrasive finishing utililzes various types and sizes of abrasive minerals.  These minerals are bonded to paper, cloth, belts, wheels, non-woven products, bonded products, rubber, sponges, film, composites, or brushes. 

When the abrasive product is moved across the workpiece with pressure applied, it will reomve material, dimension, mechanically and visually finsh with endless results. 

A few of the products finished are wood, glass, stone, composites, and metals.

Below are areas of specialized abrasive finishing knowledge:

• Surface Feet Speed Recommendations
   

• Abrasive Grit / RMS Comparisons
   

• Abrasive Grain Sizes and Comparisons
   

• Abrasive Storage and Safety Recommendations

Offhand Grinding Suggested Belt Speeds
Surface Feet Recommendation

	Material	Belt Speed (sfpm)
	Cast Iron	7000
	Carbon Steel	6500
	Stainless Steel	6500-7000
	Aluminum	7500-8000  Coarse
		6500-7000  Fine
	Brass	7000-8000
	Titanium	2500-3000
	Glass	5000          Silicon Carbide
		7500-8000  Flex Diamond
	Rubber	4500
	Stone (2000-3400 rpm)	7000
	Cobalt	4500-5500  Coarse
		3500-4000  Fine
	Magnesium	5500-6000
	Plasma Coating with Diamond	5000-6000
	Dia. CW x x RPM 12 =SFPM	SFPM x 12  Dia. CW x =RPM

THIS IS A FUNCTION OF DIAMETER OF WHEEL AND RPM.  IT'S A GIVEN SPEED (EASILY DETERMINED BY CHART) THAT AN ABRASIVE PASSES THE WORK PIECE.  EACH METAL IS CUT EFFICIENTLY, COOLER, AND WITH BETTER FINISHES AT A GIVEN SURFACE FEET.  ALSO ABRASIVES WORK BETTER AND LAST LONGER AT THESE SURFACE FEET.

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ABRASIVE GRIT / RMS COMPARISON

NOTE:  THIS INFORMATION IS BASED ON ALUMINUM OXIDE HALF LIFE BELTS.  A BELT GREASE AND SEVERELY WORN BELT WILL IMPROVE RMS FINISH.

24X 160 RMS   36X 140 RMS   40X 130 RMS   50X 110 RMS   60X 90 RMS   80X 65 RMS   100X 60 RMS   120X 50 RMS   150X 37 RMS 27 RMS WITH GREASE 180X 25 RMS 18-20 RMS WITH GREASE 220X 15 RMS 8-9 RMS WITH GREASE 320X 5-4 RMS   400X 4-5 RMS   600X 2-3 RMS

The half-belt-life principle An exmaple of the half-belt-life principle at work:  A typical 100 grit aluminum oxide paper belt will produce a finish reading of about 90 when new...and 45 when used.  If it is moved at half-life, we have the effect of two different belts.  The first produces 90 to 60 readings and the second, 60 to 45 readings.

Flat polishing finish requirements Industry experience has shown that different plating systems require different finishes. This chart shows approximate finish requirements in the automotove industry.  Generally speaking, plating systems which employ less nickel or copper have less covering power, and require finer finishes on the bare metal.   Finish requirements   PLATING TYPE FINISH REQUIRED Buffed copper plus bright nickel . . . . . . . . . . . .12-15 Buffed nickel . . . . . . . .8-10 Semi-bright plus bright nickel . . . . . . . . . . . . . .4-7 Bright nickel. . . . . Steel Buff

Effect of lubricant on finish    DRY  LOW VISC OIL  HIGH VISC OIL  GREASE   Effect of lubricant on finish When a lubricant is applied to the belt the areas between the mineral are filled somewhat by the lubricant.  This keeps the mineral from penetrating into the work piece as far as it would when dry grinding.  The thicker the lubricant, the less the penetration, thus making a fine finish with the addition of grease.

Effect of lubrication on buffing time Applying oil or grease to the belt for a polishing operation reduces buffing time.  A greased belt cuts buffing time in half as compared to a dry belt.

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ABRASIVE STORAGE AND SAFETY RECOMMENDATION

PROCEDURES FOR PROPER STORAGE OF ABRASIVES:

• All abrasives shuold be stored in areas that are maintained at 40% to 50% relative humidity and 60° to 80° F.  Glue bonded coated abrasive products are especially sensitive to high humidity.
   

• Abrasives should be kept in their original packing containers for storage.
   

• Store abrasives away from heat sources such as radiators, steam pipes, furnaces, or windows.
   

• Cartons should be kept away from damp or cold walls and floor where they may absorb moisture.
   

• Precondition abrasive belt prior to use by removing from carton and allowing to adjust to ambient air, hanging on proper peg or bars.  This is especially important for wide belts, which should be removed up to 24 hours prior to use.  (Also see recommendations for abrasive belts.)
   

• If necessary, a pre-conditioning chanber should be built to ensure constant humidity control for coated abrasives.  Humidity can cause cupping of coated abrasive products, as well as premature loading and reduced product life.  In belts, high humidity can cause tracking and creasing problems. 
   

• Bonded grinding discs and cut-off wheels should be stored flat until used.
   

• Bonded abrasives should be handled carefuly to avoid dropping or bumping.  This also applies to coated abrasive flapwheels and mop discs. 
   

• Regular stock rotation is also recommended.

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