Abrasive belts

This is a general guideline for starting recommendations. Variables such as machine type, type of metal, coolants, belt speeds etc. can require different recommendations.

Ferrous Metals

In general, steel of all types tends to generate much frictional heat during the grinding and polishing process. Particularly heat sensitive are tool steels, stainless steels and high nickel or cobalt alloy steels. Thus, these materials require slower belt speeds and the possible use of a belt lubricant or coolant.

Steels of all types are generally ground with Ceramic, Alumina Zirconia or Aluminum Oxide although occasionally Silicon Carbide is used on stainless steels to impart a fine satin finish. Cast iron is mostly ground in coarser grits using CR, AZ or SC, but most polishing operations will use AO.

The normal grit range for ferrous metal-polishing is 80 - 50 for general polishing and 180 - 320 for fine polishing leading to buffing operations. Only for very fine satin finishes or applications requiring a precision tolerance will grits of 500 or finer be used.

Non-ferrous Metals

Non-ferrous metals are those which do not contain iron as a principal element. The most common types used in metalworking are aluminum, zinc and brass. Other non-ferrous metals which necessitate grinding and polishing are bronze, copper, magnesium and so-called "exotic" metals such as titanium and zirconium.

Compared with steels, non-ferrous metals are usually softer and even "gummy". This difference causes abrasive belts to "load" (clog) more quickly unless a lubricant or a slower belt speed is used. Most non-ferrous polishing operations will use Aluminum Oxide belts, although Silicon Carbide is preferred for very fine satin finishes or where fast cutting is a priority over durability. Silicon Carbide is highly preferred for polishing on titanium and zirconium because these metals have a degree of high heat sensitivity and may react chemically with Aluminum Oxide. Normally AZ is used for removal grits 24 - 120.

Common grit ranges for non-ferrous polishing are 80 to 180 for most operations, and 150 to 240 for fine work. Aluminum which is to be anodized may need to be polished to 320 to fully smooth over imperfections in the metal.

Non-metal Materials

Glass

Silicon Carbide is used almost exclusively. Water is used as a coolant quite frequently to control heat build-up and harmful dust. Grit range is 180 to 320. Special cork-based polishing belts are used for final polishing to full clarity.

Plastic

Thermo-plastics (nylons, acrylics and urethanes) are relatively soft and are quite heat-sensitive. These plastics should be polished wet if possible to prevent melting or surface damage. Thermosetting plastics (epoxies, polyesters, poly-carbonates and phenolics) do not soften with heat and can be polished wet or dry. Silicon Carbide is the preferred abrasive mineral for all plastics, although AO can be used on thermosetting plastics if preferred. Grit range is 180 to 320 for polishing.

Stone

These include concrete, brick, ceramics, granite, marble etc. Silicon Carbide almost exclusively is used in grits 120 to 220. Stone is often ground and polished with water as a coolant and to control dust.

Rubber

Silicon Carbide almost exclusively is used in grit range 80 to 240. It is normally ground and polished dry. Most rubber polishing is seen in roll resurfacing operations.

Grit Sequencing

A proper progression of grits is necessary to ensure that unwanted coarse grit lines are not visible on the finished product. Especially in the case of fine plating or thin layers of plating, it is important not to have scratch lines which are coarse enough to show through the plating metal. The proper selection of grit is mostly a trial and error situation, because of the vast number of variables in workpiece type, machinery; contact wheels, operators, etc. can affect the sanding results received.

Generally it is best not to skip more than one grit number when moving to finer grits. For example, a possible sequence might be 80 - 120 - 180 - 140 - 320. For soft metals, a larger jump may be practical because the metal may "flow" better to cover coarser grit lines. Conversely, hard steels require a greater number of grit steps in order to remove coarser grit lines most efficiently.

For the best possible "mirror finish" on hard steels, it is advised to not skip any grits when moving through a grit series prior to buffing. The CAMI and FEPA (P) grade grit size standards have been established so each finer grit in the series will remove the next coarser grit scratch. The time required for buffing is directly related to the size of the last belt polishing grit size. Therefore, use the finest grit possible as the last step before buffing.

Belt Tension/Machine Requirements

Belts are very strong and can perform under rigorous operating conditions. However, excessive belt tension can cause failure of belts in addition to problems with finish and wear of machine bearings. Almost all belt machines are tensioned by spring mechanisms or by an air cylinder. Air-operated tensioning devices are superior because they allow for belt stretch during use and can be easily adjusted and monitored. Belt tension should be maintained in the range of 4 to 5 pounds per inch of belt width to a high of 30 to 40 pounds.

Polishing operations should use lower belt tension, especially when using soft contact wheels. A rule of thumb is to use the lowest tension possible before the belt "walks" off center.

Fixturing

The majority of workpieces which are polished on abrasive belt machinery are done "off-hand", i.e. when the workpiece is held against the belt by the operator's hands. Certain shapes lend themselves to simple fixturing, such as a cylindrical part placed into a rotating handle which allows the part to spin freely against the moving belt. More complex fixturing such as rotary automatics and even robotic set-ups are possible for a variety of shapes.

Coolants and Lubricants

Liquid coolants and lubricants involve more sophisticated machinery so as to contain the fluids and possibly to filer and re-circulate these fluids as well.

Liquids

• Water is the most effective coolant and is used for glass and plastic. The amount of water used may range from a mist to a heavy flood.
• Soluble oils are mixtures of water and oil, which are common in metal grinding and other machining operations. These mixtures serve to cool and lubricate.
• Straight oils such as mineral oil or special cutting oils are used for grinding heat sensitive metals or where optimum finish is desired.

Solid Lubricants (Grease Sticks)

Grease sticks are very common in the polishing trades for improving finish and reducing loading. The grease stick reduces scratch depth, especially on fresh belts, by filling the space between the grains. Additionally, grease sticks reduce loading by inhibiting soft metals such as aluminum from sticking directly to the belt. Once the belt becomes loaded, it can be cleaned with solvent. Finally, grease sticks can reduce heat, which improves belt life and finish.

The composition of a grease stick is usually fat or wax packed into a cardboard tube and applied directly to the moving belt. It is important to put only a light coating of great on the belt because too heavy a concentration will simply smear and cause clean-up problems.

The abrasive manufacturers may also add a dry lubricant to the coated abrasive material during manufacture. The added lubricant is either top-coated onto the finished product or is mixed into the resin bonding. These lubricants are particularly useful for stainless steel and high-performance alloys although they are also used on aluminum and brass polishing.

Non-metal Application Guide

Machine Type	Typical Sizes	Heavy Stock Grits	Medium Stock Grits	Light Stock Grits	Finishing Grits	Polishing Grits	KAI Products
Glass	4 x 106, 3 x 24, 7 x 7/8	-	80	100 or 120	180 or 220	320+	320, 321, 333, 336
Rubber	Roll grinding is typical	24 or 36	50 or 60	80 or 100	120 to 220	150 to 320	320, 333, 411, 565
Stone, brick ceramics, or concrete	Various types;Belt and disc machines	24	36	60	120	220	320, 321, 333, 565
Thermoplastics	Belts and discs	36	60	120	180 or 220	320	320, 321, 14
Leather	Wide belts and drum sanders	-	-	80	100 to 180	220 to 400	20, 22, 29, 24

Metal Application Abrasive Guide

Machine Type	Typical Sizes	Heavy Stock Grits	Medium Stock Grits	Light Stock Grits	Finishing Grits	Polishing Grits	KAI Products
Backstand or Conveyorized	2 x 132, 3 x 132, 2 x 118, 3 x 118	36 to 40	50 to 80	100 to 150	180 to 240	280 to 400	A variety of J, X and Y materials can be used based on the material & application
Grinder	2 x 148, but common length is 132"	36 to 40	50 to 80	100 or 120	180 to 240	320 or 400	-
Pedestal (Burr King)	1 1/2 x 60, 2 x 60, 2 x 72	36 or 40	50	-	-	-	-
Benchstand	1 x 30, 1 x 42, 2 x 48, 6 x 48	36	60	120	220	320	CS308, CS311, CS411
Wide belt (deburring & finishing)	25x75, 25x60, 42x103, 43 x 75, and other sizes.	60	80	120	220	320	CS412, CS341, CS310, CS311, CS411
Stroke Sander	6 x 300 or similar sizes	60	100	180	240	320	PS20, PS22, CS310X
Dynafiles	Anything less than 1" width & 30" length	50 or 60	60 or 80	120	180	220	310XF, 411Y, 710XF, 409Y
Portable Belts	3x21, 3x24, 4x21, 4x24	36	60	120	220	320	309XH, 311Y, CS308Y
Flapwheel	-	50 or 60	120	150	220	320	SM611 /KM613
Centerless and Roll Grinding	4 x 132, 6 x 168, 12 x 132	24 to 40	60	120	220	320	CS811, CS411Y, CS341
Orbital Sanders	5-8" diameter	-	60 or 80	120	150 to 240	320 or 400	PS33, PS73
Stationary Disc	10+ diameter PSA	24	40	80	120	220	310, 311, 411
Fiber Discs	4 ,4 1/2 ,5 , 7 & 9"	24 or 36	50 or 60	80	100	120	561, 565, 570, 661
Spiral Bands	-	50	80	120	180	240	Aluminum Oxide
Cartridge Rolls	-	50	60	80	120	-	Aluminum Oxide
Hand Products	Sheets and rolls	50 or 60	80 or 100	120	220	320	KL361, KL385

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