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Abrasive Belt Polishing Metal and Non-Wood Applications 

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

Applications and 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 CR, AZ or AO although occasionally SC 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 – 150 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 AO belts, although SC 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 AO.  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

A.         Liquids –

  1. 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.

  2. 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.

  3. Straight oils such as mineral oil or special cutting oils are used for grinding heat sensitive metals or where optimum finish is desired.

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

B.         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 & finer 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 & discs 36 60 120 180 or 220 320 320, 321, 14
               
Leather wide belts
drum sanders
    80 100 to 180 220 to 400 20, 22, 29, 24

NOTES:

♦ Thermo plastics are those that soften when heated, such as acrylics, nylons and urethanes. They should be wet sanded whenever practical.

♦Thermo-setting plastics do not soften when heated, such as phenolics, epoxys, polyesters, poly carbonates and melamines. This includes solid surface plastics such as DuPont Corian. These can be sanded wet or dry.

♦ Rubber is normally ground dry, or using a dry lubricant such as powdered soapstone or zinc stearate powder.
Re-finishing rubber rolls, such as those used in printing or other processes, may done wet or dry.

♦ Glass is ground wet or dry, but wet is preferred to reduce heat and dust.

♦ Stone products are ground wet or dry, but wet is preferred to reduce dust.

♦ Leather sanding operations are good abrasive users when located. Leather is always sanded dry, and typical operations are called "buffing" and "sueding". Watch for moisture from the hides!

** These recommendations are general guidelines only. Many variables influence abrasive applications.

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 tho common
length is 132"
36 or 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 & 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 see catalog for sizes 50 80 120 180 240 AO
               
Cartridge Rolls see catalog for sizes 50 60 80 120   AO
               
Hand Products sheets & rolls 50 or 60 80 or 100 120 220 320 KL361, KL385

 

 


 

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