ABRASIVE TECHNICAL INFORMATION
ABRASIVE FINISHING
Abrasive finishing combines a harder than workpiece abrasive mineral combined with a bonded or coated product that is rubbed or moved with pressure across the workpiece surface. Abrasive finishing can produce a visual or mechanical finish on metals, composites, stone, glass or wood products.
The abrasive finishing processes can be achieved by hand, portable equipment, manual or automated machinery. Processes include grinding, polishing, buffing, lapping and honing.
Surface affects from the abrasive finishing process
VISUAL MECHANICAL
Soft brushed Deburring Grained Surface refinement Swirled lines Surface preparation Non directional random scratch Radiusing Statin Peening Bright reflective(buffed)
Factors that affect Abrasive finishing
1. Abrasive minerals type, size, shape ad hardness
2. Bonding types
3. Cutting speed
4. Machinery ABRASIVE TECHNICAL INFORMATION
1. Mineral Type (most commonly used)
ALUMINUM OXIDE (AL2O3) is a man made heat treated fused alumina bauxite produced in electric-arc furnaces at temperatures exceeding 4,000 degrees Fahrenheit. After heating and then cooling, the mineral is crushed and sized and is available in grit sizes from 6 to 1200 and finer. Aluminum oxide (A/O) has a blocky structure that when fractured maintains a sharp edged blocky shape. A/Oʼs hardness is 9 on the Mohs scale. A/O is one of the widest used abrasive mineral because of its toughness and durability. Itʼs used to finish metals, composites, and wood.
SILICON CARBIDE (SIC) or carborundom is a naturally occurring but mainly man made abrasive produced by heating or fusing silicon and carbon in vast outdoor facilities. Silicon carbide (S/C) has a sharp slivery shape and is more friable than aluminum oxide. S/C hardness is 9.5 on the Mohs scale. S/C is widely used for finishing hard metal, glass and ceramic surfaces.
CERAMIC ABRASIVES is a man made non metallic crystalline structure produced by heating and cooling ceramic matrixes. Ceramic abrasives are very tough, hard and long lasting with a life of 2-3 times that of aluminum oxide. Ceramic abrasives are used on hard metals and long abrasive life requirements. Higher pressures are required to fracture the ceramic abrasives.
ZIRCONIA ALUMINA is a man made aluminum oxide enhanced with approximate 20% zirconium oxide. The zirconia increases the strength of the aluminum oxide by stress induced transformation toughening. Zirconia is stronger, tougher with life up of 1-1/2 to 2 times that of aluminum oxide. Zirconia is blocky or cubic in structure and is a good choice when longer life or tougher abrasives are required. Most applications are in the coarser grits between 24 and 120 grits. The finish is coarser than that of the same grit size of aluminum oxide.
DIAMOND And CBN ABRASIVES are naturally occurring and can be produced synthetically in a high pressure and high temperature process. Most diamonds that are mined are used industrially and most diamonds used in industry are synthetic. Diamond abrasives are used because of their hardness which is a 10 on the Mohs scale and because of their thermal conductivity. Diamonds have a face cubic structure. The diamond abrasives are used in hard grinding wheels, powders and coated abrasives and are used on hard steels, ceramics and interrupted cutting of composites. ABRASIVE TECHNICAL INFORMATION
EMERY ABRASIVE is a naturally occurring aluminum oxide mixed with other minerals such as silica. The black color material is mined. The hardness ranges between 6-8 on the Mohs scale. The softer abrasive is used in emery boards, emery cloth, and polishing abrasives reducing polishing line depth.
BUFFING ABRASIVES utilize the fine grades of aluminum oxide and silicon carbide abrasives. Buffing also uses fine graded calcined alumina, Tripoli, iron oxide and chrome oxides abrasives that are carried by greaseless or tallow based materials forced into the buffing wheels( which acts as the abrasive carrier) or sprayed onto the buffs of automated systems.
ABRASIVE SIZE Abrasive size, referred to as grits, affects the amount of work achieved as well as the finish produced.Coarse abrasive sizes range between 8-60 grit. Coarser grits remove significant material and leave coarser finishes. The coarser grit sizes are a good choice for large weld removal, de-flashing, and de-gating castings, and removal of large amounts of stock.
Medium abrasive sizes range between 80-150 grits. Medium grits will also remove a fare amount of material and leave finer and paintable surfaces. They are also good for spot weld removal, radiusing, deburring and finer weld removal.
Finer abrasive sizes range between 180-400 and super fine up to1200 grits, The material removal is less but are capable of maintaining good rms finishes. The finer abrasives remove scratches in paint and are used in lapping, polishing prior to buffing, and fine radiusing with very pleasant appearances
GRIT SIZES FOR COATED ABRASIVES AND RELATED RMS FINISH CAPABILITIES
When producing coated abrasives products (belts, discs, paper) the abrasive manufacturers of American, Europe, and Asia have slightly different abrasive grain size standards. The ISO standard FEPA designated with a P is the European designation and the CAMI is the American. Below is the size range variances and approximate finish capabilities. The RMS (root means squared surface measurement) average range is calculated at 1/2 life abrasive on coated products. Belt grease and lubricants will reduce RMS readings ABRASIVE TECHNICAL INFORMATION
ISO/FEPA Grit Standard CAMI Grit Standard Mircon size RMS Finish designation designation average Aluminum oxide 1/2 Course P12 1815 Grits P16 1324 P20 1000 P24 764 24 708 P30 642 30 632 P36 538 36 530 P40 40 425 50 348 100 RMS P50 336 60 265 95 RMS P60 269 Medium P80 201 Grits 80 190 70 RMS P100 162 100 140 60 RMS P120 125 120 115 45 RMS P150 100 150 92 35 RMS Fine grits P180 180 82 20 RMS P220 220 68 15 RMS P240 59 240 53 P280 52 P320 46 P360 41 320 36 8 RMS P400 35 P500 30 360 41 P600 36 400 23 SuperFine P800 22 Grits 500 20 P1000 18 600 16 P1200 15.3 P1500 800 12.6 P2000 1000 10.3 P2500 8.4
ABRASIVE TECHNICAL INFORMATION
GRIT SIZE FOR BONDED ABRASIVES
ANSI table1-(8-240 grit) are sized to ANSI B74.12 1976 (R1982) and ANSI table 2 (240-1200 grits) to ANSI B74 . 10-1976 are utilized for sizing for abrasive grains in grinding wheels.
This chart is designed to compare millimeters, microns and inches to match them to corresponding ANSI grit sizes. Subject to normal variations. A grit size is defined by the distribution of grits retained on sieves set up to meet the requirements of ANSI table 2 or 3.
Mill Micron Inches ASTM Sieve Tyler Sieve ANSI Table 2 ANSI Table 3 5.60 5600 0.220 3 1/2 3 1/2 S-S - 4.75 4750 0.187 4 4 4 - 4.00 4000 0.157 5 5 5 - 3.35 3350 0.132 6 6 6 - 2.80 2800 0.110 7 7 7 - 2.36 2360 0.093 8 8 8 - 2.00 2000 0.079 10 9 10 - 1.70 1700 0.067 12 10 12 - 1.40 1400 0.055 14 12 14 - 1.18 1180 0.046 16 14 16 16 1.00 1000 0.039 18 16 20 20 0.850 850 0.033 20 20 22 24 0.710 710 0.028 25 24 24 - 0.600 600 0.024 30 28 30 30 0.500 500 0.02 35 32 36 36 0.425 425 0.018 40 35 40 - 0.355 355 0.014 45 42 46 46 0.300 300 0.012 50 48 54 54 0.250 250 0.010 60 60 60 60 0.212 212 0.008 70 65 70 70 0.180 180 0.007 80 80 80 80 0.150 150 0.006 100 100 90 90 0.125 125 0.005 120 115 100 100 0.106 106 0.004 140 150 120 120 0.075 75 0.003 200 200 150 150 0.063 63 0.0025 230 250 180 180 0.053 53 0.0021 270 270 220 220 0.045 45 0.0018 325 325 240 240 ABRASIVE TECHNICAL INFORMATION
Micro Grits
Millimeters Microns Inches size) ANSI Grit Size 0.0500 50.0 0.00200 240 0.0395 39.5 0.00156 280 0.0295 29.5 0.00116 320 0.0230 23.0 0.00091 360 0.0183 18.3 0.00072 400 0.0139 13.9 0.00055 500 0.0106 10.6 0.00042 600 0.0077 7.8 0.0003 800 0.0058 5.8 0.00023 1000 0.0038 3.8 0.00015 1200 0.0450 45 0.0018 F 0.0275 27.5 0.0011 FF 0.0160 16 0.0006 FFF 0.0110 11 11 0.00043 FFFF
ABRASIVE TECHNICAL INFORMATION
ABRASIVE HARDNESS
Abrasive minerals are chosen by their hardness. The basic abrading principle is a harder material chipping, abrading, or wearing away a softer workpiece material. The abrasive minerals generally run between 7 and 10 on the Mohs scale.
Below is a chart on abrasive mineral hardness
Hardness Comparison
Abrasive Mohs Value Knoop Value
Diamond 10.0 7000
Silicon Carbide 9.5 2480
Ceramic abrasive 9+
Zirconia 9.0
Aluminum oxide 9.0 2100
Emery 7-8
Garnet 7.0 1360
Quartz 7.0 820
Sand 6.0 560
ABRASIVE TECHNICAL INFORMATION
2. BONDING TYPES
BONDED ABRASIVES ( Grinding Wheels) is an abrasive mineral contained and mixed within a matrix of metal, clay, resin, or rubber. The matrix is molded into wheels, discs, and sticks. These bonded processes are referred to as grinding.
The most common bonds are resin and vitrified. Resin wheels are plastic that are cured most often used in cut off wheels and diamond wheels. The vitrified is a ceramic glass like material fired or cured at higher temperatures and are used more commonly than resin. Vitrified wheels are used for bench wheels and surface grinding.
Hardness of the bond are rated from A-Z, A being weaker and Z the strongest. Weaker bonds ratings range between F-H, Medium bonds between I - K. and Stronger rated between L - P.
Structure or amount of openness between the grits is the grinding wheels basic structure.The ratings for structure is the higher the number the more open. The rating 12 is open in structure while 5 is a much closer structure.
The common grits used in grinding wheels are Aluminum oxide A/O ( white, pink, ruby red, brown and grey ) - Silicon carbide ( black or green) - Ceramics ( blue or pink) - Cubic boron nitrate ( CBN) - and Diamonds.
General grinding practices utilize white and pink A/O which are more friable and run cooler for carbon steels. Ruby Red A/O is a tougher semi friable grit used to grind tool steel. The Brown and Grey A/O is also semi friable and is the most common grit used in production grinding and bench wheels. The Silicon Carbide black mineral is very sharp and used to grind softer metals such as Aluminum, brass, and composites. The green Silicon Carbide is even sharper than the black and is used to grind carbides and Titanium. The Ceramic grits are very tough, it fractures but keeps a sharp blocky edge. Ceramics last longer, can be used with higher pressures removing more materials while running cooler. Ceramics are used in grinding tool steels. Diamonds and CBN are the hardest of abrasives used in grinding, they are used on grinding carbides and uninterrupted cuts on composites.
A typical grinding wheel call out or wheel identification may differ from manufactures but commonly a typical call out is as follows. A80 - J10 - VS A = grit type (Aluminum oxide 10 = structure or density 80 = grit size vs = the bond (vitrified) J = relative hardness ABRASIVE TECHNICAL INFORMATION
COATED ABRASIVES is an abrasive mineral fixed to a flexible paper, cloth, or film backed material. The abrasives are electrostatically applied with various glues or resins. The jumbo rolls are cut and converted into 9x11 paper,bench rolls, discs and various sizes of abrasive belts. The abrasive finishing processes with coated abrasives is considered polishing.
The most common backing holding the abrasives, in the metal and composite industry, is cloth and film. The Cloth varies in weight and flexibility with X and J classifications.The X is heaver and less flexible than the J. Generally The coarser grinding applications utilize X weight for their durability. The Finer finishing often times uses the J weight cloth. Both X and J have a flexible version( X-flex and J-flex) that has additional flexibility. The film backing is stronger than cloth. It also has the property of being flatter than cloth (because of less porosity) allowing the more even and accurate coating of abrasives resulting in finer lower RMS finishing. The most common abrasive used in the metal and composite industry is Aluminum oxide, used to finish steel and aluminum. Ceramic abrasives are also very popular because they are tough, last longer, can be used with higher pressures for automation, and less time is wasted on changing abrasive belts. The finish range is more constant on long run of parts with longer lasting ceramic abrasives. The ceramics are used on harder metals and composites. Other popular abrasives used is Silicon Carbide often used when a better finish is required and Zirconium Aluminum abrasives which outlast Regular Aluminum oxide by approx. 30%.
BUFFING is an ultra fine abrasive mineral that is impregnated onto and into a Round cloth buffing wheel. Buffing is the process used for a high luster shine on various materials. The terminology of cloth impregnated wheels processes for shine is buffing. There is a complete section (section 4, chapter 10) That explains buffing processes, materials,etc. ABRASIVE TECHNICAL INFORMATION
3. CUTTING SPEED
Cutting speed is affected by:
Grit size (larger grit sizes generally increase cutting speed))
Abrasive material (Hardness and shape affect cutting speed)
Bonding of abrasive
Pressure applied to the workpiece ( more pressure increases cutting speed)
Use of lubricants ( reduce heat and produce finer finishes)
Surface feet speed ( Faster surface speed = faster finishing times)
Surface Feet Speed is the speed at which the abrasive passes by the workpiece being finished. Abrasive finishing of various workpiece materials require specific ranges of surface feet speed to be finished properly.
The right surface feet speed for a given workpiece material will reduce heat, surface gauling and loading. The right surface feet speed will also increase abrasive life and effectiveness.
Below is a chart on effective surface feet speed for various materials
Approximate Surface Feet Speed Recommendations
Material Surface Speed (SFPM)
Steel 6500 Stainless Steel