The components of grinding tools: grain, bond and pores
A grinding tool consists of abrasive grain, bond and pores. Our abrasives mostly consist of the so-called conventional abrasives corundum (aluminium oxide Al2O3) or silicon carbide (SiC). In addition, there are grinding wheels made of the super hard cutting materials CBN (cubic boron nitride) or diamond.
Below you will find information on conventional abrasives, our grit qualities and grit sizes, the various bond types and the hardness and density of grinding wheels.
Below you will find information on
- conventional abrasives,
- our grit qualities and grit sizes,
- the various bond types and the hardness and density of grinding wheels.
The conventional abrasives aluminium oxide and silicon carbide and their manufacturing process
Aluminium oxide and silicon carbide belong to the group of so-called conventional abrasives, while CBN and diamond are referred to as super hard cutting materials. The hardness of the various grain types can be classified as follows:
Aluminium oxide < Silicon carbide < CBN < Diamond
Production of corundum (Aluminium oxide Al2O3)
The corundum used is crystalline aluminium oxide (Al2O3). Corundum is produced from bauxite, the starting material of aluminium. Bauxite is converted into clay/alumina using the Bayer process. Aluminium oxide (Al2O3) is then produced by melting the clay at approx. 2000 °C in an electric furnace. When it cools, it combines itself in form of crystals (crystal lattice), giving the corundum/aluminium oxide its excellent properties as an abrasive. The large lumps are then crushed in crushing plants and the various grain sizes are sieved out. The different types of aluminium oxide such as regular alumina, mixed fused alumina or fused alumina have different concentrations of aluminium oxide (Al2O3).
Production of silicon carbide (SiC)
Silicon carbide (SiC) is produced by the Acheson process also in an electric furnace. Silicon carbide (SiC) is produced from quartz sand and high carbon pet coke at temperatures of approx. 2000 °C to 2300 °C by electrochemical reaction. Silicon carbide is harder but also more brittle than aluminium oxide.
Our grain qualities and their abbreviations
Your application determines the quality of the grain for your grinding wheel. In the following you will find an overview of our abrasive grain qualities for vitrified and resin bonds with some general statements on the field of application of the respective abrasive grain. Our experienced engineers will determine the appropriate grain for your individual grinding task in collaboration with you.
Our grain qualities for vitrified bonds (V):
- NK = Regular fused alumina (grey to light grey)
For simple grinding work, to snag iron and steel (all but the hard steel), for steel castings, crucible steel, to grind hardened natural steel. - HK = Mixed fused alumina (light grey)
Splinters easier than regular aluminium oxide, therefore cooler grinding. Application: surface grinding of medium hard steels, cylindrical grinding of medium hard to hard steels. - EW, ER = White and pink fused alumina (white, pink)
For material producing long swarfs during hand operation as well as precision, flat, cylindrical or internal grinding (alloyed steel, SS- and HSS-steel (high speed steel tools)). Pink aluminium oxide for grinding with string impact in grain. White aluminium oxide for medium impact on grain e.g. for surface grinding of ring wheels, to sharpen flat edges. - EU = Dark red fused alumina (dark pink)
More tenacious than punk aluminium oxide. For grinding operations with especially high impact on grain, like medium hard steels, for example grinding of tools. - EK = Monocrystalline alumina (grey to light beige)
High breaking resistance, thus especially durable. Application: surface grinding of highly alloyed steels, profiling and grinding of steels sensitive to heat. - CD = Silicon carbide (grey to black)
Hard and brittle grain, used in working cast iron. - CG = Silicon carbide (green)
For material producing short or no swarfs such as stone, porcelain or synthetic resin. For tenacious and greasy materials (rubber, brass, carbon) and especially hard material (carbide metal, chilled cast iron). - MK = Mixed grain
Aluminium oxide enhanced with other aluminium oxides or silicon carbides. - SG = Sintered aluminium oxide / microcrystalline corundum or sol gel / 3M Cubitron™
Micro crystalline splitting grain. For high-strength steel. Extraordinary tool life can be reached in firm grinding machines.
Our grain qualities for resin bonds (B, BF):
- NK … CG – B
For special grinding machines with increased surface speed of 60 m/s as well as for very thin wheels to grind grooves or for occasional cutting. For grinding tasks that require elastic grinding. - ZR = Zirconia alumina
Very strong mechanical resistance. Application in highly condensed resin and snagging wheels as stabilizing grain. - NK BF, CD BF
Grain qualities in resin bonds fibre reinforced. For portable sanders with surface speed of 80 m/s as well as stationary machines with 100 m/s.
Grit sizes for grinding wheels
The abrasive grain size of conventional abrasives is described in mesh (mesh per inch). This unit indicates how many meshes per inch (25.4 mm) the sieve through which the grain still passes has.
In the production of grinding wheels, we manufacture with grain sizes from 14 to 600 (FEPA), depending on grain quality. For whetstones, we manufacture with the finest grain sizes up to 2000 (FEPA).
Grading of the grain size for grinding wheels according to coarse, medium and fine:
14 – very coarse
16
24
30 – coarse
36
40
46
54 – medium
60
70
80 – fine
90
100
120
150
180
220 – very fine
230
240
280
320 – finest
400
500
600
Bonds with bond type, hardness and structure
Aluminium oxide and silicon carbide belong to the group of so-called conventional abrasives, while CBN and diamond are referred to as super hard cutting materials. The hardness of the various grain types can be classified as follows:
Aluminium oxide < Silicon carbide < CBN < Diamond
Production of corundum (Aluminium oxide Al2O3)
The corundum used is crystalline aluminium oxide (Al2O3). Corundum is produced from bauxite, the starting material of aluminium. Bauxite is converted into clay/alumina using the Bayer process. Aluminium oxide (Al2O3) is then produced by melting the clay at approx. 2000 °C in an electric furnace. When it cools, it combines itself in form of crystals (crystal lattice), giving the corundum/aluminium oxide its excellent properties as an abrasive. The large lumps are then crushed in crushing plants and the various grain sizes are sieved out. The different types of aluminium oxide such as regular alumina, mixed fused alumina or fused alumina have different concentrations of aluminium oxide (Al2O3).
Production of silicon carbide (SiC)
Silicon carbide (SiC) is produced by the Acheson process also in an electric furnace. Silicon carbide (SiC) is produced from quartz sand and high carbon pet coke at temperatures of approx. 2000 °C to 2300 °C by electrochemical reaction. Silicon carbide is harder but also more brittle than aluminium oxide.