Vitrified Bond Wheels

	Applications	Types
1	Cylindrical Grinding	1-5-7
2	Surface Grinding	1-2-5-7
3	Tool Grinding	1-11-12
4	Saw Sharpening	1
5	Centerline Grinding	1-7
6	Off Hand Grinding on Bench & Floor Stand Machines	1
7	Machine Knife Grinding	2-6
8	Crankshaft Grinding	1-26-26B
9	Face Grinding	1-2-6-7
10	Portable Grinding with Cones	16-17-18-19

 

Resinoid Bond

	Applications	Types
1	Cylindrical Grinding	1-5-7
2	Surface Grinding	1-2-5-7
3	Slitting Wheels	1
4	Saw Sharpening	1
5	Centre less Grinding	1-5-7
6	Floor Stand Fitting	1
7	Machine Knife Grinding	2-6
8	Portable Fettling Including Cones	1-6-11 16-17-18-19
9	Face Grinding	1-2-6-7

 

A grinding wheel has three main components:
a) The abrasive that does the actual cutting, and
b)The bond that supports the abrasive grain while they cut.
c)Fillers to promote the metal removing action.
The arrangements of the first two components in the abrasive product gives a definite characteristic known as the STRUCTURE. In order to provide chip clearance, air spaces or voids must be left between adjacent grains. There is two basic types of manufactured abrasives, the one is aluminium oxide, and the other is silicon carbide. Aluminium Oxide is generally used for grinding carbon steel, alloy steel, high speed steel, annealed malleable iron, wrought iron, hard bronzes and similar materials. There are various different types of aluminium oxides and all abrasive manufactures source these from the same suppliers. However they designate them to suit their own methods.
A - GREY BLUE
1A - DREY BLUE
9A - WHITE
11A - PINK
31A - RUBY
Mixtures of the above types are also used and in turn have doces relevant to them.
Silicon Carbide is used for grinding grey iron, chilled iron, brass, soft bronze, copper, aluminium, stone, marble, rubber, hard facing alloys, glass and cemented carbides.There are various types of silicon carbide as in the case of aluminium oxide.
8C - GREEN
4C - BLACK
6C - BLACK (REFINED)
The reason for having various types of aluminium oxide and silicone carbide abrasives is that materials have different properties and therefore require different type of grain to readily grind it. If looked under microscope, one will find that the various types of aluminium oxide grain are different in their structure, some are very blocky in shape and are normally very tough and resist breaking down and dulling to a great degree, others will have sharp points which will break off when under the pressure and expose new sharp edge continuously. Then we get to a third category, that are reasonably sharp, and do not break down as readily but are able to resist the dulling or blunting whilst in use. The most well known one is 31A or better known as RUBBY grade. Silicon carbide on the other hand normally shows sharper edges and when in use breakaway more readily as it is a very friable but hard material.
There are four basic types of bonds used in making grinding wheels.
1) VITRIFIED BOND
2) RESINOID BOND
3) RUBBER BOND
4) SHELLAC BOND
For our purposes , we only look at the following two bonds:
VITRIFIED BOND - which is used for over 75% of grinding wheels manufactured. Porosity and strength of wheels made with this bond give high stock removal and their rigidity helps in the attainment of high precision. They are not affected by water, acid, oil or ordinary temperature variations.
VITRIFIED BOND SYMBOL: Vitrified bonded grinding wheels are fired at a temperature of approximately 1250- 1325 C. They are not sensitive to chemical influences and can be stored indefinitely. Sudden changes in temperature, shocks and blows should however be avoided.
RESINOID BOND - used for high speed wheels in foundries, welding and billet shops; also used in cut-off and thread grinding operations.
RESINOID BOND SYMBOL:B the resinoid bond is made from phenolic resins and various fillers which help to determine the characteristic of the bond. Resinoid bonded grinding wheels are cured at the temperature of approximately 180 C. They are less sensitive to sudden temperature changes, shocks or blows. Chemical influence and lengthy storage should be avoided.

HARDNESS (GRADES) wheel hardness does not refer to the grinding abrasive, but to the 'degree of strenght' with which the abrasive grains are held in the bond setting of the wheel. The wheel hardness is a measure of the resistance of the bond to the grains being torn out during the grinding process, i.e. the grain particles will break out of a soft wheel more readily than out of a hard one.

ISO METRIC STANDARDS FOR GRINDING WHEELS

Hole sizes marked thus* are considered as transitional standards which will ultimately became non-standard at some future date.