Pink Grinding Wheels

Pink Grinding wheels

are made from Pink aluminium oxide which is a highly refined form of alumina containing a small proportion of chromium oxide. This addition makes pink wheels a little tougher then pure white aluminium oxide. This increases the strength along the shear planes. This abrasive is available in range of wheels here on this site.  You also often see it on mounted points.

WHAT IS A GRINDING WHEEL?
A grinding wheel is a precision tool with thousands of cutting points. It consists of abrasive grains held in a matrix of bond and separated by pores. The abrasive grains are the cutting points while the purpose of the bond is to hold the individual grains together. The pores (hollow spaces between adjacent abrasive grains and the bond) serve to provide clearance for coolant penetration and metal chips removed in the grinding process.
When the wheel is rotated at grinding speed and applied to the work-piece, the abrasive grains cut the material that is being ground, removing the material in small chips.
Under the action of the forces imposed during grinding the abrasive cutting points are worn flat, resulting in the points becoming blunt. This causes an increase in friction, and a build-up of heat.
The increase in grinding forces causes either the abrasive to fracture, exposing new cutting edges, or fractures the bond bridges holding the abrasive grains. In the latter case fresh abrasive grains are exposed to cut the work-piece.
In normal vitrified grinding applications, the wheel has to be dressed.
By varying the properties of the abrasive, the type of bond, the make-up of the wheel, it is possible to produce grinding wheels with vast range of different grinding characteristics.

SELECTING THE RIGHT PRODUCT

THERE ARE NINE MAIN FACTORS TO BE CONSIDERED WHEN SELECTING A GRINDING WHEEL FOR ANY APPLICATION:

• The material to be ground – its type and hardness
• The stock to be removed
• The workpiece geometry and surface finishes required
• The grinding machine, the type of machine, the power available and its conditions
• Wheel speeds and feeds
• Grinding contact area
• Grinding fluid – whether the operation is wet or dry
• The severity of the grinding operation
• The dressing method.

GRIT SIZE

The number in the grinding wheel, marking designating grit size, represents the approximate number of openings per linear inch in the final screen size used to size the grain. The following rules should be followed:

SURFACE FINISH

The achievable surface finish in any grinding operation is highly dependent upon the grit size of the grinding wheel. The following chart shows the range of surface finishes achievable when using grinding wheels of different grit sizes on conventional precision grinding applications, together with the minimum form radius that can be ground using each grit size.

Other factors can affect the surface finish achieved. In particular:

• Production grinding applications, with higher stock removal ranges, will give surface finishes at the coarser end of the range
• Plunge grinding applications will often require the selection of a grit size one size finer than shown
• Dressing techniques & the type of material can also affect the surface finish achieved

 

	Surface Finish & Grit Size
Surface	Surface	Grain Size
In CLA	In Ra	46	60	80	100	120	150	180	220
42	1.10	*
32	0.80	*
26	0.70	*
21	0.50		*
16	0.40		*
14	0.35		*	*
11	0.25		*	*
8	0.20			*	*
7	0.17			*	*	*
6	0.14				*	*	*
5	0.12					*	*	*
4	0.10						*	*	*
3	0.08							*	*
2	0.05								*
Min Form	Metric	0.75	0.5	0.4	0.25	0.2	0.18	0.13	0.1
Radius	Imperial	0.030	0.020	0.015	0.010	0.008	0.007	0.005	0.004

Achieving Improved Surface Finishes

By changing the wheel dressing technique, it is possible to achieve finer surface finishes than those shown. As well as reducing the dresser infeed per revolution of the grinding wheel, it is also possible to reduce the infeed and traverse rate when grinding, thus reducing the stock removal rate. Obviously this approach will have limited application in production grinding but it can be very useful in tool room work.