A grinding body having a matrix comprising a binding agent (1), abrasive grain (2) and filling materials. The matrix which is of a Shore hardness of between D 35 to D 95, preferably D 70 to D 80, is provided with filling means comprising porous conglomerates (3).
The coolant is better entrained by the porous conglomerates, thereby providing for cooler grinding. Nonetheless the strength of the wheel is not reduced and the wear thereof is not increased.
The filling means advantageously comprise resilient material. The resilient conglomerates have been found to be oscillation-damping, whereby from time to time the service life of the grinding body is increased, a better surface is produced and in particular the burning characteristic of the grinding tool is significantly improved.
An embodiment of the invention provides that the porous conglomerates are formed by polyurethane conglomerates.
The grinding effect of the grinding body can be improved by adding to the porous conglomerates abrasive grain with a grain size of 3 my (1200 mesh) to 2000 my (10 mesh).
The pore space of the conglomerates is between 5 and 90% by volume, preferably about 50% by volume.
The abrasive grain added to the porous conglomerates is advantageously formed by corundum, silicon carbide emery or garnet.
Filling materials such as for example chalk may further be added to the porous conglomerates.
The size of the porous conglomerates is advantageously between 2 mm and 100 mm (length or diameter).
A further embodiment of the invention provides that the porous conglomerates constitute from 1 to 60% by weight and preferably from 20 to 25% by weight of the grinding body.
An embodiment of the invention is described hereinafter with reference to the figures of the accompanying drawing.
FIG. 1 is a diagrammatic view of a grinding body according to the invention, and
FIG. 2 shows the section taken from FIG. 1.
The grinding body according to the invention comprises a matrix 1, the binding agent of which is formed in conventional manner by an epoxide, an unsaturated polyester, a mineral binder, a magnesite binder or a hard-set polyurethane. The matrix 1 is relatively hard and in the described embodiment has a Shore hardness of D 75.
Abrasive grains 2 and conventional filling materials are disposed in the matrix 1.
In accordance with the invention porous conglomerates 3 are embedded in the matrix 1.
Set out below is the composition of an embodiment of the invention.
Unless otherwise stated, the percentages are percentages by weight.
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Matrix 1:
Binding agent, epoxide with amine hardener
32%
Abrasive grain 2, noble corundum white
50%
Filling material (cryolite)
8%
Porous conglomerates 3 10%
Structure of the conglomerates 3:
Binding agent; polyurethane
33%
Abrasive grain; silicon carbide with a grain
67%
size of 449 my (100 mesh)
Pore volume 40% by volume
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Example of Manufacture of Porous Conglomerates
The following are added to 24 parts by weight of a mixture of polyols, tertiary amine and water, with an OH-number of 150:
9 parts by weight of isocyanate based on diphenylmethane (MDI) and
67 parts by weight of abrasive grain, based on silicon carbide, of a grain size of 149 my (100 mesh), and cast in plate form after homogenisation.
After hardening for 2 days at ambient temperature, the result obtained is polyurethane plates with the following characteristics:
SHA about 50-70
Density about 1.15
Pore volume about 40% by volume.
They are broken up to form pieces with a mean diameter of about 20 mm and used as porous conglomerates.
I. Example of manufacture of filled grinding bodies
The following are added to 23 parts by weight of a preformulated epoxy resin with an EP-value of 0.52;
9 parts by weight of a polyamine with the H-active equivalent mass of 75
50 parts by weight of noble corundum white, grain size 177 my (80 mesh),
8 parts by weight of cryolite, and
10 parts by weight of conglomerates in accordance with the foregoing example of manufacture, followed by homogenisation.
The grinding material was then cast in suitable moulds and the grinding bodies were hardened for 10 hours at ambient temperature. After removal from the mould the grinding bodies were subjected to finishing and dressing operations by means of conventional items of equipment (round stock straightening, bore turning etc).
Those grinding bodies can be used for grinding knife blades.
II. Example of manufacture of filled grinding bodies
Manufacture similarly to Example I, but using:
14 parts by weight of epoxy resin EP-value 0.58
4 parts by weight of a polyamine H-active equivalent 50
60 parts by weight of a mixture of normal corundum and noble corundum white, grain size 500 my (36 mesh),
8 parts by weight of cryolite, and
14 parts by weight of conglomerates 3--see example of manufacture of conglomerates.
Grinding bodies in accordance with the foregoing composition are suitable for grinding spiral spring ends, valves, ball bearing races and the like.
III. Example of manufacture of filled grinding bodies
Added to 27 parts by weight of a mixture of a polyester (based on o-phthalic acid, maleic acid, 1,2-polypropyleneglycol 67% in styrene) with 0.1% dimethylaniline and 3% of 50% benzoyl peroxide are 10 parts by weight of conglomerate 3--see the example of manufacture --followed by casting.
63% silicon carbide 149 my (100 mesh).
Hardening: 2 days at ambient tmeperature.
Grinding bodies of the foregoing composition are suitable for grinding very thin parts such as vegetable knives, cake slices, baking trays etc.
