Abrading – Rigid tool – Rotary cylinder
Patent
1996-01-23
1997-08-19
Smith, James G.
Abrading
Rigid tool
Rotary cylinder
451540, 51309, 51293, B23F 2103
Patent
active
056581947
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to "superabrasive" grinding wheels. This term is used to designate grinding wheels of very high abrasivity, based on very hard abrasive particles, especially of diamond or of cubic boron nitride, and on a binder which enables these particles to be retained and maintained in place.
This binder may be of three types: it may be a resin, especially a polyimide or phenolic resin. It may also be a vitrified binder in the form of a ceramic matrix of the alumina, alumina-silica or carbide-silica type. The binder may also be based on a metallic matrix, and it is with this third type of binder that the invention is more particularly concerned, because it exhibits a particularly advantageous mechanical strength.
A constant difficulty in the grinding process is proper removal of the dust or other waste products to which the operation gives rise. To do this, a medium, generally water, is conveyed in the direction of the grinding wheel in order to entrain this dust and also, of course, to cool the grinding wheel. However, since the grinding wheel simultaneously attacks a whole portion of the surface of the article being treated, the coolant liquid has difficulty in moving forward towards the whole part being treated. Some accumulation of the waste then takes place. In the case of the treatment of articles made of glass, for example, the grinding is thus systematically accompanied by the formation of a layer of glass paste which tends to oppose the action of the grinding wheel and slows down the grinding operation, making it necessary to perform a number of runs.
The objective of the present invention is an improved type of superabrasive grinding wheels with binder with metal matrix permitting a better management of the problem of the dust and other waste.
The subject of the invention is a superabrasive grinding wheel based on very hard abrasive particles of the diamond or cubic boron nitride type and on a binder with a metallic matrix, and which additionally contains pore-forming elements. Included under this heading are elements the function of which is to create some porosity within the binder of the grinding wheel.
Until now, on the contrary, there has been a tendency rather to employ metallic binders which are as dense as possible, this being in an attempt to slow down the erosion of the grinding wheel as much as possible. However, it has been found, surprisingly, that it is in fact quite advantageous to have a certain porosity "content" in the metallic matrix of the binder, because this porosity very significantly improves the problems of accumulation of waste during the abovementioned grinding, and even result sin lengthening the lifetime of the grinding wheel.
These pore-forming elements have to be chosen as a function of the process of manufacture of the grinding wheels. In particular, they must be capable of withstanding the pressure and the appropriate temperature. This is the reason why use is preferably made of elements in the form of hollow ceramic beads, especially based on silicon and/or aluminium oxide such as alumina or mullite. Mullite is an aluminium silicate of the 2SiO.sub.2 --3Al.sub.2 O.sub.3 type. These beads are advantageously chosen with an outer diameter of between 1 micron and 3 mm, especially between 100 microns and 1 mm. Their walls preferably have a thickness of between 2 and 8, especially between 4 and 6 micrometers.
These pore-forming elements are preferably added to the grinding wheel in a proportion of 1 to 80% of the total volume of the grinding wheel, especially between 5 and 50%, or approximately 30% of the said volume.
The way in which these pore-forming elements function is as follows: as the grinding wheel becomes worn, the hollow beads situated at the surface progressively break and the surface of the grinding wheel then becomes pockmarked; the glass paste can then accumulate in these hollows without interfering with the progress of the grinding. In addition, the coolant liquid can move forward continuously at the interface between the grinding whee
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Edwards Dona C.
Norton S.A.
Smith James G.
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