GB2255923A

GB2255923A - Scaife for diamond cutting or polishing

Info

Publication number: GB2255923A
Application number: GB9211004A
Authority: GB
Inventors: Gabriel Shraga Tolkowsky
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1991-05-23
Filing date: 1992-05-22
Publication date: 1992-11-25
Anticipated expiration: 2012-05-22
Also published as: NL9200908A; IL101936A; GB9211004D0; BE1005799A3; GB2255923B

Abstract

A scaife is prepared by providing an iron-based disc (10) having one of its major surfaces (12) as a working surface, bringing a thermally stable diamond compact (18) into contact with the working surface (12), rotating the working surface (12) at high speed thereby causing diamond particles (20) to be removed from the compact (18) and embed, at least partially, in the working surface (12) and causing the compact (18) to traverse, in a radial direction, substantially the entire working surface (12) while in contact with it. <IMAGE>

Description

SCAIFE FOR DIAMOND CUTTING OR POLISHING BACKGROUND OF THE INVENTION This invention relates to the preparation of a scaife for diamond cutting or polishing.

In the diamond cutting industry, the cutting or polishing of diamonds is performed on a rapidly rotating wheel, termed a scaife, usually made from cast iron, with an abrasive powder spread evenly across one of its major surfaces.

Prior to the commencement of the cutting of a diamond, the working surface of the scaife must be prepared so that it can perform the cutting operation without causing damage to the diamond. Conventionally, this is achieved by scouring the scaife by means of a variety of emery stones followed by "striping" to create fine grooves in the surface. This action creates grooves or stopers in the surface. Thereafter, diamond powder mixed with a suitable retaining agent such as an oil, glue, resin (e.g. a phenolic resin) or a paste (e.g. rye powder with water) is rubbed into the surface by means of a sponge or cloth.

SUMMARY OF THE INVENTION According to the invention, a method of preparing a scaife includes the steps of providing an iron-based disc having one of its major surfaces as a working surface, bringing a thermally stable diamond compact into contact with the working surface, moving the working surface and compact relative to each other to cause diamond particles to be removed from the compact and embed, at least partially, in the working surface and causing the compact to traverse substantially the entire working surface while in contact with it.

A paste containing diamond particles may be applied to the working surface of the iron-based disc before contact is made with the thermally stable diamond compact.

The method of the invention may include a further optional step of applying a paste containing diamond particles to the working surface after diamond particles have already been embedded therein and again bringing the thermally stable diamond compact into contact with the working surface and moving the working surface and compact relative to each other in the manner described above.

Generally, relative movement between the compact and working surface will be achieved by rotating the disc at high speed. The compact can be caused to traverse substantially the entire working surface by moving it in a radial direction.

DESCRIPTION OF THE DRAWING The drawing illustrates a scaife prepared according to the method of the invention.

DESCRIPTION OF EMBODIMENTS The thermally stable diamond abrasive compact used in the invention will be one which is not susceptible to any substantial degradation when exposed to temperatures of up to 12000C in an inert or non-oxidising atmosphere. The compact may have a skeletal structure without a second phase, or it may contain a second phase. when the compact has a second phase, it is preferably a silicon-based second phase. An example of a suitable compact is that sold under the trade mark Syndax.3@ The working surface of the scaife prepared according to the invention, will contain diamond particles at least partially embedded therein. It is preferred that most of the particles are polycrystalline in nature.

An embodiment of the invention will now be described with reference to the accompanying drawing. Referring to this drawing, an iron-based disc 10 has major surfaces 12, 14 and an edge 16. The major surface 12 provides the working surface. A thermally stable diamond abrasive compact 18, which preferably has no grain, is brought into contact with the working surface 12. Thereafter the disc is rotated at approximately the normal working speed of a scaife. The diamond compact 18 is firmly urged against the rotating disc. This causes diamond particles 20 to be removed from the compact and embed, at least partially, in the surface 12. The diamond compact is caused to traverse the entire surface 12 in a radial direction so that a layer of fine diamond particles is deposited over the entire working surface.The achievement of this desired surface texture is indicated by the working surface taking on a darker, but ultra-smooth and shinier appearance.

The resulting product is a scaife which may be used immediately for polishing purposes, or may be prepared further as set out below.

After the diamond deposition, as described above, a layer of a paste comprising diamond powder and a liquid carrier or binder may be applied and worked into the surface 12 of the scaife. The binder may be a grease such as silicone grease or a mixture of rye powder and water. The diamond particles preferably lie in the size range 5 to 25 microns. Thereafter the diamond compact 18 may be applied to the surface 12 again in the manner described above. The scaife is now ready for use.

The diamond-containing working surface 12 can be regenerated from time to time, if required, by reapplying the compact 18 to the working surface 12 of the scaife. It is believed that the components present in the diamond compact fill the grooves and pock marks which form in the metal surface 12 during the polishing of a gem stone. For example, when the diamond compact used for treating the worn working surface is of the type sold under the trade name Syndax-3@, the filler components for the grooves and pock marks will comprise diamond and silicon or silicon carbide.

Should the scaife undergo excessive wear during a polishing period, the regeneration step may be preceded by a repetition of the diamond paste treatment step as described above. However, it has been found that such regeneration is seldom required.

The effect of the method of the invention is to impregnate the working surface of a scaife with diamond particles in the micron size range.

Each subsequent application of the diamond compact further impregnates particles from the diamond outer layer into the metal sublayer. This provides a randomly orientated layer of embedded diamond crystals. This layer serves to isolate the metal substrate of the disc from the gem workpiece being polished, reducing polishing time by at least an order of magnitude and increasing scaife life. No marking of the working surface has been observed, even after the faceting of hard corners.

Scaifes prepared according to the method of this invention have been used for polishing not only gem quality diamonds, but also other hard stones previously not considered capable of being polished because of imperfections such as mixed grains running together and metal inclusions. For example, polycrystalline boart has been polished to a mirror finish at an exceptionally high cutting rate, using a scaife prepared with a Syndax-3e abrasive compact, as described above.

Claims

1.

A method of preparing a scaife includes the steps of providing an iron based disc having one of its major surfaces as a working surface, bringing a thermally stable diamond compact into contact with the working surface, moving the working surface and compact relative to each other to cause the diamond particles to be removed from the compact and embed, at least partially, in the working surface and causing the compact to traverse substantially the entire working surface while in contact with it.

2.

A method according to claim 1 wherein the working surface of the ironbased disc has diamond particles embedded therein or applied thereto at the time that the thermally stable diamond compact is brought into contact with it.

3.

A method according to claim 1 or claim 2 wherein a paste containing diamond particles is applied to the working surface before contact is made with the thermally stable diamond compact.

4.

A method according to claim 1 or claim 2 which includes the further step, after the compact has been caused to traverse substantially the entire working surface of the disc, of applying a paste containing diamond particles to the working surface and again bringing the thermally stable diamond compact into contact with the working surface, and moving the working surface and compact relative to each other to cause diamond particles to be removed from the compact and embed, at least partially, in the working surface.

5.

A method according to any one of the preceding claims wherein relative movement between the compact and working surface is achieved by rotating the disc at high speed.

6.

A method according to any one of the preceding claims wherein the compact is caused to traverse substantially the entire working surface of the disc by moving it in a radial direction.

7.

A method of preparing a scaife substantially as hereinbefore described with reference to the accompanying Drawings.