IE42158B1

IE42158B1 - Abrasive tools and method of making them

Info

Publication number: IE42158B1
Application number: IE2079/75A
Authority: IE
Original assignee: Edenvale Eng Works
Priority date: 1974-09-23
Filing date: 1975-09-23
Publication date: 1980-06-18
Also published as: AR214043A1; DE2542103A1; IN142226B; IL48150A0; JPS5160091A; SE7510665L; NL7511214A; BE833717A; SE412183B; FR2299122A1; CH592500A5; ZA746013B; AT342452B; GB1477767A; IE42158L; ES441210A1; ATA726375A; AU8444675A; BR7506141A; IT1042591B

Abstract

1477767 Moulding abrasive tools EDENVALE ENG WORKS (PTY) Ltd 22 Sept 1975 [23 Sept 1974] 38854/75 Heading B5A [Also in Division B3] The working portion of an abrasive tool is made by mixing acicular abrasive particles (preferably having a length : width ratio of at least 3 : 1) with starting materials for a bonding matrix, pouring the mixture into a mould, applying a force field to the mixture while it is being poured so as to align a substantial proportion of the particles with their long axes substantially normal to the face which will form the working surface of the tool, and causing the bonding matrix to set, at least partially, around the aligned particles. The particles are preferably diamond or cubic boron nitride, and the bonding matrix is preferably a resin. The applied field may be electrostatic, but is preferably magnetic, in which case the abrasive particles, if non- magnetic, must first be coated with a magnetic metal, preferably nickel.

Description

This invention relates to a method of making the working portion of an abrasive tool and to a tool portion when made by said method.

A variety of abrasive tools consisting essentially 5 of an abrasive or working portion bonded to a suitable support are used in industry. The abrasive portion of such tools generally consists of abrasive particles such as diamond, cubic boron nitride, alumina or silicon carbide held in a bonding matrix. The bonding matrix may be resin, vitreous, metal or rubber. Such tools include grinding wheels, saws, drills, cutting tools and so on.

According to the invention, a method of making the working portion of an abrasive tool includes the steps of mixing with a quantity of non-acicular abrasive particles a quantity of acicular abrasive particles (as hereinafter defined) and starter ingredients for a bonding matrix, pouring the mixture through an impressed field of force into a mould defining the working portion of the tool so as to align a 4112»« substantial portion of the acicular abrasive particles with their long axes substantially normal to the face which will provide the working face of the tool, and causing the mixture in the mould to set, at least partially, around the aligned acicular abrasive particles.

The advantage of applying the impressed field of force during pouring is that a far more effective orientation of the acicular abrasive particles is achieved when compared with applying the field only to the mixture in the mould.

The impressed field of force may also be applied to the mixture in the mould prior to and during setting of the matrix and be maintained until the matrix has set, at least partially.

The impressed field of force may be an electrostatic field. Alternatively, the abrasive particles may be provided with a coating of a magnetic metal such as nickel and, the matrix may be non-magnetic in which case the impressed field of force may be a magnetic field.

The abrasive particles may be diamond, cubic boron nitride, aluminium oxide, or silicon carbide particles, but are preferably diaftond or cubic boron nitride particles.

The term acicular abrasive particle is herein defined as an abrasive particle such that the ratio of the long axis to the short axis of the particle is at least 3:1. In determining the ratio of long axis to short axis one takes the axis of greatest dimension as the long axis and the axis of greatest dimension lying in a plane normal to the long axis as the short axis. Acicular abrasive particles may be selected from a batch of particles using conventional sorting techniques. As regards synthetic particles such as synthetic diamond and cubic boron nitride, certain processes have been proposed which produce a high proportion of acicular abrasive particles.

The bonding matrix may be any suitable matrix known in the art. Suitable matrices include resins, rubber, vitreous and metal matrices. As regards suitable resins these include phenolformaldehyde, urea-formaldehyde, melamine formaldehyde, epoxy, polyimide, alkyd, polyester and polyamide resins. The preferred resin is a ipheholformaldehyde resin.

The abrasive particle content of the working portion will generally constitute about 10 to 30 volume percent. This content includes not only acicular abrasive particles, but also a certain quantity of abrasive particles which is not acicular. It is preferred that as high a percentage of the abrasive particle content as possible is acicular.

When the matrix is a resin matrix it is preferred that the abrasive particles, particularly if they are diamond orcubic boron nitride, are metal coated. Suitable metals are well known in the art and include nickel, copper, titanium, silver, cobalt, molybdenum, aluminium, manganese, chromium, vanadium, gold, tungsten, iron, Zirconium, cadmium, zinc, the platinum group metals and alloys containing one or more of these metals.

The preferred metals are copper and nickel.

The metal coating is generally provided in the range of 30 to 80 weight percent, preferably about 50 to 60 weight percent, of the coated particle. If the coating is a nonmagnetic metal such as copper and the impressed field of force is a magnetic1 field, then the particles will also be provided with a coating of a magnetic metal such as nickel. - 4 42158 The working portion may be that of a variety of tools such as grinding wheels, saws, cutting tools, drills and so on. The working portion is preferably that of a grinding wheel, preferably a resin bond grinding wheel.

The manufacture of such tools. is well known in the art and requires no detailed description.

The accompanying drawing illustrates schematically one example of orientating needle-shaped particles according to the invention. Referring to the drawing, there is shown a mould 10 of a suitable material such as stainless steel having permanent magnets of opposite poles on each of opposite sides 12, 14 thereof. A mixture of magnetic metal coated acicular abrasive particles and the starter ingredients of a non-magnetic bonding matrix is poured into the mould. The acicular abrasive particles on falling 'through the magnetic field tend to align in the direction of the magnetic lines of force, i.e. in the direction of arrows A. The acicular abrasive particles are then aligned with their long axes transverse to the faces contacting sides 12, 14 of the mould. One of these faces will provide the working face of the product.

In an embodiment of the invention, RD diamond particles in the range 80/100 U.S. Sieve Series and containing about 80% acicular abrasive particles having a ratio of long axis to short transverse axis of at least 3:1 were nickel clad. The nickel cladding constituted about 55 weight percent based on the weight of the clad particle.

The cladding was applied using conventional techniques. The clad particles were mixed, in a proportion of 12.5 volume percent (calculated as unclad particles), with 25 volume percent phenolformaldehyde resin starter and about 62.5 volume percent conventional inorganic fillers such as silicon carbide. The mixture was poured into a mould defining the working portion of a conventional resin bond grinding wheel. The mould was of nonmagnetic material. A magnetic field was applied to both the mixture being poured and to the mixture in the mould. The lines of force of the magnetic field were radial, i.e. they radiated from the centre to the periphery of the mould, the periphery defining the outer working face of the wheel.

This applied field caused the metal coated acicular abrasive particles to align with their long axes substantially transverse to the working face of the wheel, i.e. the acicular abrasive particles were oriented radially. The resin was allowed to set the cure in the usual way by applying heat and pressure.

Claims

1. A method of making the working portion of an abrasive too] including the steps of mixing with a quantity of non-acicular abrasive particles a quantity of acicular 5 abrasive particles (as hereinbefore defined) and starter ingredients for a bonding matrix, pouring the mixture through an impressed field of force into a mould defining the working portion of the tool so as to align a substantial portion of the acicular abrasive particles with their long 10 axes substantially normal to the face which will provide the working face of the tool, and causing the mixture in the mould to set, at least partially, around the aligned acicular abrasive particles.

2. The method according to claim 1 wherein the 15 abrasive particle content of the working portion is 10 to 30 volume per cent.

3. The method according to claim 1 or claim 2 wherein the impressed field of force is an electrostatic field. 20

4. The method according to claim 1 or claim 2 wherein the acicular abrasive particles are provided with a coating of a magnetic metal, the starter ingredients are non-magnetic and the impressed field of force is a magnetic field. 25

5. The method according to claim 4 wherein the magnetic metal is nickel.

6. The method according to claim 4 or claim 5 wherein the starter ingredients are those for a resin matrix.

7. The method according to any one of the preceding ,30 claims wherein the acicular abrasive particles are diamond or cubic boron nitride.

8. The method according to any one of the preceding claims wherein the working portion is that of a grinding wheel.

9. A method according to claim 1 and substantially as herein described.

10. The working portion of an abrasive tool when made by the method of any one of the preceding claims.