GB2083489A - Reinforced Articles - Google Patents

Abstract

Reinforced abrasive articles comprise an abrasive material, for example aluminium oxide particles, held within a matrix of binding agent which includes randomly oriented fibrous material as reinforcement. The fibrous material may be polyamide, polyester or, especially, vegetable fibres such as hemp or sisal or begasse. The binding agents may be one of the normal binding agents used for rubber bonded or resinoid bonded abrasive articles. The abrasive materials are also standard Rubber articles subject to wear such as bushes or bearings which have been reinforced by inclusion of randomly-oriented fibrous materials with a rubber matrix are also claimed.

Description

SPECIFICATION Reinforced Abrasive Articles This invention relates to a method of making reinforced abrasive articles, in particular abrasive wheels, discs, segments, blocks, cylinders, rings and the like for polishing, cutting, lapping, finishing, grinding and fettling, and to reinforced abrasive articles.

Abrasive wheels find many uses in industry and in general fall into three main catagories. These are vitreous bonded wheels, in which the abrasive material is held in a matrix formed from materials such as silicate; resinoid bonded wheels, in which the abrasive material is held in a matrix formed from synthetic resins; and rubber bonded wheels, in which the abrasive material is held in a rubber matrix. Vitreous bonded wheels tend to be the hardest, and hence may be subjected to the fastest operating conditions, and rubber bonded wheels tend to be the softest and hence slowest.

Often, rubber bonded wheels are flexible, which is advantageous for a number of end uses. Abrasive wheels may be reinforced, in particular resinoid bonded wheels are often reinforced, by incorporating a fabric or scrim internally or externally of the wheel, or both during production.

The scrim most commonly used is a leno woven scrim of glass fibres coated with a phenolic resin.

While reinforced wheels are often desirable, since they can be subjected to higher operating speeds and have longer operating lives, there are a number of disadvantages inherent in the current method of reinforcement. Firstly, the reinforcing scrim is expensive in relation to the remaining materials forming the abrasive wheels, and therefore considerably increases the cost. Further, the normal scrim used has a limited sheif life before the phenolic resin employed begins to go brittle which in turn leads to problems in manufacture or performance of wheels made therefrom. Further, reinforcement by means of a scrim gives reinforcement in one plane only and wheels so reinforced can be subject to delamination.Uneven wearing may lead to chipping of areas where the reinforcement has worn away before the remainder of the wheel body and reinforced wheels, particularly externally reinforced wheels, create more friction and therefore take more power in performing their function.

The invention seeks to provide an improved form of reinforced abrasive article which reduces or eliminates some or all of the above disadvantages.

According to the present invention there is provided a method of making an abrasive article which comprises mixing abrasive material with a binding agent and reinforcing fibres, mixing, shaping and curing the article. The term "curing" includes allowing to cure.

The invention also provides a reinforced abrasive article which comprises an abrasive material held within a matrix of binding agent which includes randomly oriented fibrous material as a reinforcement.

In general, any fibrous material may be used in the practice of the invention but textile fibrous material is preferred. The average staple length of the fibres should be sufficient to impart reinforcement to the article. It has been found that textile fibres of polyamide, polyester and vegetable fibres give satisfactory results, with fibres selected from sisal, hemp and bagasse giving the best results. In certain circumstances glass fibres may be used, but unless care is taken in mixing the fibres with the remaining ingredients these tend to break into lengths too short to give the desired reinforcement.The criteria for chosing suitable fibrous materials include the ability to tolerate both the temperature of curing of the abrasive article and the temperatures induced in the article in use: the ability to break away (or burn off) as the surface of the article wears away in use: as well as factors such as cost and ease of availability.

It has been found that articles in accordance with the present invention are capable of being used at speeds at least as great as conventionally reinforced articles and having proved wear lives, while their power consumption is comparable with unreinforced articles of otherwise comparable constructibn.

The abrasive material used in the articles of the invention may be any conventional abrasive material used in this type of article. Examples of abrasive materials which may be used include various metal carbides and nitrides, such as silicone carbide, diamond, and, especially, aluminium oxide particles.

Similarly, the binding agents used will normally be one of the conventional binding agents used for similar abrasive articles, and will depend on which type of article it is intended to produce. For example, if it is wished to produce a rubber bonded abrasive wheel, the binding agent will be a natural or synthetic rubber, for example, Neoprene (du pont). If it is desired to produce a resinoid wheel the binding agent may be a suitable resin, for example a phenolic resin such as a novolak resin, Vitreous bonded wheels in general do not require reinforcement, but should it be desirable to reinforce a vitreous bonded wheel then it is within the scope of the present invention to do so. However, owing to the very much more severe curing and working conditions of normal vitreous bonded wheels, textile fibres will not in general be suitable for such reinforcement.However, mineral or carbon fibres may be substituted therefor within the practice of the present invention.

The reinforcing fibres are in general added to the binding agent and abrasive material at the mixing stage. Thereafter, the ingredients are mixed, shaped and cured according to the type of article being produced in exactly the same way as an unreinforced article.

The amount of fibrous reinforcing material necessary in the practice of the invention is typically small, for example from 2 to 10% by weight of the mix, with from 5 to 7% being preferred. Less than 2% gives insufficient reinforcement, whereas amounts greater than 10% give no added advantage and in fact large quantities of reinforcing fibre will produce a diminution in the properties of the article.

As is usual in the manufacture of abrasive articles, fillers, curing agents, pigments, antioxidants, and the like may also be incorporated into the products.

The invention will be illustrated further by the following examples.

Example 1 The following ingredients are assembled: 10 kg neoprene (du pont) 500 gms zinc oxide 400 gms magnesium oxide 100 gms antioxidant 100 gms stearic acid 36 kg W. A. 20 (white aluminium oxide abrasive of 120 mesh size) 2.4 kg sisal fibres 3.3 kg manosil VN3 (silica filler) The neoprene and abrasive particles are put into a mixer and heated to about 1 200C. The remaining ingredients other than the sisal and filler are added and the rubber is mixed (or "extended") until it softens and takes up the abrasive particles. At this stage the sisal is added for further mixing. Slowly, the manosil filler is added until it is thoroughly mixed and wetted out in the mixture. The mixture is then calendered and allowed to cool in sheet form.Having cooled required shapes are cut from the sheet and placed into preheated moulds (1400C) where they are pressed under pressure of one ton per square inch for twenty minutes. The articles so formed are allowed to cool and then dressed.

Rubber bonded abrasive wheels produced in this manner exhibit great strength and durability and may be operated at up to twice the normal operating speeds of unreinforced rubber wheels, otherwise equivalent. Furthermore, the wear life of the wheels is considerably extended.

Example 2 The following ingredients are assembled: 25 parts by weight A24 (regular aluminium oxide, 24 mesh size) 25 parts by weight A30 (regular aluminium oxide, 30 mesh size) 35 parts by weight A36 (regular aluminium oxide, 36 mesh size) 10 parts.lithopon (filler) 5 parts CL 101 (liquid phenolic resin) 5 parts CR 144 (powered novolak resin) 5 parts sisal fibres The filler and powered resin are mixed dry in a mixer. Separately; the liquid resin and abrasive particles are mixed together and added to the mixed powders in the mixer. Simultaneously the sisal fibres are added and the whole is mixed for ten minutes at room temperature. The mixture is removed, allowed to age overnight, and calendered into sheets.Articles of the desired shape are cut out from the sheet and put into cold moulds where they are pressed at one ton per square inch for approximately five seconds. The pressed articles are then moved to an oven where, over a thirty six hour cycle, the temperature is progressively increased from 60 C to 2000C.

Resinoid bonded wheels so made, exhibit properties at least as good as conventionally reinforced resinoid bonded wheels, and are considerably cheaper to make. Furthermore, the power requirement for operating the wheels in use are iess than conventionally reinforced resinoid bonded wheels and are comparable with unreinforced resinoid bonded wheels. With the reinforcing fibres being evenly distributed throughout the article, the tendency of resinoid wheels to chip is considerably reduced and consequently the useful life of the wheels of the invention is considerably extended.

While the invention has been described above with reference to the reinforcement of abrasive articles, we have also found that the randomly oriented reinforcing fibrous material of the invention gives dramatically improved wear lives to resilient, for example rubber, articles subject to wear, for example bushes, bearings and the like.

The invention therefore further includes rubber articles subject to wear, for example bushes, bearings and the like, which have been reinforced by the inclusion of randomly oriented fibrous materials within the rubber matrix.

Claims (20)

Claims

1. A reinforced abrasive article which comprises an abrasive material held within a matrix of binding agent which includes randomly oriented fibrous material as a reinforcement.

2. An article as claimed in claim 1 in which the fibrous material is a textile fibrous material.

3. An article as claimed in claim 2 in which the average stable length of the textile fibres is sufficient to impart reinforcement to the article.

4. An article as claimed in either of claims 2 or 3 in which the textile fibres are chosen from polyamides, polyesters and vegetable fibres.

5. An article as claimed in claim 4 in which the fibres are sisal, hemp or bagasse.

6. An article as claimed in any one of claims s to 5 in which the abrasive materials used are metal carbides, metal nitrides, diamond, or aluminium oxide.

7. An article as claimed in claim 6 in which the abrasive materials used are aluminium oxide particles.

8. An article as claimed in any one of claims 1 to 7 in which the binding agent is a natural or synthetic rubber.

9. An article as claimed in claim 8 in which the binding agent is neoprene.

10. An article as claimed in any one of claims 1 to 7 in which the binding agent is a resin.

11. An article as claimed in claim 10 in which the binding agent is a phenolic resin.

12. An article as claimed in any one of claims 1 to 11 in which the amount of fibrous reinforcing material is in the range of from 2 to 10% by weight of the article.

13. An article as claimed in claim 12 in which the fibrous material is present in the range of 5 to 7% by weight.

14. An article as claimed in any one of claims 1 to 1 3 additionally including fillers, curing agents, pigments, and/or antioxidants.

1 5. A method of making an abrasive article as claimed in any one of claims 1 to 14 which comprises mixing abrasive material with a binding agent and reinforcing fibres, mixing, shaping and curing the article.

1 6. A method as claimed in claim 15 in which the reinforcing fibres are added to the binding agent and abrasive material at the mixing stage.

1 7. An article as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in the foregoing examples.

18. A method according to claim 1 5 substantially as hereinbefore described with reference to and as illustrated in the foregoing examples.

1 9. Rubber articles subject to wear which have been reinforced by the inclusion of randomly oriented fibrous materials within a rubber matrix.

20. An article as claimed in claim 1 9 being a bush or bearing.