EP1986819A2

EP1986819A2 - Method of making an abrasive article comprising a non-porous abrasive element

Info

Publication number: EP1986819A2
Application number: EP07750435A
Authority: EP
Inventors: Jean Le Normand
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2006-02-17
Filing date: 2007-02-09
Publication date: 2008-11-05
Also published as: EP1986819A4; WO2007097932A2; GB0603276D0; WO2007097932A3

Abstract

An abrasive article comprises an abrasive element (1) having at least a non-porous region, and a hub (3) for securing the abrasive element to a shaft (2) positioned adjacent the non-porous region, the hub having first and second flanges (4, 5) and a connection (6) joining the flanges through a bore (7) in the non-porous region, the non-porous region of the abrasive element being located between the flanges such that the hub is clamped onto the abrasive element. A method of making the abrasive article comprises: forming the hub (3) by forming first and second flanges between which the non-porous region of the abrasive element is located and by integrally forming a connection joining the flanges through a bore in the non-porous region such that the hub is clamped onto the abrasive element.

Description

METHOD OF MAKING AN ABRASIVE ARTICLE COMPRISING A NON- POROUS ABRASIVE ELEMENT

FIELD

The present invention relates to a method of making an abrasive article comprising at least one abrasive element having a non-porous region.

BACKGROUND

Abrasive elements such as abrasive discs for polishing and abrading applications are known. Generally such discs are releasably attached to an abrading machine, for which purpose there are a variety of means available. Polishing discs and abrasive discs for light abrading applications may be releasably secured to a back-up pad e.g. by pressure sensitive adhesive, hook and loop fastener etc., and the back-up pad attached to the machine by a central boss or spindle. Another means of attachment comprises providing the disc with a central hub or boss. The hub may have an internal thread for engagement with a threaded shaft mounted on the machine. Alternatively the hub may have a central aperture through which a threaded shaft mounted on the machine is inserted and secured by a nut. A further means of attachment comprises providing a disc with a central shaft which may be engaged by a rotatable chuck mounted on the machine.

Methods of making abrasive articles mounted with a central shaft have been developed for use with discs made of non-woven fibres. For example, JP 11320423 A discloses a method of making a polishing disc in which a disc of non-woven fibres having a central aperture is placed in a mould and a boss having a central through aperture is formed by injection moulding a thermoplastic material. The molten thermoplastic material penetrates between the non-woven fibres to secure the boss to the disc. The boss may be provided with an interior thread formed on the perimeter surface of the central aperture to facilitate attachment to a machine.

Another example of an abrasive article with a central shaft is the product available from 3 M Company of St. Paul, Minnesota, USA under the trade name CLEAN 'N STRIP Abrasive Disc. The abrasive articles are formed by inserting one end of a metal shaft into a central aperture in the disc, applying a circular paper label having a central aperture around the shaft and contacting one major surface of the disc, pouring curable epoxy resin into the central region of the disc from the opposite side to the label such that the epoxy resin surrounds the end of the shaft and penetrates between the fibres of the disc. The epoxy resin is cured to secure the shaft. The paper plastic label acts as a barrier to the epoxy resin to prevent it flowing out of the disc. The shaft has a knurled end to facilitate secure bonding. While this method of securing the shaft to the disc is effective, the two part epoxy resin system is expensive and the production time is undesirably long.

A further example is described in our co-pending International application WO 2006/023178 titled "Method of Making Abrasive Article" and filed on 18 July 2005. This describes a method of making an abrasive article comprising a planar abrasive disc formed of non-woven fibres and a shaft positioned at the centre of the disc. The shaft is coupled to the disc by injecting molten thermoplastic material to form a hub. Thermoplastic material penetrates between the non-woven fibres to secure the hub to the disc. Figure 8 shows five discs coupled to a single shaft.

However, these methods can be used only with abrasive discs that are porous to the injected epoxy resin or thermoplastic material, at least under the applicable process conditions. Typically, but not exclusively, that will mean abrasive discs which are made of a material, such as non-woven material, where there are continuous open channels or interconnected voids through which fluid can pass. This is because the epoxy resin or thermoplastic material penetrates into the channels or interconnected voids in the material to become secured to the abrasive disc.

A method of making a shaft-mounted abrasive article made of non-porous material, specifically the radial bristle disc available from 3M Company of St Paul, Minnesota, USA (part numbers 051 131-07542, 051131-07543 and 051 131-07544), is also known. Typically, several of those discs are mounted on a mandrel to form a bristle brush by directing a shaft, forming a first part of a mandrel, through a central bore in each disc. The first part of the mandrel is then coupled to a second part of the mandrel e.g. by a screw thread, to clamp the bristle discs between the first and second parts and onto the shaft. Although this method works well, assembly of the bristle discs onto the shaft is time consuming and cumbersome. Additionally, although the mandrel is normally reusable, it is a comparatively expensive component and makes the bristle brush costly.

The invention has been made with these points in mind.

SUMMARY

According to a first aspect of the invention there is provided a method of making a abrasive article comprising a abrasive element having at least a non-porous region, a shaft positioned adjacent the non-porous region and a hub securing an end of the shaft to the abrasive element, the method comprising forming the hub by forming first and second flanges between which the non-porous region of the abrasive element is located and by integrally forming a connection joining the flanges through a bore in the non-porous region such that the hub is clamped onto the abrasive element.

According to a second aspect of the invention there is provided an abrasive article comprising a abrasive element having at least a non-porous region, a hub having first and second flanges and a connection integrally formed with the flanges through a bore in the non-porous region, and a shaft positioned adjacent the non-porous region and secured to the abrasive element by the hub, the non-porous region of the abrasive element being located between the flanges such that the hub is clamped onto the abrasive element.

As used herein, "non-porous" means a material into which the material of the connection part of the hub does not penetrate under the applicable process conditions. Examples of non-porous materials are solid materials such as the abrasive-embedded solid polymer materials used to make the 3M Company radial bristle discs mentioned above, and closed cell foam materials such as that used to make a Scotch-Brite™ Molding Adhesive and Stripe Removal Disc (available from 3M Company). Under certain process, conditions, non-woven materials into which foam has been injected are also non-porous within the context of the present invention. These materials have in common the fact that there are no continuous open channels or interconnecting voids into which the injected material of the connection part of the hub can penetrate under the applicable process conditions.

The invention enables a hub to be coupled to a non-porous abrasive element or an abrasive element having a non-porous region, which in turn allows a shaft to be coupled to the abrasive element in a single operation. No additional assembly steps are required to mount the element to the shaft and no other components such as mandrels are needed.

The bore in the abrasive element is preferably centrally located in the abrasive element. Alternatively, more than one bore may be formed through the abrasive element, at least one of which may be displaced from the centre of the abrasive element.

Preferably, the flanges and connection are formed by injecting molten polymeric material and allowing the molten polymeric, material to cool and solidify. Advantageously, the polymeric material is a thermoplastic material, the use of which is very economical and efficient. The injected material need not, however, be a thermoplastic material: other polymeric materials suitable for injection moulding could be used including thermoset materials (for example, a blocked epoxy resin).

In one embodiment, a method in accordance with the invention further includes the step of positioning an end of the shaft at the centre of the abrasive element before forming the hub. Preferably, the shaft is positioned such that its end extends partially or completely through the bore in the abrasive element. In this case, the shaft may be made of metal, arid may have a roughened or knurled end for an improved connection with the hub.

In an alternative embodiment, the shaft is formed integrally with the flanges and the connection from the polymeric material. This removes the need to provide a separate shaft, reducing the number of steps and the raw materials involved in the method.

The abrasive element can be a substantially planar disc.

In one embodiment, two or more abrasive elements are provided. This has the advantage that several abrasive elements can be coupled to each other and to a shaft in a single operation, rather than having to separately feed individual elements onto a shaft, as is known in the prior art. The hub may be clamped onto the abrasive elements with or without compression of the elements.

The abrasive elements may be formed with teeth to interlock with teeth formed on adjacent abrasive elements. This aids to prevent rotation of one abrasive element relative to an adjacent abrasive element. The invention is applicable to different kinds of abrasive elements having at least a non- porous region. For example, the abrasive element may be a radial bristle disc, comprising a central region from which a plurality of bristles radially extend, such as the one available from 3M Company mentioned above (part numbers 051131-07542, 051131-07543 and 051131-07544); a bristle disc in which a plurality of bristles coupled to a base extend perpendicularly away from the base and parallel to the shaft, such as the Roloc™ Bristle Disc available from 3M Company; an abrasive disc made from closed cell foam material, such as the Molding Adhesive and Stripe Removal Disc (part numbers 051131-07501 or 051131-07502) available from 3M Company; or a disc as used in the Stripe Off Wheel (part numbers 051131 -07498) available from 3M Company.

Part of the abrasive element can be made of an abrasive material; alternatively, the whole of the abrasive element can be made of an abrasive material. Where the abrasive article comprises more than one abrasive element, each element may be made of different materials, for example different grades of abrasive.

Where a separate shaft is provided, the invention can further comprise providing a mould having first and second mould plates which together define a mould cavity, each of the plates having a recess formed therein, one of the plates having a bore formed therein to accommodate the shaft so that one end thereof projects into the mould cavity and one of the plates having a channel for injection of molten polymeric material into the mould cavity, wherein the abrasive element is placed in the mould cavity and molten polymeric material is injected into the cavity through the channel such that it fills the recesses to form the flanges.

Preferably, one of the first and second mould plates has the channel for injection of molten polymeric material into the mould cavity, and the other of the first and second mould plates has the recess or bore for the shaft.

Where the shaft is formed integrally with the flanges and connection, the invention further comprises providing a mould having first and second mould plates which together define a mould cavity, each of the plates having a recess formed therein, one of the plates having a bore formed therein defining the shaft and for injection of molten polymeric material into the mould cavity, wherein the abrasive element is placed in the mould cavity and molten polymeric material is injected into the cavity through the channel such that it fills the recesses to form the flanges and fills the bore to form the shaft.

Alternatively, the mould plates used when a separate shaft is provided can be used when the shaft is formed integrally with the flanges and the connection, the shaft being formed from polymeric material filling the bore sized to accommodate the separate shaft.

If a thermoplastic material is used to form the hub of the abrasive article, the selection of a suitable material from the range available will be apparent to those skilled in the art. The material is selected so that it will have a suitable viscosity at the injection temperature, generally 200 to 28O⁰C. It is preferred that the thermoplastic material contracts slightly when cooled from its molten state since this improves the mechanical interlock with the abrasive element(s) and the end of the shaft.

Exemplary thermoplastic materials include thermoplastic polyether ester elastomer block copolymers comprising hard (crystalline) segments of polybutylene terephthalate and soft (amorphous) segments based on long-chain polymether glycols commercially available from DuPont under the trade name HYTREL; polyamides such as nylon 66 e.g. commercially available from LATI Industria Termoplastic S.p.A. under the trade name LATAMID, and an injection moulding homopolymer available, under the trade name "CAPRON 8202HSBK102", from BASF CANADA of Mississauga, ON, Canada; and polyolefms, such as polyethylene and polypropylene including fibreglass filled polypropylene. The thermoplastic material may optionally contain filler and/or reinforcing fibres.

Suitable injection moulding machines for use in the invention are well known and may have vertical or horizontal orientations. A vertical orientation moulding machine provides an advantage since it facilitates positioning of the shaft and controlling the spread of the molten thermoplastic material. Suitable injection moulding machines are commercially available from Arburg GmbH under the trade name ALLROUNDER. Horizontal injection moulding machines are widely available and may also be used. They provide an advantage in that the shaft may be positioned in the opposite mould half to the abrasive elements, the shaft and abrasive elements being held by interference fits in the mould halves prior to polymer injection. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a perspective view of an abrasive article in accordance with the present invention;

Figure 2 is a cross-sectional view of the article of Figure 1 ;

Figure 3 is a cross-sectional view of a mould used to make the article of Figures 1 and 2;

Figure 4 is an exploded perspective view of another abrasive article in accordance with the present invention;

Figure 5 is a cross-sectional view of the article of Figure 4, when assembled, viewed perpendicularly to line a-a; .

Figure 6 shows a bristle disc used in the article of Figure 4;

Figure 7 is a cross-sectional view of a mould used to make an abrasive article in accordance with another embodiment of the invention;

Figure 8 is a cross-sectional view of the article made in the mould of Figure 7.

Figures 1 and 2 show an abrasive article in accordance with one embodiment of the present invention. The article has a substantially planar abrasive element (1) which is secured to a steel shaft (2) by a hub (3) formed of thermoplastic material.

The abrasive element (1) is made from closed cell foam material, such as the Molding Adhesive and Stripe Removal Disc (part numbers 051131-07501 or 051131-07502) available from 3M Company. The closed cell foam material does not have continuous open channels or interconnected voids for thermoplastic material to pass through, and so is non-porous.

The hub (3) has first (4) and second (5) disc shaped flanges and a connection (6) joining the flanges. The flanges (4,5) and the connection (6) are integrally formed, the connection extending through a cylindrical shaped central bore (7) formed in the abrasive element (1).

The flanges (4,5) are located on either side of the element (1) so as to clamp the hub (3) onto the element. This provides an effective way of coupling the hub (3) to the abrasive element (1) in the absence of a strong mechanical adhesion such as that which would be achieved if the thermoplastic material of the hub were able to penetrate into the abrasive element.

An end (8) of the steel shaft (2) extends into the bore (7) in the abrasive element (1), and is coupled to the element by the thermoplastic material forming the hub (3). The end (8) of the shaft (2) is knurled to improve the adhesion between the thermoplastic material and the shaft. The shaft (2) does not extend completely through the bore (7), as can be seen in Figure 2, although it is possible in alternative embodiments for the end of the shaft (2) to protrude beyond the abrasive element (1) into the flange (5).

Figure 3 shows a mould which can be used to make the article shown in Figures 1 and 2. The mould has first (10) and second (11) mould plates, which have first and second moulding surfaces respectively. The moulding surfaces together define a cavity (12). In each moulding surface is a recess (13,14). The first mould plate (10) is formed with a bore (15) which opens generally in the centre of the recess (13) in the first moulding surface. The second mould plate (11) is formed with a channel (16) which opens in the recess (14) in the second moulding surface, through which molten thermoplastic material can be injected.

To make the abrasive article shown in Figures 1 and 2, a shaft (2) is inserted into the bore (15) formed in the first plate (10) so that the end (8) of the shaft extends through the recess

(13) in the first mould plate (10) and into mould cavity (12). The tip of the shaft (2) does not extend as far as the recess (14) in the second mould plate (11). The shaft (2) fits tightly within the bore (15) in the first mould plate so that there is a seal there-between.

A substantially planar, disc shaped abrasive element (1) made from closed cell foam material, as described above with reference to Figures 1 and 2, is placed in the mould cavity (12) such that the shaft (2) extends partially through the bore (7) formed in the abrasive element (1).

The mould plates (10,11) are then closed and thermoplastic material is injected through the channel (16) in the second mould plate (11) into the mould cavity (12). Thermoplastic material flows through the bore (7) in the abrasive element (1), flowing around the shaft (2), and into the recesses (13,14) in the first and second mould plates.

The thermoplastic material is allowed to cool such that the thermoplastic material in the recesses (13,14) forms the flanges (4,5) and the material around the shaft (2) in the central bore (7) of the abrasive element (1) forms the connection (6). The hub (3) is clamped onto the abrasive element by way of the flanges (4,5) and the shaft (2) is fixed to the hub (3) by way of an adhesive action of the thermoplastic material. Thus the shaft (2) is secured to the abrasive element (1).

In a modified version of the abrasive article 1 of Figures 1 and 2, the shaft (2) is omitted and the hub (3) is formed for connection to a separate shaft, for example by being provided with a suitable bore or a thread. To make an article of that type, the first mould plate 10 of Fig. 3 would be modified by replacing the bore 15 with a suitably-shaped mandrel positioned on the mould plate 10 to extend into the central bore (7) of the abrasive element (1).

Another abrasive article is shown in Figures 4 to 6. In this embodiment, the abrasive article is a bristle brush which comprises a plurality of abrasive elements in the form of bristle discs (I¹) coupled to a steel shaft (2').

An example of a bristle disc is shown in Figure 6. Such bristle discs are available from 3M Company of St. Paul, Minnesota, USA (part numbers 051131-07542, 051131-07543 and 051131-07544). These bristle discs are formed from plastic embedded with abrasive and can be provided in different grades. The discs have a 7.6 cm (3inch) diameter, though other sizes can also be used. Other bristle discs and indeed other abrasive elements can be equally suitable.

The bristle disc (I¹) has a central non-porous region (20) which is substantially planar. A plurality of bristles (21) extend generally radially from the central region (20), though they are curved in a circumferential direction. The bristles (21) extend generally in the same plane as the plane of the central region (20), though, again, the bristles can curve slightly out of the plane. A bore (22) is formed through the central region (20), the bore being located generally at the centre of the bristle disc (I¹). The bristle disc (I¹) has teeth (23) surrounding the bore (22) on its front and rear faces which can interlock with teeth formed on another bristle disc when the two discs are brought together. These teeth (23) prevent one bristle disc rotating relative to adjacent bristle discs.

The bristle brush shown in Figures 4 and 5 comprises four bristle discs (I¹) of the type shown in Figure 6. The bristle discs are adjacent each other, their planes substantially parallel to the planes of the other discs. First (4') and second (5') substantially circular flanges are located on opposing sides of the set of bristle discs, the flanges (4',5') being coupled together by and integrally formed with a connection (6¹). The connection (6') extends through the bores (22) formed in the bristle discs (I¹). The flanges (4 ',5') and connection (6') form a hub (3') and are made of thermoplastic material.

The flanges (4',5') and connection (6') clamp the bristle discs (I¹) together. In Figure 5, the central regions (20) of the bristle discs are shown to be in contact. The central regions are compressed between the flanges (4',5'). In alternative embodiments, the discs (I¹) are not compressed between the flanges, and small amounts of thermoplastic material may be located between adjacent bristle discs.

An end (8') of a metallic shaft (2') extends completely through the bores (22) in the bristle discs (I¹) and extends beyond the discs. The shaft is coupled to the discs by the thermoplastic material forming the flanges (4',5') and the connection (6'). The end (8¹) of the shaft (2') is knurled or roughened to improve the adhesion between the shaft and the thermoplastic material. However, the end need not be knurled or roughened.

Also, in the embodiment shown in Figure 5, the tip (18) of the shaft is seen to be covered entirely by thermoplastic material. However, the tip of the shaft may extend beyond the second flange (5') so as to be exposed if desired. In another example, the shaft extends only through some of the bristle discs (1 '), the bores (22) in the remaining bristle discs being filled with thermoplastic material.

This embodiment of the invention therefore provides a bristle brush having bristle discs (I¹) mounted on a shaft (2¹) which can transfer rotational movement to the bristle discs. The mould shown in Figure 3 can be used to make the bristle brush shown in Figures 4 and 5, providing the mould cavity (12) is sized so as to accommodate the four bristle discs

(I')-

In a modified version of the abrasive article of Figures 4 and 5, the shaft (2) is omitted and the hub (3) is formed for connection to a separate shaft, for example by being provided with a suitable bore or a thread. To make an article of that type, the first mould plate 10 of Fig. 3 would be modified by replacing the bore 15 with a suitably-shaped mandrel positioned on the mould plate 10 to extend into the central bore (22) of one or more of the bristle discs (I⁵).

The mould shown in Figure 7 is used to make a bristle brush in accordance with another embodiment of the invention. In this embodiment, the first mould plate (30) is not formed with a bore to receive a metal shaft, and a metal shaft is not inserted into the mould cavity before injecting thermoplastic material. Instead, the channel (32) in the second mould plate (31) is sized and shaped so that, when sufficient thermoplastic material has filled the space in the mould cavity (33), the thermoplastic material in the channel (32) is allowed to cool so as to form a thermoplastic shaft (2") which is integral with the flanges (4',5') and connection (6').

Other features of the mould, such as the recesses (13,14) in each mould plate, are as described with reference to Figure 3.

Figure 8 shows the bristle brush made using the mould shown in Figure 7. Bristle discs (I¹) as described with reference to Figure 6 are clamped between the flanges (4^r,5') and the flanges are integrally formed with both the connection (6¹) and a thermoplastic shaft (2").

The bore (22) formed through the bristle discs can have a square, hexagonal or other multi-sided profile if desired, so as to prevent relative rotation of adjacent bristle discs (as an alternative to, or in addition to, the teeth 23) and to prevent rotation of the discs on the shaft (2").

The mould shown in Figure 3 can also be used to make the bristle brush shown in Figure 8. In this case, the metal shaft is not placed in the bore (15) in the first mould plate (10). Instead, thermoplastic material is allowed to enter and fill the bore (15) so as to form the shaft (2") when cool and hard.

The abrasive articles, methods of making the articles and moulds used to make the articles described in the above embodiments can be used with other kinds or other numbers of abrasive articles having at least a non-porous region. For example, the article shown in Figure 8 could comprise only one abrasive element, which may be any of the kinds of abrasive element described herein.

Example 1

A vertical orientation injection moulding machine model, commercially available under the trade name ALLROUNDER 270-90-500 from Arburg GmbH & co. KG, Arthur-Hehl- Strasse, 72290 Lossburg, Germany, was used to make a bristle brush in accordance with the invention.

The machine has a maximum clamping force of 50OkN, a maximum mould opening stroke of 325mm, a minimum mould height of 225mm, a maximum daylight of 550mm, a maximum ejector force of 31.4kN and a maximum ejector stroke of 125mm. The injection unit had the following features: a screw diameter of 25mm, a screw length of 18L/D (length to diameter ratio), a maximum screw stroke of 100mm, a maximum swept volume of 49cm³, a maximum shot capacity of 4 Ig, a maximum injection pressure of 1.86x10⁵ kPa (1860 bar), a maximum injection flow of 98cm³/s, a maximum screw rotation speed of 725 rpm, a maximum screw circumferential speed of 57m/minute and a maximum screw torque of 290Nm.

Six individual radial bristle discs were arranged in the mould cavity and a metallic shaft Was placed in a recess such that an end of the shaft protruded into the mould cavity, through bores in the discs.

Each disc had a 7.6cm (3inch) outer diameter, a lmm thickness and a bore generally through its centre. The bore had an inner diameter of 9.5mm (0.376inch).

The shaft was a zinc plated, steel shaft commercially available from STE DUBOSSON RAYMOND of 124 Rue du Noiret, 74300 Cluses, France. Its length was 50mm and it had a diameter of 6mm. The end of the shaft was knurled over 10mm, with a knurl depth of 0.2mm.

The thermoplastic polymer was "LATAMID 66 D2 G30", a nylon 66 polymer available from LATI Industria Termoplastic S.p.A. The polymer was desiccated for 5 hours at 80⁰C using a Trockenlufttrockner Digicolor KTT 100 desiccator available from Digicolor Gesellschaft fuer Kunstoffmaschinentechnik GmbH, Eckendorfer Strasse 125a, 33609, Bielefeld, Germany.

5g of the thermoplastic was injected under the following process conditions:

Heating Zone Temperatures:-

Zone l : 26O⁰C;

Zone 2: 265⁰C;

Zone 3: 275⁰C;

Nozzle: 28O⁰C;

Mould: 80⁰C;

Injection Flow: 39 cc/s;

Injection Time: 1.4 seconds;

Injection Pressure: 15% maximum.

It was found that migration of the thermoplastic polymer was incomplete due to freezing at the contact of the shaft. The thermoplastic material was therefore prevented from filling the full space in the mould cavity, and so the flanges and connection were not fully formed.

Example 2 The materials and process used in this example are those used in Example 1 unless stated otherwise.

In this example, the bore in each disc had an inner diameter of 20mm, and 7g of thermoplastic material was injected into the mould cavity.

Migration of the thermoplastic material was good and the flanges and connection formed were of good quality. The flanges had a diameter of 34mm.

It is thought that a larger diameter bore in the discs aids the migration of the thermoplastic material.

Claims

1. A method of making an abrasive article comprising an abrasive element having at least a non-porous region, and a hub for securing the abrasive element to a shaft positioned adjacent the non-porous region, the method comprising: forming the hub by forming first and second flanges between which the non-porous region of the abrasive element is located and by integrally forming a connection joining the flanges through a bore in the non-porous region such that the hub is clamped onto the abrasive element.

2. A method as claimed in claim 1, comprising the further step of positioning a shaft at the centre of the abrasive element before forming the hub, whereby the shaft is secured in the hub.

3. A method as claimed in claim 2, wherein the shaft is positioned such that its end extends partially or completely through the bore.

4. A method as claimed in any one of the preceding claims, wherein the flanges and connection are formed by injecting molten polymeric material and allowing the molten polymeric material to cool and solidify.

5. A method as claimed in claim 4 when appended to claim 2, further comprising providing a mould having first and second mould plates which together define a mould cavity, each of the plates having a recess formed therein, one of the plates having a bore formed therein to accommodate the shaft so that one end thereof projects into the mould cavity and one of the plates having a channel for injection of molten polymeric material into the mould cavity, wherein the abrasive element is placed in the mould cavity and molten polymeric material is injected into the cavity through the channel such that it fills the recesses to form the flanges.

6. A method as claimed in claim 1 , wherein the flanges and connection are formed by injecting molten polymeric material and allowing the molten polymeric material to cool and solidify, the method comprising the further step of forming a shaft integrally with the flanges and the connection from polymeric material.

7. A method as claimed in claim 6, further comprising providing a mould having first and second mould plates which together define a mould cavity, each of the plates having a recess formed therein, one of the plates having a bore formed therein defining the shaft and for injection of molten polymeric material into the mould cavity, wherein the abrasive element is placed in the mould cavity and molten polymeric material is injected into the cavity through the channel such that it fills the recesses to form the flanges and fills the bore to form the shaft.

8. A method as claimed in any one of the preceding claims, wherein two or more abrasive elements are provided.

9. An abrasive article comprising an abrasive element having at least a non-porous region, and a hub for securing the abrasive element to a shaft positioned adjacent the non- porous region, the hub having first and second flanges and a connection joining the flanges through a bore in the non-porous region, the non-porous region of the abrasive element being located between the flanges such that the hub is clamped onto the abrasive element.

10. An article as claimed in claim 15, wherein the flanges and connection are formed of injected molten polymeric material.

11. An article as claimed in claim 9 or claim 10, wherein the abrasive element is a radial bristle disc, comprising a central region from which a plurality of bristles radially extend; or a bristle brush comprising a plurality of bristles discs arranged with the central region of one disc adjacent the central region of another; or an abrasive disc made from foam-filled non-woven material.