WO1994019986A1

WO1994019986A1 - Rotary brush

Info

Publication number: WO1994019986A1
Application number: PCT/GB1994/000451
Authority: WO
Inventors: Peter Martin Zollman
Original assignee: Zollman Associates Limited
Priority date: 1993-03-12
Filing date: 1994-03-09
Publication date: 1994-09-15
Also published as: GB9305137D0

Abstract

A rotary brush is manufactured by providing a plurality of radially aligned fibres extending outwards from a hub. The fibres are impregnated away from the outer periphery with resin to form the body of the brush. The fibres at the outer periphery are cut to form the bristles of the brush. The fibres may be wound around an annular former and impregnated with resin in a mould.

Description

ROTARY BRUSH

BACKGROUND TO THE INVENTION

The present invention relates to a rotary brush and a novel process of manufacture for such a brush. The invention is particularly concerned with a brush capable of use at high angular velocities, for example up to 25000 rpm. Such a brush might have applications, for example, in tribohesion coating technology. In the present specification, the term "rotary brush" is used to denote a brush suitable for rotary use. It will be appreciated that a brush embodying the present invention may also be used in other ways, for example with the brush fixed and a workpiece rotating, and a brush so used also falls within the scope of the invention.

For use at high angular velocities a brush requires excellent dynamic balance, and high radial bursting strength and dimensional stability. Rotary brushes produced by conventional techniques are found to fall short in this respect, and so are not suitable for use at very high velocities. Hitherto, such brushes have been produced by laying pieces of fabric, for example cotton sheeting, in a mould with the warp and weft threads angularly staggered from piece to piece. Resin is then applied to the fabric. The resin impregnates the fibres over most of the surface area of the pieces, while leaving the outer fibre ends free. After hardening, the pieces are trimmed to a circular shape and the tangentially oriented fibres teased out, leaving only radial or quasi-radial bristles attached to the brush. The brush is finished by abrading it by rotating it against a hard counterpiece.

It is found that a brush produced by the above method tends to distort by way of dishing and growing radially if used at high angular velocities. Moreover, the structural fibres are not all radial and hence have a tendency to distort in the centrifugal force field. As well as these limitations in the finished product, the process in itself has the disadvantages of being laborious and difficult to perform consistently. In particular, it is difficult to introduce exactly the right amount of resin. In practice then such processes tend to have a low yield.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a method of manufacturing a rotary brush is characterised by providing a plurality of substantially radially aligned fibres extending outwards from a hub, impregnating the fibres away from the outer periphery with resin to form the body of the brush, and cutting the fibres at the outer periphery, thereby forming radial bristles. The step of cutting the fibres may be carried out prior to placing the fibres around the hub, but preferably is carried out after placing the fibres around the hub.

Preferably the fibres are provided extending radially around an annular former. This aspect of the present invention provides a process capable of producing circular or substantially circular brushes for use at high rotational speeds with a consistency and yield superior to those of conventional processes. The fibres are radially aligned around, for example, an annular former and then are impregnated with the resin. The fibres are cut in the region where they extend round the perimeter of the former thereby forming radial bristles. With the preferred method of the present invention, the fibres can be maintained in radial tension around the former until the resin has set, thereby ensuring accurate radial alignment.

The radial fibres may for example be provided in the form of a woven annular sleeve. It is much preferred however that the fibres are provided in the form of a winding around the former.

In the preferred embodiments, rather than using a woven material to form the brush, with many non-radial fibres, individual fibres or bundles of fibres are used, with substantially all the fibres radially aligned.

Preferably the former is substantially planar and tapers in profile from its periphery to the radially inner edge. Preferably the angle of taper of the former is equal in magnitude and opposite in direction to the angle of taper of the mould.

It is found that an optimum profile for the brush is produced by forming a multi-layered winding around a tapered annular former. This makes it possible to accommodate the higher fibre density needed at the hub in order to provide a given density of fibres per unit area around the periphery. Using equal and opposite tapers for the former and the mould produces a taper in the finished body which is balanced about the central radial plane of the brush.

Preferably the step of impregnating the fibres is carried out by placing the former in a mould, closing the mould, and subsequently injecting the moulding resin. Preferably the mould includes vacuum inlets at positions corresponding to a region towards the outer edge of the former, and the step of impregnation further comprises applying a vacuum to the inlets to limit the outwards movement of the resin. Once the brush is released from the mould, the centre of the brush may be bored to form the hub of the brush.

When, as in the example described below, two brushes are made on a common former, then it is the step of boring the hub which serves to separate the brushes and release the former.

Preferably a step substantially normal to the surface of the brush is formed around the hub.

It is found that the use of the brush at high speeds is further facilitated by providing a step around the hub which in use can be engaged by the mounting for the brush to hold the brush against radial movement under centrifugal force. The resin may be, for example, cyano-acrylate, epoxy or other resin. The fibres may be, for example, carbon fibres, cotton, Kevlar or other material.

According to a second aspect of the present invention, a rotary brush comprising substantially radially aligned fibres, is characterised in that the individual fibres extend for substantially the entire radial extent of the brush, the fibres being impregnated with resin from the inner hub of the brush to a region just short of the outer periphery of the brush thereby forming the body of the brush, and the fibres beyond the said region being left free of resin to form the bristles of the brush.

In the brush of this aspect of the invention, substantially all the fibres can be radially aligned, by contrast with the brushes produced hitherto. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present invention will now be described in further detail with reference to the accompanying drawings, in which: Figures la and lb are a cross-section and plan respectively of a former for use in the method of the present invention;

Figures 2a to 2d are sectional views illustrating a method in accordance with the present invention; Figure 3 is a sectional view showing in further detail the use of a pressure mould for resin impregnation; and

Figures 4a to 4d are sectional and plan views illustrating the method of an alternative embodiment. DESCRIPTION OF PREFERRED EXAMPLES As seen in Figures IA and IB, a former for use in producing a rotary brush comprises an annular disk 1 formed, in the present example, from PTFE. The former tapers in profile from its radially outer edge 2 to the radially inner edge 3. A circular groove 4 is formed around both the upper and lower surfaces of the former 1 towards the inner edge 3. The inner diameter d is 35 mm and the outer diameter D is 255 mm. The former has a thickness t of 5 mm.

In use, as will be described in further detail below, fibres are wound around the former. For clarity just a few turns of a winding are shown in Figure IB and with the dimensions and spacing of the fibre exaggerated. In practice, the former is uniformly covered by several layers of windings, to a depth of, e.g., 4 mm on the periphery. The different steps of the process for producing the brush are illustrated in Figures 2a to 2d First the winding is completed so that the former is surrounded by several layers of radially extending fibres as seen in Figure 2a. The fibres are then impregnated with resin over a region extending from the radial inner edge of the winding to a region 6 just short of the outer periphery of the winding. When the resin has set, forming the body 7 of the brush, the inside edge of the body is bored out to form a uniform hub 8 for mounting the brush. Finally the fibres are cut in the region 9 to form free radially extending bristles 10. The former can then be removed, leaving a pair of finished rotary brushes. The body 7 of the brushes includes circular step portions 11 at positions corresponding to the groove 4 in the former. In use, these step portions are used to clamp the brush to the coupling to the drive shaft which extends through the hub.

In this first example the fibre is wound around the former 1 using a toroidal winding machine of the type conventionally used for example in winding transformer coils from copper wire. A suitable machine is manufactured by Herbert Ruff of Germany comprising a base, manufacturer's reference RWA, and an RW2 winding head. In using such a machine to wind the fibres of the present invention, the winding speed has to be reduced considerably compared with the speeds conventionally used in winding copper wires. At high speed the accelerations produced tend to break the fibres. In order to reduce as far as possible the time taken to produce the _.complete winding, the toroidal winding machine may wind a bundle of multiple filaments around the hub, rather than winding a single filament at a time. As a further alternative, several fibres on several respective spools may be wound at once. Figure 4 shows an alternative method for producing the winding without using a toroidal winding machine. In this example the fibre is pre-wound around an oblong former to produce a bundle of a thousand or more windings. The winding is then clamped between fingers at one end and cut at the other end thereby freeing the former. Prior to cutting, an adhesive may be applied to the fibres to make them tacky and keep the bundle together. The bundle, still clamped by the fingers, is then inserted into the annular disc 1 with upper and lower parts of the bundle covering the upper and lower surfaces of part of the disc. This process is repeated with, for example, eight such bundles each spaced angularly by 45° and the filaments may then be combed out radially so that they are radially aligned without sharp angular transitions at the transition between bundles. The steps of impregnating the windings are then carried out as described above. There is however then no need to cut the periphery of the windings since this has already been done.

The moulding process for impregnating the fibres with resin is shown in further detail in Figure 3. The former and winding are located between the upper and lower halves 12,13 of a pressure mould. The two halves are compressed and may be surrounded by an outer ring 14. A plug having upper and lower halves 15,16 is inserted through the centre of the mould.

In use, compressed air may be applied under pressure through inlets 17 in the outer ring 14 at a suitable time after the resin is injected through inlets 18 in the plugs to assist the action of the vacuum in limiting the spread of resin. In this manner, the resin impregnates the body of the windings, extending from the centre radially outwards. The extent of the resin is limited by a vacuum applied via inlets 19 located towards the outer edge of the mould.

An appropriate resin is chosen according to the desired process and product qualities. Epoxy resin facilitates the moulding process, but in use may exhibit slow creep. Cyano-acrylate is more difficult to handle in the moulding process since it hardens on contact with moisture, but provides a finished product which is less susceptible to creep.

Claims

1. A method of manufacturing a rotary brush characterised by providing a plurality of substantially radially aligned fibres extending outwards from a hub, impregnating the fibres away from the outer periphery with resin to form the body of the brush, and cutting the fibres at their outer periphery, thereby forming radial bristles.

2. A method according to claim 1, in which the fibres are provided extending radially around an annular former (1) .

3. A method according to claim 2, in which the fibres are wound around the former.

4. A method according to claim 2 or 3, in which the former is substantially planar and tapers in profile from its periphery (2) to its radially inner edge (3) .

5. A method according to any one of the preceding claims, in which the step of impregnating the fibres is carried out by placing the former in a mould (Figure 3) , closing the mould, and subsequently injecting the moulding resin.

6. A method according to claim 5 when dependent directly or indirectly on claim 2, in which the former has a taper substantially equal in magnitude and opposite in direction to the taper of the mould.

7. A method according to claim 5 or 6, in which the mould includes vacuum inlets (19) at positions corresponding to a region towards the outer edge of the former, and the step of impregnation further comprises applying a vacuum to the inlets to limit the outwards movement of the resin.

8. A method according to any one of the preceding claims, further comprising providing a step substantially normal to the surface of the brush around the hub.

9. A method according to any one of claims 2 to 8, further comprising boring the hub of the brush subsequent to the impregnation of the fibres.

10. A method according to any one claims 2 to 9, in which a pair of rotary brushes are formed simultaneously around a single former.

11. A rotary brush characterised by a plurality of substantially radially aligned fibres having individual fibres extending for substantially the entire radial extent of the brush, the fibres being impregnated with resin from the inner hub of the brush to a region just short of the outer periphery of the brush thereby forming the body of the brush, and the fibres beyond the said region being left free of resin to form the bristles of the brush.