HK1070019B - Polishing pad and system - Google Patents

Description

Polishing pad and apparatus

Technical Field

The present invention relates to polishing pads used to polish conditioned surfaces, particularly surfaces that have been coated and from which it is desired to remove imperfections.

Background

It is well known that polishing pads for such applications should be relatively compliant, that is, they should be easily deformable to conform to the surface being polished to avoid excessive pressure being applied at one location as compared to an adjacent location. For ease of application, foam pads are typically used, either as backings for conventional abrasive-coated flexible sheets or as foam pads with abrasive particles that can be bonded directly to the foam surface or applied as a slurry between the pad and the surface.

The surface of the polishing pad in contact with the workpiece may be flat or concave-convex, and the latter is preferred, in which case it may be desirable to polish only a portion of the surface in contact with the workpiece slightly, or to apply more pressure to bring substantially the entire foam surface into contact with the workpiece. Typical foams of the above introduction are described in U.S. patent publication nos. 4,962,562, 5,007,128, and 5,396,737.

Such foams lack the versatility that they have a single composition and density, so only one type of polishing can be performed, and if different polishing is required, the polishing pad replaced.

The present invention provides a device that is adaptable and versatile, while still maintaining its simplicity of use.

Disclosure of Invention

The present invention provides a resiliently compressible foam polishing pad comprising first and second opposed major working surfaces, each surface being provided with a plurality of spaced depressions of generally hollow frusto-conical shape (or the truncated ends forming the bases of the depressions may be rounded), the depressions being spaced apart by frusto-conical portions, wherein the truncated conical portions may optionally also be rounded at their tops, and the tops all lie in the same plane and form the working surface. The truncated recess and the taper described above are typically the same size, i.e. so that a taper could conceivably fit snugly within a recess, but this is not an essential feature of the invention.

Generally, the depressions in each major working surface are of the same depth, but it is often advantageous if the depressions on the same working surface are of different depths so that, when the pressure on the foam is increased, the foam is flattened to increase the surface area in polishing contact with the workpiece, i.e., the area of the effective working surface, is achieved in two or more stages.

The portion of foam between the recesses is referred to as a "frustoconical portion," but it should be understood that when the recesses are not uniformly sized or spaced relatively far apart, the shape of the structure between the recesses may not exactly conform to the frustoconical shape and may interconnect adjacent structures. It should be understood that such structures are included within the intended scope of the invention as claimed.

Although it is generally advantageous for the first and second working surfaces to have the same working surface design, this is by no means the only structure that is permissible. If it is desired to take advantage of the benefits of providing two working surfaces on the same polishing pad, the second working surface can have a configuration that is different for a range of polishing options. This can be achieved by varying the spacing between the depressions or their depth, but more commonly such differences are achieved by using foam materials of different compressibility (possibly in addition to the surface structure variations described above).

The foam pad of the present invention must be compressible and is therefore preferably made of a polymer that is foamable to make an elastic material that can be compressed and that can substantially recover its original dimensions after the compressive force is removed. The polymer is preferably a thermoplastic or rubbery polymer such as a polyolefin, plasticized polyvinyl halide, polydiene or polyurethane. For ease of manufacture and economy, the preferred polymer is polyurethane, most preferably open-celled polyurethane, which can be foamed in a controlled manner to a large extent to produce foams of precisely controlled density.

Providing a foam pad with two working surfaces may be achieved using suitable moulding techniques, but more commonly by stacking different foam pads together. This gives rise to the possibility of producing polishing pads in which the working surfaces differ in structure and/or, more preferably, in foam density. An intermediate layer, which may simply be an adhesive layer, but is preferably a rubbery polymer layer, and which, while flexible and possibly flat foam-like, is sufficiently rigid to add dimensional stability to the polishing pad, may be used to stack the two polishing pads. A suitable polymer for bonding such foam members together to form a polishing pad is polybutylene rubber. The relative physical stiffness of the middle layer becomes especially important when the foam material is used with a mechanical polisher that requires the foam pad to be held in some sort of holder.

Accordingly, the present invention also includes a polishing apparatus suitable for use with an orbital polisher comprising:

1) a resiliently compressible foam polishing pad in the form of a disc comprising first and second opposed major working surfaces, each surface being provided with a plurality of spaced depressions of generally hollow frusto-conical shape (or the truncated ends forming the bases of the depressions may be rounded), the depressions being spaced apart by frusto-conical portions, wherein the tops of the frusto-conical portions may optionally be rounded and the tops all lie in the same plane and form the working surface;

2) a backing pad with which the foam polishing pad is in contact and with which a working surface projects beyond the backing pad, the second working surface being in contact with the backing pad; and

3) a retaining device for retaining one surface of the polishing pad in releasable contact with the backing pad.

In addition to providing a means by which the foam pad may be attached to the orbital sander (e.g., by an axially positioned spindle adapted to fit in the shaft of the orbital sander), the preferred form of retaining means restricts the polishing pad from moving relative to the backing pad during use.

When the backing pad is in the form of a holder in which the polishing pad is partially held in use, the holding means may be in the form of pins or male members adapted to fit in corresponding holes or recesses in the polishing pad. They may also take the form of clips adapted to bear on the periphery of the polishing pad or on depressions cut into the periphery between the two working surfaces of the polishing pad. Such a recess may conveniently be provided in a peripheral portion intermediate between the first and second working surfaces. When a polishing pad made by laminating two polishing pads uses a harder polymer layer, the depressions may conveniently be formed in the polymer layer to provide a cooperating surface for the clips or other retaining means that is less deformable than the foam material from which the first or second working surfaces are made.

Where the backing pad is in the form of a disk and contacts one surface of the polishing pad, the retaining means may comprise a member adapted to be positioned axially through the polishing pad and cooperate with an attachment means supported on the polishing pad in an axial recess in the working surface of the polishing pad. The axially positioned member may be, for example, an internally threaded tube or an externally threaded rod, and it cooperates with a threaded member supported on the surface of the polishing pad to hold the polishing pad in place on the backing pad. It may also be in the form of a slotted rod adapted to receive a clamping device such as a C-clamp, or in the form of a rod provided with a hole with a washer and cooperating with a cotter pin. Quick release couplings, such as where a spring seat protrusion such as a ball bearing cooperates with a groove, are sometimes used to ensure releasable attachment. Other examples well known in the art include a radial projection that cooperates with an L-shaped slot and ensures engagement by inserting the radial projection on the retaining device into the slot and then positioning the projection in the angled portion of the slot by partial rotation of the retaining device axially. Other alternative attachment means known in the art may be used in place of the above described attachment means.

The backing pad is preferably provided with a plurality of protrusions which engage the surface of the polishing pad to limit movement of the polishing pad relative to the backing pad in use.

It is generally preferred to provide the foam pad with vent channels connecting the first and second surfaces to help cool the surfaces during polishing. Such channels are also advantageously provided in the body of the retaining cup to allow air to circulate around the polishing pad as it is used.

Brief Description of Drawings

In the drawings:

FIG. 1 shows a cross-sectional view of a double-sided foam polishing pad according to the present invention.

Fig. 2 shows a plan view of the open side of a backing pad in the form of a retaining cup.

Fig. 3 shows the retaining cup of fig. 2 in a vertical section along line a-a'.

FIG. 4 shows in cross-section a different form of the backing pad with the polishing pad attached.

Detailed Description

The invention will now be described with reference to the embodiment shown in fig. 1-4. It is to be understood that other embodiments of the invention may be devised which differ from the embodiments shown without departing from the spirit of the invention.

In fig. 1 of the drawings, foam pans 1 and 2 are laminated together using a layer 3 of a rubbery polymer. The rubbery polymer layer 3 is provided around its periphery with a plurality of recesses 7 at intervals from each other. The layers 1 and 2 of the composite mat are provided with a plurality of recesses 4 in the working surfaces 5 and 6, respectively.

The foam pad shown in figure 1 is used with a backing pad and in figures 2 and 3 this has the form of a cup-shaped holder which is a shallow cylindrical cup-shaped holder 7 having a small flange 8 projecting radially inwardly. The cup-shaped member encloses a space 9, in which space 9 half of the foam mattress shown in fig. 1 can be accommodated. Four resilient clips 10 project radially inwardly from the flange of the cup. When a foam pad is received in the holder, the clips project into the recesses 7 of the rubbery polymer layer to prevent rotation of the pad relative to the cup during use. The inside surface of the cup is provided with an axially thin boss 11 which bears on the unused working surface of the polishing pad to limit the amount of deformation of the pad into the holder that can occur during use. The holder is adapted to be mounted in an orbital polisher by a spindle 12 extending from the bottom of the holder. Several vent holes 13 are provided at regular intervals around the cup to allow air circulation when the polishing pad is in use.

In an alternative embodiment shown in figure 4, the backing pad may be in the form of a plate 15 with a spindle 12, and the backing plate may be attached to an orbital sander or polisher by means of the spindle 12. The surface of the backing plate that contacts the polishing pad is provided with a plurality of protrusions 16 that are designed to contact the polishing pad surface and provide sufficient resistance to rotation relative to the back pad. The backing pad also has an axially positioned extension rod 17, the extension rod 17 passing through a cooperating hole 18 in the polishing pad. The surface of the polishing pad is provided with a plurality of axially-directed recessed regions 20 into which a retaining device 18, which cooperates with the extension rod 17 to hold the polishing pad in place on the backing pad, can be fitted. The recess is deep enough so that the rod and retaining device protrude above the surface of the polishing pad even in the most compressed position during use. In the embodiment shown, the rod has an external thread and the retaining means is in the form of a flanged nut fitted on the rod.

To use the polishing pad with an orbital polisher, the polishing pad is placed in the holder with a working surface in contact with the raised portion 11 at the bottom of the holder, and the clip 10 is received in the recessed portion 7 of the middle rubber-like layer 3 of the polishing pad. In this way, the second working surface protrudes from the retainer so that the portion of the polishing pad between the intermediate layer and the working surface can be fully compressed to form the bottom of the recessed portion of the working surface without the retainer contacting the workpiece.

When it is desired to work with a foam material having the foam characteristics provided by the second working surface, it is sufficient simply to remove the polishing pad from the holder and turn it over.

As will be appreciated, the present invention provides a very versatile polishing pad that can operate under many different polishing conditions by simply manipulating the polishing pad and backing pad.

Claims (22)

1. A resiliently compressible foam polishing pad comprising first and second opposed major working surfaces, each surface being provided with a plurality of spaced depressions of generally hollow frustoconical shape, the depressions being separated by frustoconical portions, wherein the tops of the frustoconical portions all lie in the same plane and form the working surface.

2. A foam polishing pad according to claim 1 in which the truncated end forming the base of the depression and the top of the truncated cone forming part of the working surface are rounded.

3. The foam polishing pad of claim 1 wherein the foam material providing the first working surface is different from the foam material providing the second working surface.

4. A foam polishing pad according to claim 3 in which the foam material providing the first working surface has a compressibility different from that of the foam material providing the second working surface.

5. A foam polishing pad according to claim 3 in which the polishing pad is formed by laminating two foam pads using an intermediate layer of rubbery polymer.

6. A foam polishing pad according to claim 5 in which the rubbery intermediate layer is provided with a plurality of spaced apart recesses.

7. The foam polishing pad of claim 1, wherein a plurality of holes extend through the pad and connect the first and second working surfaces.

8. The foam polishing pad of claim 7, wherein the truncated end forming the bottom of the depression and the top of the frustoconical portion forming part of the working surface are rounded.

9. A polishing apparatus suitable for use with an orbital polisher comprising the resiliently compressible foam polishing pad of claim 1 in the form of a plate; further comprising a backing pad, the foam polishing pad being in contact therewith, and a working surface projecting beyond the backing pad, the second working surface being in contact with the backing pad; and a holding device for holding one surface of the polishing pad in releasable contact with the backing pad.

10. A polishing system according to claim 9 in which the truncated end forming the base of the depression and the top of the frusto-conical portion forming part of the working surface of the polishing pad are rounded.

11. A polishing system according to claim 9 in which the backing pad is in the form of a cup in which a portion of the polishing pad is retained, the cup being provided with retaining means which co-operate with recesses in the periphery of the polishing pad to restrict its movement relative to the cup.

12. A polishing system according to claim 11 in which the bottom of the cup is provided with a thin boss which contacts the working surface of the foam pad located within the cup.

13. A polishing system according to claim 11 adapted to be mounted on an orbital polisher.

14. A polishing system according to claim 11 in which the foam providing the first working surface of the polishing pad has a compressibility different from that of the foam providing the second working surface of the polishing pad.

15. A polishing system according to claim 11 in which the polishing pad is formed by laminating two foam pads using an intermediate layer of a rubbery polymer.

16. A polishing system according to claim 11 in which the cup-shaped member is provided with a plurality of vent holes.

17. A polishing system according to claim 9 in which the backing pad is in the form of a plate with axial rod extensions; the polishing pad having an axially-located opening adapted to receive the rod extension and having a region adjacent each surface of the polishing pad having a diameter greater than the diameter of the rod; and, a retaining device releasably attached to an end of the rod to maintain one surface of the polishing pad in contact with the backing plate.

18. A polishing system according to claim 17 in which the backing pad is provided with a plurality of protrusions extending through the pad to limit rotation of the pad relative to the backing pad.

19. A polishing system according to claim 17 adapted to be mounted on an orbital polisher.

20. A polishing system according to claim 17 in which the foam providing the first working surface of the polishing pad has a compressibility different from that of the foam providing the second working surface of the polishing pad.

21. A polishing system according to claim 17 in which the polishing pad is formed by laminating two foam pads using an intermediate layer of a rubbery polymer.

22. A polishing system according to claim 17 in which the retaining means comprises a threaded member which engages with threads on the stem extension of the backing plate.