WO2007143400A2

WO2007143400A2 - Abrading article comprising a slotted abrasive disc and a back-up pad

Info

Publication number: WO2007143400A2
Application number: PCT/US2007/069594
Authority: WO
Inventors: Terry J. Elsey; Daniel R. Martin
Original assignee: 3M Innovative Properties Company
Priority date: 2006-05-30
Filing date: 2007-05-24
Publication date: 2007-12-13
Also published as: GB0610531D0; WO2007143400A3

Abstract

An abrading article (1) is described that is suitable for attachment to a powered abrading machine having a dust-extraction vacuum system. The abrading article comprises a back-up pad (3) having a major surface (8) in which are formed a plurality of dust-extraction apertures (10) connected in use to the vacuum system, the apertures occupying at least 5% of the area of the major surface. The abrading article also comprises an abrasive disc (2) having, on one side, an abrasive face (6) and, on the other side, an attachment face removably located on the major surface of the back-up pad, the disc having a plurality of equispaced dust-extraction slots (7) formed therein, extending from a central region of the disc toward the periphery of the disc, which slots occupy at least 5% of the area of the abrasive face. The dust-extraction apertures (10) in the back-up pad (3) are sufficiently numerous and so located that the amount of grinding dust removed from the abrasive face (6) of the disc (2) through the dust-extraction slots (7) during an abrading operation is substantially independent of the rotational orientation of the disc on the back-up pad.

Description

ABRADING ARTICLE COMPRISING A SLOTTED ABRASIVE DISC AND A

BACK-UP PAD

Technical Field

The present invention relates to abrading articles of the type comprising an abrasive disc in combination with a back-up pad. The invention is more especially concerned with abrading articles in which the abrasive disc comprises an abrasive layer bonded to a flexible backing layer.

Background

A back-up pad is used in the abrasives field to support an abrasive disc during an abrading operation. The back-up pad includes a generally planar major surface, to which the abrasive disc is attached. Although back-up pads may be hand held, they are more commonly used in conjunction with a powered abrading machine such as an electric or pneumatic sander.

An abrasive disc can be attached to a back-up pad in various ways. One attachment method utilizes a hook-and-loop type of system in which mechanical structures on the disc engage with mechanical structures on the back-up pad. In one version of such a system, the back-up pad includes a major surface having a plurality of hooks projecting therefrom. The hooks are shaped for mechanical engagement with attachment elements on the back face of the abrasive disc to releasably attach the disc to the back-up pad. An example of such a back-up pad is available from the 3M Company of St. Paul, MN, under the designation "HOOKIT" brand back-up pad, and an example of an abrasive disc for attachment to that back-up pad is available from the same company under the designation "HOOKIT" brand abrasive disc. Alternatively, the hooks can be provided on the back face of the abrasive disc, for mechanical engagement with attachment elements on the major surface of the back-up pad. An example of such an assembly is available from 3M Company under the designation "HOOKIT II" brand back-up pad and abrasive disc. It is recognized that, in the case of an abrasive disc comprising an abrasive layer bonded to a flexible backing layer, both the useful life and the cut rate of the disc (i.e. its ability to remove material from the workpiece) can be enhanced by removing the grinding dust that is generated at the abrasive face of the disc during an abrading operation. To that end, it is known to provide matching apertures in the abrasive disc and in the back-up pad on which it is used, to enable dust that is generated during an abrading operation to be removed by applying suction through the apertures to the abrasive surface of the disc. For example, it is known to provide an abrasive disc with five or six circular holes that are spaced regularly around the disc at the same radial distance from its centre, and to attach the disc to a back-up pad having matching circular holes on its major surface. The holes in the disc and back-up pad are aligned and suction is applied through them to remove dust generated at the front face of the disc during an abrading operation. Also known is an abrading article, available under the trade name "Norton Multi-Air" from Saint-Gobain Abrasives, Inc. of Worcester, MA, USA, in which (with a view to improving dust removal) the disc has a large number of dust-extraction holes over substantially the whole of its abrasive surface intended to be aligned with matching dust extraction holes in the major surface of the back-up pad.

An abrading article comprising an abrasive disc and back-up pad with non-matching arrangements of dust-extraction apertures has been proposed in US-A-5 810 650 (Jόst).

According to that proposal, the dust-extraction apertures in the abrasive disc take the form of a perforation substantially uniformly distributed over the entire surface of the disc, the latter being intended to be attached by a burred connection to a conventional back-up pad having six circular holes in its major surface. As an alternative, US-A-2003/0003856 proposes an arrangement in which the perforations in the abrasive disc are confined to an annular zone in the disc, overlying the zone in which the six (or possibly eight) dust extraction holes of the back-up pad are located.

An alternative type of abrasive material, available under the trade name "Abranet" from KWH Mirka Ltd of Jeppo, Finland, has been proposed to reduce dust from the sanding process entering the atmosphere. The abrasive material is available as sanding discs or strips described as having thousands of small holes.

Summary

The present invention is concerned with the provision of an abrading article, comprising an abrasive disc and back-up pad, which enables the efficient removal of dust generated at the front face of the disc during an abrading operation without requiring the user to align dust-extraction apertures in the disc with dust-extraction apertures in the back-up pad. The invention is further concerned with enabling this to be achieved with an abrading article in which the abrasive disc is comparatively straightforward to manufacture using currently- available technology.

The present invention provides an abrading article comprising:

(i) a back-up pad having a major surface in which are formed a plurality of dust-extraction apertures for connection, during an abrading operation, to a source of suction, the apertures occupying at least 5% of the area of the major surface; and

(ii) an abrasive disc having, on one side, an abrasive face and, on the other side, an attachment face removably located on the major surface of the back-up pad, the disc having a plurality of equispaced dust-extraction slots formed therein, extending from a central region of the disc toward the periphery of the disc, which slots occupy at least 5% of the area of the abrasive face; wherein the apertures in the back-up pad are sufficiently numerous and so located that the amount of grinding dust removed from the abrasive face of the disc through the dust- extraction slots during an abrading operation is substantially independent of the rotational orientation of the disc on the back-up pad.

Brief Description of the Drawings

By way of example, embodiments of the invention will be described with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic side view of an abrading machine to which is attached an abrading article comprising a back-up pad and an abrasive disc;

Fig. 2 is an enlarged diagrammatic side view of the abrading article of Fig. 1; Fig. 3 shows the front face of an abrasive disc suitable, in accordance with the invention, for use in the abrading article of Fig. 2;

Fig. 4 shows the major face of a back-up pad suitable, in accordance with the invention, for use in the abrading article of Fig. 2; Fig. 5 is an enlarged section view taken on the line V-V of Fig. 4;

Fig. 6 shows the front face of the abrasive disc of Fig. 3 attached to the back-up pad of Fig. 4 to form an abrading article in accordance with the invention; and Figs. 7 to 10 show the front faces of other abrasive discs suitable for use, in accordance with the invention, in the abrading article of Fig. 2.

Detailed Description

The present invention relates to abrading articles of the type comprising an abrasive disc removably attached to a backup pad. Within the context of this disclosure, removably attached means that the disc is secured to the back-up pad in such a way that it will not detach during an abrading operation, but can be removed from the back-up pad by hand as required. The invention is particularly concerned with abrading articles intended for attachment to a powered abrading machine provided with a dust-extraction vacuum system that removes grinding dust generated at the abrasive face of the disc. Fig. 1 shows such an abrading machine 100, the abrading article being generally designated by the reference numeral 1 , the abrasive disc by the reference numeral 2 and the back-up pad by the reference numeral 3. The abrading article 1 is shown in greater detail in Fig. 2, from which it can be seen that the abrasive disc 2 is removably located on the front, or major, face of the back-up pad 3 by means of an attachment layer 4. As described below, the attachment layer 4 is of the hook-and-loop type. A threaded stud 5 is fixed to the rear side of the back-up pad 3 to allow attachment of the latter to the abrading machine 100 so that the abrading article can be rotatably driven around the longitudinal axis of the threaded stud. The threaded stud 5 is shown simply as one example of a mechanism of attaching the abrading article 1 to an abrading machine and may be replaced by any other suitable mechanism. The abrading machine 100 typically rotates the abrading article 1 in a circular motion but may also provide an additional orbital component to this motion (as is the case, for example, when the abrading machine is a dual action sander). In accordance with the invention, the back-up pad 3 is formed with a plurality of dust- extraction apertures 10 (not visible in Figs. 1 and 2 but shown in Figs. 4 and 5 and described below). When the abrading article 1 is in use, the apertures 10 are connected, via passageways in the back-up pad, to the dust extraction vacuum system of the abrading machine 100. Likewise in accordance with the invention, the abrasive disc 2 is formed with a plurality of dust-extraction slots 7 (not visible in Figs. 1 and 2 but shown in Fig. 3 and described below) that are in at least partial registration with dust-extraction apertures in the back-up pad. As a result, suction applied to the dust-extraction apertures in the back-up pad 3 will be effective at the front face of the abrasive disc 2 to remove grinding dust generated during an abrading operation on a workpiece (not shown).

One suitable form for the abrasive disc 2 is shown in Fig. 3. On its front face 6, the disc 2 has an abrasive layer comprising a plurality of abrasive particles attached to a flexible backing by a binder system. On the rear face of the disc 2, not visible in Fig. 3, is one part of the attachment layer 4 shown in Fig. 2. A set of identical dust-extraction slots 7 is formed in the disc 2, the slots being spaced regularly around the disc and extending from a central region of the disc towards its periphery. The slots are curved slightly, as shown, so that they are concave in the direction of rotation (R_D) of the disc when in use. At the centre of the disc 2 is a circular dust-extraction hole 7 A, although that is not essential.

A suitable form for the back-up pad 3 is shown in Figs. 4 and 5. The front, or major, face 8 of the back-up pad 3 provides the other part of the attachment layer 4 shown in Fig. 2, and also comprises a plurality of dust-extraction apertures 10 which are the inlet openings of passageways 11 in the back-up pad (see the section view of Fig. 5). When the back-up pad is in use on the abrading machine 100, those passages 11 are connected to the vacuum system mentioned above for removing grinding dust generated at the face 6 of the abrasive disc 2 by the abrading action of the disc on a workpiece.

As described in greater detail below, the number and location of the dust-extraction apertures 10 in the back-up pad 3 are such that grinding dust is removed efficiently from the face 6 of the disc 2 through the dust-extraction slots 7 during an abrading operation, and that the amount of dust removed is substantially independent of the rotational orientation of the disc on the back-up pad. Consequently, there is no need for the user of the abrading machine to place the disc 2 on the back-up pad 3 in a particular orientation to ensure that effective dust removal is achieved. The use of the radially-extending slots 7 as dust-extraction apertures in the disc 2 promotes the removal of grinding dust over substantially the entire abrasive surface of the disc as the latter rotates, offering the attendant advantages of good cut rate and good disc life.

The abrasive disc 2, the back-up pad 3, and the attachment layer 4 of the abrading article 1 will now be described in greater detail.

The abrasive disc 2

Advantageously, the slots 7 should occupy at least 5% of the area of the front face 6 of the abrasive disc 2 and may occupy 15% or more of that area provided that the integrity of the disc is not adversely affected and that an effective abrasive surface is retained. The radial extent of the slots 7 should, preferably, correspond to the location of the dust-extraction apertures 10 in the back-up pad (see below). Generally, it has been found that effective dust extraction over most of the abrasive surface of the disc 2 with minimum effect on the integrity of the disc can be achieved using six equispaced slots, each having a width in the range of from about 2 mm to about 10 mm and extending from a point spaced radially outwards from the disc centre by a distance in the range of from about 5 mm to about 20 mm to a point spaced radially inwards from the disc periphery by a distance in the range of from about 3 mm to about 15 mm. Subject to those constraints, the length of the slots can be increased slightly by curving them, either so that they are concave in the direction of rotation (R_D) of the disc as shown in Fig. 3 or in the reverse direction as shown in Fig. 7. However, straight slots as shown in Fig. 8 have also been found to provide acceptable dust extraction.

It will be appreciated, however, that other forms and arrangements of the slots 7 may be appropriate depending, for example, on factors such as the materials from which the abrasive disc 2 is formed and the configuration of the back-up pad 3 with which it is intended to be used. Examples of some other forms and arrangements of slots in an abrasive disc are illustrated in US-A-2006/0019579. If required, dust extraction from the abrasive face of the disc 2 can be further enhanced by supplementing the slots 7 in the disc with other apertures, for example circular holes 12 as shown in Fig. 9. The supplementary apertures can have any suitable shape but will most advantageously be located between the outer ends of the slots 7.

Although the abrasive discs described above with reference to the drawings are all circular, that is not essential. Fig. 10, for example, shows a circular abrasive disc 20 from which three equi-spaced peripheral arcuate segments 21 have been removed. The resulting shape tessellates so that the discs 20 can be cut from a sheet of abrasive material with minimal waste. This shape of disc also offers the advantage of enabling more of a workpiece to be viewed as it is being abraded.

It will be appreciated that the abrasive discs 2, 20 described above can be produced using processes that are well known in the field of abrasives manufacture. The materials required for the abrasive front face 6 and flexible backing layer of the abrasive discs 2 are also readily available as will now be described.

The abrasive particles of the front face 6 may comprise a single abrasive mineral composition or a mixture of different abrasive mineral compositions. Useful conventional abrasive particles include fused aluminum oxide, heat treated aluminum oxide, white fused aluminum oxide, silica, silicon carbide, titanium diboride, boron carbide, tungsten carbide, titanium carbide, diamond, cubic boron nitride, garnet, fused alumina zirconia, sol gel abrasive particles and the like. The particle size of these conventional abrasive particles can range from about 0.01 to 1500 micrometers, typically between 1 to 1000 micrometers.

The binder system by which the abrasive particles are attached to the flexible backing layer conventionally includes a make coat, a size coat, and optionally a supersize coat. The make coat typically includes a tough, resilient polymer binder that adheres the abrasive particles to the backing. The size coat, which also typically includes a tough resilient polymer binder that may be the same as or different from the make coat binder, is applied over the make coat and the abrasive particles to further reinforce the particles. The supersize coat, including one or more antiloading ingredients or perhaps grinding aids, may then be applied over the size coat if desired. Suitable binders for the purpose of adhering the abrasive granules to the flexible backing layer include phenolic resins, urea- formaldehyde resins, hide glue, varnish, epoxy resins, polyurethane resins, and radiation- cured crosslinked acrylate binders. Advantageously, the binder system is a urea formaldehyde binder system as described in US-A-6 682 574.

The abrasive face of the disc 2 may, alternatively be a structured abrasive layer comprising precisely- shaped abrasive composites. Information concerning such composites, and methods for their manufacture, may be found for example in US-A-5 152 917 (Pieper et al.); 5 435 816 (Spurgeon et al.); and 5 454 844 (Hibbard et al).

The flexible backing layer to which the abrasive layer of the disc 2 is attached may be selected from any of a wide range of materials including paper, polymeric materials, cloth, vulcanized fiber or combinations of these materials.

The back-up pad 3

The dust-extraction apertures 10 in the back-up pad 3 are of a conventional size (typically at least 3 mm in diameter, to ensure that they do not become clogged by grinding dust when the back-up pad is in use, but not so large that the integrity of the back-up pad is adversely affected) and advantageously occupy at least 5% of the area of the front face 8 of the pad. To ensure that the removal of grinding dust from the front face of the abrasive disc 2 by the suction system of the abrading machine 100 is unaffected by the radial orientation of the disc on the back-up pad 3, it has been found that there should be at least thirty of those apertures 10 in the back-up pad and that they should be distributed substantially-evenly over the effective surface of the back-up pad. The term "effective surface" means substantially the entire front face 8 of the back-up pad 3, excluding a peripheral margin 8 A and a circular central region 8B such that the radial extent of the "effective surface" corresponds substantially to the radial extent of the dust-extraction slots 7 when the abrasive disc is located on the back-up pad. If number of apertures 10 in the back-up pad 3 is reduced below thirty, it has been found that the removal of grinding dust from the front face of the abrasive disc 2 becomes dependent on the radial orientation of the disc on the back-up pad. Without wishing to be bound by theory, it is believed that dust removal is not only due to the effect of suction through apertures 10 that are actually aligned with dust-extraction slots 7 in the disc 2 but also to the effect of suction, via the attachment system 4, through apertures 10 that are simply in the vicinity of dust-extraction slots. A minimum of thirty apertures 10 in the back-up pad 3 appears to be required to ensure that, regardless of the radial orientation of the disc 2, there are always sufficient apertures either aligned with, or in the vicinity of, the dust-extraction slots 7 to ensure an effective level of dust removal.

The number of apertures 10 in the back-up pad should not, on the other hand, be so great as to detract from the mechanical stability and useful life of the pad. Typically, up to fifty apertures can be provided without noticeable effect on mechanical stability and useful life.

The apertures 10 may be in the form of circular holes (corresponding to the cross-section of the passageways in the back-up pad), but that is not essential.

The back-up pad 3 may be constructed from any suitable material having regard to the abrading applications in which the pad is to be used. A typical material is a resiliently- compressible foam, for example a polyurethane foam. The back-up pad 3 can be of any appropriate shape and size.

The dust-extraction passageways 11 in the back-up pad, through which dust is removed from the front face of the abrasive disc 2, can have any suitable configuration depending on the vacuum system to which they are attached in use. The back-up pad 3 may also comprise passageways 14 (Fig. 5) that connect with additional dust-extraction apertures 15 in the side of the back-up pad.

The back-up pad 3 may be fabricated specifically for use with the abrasive disc 2 or may be any suitable, commercially-available, product that possesses the essential features described above. The attachment layer 4

As indicated above, the attachment layer 4 between the abrasive disc 2 and the back-up pad 3 comprises a hook-and loop type of attachment system (i.e. a system in which mechanical structures on the disc engage with mechanical structures on the back-up pad). The attachment system may, for example, comprise a loop fabric that is laminated to the rear face of the flexible backing of the abrasive disc 2, and an array of hooks that is provided on the front face of the back-up pad 3. Alternatively, the hook component of the attachment system may be provided on the rear face of the abrasive disc, with a loop component being provided on the front face of the back-up pad. Hook and loop attachment systems for abrasive articles are described, for example in US-A-4 609 581 (Ott); 5 254 194 (Ott et al); and 5 505 747 (Chesley et al). Other equivalent attachment systems comprising cooperating mechanical structures on the abrasive disc and the backup pad can also be used.

EXAMPLES

Abrading article I was assembled from a P400 grit abrasive disc and a foam back-up pad as follows:

The abrasive disc was a conventional, commercially-available, product having a diameter of 127 mm and five circular dust-extraction apertures having a diameter of 10 mm. The dust extraction apertures were arranged in a circle with their centres equispaced from one another at a distance of 34 mm from the centre of the disc.

The back-up pad was also a conventional, commercially-available, product having a diameter of 125 mm and five circular dust extraction apertures having a diameter of 10 mm. The location of the dust extraction apertures in the back-up pad corresponded to that of the dust-extraction apertures in the abrasive disc.

The abrasive disc was attached to the back-up pad by a hook-and-loop attachment system, with the dust-extraction apertures in the disc aligned with those in the back-up pad. Abrading article II, in accordance with the invention, was assembled from a P400 grit abrasive disc and a foam back-up pad as follows:

The abrasive disc had a diameter of 127 mm and was formed with a central dust-extraction hole 7A and with six dust-extraction slots 7 spaced regularly around the disc and curved as shown in Fig. 7. Each slot had a width of about 6 mm and a length (measured along its central axis) of about 41.5 mm, and its curvature was such that the central axis was an arc of a circle having a radius of about 61 mm. The central dust-extraction hole 7A had a radius of about 3mm. The inner end of each slot 7 was located at a radial distance of about 8 mm from the edge of the hole 7 A, and the outer end of the slot was located at a similar radial distance from the disc periphery.

The back-up pad had a diameter of 125 mm and the foam from which it was formed had a similar hardness (measured by the Shore® (Durometer) test) to that of the back-up pad of abrading article I. The dust extraction apertures 10 (see Figs. 4 and 5) were arranged in four concentric circles having diameters of approximately 30 mm, 55 mm, 71 mm and 91 mm. In increasing order of diameter, the concentric circles contained: four dust extraction apertures of 4 mm diameter; ten dust extraction apertures of 4 mm diameter; five dust extraction apertures of 4 mm diameter alternated with five dust extraction apertures of 6 mm diameter; and twenty dust extraction apertures of 4 mm diameter (i.e. a total of forty- four holes occupying about 6% of the area of the area of the front face 8 of the back-up pad). In each of the concentric circles, the apertures were equispaced, centre-to-centre, resulting in a substantially even distribution of the apertures over the effective area of the back-up pad.

The abrasive disc was attached to the back-up pad by a hook-and-loop attachment system similar to that used in abrading article I.

The dust-extraction efficiency of an abrading article was measured as follows: The abrading article was attached to a dual action sanding machine provided with a dust- extraction vacuum system to remove grinding dust generated at the abrasive face of the disc. The vacuum system was fitted with a filter bag in which the grinding dust was collected. A standard workpiece was prepared by applying a coating material, in a reproducible manner, to a metal panel and was weighed. The sanding machine was then used to abrade the coating material consistently over a pre-set period of time with the disc applied flat on the workpiece, following which the dust collected in the filter bag was weighed and the workpiece was weighed again to determine the amount of coating material that had been removed during the abrading operation. The abrading operation was repeated a sufficient number of times (maintaining the same operating conditions and, in each case, using a fresh workpiece and abrasive disc) to establish that consistent measurements were being obtained. The dust-extraction efficiency of the abrading article was then determined by calculating the amount (by weight) of grinding dust collected as a percentage of the amount (by weight) of coating material removed from the workpieces.

Result It was found that the dust collection efficiency of abrading article II, measured as described above, was higher than the dust collection efficiency of abrading article I.

Claims

1. An abrading article comprising:

(i) a back-up pad having a major surface in which are formed a plurality of dust- extraction apertures for connection, during an abrading operation, to a source of suction, the apertures occupying at least 5% of the area of the major surface; and

2. An abrading article as claimed in claim 1, in which the said abrasive face is the face of an abrasive layer that is bonded to a flexible backing layer.

3. An abrading article as claimed in claim 1, wherein the dust-extraction slots are identical.

4. An abrading article as claimed in claim 3, in which there are six identical dust- extraction slots in the abrasive disc.

5. An abrading article as claimed in claim 3, in which the inner end of each identical dust- extraction slot is spaced radially from the centre of the disc by a distance within the range of from about 5 mm to about 20 mm.

6. An abrading article as claimed in claim 3, in which the outer end of each identical dust- extraction slot is spaced radially from the periphery of the disc by a distance within the range of from about 3 mm to about 15 mm.

7. An abrading article as claimed in claim 3, in which the identical dust-extraction slots are curved.

8. An abrading article as claimed in claim 3, in which the disc has at least one additional dust-extraction aperture formed therein.

9. An abrading article as claimed in claim 1, in which the dust-extraction apertures in the back-up pad are distributed over substantially the whole of the effective major surface of the back-up pad.

10. An abrading article as claimed in claim 1, in which the dust-extraction apertures in the back-up pad are substantially-evenly distributed over substantially the whole of the effective major surface of the back-up pad.

11. An abrading article as claimed in claim 1 , in which there are at least thirty dust extraction apertures in the back up pad.

12. An abrading article as claimed claim 1, in which the dust extraction apertures are circular and have a diameter of at least 3 mm.

13. An abrading article as claimed in claim 1, in which the disc is attached to the back-up pad by a hook and loop attachment system.

14. An abrading article as claimed in claim 13, in which the attachment face of the abrasive disc comprises the loop component of the attachment system.

15. A powered abrading machine comprising an abrading article as claimed in claim 1.

16. A machine as claimed in claim 15, in combination with a vacuum system for applying suction to the dust-extraction slots in the abrasive disc via the dust extraction-apertures in the back-up pad.

17. An abrading article as claimed in claim 1, substantially as described herein with reference to the accompanying drawings.