GB2515764A - Abrasive article and adapter therefore - Google Patents

Abstract

An abrasive article 11 and an adapter therefore each include a work surface having a centre point 12, a periphery and a plurality of holes 10 extending through the work surface, through which particulate material or dust may be extracted, the work surface futher being divided into at least a first inner and a second outer zone A-E, the second zone being concentric with the first and the centre point 12, each zone having at least one hole 10 and the hole density of the first, inner zone is less than the hole density of the second, outer zone. The sizes of the holes 10 and their total number forms a hole density for that respective zone A-E. The ratio of the distance of each hole from the centre point multiplied by the total surface area of mounting or abrasive surface within the respective zone to the total surface area of the at least one hole within the respective zone may be substantially constant for the first and second zones. The adapter may be a circular back-up pad (18 fig. 5) and the abrasive article 11 may be a disc which may be used for sanding.

Description

ABRASIVE ARTTCLE AND ADAPTER THEREFORE

[he present invention relates to an abrasive article, in particular, an abrasive article comprising a hacking and an abrasive coating on a surface of the backing, the article having a centre point and apeiphery; and a plurality of holes through We hacking and the ahrasive coaling, and an adapier for an abrasive article, also being provided with holes, through which particulate material may he extracted.

Many sanding and abrasive processes are carried out in a dry environment, that is, one where a workpiccc is treated without the use of any lubricant. One situation where this occurs, for example, is the sanding of painted workpieees, such as the rectification of paint or lacquer surfaces on automotive vehicle paris during the repair process, or the sanding down of priniers and fillers used in such a process. Ibis generates fine particulate matter, commonly termed "dust" (such as paint debris), which, aside from needing to he removed from the workpiece, can create a hazard io the workers using abrasives, since the dust enters the atmosphere around the workpiece and can cause a potential hazard to health. One way of dealing with this is to use a dust extraction process, which may either he by extracting dust from around the workpiece (for example using a worktable with dust extraction capabilities, such as a downdraft workbench) or by extracting dust through the abrasive (for example, using a sanding tool with dusL extraction capabilities). This latter option is particularly popular, due to its convenience.

Coated abrasives typically comprise a backing, such as paper or cloth, coated with an abrasive coating, formed from a resin having an ahrasive grit either dispersed therein on one surface of thc hacking. In order to attach the abrasive article to a tool, such as an orbital sander, a layer of an attachment material, such as a hook and loop miatcrial. or a brushed nylon material, is provided on the opposite surface of the backing to the abrasive coating. This enables the abrasive article to he mounted on a back up pad, which in turn is attached to the tool. lb facilitate dust extraction, holcs arc placed in the abrasive article, typically through the backing, abrasive coating and attachment layer, which communicate with holes provided in the back up pad, such that dust is extracted through the holes in the abrasive article and hack up pad. Some designs of abrasive article use a small number of larger holes, that are typically aligned with holes provided in thc back up pad, such as the fifteen hole 255P abrasive disc. available in the UK from 3M United Kingdom PLC, 3M Centre, Cain Road, Braclmell, RG12 811T. Some designs of abrasive used fur dust extraction utilise a different structure, comprising many, small holes, which may or may not require alignment with corresponding holes in the hack up pad, such as the 334U and 734LJ (Purple) abrasive disc, again, available from 3M United Kingdom PLC.

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Previous approaches to maximise the amount of dust extracted have relied on including as many holes as possible in the abrasive article, thus maximising the surface arca of thc holes compared to the surface area of the abrasive. One example of this is the abrasive article discussed in EP 781 629, where a perforation comprising holes, distributed substantially uniformly over at least part of the surface of the abrasive article, in conjunction with a hook and loop attachment material, is shown to give improved dust extraction over existing abrasive articles with fewer holes. Similarly, W020l21034735 discusses the use of many small holes for improved dust extraction, although rather than proposing a uniform distribution of holes across the surface of the abrasive article, the use of a Fihonacci sequence, or golden number, to generate a hole distribution is discussed, showing that a non-uniform an'angement also gives beneficial dust extraction resulLs.

However, whilst the use of an increasing number of holes in the abrasive article, regardless of distribution or alignment with extraction holes in a back up pad undeniably increases the amount of dust extraction, using too many holes can lead to issues with the structural integrity of the abrasive article. Where many small holes are included, particularly towards the edge of the disc, there is a tendency for the abrasive to tear when used, due to the forces created by rotation of the hack up pad. There also conies a point where too much of the overall surface area of the abrasive article is given over to holes, and the cut or overall lifetime of the abrasive article drops beyond a practical, usable or economical amount. Complex patterns of many holes may also be expensive to produce, given the wear and tear on tooling and cost of conversion of webs of abrasive material into discs and sheets with precise hole patterns. But using fewer, larger holes, whilst still ideal for many applications, does not give equivalent dust extraction, therefore in previous products there has been a trade-off between number of holes and cut to enhance both dust extraction and cut. It is desirable therefore to he able to balance both cost and performance, ensuring that the dust extraction behaviour of the product does not worsen whilst maintaining a cost-competitive manufacturing approach.

The present invention aims to address these problems by providing an abrasive article comprising a hacking and an abrasive coating on a surface of the hacking, the article having a centre point and a periphery and the abrasive coating forming a work surface; and a plurality of holes extending thrnugh the backing and the abrasive coating, through which particulate material S may he extracted; wherein the article is divided into at least a first inner and a second outer zone, the second zone located outside the first zone and heing concentric with the first and the centre point; each zone having at least onc hole, wherein in each of the first and the second zone the sizes of the hole(s) and (heir total number forms a hole density for that. respective 1one; and wherein the hole density of the first zone is less than the hole density of the second zone.

By taking into consideration both (he relative amounts of surface area of abrasive and surface area of holes, and the position of the holes on the abrasive article in relation to how such holes will move on a tool in use, the dust extraction capabilities of the abrasive article can he greatly improved in contrast to existing holed abrasive articles.

Preferably, in each zone, each hole has a size and position within the respective zone such that the ratio between the distance of each hole from the centre point multiplied by the total surface area of abrasive coating within the respective zone and the total surface area of the at Icast OflC hole within the respective zone is substantially constant for the first and second zones.

Preferably, the holes in each zone arc distributed evenly alxut the centre point.

Preferably, the article is in the form of a disc.

The abrasive article may further comprise a third zone, positioned between the first and sccond zones, in which there arc no holes. Alternatively, the abrasive article may furthcr comprise a third zone, positioned between the first and second zones, comprising at least one hole.

Where the abrasive article is a disc, situation, preferably the holes arc positioned along radii of the disc. At least one further hole may he provided outside of the at least two zones. Ihe at least one further hole may he a centre hole, positioned at the centre point. Alternatively, the at least one further hole may be located away from the centre point. Preferably, the at least two holes in each zone form an overall asymmetric pattern across the abrasive article.

The holes have preferably a diameter in the range I.0mm to 25.0mm. Preferably, the abrasive article comprises between 7 and 100 holes. More preferably, the abrasive article comprises between 7 and 30 holes.

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Yet more preferably, the particulate is dust, and the abrasive article is adapted for use with dust extraction equipment.

In another aspect, the present invention also provides an adapter for an abrasive article comprising a body having a mounting surface adapted for the attachment of an abrasive article the adapter having a centre point, and a periphery; and a plurality of holes extending through the body, through which particulate InaLerial may be extracted; wherein the mounting surface is divided into at least a first inner and a second outer zone, the second zone located outside the first zone and being concentric with the first and the centre point; each zone having at least one hole, wherein in each of the first and the second zone the sizes of the holes and their total number forms a hole density for thaL respective zone; and wherein the hole density of Lhe first zone is less than the hole density of the second zone.

By taking mb consideration both the relative aniounts of surface area of mounting surface and surface area of holes, and the position of the holes on the abrasive article in relation to how such holes will move on a tool in use, the dust extraction capabilities of the adapter can he greatly improved in contrast to existing devices. This niay be with or without the optiniisation of an associated abrasive article.

Preferably, in each zone, each hole has a size and position within the respective zone such that the ratio between the distance of each hole from the centre point multiplied by the total surface area of mounting surface within the respective zone and the total surface area of the at least one hole within the respective zone is substantially constant for the first and second zones.

Preferably, the at least two holes are provided in each zone, and the holes in each zone are distributed evenly about the centre point.

Preferably, the adapter is in the form of a circular back up pad.

The adapter may further comprise a third zone, positioned between the first and second zones, in which there are no holes. Alternatively, the adapter may further comprise a third zone, positioned between thu first and second zones, comprising at least one hole.

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Where there adapter is a circular hack up pad, the holes are positioned along radii of the circular hackuppad.

At least one further hole may he provided outside of the at least two iones. The at least one further hole may he a centre hole, positioned at the centre point. Alternatively, the at least one further hole is located away from the cenle point.. The at. least two holes in each zone may fonn an overall asymmetric pattern across the adapter.

Preferably, the holes have a diameter in the range 1.0mm to 25.0mm. Preferably, the adapter comprises twcen 7 and 100 holes, more preferably, between 7 and 30 holes.

Preferably, the particulate is dust, and the adapter is adapted for use with dust extraction equipment.

The present invention will now he described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-section showing the construction of an abrasive article suitable for use with any of the embodiments of the present invention; Figure 2 is a schematic diagram of an abrasive article in accordance with a first embodiment of the present invention; Figure 3 is a schematic diagram of an abrasive article in accordance with a second embodiment of the present invention; Figure 4 is a schematic diagram of thc fifteen hole and seventy-eight hole abrasives used in comparative experiments with the first and second embodiments of the pmsent invention; Figure 5 is a schematic cross-section view of an adapter for an abrasive article in accordance with a third embodiment of the present invention; and Figure 6 is a schematic plan view of an adapter for an abrasive article in accordance with a third embodiment of the present invention.

The present invention takes the approach of understanding that not only is a uniform level of S dust extraction across the surlace ol an abrasive article is required for good performance, this should ideally take into account situations where the abrasive article is used on a tool providing an orbit and/or the rotation of the abrasive article in use. For example, a random orbital or dual action (DA) sander, such as the 3M Random Orbital Sander range, available from 3M as above, not only spins the abrasive article, hut moves it in an elliptical orbit pattern, giving a translational motion component to the rotational motion of the abrasive article. For abrasive articles such as discs that. rotate during use, the relative linear speed near the centre of the abrasive disc is significantly lower than that at the outer edge of the disc, dependent on the rotational speed of the abrasive disc.

Without wishing to be bound by theory it is thought that the increased speed at the edge of the abrasive article generates increased cut on the surface of the workpiece, as a greater area of abrasive matenal passes over the surface of the workpiece, creating a more aggressive cut due to the difference in speed. This generates an increased amount of particulate material being removed from the surface of the workpiece, typically dust composed of paint debris or 1111cr, depending on the application, which requires timely imoval to reduce the clogging of the surfaces of the abrasive article and the expulsion of particulate material into the surrounding atmosphere.

Ihe present invention addresses this by dividing the work surface abrasive article, formed by the abrasive coating, into at least a first inner and a second outer zone, the second zone being concentric with the first and the centre point. Each zone has at least one hole, and in each of the first and the second zone the sizes of the holes and their total number forms a hole density for that respective zone. The hole density of the first zone is less than the hole density of the second zone. The hole density is therefore a measure of the surface area of the abrasive article dedicated to holes, and its relationship to the surface area of the abrasive article that is solely abrasive coating, i.e. not provided with holes. In each zone, each hole has a size and position within the respective zone such that the ratio between the distance of each hole from the centre point multiplied by the total surface area of abrasive coating within the respective zone and the total surface area of the at least one hole within the respective zone is substantially constant for the first and second zones. One way of doing this is to provide at least one hole in each zone, and to ensure that these holes are distributed evenly about the centre point.

S This relationship elfectively detemiines the amount of particulate matter that can he removed br each zone, such that increased extraction capability is provided for regions of the abrasive article whcrc grcater amounts of particulatc matter arc crcatcd, thus causing thc constant K to he kcpt substantially constant for each zone. Overall this improves the extraction capabilities of the abrasive article, beyond both those of traditional holed abrasive articles (fewer, larger holes) and more modem so-called "multi-holc" (many, smallcr holes) abrasive articles. this is due to the abrasive article in accordance with the present invention having a variable hole density, that. is, the number and size of holes in each zone is different for each zone depending on the relative positions of each zone.

Figure 1 is a schematic cross-section showing the construction of an abrasive article suitable for use with any of the embodiments of the present invention. An abrasive article I comprises backing 2 having a first surface 3 and a second surface 4, and an abrasive coating 5 on the first surface 3 of the hacking 2. The abrasive coating S comprises a resin layer 6 having ahrasivc particles 7 dispersed therein, fonning a work surface 8 intended to be used to sand a workpiece (not shown). An attachment layer 9, in this example, a hook and ioop attachment layer, is provided on the second surface of the backing 2. This enables the abrasive disc to he mountcd on the back up pad of a tool (not shown), the tool being provided with dust extraction capability.

A plurality of holes 10 are provided, extending through the backing 2 and the abrasive coating 5.

ftc plurality of holes 10 also extend through the attachment layer 9. Ibis enables fluid communication between the work surface 8 and the tool, such that dust generated at the work surface 8 by the abrasive article 1 can be extracted away from the workpiece through the holes IC) to the tool.

The first embodiment of the present invention uses an abrasive disc intended for dust extraction as an example, although it should he understood that the same approach may he used with other shapes of abrasive article, or abrasive articles used for other types of particulate extraction, such as those used wet or damp, as well as dry. I'hercfore the use of an abrasive disc should not been seen as limiting the present invention, nor should the use of circular holes, Figure 2 is a

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schematic diagram of an abrasive article in accordance with a first embodiment of the present invention. This shows a circular abrasive disc I I having the structure shown in Figure I, and divided into five zones (first to fifth): A (central 0-l4nim radius), B (14 -28mm radius), C (28 -42mm radius), D (42 -56mm) and E (56 -70mm), centrcd around a centre Point 12 and S concentric wuli each other. The abrasive disc had a diameter of 150mm. A total of lilly-nine holes are included in the disc, distributed evenly about the centre point 12. Ihe position and size of the holes was dctcrmined as follows.

Such a circular abrasive disc is intended to he used on an orbital sander that causes the disc to rotatc at an angular velocity cv, leading to a linear speed v (where v = oar), and moves thc disc in an orhii 0. Therefoft a uniform placeniein of holes 10 across the surface of the abrasive disc 11 does not allow for optimum dust extraction since there will be an effect on the cut and therefore the amount of dust created based upon both the rotational speed of the abrasive disc 11 and the orbit generated by the tool. A non-uniform distribution would also suffer from the same issues, hence an adjustment of the hole positions due to the effect of the disc rotation and orbit needs to be made. The amount of dust extracted will be proportional to the amount of open area, ic, the surface area of the holes 10 provided across the abrasive disc II. to determine the surface area of the holes required, the following equation is used: ((O+v) K = A abrasive \ hole Equation I Where K is a constant, 0 is the orbit and v the linear speed as above at the point of consideration, is the surface area of the abrasive disc 11 occupied by holes, and Ab,-,Sn?. is the surface area of the abrasive disc 11 remaining. To determine a theoretical value of K. an ideal amount of hole area is choscn for the abrasive disc 11. l'o he in line with other existing articles from a manufacturing cost perspective, the hole area was chosen to he 10% of the overall surface area of the abrasive disc 11, and Equation 1 solved to give K, using an orbit of 2.Smni and a rotational speed of 4000rpm. This yielded a value of K of 199. holes 10 were then chosen in accordance with manufacturing constraints to try to reach this theoretical value of K using Equation 1 for each zone.

Holes 10 were sized and çxsitioned as follows and as shown in Table I below (all measurements are in mm). Holes were positioned at the edges of each zone, with half of the number of holes in each zone being positioned on the inner edge of the zone and half positioned on the outer edge of the zone for each of zones B, C and D, and one third of the holes in Zone F were placed on the boundary between zone I) and inne F. As discussed above, the orbit 0 used in the calculation was 2.5mm and the rotational speed ci was 4000rpm. Calculated hole diameters are shown in brackets in fable 1, actual hole diameters arc also shown: 11) Zone A Zone B Zone C Zone I) Zone F JnnerZone 0 14 28 42 56 Radius Outer Zone 14 28 42 56 70 Radius hole 3.5 (2.73) 4.0 (5.72) 5.0 (5.64) 6.0 (6.01) 7.0 (6.5) Diameter 1 Hole 4.0 (4.0) 6.0 (6.1)) 6.0 (6.5) Diameter 2 Hole 6.0 (5.36) Diameter 3 NaHolesi 3 4 8 8 8 No. IIoles2 4 8 8 No. Holes 3 8 Total hole 28.87 50.27 207.35 452.39 841.95 Area Total 586.89 1796.99 2871.42 3857.88 4699.82 Abrasive Area K 119 419 244 200 164 Fable 1 Total number of holes: 59 The ratio of the surface area of the abrasive disc II occupied by holes to the surface area of the abrasive disc II remaining was 0098 (9-8%). Holes 10 were placed in each zone so as to he evenly distributed around the centre point 12 of the abrasive disc 1. It can be seen that the manufacturing constraints on hole size and position led to a discrepancy in K values for some S zones in practice, despite the Equation being solved for the required surface area (hole diameters in accordance with Fquation I are given in brackets in Fable I, actual hole diameters are also shown). Testing of the abrasive disc 11 was carried out to determine if this resulted in a detrimental effect on performnance.

Comparative tests between an abrasive disc 11 in accordance with the first embodiment of the present invention, an abrasive disc l5Onun in diameter and having fifteen holes, and an abrasive disc 150mm in diameter having seventy-eight holes were carried out. All three abrasive discs were made from 255P abrasive material, available from 3M as above, and in a P500 grade. l'he fifteen hole disc had a ratio of the surface area of the abrasive disc occupied by holes to the surface area of the abrasive disc remaining of 0.062 (6.2%) and the seventy-eight hole disc 0.05 (5%). Each disc comprised a centre hole with the remaining holes distributed evenly across the surface of the abrasive disc, as illustrated in Figure 4 below.

All tests were carried out on a Fanue Robotics robot using a 150mm National Detroit Air Powered Sander, available from National Detroit, 1590 Northroek Court, Roekthrd, Illinois 61103, US. A 600 x 6(Xinini primer panel was painted with a Standox VOC System filler, available from Standox, Wedgwood Way, Stevenage, Ilertfordshire, SG1 4QN to a thickness of approximately i00im, weighed, and the weight recorded. Before sanding, the surface of the primer panel was wiped down with a clean tack cloth, which was then disposed of. jo begin thc test, the robot sanded the surface of the primer panel at a medium pressure (5.51bs12.Skg) in alternating north-south and cast-west direction for fifteen seconds. The primer panel was then weighed a second time, and the weight recorded. I'his was repeated for a further forty-five second period and a one-hundred and eighty second period, with the panel being weighed after each sanding session. After the forty-five second period the panel was cleaned with a second tack cloth of known initial weight, the second tack cloth was then weighed, and placed in an airtight bag. [he second tack cloth was subsequently weighed to determine the amount of dust left on the panel. F3y measuring the weight of the primer panel the total amount of material removed in grams gives the amount of cut, and by measuring the weight of the tack cloth the additional weight of dust in grams indicates the efficiency of the dust extraction process.

Six of each abrasive disc wcre tested, with all abrasive discs being grade P500. Both the fifteen and seventy-eight hole ahrasive discs had their holes aligned with the holes in LIle hack up pad, whereas it was not possihle to align the holes in the fifty-nine hole ahrasive disc in accordance with the first embodiment of the present invention. Results of the tests are shown in I'able 2 below: Dust Remaining Cumulative Cut Cumulative Cut Cumulative Cut after ôOs (g) After 15s (g) After 60s (g) After 240s (g) holes 0.043g 85.2 85.1 84.6 59 holes 0.037g 99.0 100.5 102.8 78 holes 0.043g 100.0 100.0 100.0

Table 2

The fifty-nine hole disc showed an improvement in both dust extraction, with less dust remaining S on (he surface of the paiiel after testing (han both the fifl.een hole and seventy-eight hole abrasive discs, and caL. Despite having a smaller overall surFace area and fewer aligned holes @1 the abrasive article dedicated to holes to enable dust extraction than the seventy-eight hole disc, the fifty-nine hole abrasive article in accordance with the present invention gives the better performance.

Figure 3 is a schematic diagram of an abrasive article in accordance with a second embodiment of the present invention. This shows an abrasive disc 13 having a centre point 14, and divided into four zones A, B, C, and I), similar to the first embodiment described above. Ihe abrasive disc had a diameter of 150mm. Twenty-one holes 15 were provided using the same methodology as above, in each zone as shown in Table 3 below, Initially Equation 1 was solved to give a desired surface area of 0.066 (6.6%, so as to be the same as an existing 15 hole abrasive disc) and a theoretical value of K of 316. Ilie orbit 0 was 2.5mm and the speed w 40(X)rpm, again all measurements are in mm. Using twenty-one holes in four zones, the ratio of the surface area of the abrasive disc 13 occupied by holes 15 to the surface area of the abrasive disc 13 remaining was 0.063 (6.8%). 1-lole diameters in accordance with Equation I are given in brackets in Table 3, actual hole diameters are also shown: Zone A Zone B Zone C Zone I) Inner Zone Radius () 18 34 52 Outer Zone Radius 18 34 52 70 Hole Dianieter 1 7.0 (5.49) 7.0 (4.89) 8.5 (8.16) 10.0 (9.65) No.Ilolesl 1 6 6 8 Total Hole Area 38.48 230.91 340.47 628.32 Total Abrasive 979.39 2382.90 4522.72 6270.62 Area o 0.0025 0.0025 0.0025 0.0025 (0 4000 4000 4000 4000 K 192 147 289 293 Fable 3 Total numhcr of holes: 21 All tests were carried out on a Fanuc Robotics robot, using an Elite orbital sander, available from 3M as above, having a theoretical free rotational speed of 12000rpm and 40(Xkpm under loading, and an orbit of 2.5mm. A back up pad having fifty-one holes was used. A wooden panel (pine) measuring approximately 200 x 400mm was weighed, and the weight recorded. Ibis was then placed on a painted metal panel approximately 600 x 600mm in size for sanding. Before sanding, the surface of the wooden panel and the painted panel it rested on was wiped down with a tack cloth, which was then discarded. lo begin (he test, (he robot sanded (he surface of the wooden panel al a niediuni pressure (5.Slbs/2.Skg) in alterna(ing north-south and east-west direction for two minutes. The wooden panel was thcn weighed a second time, and the weight recorded. This was repeated for a further minute period and a one minute period. After a total of five niinuies of sanding the wooden panel was cleaned using a second (ack cloth of known initial weight, the painted metal panel was also wiped clean with the same tack cloth and then the tack cloth placed in an airtight bag for subsequent weighing. The tack cloth was weighed to detenuine the amount of dust leli. on the panels. By measuring (he weight of (he wooden panel the total amount of material removed in grams gives the amount ol cut, and the measurement oF thc weight of the tack cloth gives the additional weight of dust in grains remaining in the working area, which is indicative of the efficiency of the dust extraction process.

This was used to compare an abrasive disc 13 in accordance with the second embodiment of the present invention and a fifteen hole disc. However, the hack up pad used was a 51 hole back up pad, against which the holes in both the fifteen hole abrasive disc and the twenty-one hole abrasive disc in accordance with the present invention could he aligned. Again, the ralio of the surface area of the abrasive disc occupied by holes to the surface area of the abrasive disc remaining was 0.066 (6.6%) for the fifteen hole disc. Both abrasive discs were formed from 236U abrasive material, available from 3M as above, and in a P320 grade. Five discs of each type were tested. Results of the comparative testing are shown in TaNe 4 below: Cumulative Cut After 5 wins Dust Remaining After 5 wins (g) (g) holes 4.08 0.0493 21 holes 3.92 0.0427 Fable 4 Again, the abrasive disc 13 in accordance with the present invention removed more dust. during use than a fifteen hole abrasive disc. I"igure 4 isa schematic diagram of the fifteen hole 16 and seventy-eight hole 17 abrasives used in comparative experiments with the first and second embodiment.s of the present invention. This illustrates that the present invention offers similar or improved perlornianee when compared with traditional hole patterns and multihole abrasive discs, as the ratio between the surface area of abrasive coating within the zone and the surface area of the holes is optiniased for the hole size and distribution.

I'he level of accuracy of the constant K will also he influenced by the method used to form the holes in the abrasive article. lor example, if them is a limit on the hole size achievable, either in tenus of absolute size (minimum radius) or engineering tolerance, then (here may he sonic variability in K. Therefore where Equation I is best satisfied by a hole size that is not practicable, a more reasonable hole size may he used. Methods to create the holes in the abrasive article include mechanical punching and cutting using a laser. In addition, it may he desirable to adjust. the size of (he hole in the abrasive article to fonn a complete system with the hack up pad. For example, if it is convenient to create a 7mm hole in the abrasive article, hut the back up pad is provided with an alignable 5mm hole, the overall dust extraction is influenced by the 5mm hole. This will also affect the level of accuracy of the constant K, for example, if Fquation I predicts an ideal hole size of 4.89mm as in the second embodiment described above, the use of a hack up pad with a 5mm hole has a considerable effect on K, as this may he effectively substituted into the calculations. This gives a K value closer to that predicted by Equation 1.

In the examples described above, circular abrasive articles intended for use in situations where dust extraction is necessary, however, other shapes of abrasive article may he formed, such as sheets, for example rectangular sheets, where the sheets also have a centi point and a periphery, as the above equation may he re-written to he in terms of distance, d, of the zone from the centre, rather than rotational speed: ((d+o) K = I A A abrasive \ Thole Equation 2 In the same manner as described in relation to the circular abrasive discs in the first anti second embodiments of the present invention, in this situation thc article is divided into at least two zones, being concentric with each other and the centre point. Each zone has at least one hole, preferably two holes distributed evenly about the centre point. Each hole has a size and position such that the ratio between the distance of the zone from the centre point multiplied by the surface area of abrasive coating within the zone and the surface area of the holes within the zone is approximately constant for each zone. Thus, in the example above, the abrasive article is an abrasive disc, such (hat the holes are posit.ioned along radii of the disc. The orbit. may he a linear translation in the case of a tool used with an abrasive sheet, such that the constant 0 represents thc amplitude of thc translational motion. In situations whcrc thc abrasivc article is used with a tool that does not provide an orbit or other translational motion, the constant 0 may he omitted.

Furthermore, the holes used need not necessarily he circular, but shaped so as to be suitabic for their intended use, for example, triangular, square, rectangular, or other polygonal or curved shape. In (he above examples, Iwenty-one and fifty-nine holes were used. However, the equations 1 and 2 may he used to position any number of holes as required. Preferably this may he between 7 and 100 holes, more preferably between 7 and 30 holes. The sizes of the holes used in the above examples is within the range of 3.5mm to 10mm in diameter, but may preferably he between 1.0mm and 25.0mm in diameter if desired.

The usc of a hook and loop layer as the attachmcnt layer is particularly suitable, since this is permeable to the passage of both air (hence allowing ext.ract.ion by means of a vacuunl) and dust (of a typical particulate size Found in sanding) with little or no clogging during normal use.

Other materials offering similar advantages include brushed nylon. In the above examples, the abrasive coating comprises a resin material having abrasive particles dispersed therein. is

However, the abrasive coating may comprise other materials, such as grinding aids, other layers, such as a supersize layer, or may he formed from an adhesive material or a slurry. Other layers, such as a tie-coat or other strengthening or reinforcing layer may he provided between the backing and thc abrasive coating. Microrcplication techniqucs may he used to form the abrasive S coaling if desired, or tte coaling may comprise and adhesive and various abrasive grains or particles. Suitable hacking materials include paper and textiles (both treated and untreated), foams, and other materials generally used in the manufacture of coated abrasive articles.

In the above examples, the particulate is dust, and the abrasive article is adapted for use with dust extraction equipment. Such equipment either comprises vacuum extraction means or self-generated vacuum extraction means, or may just. rely on centripetal forces to move dust and air through tic holes and away from the surface of the workpieec. however, other types of particulate extraction may be carried out. One situation where this is the case is where an abrasive is used wet or damp or with a polish, and the motion of the tool causes swarf, paint or other particulate debris to uiove within a liquid carrier. henec through the holes of the abrasive article.

It may he desirable to include further zones in the abrasive article. For example, the abrasive article may comprise a third Lone, positioned between the first and second zones, in which there are no holes. Alternatively, the abrasive article may comprise a third zone, positioned between the first and second zones, comprising at least one hole.

In the above embodiments, the holes 10, 15 are distributed evenly around the centre point 12.

However, this need not be the case. l'he holes may be distributed in any fashion, whether this forms a regular array or pattern or not, since as long as the above Equation 1 and Equation 2 are satisfied the dust extraction performance of the abrasive article is optimiscd.

In the above embodiments, at least one further hole may provided outside of the at least two zones. This may he, for example, a centre hole, positioned at the centre point. Often this is required to align with holes provided on a standard hack up pad or other tool attachment means, such as a block for an abrasive sheet, Alternatively, or additionally, the at least one further hole may he positioned elsewhere on the abrasive article, such as away from the centre point. The at least two holes in each zone may form an overall asymmetric pattern across the surface of the abrasive article. This may he desirable from an aesthetic point of view, or for ease of manufacture. Alternatively the least two holes in each zone may form an overall symmetric pattern across the surface of the abrasive article. For example, the arrangement of holes shown in both the first and second embodiments of the prcsent invention are approximately spiral, or S having arms distrihuled in a spiral arrangement, this should not he seen as limiting, as any arrangement of holes within each zone satisfying the above equations i and 2 will fall within the scope of the appended claims.

In the above examples, Equations I and 2 are applied to abrasive articles, such as abrasive discs and sheets. However, the equations may also he applied to the accessories used with such abrasive articles, as follows. Although the accessories do not themselves generate dust. or other particulate matter at a workpieee, they drive the behaviour of the abrasive article, hence similar considerations apply. Figure 5 is a schematic cross-section view of an adapter for an abrasive article in accordance with a third embodiment of the present invention. I'his is used to mount an abrasive article, such as an abrasive disc, onto a tool, such as a sander. In this example, the adapter is a circular back up pad, but it may alternatively or additionally be an interface pad (which is placed between an abrasive article and a back up pad to provide a cushioning effect in usc) or other adapter such as a hand block. The hack up pad 18 comprises a body 19, a mounting surface 20, adapted for the attachment of an abrasive article such as an abrasive disc 11, 13, as shown in Figures 2 and 3. and a tool attachment means 21, for attaching to a tool (not shown).

Fhe mounting surface 20 comprises a hook material 22 suitable for engagement with the hook and loop or brushed nylon layer 9 provided on the abrasive disc 11, 13, such that the abrasive disc 11, 13 is attached firmly to the back up pad 18 during use. The back up pad 18 is pmvided with a plurality of holes 23, extending through the mounting surface 20 and through at least a portion of the body 19, thmugh which particular matter is extracted. This enables fluid connection between dust extraction means (not shown) and the surface of a workpieec (also not shown) during use. Ihus, dust or other particulate matter generated at the surface of the workpiece during use is removed via the holes 23 in the back up pad.

Figure 6 is a schematic plan view of an adapter for an abrasive article in accordance with a third embodiment of the present invention. [he back up pad 18 has a periphery 24 and a centre point 25. and is divided into a series of zones, A, 13, C, I), as with the abrasive articles deserihcd above. Each zone comprises at least two holes, distributed evenly about the centre point 15. The plurality of holes 23 are arranged as follows. Since the hack up pad 18 will he suhject to the same rotational and/or translational or orbital movement as the ahrasive article, Equations I and 2 can he modified to apply to the hack up pad 18. For a circular back up pad: / (0+12 K = A2ttachnlent Equation 3 Where K is a constant, 0 is the orbit and v the linear speed as above, is the surface area of the hack up pad 18 occupied by holes, and A,fach;nc,/ is the surface area of the back up pad remaining. In this situation, holes are positioned along the radii of the circular back up pad. For a non-circular back up pad, for example, a sheet holder: ((d+0) K = A AartachpTcmt \ hole Equation 4 Where K is a constant, 0 is the orbit and d the distance of thc holcs from the centre point 25, Ajwe is the surface area of the back up pad 18 occupied by holes, and Aiita,neni is the surface area of the hack up pad remaining.

l'hus, as in thc first and second emhodiments discussed above, the mounting surface is divided into at least a first inner and a second outer tone, the second zone being concentric with the first and t.he centre point. Each Lone has at least one hole, wherein in each of the lirst and (he second tone the sites of the holes and their total numher forms a hole density for that respective tone, and the hole density of the first zonc is less than thc hole density of thc sccond zone.

For a circular hack up pad, in each tone, each hole has a site and position within the respective tone such that the ratio between the distance of each hole from the centre point multiplied by the total surface area of mounting surface within the respective zone and the total surface area of the at. least two holes within the respective zone is substantially constant. for the first and second tones. As ahove, K is calculated for a particular desired hole area. Ibis may he desired to he a match for a particular abrasive article, for example, with the holes 23 positioned on both the back up pad 18 and an abrasive disc II, 13 or other abrasive article such that the holes 10, IS, in the abrasive disc II, 13, or other abrasive article align completely with the holes 23 in the back up pad. Alternatively, the holes 23 may he positioned such that there is no or only partial alignment, or the holes 23 in the back up pad 18 may he greater or lesser in diameter than corresponding holes 10, 15 in the abrasive disc I I, 13 or other abrasive article. In addition or alternatively, if Nquations 3 and 4 are also applied to an interface pad, the holes in the interface pad may he adjusted similarly to align or not as desired with both the holes 23 in the back up pad and in any abrasive article niouned on the interface pad.

In the above example, at least two holes are pmvided in each zone, and the holes in each zone are distrihued evenly about (he centre point, although only one hole is necessary. however, the holes may be distributed in an uneven or non-regular pattern, as with the abrasive article described above. For example, holes may be distributed in an overall asymmetric pattern across the adapter. ibis may he the case regardless of whether the adapter is used with or without an abrasive article in accordance with an embodiment of the present invention, or whether the abrasive article has an even or uneven distribudon of holes, The adapter may comprise a third zone, positioned between the fitt and second zones, in which there are no holes. Alternatively, the adapter may further comprise a third zone, positioned between the first and second zones, comprising a least one hole. This allows for further freedom in design of the adapter and optimisation of the adapter/abrasive article combination as a whole. To aid in this, at least one further hole may he provided outside of the at least two zones. I'his one further hole may he a centre hole, positioned at the centre point, or it may be located away from the centre point.

Preferably, the holes have a diameter in the range I. 0mm to 25.0mm. Preferably, the adapter comprises between 7 and 100 holes, more preferably between 7 and 30 holes. Preferably, the particulate is dust, and the adapter is adapted for use with dust extraction equipment.

Claims (30)

1. CLAIMS1. An abrasive article comprising a hacking and an abrasive coating on a surface of the backing, the article having a centre point and a periphery and the abrasive coating forming a work surface; and a plurality of holes extending through the backing and the abrasive coating, through which particulate material may he extracted; wherein the work surface is divided into at least a first inner and a second outer zone, the second zone being concentric with the first and the centre point.; each zone having at least one hole, wherein in each of the first and the second zone the sizes of the boles and their total number forms a hole density for that respective zone; and wherein (he hole densit.y of the first zone is less than the hole density of the second zone.
2. 2. Abrasive article according to claim 1, wherein in each zone, each hole has a size and position within the respcctive zone such that the ratio between thc distance of each hole from the centre point multiplied by the total surface area of abrasive coating within the respective zone and the total surlace area ol the at least one hole within the respective zone is substantially constant for the first and second zones.
3. 3. Abrasive article according to claim 1, wherein the at. least two holes are provided in each zone, and the holes in each zone are distributed evenly about the centre point.
4. 4. Abrasive article according to claim 1, wherein the article is in the form of a disc.
5. 5. Abrasivc article according to claim 1, further comprising a third zone, positioned between the first and second zones, in which there are no holes.
6. 6. Abrasive article according to claim 1, further comprising a third zone, positioned between the first and second zones, comprising at least one hole.
7. 7. Abrasive article according to claim 4, wherein the holes are positioned along radii of the disc.
8. 8. Abrasive article accoitling to claim 1, wherein at least one further hole is provided outside of the at least two 7nnes.
9. 9. Abrasive article according to claim 8, wheitin the at least one further hole is a ccnnu hole, positioned at the centre point.
10. 10. Abrasive article according to claim 8, wherein the at least one further hole is located away from the centre point.
11. 11. Abrasive article according to claim 1, wherein the at least two holes in each zone fonu an overall asymmetric pattern across the abrasive article.
12. 12. Abrasive article according to any preceding claim, wherein the holes have a diameter in the range l.Ommto25.Omm.
13. 13. Abrasive article according to claim 1, comprising between 7 and 100 holes.
14. 14. Abrasive article according to claim 1, comprising between land 30 holes.
15. 15. Abrasive article according to claim!, wherein the particulate is dust, and the abrasive article is adapted for use with dust extraction equipment
16. 16. An adapter for an abrasive article comprising a body having a mounting surface adapted for the attachment of an abrasive article, the adapter having a centre point and a periphery; and a plurality of holes extending through the body, through which particulate material may be extracted; wherein the mounting surface is divided into at least a fimt inner and a second outer zone, the second zone being concentric with the first and the centre point; each zone having at least one hole, wherein in each of the first and the second zone the sizes of the holes and their total number fonns a hole density for that respective zone; and wherein the hole density of the first zone is less than the hole density of the second zone.
17. 17. Adapter according to claim 16, wherein in each zone, each hole has a size and position within the respective zone such that the ratio between the distance of each hole from the centre point multiplied by the total surface area of mounting surface within the respective zone and the total surface area of the at least one hole within the respective zone is substantially constant for the first and second tones.
18. 18. Adapter according to claim 16, wherein the at least two holes are provided in each zone, and the holes in each zone are distributed evenly about the centre point..
19. 19. Adapter according to claim 16, wherein the adapter is in the foim of a circular back up pad.
20. 20. Adapter according to claim 16, further comprising a third zone, positioned between the first and second zones, in which there are no holes.
21. 21. Adapter according to claim 16, further comprising a third zone, positioned between the first and second zones, comprising at least one hole.
22. 22. Adapter according to claim 19, wherein the holes are positioned along radii of the circular hack up pad.
23. 23. Adapter according to claim 16, wherein at least one further hole is provided outside of the at least two zones.
24. 24. Adapter according to claim 23, wherein the at least one further hole is a centre hole, positioned at the centre point.
25. 25. Adapter according to claim 23, wherein the at least one further hole is located away from the centre point.
26. 26. Adapter according to claim i 6, wherein the at least two holes in each zone form an overall asymmetric pattern across the adapter.
27. 27. Adapter according to any preceding claim, wherein the holes have a diameter in the range I.0mm to 25.0mm.
28. 28. Adapter according to claim 16, comprising between 7 and 100 hciles.
29. 29. Adapter according to claim 16, comprising between 7 and 30 holes.
30. 30. Adapter according t.o daim 16, wherein the particulat.e is dust, and the adapter is adapted for use with dust extraction equipment.