WO2003064110A1

WO2003064110A1 - An abrasive article and method of forming

Info

Publication number: WO2003064110A1
Application number: PCT/NZ2003/000011
Authority: WO
Inventors: Martin Franz
Original assignee: Ultimate Manufacturing Limited
Priority date: 2002-01-31
Filing date: 2003-01-31
Publication date: 2003-08-07

Abstract

A method of modifying abrasive stock (10), being an open porous lofty web of undulated filaments with a multitude of abrasive particles dispersed within the web and bonded to the filaments, is disclosed. The modified abrasive stock of the present invention gives a significantly improved surface finish while the service life of the modified abrasive article is not substantially changed compared to the known unfilled abrasive stock. These advantages are achieved by coating the abrasive stock with a partially foamed polyurethane polymer coating, infiltrated into the open web of the abrasive stock. The partially foamed polyurethane polymer coats the filaments of the web, partially but not completely filling the interstitial spaces of the web.

Description

"AN ABRASIVE ARTICLE AND METHOD OF FORMING"

BACKGROUND TO THE INVENTION

Field of The Invention

The present invention relates to low density non woven abrasive articles and methods for forming same.

Summary of the Prior Art Non woven abrasive articles are known and have been described for example in US Patent 4,227,350, Fitzer. The abrasive article in Fitzer has a low density abrasive product formed of a uniform cross section lofty web with three dimensionally undulated inter-engaged bonded filaments of a polyamide thermoplastic material. The filaments are bonded by a binder resin, and abrasive particles are uniformly distributed into the web and bonded therein by the binder resin. A second coat of binder resin is subsequently applied to further adhere the granules to the surface of the filaments.

Typically this base material is formed as large sheets and parts for abrasive tools are cut from the sheet for assembly into an abrasive tool product. An example product involves mounting circular portions of the abrasive material on a rigid plastic backing member for connection to a rotary tool such as an angle grinder.

A modified version of this abrasive media is known in which sections of the abrasive media as described above are placed in an enclosed mould and blown polyurethane foam is dispensed into the mould completely filling the mould cavity and fully infiltrating and filling the open fibre web of the base material. The subsequent foam filled product has been used as a combined stripping and polishing tool, giving a less aggressive cut and a shinier polished surface finish than the equivalent tool made with the standard base material. However it has been found that the foam filled product has a significantly shorter useful life than the product formed with the standard base material. Summary of the Invention

It is an object of the present invention to provide an abrasive article that has a longer useful life than the foam filled product, but leaves a more desirable surface finish than the standard product, or which will at least provide users with a useful choice.

In a first aspect the invention may broadly be said to consist in a low density abrasive product comprising: an open porous lofty web of continuous three dimensionally undulated filaments bonded where they touch one another, a multitude of abrasive particles dispersed within the web and bonded to the filaments, and a partially foamed polymer, coating the filaments of said web and partially but not completely filling the interstitial spaces of the web.

Preferably said partially foamed polymer is a polyurethane elastomer and has a specific gravity from 1.08 to 1.14.

Preferably said foamed polymer occupies from 32% to 47% of the available open space within said web.

In a further aspect the invention may broadly be said to consist in a method of forming a modified abrasive stock characterised by the steps of: a) retrieving an item of abrasive stock, b) spraying a partially foamed polymer composition onto said abrasive stock from at least one side, c) blowing a gases stream through said coated abrasive stock such that said coating penetrates the web of said stock and excess polymer coating composition is removed, and d) curing said foamed coating by active heating. In a further aspect the invention may broadly be said to consist in a modified abrasive stock produced by the method set forth above, or abrasive article incorporating same.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

Brief Description of the Drawings

The preferred embodiment of the present invention will now be described with reference to the accompanying drawings.

Figure 1 is a diagrammatic side elevation of apparatus for forming modified abrasive stock according to the present invention.

Figure 2 is a diagrammatic side elevation of the portion of the apparatus of Figure 1 relating to the spray nozzle for supplying the foam polymer coating.

Figure 3 is a view of a test rig performing a product life test on an abrasive tool in accordance with the present invention. Figure 4 is a schematic drawing of an abrasive disc cut from a sheet of modified abrasive stock.

Figure 5 is an assembly drawing showing an example of an abrasive article according to the present invention.

Detailed Description

According to the present invention a known abrasive stock is modified to provide a stock for manufacturing implements that give improved surface finish characteristics while not significantly effecting service life compared to the known abrasive stock. These advantages are achieved by coating the abrasive stock with a partially foamed polyurethane polymer coating infiltrated into the open web of the abrasive stock. The preferred abrasive stock is prepared in accordance with the disclosure of US 4,227,350, and in particular includes a non woven continuous fibre web, a polyurethane binding coat binding the continuous fibres of the web and receiving abrasive particles, and a further polythene binding coat coating the web and particles to adhere and bond the particles within the web.

In the present invention stock portions of this abrasive coated web are further processed to receive the partially foamed polyurethane coating. One preferred apparatus for performing this further processing is illustrated in Figures 1 and 2 and will now be described.

Referring to the apparatus in Figure 1 a plurality of portions 10 of abrasive stock are held in a magazine 12. The magazine 12 is located above a conveyor 14 whose top surface advances toward a spraying zone 22 above an over spray catchment 35. The conveyor 14 advances as indicated by arrow 16 to bring stock items on its upper surface from left to right as drawn.

A spray nozzle 28 receives a polyurethane polymer from conduit 26 and a modified isocyanide blowing agent from conduit 27. The spray nozzle 28 preferably provides a spray curtain across the conveyor width. An air containment shield 39 preferably encloses the spray curtain down to the immediate vicinity of abrasive stock passing over the space 22. The relative quantities of polymer and blowing agent through conduits 26 and 27 respectively are controlled by a mixing control unit 60. The variable control unit 60 receives polymer from a polymer reservoir 43 and blowing agent from a blowing agent reservoir 41 and discharges these to the respective supply conduits 26 and 27 through variable control valves 52 and 50 respectively.

Immediately subsequent to the nozzle 28 is an air knife 29, discharging a pressurised air flow at the upper surface of the coated stock. A second conveyor 18, operating in a direction as indicated by arrow 20, receives coated stock from the spray zone 22. A heater 33 is disposed above conveyor 18 to rapidly set off the sprayed polymer, preferably within one minute of application.

Therefore, in use an item 24 of stock 10 progresses from the magazine 12 along the upper surface of conveyor 14 to the spray zone 22. The short setting time polyurethane resin, with a reduced quantity of blowing agent, is sprayed uniformly on the upper surface of the abrasive stock as the abrasive stock passes underneath the spray nozzle 28. The air flow 31 from air knife 29 forces the partially foamed polyurethane into the interstitial spaces of the abrasive carrying web. The stock proceeds from the spraying zone 22 along the upper surface of conveyor 18 to pass beneath heater 33 where the resin rapidly begins to set. The coated stock may subsequently be cured in a curing oven as appropriate.

Depending on the application, the stock maybe required to be coated on both sides. In such case the stock may be returned through the same apparatus in its other orientation. Alternatively it may proceed through a second apparatus immediately post coating on its first side.

The modified stock may then be cut for use in abrasive products such as grinding and polishing discs etc. Alternatively, it is envisaged that a modified abrasive product according to the present invention may be manufactured by first cutting an unfilled abrasive coated web into a desired shape, for example a disc. The individual may then be subsequently partially foamed according to the method of the present invention in order to complete the manufacture of the modified abrasive product. However, it is thought that this may lead to uneven filling of the product, particularly at the edges, which may be detrimental. Therefore manufacture from sheets of modified stock is preferred.

Figure 4 shows a product, for example an abrasive disc, that is cut from a sheet of modified abrasive stock.

With reference to Figure 5, an example of an abrasive product according to the present invention is illustrated. A modified abrasive disc 45 manufactured according to the present invention is bonded to a backing disc 48. The backing disc 48 includes a boss portion 49 which has a threaded attachment portion 47. The boss 49 and attachment portion 47 are intended to provide a means for engagement of the abrasive product to a power tool or the like. In is envisaged that there are many possible types, sizes, shapes and methods of attachment of abrasive products using the modified stock of the present invention that will present themselves to those skilled in the art. Consequently, the above description is meant to serve as an example only.

It has been found that products assembled using abrasive stock prepared according to the above method provide an improved polished surface finish compared to that using the fully filled polyurethane products of the prior art, while retaining the longevity of the unfilled products. It is thought that the additional partially foamed coating provides the surface finish polishing effect, but that incomplete filling of the interstitial spaces allows cooling air flow within the implement in use, leading to improved service life.

In particular a 1000m x 1000mm x 15mm web of abrasive stock has been modified in accordance with this method by overspraying with a 1390-2870g coat of MDI ether polyurethane resin (available from Bayer AG of Germany), formulated to have an initial set- off time of 30 to 90 seconds, mixed at the foam head with 695-1435g of modified isocyanate ( 1 ,4 Butane Diol) curative (available from B ayer AG of Germany) . The amount of blowing agent is reduced to about 5-10% of the quantity usually applied for full foaming.

In this example the partially foamed polymer is a polyurethane elastomer and has a specific gravity from 1.08 to 1.14. The foamed polymer occupies from 32% to 47% of the available open space within the web.

Abrasive discs assembled with sections of the resulting stock have exhibited surface finish equivalent to a corresponding fully foam filled product at service life equivalent to a corresponding product using the unmodified stock. Product Life - Test 1

Product life tests were conducted on an automated test rig illustrated in Figure 3. A 115 mm angle grinder 53 was fitted to the swing arm 51 of a testing rig for grinding tests.

The swing arm moves the angle grinder 53, with attached grinding disc 54, attached to it from the centre 57 of a rotating steel plate 55 right to the periphery of the plate. The steel plates 55 are 370mm hexagonal shaped and coated with paint 56. In the test the paint was an acrylic exterior paint.

The swing arm moves the rotating disc 54 from the centre of the spinning steel plate 55 to the periphery and back as indicated by arrows 58 until all original paint coat is removed from the plate. At the periphery of the plate the disc is exposed to the fast changing angle of the sharp edge of the hexagonal shaped plate.

The hardest test for the durability of the disc takes place at the periphery of the plate.

Once the steel plate was completely cleared of paint a new plate was fitted and polished.

In this trial for each tested disc a total of six plates were cleaned from one side only.

Results - Test 1

A test was conducted using a standard disc made from unmodified abrasive stock. The standard disc started cleaning the steel plate fast and efficiently. The paint was removed leaving a shiny steel surface. The biggest stress was applied to the disc when the swing arm reached the edge of the hexagonal shaped steel plate. The sharp edge of the plate cut into the nylon web. Filament particles were flying of the disc until the angle grinder stated moving towards the centre again. The standard disc reached the end of its life after cleaiiing six plate surfaces.

The test was repeated using a fully foam filled abrasive disc. The fully foam filled disc removed the paint from the plate but left some residue due to clogging of the disc. Therefore it took longer to remove all the paint from the six plates. When cleaning on the edge of the steel plate the disc proved to be more durable than the standard product.

The volume of the disc was reduced to 47% of the original volume after polishing the six plates.

The test was repeated using a disc incorporating the modified abrasive of the present invention stock manufactured as above. The modified stock disc removed the paint leaving a shiny steel surface with no residue.

When cleaning the plates and the sharp edge of the plate the modified stock disc provided to be more rigid and durable than the standard disc and the foam filled product. The new disc used in this trial cleaned all 6 steel plates.

The volume of the disc was reduced to 73% of the original volume after polishing the six plates.

Summary - Test 1

In a paint removal application under controlled conditions (testing rig) the new disc was reduced to 73% of it's original volume (27% reduction), the fully foam filled product was reduced to 47% of it's original volume (53% reduction) and the standard product was not useable anymore after six 370mm steel plates have been cleaned.

Product Life - Test 2 A 115mm angle grinder was fitted to the swing arm of the testing rig described above. In this test the steel plates were 370mm hexagonal shaped and coated with a layer of rust.

The swing ami moves the rotating disc from the centre of the spinning steel plate to the peripheiy and back until all rust was removed from the plate.

Once a steel plate was completely cleared from the rust the plate was turned around and cleaned from the other side.

The disc was deemed to be at the end of its life when rust was no longer being removed and the nylon web was worn down to the glue on the backing plate.

The number of plates cleaned was counted and recorded.

Results - Test 2

The test was repeated twice using a standard disc made from unmodified stock and once using a new disc made using the modified stock. The test was not conducted using a fully foam filled product of the present invention as these are generally unsuited to rust removal applications.

The standard disc started cleaning the steel plate fast and efficiently. The rust was removed leaving a shiny steel surface. The biggest stress was applied to the disc when the swing arm reached the edge of the hexagonal shaped steel plate. The sharp edge of the plate cut into the nylon web. Filament particles were flying off the disc until the angle grinder started moving towards the centre again.

The first standard disc cleaned 2.5 steel plates (2 plates from both sides and one plate from one side) before it reached the end of its life. The second standard disc cleaned 3 plates (from both sides), before it reached the end of its life.

The disc incoiporating modified abrasive stock removed the complete coat of rust leaving a very smooth and shiny steel surface. There was an obvious visible improvement of the surface finish when comparing the steel plate with the plate cleaned by the standard disc (see surface roughness testing results below).

When cleaning the plates and the sharp edge of the plate the new disc proved to be more rigid and durable than the standard disc. The new disc used in this trial cleaned 17 steel plates from both sides before reaching the end of its life.

Surface Roughness - Test 3

Alumimum, stainless steel and mild steel plate samples were prepared by free hand grinding regions of each sample using a range of abrasive discs, including a standard disc and a disc incorporating the modified abrasive stock.

Each sample was submitted to Materials Performance Testing Limited, of Auckland, New Zealand for surface roughness testing with nine marked areas defined where surface roughness measurements were required. Five readings were taken for each area, and the mean, maximum and minimum value was reported. The surface texture roughness values (Ra) of the samples were compared to reference glass surface texture standards using a Surtronic 3+ as the comparator. The glass standards have calibrations that are traceable to national standards. The temperature range during test was in the range of 19.9°C to 20.3°C.

Results - Test 3

The Ra values for the areas of each plate corresponding to the two relevant discs are summarised in Table 1 together with the surface roughness values for the unabraded surfaces. The uncertainty of measurement expressed at the 95% confidence level is ±5% of the reading.

Table 1. Results of surface roughness testing

The mean surface roughness result for the new disc incorporating the modified abraded stock was significantly lower than for the standard disc for both the alurninium and mild steel plates. The mean surface roughness result for the new disc was the same as for the standard disc for the stainless steel plate.

Claims

CLAIMS:

1. A low density abrasive product comprising: an open porous lofty web of continuous three dimensionally undulated filaments bonded where they touch one another, a multitude of abrasive particles dispersed within the web and bonded to the filaments, and a partially foamed polymer, coating the filaments of said web and partially but not completely filling the interstitial spaces of the web.

2. A low density abrasive product as claimed in claim 1 wherein said partially foamed polymer is a polyurethane elastomer and has a specific gravity from 1.08 to 1.14.

3. A low density abrasive product as claimed in claim 1 or claim 2 wherein said foamed polymer occupies from 32% to 47% of the available open space within said web.

4. A method of forming a modified abrasive stock characterised by the steps of: a) retrieving an item of abrasive stock, b) spraying a partially foamed polymer composition onto said abrasive stock from at least one side, c) blowing a gases stream through said coated abrasive stock such that said coating penetrates the web of said stock and excess polymer coating composition is removed, and d) curing said foamed coating by active heating.

5. A modified abrasive stock produced by the method as claimed in claim 4.

6. An abrasive article incorporating an abrasive stock as claimed in claim 5.

7. An abrasive product as described in any of the embodiments herein with reference to and as illustrated by any of the accompanying drawings.

8. A method of forming a modified abrasive stock as described in any of the embodiments herein with reference to and as illustrated by any of the accompanying drawings.

9. An abrasive stock as described in any of the embodiments herein with reference to and as illustrated by any of the accompanying drawings.

10. An abrasive article as described in any of the embodiments herein with reference to and as illustrated by any of the accompanying drawings.