GB2326361A - Abrasive elements - Google Patents

Abstract

An abrasive element for mounting on a mechanical abrading device such as a sander is disclosed. The abrasive element has a substrate formed of a flexible foam sheet 4 upon a first surface of which a layer 2 of abrasive particles is adhered. A releasable attachment layer 6 is adhered to an opposite surface of the sheet 4 and permits the releasable attachment of the abrasive element to a working surface of the mechanical abrading device.

Description

ABRASIVE ELEMENTS The present invention relates to abrasive elements for use with abrading devices such as sanders and the like.

It is an object of the present invention to provide an abrasive element with improved characteristics.

According to a first aspect of the present invention, there is provided an abrasive element adapted and constructed to be mounted on a mechanical abrading device, said element comprising a substrate upon a first surface of which a layer of abrasive particles is adhered and upon an opposite second surface of which a releasable attachment layer is adhered, wherein said substrate is a flexible foam and said attachment layer permits the releasable attachment of the element to a working surface of the mechanical abrading device.

The layer of abrasive particles is preferably adhered to the first surface by means of a first binder, and a second binder, or size coating is preferably provided over the abrasive particles and first binder.

The first and second binders may be independently selected from a water- or solvent-based adhesive, for example, an adhesive selected from phenolic resin, urea-formaldehyde resins, polyurethane resins, EVA resins, polyamide resins and any combination of two or more of these resins. A flexible adhesive is preferred. The first binder may be a moisture-cured hot-melt polyurethane adhesive. This provides a number of advantages over more traditional water- and solvent-based adhesives.

The hot melt adhesive used has a 100% solids content and by suitably selecting the temperature at which the adhesive is applied, it will ensure the desired orientation of the abrasive particles.

The hot-melt polyurethane adhesive used in a given application will be selected according to the particular requirements. As a general guide, polyurethanes having viscosities in the range of 3000 to 12000 mPa.s (Brookfield) at 120C are suitable, although if a lower coating temperature is used then a lower viscous polyurethane would be used.

The individual abrasive particles used may be selected from those commonly used in the abrasive industry, however, the size and type of the abrasive particles will be chosen with the application of the abrasive article in mind. The composition of the abrasive particles used in this type of operation can be divided into two classes: natural abrasives and manufactured abrasives. Examples of the former class include diamond, emery, corundum, garnet silica, pumice and quartzite. Examples of manufactured abrasives include fused alumina, heat treated aluminium oxide, carbide and glass.

Abrasive particles used in the present invention typically have a particle size ranging from about 0.1 micrometer to about 1200 micrometers.

Most preferable is a particle size ranging from about 1 to 100 micrometers. It is preferred that abrasive particles used in the present invention have a Moh's hardness of at least 8, more preferably above 9.

Although for specific applications softer particles may be used.

Examples of mechanical abrading devices include rotary and randomorbital sanders. Reference to such abrading devices also includes those tools, such as drills, which are designed to be multi-functional and may be used as sanders. The invention is most preferably applicable to randomorbital sanders.

Preferably, the attachment layer comprises hooks or filamentary loops which are releasably engagable with corresponding filamentary loops or hooks on the working surface of the abrading device. An example of a securing system using mutually engaging hooks and loops is sold under the Registered Trademark "Velcro".

Preferably, the flexible foam is a foamed polymer having a density of 8 to 120 kg/m3. Suitable polymeric foams include polyurethane, polyester and polyether based foams. Preferably, the substrate is formed from a sheet having a thickness of 3 mm to 12 mm between the first and second surfaces.

The adhesive used to secure the attachment layer to the foam substrate is not particularly limited, although it is preferred to use a moisture-cured polyurethane hot-melt adhesive.

According to a second aspect of the present invention, there is provided a method of making an abrasive element, comprising the steps of (a) adhering abrasive particles to a first surface of a flexible foam sheet, (b) adhering a releasable attachment layer to an opposite second surface of said foam sheet, and (c) cutting the foam sheet to form an abrasive element of a desired shape and size.

Preferably step (a) is achieved by coating the foam sheet with an adhesive followed by application of the abrasive particles to the adhesive-coated foam sheet. Step (a) may optionally include the application of an adhesive coat onto the first surface after the abrasive particles have been adhered to the foam. The adhesive used for this optional application need not be the same as that used initially to coat the foam sheet.

Preferably step (b) is achieved using a hot-melt adhesive. Step (c) is preferably achieved by a die-cutting procedure.

Preferably step (a) is performed before step (b).

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig 1 is a schematic illustration of a composite from which an abrasive element according to said first aspect of the present invention is constructed, and Fig 2 is a plan view of an element cut from the composite of Fig 1.

Abrasive particles (grit) 2 made from aluminium oxide or silicon carbide and having a grade of between 36 and 600 based on the FEPA scale were applied to one surface of a foam sheet 4 having a density of 85 kg/m3 and thickness of 5 mm which had been coated with a nitrile adhesive. A securing layer or size coating of adhesive was then applied to the same surface. To the opposite surface, a releasable attachment layer 6 formed of a mat with protruding flexible loops of polymer filaments was adhered using a moisture-cured polyurethane hot- melt adhesive. This three layer composite was then die cut to form the desired delta-like element 8 (Fig 2).

In use, the abrasive element 8 is secured to an abrading device having a working surface covered with a mat having protruding hooks. The hooks inter-engage with the loops to secure the element releasably to the working surface. The element 8 remains in position during operation of the abrading device but is easily removed by peeling it away when desired because of the different nature of the forces involved. The flexibility of the foam sheet 4 permits an improved contact with the work piece being abraded and thereby results in a smoother finish than that achieved by an abrasive element with a paper substrate.

Comparative tests with standard abrasive elements having a paper substrate showing the improved finish of elements according to the present invention are shown in Table 1.

Grade (present invention) Equivalent (paper) (FEPA) (FEPA) 60 12S180 120 320400 220 500-600 Table 1. Comparison of finish between abrasive elements having paper and foam substrates.

Thus, it can be seen that the 60 grade element described in the above embodiment gives a smoothness of finish comparable to a standard paper element of 120-180 grade.

It will be appreciated that the elements of the present invention allow the use of a coarser than usual grade grit, which speeds up the abrading process whilst maintaining the desired smoothness of finish. In addition, the useful life of an element required for a given finish is longer, since a coarse grade grit becomes clogged less quickly. If an anti-loading coat, eg. of a stearate, is additionally applied, durability is further enhanced.

Claims (16)

1. An abrasive element adapted and constructed to be mounted on a mechanical abrading device, said element comprising a substrate upon a first surface of which a layer of abrasive particles is adhered and upon an opposite second surface of which a releasable attachment layer is adhered, wherein said substrate is a flexible foam and said attachment layer permits the releasable attachment of the element to a working surface of the mechanical abrading device.

2. An element as claimed in claim 1, wherein the layer of abrasive particles is adhered to the first surface by means of a first binder.

3. An element as claimed in claim 2, wherein a second binder or size coating is provided over the abrasive particles and first binder.

4. An element as claimed in claim 2 or 3, wherein the first binder is a moisturecured hot-melt polyurethane adhesive.

5. An element as claimed in any preceding claim, wherein the binder is flexible.

6. An element as claimed in any preceding claim, wherein the attachment layer comprises hooks or filamentary loops which are releasably engagable with corresponding filamentary loops or hooks on the working surface of the abrading device.

7. An element as claimed in any preceding claim, wherein the flexible foam is a foamed polymer having a density of 8 to 120 kg/m3.

8. An element as claimed in any preceding claim, wherein the substrate is formed from a sheet having a thickness of 3 mm to 12 mm between the first and second surfaces.

9. A method of making an abrasive element, comprising the steps of (a) adhering abrasive particles to a first surface of a flexible foam sheet, (b) adhering a releasable attachment layer to an opposite second surface of said foam sheet, and (c) cutting the foam sheet to form an abrasive element of a desired shape and size.

10. A method as claimed in claim 9, wherein step (a) is achieved by coating the foam sheet with an adhesive followed by application of the abrasive particles to the adhesive-coated foam sheet.

11. A method as claimed in claim 10, wherein step (a) includes the application of an adhesive coat onto the first surface after the abrasive particles have been adhered to the foam.

12. A method as claimed in claim 9, 10 or 11, wherein step (b) is achieved using a hot-melt adhesive.

13. A method as claimed in claim 9, 10 or 11, wherein step (c) is achieved by a die-cutting procedure.

14. A method as claimed in any one of claims 9 to 13, wherein step (a) is performed before step (b).

15. A method as claimed in claim 9, substantially as hereinbefore described with reference to the accompanying drawings.

16. An element as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

16. An element when produced by a method as claimed in any one of claims 9 to 15.