CA1036800A - Sanding pads - Google Patents

Abstract

Abstract A process for making sanding pads employs a substantially rectangularly cross-sectional foam plastics material strip having a hardness of 650 to 1000 Newtons according to BS 4443 whose sides are treated in a two step procedure in adjacent pairs by applying to each pair of adjacent sides a thick adhesive and abrasive grit.

Description

The invention relates to processes for making sanding pads or blocks for use in woodworking, painting and decorating for example. Sanding pads of the kind with which the invention is concerned are described in the Briti~h Patent Specification No. 1,328,292.
Back~round o~ the invention The application of abrasive onto foam plastics substrates is known for example from the British Patent Specifications Nos. 720,837 and 955,713 and the United States Patent Specification No. 3,021,649. The resulting abrasive devices are generally intended for use as scouring pads for kitchen utensils, and not suited for woodworking, painting and decorating where a high friction may have to be overcome. The British Patent Specification No. 1,328,292 discloses the latter applications but the ~anding pads described may be difficult to clean reducing the life of the sanding pads; may be too flexible to permit a vigorous rubbing action and may have angled portions which have irregular edges.
It is an object of the invention to provide a process for manufacturing sanding pads having a long useful life, which are easy to clean and ean be roughly used and which can be used to rub edges of recesses smoothly.

-2-1o36800 Summary of Invention.
The invention provides a process for making a sanding pad comprising (A) applyihg a highly viscous adhesive to a first pair of adjacent side surfaces of a strip of a foam material having a subs~nT;~I~ y rectangular section to form a continuous layer extending across the adjacent side surfaces, the strip having a hardness of at lo~st 650 to 1000 Newtons according to BS 4443;
(B) applying abrasive grit on to the adhesive layer across the first pair of adjacent side surfaces;
~C) applying a highly viscous adhesive to a second remaining, pair of adjacent side surfaces of the aforesaid strip of foam to form a continuous layer extending across the second pair of side surfaces; and (D) applying abrasive grit onto the adhesive layer across the second pair o~ adjacent side surfaces~
whereby a continuous sleeve of adhesive and abrasive grit surrounds the foam material strip.
Brief description of the drawin~:
The Figure shows a perspective sanding pad on completion of the process of the invention Detailed description of the invention A block of foam material is cut into strips of 3 to 4 meters long having a rectangular section, generally with a width of twice the height of the section.
The foam may be of any material which is light resistant and water resistant and which has a hardness within a range of 650 to 1000 Newtons according to ss 4443.
A suitable foam material is so-called "chip-foam"
consisting of fragments of an open pore foam material bonded together by aflexible water resistant adhesive. Examples of such materials are foamed polyesters and polyethers. Such foams can be prepared with different degrees of hardness depending on the extent to which the fragments are compressed when the adhesive that bonds them sets.
A waterproof, highly viscous adhesive is then metered through a slit nozzle under pressure onto a pair of adjacent side surfaces of the foam strip. Excess adhesive is cut off at the edges of the surfaces so that no adhesive projects. The strip is held with the edge between the adjacent side surfaces uppermost, arranging the surfaces at a 45 angle to the horizontal. Abrasive grit i5 then dropped on the surfaces of the adhesive, excess grit running off over the surfaces.
~he abrasive grit is applied immediately after the adhesive.
After drying and, optionally fettling the edges of the adhesive-abrasive layer, the remaining pair of side surfaces can then be similarly treated. If a coarse grit is used (such as grade 36 Aluminum oxide) a low viscosity adhe,sive may be coated on the treated surfaces to bind the grit o .

10368~0 more firmly. The adhesive can be selected from the many adhesives suitably solvent based having the characteristics set out and a high degree of flexibility when dry and solidified so that the foam material and the abrasive--adhesive layer may be deformed simultaneously.
Different grades of grit may be applied to adjacent pairs of side surfaces. Preferably one pair has a coarser grit and the other a relatively finer grit.
Where necessary, excess adhesive and abrasive can be removed by rubbing from the edge where ~he two successively applied adhesive-abras;ve layers join.
Subsequently the strip is cut into lengths.
The resulting pads thus have four adhesive-abrasive surfaces forming a sleeve around an open ended foam material core. The edges between the surface are linear, well defined and relatively sharp. In the Figure an exemplary sanding pad is shown with an open end 2 of a foam 6I material core, and a pair of faces 4 and 6 forming by the adhesive with the abrasive particles secured to the adhesive.
The sanding pad has a hardness intermediate that of the prior art scouring pads and the customary wooden sanding blocks for carrying sanding paper. The hardness should be more than 650 Newtons so that the pad would be difficult to deform by hand in operation. This ~036~00 prevents folding and wrinkling when rubbing and uneven wear of the abrasive surfaces. The hardness should be less than 1000 Newtons so that the sanding pad abrasive surface will yield to minor protrusions on a surface to be smoothed. This also enables the abrasive surfaces to conform to concave or convex surfaces. The selected range of hardness also assists in other respects. An abrasive is never perfectly flat and portions will project above others to a small extent. The hardness is such that the abrasive surface can yield in parts so that its whole surface can be utilized. Thùs it takes relatively long for the surface to become clogged with abraded material compared with, say, a wooden sanding block. Also the pressure applied by an operative by hand to the top of the block is concentrated on the more projecting parts o~ the surface underneath without the operative having ~o app~y pressure in a speci~ic area. Thi~ is contrary to the way in which scouring pads and sand - paper operate in practice.
The use of the continuous sleeve of adhesive abrasive surface provides structural integrity which enables the sanding pad to be used on rough surfaces without the foam material supporting the abrasive being worn away. The sharp edges of the sleeve also enable the pad to smooth right angled rebates, which could be difficult to reach otherwise.
The open ends of the sanding pad, produced in this process of manufacture, provide a means of draining the porous foam. When the sanding pad is clogged it can be rinsed in water under a tap to remove the abraded material from the abrasive surface. Sub~equently the pad can be twisted in two hands and wrung out to remove the water retained in the foam material. The water can leave easily due to the absence of a water impermeable layer and in squashing the pad, the abrasive surface can be brought together and the foam compacted without damaging the abrasive surfaces.
The pads may be used for cleaning priming surfaces, smoothing curved surfaces and angles and for keying successive coats of paints firmly to each other.
They may also be employed using water as a lubricant, due to the uncoated block ends, which provide drainage as described above.

Claims (7)

What is claimed is:

1. A process for making a sanding pad comprising (A) applying a highly viscous adhesive to a first pair of adjacent side surfaces of a strip of a foam material having a substantially rectangular section to form a continuous layer extending across the adjacent side surfaces, the strip having a hardness of 650 to 1000 Newtons according to BS 4443;
(B) applying abrasive grit on to the adhesive layer across the first pair of adjacent side surfaces;
(C) applying a highly viscous adhesive to a second remaining, pair of adjacent side surfaces of the aforesaid strip of foam to form a continuous layer extending across the second pair of side surfaces; and (D) applying abrasive grit onto the adhesive layer across the second pair of adjacent side surfaces, whereby a continuous sleeve of adhesive and abrasive grit surrounds the foam material strip.

2. A process as claimed in claim 1 in which the adhesive is applied by a slit nozzle and any adhesive extending beyond the first pair of surfaces is cut off before applying the abrasive grit.

3. A process as claimed in claim 1 in which the abrasive grit is applied by running the grit onto the first pair of adjacent surfaces simultaneously, the surfaces being held at an angle to the horizontal.

4. A process as claimed in claim 1 in which the strip is cut into lenths to form sanding pads and the cut ends are left uncovered.

5. A process as claimed in claim 1 in which a coarse type of grit is applied to the first pair of adjacent surfaces and the surface is treated with a dilute adhesive to bind the grit.

6. A process as claimed in claim 1 in which a coarse type of grit is applied onto one of the pairs of adjacent surfaces and a finer type of grit to the other pair of adjacent surfaces.

7. A process as claimed in claim 6 in which the foam material has a density of at least 120 kg per m3.