GB2075384A - Improvements in or relating to a means for wet grinding - Google Patents

Abstract

A means for wet grinding flat and curved surfaces comprising a body to receive a wet-strength abrasive sheet (17) which is detachably stretched over the body. The invention is characterised in that said body has a space (8) therein to receive a liquid through an inlet (4) in the body; that the body has at least one grinding sole (13) with outlets (14) to allow liquid to flow out of the space (8) in the body; that a layer (16) of soft, sponge- like material capable of absorbing and allowing liquid through is arranged to cover the grinding sole (13) and its outlets (14) and to distribute the liquid to the abrasive sheet (17) covering the layer (16); and that within the area covered by the grinding sole (13) the abrasive sheet (17) is provided with a number of perforations (25) to allow liquid from the layer (16) to flow to the outside of the abrasive sheet (17). <IMAGE>

Description

SPECIFICATION Improvements in or relating to a means for wet grinding The present invention relates to a novel means for wet grinding surfaces preferably flat or curved surfaces, said means comprising a body to receive a wet-strength abrasive sheet which is detachably mounted and stretched over the body.

Wet grinding has long been used for grinding and polishing surfaces with the object of removing undesirable material or in order to obtain the desired surface smoothness.

Wet grinding generally entails the use of an abrasive, usually silicon carbide or aluminium oxide covering a sheet, such as a paper sheet, or cloth of wet-strength material, together with water supplied while grinding is in progress.

The purpose of the water is to prevent harmful heating of the work surface, to eliminate dust formation which can be troublesome, to clean the paper from material which has been ground away and to control the friction between work surface and abrasive material so that the brinding goes easily while at the same time being effective.

Hitherto wet grinding has generally been performed by applying a wet grinding paper or cloth on a body of suitable material, immersing in water and then carrying out the grinding manually, i.e. moving the body by the hand with the paper or cloth thereon.

This primitive method previously used has many obvious disadvantages. Admittedly the abrasive paper is cleaned when immersed in the water but only a very small quantity of water remains on the surface of the paper and after only a few grinding movements a considerable amount of the product being removed has collected so that the paper must be cleaned again. This process is time-consuming and means that a container with water must always be available and the work must be interrupted to change the water in the container. Furthermore, the person carrying out the wet grinding must immerse his hands in the water containing suspended grinding dust and when grinding surfaces which are inconveniently placed, such as the underwater body of leisure boats it is unavoidable that water and grinding dust run down the arms.Skin contact with the water containing grinding material should be avoided and is highly unsuitable in the case of cleaning the underwater body of boats since the boats are usually coated with antifouling paints the ingredients of which constituting a serious environmental risk from the point of view of labour safety. In many cases these ingredients are highly toxic and can be absorbed directly through the skin in water solution.

The object of the invention is to provide a means for wet grinding which to a considerable extent reduces the above-mentioned drawbacks in connection with conventional wet grinding and with which wet grinding can be performed quickly and efficiently without the operator being forced to come into contact with the water mixed with grinding dust, and with the additional considerable improvement that a fluid film which is favourable in many respects for the grinding process, can be continuously maintained between the abrasive sheet and the work surface, thus, among other things, resulting in a uniform grinding result.

This is achieved according to the present invention in that the body has a space therein to receive a liquid through an inlet in the body; that the body has at least one grinding sole with outlets to allow liquid to flow out of the space in the body; that a layer of soft, sponge-like material capable of absorbing and allowing liquid through is arranged to cover the grinding sole and its outlets and to distribute the liquid to the abrasive sheet covering the layer; and that within the area covered by the grinding sole the abrasive sheet is provided with a number of perforations to allow liquid from the layer to flow to the outside of the abrasive sheet.

The invention will be further described by way of example in the following by means of a preferred embodiment of the novel implement which has been especially developed for wet grinding the underwater body of boats, and with reference to the drawings wherein Figure 1 shows the implement in perspective seen from its working surface, Figure 2 shows the implement according to Figure 1 in a longitudinal section, and Figure 3 shows the implement according to Figure 1 in an exploded view but without the shaft attached.

The implement shown in the drawings comprises an angular grinding body 1 of rigid material such as metal or plastic thereby being shape permanent. The body comprises generally a substantially rectangular first part 2 and a substantially rectangular second part 3, said parts being located in different planes forming an obtuse angle with each other. At the rear of the body is a central inlet 4 and a short connecting pipe 5 enclosing said opening and designed to receive a hollow shaft 6 with a nipple 7 for connection of a hose for the supply of ordinary water or some other suitable liquid to the head of the implement through the shaft 6, connecting pipe 5 and inlet 4 of the body.

The body is provided with an inner space 8 which communicates with the connecting pipe 5 through said inlet 4. In the embodiment shown the space 8 is located in the second body part 3 and is limited by a longitudinal partition 9 extending between the short sides 10, 11 of the implement in the vicinity of the longitudinal centre line of the implement.

Due to the angular shape of the implement, the abrasive surface is divided into two grinding soles 12, 1 3 located in different planes, the junction between the soles preferably consisting of a curved convex surface. The sole of the second body part 3 is provided with a number of outlets 14 arranged in two rows extending parallel to and close to the longitudinal side edge 15 of the part 3, the area of the inner row of holes being slightly less than that of the outer row to compensate for pressure differences in the water at the different levels.

A soft, porous,sponge-like layer or coating 1 6 with high water absorption ability is adhered to the grinding soles. The layer is glued on to the grinding soles in such a way that the water forced out through the holes 14 in the upper sole is distributed homogeneously and thoroughly in the layer and does not follow the smooth surfaces of the soles out towards the edges. In other words, the layer is adhered to the grinding soles over the entire surface facing the soles.

The soft, porous layer is covered on its outer side by an abrasive sheet 1 7 lying edge to edge with the end edges 10, 11 of the body and having its opposite end sections 18, 1 9 folded around the longitudinal side edges 15,20 of the body. The abrasive sheet is detachably clamped at the end sections with the help of an attachment means arranged close to each side edge 15, 20 on the rear face of the body: The attachment means may consist, for instance, of a rectangular clamp plate 21 which is pressed against the rear face of the body, clamping the abrasive sheet between itself and the body with the help of two wing nuts 22 on bolts 23 fixed in the body and extending-through holes in the plate 21.The bolts are also provided with springs 24 located under the clamping plate 21 to force the clamping plate from the body thereby facilitating insertion of the end sections of the abrasive sheet under each clamping plate.

The attachment means can of course be of any suitable design in order to achieve the desired detachable retention of the abrasive sheet so that this is kept stretched in the desired manner over the entire sponge-like layer and in close and intimate contact therewith. With this or any other suitable attachment means the abrasive sheet can thus easily be exchanged.

The abrasive sheet is provided with a number of perforations 25 arranged in a certain pattern over the section 26 available for the grinding process, which covers the layer 1 6. The holes are arranged in rows with predetermined spacing between the rows and predetermined spacing between the holes in each row. The holes may have a diameter of 0.5-7 mm, preferably 2-5 mm. However, other hole diameters may be used if desired depending, inter alia, on the number of holes per surface unit.

In the embodiment shown the body is composed of a rear piece 27 and a front piece 28 forming the grinding soles, having end pieces 29 arranged to limit the inner space 8 of the body laterally, the rear piece being received in and in sealing engagement with the front piece 28.

The connecting pipe 5, and thus the shaft 6, are inclined in relation to the first part 2 of the body, the first part having no space to contain liquid, or at least no outlets, so that the connecting pipe as well as the shaft form an obtuse angle of about 95 100 with respect to this first part 2.

The implement shown in the drawings has been especially designed for wet grinding the underwater body of boats. However, with minor modifications, the implement can also be used for wet grinding other surfaces such as shell plating and decks on boats, car bodies, walls etc. where wet grinding is preferred over dry grinding. When wet grinding the underwater body of a boat, the first part 2 or grinding sole 12 is used for vertical or substantially vertical surfaces such as the keel while the other part 3 or grinding sole 13 with outlet openings arranged at the top is used for grinding the more horizontal parts of the hull. The inclination, i.e. the obtuse angle, between the two grinding soles 12, 1 3 is chosen to suit the most usual shapes for hull and underwater body of modern sailing boats, motor cruisers and largish motor-boats.The curved or bulging junction connecting the two grinding soles gives good contact between implement and underside of the boat when grinding concave surfaces between the keel and hull.

As mentioned above, the shaft extends obliquely from the rear piece in relation to the first body part 2 in such a way that it forms an angle of 50--100 up from the horizontal plane regarded from the position when the first body part assumes vertical position for wet grinding a vertical surface. This upwardly directed position of the shaft 6 and its connecting pipe 5, together with a drip-ring 30 on the shaft, effectively prevents water and material grinded away from running down the shaft. The length of the shaft is selected to give a comfortable working position.

Furthermore, there is a requisite distance between working surface and grinding body so that the risk of contact with often unhealthy material is avoided to a considerable extent. The nipple 7 on the shaft 6 is designed to fit normal hose dimensions. The channel in the nipple has been tested and adjusted so that a suitable volume of water for the implement is obtained at normal water pressure.

The perforated abrasive sheet which is stretched over the grinding soles and porous layer and can be exchanged, is chosen depending on the condition of the surfaces to be treated and the desired result of grinding. When grinding surfaces where a certain amount of material is to be removed, such as old paint, plastic or the like, and where there must be good adhesion upon subsequent surface treatment, a medium-fine or fine grinding-paper or grinding-cloth should be chosen, where an extra-fine paper should be chosen for polishing surfaces, requiring an extremely smooth and high finish, such as polishing polishable bottom paints.

When using the implement shown in the drawings, water is supplied through a hose and flows continuously through the shaft 6 and connecting pipe 5, into the space 8 inside the body as illustrated by the arrows in Figure 2.

Water flows continuously out through the outlet openings 14 in the upper grinding sole 3 and is soaked up by the porous layer to saturation point so that the water is homogenously distributed throughout the layer. Water then flows from the spongelike layer through the holes 25 in the abrasive layer so that, by adjustment of the placing and size of the holes, a uniform, continuous film of water is obtained between the abrasive sheet and the surface to be treated. This film of water is continually renewed since the water is constantly forced out through the holes in the wet-strength abrasive sheet.The water film provides a cooling effect which prevents a harmful increase in temperature and a tendency to stick, as well as continuously and efficiently clearing the abrasive sheet from products ground away from the surface being treated and facilitating the grinding work by decreasing friction.

The soft, porous layer has, inter alia, two important functions. It distributes the water flowing from the body uniformly to the holes of the abrasive sheet and also provides an even and uniform contact of the entire surface of the abrasive sheet against the surface to be treated.

The thickness of the layer may vary within wide limits for various reasons. A suitable thickness is 0.4-2 cm. A suitable material for the layer is cellular plastic of polyester type with open pores, which also has the desired elasticity. If desired the layer may be constructed of different materials, of said type or any other suitable cellular plastic type, for instance a laminate of two layers having different porosity.

The wet grinding or water-sanding implement according to the present invention can be varied and modified in many ways within the scope of the following claims. In its simplest form the implement may, instead of an angular body, have a body forming a single substantially plane grinding sole, the body being hollow in the same way as the second part 3 in the embodiment described above and with a number of outlets arranges in the grinding sole over its entire surface or only over a limited part thereof. A sponge-like layer is glued on to such a sole in the same way as previously described so that the water is distributed to the abrasive sheet stretched over the layer, the sheet being perforated as described previously. The water may also be supplied directly without passing through a hollow shaft. A water hose is thus connected directly to the body of the implement by means of a connection mounted on a suitable place of the body, the hose being suitably held on and along the shaft (may be solid) manually or with special clamping means.

The shaft may alternatively be omitted, in which case the implement is operated by grasping the hose and possibly also said connection by hand.

Claims (10)

1. A means for wet grinding flat and curved surfaces comprising a body (1) to receive a wetstrength abrasive sheet (17) which is detachably stretched over the body, characterised in that the body (1) has a space (8) therein to receive a liquid through an inlet (4) in the body; that the body (1 ) has at least one grinding sole (13) with outlets (14) to allow liquid to flow out of the space (8) in the body; that a layer (16) of soft, sponge-like material capable of absorbing and allowing liquid through is arranged to cover the grinding sole (13) and its outlets (14) and to distribute the liquid to the abrasive sheet (17) covering the layer (16); and that within the area covered by the grinding sole (13) the abrasive sheet (17) is provided with a number of perforations (25) to allow liquid from the layer (1 6) to flow to the outside of the abrasive sheet (17).

2. A means according to claim 1, characterised in that the body (1) comprises two grinding soles (12, 13) arranged in different planes and forming an obtuse angle with each other; that the grinding soles (12, 13) are covered buy a layer (16) made in one piece; and that only one grinding sole (13) is provided with outlets (14).

3. A means according to claim 2, characterised in that the outlets (14) in said one grinding sole (13) are arranged close to the edge ( 1 5) located at a distance from the other grinding sole (12).

4. A means according to claim 1, 2 or 3, characterised in that it comprises a hollow shaft (6) joined to a rear piece (27) of the body, for manual operation of the body and for continuous supply of liquid to the grinding body through said inlet (4).

5. A means according to claim 2 or 3 and 4, characterised in that the shaft (6) forms an obtuse angle with the second grinding sole (12) free of outlets.

6. A means according to claim 5, characterised in that said angle is about 95o1 000.

7. A means according to claim 1, characterised in that two adjacent holes (25.) in the abrasive sheet, seen from one end section (18) to the other end section (1 9) thereof, are laterally displaced in relation to each other so that a uniform water film is formed across the abrasive sheet within the area of the grinding soles.

8. A means according to claim 1 or 7, characterised in that the holes (25) are arranged in rows substantially parallel to the end sections (1 8, 1 9) of the abrasive sheet.

9. A means according to claim 8, characterised in that the holes (25) of two adjacent rows are displaced in relation to each other.

10. A means according to claim 1, characterised in that the inlet (4) and/or a connection nipple (7) close to or spaced from the inlet (4) have/has a throttling function.