This invention relates to a surface stripping device. Although primarily intended as a stripping device for wall coverings such as wallpaper, it is envisaged that the device could have a variety of uses such as for paint or varnish stripping, stripping of floor coverings such as vinyl tiles, general descaling operations in industry, removal of road surfaces prior to resurfacing and in boat antifouling.

According to the invention the device comprises a blade in the form of a generally circular disc having one or more cutting edges around its periphery, together with means for causing said disc to undertake an orbital motion in a plane generally parallel to the general plane of the disc. The blade may be circular, defining a single circular cutting edge, or multi-sided (for example, 12 sided), thus defining a plurality of straight cutting edges. The cutting action may be enhanced by specially treating the edge: for example by serrating it, or by forming a burr on it, or both.

The blade is mounted for use on a drive unit capable of providing the required orbital motion. Such units are already known and are used, for example, to power orbital sanders. Generally such units comprise an eleetric motor housed within a generally cylindrical casing having a handle which in use is gripped by the operator. ^' A gearbox is used to convert the rotary output from the motor into an orbital motion, this usually involving a turn through 90°. Thus, the general plane of the blade is parallel to the axis of the cylindrical casing.

The blade may be rigidly mounted on the drive unit, but in practice is preferably flexibly mounted since this assists the operator in not penetrating the

surface during stripping, which can happen if the blade is not kept parallel to the surface. Thus, the blade may be tightened against a rubber o r similar flexible washer, or the drive may incorporate a rubber "cush drive" which both reduces vibration and allows a considerable degree of blade movement relative to the power unit. A spring mounting could also be used, using a helical coil spring to transmit the drive.

This problem of penetration of the surface during stripping may also be reduced by segmenting the blades as this increases the flexibility of the blade itself. This segmenting may be achieved by forming a plurality of radial slots extending towards the centre of the blade from the periphery. In a multi-sided blade, each segment can be separated from the rest by such a slot. The slots are typically 1mm wide.

The blades may be made from steel, for example stainless steel, or plastics material. The general flexibility of the blades may however be improved by manufacturing them from flexible material such as spring steel, or even hard plastics materials such as polycarbonates. The periphery of the blade may be hardened, to improve wear, or may be faced with carbide to provide a cutting edge having a long life expectancy. The use of flexible blades enables a reciproc- atory action to be applied to the blade, as well as the orbital motion described above. Such reciprocatory action would be in a direction at right angles to the general plane of the disc. This effectively means that the orbital motion, instead of being in a single plane, is in a plane which reciprocates backwards and forwards towards and away from the wall surface being stripped. Flexible blades can take up this movement and, indeed, will benefit by additionally cutting as radial movement of the blade perphery takes place. In order that the invention may be better

understood several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which:-

Figure 1 is a diagrammatic side view of a stripping device according to the invention;

Figures 2, 3 and 4 are plan, side section and sectional detail respectively of a first embodiment of a blade for use with the stripping device of the invention ;

Figures 5, 6 and 7 are views corresponding to Figures 2, 3 and 4 respectively showing a second embod¬ iment;

Figures 8, 9 and 10 are views corresponding to Figures 2, 3 and 4 respectively, showing a third embodiment;

Figure 11 is a plan view of a fourth embodiment of a blade for use with the stripping device of the invention;

Figures 12 and 13 are side sections of the blade of Figure 11 showing the manufactured profile of the blade (Figure 12) and the working profile of the blade (Figure 13);

Figures 14, 15 and 16 are views corresponding to Figures 11, 12 and 13 respectively, showing a fifth embodiment;

Figures 17, 18 and 19 are views corresponding to Figures 11 , 12 and 13 respectively, showing a sixth embodiment;

Figures 20 and 21 are views corresponding to Figures 11 and 12 respectively showing a seventh embodiment;

Figure 22 is an enlarged sectional view of the cutting edge in the embodiment of Figures 20 and 21;

Figure 23 is an exploded side sectional view of a combination blade for use with the stripping device of the present invention;

Figure 24 is an exploded side sectional view of a rigidly mounted annu-lar blade for use with the stripping device of the present invention;

Figure 25 is a side sectional view of the annular blade system of Figure 24; and

Figure 26 is an underside view of part of the holding device for the annular blade of Figure 24.

Referring to Figure 1 there is shown a typical stripping device made in accordance with the invention. The device comprises a generally cylindrical casing 1 which contains an electric motor and supplies drive to a gearbox 2. The gearbox turns the drive through 90 and converts the rotary output of the motor into an orbital action in a plane at right angles to that of the drawing. Such gearboxes are well known and will not be described in detail; suffice to say that, with the motor switched on, the output boss 3 executes an orbital motion in a plane at right angles to that of the drawing. Switch means (not shown) are provided for switching the motor on and off. In use, the user may grip the casing 1 or, in larger sizes, an integral handle may be provided.

Attached to the boss 3 is a blade 4 in the form of a generally circular disc which has one or more cutting edges at its periphery. Various designs of blade are to be discussed hereinafter in detail. The disc has a central aperture by which it is located on the boss 3 by means of a bolt 5.

When the motor is energised the disc executes an orbital motion in a plane at right angles to the drawing. In order to use the device, the operator places the blade flat against the surface to be stripped and the orbital motion of the blade in the plane of the wall rapidly strips off the covering. The device may be used wet or dry.

It will be seen that a certain degree of flex-

ibility in the blade is advantageous in reducing the possibility of digging. in to the surface. Some designs for flexible blades are to be discussed. Alternatively or in addition, the blade may be mounted flexibly with respect to the drive unit. This may be achieved by making the boss 3 of tough flexible material such as rubber in the manner of a "cush" drive or simply by making the boss of steel, aluminium, or the like and fitting a washer of flexible material such

10 as plastics or rubber between the blade and the boss.

A conical guard 6 made for example of plastics material is attached to the gearbox housing and protects the operator from the blade. The presence of the guard also acts to prevent the blade being tipped ^τ too far from its desired operating position parallel to the surface, and thus additionally acts to prevent sur¬ face damage through careless use of the device.

The orbital motion which the blade undertakes when the device is in use is produced by a conventional ⁰ mechanism which will not be described in detail. Some types of such mechanism cause the blade to rotate or precess, as well as orbiting and this action may be desirable in some circumstances. In order to prevent this rotation, particularly on start-up, means may be ^ provided for inhibiting rotation of the blade, and one way of achieving this is shown in Figure 1. The mechanism comprises a coil spring 7 which is attached at one end to the casing 1 and extends parallel to the axis of the blade, through an aperture 8 in the guard 6 0 to end immediately behind the blade 4. A lever 9 is attached behind the blade and has a small lug 10 which enters the end of the spring. A similar effect can be obtained by striking the lug 10 out of the material of the blade itself. ⁵ The effect of this arrangement is to allow the orbital motion of the blade to continue unhindered, but

to inhibit rotation of the blade. Due to the flexib¬ ility of the spring th-e blade is allowed to rotate through a small arc, but cannot rotate continuously. A reciprocatory rotary motion about a small arc thus results, this motion being on top of the main orbital motion.

There will now be described various configur¬ ations of blade 4 which can be used with the stripper described above. The first three blades to be desc- ⁰ ribed with reference to Figures 2 to 10 are made from relatively rigid material such as 22 gauge steel or hard plastics material; those described with reference -to Figures 11 to 16 are made from flexible material such as spring steel; Figure 17 shows a combination 5 blade and Figures 18 and 19 show a blade system comp¬ rising a holder and annular blade.

Referring firstly to Figures 2, 3 and 4 there is shown a twelve-sided blade 4 having a generally concave profile shaped as shown in Figure 3. A 0 central aperture 11 is used to mount the blade on the boss 3 as described above. The blade typically has a diameter of approximately 150 mm. Each straight cutting edge 12 is separated from its neighbour by a radially inwards-directed slot 13, typically of 1 mm ⁵ width.

Figure 4 shows enlarged detail of the cutting edge, encircled A in Figure 3. It will be seen that the edge is ground or otherwise formed to a 15° cutting angle and is formed with a continuous burr 14. Typ- ° ically the burr protrudes downwards by approximately

0.254 mm. Immediately behind the blade is a peripheral land 15 of generally annular shape and typically of 10 mm width. This land is important in operation since it represents a largish flat surface which can be 5 pressed against the wall reasonably firmly without fear of damaging the wall. The land prevents the blade

from entering or piercing the surface being stripped by virtue of its surface area; meanwhile, because the burr is substantially smaller than the land, it (the burr) will penetrate the surface covering to enable removal of same, the depth of such penetration being limited by the adjacent land.

The segmenting of the blade by means of the slots 13 enables the individual segments to act indep¬ endently of one another on an uneven surface.

Figures 5, 6 and 7 show a blade similar to that just described but which is circular with a burred cutting edge 12 around its perimeter in the manner described previously.

This is a general-purpose blade useful for stripping a variety of wall coverings such as wallpaper, paint or ARTEX from flat regular wall or ceiling sur¬ faces.

Figures 8, 9 and 10 show another blade similar to that of Figures 1, 2 and 3 but in which the peripheral edge is serrated. The number of serrations 16 can be varied, but is typically 64. As shown, each circular serration 16 has a burr of its own.

This blade is primarily intended for plaster- like wall coverings, such as ARTEX, but is also useful for scratching or pricking wallpapers prior to stripping if exceptional difficulty is experienced.

The two blades shown in Figures 11 to 13 and 14 to 16 will be described together as they are very similar. Both blades are intended to be highly flexible and, to this end, are made of spring steel or similar, and are formed with sixteen radial slots 13, each 2 mm wide. The only difference between the two blades is that the first (Figures 11 to 13) is left entirely circular, while the second (Figures 14 to 16) is formed into 16 straight sided cutting edges.

The flexibility of the blades is shown in

Figures 12/13 and 15/16. In each case these represent the profile as manufactured (Figures 12 and 15) and the compressed working profile (Figures 13 and 16). These blades are typically 120 mm in diameter. As before the cutting edges are formed with a 15 cutting angle and continuous burr. A feature of these flexible blades is that the diameter increases as they are pushed towards the wall surface - this is represented by the dotted outline 28 in Figures 13 and 16. This increase in diameter enables an enhanced cutting action when the blade is moved backwards and forwards towards the surface, thus causing the diameter to increase and decrease.

The blade shown in Figures 17 to 19 is very similar to that described above with reference to Figures 11 to 13. The main differences are a slightly different' sectional shape (see Figures 18 and 19), and a slightly different arrangement for forming the cutting edge, as shown in the enlarged section of Figure 18. In this case, the peripheral land 15 terminates at the peripheral edge in a downwardly extending nose portion 30 extending around the perimeter. The bottom (i.e. surface-facing) surface of the nose portion 30 is sharpened to give an undercut edge 31 defining a cutting angle cλ- with the general plane of the blade. The angle «λ depends upon the particular covering to be stripped. Thus, the exact value of angle e*. will vary according to the anticip¬ ated circumstances of use, but angles in the range 16° to 34° have been found particularly successful for the normal range of wall coverings..

The blade shown in Figures 20 to 22 is again similar to that described above with reference to Figures 11 to 13, but with a double-ground cutting edge shown in detail in Figure 22. The cutting edge is actually formed by two ground surfaces 32,33, defining

respective angles X and Y, as shown. Angles X and Y may each range between 0°.and 60 , but a typical practicable range is: angle X between 26° and 40°; angle Y between 24° and 40°. It is found that increasing the angle X results in a faster cutting speed, but the blade is less able to cope with tough material. The square edge profile shown in Figure 21 and in outline in Figure 22 depicts the blade prior to grinding. It will be noted also that the slope of the

T Q peripheral land 15 is zero in this embodiment. In practice, it is found that the slope of land 15 can vary between 0° and 45°.

The blade shown in Figure 23 is a combination blade comprising an upper blade 17 similar to the

¹⁵ Figure 5 blade described above and a lower blade 18 similar to the Figure 14 blade described above. A spacer washer 19 separates the two.

The blade shown in Figures 24 to 26 is actually a blade "system", comprising a blade itself (reference ⁰ 4) and a two-part holder for the blade, which latter is attached to the boss 3 in the manner described above. As manufactured, the blade 4 is annular in shape and is planar, as shown in Figure 24. The action of screwing the two parts 20, 21 of the holder together by means of ^ screws 22 is to force the blade into a conical profile for cutting.

The underside of the upper part 20 of the holder is shown in Figure 26 and will be seen to consist of a segmented circular ridge 23 and, upon ° assembly, this fits into a correspondingly shaped groove 24 in the lower part 21. The inner diameter of the blade 4 is such as to fit readily and locate over the outer edge of the ridge 23. Radially outwardly from the ridge 23, the underside surface 25 of the upper part 20 is conical, this corresponding to an equivalent conical top surface 26 of the lower part 21.

Thus, when the two parts 20, 21 are brought together with the blade 4 inbetween, the blade is forced into a conical shape by virtue of being pressed between opposing surfaces 25 and 26 - see Figure 25.

The outer diameter of blade 4 is such that, when the parts 20 and 21 are fully tightened together, the perimeter of the blade protrudes below the undersurface 27 of the lower part 21 thus taking the place of the burr of previous embodiments. The peri¬ meter edge of the blade may be sharpened to a razor edge, or may be formed in the same manner as the perimeter of the blade of Figure 2 with a 15 ground edge and burr, or in the same manner as the blade of Figures 17 or 20.

Various modifications may be made to the device described above. For example, in order to enable the blades to be changed rapidly, a bayonet-type locking mechanism could be used to attach the blades to the boss 3.