GB2057782A - Accessory boxes - Google Patents

Abstract

A moulded accessory box of plastics material is provided with inner and outer wall recesses (12, 13) overlapping to form knock-out portions, the recesses having walls parallel or diverging in the directions of withdrawal of dies used for moulding the box so that no retractable die cores are required during manufacture. The recesses may be of uniform depth or of lesser depth where they overlap to form a knock- out. <IMAGE>

Description

SPECIFICATION Accessory boxes This invention relates to accessory boxes for containing switches and other electrical components.

Such boxes are commonly mounted on surfaces such as walls to contain various components and are generally provided in their sides or base with holes to receive cables passing from the outside to the inside of the box.

These holes may be provided by a number of knock-out portions in the walls of the box which are knocked out at the time of installation to provide the required holes. Unwanted holes are blocked by the knock-out portions which remain in place. The box is then closed apart from the holes through which cables actually pass, minimising the risk of water, wall plaster or other unwanted material entering the box.

Such boxes are commonly made of steel or of moulded thermoplastics material such as polyvinyl chloride. With steel boxes the knockout portions generally have to be provided by punching out the knock-outs and then reinserting the punched-out pieces in the holes.

With plastics boxes it is possible to avoid this operation by forming the boxes by moulding and providing moulds such that the peripheries of the portions to be knocked out have a wall thickness which is significantly less than the thickness of the surrounding wall. This reduced thickness provides a line of weakness which enables the portion to be knocked out without damaging the surrounding wall. However to make such boxes it has hitherto been necessary to use male mould dies with retractable cores, the cores being retracted before the male die is removed from the moulded box. This feature increases the cost and complexity of the die and significantly reduces the rate of production which may be achieved with a given moulding machine.

It is an object of the present invention to provide an accessory box having knock-outs which can be made by moulding of plastics material without the use of retractable cores.

According to one aspect of the invention, there is provided a moulded box of plastics material of which the inner and outer surface of at least one wall are provided with respective recesses, the recesses overlapping to define an aperture area in the wall and the overlapping portions of the recesses being of lesser depth to form a knock-out wall portion occupying the aperture area which may be knocked out to form an aperture, the walls of the recesses being parallel or divergent in the direction of withdrawal of respective mould dies used to form the inner and outer walls so that no retractable cores are required during moulding.

The material of the box may be a thermoplastic such as PVC (polyvinyl chloride) and the box may be moulded using a simple twopart mould, a male die forming the inner surface of the box and a female die the outer surface. The box normally comprises a flat rectangular bottom and four upstanding walls, the box as moulded being open: when the box is installed it will be closed by a cover which may be attached to the box by screws or other known means. The recess on the inner wall of the box will extend from the aperture area to the edge of the open box and its walls must be parallel or divergent in this direction as it is in this direction that the male die is removed after moulding: the recess in the outer wall, conversely, must extend in the direction towards the bottom of the box.

It is normally desirable to provide a number of similar recesses on the walls in order to give a choice of apertures which may be formed by knocking-out. It may also be desirable to provide knock-out portions in the bottom of the box but these do not require overlapping recesses.

The knock-out portions are attached to the remainder of the box by thin portions of moulded material around their peripheries.

The thickness of these thin portions may fall to zero, in which case provision must be made to hold the knock-out portions in place before use. This may be achieved by providing a thin bridge of the moulded material at one point on the periphery connecting the knock-out portion to the surrounding material. During the moulding operation it may be necessary to provide such a bridge in any case as the bridge may be required to allow flow of the plastics material during moulding.

According to another aspect of the invention, the walls of the box are provided with overlapping inner and outer recesses as described above but in this case the depths of the recesses are such that a portion of wall material of finite thickness occupies the area of overlap of the recesses. This portion may be of suitable thickness to itself form a knockout and thus the recesses may have a constant depth, i.e. be unrelieved. This arrangement can simplify construction of the dies and avoid the need to provide side cores to define the lateral edges of the knock-out discs described above.

Accessory boxes according to the invention will be described by way of example with reference to the accompanying drawings in which: Figure 1 is a plan view of a box according to one embodiment of the invention, Figure 2 is a section along A-A of Fig. 1, Figure 3 is a view from the outside of the box of a wall of the box, Figure 4 is a section of part of the bottom of the box, Figure 5 is a section of walls and bottom of a box according to another embodiment of the invention, Referring to Fig. 1, an accessory box is moulded of a thermoplastic material such as PVC and comprises a bottom 1 provided with holes 2 to receive screws whereby the box may be mounted on a surface such as a wall.

The box is enclosed by walls 3 and 4 containing respective knock-out portions 5 and 6.

The box is made by moulding in known manner, the inner surface of the box being formed by a male mould die and the outer surface being formed by a female die.

As most easily seen from Fig. 2, the walls containing knock-out portions are provided on their inner surfaces with recesses 7. Recesses 7 extend to the upper edge of the wall (i.e.

the edge remote from the bottom) and have substantially parallel sides so that no retractable core is needed when these recesses are formed on moulding of the box. If these sides converged upwardly a retractable core would be required in the male die to form such a recess inside the box.

The outside wall of the box is provided with similar recesses 8 (see Fig. 3) which are also parallel-sided but these recesses extend downwardly, i.e. in the direction of the box bottom.

Again, no retractable cores on the female die are required to form these recesses on moulding.

Recesses 7 and 8 overlap to define a circular area 9 and the depths of the recesses are such, in relation to the thickness of the wall, that this circular area forms an aperture in the wall through which a cable or the like may pass from the outside to the inside of the box.

However the dies are shaped such that the depth of the recesses in this circular area of overlap are less than the recess depths in the non-overlapping areas. The effect of this arrangement is that on moulding the overlap of the recesses defines a circular aperture which is closed by a circular disc which is joined to the surrounding wall at its periphery by only a thin portion of material. The discs can then easily be knocked out to open the aperture by exercising only a moderate force on the disc and the disc is removed without risk of breakage of the adjacent plastics material of the wall.

The bottom of the box is also provided with knock-out portions 10 but in this case no special arrangement is required to avoid the use of retractable cores and so there is no need to provide overlapping recesses. A knock-out portion 10 of the bottom of the box is shown in Fig. 4. Around most of the periphery of portion 10 the thickness of the material gripping the knock-out portion 10 to the rest of the bottom 1 is very small and may even be zero, so that the knock-out portion would fall out without any force at all being exerted. In order to prevent this a small portion of extra material 11 is provided at one point of the periphery to hold the disc in place until a force is exerted on it. A similar portion of extra material is provided for the knock-out discs formed by recesses 7 and 8 to avoid accidental removal of the dices.The portion 11 is small enough to fracture easily, without damaging the rest of the box, wheri the respective disc is knocked out.

The knock-out portions in the embodiment described above are circular but they may be of any shape (such as square or hexagorial) which does not require the use of retractable cores to form them in the manner described above.

Depending on the dimensioris of the box and the knock-out portions, the bottom and walls of the box may be provided with any desired number of knock-out portions, formed by a corresponding number of overlapping inside and outside recesses in the case of the wall knock-out portions.

In use, the box may be attached to a surface by screws or the like passing through holes 2, which are elongated in one dimen sion to allow for play during attachment. The required number of discs may be knocked out before or after mounting. Cables passing through the knock-out apertures may be surrounded by a rigid tube which fits into the apertures and may be clamped in place by nuts and/or flanges attached to the Outside of the tube, the nuts or flanges abutting the inside and outside surfaces of the wall or bottom. When only the number of knock-out portions required to admit cables are removed the walls and bottom of the box are then substantially impervious to material, such as wall plaster, which might otherwise enter the box.The box may thus be mounted in a recess in a wall and subsequently grouted in with plaster without unwanted material penetrating the box. After installation the box may be closed with a lid in known manner: the lid may be secured by screws engaging threaded portions of the interior of the box, not shown in the drawings.

Another possible arrangement of the knockout in a wall of the box is shown in Fig. 5. In this case the wall is provided with overlapping recesses 1 2 and 13, as in the embodiment of Fig. 1, but the depths of the recesses are constant and such that a thin portion of the wall material remains in the overlapping portion, instead of an aperture. The thickness of this portion is low enough to provide a satisfactory knock-out. When the material of the box is polyvinylchloride a suitable thickness for the knock-out portion is 0.38 mm.

The sides of the recesses are again parallel or divergent so that the mould dies do not require retractable cores.

The arrangement of Fig. 5 has the advantage that the depth of the recesses may be constant throughout, no relieved portion being required to provide a disc closing the aperture formed by overlap of the recesses. The dies used for moulding may thus be simpler and cheaper.

Fig. 5 also shows an alternative method of providing a knock-out portion in the bottom of the box. The knock-out portion is defined by a notch line 14 formed inside the box and surrounding an area 15, constituting the knock-out. The notch line 1 4 is broken by a bridge which enables the material of the box to flow. The thickness of the material between the notch and the outside surface, i.e. the material which is broken on knocking-out, is suitably 0.38 mm.

Claims (8)

1. A moulded accessory box of plastics material of which the inner and outer surfaces of at least one wall are provided with respective recesses, the recesses overlapping to define an aperture area in the wall, the aperture area being obturated by a knock-out portion of the plastics material of the wall which may be knocked out to form an aperture, the walls of the recesses being parallel or divergent in the direction of withdrawal of respective male and female mould dies used to form the inner and outer walls of the box so that no retractable cores are required during moulding.

2. A box according to Claim 1, in which the overlapping portion of at least one of the recesses is of lesser depth than the remainder of the recess, the portion of lesser depth comprising the knock-out portion.

3. A box according to Claim 2, in which the knock-out portion is attached to the remainder of the box by at least one breakable bridge of plastics material.

4. A box according to Claim 1, in which the recesses are of uniform depth.

5. A box according to any preceding claim, in which the knock-out portions are circular.

6. A box according to any preceding claim, in which the bottom of the box is also provided with at least one knock-out portion.

7. A box according to any preceding claim, in which the plastics material is polyvinyl chloride.

8. An accessory box, substantially as herein before described with reference to Figs. 1 to 4 or Fig. 5 of the accompanying drawings.