GB2331265A

GB2331265A - A plastics moulding with a removable panel part

Info

Publication number: GB2331265A
Application number: GB9724010A
Authority: GB
Inventors: Keith Robert Weedon; Peter Arnall; Bernard Barton; Richard Johnson
Original assignee: Linpac Mouldings Ltd
Current assignee: Linpac Mouldings Ltd
Priority date: 1997-11-13
Filing date: 1997-11-13
Publication date: 1999-05-19
Anticipated expiration: 2017-11-13
Also published as: GB9724010D0; GB2331265B; GB2331265A9

Abstract

A plastics moulded component 1 has a line of weakness 3 by which a panel part 2 can be knocked-out of the component. The line of weakness has opposed sidewalls 4 and 5 which converge to shoulders 8 and 9 respectively and therethrough communicate with a V-section recess 7. At the apex of recess 7 is formed a membrane 10 along which the panel part 2 is to be broken off from the component 1 so that the resultant aperture in the component is defined by a clean edge. Preferably the component is rotationally moulded. The component may be in the form of a liquid storage tank or a lid for such a tank and preferably has two concentric lines of weakness (Fig 2).

Description

A PLASTICS MOULDING WITH A REMOVABLE PANEL PART

Technical Field and Background Art

2331265 The present invention relates to plastics moulded components and in particular to such components which have panel parts defined by readily apparent endless lines of weakness which facilitate removal of the panel parts from the respective mouldings to form apertures in the components. The removable panel parts are usually provided to facilitate the fitment of a particular element or structure to the moulding, such element or structure being received within the aperture presented when the panel part is removed. A typical example is a liquid storage tank in which the tank or a fitting such as a lid for the tank is manufactured as a plastics moulding and is provided with the removable panel part defined by a line of weakness so that such part may be removed to facilitate the fitment of a pipe or other element into the tank. often two or more endless lines of weakness are formed in the plastics moulding, one within the confines of the other (or concentrically in the case of circular lines of weakness) so that a panel part of a predetermined size or area may be removed as selected from the different sized panel parts defined by the various lines of weakness.

An example of a plastics moulded component in the form of a tank lid having a removable panel part is disclosed in our UK Patent 2 219 029. In this prior disclosure, the or each endless line of weakness which defines a panel part is formed by a channel of V-shape in lateral section. At.the apex of this V-shape channel is provided a membrane of the plastics material which may readily be cut with a knife to facilitate removal of the panel part (or the selected one of the panel parts where there are several concentric lines of weakness in the moulding). The panel part is easily removed by a fitter on site, typically by a plumber when installing a new tank which comprises the plastics moulding. It may be necessary to remove a panel part from a wall of the tank or a lid of the tank to facilitate fitment of a pipe. In practice, it is found that the fitter frequently removes the panel part by striking it with a hammer or other handy tool, particularly if a knife is not conveniently available. In such circumstances, whilst the panel part will break away along the line of weakness when subjected to an impact, it is often found, disadvantageously, that a ragged or rough edge results on the plastics moulding where it defines the aperture that is formed. Such a rough edge may be unacceptable as being unsightly or as not providing a reasonable seal with the component which is to be received in the aperture.

It is an object of the present invention to provide a plastics moulding which alleviates the aforementioned disadvantage whereby a clean edge may be formed upon the moulding when a panel part is removed therefrom along an endless line of weakness in response to an impact on that panel part.

Statement of Invention and Advantages

According to the present invention, there is provided a plastics moulded component having a panel part defined by a readily apparent endless line of weakness which facilitates removal of the panel part from the component to form an aperture in the component in response to an impact on the panel part; said line of weakness being formed by a channel having an outer part with opposed side walls which converge to a root part of the channel, said root part having a rec ess of Vshape in lateral section and shoulders through which the V-section recess communicates with the opposed side walls of the outer part so that the shoulders provide steps between the opposed side walls and the V-section recess, the apex of said V-section recess coinciding with a line of plastics of minimal thickness in the component along which the panel part is to break of f from the component.

It has been found that when a panel part of the plastics moulded component in accordance with the present invention is subjected to an impact, for example from a hammer, the panel part can be broken away from the moulding along the line of weakness and that a relatively clean edge is presented along that line which defines the aperture that is formed. It is believed that the side walls of the outer part and the shoulders of the root part of the line of weakness channel serve to concentrate the stresses in the plastics material of the component (which result from the impact on the panel part) to cause the panel part to break away with a clean fracture line along the line of weakness presented by the plastics of minimal thickness (or the plastics membrane) that is formed at the apex of the V-section recess. This has been found to be particularly so for plastics material such as polyethylene and polypropylene as may be used in the manufacture of liquid storage tanks, lids for such tanks or other plastics moulded components in which removable panel parts are desirable.

Preferably, the opposed side walls of the channel which converge to the root part are straight in lateral section (relative to the longitudinal extent of the channel) to present a truncated V-shape in lateral section as the side walls converge to the shoulders which provide the steps through to the V-section recess.

Conveniently, the plastics component of the present invention is formed by rotational moulding although it will be appreciated that other moulding techniques may be employed for its manufacture.

Drawings one embodiment of a plastics moulded component constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings, in which:- Figure 1 shows part of a wall of the component in a lateral section through a line of weakness; Figure 2 shows a larger part of the wall of the component with two concentric circular lines of weakness with a lateral section being taken through those lines, and Figure 3 diagrammatically illustrates part of a moulding tool within which the plastics component is rotationally moulded.

Detailed Description of Drawings

The plastics moulded component 1 of the present Example is formed, for example, of polyethylene by rotational moulding and typically will be a liquid storage tank or a lid for such a tank, a generally flat wall of which is shown as comprising the component in the drawings. The component 1 has a panel part 2 which is defined by a readily apparent endless line of weakness 3. The line of weakness 3 will usually be circular as indicated by the perspective of Figure 2 but it will be appreciated that other shapes may be provided (for example elliptical) depending upon the peripheral shape that is required for the aperture that is to be formed in the component 1 by removal of the panel part 2.

The line of weakness 3 extends longitudinally as a channel and in its lateral section (as shown in Figure 1) this channel is formed with an outer part having substantially straight opposed side walls 4 and 5 which converige as a truncated V- shape to a root part 6 of the channel. The root part 6 has a recess 7 which is of V-shape in lateral section and shoulders 8 and 9 that provide steps through which the side walls 4 and 5 respectively communicate with the V-sectional recess 7. At the apex of the V-sectional recess 7, there is formed a membrane or line of plastics 10 of minimal thickness which effectively constitutes the line of weakness that defines the panel part 2.

The panel part 2 is intended to be removed from the component 1 as the result of an impact from a hammer or other tool being applied to that part. In response to such an impact, the plastics material of the membrane 10 shears along the line of weakness so that the panel part is knocked-out to present an aperture in the component 1. The aperture will be defined, in substance, by the edge that is presented on the component along the break line of the membrane 10 and this edge is desirably of relatively clean or smooth form. With the component illustrated formed of polyethylene plastics material, it has been found that an acceptably clean edge is formed on the component when the panel is knocked out. This is believed to be due to the concentration of the stresses which result from the impact on the panel part 2 being directed through the convergent side walls 4 and 5 and by way of the steps or shoulders 8 and 9 so that they are concentrated through the Vsection recess 7 to cause the line of weakness to break cleanly along the membrane 10.

Usually two or more concentric lines of weakness will be provided in the component 1. Figure 2 shows the component having two concentric lines of weakness, the aforementioned line of weakness 3 providing an inner such line and there being an outer line of weakness 3A. The line of weakness 3A is formed similarly to the line 3 so that there are outer convergent side walls 4A and 5A which communicate through shoulders 8A and 9A with a V-section recess 7A, at the apex of which is formed a line 10A of a membrane or plastics of minimal thickness which defines a panel part of larger diameter than that def ined by the line of weakness 3. The two lines of weakness 3 and 3A provides a fitter with the option of selecting the aperture size from two diameters, either by knocking out an inner panel part 2 to form an aperture defined 1 along the membrane 10 or by additionally knocking out the panel part defined along the membrane 10A.

The component 1 is formed by a conventional rotary moulding process in a moulding tool, part of which is indicated at 12 in Figure 3. The part of the tool shown at 12 has the profile for defining the endless channels 3 and 3A so that as the plastics material is rotationally moulded onto the profiled wall of the tool 12, the face of the component 1 that is formed adjacent to the tool 12 will usually be smooth (depending upon the characteristics of the face of the tool 12 onto which the plastics is moulded) whilst the face of the moulded plastics remote from the tool 12 may be formed with a relatively uneven finish. However, it will be noted from Figure 3 (and also from Figures 1 and 2) that during the rotational moulding the component 1 is formed with a relatively uniform wall thickness which follows the contours of the moulding tool other than for those parts of the moulding tool which correspond to the formation of the V-section recesses 7 and 7A where the rotational moulding forms membranes or lines of plastics of minimal thickness.

Claims

C L A I M S

1. A plastics moulded component having a panel part defined by a readily apparent endless line of weakness which facilitates removal of the panel part from the component to form an aperture in the component in response to an impact on the panel part; said line of weakness being formed by a channel having an outer part with opposed side walls which converge to a root part of the channel, said root part having a recess of V-shape in lateral section and shoulders through which the V- section recess communicates with the opposed side walls of the outer part so that the shoulders provide steps between the opposed side walls and the V-section recess, the apex of said V-section recess coinciding with a line of plastics of minimal thickness in the component along which the panel part is to break off from the component.

2. A component as claimed in claim 1, in which in a lateral section of the line of weakness (relative to the longitudinal extent of the channel), the opposed side walls of the outer part of the channel are substantially straight to converge as a truncated V-shape to the shoulders of the root part.

3. A component as claimed in either claim 1 or claim 2, and comprising two said lines of weakness, one of which is disposed on the component inwardly of the other, whereby either of two panel parts may be removed optionally from the component to provide either of two different sized apertures in the component.

4. A component as claimed in any one of the preceding claims, in which the line or lines of weakness are circular.

5. A component as claimed in claim 4, when appendant to claim 3, in which the two lines of weakness are concentric.

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6. A component as claimed in any one of the preceding claims, formed as a rotational moulding.

7. A component as claimed in any one of the preceding claims, and moulded in polyethylene.

8. A component as claimed in any one of the preceding claims, and moulded with its removable panel part in a wall having a thickness of plastics which is substantially uniform other than for a line or membrane of minimal thickness which coincides with the apex of the V-sectional recess of the or each line of weakness.

9. A component as claimed in any one of the preceding claims, and in the form of a liquid tank or a lid for such a tank.

10. A plastics moulded component substantially as herein described with reference to the accompanying illustrative drawings.