GB2567167A

GB2567167A - Cover

Info

Publication number: GB2567167A
Application number: GB1716184.5A
Authority: GB
Inventors: Francis Clark Ronald
Original assignee: CLARK DRAIN Ltd
Current assignee: CLARK DRAIN Ltd
Priority date: 2017-10-04
Filing date: 2017-10-04
Publication date: 2019-04-10
Anticipated expiration: 2037-10-04
Also published as: GB2567167B; GB201716184D0

Abstract

A method of manufacture of a cover 10, such as a manhole cover, comprising a cover plate 12 and a series of strengthening formations 24 integrally formed with the cover plate, comprising supplying a plastics material to a mould cavity shaped to define a cover plate section and a strengthening formation section, where an injection inlet is spaced from the strengthening formation section. The cover plate section may increase in thickness with distance from the inlet; or it may have uniform thickness. Preferably the plastics material is a fibre reinforced material. Preferably, the strengthening section may comprise a series of walls defining a hexagonal honeycomb structure. A slip or skid resistant surface may be integrally moulded on the cover plate. The inlet position helps prevent weld lines causing weakness in the cover. A cover is further provided.

Description

This invention relates to a cover, and in particular to a cover of the type used to cover an access opening to an underground chamber or sub-surface system. Such covers are commonly known as manhole covers.

Where covers of this type are located on trafficked surfaces, there is a need for the covers to be of high strength in order to have a sufficiently high weight bearing capacity as to bear the weight of vehicles. By way of example, the covers may be required to have a load bearing capacity sufficient to bear a load in the region of 12.5 tonne to be considered suitable for driveway and pavement use. Typically, in order to be of sufficient weight bearing capacity, covers used in these areas have been of metallic form. There is a desire to use relatively light weight plastics materials in such covers.

The use of plastics materials in the formation of covers with a lower weight bearing capacity is well known. By way of example, plastics material covers are used in applications in which the maximum required weight bearing capacity is in the region of 2.5-3.5 tonne. Such covers typically take the form of a cover plate provided, on its underside with a series of strengthening formations. The strengthening formations are formed integrally with the cover plate during the moulding of the cover. To date, covers of this general type have not been able to bear the higher loads now required, as set out in a recent revision to European standards.

It has been found that, during the manufacture of plastics material moulded covers, where the plastics material flows around or through the mould cavity in a number of directions or following a number of routes, interfaces may be formed where material that flowed in one direction or route through the mould abuts material that flowed in another direction or route through the mould cavity. These interfaces form as a result of the material having cooled a little after introduction into the mould before the different material sections become abutted with one another. Although the materials that flowed in the different directions along different routes will adhere to one another at the interfaces, and limited load transmission may occur between these material sections, the presence of these interfaces results in the moulded cover not being of homogenous form, and the interfaces represent relatively weak points in the cover, limiting its weight bearing capacity as the load transmission capacity between the material sections is limited.

It is an object of the invention to provide a method of manufacture of a cover, and a cover manufactured in accordance with the method, in which at least some of the disadvantages associated with known covers are overcome or are of reduced impact.

According to the present invention there is provided a method of manufacture of a cover comprising a cover plate and a series of strengthening formations integrally formed with the cover plate, the method comprising the steps of supplying a plastics material to a mould, the mould having a mould cavity shaped to define a cover plate section and a strengthening formation section, where a material inlet by which the plastics material is supplied to the mould cavity is located to supply the plastics material to the cover plate section at a location spaced from the strengthening formation section.

The cover plate section may be of non-uniform thickness, for example being of relatively small thickness adjacent the material inlet, gradually increasing to a relatively large thickness at a location spaced from the material inlet. By way of example, the cover plate section may increase in thickness by around 1-2mm from the relatively small thickness adjacent the material inlet to the relatively large thickness at the location spaced therefrom. However, this is not essential to the invention and arrangements in which the cover plate section is of uniform thickness are also possible within the scope of the invention

By supplying the plastics material to the mould cavity via a material injection point or inlet located where no strengthening formations are to be formed, the material supplied to the mould cavity is urged to flow in a direction preferentially filling or substantially filling the cover plate section before entering the strengthening formation section. The use of a cover plate section of non-uniform thickness may further aid in preferentially filling the cover plate section. Once the cover plate section is filled or substantially filled, plastics material flows into the strengthening formation section, gradually substantially uniformly filling the strengthening formation section. In this manner, the formation of interfaces or ‘weld lines’ as described hereinbefore can be reduced or avoided, enhancing the load bearing capacity of the cover.

Preferably, the plastics material is a fibre reinforced plastics material. The avoidance of the formation of interfaces where a fibre reinforced plastics material is used is especially advantageous as the presence of such interfaces in a fibre reinforced plastics material product represent significant weak points in the product as the reinforcing fibres do not extend across the interfaces.

The strengthening formation section may be shaped to define a series of walls defining hexagonal pockets in the underside of the finished cover, the strengthening formations being of honeycomb-like form or appearance. It will be appreciated, however, that this represents just one form of strengthen formation that may be used, and the invention is also applicable to other designs.

Conveniently, a surface of the cover plate opposite that from which the strengthening formations extend is provided with a plurality of raised features defining a slip or skid resistant surface. The raised features are conveniently integrally formed with the cover plate as part of the moulding process.

The material inlet may be located to the same side or surface of the cover plate section as the strengthening formation section. However, the reverse is also possible within the scope of the invention.

The invention also relates to cover plate manufactured in accordance with the method defined hereinbefore. In accordance with another aspect of the invention, therefore, there is provided a cover comprising a plastics material element defining a cover plate and a series of strengthening formations integrally formed with the cover plate, wherein the cover includes a region free of strengthening formations in the vicinity of an injection feature. The cover plate may be of non-uniform thickness, for example being of relatively small thickness adjacent the injection feature and of relatively great thickness at a location spaced from the injection feature.

The invention will further be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a plan view of a cover in accordance with an embodiment of the invention;

Figure 2 is a view illustrating the underside of the cover of Figure 1;

Figure 3 is a sectional view illustrating the cover of Figures 1 and 2; and

Figure 4 is a diagrammatic view illustrating part of a mould for use in the manufacture of the cover.

Referring to Figures 1 to 3 of the accompanying drawings, a cover 10 is illustrated. The cover 10 is of moulded, preferably injection moulded, fibre reinforced plastics material, and is intended for use in closing or covering access openings, cavities or the like, sometimes referred to as manholes, in footpaths and trafficked areas such as pavements and driveways. The cover 10 is designed and manufactured in such a manner as to be of good weight bearing capacity. In the arrangement shown in the accompanying drawings, the cover 10 is designed and manufactured in such a manner as to be able to safely bear a load of at least 12.5 tonne. However, it will be appreciated that the weight bearing capacity of the cover is a matter of design, and that the invention is also applicable to covers having other weight bearing capacities, either lower or higher than the value mentioned above.

The cover 10 includes a part defining cover plate 12 of generally circular shape. The cover plate 12 includes an upper surface 14 and a lower surface 16. Integrally moulded with the cover plate 12, on the upper surface 14 thereof, are a series of small projections 18, the primary purpose of which is to reduce the risk of vehicles passing over the cover 10 from slipping or skidding. Whilst one pattern of projections 18 is illustrated, it will be appreciated that the projections 18 may be of range of different shapes and sizes, and may be laid out in a range of patterns, without departing from the scope of the invention.

The outer periphery of the cover plate 12 is formed with an integral downwardly depending lip 20 defining, in part, an annular channel 22 which, in use, receives part of a frame (not shown) defining the opening to be closed or covered by the cover 10, the interengagement between this part of the cover 10 and the frame supporting the cover 10 in position, resisting lateral movement thereof in use and allowing loads borne by the cover 10 to be transmitted to the frame and the ground in which the frame is installed.

Integrally formed with the cover plate 12, and depending downwardly therefrom, are a series of reinforcing or strengthening formations in the form of walls 24, the walls 24 interconnecting with one another to form a series of hexagonal pockets, giving the underside of the cover 10 a honey comb-like appearance, as shown in Figure 2. As best seen in Figure 3, the walls 24 are not all of the same height, the heights of the walls 24 being such as to give the underside of the cover 10 a curved profile.

As shown in Figures 2 and 3, close to its centre the cover 10 is devoid of strengthening formations, the walls 24 defining a central, relatively large hexagonal chamber or recess at this point.

Although not shown in the drawings, the thickness of the cover plate 12 may be nonuniform. For example it may taper from a minimum at or close to the centre thereof to a maximum close to the periphery thereof. The variation in thickness between these locations may be in the region of 1-2mm. Similarly, the strengthening walls 24 may be of tapering thickness, for example being of maximum thickness adjacent the cover plate 12, tapering to a reduced thickness at their ends remote from the cover plate 12.

The cover 10 is manufactured by injection moulding using a mould 26 (see Figure 4) having a mould cavity 28 shaped to define a cover plate section 28a in which the cover plate 12 is formed and a strengthening formation section 28b in which the walls 24 are formed, these sections opening into one another such that the walls 24 are formed integrally with the cover plate 12 during the moulding operation. The mould includes an injection point 30 which opens into the mould cavity at substantially the centre of the cover plate section, and hence at a location spaced from any ofthe strengthening walls

24. In the arrangement shown, the injection point 30 is located to the same side as the strengthening walls, but is may be located to the other side, if desired.

During manufacture, a suitable fibre reinforced plastics material is injected via the injection point 30 into the mould cavity 28 with the mould cavity 28 orientated such that the cover plate section 28a is uppermost, the strengthening formation section 28b extending downwardly from the cover plate section 28a. The shape of the mould cavity

28, in particular the lack of strengthening features in the vicinity of the injection point 30 and the tapering thickness of the cover plate (where provided), is such that the injected material preferentially fills the cover plate section 28a. Only once the cover plate section 28a is filled or substantially filled does the material enter the strengthening formation section 28b, gradually and uniformly filling the entirety of the strengthening formation section 28b from the upper end thereof adjacent the cover plate section 28a to the lower end thereof remote from the cover plate section 28a, the filling of the strengthening formation section 28b being substantially uniform across the entire cavity

28. In this manner, it will be appreciated that the formation of interfaces where material flowing along two different routes through the mould cavity 28 move into contact with and abut one another is avoided or significantly reduced. The presence of such interfaces forms significant weak points in a moulded structure, and so the avoidance of the formation thereof, or reduction in the number of such interfaces formed, allows a significant enhancement in the load bearing capacity of the cover to be made. Furthermore, as, where such interfaces are present, the reinforcing fibres do not extend across the interface, the avoidance of the formation of such interfaces is especially advantageous where a cover is formed from a fibre reinforced plastics material. It will be understood that, if desired, the moulding operation may be undertaken with the mould in different orientations to that described above.

It will be appreciated that the use of the method described hereinbefore in the manufacture of a cover is advantageous in that plastics material covers of significantly increased weight bearing capacity compared to known plastics material covers can be provided.

Although one embodiment of the invention is described hereinbefore with reference to the accompanying drawings, it will be appreciated that a wide range of modifications and alterations may be made thereto without departing from the scope of the invention as defined by the appended claims. By way of example, the strengthening formations may take a wide range of shapes and layouts, and the invention is not restricted to the hexagonal, honey comb-like structure illustrated in the accompanying drawings, although this does represent one way of achieving a cover of good load bearing capacity.

Claims

1. A method of manufacture of a cover comprising a cover plate and a series of strengthening formations integrally formed with the cover plate, the method comprising the steps of supplying a plastics material to a mould, the mould having a mould cavity shaped to define a cover plate section and a strengthening formation section, where a material inlet by which the plastics material is supplied to the mould cavity is located to supply the plastics material to the cover plate section at a location spaced from the strengthening formation section.

2. A method according to Claim 1, wherein the cover plate section is of nonuniform thickness, being of relatively small thickness adjacent the material inlet, gradually increasing to a relatively large thickness at a location spaced from the material inlet.

3. A method according to Claim 2, wherein the cover plate section increases in thickness by around 1-2mm from the relatively small thickness adjacent the material inlet to the relatively large thickness at the location spaced therefrom.

4. A method according to Claim 1, wherein the cover plate section is of uniform thickness.

5. A method according to any of the preceding claims, wherein the plastics material is a fibre reinforced plastics material.

6. A method according to any of the preceding claims, wherein the strengthening formation section is shaped to define a series of walls defining hexagonal pockets in the underside of the finished cover, the strengthening formations being of honeycomblike form or appearance.

7. A method according to any of the preceding claims, wherein a surface of the cover plate opposite that from which the strengthening formations extend is provided with a plurality of raised features defining a slip or skid resistant surface.

8. A method according to Claim 7, wherein the raised features are integrally formed with the cover plate as part of the moulding process.

9. A method according to any of the preceding claims, wherein the material inlet is located to the same side or surface of the cover plate section as the strengthening formation section.

10. A method according to any of Claims 1 to 8, wherein the material inlet is located to the opposite side or surface of the cover plate section than the strengthening formation section.

11. A method according to any of the preceding claims, wherein the material inlet is located at a central part of the cover plate section.

12. A cover plate manufactured in accordance with the method of any of Claims 1 to 11.

13. A cover comprising a plastics material element defining a cover plate and a series of strengthening formations integrally formed with the cover plate, wherein the cover includes a region free of strengthening formations in the vicinity of an injection feature.

14. A cover according to Claim 13, wherein the cover plate is of non-uniform thickness, being of relatively small thickness adjacent the injection feature and of relatively great thickness at a location spaced from the injection feature.

15. A cover according to Claim 13, wherein the cover plate is of uniform thickness.