GB2232179A

GB2232179A - An access cover

Info

Publication number: GB2232179A
Application number: GB8911800A
Authority: GB
Inventors: Francis Sidney Clark; Ronald Francis Clark; Anthony Burgess
Original assignee: CLARKSTEEL Ltd
Current assignee: CLARKSTEEL Ltd
Priority date: 1989-05-23
Filing date: 1989-05-23
Publication date: 1990-12-05
Anticipated expiration: 2009-05-23
Also published as: GB2232179B; GB8911800D0

Abstract

The access cover is pressed from metal plate and has a raised skid resistant pattern, formed by protuberances 2, on the upper surface of the plate 1. The protuberances are part-sheared or pressed from the plate 1 and have substantially vertical sides. Also, the protuberances are, conveniently, each of oval shape and formed in a so-called Durbar pattern. <IMAGE>

Description

An Access Cover This invention relates to an access cover and more particularly to a load-bearing access cover for an inspection chamber or access hole, e.g. a sewage manhole, in a traffic bearing surface, such as a road surface, a pavement or a floor of a building.

It is known to press access covers, e.g. in mild steel plate. These known pressed covers have surface protuberances in the form of small bulges to give the cover added strength and to provide the cover with some degree of skid resistance. These bulges in known pressed access covers are formed by male die parts which are very much smaller than the corresponding openings in the female die so that the transition from the plane of the plate is very gradual and the sides of tlie bulges are inclined at a relatively shallow angle to the plane of the plate.

According to the present invention, there is provided an access cover pressed from metal plate and having a raised pattern, formed by protuberances, on the upper surface of the plate, wherein the protuberances are pressed or part-sheared from the plate and have substantially vertical sides.

By forming the protuberances with substantially vertical sides, the skid resistance of the cover is enhanced and it is also believed that the cover will have greater rigidity and, if hot dip galvanised after cold forming, will be less prone to twisting and buckling during the galvanising process.

Each protuberance may have a substantially flat upper surface or may, for example, have a ridge extending along its upper surface.

Preferably, each protuberance is part-sheared from the plate and more preferably at least half-sheared from the plate.

The protuberances may be oval as seen in plan and in this case the protuberances are typically more than twice as long as they are wide.

Where the protuberances are oval, they are advantageously arranged so that the major axes of each pair of adjacent protuberances are transverse to one another.

The access cover may have a continuous peripheral flange pressed from the plate and in this case the plate may be formed in a single pressing operation, which includes forming the continuous peripheral flange, and part-shearing or pressing the surface protuberances from the plate.

The access cover may have a lifting device, which may be in the form of a recess pressed in the plate and a lifting bar attached to the plate and extending across the recess.

Conveniently, the cover is of mild steel or ductile iron.

Preferably the cover has a thickness of at least 1 mm and, more preferably, a thickness of at least 3 mm, and in the latter case the protuberances, preferably, have a height of at least 2 mm.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of one embodiment of an access cover according to the present invention, Figure 2 is a plan view of part of the cover shown in Figure 1, on an enlarged scale, Figure 3 is a section along the plane III-III in Figure 2, on an even larger scale, and also showing male and female die parts, and Figure 4 is a section similar to that of Figure 3 but showing a protuberance pressed, as opposed to semi-sheared, from the plate.

Figure 1 shows a pressed and galvanised steel access cover of rectangular shape. By way of example, the cover is made of 3 mm thick, flat mild steel plate 1, although the thickness of the plate may be from 1.6 mm to 4 mm. Typically, the steel is HL115 black steel.

The cover must be capable of bearing at least pedestrian traffic, and if of 3 mm thickness, it will bear significantly heavier loads.

The upper surface of the cover has a raised pattern, formed by protuberances 2 which are oval as seen in plan. The protuberances are formed in a so called Durbar pattern with the major axes of each pair of adjacent protuberances extending in a direction perpendicular to one another. The protuberances are more than twice as long as they are wide as seen in plan and are spaced from one another by a distance corresponding to their width. The major and minor axes of the protuberances 2 are preferably, as shown, arranged at an angle to the sides of the cover.

The cross-sectional shape of a protuberance 2 is shown in Figure 3. The protuberance has substantially vertical sides 3 with a flat upper surface 4 and very small radiusing at the junction 5 of the sides 3 and upper surface 4.

The protuberances 2 are part-sheared from the plate 1 in a manner -which will be described hereinafter. As a result of hnving been formed by a part-shearing action, the height of the protuberance is less than the thickness of the plate, and typically the height of the protuberance 2 is between one half and two thirds the thickness of the plate. Naturally, the lower surface of the plate has recesses which coincide with the protuberances in the upper surface of the plate, these recesses being less than the thickness of the plate, and corresponding in depth to the height of the respective protuberances.

The access cover has a continuous peripheral flange 6 pressed from the plate in a manner which is described in GB-B-2150619. The single flange 6 has four flange portions 6' each extending along a side of the cover; adjoining flange portions are integral with one another. No welding at the corners is, therefore, necessary.

The cover also includes two lifting devices in the form of dished recesses 7 in the plate 1 and a lifting bar 8 attached to the plate and extending across each respective recess 7. A lip 9 surrounds each recess. The cover also has frame 10 for framing the makers name.

The plate 1 is formed in a single operation which includes pressing the flange 6 around the cover, pressing the recesses 7, lips 9 and frame 10, and partshearing the protuberances 2 from the plate 1.

Each protuberance 2 is part-sheared from the plate 1 by a male die part or punch 11, which forces the material of the plate out of the plane of the plate and into an opening in a female die 12 by a distance determined by the length of the punch 11. The size of each punch 11 is only slightly less than the size of a corresponding opening in the die 12. Indeed, if the punch were to be inserted in a corresponding opening in the die, the horizontal clearance between the opening in the die 12 and the punch 11 on each side would be significantly less than the thickness of the plate 1, and typically only about 10 % of the thickness of the plate 1.

The part-shearing of 3 mm thick mild steel plate can be achieved using an 800 ton press.

The cover is provided with a protective coating, e.g. by hot dip galvanising, before or after cold forming, or both before and after cold forming.

Alternatively, the cover could be coated with bitumen.

The invention is not limited to rectangular covers or to covers with a continuous peripheral flange.

Instead of being rectangular the covers could be circular, and instead of being continuous the flange could be made in sections which may or may not be welded together. Also, the protuberances 2 need not have flat upper surfaces 4. Indeed, it may be advantageous to provide a ridge along the upper surface of each protuberance as this may further enhance the skid resistance of the cover. The protuberances 2 need not be oval and could for example be square or of diamond shape. Also the cover could be formed of ductile iron instead of mild steel.

The protuberances could be pressed, instead of being part-sheared, from the plate. A protuberance 2 formed in this manner is shown in Figure 4. In this case a male die part or punch 11' enters an opening in a female die 12' and passes into the opening by a distance at least equal to the thickness of the plate. The horizontal clearance between the punch 11' and the female die 12' is equal to or substantially equal to the thickness of the plate, and in no event is more than 10% greater than the thickness of the plate in order to provide the protuberance with substantially vertical sides.

Other modifications will be apparent to persons skilled in the art without departing from the scope of the invention defined by the appended claims.

Claims

1. An access cover pressed from metal plate and having raised a pattern, formed by protuberances, on the upper surface of the plate, wherein the protuberances are pressed or part-sheared from the plate and have substantially vertical sides

2. An access cover as claimed in Claim 1, wherein each protuberance has a substantially flat upper surface.

3. An access cover as claimed in Claim 1, wherein each protuberance has a ridge extending along its upper surface.

4. An access cover as claimed in any one of Claims 1 to 3, wherein each protuberance is part-sheared from the plate.

5. An access cover as claimed in Claim 4, wherein each protuberance is at least half-sheared from the plate.

6. An access cover as claimed in Claim 4 or Claim 5, wherein each protuberance has been part-sheared from a flat plate by a punch which forced material of the plate into an opening in a die, the horizontal clearance between the punch and the opening, if the punch wero to have entered the opening, being less than the thickness of the plate.

7. An access cover as claimed in any one of Claims 1 to 3, wherein each protuberance has been pressed from a flat plate by a punch which entered an opening in a die with a clearance on each side substantially equal to the thickness of the plate.

8. An access cover as claimed in Claim 7, wherein the punch passed into the opening by a distance at least equal to the thickness of the plate.

9. An access cover as claimed in any one of the preceding claims, wherein the protuberances are oval as seen in plan.

10. An access cover as claimed in Claim 9, wherein the protuberances are more than twice as long as they are wide as seen in plan.

11. An access cover as claimed in Claim 9 or Claim 10, wherein the major axes of each pair of adjacent protuberances are transverse to one another.

12. An access cover as claimed in any one of the preceding claims, and having a continuous peripheral flange pressed from the plate.

13. An access cover as claimed in Claim 12, wherein the plate has beeii formed in a single operation which included forming the continuous peripheral flange, and part-shearing or pressing the surface protuberances from the plate.

14. An access cover as claimed in any one of the preceding claims, wherein the cover has a lifting device.

15. An access cover as claimed in Claim 14, wherein the lifting device is in the form of a recess pressed in the plate and a lifting bar attached to the plate and extending across the recess.

16. An access cover as claimed in any one of the preceding claims, wherein the cover is of mild steel or ductile iron.

17. An access cover as claimed in any one of the preceding claims, wherein the cover has a thickness of at least 1 mm.

18. An access cover as claimed in any one of the preceding claims, wherein the cover has a thickness of at least 3 mm.

19. An access cover as claimed in Claim 18, wherein the protuberances have a height of at least 2 mm.

20. An access cover substantially as hereinbefore described with reference to Figures 1 to 3, or Figures 1, 2 and 4, of the accompanying drawings.