The present invention relates to an improved access hole cover and frame assembly incorporating a seal between the cover and the frame, and to a method of manufacturing a frame forming part of said assembly.

Access holes ("manholes") are closed by means of a frame fixed within the ground surrounding the hole, and a cover which fits within the frame, the two being referred to as a "cover and frame assembly". The cover may be of the raised edge type, in which the outer periphery of the cover extends over the frame, so that the gap between the frame and the cover is protected from ingress of water, dirt etc. A preferred alternative is one in which the cover does not have such a raised edge and is to all intents and purposes flush with the frame, leaving exposed the gap between cover and frame. The present invention is intended primarily, though not exclusively, to apply to the latter "flush" type of cover and provides an improved means of sealing the gap between cover and frame.

Conventionally, covers of the "flush" type have been sealed within the frame by means of a horizontally disposed rubber seal fixed to a ledge running around the interior of the lower region of the frame such that the weight of the cover bearing down upon this seal effects the sealing action. There are two disadvantages with this arrangement, known as "base sealing", one being that on removal of the cover from the frame, which is done frequently, any dirt which has collected in the gap will fall down and land on the ledge, causing ineffective sealing and premature wear. The other disadvantage is that as vehicles pass over the cover whilst it is seated in the frame, there will be a rocking effect on the base seal which causes increased wear on the seal, and may cause the sealing between the cover and the frame to be broken.

According to a first aspect of the present invention there is

provided a cover and frame assembly for an access hole, the frame having a lower section for engaging with and supporting a cover when the latter is seated within the frame, and an upper section incorporating a substantially vertically disposed resiliently deformable seal which is deformed by insertion of the cover within the frame to provide effective sealing of the gap between cover and frame.

Conveniently, the frame and the cover are both made from injection moulded composite material, although in accordance with one preferred aspect of the invention, described more fully hereinafter, the frame may be of metal, e.g. aluminium.

In order to provide seating means for the seal, a recess or insert is incorporated into the frame during manufacture. Where an insert is employed, this may be permanently secured (for example by integral moulding with the frame) to the interior surface of the upper region of the frame, and including detent means for releasably securing the seal within the insert. Such an arrangement provides ease of assembly, the seal simply being pushed into the insert, as well as ease of replacement when the worn seal is simply pulled out of the insert and replaced. The detent may be formed in the recess or insert and/or may comprise a sealing strip.

Preferably, where the frame is moulded, the insert may be an aluminium extrusion incorporating two separate detents which engage with cooperating members on the seal itself.

Conveniently, the seal is generally "D" shaped in cross section with small flanges extending above and below, these engaging within the detents in the insert to releasably secure the seal within the insert. Alternatively, the seal may comprise a main body portion located in the insert or recess and a plurality of fin members providing the sealing surfaces.

The exact shape of the seal is not important, merely that it

should be of sufficient size, having regard to the size of the gap between the cover and the frame when the cover is seated within the frame, to be deformed by insertion of the cover thereby provide the sealing effect.

One important advantage of the present invention is that the seal has a self wiping effect as the cover pushes past the seal as it is inserted within the cover such that the sealing surface between the seal and the cover is always kept free from dirt, thus prolonging the life of the seal.

The other advantage is that because the seal is disposed substantially vertically and not horizontally as with the closest prior art arrangements, any dirt which does fall into the gap between cover and seal will, when the cover is removed, continue to fall into the access hole rather than collecting on the seal.

According to a second aspect of the present invention there is provided a method of manufacturing a frame for use in a cover and frame assembly for an access cover, the method comprising laying in a mould an insert having detent means for releasably securing a seal thereto, placing a structure including fibres into the mould and injecting a liquid resin into the mould having first masked the detent means in the insert to prevent ingress of resin, allowing the assembly to set or cure, demoulding the frame with the insert integrally moulded therewith and removing the masking to reveal the detent means, and inserting one or more cooperating flange members of a resiliently deformable seal into said detent means to releasably secure the seal to the insert.

By the term "masking" is meant both taping over the access to the detents in the insert by masking tape, or filling with some kind of packing or stopping material, or a combination of the two.

As mentioned above, covers of the 'flush' type have been subject to rocking movement which very much increases wear. As well as improving matters by the use of a vertical seal in accordance with the invention, it is desirable to manufacture the frames and the covers very flat and to very close tolerances. Where the covers are moulded this is possible, but hitherto the use of metal frames has been unsatisfactory as the tolerances needed cannot be achieved at commercial prices.

According to a third aspect of the present invention there is provided a method of manufacturing an access cover frame from prefabricated parts to very close tolerances which comprises providing side sections of the desired profile and length; fitting prefabricated corner sections of complementary profile into the ends of the side sections to form a frame with a curable adhesive included to bond the corners to the sides; before curing the adhesive, setting the frame to the exact desired tolerances on a jig; partly or completely curing the adhesive to fix the frame at the desired dimensions; and thereafter, if required, completing the curing of the adhesive to produce an accurate product.

The method of the third aspect has great advantages over previous methods of producing frames. It enables large (e.g. three-quarter meter square) frame to be produced very flat and to tolerances of plus or minus 0.25 mm from metal, which is unnattainable by normal methods. Since no moulding is involved, no moulds are needed for the frame and the size of frame produced can be altered simply by cutting the side sections to size. A mould for die casting the corner oieces is needed but the corner piece is the same size for a wide range of frame sizes and therefore only one mould for this is needed. The covers can be moulded as before, which allows very close tolerances, and the cover and frame assembly is then very accurate and very flat so that no rocking occurs when a vehicle passes over it and the gap into which dirt can pass is reduced

to a minimum.

The sections preferably include a vertical seal as before and a suitable recess for receiving the seal can be formed in them during manufacture. Similarly, the corner sections include a corresponding recess and the seal can therefore extend completely round the frame. Conveniently, the seal can be formed as an endless loop for a given frame size to prevent gaps. The seal is preferably locked in place by means of a removable locking strip. The latter enables easy replacement of worn seals in service.

The resin used is preferably an epoxy resin which is very strong and can be partially cured or 'gelled' by a short application of heat to stabilise the frame for further handling and final curing. The term 'curing' includes 'allowing to cure' where heat or other non-ambient conditions are not required.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is a cross sectional view through the frame and cover assembly of one embodiment of the present invention, showing the frame;

Figure 2 is a detailed cross sectional view of the frame and cover assembly, showing the deformed and undeformed shapes of the seal;

Figure 3 is a partial cross sectional view through the cover;

Figure 3(A) is a side view of the cover;

Figure 4 is a plan view from underneath the cover;

Figure 5 is a plan view from above the cover;

Figure 5(i) through 5(iv) illustrate the surface detail on the cover;

Figure 6 is a side view of the frame;

Figure 6(A) is a plan view from above the frame;

Figure 6(B) is a partial cross-section through the frame;

Figure 7 is a similar view to Figure 6 of a second embodiment;

Figure 8 is a similar view to Figure 6(A) of the the embodiment of figure 7; and

Figure 9 is a section of line X-X in figure 8 on an enlarged scale.

Referring to the drawings, in particular Figures 1 to 6, the cover and frame assembly 10 of the present invention comprises a frame 12 fixed within the ground surrounding an access hole 14 to for example a petrol tank or other underground facility, and a cover 16 dimensioned such that when it is seated within the frame 12 as shown in Figure 1, there is a small gap 18 between the cover and the frame. The frame and cover may be square, circular or any other desired shape.

The frame, which is injection moulded composite fibre material, has integrally moulded therewith a core 20 of foamed plastics material, for example polyurethane closed cell foam, and an insert in the form of an aluminium extrusion 22 having two detents extending at the uppermost and lowermost ends respectively of a recessed portion 22c. The recess 22c (including the detents 22a and 22b) are masked prior to placing the insert 22 in the mould. The masked insert 22 is formed

into a shape corresponding to the shape it will assume when moulded as part of the frame, and it is then placed in the mould. A pre-for comprising the core 20, and composite fibres (glass, Kevlar (TM) , carbon or similar) is then placed in the mould around the insert 22 and resin is then injected and the whole assembly allowed to cure in the mould.

The insert also includes a keying recess 26 which will become filled with fibre and resin during the moulding process to enhance the moulded bond between the frame 12 and the insert 22

After curing, the frame is demoulded and the masking removed to reveal the recess 22c and detents 22a, 22b, into which a rubber seal 24 is releasably secured.

As can be seen from Figure 2, the seal 24 is generally D shaped in cross section with flanges 24a and 24b extending above and below the main seal. These flanges 24a, 24b are pushed into the detents 22a, 22b by first inserting one and then tucking the other in with a tool , so that the seal 24 is releasably secured to the insert 22 and hence to the frame 12 all around its internal perimeter, the seal having a substantially vertical orientation when so installed.

As is illustrated in Figure 2, each time the cover 16 is inserted within the frame 12, the seal 24 which originally has the undeformed shape shown in broken lines, is deformed as it is squeezed against the cover, and this also results in the sealing faces of the seal 24 and the cover 16 each being wiped clean of any dirt or debris, providing for a good, effective sealing engagement between the two. Furthermore, the cover is designed to seat positively within the frame such that when fully seated, the cover does not move relative to the seal. This is particularly shown in Figures 3 through 6(B) and described in more detail below.

Referring to Figures 3 and 3(A), the cover 16 comprises a

substantially vertical section 16a which depends downwardly from the uppermost surface of the cover and continues into a first tapering section 16b which in turn continues into a third tapering section 16c and subsequently into a fourth tapering section 16d. In circumference the shape of the cover is generally square with rounded corners. To each side of all corners, within tapering section 16d there is provided small protrusions 30 which each have a central portion comprising two faces 30a, 30b each side of both of these faces continuing via respective side faces 31a,31b and 32a,32b into the remainder of tapering section 16d. In use, when the cover 16 is placed within the frame, the protrusions 30 engage the frame when the cover is fully seated within the frame. The cover seats in a vertical diection on the sloping surface 44 which therefore needs to be accurately true to prevent rocking of the cover when vehicles pass over it. The horizontal positioning of the cover within the frame is controlled by the contact between the protrusions 30 and the slightly inclined (5° to the vertical) surface 45. The cooperation between the surface 45 and the protrusions 30 accurately locates the cover within the frame and prevents horizontal movement which could break the sealing or cause wear on the seal 24, despite traffic passing over the cover.

Figures 5(i) through 5(iv) illustrate in different views and sections the surface pattern on the cover 16.

When the frame and the cover are made by the composite fibre and resin injection method described, the manufacturing tolerances on both are very small (of the order of 0.5mm in 1 metre) and therefore the gap 18 between the cover 16 and the frame 12 can also be made very small, giving the advantage that the seal 24 does not have to be large to fill the gap. Consequently, the seal 24 can be made from the highest quality rubber without the cost being too prohibitive, the preferred material being extruded EPDM (ethylene propylene diene monomer) .

However, the invention comprising the use of a vertically disposed, resiliently deformable seal to seal the gap between cover and frame may be utilised to give similar advantages with access hole cover and frame assemblies made by other methods eg casting in metal, but in this case the manufacturing tolerances are higher and the gap and hence the seal would have to be larger with resultant cost considerations affecting the choice of material for the seal. In order to improve the tolerances of metal frames, a second embodiment of the method of the invention is described in relation to Figures 7 to 9, where like numerals are employed for like parts.

In this embodiment the frame 12 is made from metal, e.g aluminium, side sections 40 and prefabricated corner pieces 42. The side sections 40 are profiled as illustrated in Figure 9, i.e. in essence the same profile as in the embodiment shown in Figure 1, although the shape of the seal 24 is different. The cover (not shown) rests on the abutment surface 44 and is locked horizontally by the surfaces 45, as before. The corner pieces 42- have end sections 46 which are a slidable fit into the ends of the side sections 40. The corners 42 are preferably die cast in two halves, split horizontally to acco odate the recess 22 which extends around them as well as the sections 40. The two halves are then bonded together, e.g. by the same epoxy resin used in affixing the corners to the sections 40 as described below.

The side sections 40 have a recess 22(c) having detent portions 22a and 22b for the seal 24 as before. In this embodiment, however, the seal 24 is locked into place by means of a locking strip 48 which is an interference fit within a corresponding channel in the seal 24 and has to be forced into place with a suitable tool in a manner known per se. In this case, the seal 24, instead of a generally 'D'-shaped profile, has a pair of fins 50, 52 which in use sealingly contact the cover 16.

To assemble the frame in accordance with this embodiment of the invention, side sections 40 are cut to the desired length, the end sections 46 of the corner pieces 42 are coated with an epoxy adhesive, and the ends 46 inserted into the sections 40 to form a frame 12. The frame 12 is placed on a jig and the play or 'float' between the corners 42 and the sides 40 utilised to manipulate the frame 12 until it is truly flat and of the right dimensions to within 0.25.mm. The portions 46 are then briefly heated (using any suitable means including infra red) to 'gel' the epoxy and set the frame in the configuration determined by the jig. The frame can then safely be removed from the jig and transferred, e.g. to an oven for baking and final curing of the resin. In this way an extremely accurate frame as to both flatness and dimensions can be made.

The corner pieces 42 have recesses similar to those 22c in the sides 40 so that the seal 24 can go right _. around the finished product. It is preferred to cut the seal 24 to length and adhere the opposed ends to produce an 'endless' seal which eliminates any gap.

The method of the invention enables a cover and frame assembly to be made which will in use fit flush with the ground, will not rock when vehicles pass over it, has long seal life and yet easy seal replacement, and owing to the close tolerances a small gap 18 which enables a smaller amount of high quality rubber to be used in the seal.