GB2541694B

GB2541694B - Access cover or grate for use in paved surface

Info

Publication number: GB2541694B
Application number: GB1515155.8A
Authority: GB
Inventors: Charles Brooksbank Andrew
Original assignee: A2b Plastics Ltd
Current assignee: A2b Plastics Ltd
Priority date: 2015-08-26
Filing date: 2015-08-26
Publication date: 2019-08-14
Anticipated expiration: 2035-08-26
Also published as: GB201515155D0; GB2541694B8; GB2541694A

Description

Access cover or grate for use in paved surface

The present invention relates to access covers or grates for use in a paved surface.Such grates include gully grates, channel gratings and kerb drains for example. Theinvention relates particularly but not exclusively to road gully grates.

Traditionally such access covers or grates have been made of cast iron but thismaterial has certain disadvantages. In particular it is slippery when wet and is prone torust. Cast iron road gully grates (which typically need to withstand loads of 40tonnes) are heavy. Because of the considerable weight of cast iron in a road gullygrate, such a grate is attractive to thieves for its scrap value.

In order to alleviate some of the above disadvantages, grates have been made ofsynthetic composite materials such as fibreglass and wood-plastic composites such aswood fibres coated with HDPE, polyurethane and polyester DMC.

However known synthetic composite materials have various disadvantages includinglimited strength to weight ratio and limited product life. Many of the above materialscannot easily be recycled.

An object of the present invention is to provide an access cover or grate for use in apaved surface in which at least some of the above disadvantages are alleviated orovercome.

The invention provides an access cover or grate for use in a paved surface, the accesscover or grate comprising one or more metal structural members embedded in amatrix of injection-moulded fibre-reinforced thermoplastic polymer material, whereinat least one of said metal structural members is elongate and extends substantiallyhorizontally beneath a load-bearing mid-region of the access cover or grate and has atransverse cross-section whose height is greater than its width.

It is believed that the structural strength of the above cover or grate is enhanced by thefibres in the polymer material, which tend to prevent movement of the metalstructural members within the polymer when the cover or grate is loaded.

By the same token, extraction of the metal structural members from the polymermaterial is difficult, reducing the scrap value of the cover or grate and hence reducingthe risk of theft.

Preferably the total volume of said one or more metal structural members is less than(preferably less than 30%, more preferably less than 15%) of the volume of saidmatrix of injection-moulded fibre-reinforced polymer material. These featuresenhance the above-noted advantages.

The feature that at least one of said metal structural members is elongate and extendssubstantially horizontally beneath a load-bearing mid-region of the access cover orgrate maximises the load-bearing capacity of the access cover or grate.

Because at least one of said structural members has a transverse cross-section whoseheight is greater than its width, the surrounding fibre-loaded polymer material tends toprevent twisting of the structural member(s) and thereby enables full advantage to betaken of the optimum tall, narrow cross-section.

In a preferred embodiment a grate has one or more load-bearing portions in a mid-region thereof whose transverse cross-section reduces in width from an upper regionto a lower region thereof. Since the fibre-loaded polymer (which is relatively strong incompression and relatively weak in tension) is concentrated in the upper region, thestructure is optimised to bear a typical load from eg a vehicle, which will compressthe upper region and tension of the lower region.

In preferred embodiments said one or more metal structural members is composed ofsteel. However other metals such as aluminium for example can also be used whereload-bearing requirements are less stringent or weight must be minimised.Preferably said polymer is polypropylene or polyethylene (eg HDPE).

Preferably said reinforcing material is cut reinforcing fibres dispersed in said polymermaterial.

Preferably said reinforcing fibre is glass fibre or carbon fibre or metal (eg stainlesssteel) fibre.

Preferably said reinforcing material is long fibre material having a number averagemean length in the range 3 mm to 10 mm.

Other preferred features are defined in the dependent claims. A preferred embodiment is described below by way of example only with reference toFigures 1 to 7 of the accompanying drawings, wherein:

Figure 1 is a somewhat diagrammatic perspective view from above of a road gullygrate in accordance with the invention;

Figure 2 is a top plan view of the road gully grate of Figure 1;

Figure 3 is a section taken on III-III of Figure 2;

Figure 4 is a section taken on IV-IV of Figure 3;

Figure 5 is a section taken on V-V of Figure 2;

Figure 6 is a detailed sectional view of one of the grating bars 10 of Figure 3 showinga metal reinforcing bar 5 and the surrounding polymer and fibres F, and

Figure 7 is a diagrammatic longitudinal cross-section through an injection mouldarrangement for making the grate of Figures 1 to 6.

Referring to Figure 1, the road gully grate shown is in the form of a generallyrectangular shell which is open at its underside and has a peripheral sidewall 2 and acentral longitudinal rib 3 as shown in cross-section in Figure 3. Two aligned rows offive elongate apertures 1 are formed in the upper wall of the shell on either side of thecentral longitudinal rib 3.

The shell is formed of injection-moulded 50% glass fibre-filled polyamide. The fibrelength is 5 mm. A ribbed anti-slip pattern 4 formed in the upper surface of the grate.

The outer side faces 8 of the shell are inclined inwardly towards the underside of theshell as best seen in Figures 3 and 5.

Referring to Figure 2, the rows of apertures 1 define four transverse ribs 10 in whichare embedded respective transverse steel strips 5. These steel strips extendhorizontally across substantially the full width of the grate and act as structuralmembers which bear the load of any vehicle wheel which bears on the upper surfaceof the grate. The strips are 325 mm long, 8 mm wide and 40 mm high.

As best seen in Figure 5, the surrounding glass fibre-loaded polymer of the transverseribs 10 is tapered inwardly in cross-section from the upper side to the under side.When loaded by eg a vehicle wheel, the upper portion of each rib is compressed andthe lower portion is tensioned. The glass fibre-loaded polymer is mainly at the top ofthe rib and, being strong in compression, resists deformation, whereas the steel strip,being strong in tension, bears most of the load at the bottom of the rib. Thus thetapered cross section optimises the strength-to-weight ratio of the ribs 10.

The glass fibres F are shown diagrammatically in Figure 6. It will be seen that thesetend to prevent plastic flow of the polymer around strip 5 when the rib 10 is loaded. In this manner the glass fibres F tie together the steel strip 5 and the surroundingpolymer and ensure that each contributes to the overall strength of the rib 10.

Referring to Figure 4, the underside of the grate has six blind locating holes 6 formedin the sidewall 2. Shelf portions 7 and 9 are formed between the apertures 1 at theends of the grate and the sidewall 2, as shown also in Figure 5.

Referring now to Figure 7, two complementary carbon steel moulds 11 and 12 areheld together (by a platen arrangement in a conventional injection moulding machine,not shown) and define cavities C for receiving glass fibre loaded polyamide (Nylon®)which is injected in fluid form through a sprue 14 by a screw feeder of the injectionmoulding machine. The cavities C locate together and are shaped to correspond to theshell of the grate shown in Figures 1 to 6.

The four inner cavities C correspond to the ribs 10 of the grate and support steel strips5 by means of plastic clips 13 which each have a central rectangular borecorresponding to the cross-section of strip 5 and have an outer profile whose cross-section is in the form of a double arrow which defines ridges which bear against threesides of the cavity, as shown.

The two innermost cavity portions of lower mould 12 are provided with borescarrying ejector pins 15. The ejector pins 15 are used to eject the moulded grate afterthe injected polymer has solidified. It will be noted that the cavities taper inwardlytowards the bottom of lower mould 12 to facilitate take out (ejection) of the moulding.

The following polymers can be take out moulded in the manner described above toform a grate as described above: polypropylenepolycarbonatepolyetheretherketone PET (polyethylene terephthalate) AB S (aery 1 onitril e-butadi ene-styrene)polyurethanepolyesterphenolic.

Thermoplastic polymers are however preferred. Using the polymer glass-filledNylon®, the above grate was found to have a load capacity in excess of 40 tonnes,meeting the requirement of group 4 of BS EN 124:1994.

Claims

1. An access cover or grate for use in a paved surface, the access cover or gratecomprising one or more metal structural members embedded in a matrix of injection-moulded fibre-reinforced thermoplastic polymer material, wherein at least one of saidmetal structural members is elongate and extends substantially horizontally beneath a load-bearing mid-region of the access cover or grate and has a transverse cross-section whoseheight is greater than its width.

2. A grate according to claim 1, having one or more load-bearing portions in a mid-regionthereof whose transverse cross-section reduces in width from an upper region to a lowerregion thereof.

3. An access cover or grate according to any preceding claim, wherein the total volume ofsaid one or more metal structural members is less than the volume of said matrix ofinjection-moulded fibre-reinforced polymer material.

4. An access cover or grate according to claim 3, wherein the total volume of said one ormore metal structural members is less than 30% of the volume of said matrix of injection-moulded fibre-reinforced polymer material.

5. An access cover or grate according to claim3, wherein the total volume of said one ormore metal structural members is less than 15% of the volume of said matrix of injection-moulded fibre-reinforced polymer material.

6. An access cover or grate according to any preceding claim wherein said one or moremetal structural members is composed of steel.

7. An access cover or grate according to any preceding claim wherein said polymer ispolypropylene or polyethylene.

8. An access cover or grate according to any preceding claim wherein said reinforcingmaterial is cut reinforcing fibres dispersed in said polymer material.

9. An access cover or grate according to claim 9wherein said reinforcing fibre is glass fibreor carbon fibre or polyamide fibre or metal fibre.

10. An access cover or grate according to any preceding claim wherein said reinforcingmaterial is long fibre material having a number average mean length in the range 3 mm to10 mm.

11. An access cover or grate according to any preceding claim wherein said polymer matrixis: polypropylene loaded with glass fibre or carbon fibre, orpolyethylene loaded with glass fibre or carbon fibre.

12. An access cover or grate according to any preceding claim for use in a road.

13. An access cover or grate according to any preceding claim which complies with group4 ofBSEN 124:1994.

14. An access cover or grate according to any preceding claim which is a road gully grate.