GB2046811A

GB2046811A - Drainage inspection chambers

Info

Publication number: GB2046811A
Application number: GB8008182A
Authority: GB
Original assignee: Plastiers Ltd
Current assignee: Plastiers Ltd
Priority date: 1979-03-12
Filing date: 1980-03-11
Publication date: 1980-11-19
Also published as: GB2046811B

Abstract

A plastics drainage inspection, manhole access chamber 1 having integral main and branch base channels 3 and outlets 4 is rotation- moulded with integral access and outlet closures 7 which are subsequently cut away as required. The outlets 4 are stopped to provide serially connected portions of different diameter whereby a particular inlet/outlet diameter may be selected. <IMAGE>

Description

SPECIFICATION Method of producing an inspection chamber This invention relates to a method of producing an inspection chamber for use in an underground drainage or sewage system and to an inspection chamber when so produced.

An inspection chamber of the type referred to generally comprises an upright cylindrical or polyhedral portion and a base portion having a series of inlets and/or outlets spaced about its circumference and adapted for connection with pipes. Usually the floor of the base portion is provided with a plurality of interconnected benched channels for conducting liquid from one or more of the inlets to the outlet.

Hitherto prefabricated inspection chambers have been made by various methods as follows: a) Injection moulding of a base portion and subsequent affixing to the moulded base portion of a cylindrical or polyhedral portion.

b) Injection moulding of a one piece inspection chamber.

c) Laying up of glass reinforced plastics material over a dismantleable former to produce a one piece inspection chamber.

These known methods of production possess various disadvantages, the main one being the very high cost of tooling the necessary moulds, cores and formers. Because of the intricate shape required of an inspection chamber such a mould is inevitably a complex and multi-part device. Additionally, in the case of a one piece inspection chamber a very large core or former is required which again is very expensive.

According to the present invention there is provided a method of producing an inspection chamber for use in a piping system, in which the inspection chamber is produced by rotational moulding.

Rotational moulding is a known process used for example for the production of plastics footballs, in which a plurality of mould shell parts are assembled to define a closed volume arranged to contain a quantity of plastics material usually in powdered or granular form.

The mould constituted by the assembled mould shell parts is then heated in an oven and rotated about two or more (generally perpendicular) axes to coat the interior of the mould with melted plastics material to a desired thickness. The mould is subsequently cooled and dismantled and the moulded article removed therefrom. In an alternative rotational moulding procedure there may be used a chemically curable liquid plastics material arranged to cure during rotation of the mould, for example by application of heat thereto.

Rotational moulding is a process which, when applied to the production of an inspection chamber, results in a number of unexpected and marked advantages, at least some of which will become apparent from the following discussion.

The inspection chamber produced by rotational moulding is of a one piece construction which is a desirable feature.

i. The cost of production is far less than in conventional procedures since the need for internal cores and formers is dispensed with and only a simply constructed mould shell is required.

ii. The resultant product has its inlets and/or outlets closed unlike conventional inspection chambers which are made with open inlets and outlets and which hence require the manufacture of separate end caps to close off individual inlets and outlets. In practice it is usual for there to be provided more such inlets/outlets than are likely to be required for any single application so it is useful to have the inlets/outlets already blanked off. By simply cutting or breaking off the closed end of an inlet/outlet any particular inlet or outlet can be made operative. Additionally the use of integral closures eliminates a possible source of leaks.

iii. The absence of cores for moulding the inlets and outlets means that the inlets and outlets can readily be provided with portions of differing diameter. The advantage of this is that an inspection chamber may be utilised with pipes not all of the same diameter and, to adapt say a 6" inlet for junction with a 4" pipe it has hither to been necessary to employ a separately manufactured adaptor. By the present invention an inlet/outlet can be provided with portions of progressively changing diameters and it is only necessary to cut or break off portions of the inlet/outlet to select the appropriate diameter therefor.

iv. An advantage of rotational moulding is that the circumferential and/or axial strengthening ribs or grooves may be provided without the need for a complicated mould core, or without the excess material that would be required if the internal bore were a smooth cylinder.

Any materials conventionally used in rotational moulding may be employed for the inspection chamber of this invention provided only that the finished article possesses the strength and resistance to corrosion and heat required of it. Examples of such materials are plastics such as polyolefins, preferably polyethylene or polypropylene. Any other suitable plastics material may be employed if desired; for example polybutylene is useful where the inspection chamber has to withstand hot water.

An embodiment of the method of the present invention will now be described, by way of example only.

A mould is made up for an inspection chamber from a suitable plastics material, from cast metal e.g. aluminium or from sheet metal e.g. steel and preferably comprises three parts, a base portion including channel ways on its base and semi-circular section recesses for partially defining inlets and two generally semi-cylindrical portions each including a lower peripheral flange having therein further semi-circular section recesses corresponding with those in the base portion to define the inlets and outlets, and also including a semi-circular end cap to define a temporary top of the inspection chamber. It will be understood however, that in another embodiment a two part mould may be employed to produce an inspection chamber, if necessary relying on an inbuilt flexibility in the resulting inspection chamber to remove it from the mould.The inspection chamber to be produced generally has a height of 36" (though this can be 18") and a diameter of 18" and for such an inspection chamber approximately 10 kilogrammes of finely divided polyethylene of melting point approximately 120 C is charged into the mould base and the mould assembled from its constituent parts.

The mould is then secured for rotation about at least two axes at the end of a boom and passed into an oven where it is rotated at about 60 r.p.m. about said axes and heated to a temperature of approximately 1 50 C. The powdered polyethylene melts and coats the whole of the inside of the mould to a depth of approximately 41'. Subsequently the mould is cooled, rotation of the mould is halted, and the mould is parted and the inspection chamber removed therefrom.

Referring to the drawings an inspection chamber is shown produced by a method according to the present invention which comprises an upright cylindrical portion 1, a base portion 2 having interconnected channels 3 in its base and a plurality of circumferentially arranged inlets/outlets 4 communicating with the said channels 3.

One or more corrugations or ribs 5 may be provided extending upwardly or circumferentially of the cylindrical portion for reinforcement and, in the case of the circumferential ribs, to provide guides for any subsequent cutting of the cylinder to reduce its height. By virtue of the moulding method of this invention the unfinished inspection chamber is provided with a temporary closure 6 across its top end and this temporary closure 6 is removed, e.g.

by cutting, before the inspection chamber is utilized. The presence of this temporary closure ensures that the interior of the inspection chamber remains clean and uncontaminated by objects dropping thereinto during storage.

The inlets/outlets are provided with integral closures 7 at their ends some or all of which are removed, e.g. by cutting, when the inspection chamber is to be utilized.

One or more of the inlets/outlets 4 is provided along its length with one or more portions of reduced diameter 8 so that pipes of differing diameters can be catered for simply by cutting off the unwanted portions of the inlets/outlets 4 as required. To facilitate such removal a pair of annular flanges 9, 9, may be provided before a said reduced diameter portion 8 to guide a saw. A flange 9 which will be left after such a cutting operation may suitably be shaped so as to receive a gasket for making sealing engagement with a pipe inserted in the inlet/outlet.

Stop members 10 may be moulded into the inspection chamber to predetermine the extent into the inlets/outlets 4 to which a pipe may be inserted thereinto.

It will be understood that by varying such parameters as the viscosity of the moulding mterial, the relative rates of rotation about the respective axes, heating temperatures, etc. It is possible to coat the inside of the mould to different extents in different regions thereof.

This may be useful to reinforce certain areas or to facilitate subsequent removal of unwanted portions of the inspection chamber.

The method of the present invention provides an inspection chamber of high quality and with many desirable features, at an exceptionally low cost compared with conventional methods of production.

Claims

1. A method of producing an inspection chamber for use in a piping system, which includes a rotational moulding step.

2. A method according to claim 1, wherein a three part rotational mould is employed.

3. A method according to claim 1, wherein a two part rotational mould is em ployed.

4. A method according to any preceding claim, wherein the inspection chamber is produced from polyolefin.

5. A method according to claim 4, wherein the polyolefin comprises polyethylene or polypropylene.

6. A method according to any preceding claim, wherein the inspection chamber is provided with one or more circumferential and/or axially extending ribs or grooves.

7. A method according to any preceding claim, wherein one or more of the inlet(s) and/or outlet(s) of the inspection chamber is provided with serially connected portions of different diameters whereby a particular inlet/outlet diameter to be employed may be selected.

8. A method according to any preceding claim, wherein one or more of the inlet(s) and/or outlet(s) is provided with means for receiving a seal for making sealing engagement with a pipe to be connected to the inspection chamber.

9. A method of producing an inspection chamber substantially as hereinbefore de scribe.

1 0. An inspection chamber precursor which comprises a one-piece enclosed hollow body generally of inspection chamber shape and the mouth of which and the inlet(s) and outlet(s) of which are provided with integral closures.

11. An inspection chamber precursor according to claim 10, wherein one or more of the inlet(s) and/or outlet(s) is provided with serially connected portions of different diameters, whereby a particular inlet/outlet diameter to be employed may be selected.

1 2. An inspection chamber precursor substantially as hereinbefore described and with reference to the accompanying drawing.

13. An inspection chamber produced from an inspection chamber precursor as claimed in claim 10, 11 or 12.

14. A rotationally-moulded inspection chamber.

15. An inspection chamber according to claim 14, of polyolefin.

16. An inspection chamber according to claim 15, of polyethylene or polypropylene.

17. An inspection chamber according to any of claims 14 to 16, provided with one or more circumferential and/or axially extending ribs or grooves.

18. An inspection chamber according to any of claims 14 to 17, wherein one or more of the inlet(s) and/or outlet(s) is provided with means for receiving a seal for making a sealing engagement with a pipe to be connected to the inspection chamber.

19. An inspection chamber according to any of claims 14 to 18, wherein one or more of the inlet(s) and/or outlet(s) is provided with serially connected portions of different diameters, whereby a particular inlet/outlet diameter to be employed may be selected.

20. An inspection chamber substantially as hereinbefore described.

21. The features hereinbefore disclosed, or their equivalents, in any novel selection.