GB2222548A

GB2222548A - Inserts in rotationally moulded articles

Info

Publication number: GB2222548A
Application number: GB8821227A
Authority: GB
Inventors: John David Thurman
Original assignee: Lin Pac Mouldings Ltd
Current assignee: Linpac Mouldings Ltd
Priority date: 1988-09-09
Filing date: 1988-09-09
Publication date: 1990-03-14
Also published as: DE3929102A1; FR2636265A1; GB8821227D0

Description

1 22T2548 TITLE "Rotational moulding"

TECHNICAL FIELD & BACKGROUND ART

The present invention relates to rotational moulding and is particularly concerned with a method of rotationally moulding an article having an insert in a plastics wall thereof.

It is well known to rotationally mould plastics articles by introducing into a moulding tool plastics in powder or granular form; the to"ol is then heated and rotated in known manner so that the plastics becomes molten and is tumbled to flow under gravity to coat and follow the form of the appropriate interior face or faces of the tool. The tool is then cooled for the plastics to solidify and the moulded article removed. In the majority of instances rotational moulding is used for the manufacture of hollow articles although it is used on occasion for moulding articles having a sheet-like structure, particularly where the plastics sheet is relatively thick and has a complex profile corresponding to a f ace of the moulding tool.

It is also known to rotationally mould a plastics wall of an article where an insert is moulded into the wall to be presented on (and often project from) at least one face of the wall. Such inserts are typically metallic, for example being in the nature of either a shaft projecting from or through the article or a bearing which the article incorporates. -Conventionally such an insert is located within the moulding tool and rotational moulding effected as previously discussed so that the wall of the article interfaces with the insert. However, such technique leaves much to be desired in so far as when the plastics wall of the article cools it contracts and shrinks away from the insert. Although this shrinkage may be exceedingly small it is often unacceptable as permitting 2 fluid leakage between the insert and wall or permitting undesirable relative movement between the insert and wall. It is an object of the present invention to provide a method of rotationally moulding an article having an insert in a plastics wall thereof and by which the disadvantages as aforementioned of the prior proposals can be alleviated. STATEMENT OF INVENTION & ADVANTAGES

According to the present invention there is provided a method of rotationally moulding an article having an insert in a plastics wall thereof which comprises providing a plastics sleeve part within which the insert is received in sealing engagement, the sleeve part being located at a position on the insert which is to co- incide with a plastics wall that is to be rotationally moulded, locating the insert and sleeve part in a rotary moulding tool and rotationally moulding the plastics wall in forming the article so that the plastics of the wall bonds in sealing engagement with the sleeve part.

The sleeve part can be formed as a component which is pre-moulded in situ on the insert or as a component which is pre-moulded and subsequently fitted to the insert. In either case the sleeve part will be in tight sealing engagement with the insert - with this in mind the in situ pre-moulded component will usually be formed as an injection moulding under pressure while the pre-moulded and fitted component will usually be a tight press-fit or a contraction fit 9n the component. By this proposal, if the sleeve part becomes heated during rotational moulding and this reduces its sealing effect with the insert, the subsequent cooling of the article and the plastics memory of the sleeve part will cause that part again to adopt a tight sealing engagement with the insert. If required however, the inner region of the sleeve part which is adjacent to the insert may be cooled during the rotational moulding process to alleviate the aforementioned loss of 3 sealing engagement between the insert and the sleeve part. This cooling of the inner region can conveniently be achieved by passing cooling fluid through the insert if the latter is hollow.

Preferably the plastics of the rotationally moulded wall and that of the sleeve part are compatible materials so that the bond is formed by the plastics wall welding or fusing to the sleeve part. Consequently in a preferred arrangement it is envisaged that at least the outer region of the sleeve part (that is the region of the sleeve part remote from the insert) can become molten to weld with the molten plastics of the wall during the rotational moulding. The outer region of the sleeve part may have an external projection (such as a radially extending flange) which facilitates bonding, particularly welding, between the rotationally moulded wall and the projection of the sleeve part.

The sleeve part will typically be a collar through which the insert extends although it is envisaged that the sleeve part can have other forms, for example, it may be of a cup shape or of a similarly recessed component in which an end of the insert is received.

Further according to the present invention there is provided an article having an insert therein when rotationally moulded by the method of the present invention.

DRAWING One embodiment of the method of rotationally moulding an article having an insert in a plastics wall thereof in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawing which shows a part of the article wall (in section) with the insert extending therethrough.

DETAILED DESCRIPTION OF DRAWING

4 The article which is to be formed has a plastics wall 1 through which extends a cylindrical metal shaft 2. The wall 1 may be a sheet-like component or may be closed to form a hollow structure (such as a spherical ball member or roller) in which case the shaft 2 may extend to project completely through the hollow structure (for example diametrically in the case of a spherical ball member). The wall 1 is to be rotationally moulded in plastics, such moulding being effected around the shaft 2 in a rotary moulding tool (not shown).

Prior to locating the shaft 2 in the moulding tool, an injection moulded plastics collar 3 of generally annular configuration is pushed onto the shaft 2 to form a tight sealing fit therewith. This fit is preferably so that a cylindrical inner face 4 of the collar is urged by the resilience of the plastics into face-to-face sealing abutment with the cylindrical face of the shaft 2. The collar 3 includes an annular flange 5 which projects outwardly on the collar and this flange is located to coincide with the position at which the wall 1 is intended to engage with the shaft 2 through the collar 3.

The collar 3 is injection moulded in a plastics material which is compatible with the plastics material from which the wall 1 is to be rotationally moulded (in the sense that the two materials can be welded together by heating and cooling) - conveniently the collar 3 and wall 1 are to be of the same plastics.

As an alternative to push fitting the collar 3 onto the shaft 2, the collar 3 can be injection moulded in situ onto the shaft 2 - again forming a tight seal between the abutting faces of the collar and shaft.

The shaft 2 with its fitted collar 3 is mounted in the rotary moulding tool and the wall 1 is rotationally moulded in conventional manner. During this moulding the tool is heated and molten plastics flows under gravity over the face of the tool as the latter is slowly rotated or tumbled to build up the thickness of the wall 1 with a face la of that wall abutting and conforming to the profile of the moulding tool. During this rotational moulding at least the flange 5 of the collar is heated sufficiently and possibly becomes molten to bond by welding with the material of the wall 1 when the moulding tool is subsequently cooled. Possibly the collar 3 may be heated over its entirety from the moulding tool to reduce its sealing engagement on the shaft 2. However, as the tool and plastics cool, the memory of the plastics in the collar 3 causes the collar to revert into tight sealing engagement on the shaf t 2.

If required the inner region of the collar 3 (that is 15 the plastics material of the collar 3 immediately adjacent to its cylindrical face 4) may be cooled during the rotational moulding process so that tight sealing engagement between the collar and shaft is maintained. This cooling is conveniently achieved by having a tubular or hollow insert as indicated at 2a and passing cooling fluid through the insert.

6

Claims

1. A method of rotationally moulding an article having an insert in a plastics wall thereof which comprises providing a plastics sleeve part within which the insert is received in sealing engagement, the sleeve part being located at a position on the insert which i's to co-incide with a plastics wall that is to be rotationally moulded, locating the insert and sleeve part in a rotary moulding tool and rotationally moulding the plastics wall in forming the article so that the plastics of the wall bonds in sealing engagement with the sleeve part.

2. A method as claimed in claim 1 which comprises moulding the sleeve part in situ on the insert.

3. A method as claimed in claim I which comprises premoulding the sleeve part and fitting that part to the insert.

4. A method as claimed in any one of the preceding claims which comprises forming the sleeve part by injection moulding.

5. A method as claimed in any one of the preceding claims which comprises forming a welded bond between the plastics wall and sleeve part during the rotational moulding.

6. A method as claimed in claim 5 which comprises forming the weld between the rotationally moulded plastics wall and an outer region of the sleeve part.

7. A method as claimed in any one of the preceding claims which compris!s pyoviding the sleeve part with an external projection and bonding the rotationally moulded plastics wall to said external projection.

8. A method as claimed in any one of the preceding claims which comprises forming the sleeve part as a collar through which the insert extends.

9. A method as claimed in any one of claims 1 to 7 which comprises forming the sleeve part as a recessed component in which an end of the insert is received.

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10. A method as claimed in any one of the preceding claims which comprises cooling an i.nner region of the sleeve part which is adjacent to the insert during rotational moulding to maintain said inner region substantially solid.

11. A method as claimed in claim 10 which comprises providing a hollow insert and cool.ing said inner region of the sleeve part by passing cooling fluid through the insert.

12. A method of rotationally moulding an article as 10 claimed in claim 1 and substantially as herein described.

13. An article having an insert in a plastics wall thereof and formed by the method as claimed in any one of the preceding claims.

1 Published I Mat The Patent Office. Staw House, 86-71 Fligh Holburn. I. 4ndon WC 1A 4TP Further copies maybe obtaindfrom The Patent Ofnes. Silos Branch. St M&z7 Cray, Orpington. Knt WL5 3RD. Printed by Multiplex techniques ItcL St Mary Cray. Nent. CorL 1:87