Patent GB-690491-A (GB)
Title: Apparatus suitable for the centrifugal moulding of tubes and tube liners from thermoplastic materials
Inventor: WOOD HAROLD BROOMFIELD
IPC: B29C41/04
Filed: 1950-03-13
Abstract: 690,491. Centrifugal moulding of thermoplastic tubes &c. IMPERIAL CHEMICAL INDUSTRIES, Ltd. March 13, 1951 [March 13, 1950], No. 6214/50. Class 87 (ii). A centrifugal moulding apparatus for producing tubes of thermoplastic material comprises a mould open at each end, closures maintained against the ends of the mould by selective clamping pressure means, mould end fittings supporting the clamping means, the clamping means and closures being removable from the mould end fittings without the fittings being removed from the mould, the end fittings being adapted to connect the mould, without affecting the clamping pressure, with end supports for a horizontal mould, at least one of said end supports being rotatably driven and at least one retractable. In the arrangement described the end supports are shafts, one of which is retractable longitudinally to allow for the removal of the mould and the other of which is longitudinally fixed, the fixed shaft being driven to rotate the mould. The retracting of the shaft may be accomplished by a hand-wheel operating a sliding block and bellcrank, the longitudinal thrust of the shaft when supporting the mould being controlled by a spring. In the Figure, showing the arrangement at one end, the mould is shown at 10 and a supporting shaft at 28. A sleeve 11 is secured to the mould by a split collar 14 and threaded ring 15, or the sleeve and mould may be integral. The sleeve carries a brass liner 12 with an internal conical bore and has an annular groove which accommodates lugs 20 on the arms of a spider 18. The closure 16 is pressed on the end of the mould by a screw 21 in the hub of the spider 18, a gasket 17 being interposed. The screw 21 is turned by a hand-wheel 23 with holes for a tommy bar. A hub 26 keyed to the shaft 28 carries a ring 25 on which is a sleeve 24 with a conical surface registering with the conical bore 12. To reduce scoring between the conical surfaces when they are in contact the ring 25 is resiliently mounted to have slight axial movement allowed by rubber mountings 30. The conical sleeve 24 is of wear resisting composition, such material being mounted on the shaft and not on the mould because otherwise its surface would be exposed to any liquid that might be spilt when being poured into the mould. Alternatively the sleeve 24 and liner 12 may both be of steel. For ease of handling the mould is preferably of drawn aluminium alloy tube and the parts 11, 18, 26 of cast aluminium. The rotating mould may be heated by a spray of hot water or by electric heaters placed round it to form an oven. The internal surface of the mould is preferably smooth but not polished, the moulded tube being polished outside the mould afterwards, if required. To remove the tube the mould is taken off the centrifugal mounting and placed in a hot water bath, and it is then cooled in air, when the shrinkage of the moulded tube permits its easy removal. The Specification mentions suitable moulding materials for use in the apparatus and gives an example of moulding a tube in which a syrup prepared from monomeric methyl methacrylate was poured into the mould, the mould was closed and rotated at 800 r.p.m. at temperatures of 52 C. and 70 C. for 13 hours and 1 hour respectively. The mould, then containing a tube of polymethyl methacrylate, was immersed in a bath with the temperature gradually raised from 60" to 98 C. and restored to 60 C., then put in an air oven with the temperature raised from 60 to 100 C. and subsequently allowed to cool the moulded tube then being easily removed. Specifications 475,552 and 585,395 are referred to.