Patent GB-711510-A (GB)
Title: Apparatus for moulding hollow plastic articles
Inventor: REMPEL DIETRICH GUSTAF
IPC: B29C41/06
Filed: 1951-12-11
Abstract: 711,510. Moulding hollow plastic balls &c. SOC. FRANCAISE D'ETUDES & DE RECHERCHES TECHNIQUES. Dec. 11, 1951, No. 29031/51. Class 87 (2) Apparatus for producing hollow articles' of plastic material comprises a conveyer arranged to move a hollow sectional mould over a closed path through a number of successive treating stations, including a loading station for supplying the mould with liquid plastic material, a pre-heating station where the mould can be rotated about two axes to cause uniform distribution of the material on the inner wall of the mould, a station for polymerizing the material by the application of heat while the mould remains stationary, a cooling station, and a station where the moulded articles can be removed from the apparatus. A number of mould halves, e.g. hollow hemispheres 25, Fig. 2, are fixed to a plate 23 and the same number of complementary mould halves 26 are fixed to a plate 24. Several pairs of plates 23, 24 are stacked on a spindle 29 and clamped together by a handled nut 30 to form a mould unit 16. The other end of the spindle 29 is rotatable by a stub shaft 33 'which projects at right angles from the end of a tubular arm 37. As shown, Fig. 1, there are four arms 37, equally spaced and radiat:ng from the top of a central tubular upright 46 through which passes a shaft 44. The shaft 44 is rotated at intervals by a motor 54 under the control of a timer 57, these sweeping the arms 37 through a horizontal plane. The arms 37, supported by a fixed shaft 40, are rotatable on their own axes by gears 60 or 71. These means provide for the following operations : (i) At position A the moulds are opened, the moulded articles removed, the correct quantity of moulding material put in each mould and the moulds closed and clamped together, the spindle 29 being upright as in Fig. 2; and the mould unit 16 is then swung in an arc to position B, where it is suspended in the bottom half of a steam housing 100, the spindle 29 projecting vertically downwards from the end of the arm 37. (ii) At position B rotation of the arm 37 causes the spindle 29 to rotate radially about its junction with the arm 37 and swing the mould unit 16 in a plane at right angles to the arm, and axial rotation of the spindle 29 also causes the mould unit to rotate about its own axis. There is thus compound rotation of the moulds in the steam housing causing. the material in the moulds to be preheated and built up in layers to the required thickness. (iii) The mould unit, no longer rotating, is swung in an arc out of the bottom half of the housing 100 and then downwards in an arc into an open tank 96 containing heating fluid, e.g. molten paraffin wax, position C, where it remains stationary, depending downwards from the end of the arm 37, while the material is fully polymerized in the moulds. (iv) With a movement similar to that in and out of the steam housing 100 the mould unit 16 is transferred from position C to position D, where it is cooled in a medium such as circulating water in a tank 97. (v) The mould unit is swung upwards back to position A, where it stands erect at the end of the arm 37, Fig. 2, as above referred to. The timer 57 operates in conjunction with limit switches which are tripped by the arms 37 at the ends of their quarter-turn movements in a horizontal plane, and the timer causes the arms to remain at positions A, B, C or D for an interval of, e.g., seven minutes. As the arms 37 move in their horizontal plane the bevel gears 60 thereon roll on a large fixed bevel gear 61 and causes axial rotation of the arms between positions. The amount of this axial rotation between positions B-C and C-D is twice that between positions D-A and A-B, and to achieve this the bevel 61 is blank for a quarter circumference at 62, the arm 37 concerned then rolling on a track 63. The axial rotation of an arm 37 while it remains at position B is achieved by the other gear 71 thereon which moves into engagement with a rotating gear 72, Fig. 4, driven by a motor 89 and resiliently mounted. The drive which is through a chain 83, may be continuous or intermittent, in the latter case being started by the timer 57 and stopped by a cam on the appropriate arm 37 operating a limit switch. At the instant these gears are engaged the timer 57 causes fluid pressure in a cylinder 69 to move a lever 68 which carries a small loose segment 67 of the large fixed gear 61 out of engagement with the bevel 60. A probe 121 is fixed to the segment 67, which can thus only re-engage with the bevel 60 when an opening 120 in the hub thereon is exactly opposite the probe, i.e. when the moved unit 16 is in the vertically downward position at the end of the compound rotation of the mould unit 16. The other component of the compound rotation is derived from a bevel gear, on the stub shaft 33, rolling round in engagement with a fixed bevel gear on the end of the shaft 40, which causes the mould unit 16 to rotate about its own axis. The housing 100, Fig. 10, is large enough to enclose the mould unit during its compound rotation and is opened to allow its entry and departure by the top half or cover 103 being raised by cables 107, 108 connected to a counterweight 113. The opening and closing of the cover are caused by the admission and release of fluid pressure to or from a cylinder 115, under the control of the timer 57 in combination with limit switches 122, 123 operated by the segment 67 and the cover 103 respectively, whereby continued operation of the machine to move the mould unit 16 out of station B is dependent both on the proper terminal position of the arm 37 and on the opening of the housing cover 103. Suitable moulding materials are polyvinyl chloride, acetate, aceto chloride; and suitable plasticizers are tricresylpthosphate and butyl-phthalate. It is also possible to use pre-made polymers, single or mixed monomers, with or without a plasticizer, to which a polymerization catalyst has been added. The moulds 20 are of metal, e.g. steel or aluminium.