Patent GB-645370-A (GB)
Title: Improvements in injection moulding apparatus
IPC: B29C45/53
Filed: 1947-12-19
Abstract: 645,370. Injection - moulding machines. UNITED STATES RUBBER CO. Dec. 19, 1947, No. 33596. Convention date, March 26. [Class 87 (ii)] A device for injecting mouldable material into the cavity of the mould of a compressiontype closed mould press, comprises, in combination, a cylinder for receiving a charge of mouldable material, a piston co-operating with the cylinder for compressing the charge and extruding it from the cylinder through an orifice, and a support for the cylinder attachable to the mould of the compression-type press and on which the cylinder is movable towards and away from the mould to position the orifice in register with the mould cavity, the movement of the cylinder being derived from the movement of the piston. A compression-type press 1, Fig. 6, is connected to an injection moulding unit 2, which unit is utilized to inject mouldable material such as rubber into the cavity of a mould having an upper part 3 and a lower part 4. The mould part 3 is carried by an upper cross-head 5 and the other half of the mould is carried by a lower cross-head 6 which may be moved to place the mould parts under compression. The unit 2 is supported in position in any convenient way as by a hoist 9, so that it may be moved from one press or mould to another. The unit, Fig. 1, includes an injection cylinder 10 having a nozzle 12, and in order to heat the material as well as reduce friction on the cylinder the wall of the cylinder is provided with steam heating channels 13a, interconnected at one end by grooves 15 in an end-plate 16, which plate has steam supply and return pipes 77. Electrical heaters may, however, be provided instead of steam. An electrical heating coil 17a is provided for nozzle 12 to reduce friction in the nozzle and to cure any compound remaining in the passage 43 after moulding so that the compound may be easily removed. The cylinder 10 is positioned at approximately its middle point in a pivoted yoke 17 having trunnions 20 seated on bearing blocks 21 supported on tie-bars 22, thus permitting the cylinder to be pivoted for charging. As shown in Figs. 1, 4, the yoke may be moved along the tie-bars. The end of the cylinder remote from the nozzle 12 normally rests in a cradle 26 which is also supported on the tie-bars 22, the cylinder being positioned and held horizontally by adjustable screws 30 and a pivoted locking-bar 33. The parts 3 and 4 of the mould are each provided with an adapter plate 39, Figs. 1, 4, designed to accommodate the forward ends of the tiebars in " T "-shaped slots 41. Thus the injection unit may be mounted on the press by inserting the ends 40 of the bars 22 in the slots 41 and moving the unit into position, aligning channels 42 in the adapter plates with passages 43 in the nozzle 12, and with a channel provided in the mould itself. If the compression mould technique only is used the inlet channels in the mould may be plugged with a low-melting point alloy. To facilitate positioning of the cylinder and nozzle during injection the nozzle 12 is provided with a recessed end surface 44 which mates with a nipple 45 formed on the two adapter plates 39, thus assuring a tight connection. The material is compressed within the cylinder 10 by means of a double-acting piston 46 reciprocating in a cylinder 47 closed by heads 48, 49, which are provided with channels 54, 57 respectively, for connection to high-pressure fluid lines 55, 58. The two lines are connected to a valve 59 of conventional construction operated by a handle 60, the valve being also connected to a high-pressure fluid supply line 61 and a discharge line 62, so that pressure may be applied to either side of the piston head 63 to move the piston 46 back and forth in the cylinder 10. The pressure unit, comprising the piston 46, cylinder 47, and associated control mechanism, may be mounted on or disconnected from the tie-rods 22 by means of " T " slots 64 in the head 48, and the entire injection unit may be suspended by hooks 65 from the hoist 9. In operation, the tie-bars 22 are first inserted in the slots 41 in the adapter plates 39 and the unit supported in balanced position from the hoist. The cylinder 10 is tipped and charged with material and then returned to the horizontal position and locked by means of the bar 33. The material is heated bv steam admitted via the supply lines 77 to the channels 13a and the piston 46 moved to enter the chamber 25 in cylinder 10 to compress the charge of material. Due to the pressure on the charge and also because of the frictional engagement of the piston 46 with the inner walls of the chamber 25 the entire cylinder 10 and the yoke 17 are moved along the tie-rods until the nozzle 12 engages on and is centred upon the nipple 45. Continued movement of the piston 46 injects the charge into the mould where it is cured by heat from the press. After injection the piston 46 is forced backwards under fluid pressure, the frictional engagement between it and the chamber 25 causing the cylinder and yoke 17 to slide backwards along the tie-rods 22 to a position such that the yoke 17 engages a stop 166 on the rods 22. These stops limit the retractive movement of the cylinder 10 so that the piston 46 as it moves on is completely with drawn from the cylinder 10. The cycle of operation may then be repeated.