Patent GB-1371198-A (GB)
Title: Clamping unit for the casting mould of an injection moulding machine
IPC: B29C45/67
Filed: 1971-10-12
Abstract: 1371198 Injection moulding machines K HEHL 12 Oct 1971 [17 Oct 1970 28 Jan 1971] 47376/71 Heading B5A In an hydraulic clamping device for a two part mould (not shown) comprising a movable mould carrier 51 attached to the piston-rods 52, 53 of first cylinders 126 to which a fixed mould carrier 50 is attached, each cylinder 126 contains a piston 54, 55 dividing the cylinder into two chambers 57, 78 or 58, 79 which are interconnected by a channel 83 containing a shut-off valve 73, each piston has an annular seal 80 engaging the bore of its cylinder 126, second cylinders 102 are fastened coaxially with the first cylinders and each contains a piston 52<SP>1</SP> which is connected to move with a piston 54 and which forms a larger diameter extension of a piston 52, and an hydraulic drive including a pump alternatingly supplies fluid at a pressure in a relatively low pressure range and in a relatively high pressure range, the first cylinders being supplied with fluid in the low pressure for mould closing and in the high pressure range for mould clamping, the shut-off valve being open during mould opening and closing and closed during mould clamping, and the annular seals being substantially undistorted by the fluid in the low pressure range but being compressed by fluid in the high pressure range. To open the mould fluid is pumped at low pressure through line 69 into chambers 76 of the second cylinders moving pistons 52<SP>1</SP> and thus pistons 54, 55 to the left. Fluid passes from the interconnected chambers 57, 58 through the open valve 73 to the chambers 78, 79 which are also interconnected. The reduction in the overall fluid space in cylinders 126 due to the larger diameter of the pistons 52<SP>1</SP> which replace the piston-rods 52<SP>1</SP> causes fluid to be discharged from cylinders 126 through valve 67 and line 70 to a reservoir. A valve may be provided so that during the opening stroke the line 70 may be connected to the line 69 instead of the reservoir, thus all the cavities of the first and second cylinders are interconnected and fluid displaced from cylinders (126) assists in filling cavities 76. In this case the opening force is reduced since the effective piston area is equal to the cross-sectional area of the piston-rod 52. The higher opening force is preferable when moulding items which resist mould opening, e.g. containers formed on cores. To close the mould fluid is pumped at low pressure through line 70 into the cavities of the cylinders 126 while the cavities 76 of the cylinder 102 are discharged through valve 66 and line 69 to the reservoirs. Both cavities of each cylinder 126 are at the same pressure since the valve 73 is open, thus the pistons 54, 55 are moved to the right due to the difference in the effective area of the opposite sides of the pistons. When the mould is closed valve 73 is closed and the pump supplies fluid at a higher pressure to the chambers 57, 58 of cylinders 126. The fluid pressure in the other chambers 78, 79 of these cylinders is kept low by the adjustable pressure relief valve 75 leading to the reservoir. In the embodiments the different pressure ranges (values are quoted) are provided by using an electrically driven pump (not shown) which operates at a low pressure when providing a high output but produces a higher pressure when providing a low output. Two of the four cylinders 126 are provided with second cylinders 102 and one of the others carries an extension 53<SP>1</SP> to which is attached an arm 95 carrying cams 96, 97 to operate limit switch 94. The moving carrier 51 has an arm 85 carrying cams 87 (only one shown) which directly operate flow control valves 66, 67 to determine the rate of opening and closing the mould. A cam 101 connected to a sliding guard 82 also operates valves 66, 67 to block the flow of fluid when the guard is not in position.  The annular seal 80 comprises a sealing ring 80<SP>1</SP> between two woven rings 80<SP>111</SP> and two plastics rings 81. High pressure displaces a plastic ring 81 and compresses the rings 80<SP>1</SP> and 80<SP>111</SP>. Reference is made to Specification 1,371,199.