GB922401A - Improvements in or relating to the manufacture of shoes - Google Patents

Abstract

922,401. Moulding microcellular rubber soles on to footwear uppers. BRITISH UNITED SHOE MACHINERY CO. Ltd. April 30, 1959 [May 1, 1958; June 14, 1958; April 16, 1959], Nos. 13895/58, 19096/58 and 12968/59. Class 87(2). Heat and pressure are applied to a mass of unvulcanised microcellular rubber (incorporating a suitable blowing agent) in a sole forming cavity provided by a mould arrangement (comprising a sole mould and, conveniently, a pair of side moulds) arranged to be closed about a lasted shoe bottom, to cause it to flow and fill the cavity and to initiate the action of the blowing agent, a limited movement between the sole mould and the last being brought about at a controlled rate after the rubber has been partially vulcanised to allow it to expand under the action of the blowing agent in the direction of thickness of the sole, the vulcanisation of the rubber then being completed. The use of a metal last the bottom of which is formed by a layer of heat-insulating material reduces the amount of heat conducted from the sole to the last and thus allows the upper surface of the sole to reach a higher temperature than is possible when the metal last bottom is used directly in contact with the insole (or sock) of the shoe. In order to rapidly establish a uniform temperature throughout the rubber mix during its vulcanisation, the required amount of mix may be preheated in a suitable oven (but not to a temperature sufficient to cause the blowing agent to become active) and then transferred to the sole cavity in the vulcanising machine. For a final sole thickness of # inch the expansion of the rubber should be between # inch and 3/16 inch. If the total vulcanising time is 12 min., the initial pressure stage should last for about 1¢ min. and the expansion stage for 5 to 10 min. As shown in Fig. 1, fluid from a low-pressure pump Pi passes via valves V 1 , V 2 , V 3 to the bottom of the cylinder 8 housing the piston 6 which is connected to the table 2 supporting the sole mould. At the termination of a preset time, a timing device T causes the change-over valve V 1 to operate and to connect the highpressure pump P 2 via valve V 12 to pilot H 2 of control valve V 3 . As pilot H 1 is still connected to pump P 1 , there is a pressure difference which changes valve V 3 over (to the lower position as shown in Fig. 1) against the action of spring 29. The high pressure fluid is thus diverted to operate valves V 7 , V 8 and fluid from beneath the piston 6 now flows (under the influence of downward pressure exerted by low pressure fluid supplied via pressurereducing valve V 4 ) via valve V 7 to the metering device M. Fluid from the lower end of this device flows to the sump S through valve V 8 and the needle valve Vs and expansion of the rubber in the mould cavity continues until the head 48 on the piston rod 46 of the device M engages an adjustable stop screw 50. Hence the rate and amount of expansion can be controlled by adjusting valve V 9 and screw 50 respectively. The valve V 12 can be closed in which case the machine can be used for the twostage vulcanising of soles of hard rubber. In this case the valve V 1 first connects the lowpressure pump P 1 to the cylinder 8 and then, after a predetermined time, is changed over by the timing device T so that fluid is supplied by pump P 2 to the cylinder 8 to complete the sole vulcanisation under high pressure. By using the modified metering device M 1 shown in Fig. 2, the expansion of the rubber takes place in two stages, first at a relatively slow rate and then at a faster rate. The housing 101 provides a main chamber 103 and a secondary chamber 105 and the valve member 107 slidably mounted in the housing comprises a piston 109 and a cylindrical stem 111, the latter having a reduced portion 117. The initial position of the piston is set by the screw 115 and the escape of the fluid beneath it is limited to valve V 9A until the two chambers 103, 105 are interconnected via the reduced portion 117 when the fluid escapes via both valves V 9A and V 9B and consequently at a faster rate. The movement of the valve member towards the right is limited by the adjustable stop screw 50A. A further modification is to control the rate of movement of the piston of the metering device by means of a dash-pot arrangement in which the fluid circuit is separate from the main fluid circuit of the machine in order to avoid overheating and consequent re-adjustment of the control circuit. Should it be desired to have the rate of expansion continuously variable the piston rod of the metering device may carry a cam member which acts on a cam follower connected to the control needle valve so as to vary the flow through it to a predetermined extent. Specifications 824,106, 859,671 and 892,465 are referred to.