GB1186951A - Improvements in or relating to Dimensional Control Systems - Google Patents

Abstract

1,186,951. Hydraulic presses for moulding &c. OSTRANDER-SEYMOUR CO. 24 May, 1968, No. 24940/68. Headings B5A and B5F. [Also in Division G3] An automatic dimensional control system for a press 10 of the type wherein an article is positioned between fixed and movable platens 20, 26 bored to provide passageways for steam, oil or electrical heating comprises a transducer 121 (see Fig. 6) which is responsive to changes in the air pressure of a system including orifices 104, 105 in the platen 20 and which controls the position of a relief valve 96 (see Fig. 5) controlling the flow of hydraulic fluid to the cylinder 81 and ram 82 determining the position of the movable platen 26. The orifices 104, 105 are formed at opposite corners of the platen 20, Fig. 7 (not shown) and are accurately gauged so that a predetermined pressure is established between the platens when bearers (not shown) of substantially the dimensions desired for the article are engaged therebetween spring-loaded plungers being provided adjacent the orifices to ensure accurate positioning of the bearers. During a forming operation variations from the predetermined pressure cause opening and closing of contacts 163, 164 (see Fig. 3) controlled by the transducer 121, these contacts controlling relays 1CR, 2CR which determine the direction of rotation of a D.C. motor controlling the position of the valve 96, so that a predetermined pressure on the article is maintained. The contacts of relays 1CR, 2CR control further relays for reversing the armature current of the motor, whose speed is determined by the firing instant of a silicon controlled rectifier controlled by a unijunction transistor and adjustable RC circuit, Fig. 4 (not shown). The transducer 121 forms part of a conventional control device 118 which monitors air from a constant volume source 117 and includes members 120, 122 for respectively controlling the pressure and rate of flow of the air to orifices 104, 105. The control system of the invention is stated to ensure parallelism of the platens 20, 26 under conditions of workpiece misalignment, since the press will continue to close until the predetermined pressure corresponding to equal platen spacing at the orifices is attained. Fluid flow to the cylinder 81 may be controlled directly instead of by the relief valve 96. The press 10 is of conventional design and has the usual control circuitry to co-ordinate the movements of the platen 26 and the work-table 56 with the pre-heating and curing operations controlled respectively by the timers T1, T2. Operation of the hydraulic control system of Fig. 5 is described for each of the positions of the approach selector switch 52 enabling the operator to alter the speed of the movable platen 26 according to the type of material being formed. The switch 52 provides three modes of operation for raising the platen 26, the dimensional control system functioning as described above for each of these modes.