Patent GB-905395-A (GB)
Title: Fabrication of hollow articles
IPC: B21D53/04
Filed: 1960-06-22
Abstract: 905,395. Making heat-exchanger panels; stamping. OLIN MATHIESON CHEMICAL CORPORATION. June 22, 1960 [June 23, 1959], No. 21894/60. Classes 83 (2) and 83 (4). A method of making a hollow panel for a heat-exchanger from a blank having an unjoined interior portion contained within opposite outer faces of said blank is characterized by holding said blank against a rigid surface adjacent one face of said blank by uniform application of an hydraulic blank-holding pressure on the other face of said blank, maintaining said blank-holding pressure for a predetermined time interval, distending said unjoined portion with hydraulic pressure and releasing said blank-holding and blankexpanding pressures at a rate such that during discharge the difference between the blank-holding pressure and the blank-expanding pressure is maintained between the bulging pressure of the blank and the collapsing pressure of the expanded unjoined portion. The aluminium blank 1 can be any shape, e.g. flat or curved sheet, a cup, a cone or other surface of revolution. Apparatus for carrying out the method comprises a die 7 having a flat face 6 on which the blank 1 is placed the die being raised or lowered by an hydraulic cylinder 10 controlled by a pressure switch 13, a solenoid-operated valve 14, a check valve 15 and a pressure regulator 16 set to approximately 3000 p.s.i. Pressure switch 13 is preset so as to be activated at a predetermined die closing fluid pressure in cylinder 10, e.g. 2500 p.s.i. Above the movable die 7 is a fixed die 40 having a chamber 41 in its lower face surrounded by a sealing ring 44. A fluid-pressure conduit 45 leads to the die chamber 41 via a pressure switch 46, a solenoid operated 3-way valve 47 for venting the chamber 41, check valve 48 and pressure regulator 49 set to e.g. 850 p.s.i. The pressure switch 46 is actuated in response to a predetermined pressure level, e.g. 850 p.s.i. to activate a delay timer 64 which transmits a signal after, e.g. a 3 seconds delay, to actuate a solenoid 66. As the pressure in the die chamber 41 builds up to 850 p.s.i. the die closing pressure reaches its maximum pressure of 3000 p.s.i. The blank inflation pressure fluid is applied internally to the blank through a conduit 67 via a contact switch 68, valve 69, check valve 70 and a pressure regulator 71 set at approximately 2800 p.s.i. The contact switch 68 is actuated at a predetermined pressure level, e.g. 2800 p.s.i. to energize a 10-second delay timer 85. In operation, push-button switch 25 is operated and fluid pressure controlled by the regulator 16 closes the die 7 into sealing engagement with the upper die 40. When the closing pressure reaches, e.g. 2500 p.s.i. the pressure switch 13 is actuated to divert pressure fluid to the die chamber 41. At a blank holding pressure of e.g. 850 p.s.i. the pressure switch 46 actuates the timer 64 to give a 3-seconds delay before delivering the blank expanding fluid pressure to enable sufficient time for the blank-holding pressure to build up and to eliminate the effects of pressure surges. As the blank expanding pressure rises to 2800 p.s.i. the switch 68 preset to be actuated at the predetermined blank-expanding pressure provides a momentary activation of delay timer 85 which after a delay of e.g. 10 seconds transmits an electrical impulse to release the pressure fluids from the die recess and the blank interior in a controlled manner so that the difference between them will not be greater than the bulging pressure and the collapsing pressures of the expanded configuration. Control means are provided for automatically releasing these pressures in the desired ratio and the fluid pressure from cylinder 10. The delay eliminates surge effects and prevents the full-forming pressure being reached before the blank is fully expanded, thus preventing damage to lightly tacked laminations of the blank and gives the unjoined areas of the blank a chance to expand to a uniform height, Fig. 3. The use of the control means to maintain a desired relationship between the rates of discharge of the blank-holding and blank-expanding pressures permits fabrication of a panel, as shown in Fig. 6, wherein the web portions 120 of the blank are also bulged. The die faces may be contoured to provide the required configuration. Various electrical circuits for controlling the fluid pressures are disclosed in the Specification. Specification 759,831 is referred to.