GB1239367A - - Google Patents

Abstract

1,239,367. Sheet forming. COMET INDUSTRIES Inc. 10 March, 1970 [18 March, 1969], No. 11468/70. Heading B5A. [Also in Division G3] In a thermoforming machine, the various operations of the parts of the machine are controlled by programme card 116 comprising a flat plastics plate provided with longitudinal notched ridges 118, the card being forwarded, by means of a motor driven pinion gear engaging a central rack 120, under a series of press-button switches there being one switch corresponding to each ridge. The switches are selectively closed by the notches and the various operations are thus controlled. The plate is forwarded intermittently and, during its periods of motion, the switches are closed by engagement with the notches and the operations controlled according to a pre-set time sequence dependent upon the speed of the plate. During its periods of rest the operations are controlled by sensing devices located in the machine, the sensing devices also acting to resinstate the movement of the plate when desired conditions occur so that further control is obtained from the plate. In the embodiment shown in Fig. 1, the sheet to be formed is clamped by a fixture 46 comprising four pneumatically operated clamping bars (see Fig. 5, not shown) over an aperture in a vacuum tank 24 and is heated by upper and lower radiant heaters 38, 36 reciprocable over and away from the sheet along tracks 26 and 28 by means of a pneumatically actuated lever 82. The sheet is screened from the upper heater to control the temperature of different areas of the sheet by a screen 52 carried by a frame 48 reciprocable to and from a position above the sheet along tracks 40, upon which screen a selected template 54 may be positioned. After heating, the sheet is pre-stretched by blowing and then formed between a lower mould to which vacuum is applied and an upper mould, the moulds being carried by platens 100 and 98, respectively, reciprocable along racks 92 by drive pinions 102. After moulding, the moulded article is ejected by a blast of air through the lower mould. To control the sequence of operations, the card is forwarded until a first switch is closed to admit compressed air to the vacuum tank and movement of the card is continued until second and third switches are closed to start the heating, movement of the card being arrested at this point. After the sheet has been pre-stretched and heated to the required degree as determined by a photo-cell device and a temperature sensing device, the temperature sensing device arrests the heating and causes the plate to be further forwarded to bring further notches under further switches to control the rest of the forming operation. Sets of screen template/programme card pairs may be stored, each pair corresponding to the manufacture of a different type of article.