GB857973A - Improvements in or relating to apparatus for the production of shaped plastic workpieces - Google Patents

Abstract

857,973. Vacuum-moulding hollow articles. THIEL, A. W. Nov. 7, 1958 [Nov. 8, 1957(3)], No. 35884/58. Class 87(2). [Also in Group XI] Hollow articles are made by feeding a thermoplastic sheet 114 by upper and lower conveying chains 171, 172, each having rubber gripping elements (see Figs, 3, 3a not shown), between upper and lower radiant heating elements 101 and then vacuum forming the hot sheet in a shaping die 111, cooling the formed articles at 103, punching-out for formed articles by dies mounted on a carrier 212, and removing the formed articles at 105. The chains 171, 172 are driven intermittently by a motor 175 controlled by a switch 179, which is closed when the die 111 and the punching out die 122 are in their upper position. A switch 180 is opened automatically after the motor has carried out a desired number of revolutions. The radiant heating elements 193, Fig. 8, may be arranged longitudinally and transversely with the outer heating elements arranged closer together. The elements are adjustably mounted between end contact strips. In a modification (see Fig. 14, not shown) the heating may be carried out in more than one stage by independent heating elements, the wavelengths of the infra red in the first stage being such that it tends to soften the inner zone of the sheet, whilst the second stage tends to heat the surface. When the hot sheet is moved to a position beneath the shaping die 111, the die is lowered by hydraulic cylinders 132 to the position shown in Fig. 2. If desired a pre-suction may be applied to the sheet, to give it the correct sag. Tools 141 (see Fig. 2b, not shown) are then moved upwardly to prestretch the sheet, during this upward movement a valve 123 is opened to allow air to excape from the dies through an adjustable pressure valve 122. The valve 123 is then closed, and a valve opened to cause the full suction to draw the hot sheet into contact with the cold walls of the die cavities. In order to ensure the sheet 114 is correctly positioned against the lower edges of the die 111, a pattern frame 161 is swung upwardly with the member 141. After the sheet has cooled in the cavities, the die 111 is lifted to its rest position and the shaped portions of the sheet are withdrawn from the cavities. In a modification, Figs. 14 to 16 (not shown), a spring urged ejecting plate and compressed air may be used to aid the withdrawal of the articles from the dies. The tools 141 may have a felt or foamed plastic surface to act as a heat insulator and through which hot compressed air is blown during the initial shaping operation. After the cooling stage 103, the shaped articles are received in the punching- out device 104 which is relatively adjustable to the forming die 111. The punching-out device comprises cutting dies 211, Fig. 5, associated with locating sleeves 224 which first engage the shaped articles and align them with the apertures 221 in a punching platform 220, which may have a covering of, e.g. celluloid. The dies 211 are raised and lowered by hydraulic cylinders 215. After cutting, the dies are raised and the moulded articles ejected by rubber bellows 225 which are fed with compressed air through a pipe 227, alternatively the articles may be ejected by pistons. In a modification (see Fig. 6, not shown) stripping plates remove the remnants of the sheet 114. The trimmed articles are removed from the cavities 221 Fig. 11, by members 308 which are raised and lowered hydraulically and to which suction may be applied to hold the trimmed articles. The operation of these members is controlled by a switch 324 which is operated by the carrier 302 on which the members 308 are mounted. When the shaped articles have been lowered on to the platform 307, the suction is cut off, the shaped articles are pushed along the platform 307 by a bellows 322, and the articles fed by a rotating disc 331 and rollers 341 to a final trimming die 352. The finished articles may then be tested for shape and quality and are fed over a deflecting device 362, past a counting device 366, and collected at 365. In a modification, Figs. 17 to 20 (not shown) a modified collecting device is described and a rotating disc shapes the rim.