Patent GB-1045932-A (GB)
Title: Apparatus for fabricating plastic pipe
IPC: B29C53/60
Filed: 1964-01-21
Abstract: 1,045,932. Making reinforced plastic tubes. DOWSMITH Inc. Jan. 21, 1964 [Jan. 22, 1963], No. 2662/64. Heading F2P. Apparatus for fabricating reinforced plastic pipe by winding a strip of fibrous material impregnated with uncured resin, in which provision is made for accurately controlling the temperature of the resin during the winding operation, comprises a mandrel 4, a distribution member 21 mounted adjacent the mandrel, a plurality of guide members 18 for winding the strip over the distribution member and on to the mandrel in a generally helical pattern, elements for supplying heat to the member 21 to melt the resin as the strip passes over the member, a device 45 for sensing the heat of the portion of the strip passing from the member 21 to the mandrel and an intermediate member operably connecting the heat sensing device with the heater to vary the output of the heater in accordance with the temperature of the strip. A reel 2 holding the resin-impregnated strip rotates with the winding head 1 around the mandrel 4, Fig. 1, which is supported by rollers 15 and advanced by a drive wheel 16. A disc 9 also rotates with the winding head and on the disc is a curved support plate 19, Fig. 2 (not shown) with a series of guide rollers 18 so disposed that a slight twist is imparted to the strip, which then passes over a guide roller 20 and a heated roller 21 to the mandrel on which it is wound. The rollers 20, 21 are mounted in a frame 22 which also rotates about the mandrel, so forming the distribution member, the roller 21 housing heating elements 26 which are supplied with current through slip rings 30 as the roller 21 is rotated by the strip passing over it. The brushes 31, Fig. 5 (not shown), of the slip rings 30 are connected to other slip rings which are concentrically located on the face of the disc 9 and supplied by stationary brushes. The sensing unit 45 is directed to sense the infra-red radiation of heat from the part of the strip passing from the roller 21 to the mandrel, and is connected to the control circuit in the member 50, Fig. 6 (not shown), while that part of the strip is passing under it by the closing of a switch 47, due to the operation of a cam surface 48 on the disc 9. The control circuit includes a four-leg resistor bridge 52 with a pair of input junctions connected to a D.C. source and may be set to establish a predetermined output voltage, corresponding to a preselected tape temperature, by a resistor 54. The voltage output of the bridge 52, and of the sensing unit 45 as amplified by an amplifier 49, are connected in opposition and in accordance with the difference between them an input is applied to an amplifier 55. A two-phase reversible induction motor 56 has one phase 63 connected to the amplifier 55 and the other phase 66 connected to an A.C. source 69, controlled also by the switch 47. If the output from the amplifier 49 exceeds that of the bridge 52 a voltage of one polarity is applied to the phase 63 and if it is less a voltage of opposite polarity is applied. Thus the motor 56 runs in opposite directions according to whether the temperature of the strip 3 increases or decreases, and moves the slider 70 of a potentiometer 71 one way or the other. The potentiometer 71 is connected as part of a known modulator control 72 and the resulting voltage drop is imposed on a D.C. amplifying unit 73, the output of which is connected to actuate a saturable reactor 74. An A.C. reactive winding 77 around the core of the reactor 74 is connected in series with the leads supplying current to the heating elements 26 in the roller 21. Thus the periodic sensing of the tape temperature and the corresponding operation of the control circuit result in a continuous modulation of the energizing of the heating elements 26 to maintain the required strip temperature. A temperature sensitive element 41, Fig. 4 (not shown), is connected to a relay 78 whose contacts 78-1 open if the roller 21 is excessively heated. Previously, the resin is applied to the reinforcing strip in any conventional manner. After the resin and cooling agent are applied to the strip, the resin will begin to cure or polymerize and the curing of the resin is halted at a predetermined stage by refrigerating the strip, which can then be coiled on the reel 2 in preparation for the pipe fabricating process. Epoxy resins, prepared by condensing a polyhydric phenol with a polyepoxide or polyfunctional halohydrin, are recommended as the impregnant or coating for the reinforcing material, which may take the form of mineral fibres such as glass or asbestos, synthetic fibres such as nylon or rayon, vegetable or animal fibres and metal wire.