Patent GB-454469-A (GB)
Title: Method and apparatus for producing articles of continuous length and constant cross-section from fluid materials such as latex
IPC: B29D99/00
Filed: 1935-11-14
Abstract: 454,469. Automatic control systems. INTERNATIONAL LATEX PROCESSES, Ltd., 10, Lefebvre Street, St. Peter Port, Guernsey. Nov. 14, 1935, No. 31536. Convention date, Nov. 16, 1934. [Class 38 (iv)] [See also Groups XIX and XXXVII] Linear dimensions.-The cross section of an article produced by extrusion or flowing of fluid material, e.g. rubber thread, tube, &c. made from latex, in which the flow characteristics of the material may vary, is rendered constant by controlling the flow in accordance with the ratio between the length of the article made and the weight of material used. The invention provides for intermittent measurement and recording by an electrically operated device of the length of thread made from a fixed weight of latex and the apparatus described effects the automatic adjustment of the hydrostatic head of latex, in accordance with variations from a standard length, by a second electrically operated device. Other means for adjusting the fluid flow may be used, for example, variation of a fluid pressure superimposed on the hydrostatic pressure, or of the fluid pressure applied in a pressure tank feeding the latex, of the flow resistance of the delivery line, as by a valve with a plunger of variable effective length, a stretched rubber tube forming part of the supply line, or a heating element surrounding a part of the supply line. Alternatively the rate of thread production may be varied, as by changing the speed of the pull-off and belt mechanism to be described, or, instead of measuring the thread, the consumption of latex producing a fixed thread. length may be measured, for example by a dropper feed and an " electric eye " operating a counting device. Latex is fed continuously to nozzles 31 from a tank 24 intermittently supplied through a pinch valve 61. The head of latex is unchanged as the tank content changes, owing to the adjustable spring suspension 38. The fluid issues into a coagulant and is withdrawn at constant speed over a pull roll 34 and belt 35. A cam 100 and switch 101 control the length measuring and recording device B which is driven by an electric torque motor 107 and escapement 114, 116, the latter being electromagnetically rocked in accordance with the movements of switch 101. The record pen 149 is driven by a spindle 132 carrying worms 131, 133 and pivotally secured to the shaft of the escapement wheel. A spring 140 maintains the drive, but an electromagnet 141 disengages it to allow a counterweight to zeroize the pen when the measured quantity of latex has been consumed. To adjust the hydrostatic head of the latex an arm 164 pivoted on a bracket on the recorder is set to the standard length required by a screwed spindle with a squared end 174. This arm carries two counterweighted contact levers 184, 185 co-operating with a contact carried by the arm 164. The permissible variation in thread length is determined by a screw 191 which sets the distance between the contacts on arms 164, 185. The pen arm 149 by engaging the end of the lever 184 determines the sense of any adjustment of hydrostatic head required, according as connection is maintained between contacts on levers 184 and 164 or made between those on levers 184 and 185. Adjustment is effected to an extent determined by the distance between two of the pins 215 on a disc driven by a reversible motor 202 operating a cable drum 200 to vary the height of a bracket 22 carrying the latex tank 24. The contacts on the length recorder selectively actuate relays 303, 331 of a standard reversing control for the motor 202 and the pins 215 engage a lever 217 which passes a trigger 223 on a pendulum 221 when the motor starts and is caused by the next pin to tilt the pendulum to the left and release it. The pendulum carries a mercury switch 220 which is in the retaining circuit of the relays mentioned and momentarily opens this circuit as the pendulum swings to the right. The adjustment in the hydrostatic head of latex may be rendered proportional to the height of the tank 24, by such means as coning the cable drum 200. The tank 24 is continuously dis. charging through a syphon 27 and is filled intermittently through a pipe 26, the orifices of these remaining at all times in the same relation to the level of latex in the tank owing to the spring suspension 38, which is adjustable. The operation of the valve 61 is automatically offected by rotary mercury switches secured on the shaft 44 of a disc 42 coupled to the tank by a counterweighted cord 41. These switches are adjusted to close the respective circuits of a split field motor 62 actuating the valve 60 through reduction gear, a crank 67 and levers 75, 71, the motor running on each occasion until a lever 70 driven by the crank 67 has opened one limit switch and closed the other to prepare the return circuit. The sequence of the automatic control operations is determined by contacts 51, 52 adjustably mounted on a bracket secured to the carriage 22 and cooperating with a contact 46 on an arm fixed to the disc 42 and mercury switches 76, 77 carried by the lever 75 oscillated by the valve motor 62. The circuits of the electromagnets oscillating the escapement 116 pass through a contact 122 on a relay 400, and this relay also actuates a mercury switch, having a time element, in series with the flow control contacts actuated by the length recorder. The measured quantity of latex is consumed and contact 46 has thus passed contact 52, the motor 62 is actuated to open the valve 61. Where the valve 61 is open switch 77 energizes the magnet 142 to zeroize the pen arm 149. When the tank 24 has filled, the second mercury switch on shaft 44 closes and the valve 61 is caused to close whereupon switch 77 opens and 76 closes to energize contact 46. When this passes contact 51, the relay 400 is energized and the switch 101 is then effective to actuate the length measuring and recording apparatus. The relay 400 closes at contact 411 its own retaining circuit. When contact 46 passes contact 52, the relay 400 is short-circuited ; the contact 122 opens to stop the measurement of length and the switch 415 closes the circuit of the control contacts on the recorder. Any adjustment of hydrostatic head required then proceeds as the tank 24 is refilling and the sequence is repeated. The switch 415 is shown in Fig. 11 and comprises two contact members 421, 422 arranged so that when the switch is tilted by the relay to the position shown, contact is not made between the members by the mercury, but an insulating barrier 423, having a passage below for the mercury 425 and above for gases, causes the mercury to bridge both contacts when the switch is reversely tilted ; the connection persists for a short interval until sufficient mercury has passed under the barrier.