SU865671A1 - Method of automatic control of volumetric doze of melt at pressure-moulding of plastic articles - Google Patents

Description

(54) AUTOMATIC REGULATION METHOD

LARGE DOSE OF MELT DURING MOLDING UNDER PRESSURE

PLASTIC PRODUCTS

one

This invention relates to the automation of plastic processing processes and can be used in the pressure casting process.

There is a known method for automatically controlling the volume dose of a melt during injection molding of plastic products, based on measuring the size of the gap formed between the molds during the injection of polymer melt into the mold cavity. This method is based on determining the mismatch between the size of the gap formed and the predetermined value, determined empirically.

In accordance with the magnitude and mismatch sign, the volume of the meltable mixture is molded for injection in the subsequent casting cycle 1.

However, fluctuations in the size of the gap between the molds due to improper dosage are extremely difficult to measure with the required accuracy under conditions of shock loads and high temperatures, since with proper organization of the technological process these fluctuations do not exceed 0.015 mm.

The closest to the invention according to the technical essence is a method for automatically controlling the volumetric dose of the melt during injection molding of plastic products, which consists in determining the magnitude and sign of the mismatch between the current and predetermined coordinates of the screw at the end of the injection process, summing the mismatch value found with movement of the worm during the injection and change depending on the magnitude of the resulting

10 the sum of the movement of the screw during the kneading in the subsequent cycle of pouring 2.

The b + cone of the known method is that when adjusting the volume dose for the next cycle, the fact that the specific || the volume of the melt substantially depends on the pressure acting on the melt, which does not allow to increase the stability of the mass of molded products.

The purpose of the invention is to increase the stability of the mass of molded products.

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Claims (2)

This goal is achieved by the fact that in a known method of automatically adjusting the volumetric dose of the melt during injection molding of plastic products, which consists in changing the linear displacement of the screw during melting, melt detection and the sign of the mismatch between the current and specified coordinates of the screw at the end of the process injection, the additional values of the specific pressures acting on the melt at the time of the end of the injection process and in the process of kneading are determined, the specified specific pressures, determine the linear displacement of the screw during the melting of the melt in each subsequent cycle of casting by summing the path size passed by the screw in the melt injection in the previous cycle and casting and multiplying said error value between the current and specified coordinates of the wind by the value proportional to the specified difference in specific pressures, and the proportionality coefficient is chosen depending on the compressibility of the polymer being processed. The drawing shows a block diagram of a device that implements the proposed method for automatically controlling the volume dose of the melt. The wormhole 1 during the injection process performs axial movement in the plasticization cylinder 2, controlled by the displacement sensor 3, injecting the prepared melt dose into the cavity of the mold 4 under the pressure of the working fluid in the piston cavity of the hydraulic cylinder 5, which is controlled by the pressure sensor 6. The signal of the motion sensor 3 in the comparison unit 7 is compared with the signal coming from the target, ". 8. "". "" "-J... 8. The signal from pressure sensor 6 enters the arithmetic unit 9, which calculates the difference between the specific pressures acting on the melt at the time of completion of the injection process and during the kneading process. This signal enters the logic block 10, which generates a correction signal by the actuator to stop the screw 1 after the end of the kneading. The device works as follows. At the time of the end of the injection process, the comparison unit 7 determines the magnitude and mismatch sign between the actual coordinate screw 1, detected by sensor 3, and set by unit 8. At the same time, the signal from pressure sensor 6 is proportional to the specific pressure of the working fluid in the hydraulic cylinder cavity 5 , is fixed at the inlet of the arithmetic unit 9. During the plastification of the melt, carried out during the rotational-translational movement of the screw 1, the rasplavl accumulates in the front of the cylinder 2 of the kneading. A signal proportional to the pressure applied to the melt in the process of kneading from pressure sensor 6 is fed to the input of unit 9, the output of which produces a signal proportional to the difference between the signals proportional to the measured specific pressures at the time of injection and plasticization. This signal arrives at the first input of logic unit 10, the second input of which receives a signal proportional to the magnitude and sign of the mismatch between the real and given coordinates of the worm 1 at the time of the end of the injection process. Logic unit 10 determines the product of the signals at its inputs, taking into account the proportionality coefficient, selected depending on the compressibility of the polymer being processed. At the same time, at the output of logic unit 10, a correction signal is generated for the linear displacement value of the worm 1 during kneading in the subsequent casting cycle, taking into account the value of the compressibility of the melt. The implementation of the proposed automatic control method will improve the accuracy of the volumetric dosing of the melt, taking into account its compressibility as a function of the specific pressure acting on the melt. Experimental verification of the method showed that with its implementation an accuracy of 0.4% of the mass of products in a batch of 1000 pieces can be achieved. The invention The method of automatically controlling the volumetric dose of the melt during injection molding of plastic products, which involves changing the linear displacement of the screw during the kneading of the melt, determining the magnitude and sign of the mismatch between the current and the specified coordinates of the screw, at the end of the injection process, differing in that, in order to increase the stability of the mass of the molded products, the values of specific pressures acting on the melt are found at the time of the end of the injection process and in the process of tications, determine the difference between the specified specific pressures, determine the linear displacement of the screw during melt kneading in each subsequent casting cycle by summing the path size passed by the worm during melt injection in the previous cycle and casting the said error value between the current and the specified coordinates a worm by an amount proportional to the specified difference in specific pressures, the proportionality coefficient being chosen depending on the compressibility of the processed of the polymer. Sources of information taken into account in the examination 1. Hartmann E. Vollautomatisch Regelung des Fbrmuest-Fullvolumens hein VerarBeiten von Duroplasten.4Kunststoffea 1974 № 3 S.I06-109. 2. US patent No. 3666141, cl. 222-1, pub. 1972. (prototype).