SU952888A1 - Method for controlling process for molding products from cellulose triacetate - Google Patents

Description

le and implementation method; in fig. 2 dependence of the value of the required change in it (correction) of the temperature of the vapor-gas mixture supplied to the crushing machine, on the change in & Q condensate at the outlet of the condenser (for a typical process). As shown by studies carried out on existing tape machines, a change in the temperature of the vapor-gas mixture from a fixed value of 1 ° C causes a change in uQ of the solvent consumption at the output, of the condenser, by 1.6-1.7%. The tape casting machine consists of a casting part, a drying part and a coiling unit. The casting part of the machine consists of two drums 1, on which tension is infinite metal strip 2. To apply a layer of film-forming solution to the surface of the tape 2, there is a slit of the die 3 into which the film-forming solution comes from the temrostat tank. The casting part of the machine is enclosed in an airtight duct 4, which forms two drying channels — the upper and lower parts of the belt 2. The drying of the film-forming solution occurs due to the circulation of the drying agent of the vapor-gas mixture in the channels during continuous movement of the ribbon 2 The molded film (base) 5 is removed from tape 2 with some content of residual solvents and through the bolster comes into the dryer part 7 of the machine, where it is finally dried and with the help of the coiling unit 8 is wound into a roll. In the process of film formation and drying of the film in the channels of the casting part of the belt machine, a large amount of solvent is evaporated from the solution. With a closed air exchange cycle, the vapor-gas mixture is recirculated in the circulation circuit 12. Coming out of the drying channels of the duct 4, the vapor-gas mixture enters the condenser, 9, where it is subjected to cooling, as a result of which a part of the solvents condenses and is discharged through a siphon for regeneration. The cooled vapor-gas mixture using a centrifugal fan 10 is fed into the heater 11 and again enters the box 4 of the casting part of the machine. The fan 10 provides a constant flow rate of the vapor-gas mixture in the closed sealed circuit 12 of the circulation. Heating the steam gas mixture to a predetermined value is ensured by a control system that includes a measuring device 13, a regulator 14 and an actuator 15. The control method is implemented in a very small way, for the first time, using an automatic control system that includes a measuring device 13 of the vapor – gas mixture temperature the output of the heater 11, the controller 14 p, the actuator 15 with a regulating authority on the steam supply line to the heater 11, stabilize the set value of the steam temperature AZOV mixture at the outlet of the preheater 11. The temperature of the mixture Stabilizability value is selected based on the desired rate of solvent evaporation moldable substrate. Then, using the measuring device 16, the flow rate of condensed solvents at the output of the condenser 9 is measured. After that, the required value D t of change (correction) of the mixture temperature supplied to the box, c, is determined according to the schedule (Fig. 2). depending on the change in other consumption of condensed solvents at the condenser outlet, and using the scaling unit 17, changing the task to the controller 14 for the temperature of the vapor-gas mixture. When forming a base from a polymer solution on the structure and the physical and mechanical properties of the base (tensile strength, shrinkage, brittleness, etc.), the rate of evaporation of solvents from the layer deposited on the metal tape of the machine is significant. At the same time, the main parameters affecting the evaporation rate of solvents are the temperature and consumption of the vapor-gas mixture fed to the machine box. Increasing the temperature and flow rate of the mixture increases the evaporation rate of the solvents and vice versa. In addition, a number of other indicators of the process, such as partial pressure of a vapor or concentration of solvents, vary in the mixture due to the gradual freezing of the condenser 9, temperature and viscosity of the polymer solution fed to the die plate, have a significant impact on the rate of evaporation. machines, the surface temperature of the metal tape 4. The fluctuations and changes in time of these indicators leads to the release of a substrate having a variation in structure and physicomechanical properties. With a closed circulation system of the vapor-gas mixture in the circuit 12, the solvents evaporating from the layer of solution deposited on the metal tape are transferred to a liquid in the condenser 9 with sufficiently deep cooling of the vapor-gas mixture and are diverted through the siphon to regeneration. At steady state at constant flow mixtures in office 12 cir; kulntsii and temperature stabilization

tgx of the mixture at the entrance to the duct 4 the amount of solvents (unit of condensate) condensing 9 per unit time (condensate) is (with a slight deviation of 1-2% due to possible loss of solvents due to incomplete sealing of circuit 12) the amount of solvents evaporating per unit time those. the consumption of condensates; solvents (liquids) at the outlet of the condenser 9 directly characterizes the evaporation rate, solvents in the box 4 of the machine, and the sign and magnitude of changes in the consumption of condensed solvents characterize the sign and the magnitude of changes in the rate of solvent evaporation.

The introduction of temperature correction of the vapor – gas mixture depending on the actually measured consumption of liquid solvents at the outlet of the condenser 9 allows one to maintain the constant evaporation capacity of the vapor – gas mixture over time.

Thus, a disturbing effect on the process of forming the base, caused by changes in the partial vapor pressure and solvent concentration in the mixture, temperature and viscosity of the film-forming solution, temperature of the surfaces of the drums and the metal tape, will be compensated for changes in temperature tgx of the gas-vapor mixture supplied to the machine box . This provides stabilization of the structure and the physicomechanical parameters of the base produced.

g

The proposed method can be implemented using mass-produced technical means.

The introduction of the method will significantly reduce the instability of the quality characteristics of the base being injected, such as shrinkage, curl, tensile and impact strength, relative elongation, and increase output by reducing rejects. According to the initial data, the stabilization of the conditions for the formation of the triacetate base on casting tape machines will increase the yield of the base by 0.5%.

15

Claims (2)

1. USSR author's certificate number 525758, cl. D 01 D 5/04, 1975. 2. Author's certificate. USSR s 577260, class D .01 D 5/04, 1975 (prototype). 3 f L -n -9 -b -j 0 3 i-s -ig Fm.t