JPH0380609B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to a resin temperature control method in a plastic molding machine for controlling the resin temperature in the molding machine to the optimum temperature for molding when plastic is molded using a plastic molding machine such as an extruder. Prior art and its disadvantages In plastic extrusion molding, etc., controlling the resin temperature in each zone in the extruder cylinder to a temperature suitable for the resin used increases the extrusion amount, reduces scorch, reduces energy costs, Furthermore, it has a very important meaning from the point of view of improving electrical properties as an insulating material for power supplies and cables. As shown in Fig. 1, conventional extruder resin temperature control involves drilling a plurality of temperature measuring holes 3 in the cylinder 2 of the extruder 1, which do not penetrate the cylinder 2, and inserting the temperature into the temperature measuring holes 3. Insert the temperature element 4... and measure the temperature of each temperature measurement zone of the cylinder 2, C ₁ , C ₂ , C ₃ , C ₄ ,
These temperatures are input to the temperature controllers 5, and the heating devices 6, such as band heaters and embedded heaters, provided outside the cylinder 2, and the cooling devices 7, such as cooling blowers, are controlled by these temperature controllers 5. This is done by the method of However, it has become clear that this method has the following problems. That is, in the above control method, there is a difference between the temperature measured by the temperature measuring element 4 and the temperature of the molten resin in the cylinder 2 due to changes in the room temperature around the extruder 1. During the extrusion process, a temperature difference (△T ₁ ) as shown in Figure 2 occurs in each temperature measurement zone (C ₂ , C ₃ , C ₄ ), or when the resin is poured into the extruder 1. Due to a change in the rotational speed of the screw 8 of the machine 1, the temperature difference between the actual resin temperature and the temperature of the cylinder 2 as shown in FIG. 3 further increases by ΔT ₂ . Therefore, it was found that due to these influences, the temperature of the molten resin in the cylinder 2 was heated to a temperature higher than the desired temperature, and energy was wasted. (Please note that in Figures 2 and 3
C ₂ , C ₃ , C ₄ represent the temperature measurement positions of cylinder 2, and are shown in each temperature controller 5 in Figure 1.
It corresponds to each temperature measurement zone of C ₂ , C ₃ and C ₄ . ) Furthermore, according to recent studies, the temperature of the molten resin in the cylinder 2 is determined by not only the room temperature and screw rotation speed as mentioned above, but also the set temperature of the extruder 1, the shape and structure of the screw, and the type of molten resin (same It has become clear that this is influenced by differences in resin grades. For example, when extruding polyethylene resin, even if the set temperature of the temperature controller 5 is 120°C and the temperature measured by the temperature measuring element 4 is 120°C, the actual molten resin temperature is 130 to 150°C. . Therefore, it has been impossible to accurately determine the actual temperature of the molten resin by simply measuring the temperature using the temperature measuring holes 3. Therefore, the present inventors first proposed a resin temperature control method that can control the resin temperature with high precision in patent application No. 58-41038.
No. (see Japanese Patent Application Publication No. 59-167241) and patent application No.
It is proposed as No. 58-41039 (see Japanese Patent Application Laid-open No. 59-167242). These methods involve arranging two or more temperature measuring elements at different distances from the inner surface of the cylinder in the thickness direction of the cylinder wall of a plastic molding machine, and measuring the temperature of the cylinder measured by these temperature measuring elements. The temperature of the inner surface of the cylinder is determined from the temperature, and at least 3 of the parameters that vary the temperature of the molten resin, such as the screw rotation speed, room temperature, set temperature, screw shape, and type of resin, are determined, including the screw rotation speed and room temperature. Add the corrected temperature using the above parameters, predict the temperature of the molten resin in the cylinder, find the deviation between this predicted temperature and the desired resin temperature, and control the temperature of the molten resin in the cylinder based on this deviation. Measure the temperature of the plastic molding machine and the cylinder of the plastic molding machine, and add to this temperature the room temperature, screw rotation speed, screw shape, set temperature, type of resin, and other parameters that change the molten resin temperature. The temperature of the molten resin in the cylinder is predicted by adding the corrected temperature from at least three or more parameters, the deviation between this predicted temperature and the desired resin temperature is determined, and the temperature of the molten resin in the cylinder is controlled based on this deviation. It is something to do. In these methods, no matter what the distribution of the desired resin temperature of the molten resin in the cylinder (temperature in each temperature measurement zone in the cylinder), once the desired resin temperature is set before operation, the rest is as described above. It has the advantage that it can be automatically controlled no matter how much the parameters fluctuate, and its accuracy is extremely high at about ±0.5°C to ±1°C. However, in implementing these methods, it is necessary to create basic data by varying each of the above parameters and determining in advance the influence of these parameters on the molten resin temperature (temperature fluctuation). However, there was a problem in that creating the basic data required a large amount of resin and a long time. Purpose of the invention This invention was made in view of the above circumstances,
To provide a resin temperature control method for a plastic molding machine that can greatly reduce the effort and cost of creating basic data, can control the resin temperature with high precision, increases resin discharge amount, reduces scorch, and saves energy. The purpose is to Structure of the Invention The resin temperature control method for a plastic molding machine of the present invention involves separately setting the optimal resin temperature distribution of the molten resin in a cylinder that is optimal for molding the resin, and then controlling the temperature of the molten resin. Equipped with a temperature measuring screw that can directly measure the temperature of
In addition, using a temperature measuring plastic molding machine that is equipped with a plurality of temperature measuring elements corresponding to each temperature measuring zone of the cylinder so that the temperature of the cylinder itself can also be measured, at a certain screw rotation speed, the temperature measuring screw Compare the molten resin temperature distribution of the resin determined by the method with the above-mentioned optimum resin temperature distribution, and calculate the temperature of the cylinder itself obtained by the above-mentioned temperature measuring elements installed in each temperature measuring zone of the cylinder so that both temperature distributions match. By adjusting the temperature distribution using the above-mentioned temperature measuring element and temperature controller, the optimum cylinder temperature distribution of the cylinder itself that can obtain the above-mentioned optimum resin temperature distribution for the resin is determined, and then the screw rotation speed is changed. The first step is to calculate the change in the optimum cylinder temperature distribution of the cylinder itself corresponding to the change in the screw rotation speed as a relational expression, and the temperature of the cylinder itself is determined by providing a plurality of temperature measuring elements corresponding to each temperature measuring zone of the cylinder. Using an operational plastic molding machine with a structure that allows temperature measurement, the relational expression obtained in the first step and the temperature distribution of the cylinder itself when actually molding the resin are compared with reference to the screw rotation speed. , a second step of determining the deviation distribution, determining the set temperature distribution of the cylinder based on this deviation distribution, and matching the temperature distribution of the cylinder itself with this set temperature distribution. Principle of the Invention In general, if plastic molding is limited to a specific operation such as extrusion coating of insulators made of cross-linked polyethylene resin for electric wires, cables, etc., then Resin temperature distribution (this temperature distribution is sometimes called a pattern) is limited to only a few types. Therefore, in order to reproduce such a limited pattern, it is not necessary to deliberately select many parameters and examine their effects as in the previous patent application No. 58-41038, and in addition, There is no need to predict the distribution of molten resin temperature; all you need to do is find the cylinder temperature distribution necessary to reproduce this pattern, which greatly reduces the effort required to create basic data. becomes possible. Specific Structure and Effects of the Invention Hereinafter, an example in which the present invention is applied to an extruder and extrusion molds a crosslinking agent-added polyethylene resin will be specifically described. First, when extrusion molding a certain brand of crosslinking agent-added polyethylene resin, the temperature distribution of the molten crosslinking agent-added polyethylene resin in the cylinder of the extruder (each temperature measurement zone in the longitudinal direction of the cylinder)
(Temperature distribution at temperature measurement positions such as C ₁ , C ₂ , C ₃ ...)
It is necessary to separately find out what the conditions are for extrusion molding work to be carried out successfully without the occurrence of inconveniences such as scorch. This is because the same brand of crosslinking agent-added polyethylene resin has often been extruded previously, and this can often be determined by collecting temperature data collected during these operations. Therefore, in many cases, it is not necessary to obtain this temperature distribution again. This temperature distribution is defined as the optimum resin temperature distribution. Next, the first step will be explained. This first
The process involves determining the temperature distribution (optimum This is a step in which the cylinder temperature distribution (hereinafter referred to as cylinder temperature distribution for short) is determined, and then the screw rotation speed is changed to determine a change in the optimum cylinder temperature distribution corresponding to the change in the screw rotation speed as a relational expression. In this process, a temperature measuring element is exposed on the surface, a temperature measuring screw is installed that can directly measure the temperature of the molten resin, and each temperature measuring zone of the cylinder is equipped with a temperature measuring screw that can directly measure the temperature of the molten resin.
C ₁ , C ₂ , C ₃ . . . are provided with a plurality of temperature measuring elements in the same manner as in the past, and an extruder for temperature measurement is used, which is structured so that the temperature of the cylinder itself can be measured at the same time. This extruder is used to actually extrude the above-mentioned brand of cross-linking agent-added polyethylene resin, and the screw rotation speed is set so that the temperature distribution of the molten resin matches the optimal resin temperature distribution known in advance as described above. , for example, at 5 rpm to control the temperature distribution of the cylinder itself. Specifically, this control is performed as follows. That is, the temperature distribution of the crosslinking agent-added polyethylene resin in the molten state determined by the temperature measuring screw is compared with the optimum resin temperature distribution. This comparison is performed by recording the optimal resin temperature distribution known in advance in the memory of a microcomputer, etc., inputting the temperature distribution of the molten polyethylene resin obtained from the temperature measuring screw into the microcomputer, and performing the subtraction process. and calculate the difference. This arithmetic processing is performed for a certain period of time, for example, every 2 to 10 minutes, and the difference is obtained each time. Then, the temperature distribution of the cylinder itself obtained from the temperature measuring elements provided in each temperature measuring zone of the cylinder is adjusted so that this difference becomes zero, in other words, so that both temperature distributions match. Adjustment of this temperature distribution is performed for each temperature measuring zone of the cylinder using the temperature measuring element and a normal temperature controller. That is, the above difference is input to the temperature controller, and the temperature controller sets a new set temperature of the cylinder itself based on this difference and the temperature of the cylinder itself obtained from the temperature measuring element, and adjusts the temperature of the cylinder itself. Change for each temperature measurement zone. This changes the temperature distribution of the molten polyethylene resin. This changed resin temperature distribution is
The temperature is measured by the temperature measuring screw, inputted to the microcomputer, and compared with the above-mentioned optimum resin temperature distribution in the same way as before, and a subtraction process is performed to obtain a new difference. This new difference is again input to the temperature controller in the same manner as before, and becomes data for determining a new set temperature distribution. By repeating such a temperature control operation several times, the temperature distribution of the molten polyethylene resin determined by the temperature measuring screw gradually approaches and finally coincides with the optimum resin temperature distribution. The temperature distribution of the cylinder itself when these two temperature distributions match becomes the optimum cylinder temperature distribution. Once the optimum cylinder temperature distribution at a screw rotation speed of 5 rpm is determined in this way,
Record the optimum cylinder temperature distribution at 5 rpm. Next, the screw rotation speed is changed to, for example, 10 rpm, and the temperature in each temperature measurement zone of the cylinder is changed and controlled so that the same desired temperature distribution as before is obtained. As mentioned earlier, if the screw rotation speed changes, the resin temperature will change accordingly, so the optimum temperature distribution of the cylinder will naturally be different from that at 5 rpm.
In this way, the optimum cylinder temperature distribution at 10 rpm is determined. Then, one after another, the screw rotation speed
Find the optimum cylinder temperature distribution at each screw rotation speed as 15 rpm, 20 rpm, etc. Thus, the optimum cylinder temperature in each temperature measurement zone of the cylinder is expressed as a function using the screw rotation speed as a variable. Then, if the screw rotation speed is divided into narrow ranges such as 5 to 10 rpm, 11 to 15 rpm, etc., the above function becomes Y=
It can be expressed as a linear expression of ax+b. Therefore, by dividing the commonly used screw rotation speed into, for example, four ranges for each temperature measurement zone of the cylinder, the following relational expression can be obtained.

[Table] In the above, the screw rotation speed is classified by outputting the screw rotation speed as a voltage by a rotary generator attached to the screw shaft, and classifying the screw rotation speed based on this voltage. Then, these relational expressions are
It is determined for each brand of crosslinking agent-added polyethylene resin and recorded, for example, by storing it in a computer memory. FIGS. 4 and 5 are graphs of the above relationship. The graph in Figure 4 shows the optimum results when the screw rotation speed is changed from 5 to 30 rpm for melt index (MI) 3 and 2, and the graph in Figure 5 shows the optimum cross-linking agent-added polyethylene resin with melt index (MI) 1 and 2. Cylinder temperature measurement zone
It is plotted for C ₂ , C ₃ , C ₄ and the adapter part (C _{5 )} . From this graph, a ₁ , ₂ ..., b ₁ , ₂ , ₃ , ... in the above relational expression are the straight lines of each curve. From these graphs, using crosslinking agent-added polyethylene resins with melt indexes of 3 and 2,
The optimum cylinder temperature when extruding at a screw rotation speed of 20 rpm, for example, is 123.3℃ for _C2 and 119.6℃ for _C3 .
℃, 116.2℃ at C ₄ and 115.6℃ at C _5. When changing the screw rotation speed from 20 rpm to 30 rpm, the temperature of each zone is changed along the straight line of the graph, in other words, the above linear equation All you have to do is change it according to the relational expression expressed by . With the above steps, basic data creation in the first step is completed. Next, the second step of controlling the resin temperature during actual extrusion operation will be described. 6a and 6b show an example of the configuration of an operating extruder that performs the above control, and the extruder 1 in this example has an aluminum casting heater 6a attached to the outer peripheral surface of the cylinder 2 as a heating device 6 for the cylinder 2, Further, as a cooling device 7, a cooling oil jacket 7a through which cooling oil circulates is provided on the outer peripheral surface of the cylinder 2.
The cooling oil jacket 7a is formed with a spiral groove 7b provided for each temperature measurement zone, and allows cooling oil sent from a cooling oil circulation device (not shown) to flow through the groove 7b. The cylinder 2 is cooled by this. In this example, control is performed in temperature measurement zones C ₂ , C ₃ , C ₄ , and C ₅ of cylinder 2 corresponding to FIGS. element
Temperature measuring holes 3 where TC ₂ , TC ₃ , TC ₄ , and TC ₅ are bored from the inner surface of the cylinder 2 leaving a thickness of about 10 mm...
is inserted into. The depth of the temperature measurement hole 3 is determined by considering the extruder 1, extrusion conditions, etc., but it should be the same as the depth of the temperature measurement hole when creating the basic data in the first step. is necessary. Further, at the base of the screw 8, there is a rotary generator 9 that detects the rotation speed of the screw 8 and outputs a voltage proportional to this.
is installed. And the temperature measuring elements TC ₂ , TC ₃ , TC ₄ , TC ₅
The output signal from the rotary generator 9 is sent to a processing system as shown in FIG. 7, for example.
It is processed. The output from the rotary generator 9 is input to an A/D converter 10, digitized, and then input to a microcomputer 11. The above relational expression (optimum cylinder temperature corresponding to changes in screw rotation speed and resin brand) determined in the first step is input into the microcomputer 11 in advance. In other words, the optimum cylinder temperature distribution (pattern) using the screw rotation speed and the type of resin as parameters is input. In addition, each of the above temperature measuring elements TC ₂ , TC ₃ , TC ₄ , TC ₅
Output signals sent from the temperature measuring elements are sent to temperature controllers 12 provided corresponding to these temperature measuring elements. These temperature controllers 12... have A/D conversion function, D/
It is equipped with an A conversion function and a linearization function, and the above output signal is linearized and A/D converted here, and then sent to the microcomputer 11.
is input. And microcomputer 1
1 compares the optimal cylinder temperature distribution input in advance and the temperature of each temperature measurement zone from temperature measurement elements TC ₂ to TC ₅ with reference to the screw rotation speed input separately as described above. , find its deviation. That is, for example, if the screw rotation speed is 10 rpm, the optimum cylinder temperature distribution when the screw rotation speed is 10 rpm is called from among the optimum cylinder temperature distributions (the above-mentioned relational expression) stored in advance in the microcomputer 11, and this optimum cylinder temperature distribution is called. Compare the cylinder temperature distribution and the temperature of each temperature measurement zone mentioned above, in other words, the temperature distribution of the cylinder itself, and determine the deviation distribution.
In other words, the temperature deviation for each temperature measurement zone of the cylinder is determined. Then, the set temperature of the temperature controller 12 is calculated based on this deviation. This set temperature is sent from the microcomputer 11 to each temperature controller 12 corresponding to the temperature measurement zone. The temperature controller 12... compares this set temperature with the temperature of the cylinder 2 in each temperature measurement zone from the temperature measurement elements TC ₂ to TC ₅ , and controls the heating device 6 such as a band heater or embedded heater or the cooling oil circulation. A cooling device 7 such as a device is operated to match the set temperature and the cylinder temperature. Thus, by repeating the above calculation and comparison process two to three times, the temperature distribution in each temperature measurement zone of cylinder 2 matches the optimum cylinder temperature distribution, and the temperature of the molten resin in cylinder 2 matches the optimum temperature distribution for extrusion. (desired resin temperature distribution). Furthermore, when the screw rotation speed is changed during extrusion work, the screw rotation speed signal input to the microcomputer 11 changes, and the optimum cylinder temperature distribution at the new screw rotation speed is calculated and determined using the above relational expression. Then, the same process as before is performed on this new optimum cylinder temperature distribution, and the temperature distribution of the molten resin in the cylinder 2 is made to match the desired resin temperature distribution. Furthermore, when the type or brand of resin changes, the above-mentioned relational expression previously determined for the new type or brand of resin is read into the microcomputer 11, and the above-mentioned calculation and control processing is performed. The above is the second step in this invention. According to such a temperature control method, the optimum cylinder temperature corresponding to several predetermined desired resin temperature distributions is determined, and control is performed using this optimum cylinder temperature as an index. The cost (amount of resin used, testing time) to determine the value is small. However, although only a limited temperature distribution can be controlled, in the case of general extrusion work, the extrusion work conditions are naturally limited as described above, so this does not cause any practical problems. In addition, since the optimum cylinder temperature is determined in response to temperature fluctuations due to the screw rotation speed and resin type, which are parameters that cause large fluctuations in resin temperature, highly accurate control is always possible. Furthermore, in the present invention, the desired resin temperature distribution is within a limited range, and there is no process of predicting the resin temperature during control, so there is no need to particularly consider the room temperature.
As long as the temperature distribution of the cylinder itself is maintained at a predetermined temperature, the desired resin temperature distribution can always be obtained. In the above example, this temperature control method is applied only to the temperature measuring elements TC ₂ , TC ₃ , TC ₄ , and TC ₅ corresponding to the temperature measuring zones of the extruder 1, but the temperature measuring elements on the popper side This temperature control method may be similarly applied to the temperature measuring element _TC1 corresponding to . However, in normal extrusion operations, temperature control in the four zones described above is sufficient. Further, the heating and cooling means for the cylinder 2 are not limited to the above examples, and heating and cooling means using a liquid heat medium such as silicone oil, cooling means using a blower, etc. may be used. Effects of the Invention As explained above, according to the resin temperature control method of the present invention, although the molten resin temperature can only be controlled within a certain limited resin temperature distribution, the cost of creating basic data is small, and moreover, the resin temperature control method of the present invention If the temperature distribution is selected, there will be no practical inconvenience. In addition, since the resin temperature can be controlled with high precision at all times, it is possible to increase the discharge amount, reduce scorch, and save thermal energy.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram showing an extruder using a conventional resin temperature control method, Figure 2 is a graph showing the relationship between room temperature and △T ₁ , and Figure 3 is a graph showing the relationship between screw rotation speed and △T ₂ . Graphs showing the relationship, Figures 4 and 5
Both figures are graphs of the optimum cylinder temperature distribution of crosslinking agent-added polyethylene resin obtained by varying the screw rotation speed. Figure 6a is a schematic configuration diagram showing an example of an extruder to which this temperature control method is applied. Figure 6 b is a schematic sectional view of the cylinder of this extruder, and FIG. 7 is a block diagram showing an example of a control processing system used in this temperature control method. DESCRIPTION OF SYMBOLS 1...Extruder, 2...Cylinder, 6...Heating device, 7...Cooling device, 8...Screw, 9...Rotary generator, 11...Microcomputer, 12
... Temperature controller, TC ₂ , TC ₃ , TC ₄ , TC ₅ ... Temperature measuring element.

Claims (1)

[Claims] 1. For a certain resin, the optimal resin temperature distribution of the molten resin in the cylinder that is optimal for molding the resin is separately set, and then a temperature measuring screw that can directly measure the temperature of the molten resin is provided. Using a plastic molding machine for temperature measurement, which is equipped with a thermometer and is equipped with multiple temperature measurement elements corresponding to each temperature measurement zone of the cylinder so that the temperature of the cylinder itself can also be measured, at a certain screw rotation speed, Compare the molten resin temperature distribution of the resin determined by the temperature measuring screw with the above optimal resin temperature distribution, and use the temperature measuring element installed in each temperature measuring zone of the cylinder to make sure that both temperature distributions match. By adjusting the temperature distribution of the obtained cylinder itself using the temperature measuring element and temperature controller, determining the optimum cylinder temperature distribution of the cylinder itself that can obtain the optimum resin temperature distribution of the resin,
Next, the first step is to change the screw rotation speed and calculate the change in the optimum cylinder temperature distribution of the cylinder itself corresponding to the change in the screw rotation speed as a relational expression, and to measure a plurality of temperatures corresponding to each temperature measurement zone of the cylinder. Using an operating plastic molding machine with a structure that allows temperature measurement of the cylinder itself, the relational expression obtained in the first step and the above-mentioned temperature measurement elements when actually molding the resin are used. Compare the temperature distribution of the cylinder itself to be measured with reference to the screw rotation speed, find the deviation distribution, find the set temperature distribution of the cylinder based on this deviation distribution, and add the temperature distribution of the cylinder itself to this set temperature distribution. A method for controlling resin temperature in a plastic molding machine, characterized in that the method comprises a second step of matching the temperature of the resin.