JPH0355292B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin temperature control method in a plastic molding machine for controlling the resin temperature in the molding machine to an optimal temperature for molding when plastic is molded using a plastic molding machine such as an extruder. 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 extrusion volume, reduces scorch, reduces energy costs, and also reduces wires and cables. It has a very important meaning from the point of view of improving the electrical properties etc. of insulating materials etc. Conventional resin temperature control in an extruder, as shown in FIG. Insert the temperature measuring element 4... into the cylinder 2, measure the temperature of each temperature measuring zone, C ₁ , C ₂ , C ₃ , C ₄ , enter these temperatures into the temperature controller 5..., A heating device 6 such as a band heater or an embedded heater provided on the outside of the temperature controller 2 and a cooling device 7 such as a cooling blower are connected to the temperature controller 5.
This is done by controlling the... 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 this period, a temperature difference (△T ₁ ) as shown in Fig. 2 occurs in each temperature measurement zone (C ₂ , C ₃ , C ₄ ), and 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 , and C ₄ represent the temperature measurement positions of the cylinder 2, and the temperature measurement zones C ₂ , C ₃ , and C ₄ shown in each temperature controller 5 in Fig. 1. Compatible. ) 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 140°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, as an improvement over the conventional system, a resin temperature control device for an extruder has been proposed in JP-A-55-121042. This temperature control device is
A first temperature sensor installed at a position slightly outward from the inner wall surface of the cylinder of the extruder and taken out as a temperature detection signal at the position; and a first temperature sensor installed at a position slightly inward from the outer wall surface of the cylinder of the extruder. , a second temperature detector that takes out the temperature detection signal at the position, a first temperature setter whose set output is a target temperature signal at the position where the first temperature detector is installed, and the second temperature sensor. a second temperature setting device whose set output is a target temperature signal at a position where the temperature sensor is installed;
a first comparison calculator that compares and calculates the temperature signal detected by the first temperature detector and a first target temperature signal from the first temperature setter; and the second temperature detector. a second comparison calculator that compares and calculates the detected temperature signal and a correction signal of the second target temperature signal from the second temperature setting device based on the output signal of the first comparison calculator; and an output device that selectively adjusts the amount of heat of the heating/cooling device according to the output signal of the comparator. Then, if the temperature near the inner surface of the cylinder is lower than the set temperature of the first temperature setter, the first comparator sends a positive output signal, which signal is the target temperature signal from the second temperature setter. The heating/cooling device is heated based on the output signal from the second comparator, and the temperature near the inner surface of the cylinder is increased. Conversely, if the temperature near the inner surface of the cylinder is higher than its target temperature, the heating/cooling device is operated for cooling. Similarly, if the temperature near the outer surface of the cylinder is lower than the target temperature of the second temperature setter corrected by the output signal of the first comparator, the heating/cooling device is activated via the second comparator. be done. Conversely, if the temperature near the outer surface of the cylinder is higher than the corrected target temperature, the heating/cooling device is operated for cooling. However, even with this conventional resin temperature control device, the temperature of the cylinder is simply controlled by measuring the temperature of the cylinder wall, so as mentioned above, the set temperature and the actual resin temperature depend on various parameters. Since a large temperature difference is observed, even such a temperature control device has the disadvantage that the actual resin temperature cannot be accurately controlled. Therefore, in order to eliminate the drawbacks of the two conventional resin temperature control methods, the present inventors installed a temperature sensing part of a temperature measuring element on the inner surface of the cylinder or the outer surface of the screw so as to directly contact the molten resin. We have proposed methods for directly measuring the temperature of the molten resin in the cylinder, but in these methods, the temperature sensing part of the temperature sensing element is in direct contact with the molten resin at all times. There are problems with wear and resin retention, the temperature measuring element must be replaced frequently, and there are problems with long-term continuous operation of the extruder. Furthermore, it has been found that cylinders with through holes have problems such as cracks occurring around the through holes due to long-term use. Therefore, a temperature control method equipped with a means for correcting fluctuations in resin temperature due to the screw rotation speed of the molding machine and room temperature has been proposed in Japanese Patent Application Laid-open No. 108119/1983 (Japanese Patent Application No.
56-191906) by the present inventors. This method measures the temperature of the cylinder, corrects the temperature calculated from parameters that fluctuate the molten resin temperature, such as room temperature and screw rotation speed, and predicts the molten resin temperature inside the cylinder. The deviation between the temperature and the desired resin temperature is determined, and the temperature of the molten resin in the cylinder is controlled based on this deviation, but even with this method, it is not possible to control the resin temperature with the desired accuracy. It was possible. The inventors of the present invention conducted further studies and found that there is a temperature distribution in the thickness direction of the cylinder 2, for example, as shown in FIG. 4. The horizontal axis in Figure 4 indicates the distance (mm) from the inner surface of cylinder 2; in this case, 0 mm is the inner surface of cylinder 2, and 50 mm is the distance from the inner surface of cylinder 2.
represents the outer surface of cylinder 2. Further, the vertical axis represents the temperature of the cylinder 2. And the curves C ₂ , C ₃ ,
C ₄ represents the temperature distribution of the cylinder 2 at positions corresponding to the temperature measurement zones C ₂ , C ₃ , and C ₄ of the extruder 1 in FIG. 1, respectively. Then, I learned that if each curve is extrapolated from this graph to the position of the inner surface of the cylinder 2, it is possible to predict the temperature of the molten resin on the inner surface of the cylinder 2. This invention was made in view of the above circumstances,
The temperature of the molten resin inside the cylinder can be accurately predicted,
The resin temperature can always be maintained at the desired temperature,
The purpose of the present invention is to provide a resin temperature control method for a plastic molding machine that increases the amount of resin discharged, reduces scorch, and saves energy, does not wear out the temperature measuring element, and allows extruders to operate continuously for long periods of time. Then, two or more temperature measuring elements are arranged at different distances from the inner surface of the cylinder in the thickness direction of the cylinder wall, and the temperature of the inner surface of the cylinder is calculated from the measured temperature obtained by these temperature measuring elements. Find the screw rotation speed that changes the temperature of the molten resin to this temperature,
The corrected temperature obtained from five parameters: room temperature, set temperature, screw shape, and resin type is added to predict the molten resin temperature in the cylinder, and the melting temperature is calculated based on the deviation between this predicted temperature and the desired resin temperature. This method is characterized by controlling the resin temperature. Hereinafter, the present invention will be explained in detail with reference to the drawings. First, the arrangement of temperature measuring elements in the temperature control method of the present invention will be explained with reference to FIG. Figure 5 shows
This figure shows a cross section of the cylinder 2 of the extruder 1 to which the present invention is applied, taken along a plane perpendicular to the axis of the cylinder 2, and the same components as those shown in FIG. 1 are given the same reference numerals. be. Further, the screw 8 is omitted. Cylinder 2 temperature measurement zone
There are three temperature measurement holes 3a, 3 at the position corresponding to C ₂ .
b and 3c are bored in the same plane, for example, at an angle of 120° to each other toward the central axis of the cylinder 2. Of these three temperature measuring holes 3a, 3b, 3c,
The first temperature measurement hole 3a is approximately 5 mm from the inner surface of the cylinder 2.
The second temperature measurement hole 3b is drilled leaving a thickness of mm.
is bored leaving a thickness of about 8 mm from the inner surface of the cylinder 2, and the third temperature measuring hole 3c is also bored leaving a thickness of about 15 mm. These temperature holes 3
The depths of a, 3b, and 3c are the depths of cylinder 2 of extruder 1.
The above depth varies depending on the thickness of cylinder 2.
This is a preferable value when the thickness is 25 to 50 mm. Depending on the conditions, the shallowest position of the temperature measurement hole (3
In c), it is preferable to set the position up to about 1/2 of the cylinder wall thickness from the viewpoint of improving the accuracy of temperature control. Temperature measuring elements 4a, 4b, 4c such as thermocouples are inserted and fixed into the bottoms of these temperature measuring holes 3a, 3b, 3c, respectively, and these temperature measuring elements 4a, 4b, 4c are arranged. cylinder 2 in position
temperature is now being measured. In this way, by arranging the temperature measuring elements 4a, 4b, and 4c in the cylinder 2 at different distances from the inner surface of the cylinder 2, one temperature measuring zone shown in FIG.
A temperature distribution curve corresponding to C ₂ will be obtained. Then, the temperature measurement position by the first temperature measurement hole 3a is L, the temperature measurement position by the second temperature measurement hole 3b is M, 3.
The temperature measurement position by the temperature measurement hole 3c is denoted as N, the temperature measured by each temperature measurement element 4a, 4b, 4c is denoted as T _L , T _M , T _N , and the temperature measurement position of the temperature measurement element 4a, 4
The output signals from b and 4c are T _L signal, T _M signal, T _N
Signal. In addition, a temperature measuring element group consisting of three temperature measuring elements 4a, 4b, 4c is similarly arranged at the position of the cylinder 2 corresponding to the other temperature measuring zones _C3 and _C4 of the extruder 1. Temperature distribution curves corresponding to zones C ₃ and C ₄ can be obtained. Then, the T L signal, T M signal, and _{T N} representing the temperatures T _L , T _M , and T N at the L, M, and N positions of the cylinder 2 measured by these temperature measuring elements 4a, 4b, and _4c are transmitted _.
The signal is processed by the processing system shown in FIG. FIG. 6 shows an example of a processing system for this temperature control method, and only one corresponding to one temperature measurement zone _C2 is shown. First, temperature measuring element 4
The T _L signal, T _M signal, and T _N signal detected and outputted from a, 4b, and 4c are respectively input to linearizers 9, 9, and 9, and then linearized to A/D converters 10, 10, and 10. The data is digitized and input to the microprocessor 11. At the same time, the rotational speed of the screw 8 and the room temperature, which change the temperature of the molten resin, are measured and similarly input to the microprocessor 11 via the linearizer 9 and A/D converter 10. Furthermore, data regarding the shape of the screw 8, the type of resin, and the set temperature are also input to the microprocessor 11. Note that the above-mentioned linearizer 9 and A/D converter 10
are not required if they are incorporated in each detection means. Moreover, the linearizer 9 has an A/
It may be installed after the D converter 10, and the installation position is determined as necessary. The microprocessor 11 calculates a temperature distribution curve from the T _L signal, T _M signal, and T _N signal. For example, if the temperature distribution curve is expressed as a quadratic curve, assume the following equation: y=ax ² +bx+c (1) y: Temperature of cylinder 2 x: Distance from the inner surface of cylinder 2 to the temperature measurement position This equation (1) corresponds to each position of L, M, and N above.
Substitute xL, xM, xN and yT _L , yT _M , yT _N ,
By solving the ternary quadratic equation, a, b, in equation (1),
c is determined, and an equation representing the temperature distribution curve is determined. Then, in this equation, x = 0 (inner surface of cylinder 2)
By substituting , the temperature of the inner surface of the cylinder 2 can be found. Next, the temperature of the inner surface of the cylinder 2 is determined by the screw rotation speed, room temperature, set temperature,
A correction temperature determined by a program stored in advance from five parameters that vary the temperature of molten resin depending on the screw shape and resin type (including differences in grade within the same resin), and determined by these parameters. are added to calculate the predicted temperature of the molten resin. Further, this predicted temperature is compared with a separately stored desired resin temperature, the deviation thereof is determined, and the set temperature of the temperature controller 5 is calculated based on this deviation. This set temperature signal is input to the D/A converter 12, converted into an analog signal, and input to the temperature controller 5. A T _N signal from a temperature measuring element 4c is separately inputted to the temperature controller 5, and this T _N signal is compared with a set temperature, and the heating device 6 such as a band heater or an embedded heater, or a cooling blower, etc. The cooling device 7 is operated to make T _N match the set temperature. In addition,
The temperature measurement signal input to the temperature controller 5 at this time is
Not limited to the T _N signal from the temperature measuring element 4c,
Although the T _L and T _M signals from the temperature measuring elements 4a and 4b may be used, it is preferable to perform the measurement at the farthest position from the inner surface of the cylinder 2 in order to prevent variations in resin temperature. At the same time, the microprocessor 11 controls the temperature controller 5 at the set temperature based on the temperature changes at the L, M, and N positions from the temperature measuring elements 4a, 4b, and 4c.
The input timing to the temperature controller 5 is calculated, and the timing for inputting the set temperature to the temperature controller 5 is instructed. Thus, by matching T _N to the set temperature,
The predicted temperature now matches the desired resin temperature. According to such a temperature control method, three temperature measuring elements 4a, 4b, 4c are arranged inside the cylinder 2 at varying distances from the inner surface of the cylinder 2, thereby controlling the temperature inside the cylinder 2. Since the temperature of the molten resin in the cylinder 2 is determined from the distribution, the temperature measuring element 4 does not have to come into direct contact with the molten resin, so the temperature measuring element 4 does not wear out. In addition, to the molten resin temperature obtained in this way, a correction temperature obtained from five parameters that change the temperature of the molten resin: screw rotation speed, room temperature, screw shape, set temperature, and resin type is added, Since the predicted temperature is calculated, this predicted temperature is always accurate even if the screw rotation speed, room temperature, screw shape, set temperature, and type of resin change. Then, the deviation between this predicted temperature and the desired resin temperature is determined, the set temperature of the temperature controller 5 is calculated based on this deviation, and the temperature at the N point furthest from the inner surface of the cylinder 2 is controlled using this set temperature. Therefore, the molten resin temperature quickly matches the desired temperature, and the cycling phenomenon of the molten resin temperature caused by the time delay of the heat passing through the cylinder 2 is reduced. Further, since the above calculation processing is performed by the microprocessor 11, the control speed is increased, and the molten resin temperature can be brought to the desired desired temperature in a short time. In the above example, three temperature measuring elements 4 were arranged in one temperature measuring zone, but depending on the type of extruder 1 and extrusion conditions, the temperature distribution of the cylinder 2 may be y = ax.
+b or y=alnx+b, and in this case, two temperature measuring elements 4
a, 4b are sufficient. Alternatively, three or more temperature measuring elements 4 may be provided to predict the resin temperature more precisely.
Further, although the three temperature measuring elements 4a, 4b, and 4c are arranged radially, the arrangement is not limited to this, and in short, they may be arranged at different distances from the inner surface of the cylinder 2. In addition, in the above example, the temperature measuring zone C ₂ of the extruder 1,
Although the temperature control method according to the present invention is applied to C ₃ and C ₄ , the temperature control method may be similarly applied to temperature measurement zone C ₁ . However, in normal extrusion operations, temperature control in three zones, _C2 , _C3 , and _C4 , is sufficient. Further, the means for heating and cooling the cylinder 2 is not limited to the above example, and heating and cooling means using a fluid heat medium such as silicone oil may also be used. Hereinafter, a specific explanation will be given by showing examples. Example 1 Screw diameter 50mm, L/D=20, cylinder wall thickness 25
mm, heater capacity C ₁ ...2.2KW, C ₂ , C ₃ , C ₄ ...
...A low density polyethylene containing a crosslinking agent was extruded using a 0.7KW extruder 1 equipped with a PID temperature controller and applying the temperature control method of the present invention. The temperature measuring elements are assumed to be two points 4a and 4b corresponding to the temperature measuring positions L and M in FIG. 5, and the temperature of the cylinder 2 is expressed as y=ax+b (2).
However, y is the temperature of the cylinder 2 (°C), and x is the distance (mm) from the inner surface of the cylinder 2 to the temperature measurement position. Then, let Y be the temperature after addition of the corrected temperature in equation (2), that is, the predicted temperature. The values corresponding to the measurement positions L and M are xL, yL, xM,
If yM, a=y _L −y _M ／x _L −x _M b=y _L x _M −y _M x _L ／x _M −x _L , so y=y _L −y _M ／x _L −x _M x+y _L x _M −y _M x _L ／x _M −x _L ……(2
') The addition term for the correction temperature is (y _L - y _M ) × n, and the n value is determined by the screw rotation speed, room temperature, screw shape, set temperature, and resin type (including differences in grades of the same resin). It is determined by measuring the actual resin temperature in advance using a temperature measuring screw or the like using the following parameters. Since x=0mm on the inner surface of the cylinder (2')
is y=y _L x _M −y _M x _L /x _M −x _L ...(2″). Therefore, the predicted temperature Y (℃) is Y=y _L x _M −y _M x _L / x _M −x _L + (y _L −y _M )×n ...(3) Now, if x _M = 10 mm and x _L = 5 mm, equation (3) becomes Y = 2y _L − y _M It is expressed as +(y _L −y _M )×n...(3').The set temperature of temperature measurement position M is: _C1 zone...Fixed at 120℃ _C2 , _C3 , _C4 zone...Micropro Setusa 1
According to instructions from 1. The desired resin temperature E (°C) for each zone is C ₁ ... not specified in particular C ₂ ... 126 °C C ₃ ... 128 °C C ₄ ... 130 °C previously stored in the memory in the microprocessor 11. shall be. The temperature control method is to calculate a new set temperature using the following equation and issue a command to the temperature controller 5. New set temperature = current set temperature - {Y - E} × 0.9 ...(4) The factor 0.9 in equation (4) is designed to asymptotically approach the desired resin temperature from a low point, and it may be 1, but it is not 1. The desired resin temperature may be exceeded. Under the above conditions, the screw rotation speed is
The actual resin temperature A was measured by changing the rpm to 30 rpm, 60 rpm, and 70 rpm, and the difference from the desired resin temperature E was compared. Table 1 shows y _L , y _M , n, Y, actual resin temperature (A), desired resin temperature (E), and (A )−(E). The actual resin temperature (A) was measured by drilling a through hole in each zone of the cylinder 2 and inserting a temperature measuring element until it came into contact with the molten resin.

[Table] From Table 1, actual resin temperature (A) and desired resin temperature (E)
The deviation |A−E| is approximately 1° C. at most, and extremely precise resin temperature control is performed. When the extruder is operated for a long period of time in this manner, the quality, productivity, etc. of the molded product are significantly improved compared to Conventional Examples 1 and 2, which will be described later. Example 2 An extrusion operation similar to Example 1 was carried out using a medium density polyethylene blend for silane crosslinking. Table 2 shows _yL , _yM , n, Y, actual resin temperature (A), desired resin temperature (E) and Indicates the value of (A)−(E).

[Table] From Table 2, the deviation |A-E| is approximately 0.6 at most.
℃, and it can be seen that the resin temperature is controlled with extremely high precision. Next, a conventional example to which a conventional temperature control method is applied will be shown. Conventional Example 1 Using an extruder similar to that of Example 1, C ₁ ,
Measure the temperature at temperature measurement position M in each zone of C ₂ , C ₃ , and C ₄ , and adjust this temperature to 120℃ using a normal PID temperature controller.
was controlled. This control method is a very common temperature control method for an extruder shown in FIG. The resin used, actual resin temperature measurement, desired resin temperature, and screw rotation speed are the same as in Example 1. Table 3 shows the temperature at point M in each zone, the actual resin temperature A, and the desired resin temperature E, A-E.

[Table] Conventional Example 2 Using the same extruder as in Example 1, measuring the temperature only at point M in each zone, the resin temperature prediction formula is as follows: Y=y _M +△T ₁ +△T ₂ ……( 5) However, Y...Predicted resin temperature y _M ...Cylinder temperature at point M △T ₁ ...Temperature corrected by room temperature △ _T2 ...Temperature corrected by screw rotation speed Extruded polyethylene. This method is an example of the temperature control method disclosed in Japanese Patent Application No. 191906/1982. The set temperature of each zone is: _C1 ...Fixed at 120℃ _C2 , _C3 , _C4 ...Based on commands from the microprocessor. Further, the desired resin temperature E for each zone is _C1 ...not specified in particular _C2 ...126°C _C3 ...128°C _C4 ...130°C and is stored in advance in the microprocessor. shall be. The temperature control method is to calculate a new set temperature using the following equation and issue a command to the temperature controller that controls the temperature at point M. New set temperature = Current set temperature - {Y-E} x 0.9
...(6) Extrusion was carried out under the same conditions as in Example 1. Table 4 shows y _M , Y, actual resin temperature A, desired resin temperature E, and A-E of each zone after two to four set temperature change commands after the start of extrusion.

[Table] From Table 4, actual resin temperature A and desired resin temperature E
The maximum deviation |A−E| is about 4.5° C., which is smaller than that of Conventional Example 1, but this still cannot be said to be precise resin temperature control. Conventional Example 3 In Example 1, to calculate the n value of the corrected temperature,
Extrusion work was carried out in exactly the same manner except that two parameters were adopted: screw rotation speed and room temperature. Table 5 shows the results. This method is an example of the temperature control method disclosed in Japanese Patent Application No. 57-31575.

[Table] From the table above, the deviation between the actual resin temperature (A) and the desired resin temperature (E) |(A)−(E)| is approximately 2.5℃ at maximum, and Conventional Example 1
Compared to 2, resin temperature control is much more precise, but it still cannot be said to be accurate enough. This is because two parameters, the screw rotation speed and the room temperature, are used to change the temperature of the molten resin. As explained above, the resin temperature control method for a plastic molding machine of the present invention includes 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 the plastic molding machine. The temperature measured by these temperature measuring elements and the correction value obtained from five parameters that vary the temperature of the molten resin of the screw rotation speed, screw shape, room temperature, set temperature, and resin type measured in advance. The temperature of the molten resin in the cylinder is predicted from the temperature of the molten resin, and the temperature of the molten resin is controlled based on the deviation between the predicted temperature and the desired resin temperature. Therefore, according to this temperature control method, even if the above parameters change, the molten resin temperature can always be maintained at the desired resin temperature. Furthermore, the phenomenon of cycling of the molten resin temperature due to the delay of heat passing through the cylinder is reduced, and temperature fluctuations are reduced. Therefore, it is possible to increase the amount of molten resin discharged, reduce scorch, and save thermal energy, and high-quality molded products can be manufactured at low cost. Furthermore, compared to a method in which the temperature measuring element is brought into direct contact with the molten resin, there is almost no need to replace the temperature measuring element, and furthermore, there is no trouble such as damage to the cylinder or screw, and the molding machine can be operated continuously for a long period of time.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram showing an extruder using the conventional resin temperature control method, and Figure 2 shows changes in room temperature and △
FIG. ₃ is a graph showing the relationship between screw rotation speed and ΔT _2. FIG. 4 is a graph showing the temperature distribution inside the cylinder of the extruder. FIG. 6 is a cross-sectional view showing an example of the arrangement of temperature measuring elements inside the cylinder of an extruder to which the method of the present invention is applied, and FIG. 6 is a block diagram showing an example of a processing system used in the method of the present invention. DESCRIPTION OF SYMBOLS 1... Extruder, 2... Cylinder, 5... Temperature controller, 6... Heating device, 7... Cooling device, 11...
...Microprocessor, 3a...First temperature measurement hole, 3b...Second temperature measurement hole, 3c...Third temperature measurement hole, 4a...First temperature measurement element, 4b
...Second temperature measuring element, 4c...Third temperature measuring element.

Claims (1)

[Claims] 1 Two or more temperature measuring elements are arranged at different distances from the inner surface of the cylinder in the thickness direction of the cylinder wall of a plastic molding machine, and the inner surface of the cylinder is determined from the temperature of the cylinder measured by these temperature measuring elements. The temperature in the cylinder is determined by adding to this temperature the correction temperature determined from five parameters that vary the temperature of the molten resin: screw rotation speed, room temperature, set temperature, screw shape, and resin type. A resin temperature control method for a plastic molding machine, which comprises predicting the temperature of a molten resin, determining the deviation between the predicted temperature and a desired resin temperature, and controlling the temperature of the molten resin in a cylinder based on this deviation.