JPH0911327A - Control method for heating plate temperature in contact heating type molding machine - Google Patents

Abstract

PURPOSE: To stabilize molding and to remarkably improve the yield of molded articles at the beginning of the molding by inputting a molding standard temperature of a heating plate on the side of a material to be heated and controlling the heating power of a heater. CONSTITUTION: On the basis of intrinsic data such as the material and thickness of a resin sheet S to be molded, a heating cycle, and an outside air temperature, the preheating temperature and molding temperature of a heating plate 10 on the side of a heater 12 and the molding standard temperature, the number of shots, etc., of the heating plate 10 on the side of the resin sheet S are input in a input means CRT. Next, the plane resin sheet S is set on the heating plate 10 which is heated by a heater 12. The heating plate 10 is controlled at a molding temperature by the start of molding and adjusted at a moldable temperature, and when the temperature does not reach the moldable temperature, a signal of a forcible control value which was set internally in advance is sent through a timer to increase the temperature of the heating plate 10 quickly. The heating power of the heater 12 is controlled automatically so that the temperature approaches the molding standard temperature every several shots.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot plate temperature control method for heating a resin sheet to a temperature suitable for molding in a contact heating molding machine.

[0002]

2. Description of the Related Art In a conventional hot plate temperature control method, the temperature of a hot plate heated by a heater is controlled to a set temperature by various automatic control systems such as so-called P control, PI control, and PID control. I was In these control methods, the temperature of the hot plate near the object to be heated (resin sheet) decreases at the same time as the start of molding, and, of course, the material, thickness,
Due to factors such as heating cycle and outside air temperature,
It has been difficult to make the temperature of the object to be heated substantially constant.
As a specific example, HIPS (high impact polystyrene)
FIGS. 4 and 5 show a case where a resin sheet having a thickness of 0.4 mm and made of a resin is formed. FIG. 4 is a graph showing the relationship between the temperature of the resin sheet (object to be heated) and the molding time during molding in the conventional temperature control method for keeping the temperature on the heater side constant. FIG. 3 is a graph showing the relationship between the temperature on the heater side, the temperature on the resin sheet side during molding, and the molding time in the temperature control method for controlling the temperature of FIG.

[0003]

According to the former method of controlling the temperature of the heater, the temperature of the heater is controlled to be substantially constant at 133 ° C., but the temperature of the object to be heated is controlled to 133 ° C. Immediately after the start of molding from C, the temperature suddenly drops to 122 ° C., and then becomes a stable state. However, since the temperature of the object to be heated is reduced by about 11 ° C., there is a disadvantage that molding defects are likely to occur at the beginning of molding. In the case of the latter method of controlling the temperature of the object to be heated, the temperature of the object to be heated is reduced by about 13 ° C. at the start of molding,
The temperature of the heater is greatly increased in order to return to the initial set temperature. Then, the temperature on the heater side exhibits a large wavy temperature change with a decrease in the temperature on the object to be heated, and thereafter a small temperature change occurs. On the other hand, after the temperature of the object to be heated decreases by about 13 ° C. at the beginning of molding, it takes about 7 minutes for the temperature to rise and settle to the initial set temperature,
Thereafter, hunting at 2-3 ° C. is repeated. However, it is very difficult to control the temperature of the heater, and similarly to the former, there is an inconvenience that the temperature is drastically lowered at the beginning of molding and molding defects occur.

Accordingly, the present invention preliminarily inputs a forming reference temperature of the hot plate on the side of the object to be heated and controls the calorific value of the heater so as to approach the temperature, thereby enabling stable forming. It is another object of the present invention to provide a temperature control method that significantly improves the yield of molded products at the beginning of molding.

[0005]

According to the first aspect of the present invention, a resin sheet on a hot plate heated by a heater is fixed from above by a molding die, and the resin sheet is heated. A hot plate temperature control method for controlling the amount of heat generated by a heater by detecting the temperature of a hot plate with a temperature sensor in a contact heating molding machine in which the heating is performed in close contact with a plate and then performed by pressurized air means. The preheating temperature T ₁ and the molding temperature T ₂ of the hot plate, the forming reference temperature T ₃ of the hot plate on the resin sheet side to be heated, the number of shots, and the like are set by the input means CRT, respectively, and the heat on the heater side is set. the actual heating temperature Ta of the plate is detected by the first temperature sensor S ₁ and controls the heater to maintain the preheating temperature T _1, after being controlled by the molding at temperature T ₂ on the basis of the molding start command, Molding of several shots And, the measured value Tb of the hot plate of the resin sheet side at this time is detected by the second temperature sensor S _2, proportional to the deviation a of the forming reference temperature T ₃ which is set in advance and the detected actual values Tb Calculating means CPU for calculating the corrected molding temperature value Tc
Calculated by the correction molding temperature value Tc by substituting the the molding at temperature T ₂ and feeds back the signal to the control means SSR which controls the heating value of the heater, then the corrected during molding temperature T ₂ Repeat applying molding several shots, and controls so as to approach the heating value of the heater to the molding reference temperature T ₃ every several shots.

According to a second aspect of the present invention, there is provided a hot plate temperature control method for a contact heating molding machine according to the first aspect, wherein the hot plate is formed by cooling means C after the completion of the forming. wherein the cooling below the reference temperature T _3.

[0007]

The operation of the hot plate temperature control method in the contact heating molding machine thus configured will be described. First, the material of the resin sheet, the thickness, based on the specific data, such as the heating cycle and the outside air temperature, the preheating temperature T ₁ and during molding temperature T ₂ of the heater side of the heat plate, the resin sheet side which is an object to be heated heat The plate forming reference temperature T ₃ , the number of shots, and the like are input to input means CRT. In the hot plate of the molding machine by which, when the actual heating temperature Ta of the heater side is detected by the first temperature sensor S _1, the heater is in the standby state is controlled to maintain the preheating temperature T _1. Therefore, when the molding start command is issued, after the moldable temperature hot plate is controlled to molding at a temperature T _2, the molding is started.

[0008] Subsequently when the number shot molding is carried out, since the actual molding temperature Tb of the resin sheet side of the heat plate is detected by the second temperature sensor S _2, and the molding reference temperature T ₃ a preset detection The correction molding temperature value Tc proportional to the deviation a from the measured value Tb is calculated by the calculation means CPU. Its calculated correction molding temperature value Tc is, the are replaced during molding temperature T _2, the replacement signal is fed back to the control means SSR which controls the heating value of the heater. Shaping the subsequent several shots is performed by the corrected during molding temperature T _2. The heating value of the heater is automatically controlled so as to approach the shaping reference temperature T ₃ every several shots. After the molding is completed, the molding temperature T ₂
It switched to the preheating temperature T ₁ from. Moreover, hot plate is preferably cooled by the cooling means C, such as blowing compressed air in preparation for the next molding below the molding reference temperature T _3.

When the molding reference temperature of the hot plate on the resin sheet side is input in advance, the calorific value of the heater is controlled so as to approach the temperature, whereby stable molding can be performed. The product yield is significantly improved. In addition, even when the allowable temperature range for forming the resin sheet is small, the forming reference temperature of the hot plate can be finely and optimally controlled. It became possible to do.

[0010]

Embodiments of the present invention will be described below. 1 is an explanatory view showing an outline of a contact heating molding machine suitable for the method of the present invention, FIG. 2 is a flowchart of molding by a hot plate temperature control method of the present invention, and FIG. 3 is a relationship between a resin sheet side temperature and molding time during molding. It is a graph showing.

FIG. 1 shows a schematic configuration of a contact heating molding machine 1 suitable for carrying out the method of the present invention. A hot plate 10 for heating a resin sheet s set on an upper surface and a hot plate 10 above the hot plate 10 are provided. A molding die 20 is provided which is arranged and descends during molding to press the peripheral edge of the resin sheet s. On the hot plate 10,
A plurality of small holes 11 for adhering the resin sheet s by vacuum suction are provided, and several heaters 12 are attached to the bottom surface. The molding die 20 is a female die, in which a cavity 21 corresponding to the shape of a molded product is recessed, and a plurality of small holes 22 for suction-molding the resin sheet s are provided. Further, a cooling means C for cooling the hot plate 10 by, for example, blowing out compressed air from the small holes 11 after the completion of molding is provided.

SSR is a control means such as a thyristor for controlling the amount of heat generated by the heater 12, S ₁ is a first temperature sensor for detecting the temperature of the heating plate 10 on the heater 12 side (actual heating temperature Ta), S 1 ₂ is a second temperature sensor for detecting the temperature of the resin sheet s side heat plate 10 which is an object to be heated (actual measurement value Tb). The CRT is used to input a preheating temperature T ₁ and a molding temperature T ₂ of the heating plate 10 on the heater 12 side, a molding reference temperature T ₃ of the heating plate 10 on the side of the resin sheet s to be heated, the number of shots, and the like. input means, CPU is an arithmetic means for calculating a correction molding temperature value Tc in proportion to the deviation amount a of the forming reference temperature T ₃ which is set in advance and the detected actual values Tb.

Next, the operation of the hot plate temperature control method in the contact heating molding machine will be described with reference to the flowchart of FIG. First, based on the material and thickness of the resin sheet s to be molded, the heating cycle, the outside temperature, etc., the heater 1
The preheating temperature T ₁ and the molding temperature T ₂ of the hot plate 10 on the second side, the molding reference temperature T ₃ of the hot plate 10 on the resin sheet s side, the number of shots, etc. are input to the input means CRT. This makes the molding machine 1
In the heating plate 10 of FIG.
Is detected by the first temperature sensor S ₁ , and the heater 12 is controlled to maintain the preheating temperature T ₁ and enters a standby state. A flat resin sheet s is set on a hot plate 10 heated by a heater 12. As a result, the resin sheet s is vacuum-sucked through the small holes 11 and adheres to the hot plate 10. Next, the mold 20 descends and presses the peripheral edge of the resin sheet s. Therefore, when the molding start command is issued, the heat plate 10 is a molded at temperature T ₂ in controlled and moldable temperature, molding is started. This molding is a known molding method, and the heat-softened resin sheet s is sucked through the small holes 22, so that the resin sheet s is formed in close contact with the surface of the cavity 21 of the molding die 20. At this time, if the moldable temperature has not been reached, a signal of a forced control value set internally in advance is issued via a timer, and the temperature of the hot plate 10 is quickly raised.

When the X-shot molding is subsequently performed, the actual molding temperature Tb of the hot plate 10 on the resin sheet s side is detected by the second temperature sensor S ₂ , so that the preset molding reference temperature T is set. _The corrected molding temperature value Tc proportional to the deviation amount a between ₃ and the detected actual measurement value Tb is calculated by the calculation means CPU.
Is calculated by The calculated corrected molding temperature value Tc
Is replaced with the molding temperature T ₂ , and the replacement signal is fed back to the control means SSR for controlling the heat generation amount of the heater 12. The subsequent Y-shot molding is performed at the corrected molding temperature T.
_Done by ₂ . And, the calorific value of the heater 12 is
It is automatically controlled so as to approach the molding reference temperature T ₃ every few shots. When all the molding is completed, the hot plate 1 on the heater 12 side
At 0, the molding temperature T ₂ is switched to the preheating temperature T ₁ .
Further, the hot plate 10 is cooled to the molding reference temperature T ₃ or less in preparation for the next molding by the cooling means C configured to blow compressed air through the small holes 22.

(Experimental Example) FIG. 3 is a graph showing the relationship between the temperature of the resin sheet and the molding time when a resin sheet having a thickness of 0.4 mm and made of HIPS (high impact polystyrene) is molded. Show. (Heater side preheating temperature T ₁ = 131 ° C., resin sheet s side molding reference temperature T ₃ =
126 ° C. From this graph, it can be seen that the temperature of the resin sheet s side gradually decreases from 131 ° C. immediately after the start of molding, and becomes one of the molding reference temperature T ₃ .
26 ° C., and it is clear that the state thereafter becomes a stable state. Thus, according to the hot plate temperature control method of the present invention,
Since the temperature drop immediately after the start of molding is as small as about 5 ° C. and the temperature gradient is gentle, temperature control becomes easy and stable molding can be performed. Further, it was confirmed that the yield of the molded product at the beginning of molding was also improved.

[0016]

As described above, the method of the present invention inputs the molding reference temperature of the hot plate on the side of the object to be heated in advance and controls the heating value of the heater so as to approach this temperature. Since there is little temperature drop immediately after the start of molding and the temperature gradient is gentle, temperature control is facilitated, stable molding is possible, and the yield of molded products at the beginning of molding is significantly improved. Furthermore, even in the case where the range of the allowable molding temperature of the resin sheet is small, the molding reference temperature of the hot plate can be finely and optimally controlled. It also has an excellent effect that molding can be performed.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of a contact heating molding machine suitable for the method of the present invention.

FIG. 2 is a flowchart of forming by the hot plate temperature control method of the present invention.

FIG. 3 is a graph showing a relationship between a resin sheet side temperature and a molding time during molding.

FIG. 4 is a graph showing the relationship between the molding time and the temperature of the resin sheet (object to be heated) at the time of molding in the conventional temperature control method for keeping the temperature on the heater side constant.

FIG. 5 is a graph showing the relationship between the temperature on the heater side, the temperature on the resin sheet side during molding, and the molding time in a conventional temperature control method for controlling the temperature on the heated object side.

[Explanation of symbols]

CRT → Input means CPU → Calculation means SSR → Control means C → Cooling means T ₁ → Preheating temperature of the hot plate on the heater side T ₂ → Temperature when forming the hot plate on the heater side T ₃ → Molding of the hot plate on the resin sheet side Reference temperature Ta → actual heating temperature of heating plate on heater side Tb → actual measurement value of heating plate on resin sheet side Tc → correction molding temperature value S ₁ → first temperature sensor S ₂ →
2nd temperature sensor a → deviation b → coefficient s → resin sheet 1 → contact heating molding machine 10 → hot plate 11 → small hole 12 →
Heater 20 → Mold 21 → Cavity 22 → Small hole

[Procedure amendment]

[Submission date] April 18, 1996

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (2)

[Claims] 1. A contact heating molding machine in which a resin sheet on a hot plate heated by a heater is fixed from above with a molding die, and the resin sheet is heated in close contact with the hot plate and then molded by a compressed air means. A heating plate temperature control method for controlling the heating value of a heater by detecting the temperature of a heating plate with a temperature sensor, wherein a preheating temperature T ₁ and a molding temperature T ₂ of the heating plate on the heater side, The molding reference temperature T ₃ , the number of shots, etc. of the hot plate on the resin sheet side are set by the input means CRT, and the actual heating temperature Ta of the hot plate on the heater side is detected by the first temperature sensor S ₁ , and the preheating temperature is determined. and controls the heater to maintain a T _1, after the controlled in during molding temperature T ₂ on the basis of the molding start command, performs shaping of several shots, found Tb of the heating plate of the resin sheet side at this time in the second temperature sensor S ₂ Put out, calculated by preset molded reference temperature T ₃ and the detected actual values Tb and deviation amount a proportional correction molding temperature value Tc calculation means CPU of, during the shaping the correction molding temperature value Tc The signal is fed back to the control means SSR for controlling the calorific value of the heater by replacing the signal with the temperature T ₂ , and then forming a few shots with the corrected forming temperature T ₂ is repeated. The heating value of the heater to the molding reference temperature T
A hot plate temperature control method for a contact heating molding machine, wherein the method is controlled to approach ₃ . 2. The method of controlling a hot plate temperature in a contact heating molding machine according to claim 1, wherein said hot plate is cooled to a forming reference temperature T ₃ or lower by a cooling means C after the forming is completed. Hot plate temperature control method for molding machine.