JPS63239000A - Hot press - Google Patents

Abstract

PURPOSE:To safely and surely execute the press forming necessary for the low pressure output holding like an IC card especially by equipping with an electromagnetic relief valve and a directional control valve respectively on the primary side and secondary side pipe line of a closing cylinder. CONSTITUTION:The set pressure of electromagnetic relief valves 21, 22 are set so as to balance both side pressures based on the piston diameters at the primary and secondary sides of a closing cylinder. The respective position of directional control valves 19, 20 is set to P side and the oil pressure from pumps 15, 16 is fed into ths closing cylinder 3 through pipe lines 17, 18 to make the pressure difference between the primary side and secondary side in zero. Then, the set pressure of the electromagnetic relief valve 21 is devided in relation to the set pressure of the valve 22 so as to generate specific pressure difference in order to enable the operation with the low pressure necessitating the closing output by the ram 3a of the closing cylinder. The oil pressure from the pump 15 is therefore fed into the closing cylinder 3 from an oil port 13 according to the set pressure of the electromagnetic relief valve 21 and the holding of the necessary low pressure output is enabled.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a hot press for press-molding printed wiring boards, etc. by heating and pressurizing, and particularly for molding IO cards that require low-pressure output maintenance. Regarding hot press.

(Prior art) Conventionally, in a hot press, a ram 30a of a single-acting mold clamping cylinder sO shown in FIG. The ram is heated and pressurized to perform press forming, after which the ram descends under its own weight.

Pressure control of the electromagnetic relief valve in such a conventional hot press has a limit in setting the minimum pressure due to the characteristics of the electromagnetic +71J-7 valve.

Increasing the ram diameter of the mold clamping cylinder results in higher output and higher mold clamping force.

As the ram diameter increases, even if the electromagnetic relief valve is set to the same low pressure, the mold clamping force from the mold clamping cylinder will increase.
Maintaining low power is becoming more difficult.

In other embodiments, a method is adopted in which the ram of the mold clamping cylinder is driven by two hydraulic cylinders 31 and the mold clamping force is divided. (See Figure 5).

This is done by first clamping the mold with one side cylinder,
The device is designed for low output, and all cylinders are operated to produce high output.

(Problems to be Solved by the Invention) However, with the device that divides the mold clamping force, for example, although it is possible to control the output in the range of the mold clamping force (L6 to 13 tons and 28 to 600 tons), It becomes impossible to control the output in the intermediate range of ~28 tons.Also, when the ram diameter is increased to obtain a high mold clamping force, it is not possible to maintain a low output, so the contact pressure becomes okv'dl. It is not suitable for manufacturing molded products such as IO cards that require continuous pressure control over a wide range from a low output state to a maximum predetermined pressure.

Furthermore, when molding an IO card, it is necessary to heat and melt a thermosetting adhesive resin between very thin card plates and press them under low pressure to uniformly melt the adhesive resin. After that, the mold is clamped under high pressure. At this time, if the thermoset adhesive resin cannot stop the pressing force of 2 mm in accordance with the resistance of the adhesive, a problem arises in that the adhesive resin protrudes from between the card plates.

In view of these circumstances, the present invention, when hot-pressing a press-molded product such as an IO card, first controls the output to a low pressure, and after the adhesive resin of the press-molded product has uniformly melted, the output is increased to a high pressure. The purpose of the present invention is to provide a hot press that enables pressure control over a wide range by performing appropriate compression.

(Means for Solving the Problems) In order to achieve the above object, the hot press of the present invention provides a press-formed product between a fixed platen and a movable platen movably provided with respect to the fixed platen. A double-acting mold clamping cylinder is provided with a hot plate for pressurizing and clamping the mold, and further drives the movable platen.

An electromagnetic +71J-7 valve and a directional control valve are installed in the primary and secondary pipes of this clamping cylinder, respectively, to balance the primary and secondary pressures of the clamping cylinder. It is characterized by being equipped with a pressure control circuit that can obtain a predetermined mold clamping force by the pressure difference between the sides and can be driven at low pressure.

(Function) With this configuration, when performing hot press molding, pressure is controlled by the differential pressure between the electromagnetic 171J valves provided on the primary and secondary sides of the mold clamping cylinder.
Even if the set pressure of each electromagnetic relief valve is set to an appropriate pressure rather than a low pressure that has problems due to its characteristics, the mold clamping force can be maintained at the desired low output, and the output can be controlled continuously from low pressure to high pressure. Become.

(Example) Embodiments of the present invention will be described based on the drawings.

In a hot press, a hot plate is heated by steam or electricity, and the temperature is raised to about 150 to 400°C.

In FIG. 2, 1 is a fixed plate and 2 is a movable plate, which are arranged vertically to face each other at a predetermined interval.

The movable platen 2 is fixed to the ram 3a of the mold clamping cylinder 5, and is movable toward and away from the fixed platen 1. A support 4.・
... are attached, and each support column 4 passes through the through-holes of four arms 6, ... formed at the four corners of the movable platen 2, as shown in Fig. 3, and the protruding ends thereof are attached to the fixed platen 1. Fixed.

Parallel to the arm 6, stepped boards 7 are provided on both sides of the support 40 corresponding to each support 4, and the stairs 7 have seat portions 8a, 8b formed by steps at a predetermined interval in the vertical direction.
8c, respectively.

Between the fixed platen 1 and the movable platen 2, there are printed wiring boards and
In order to press and clamp the pressed molded product such as an O card, a plurality of hot plates 9 are provided, and each of the four corners of the hot plate 9 is placed on a step plate 7. Bracket 10 is attached.

The length of the bracket 10 is shortened from the upper heating plate 9 to the lower part, and each seat portion 8a is formed.

A bracket 10a is placed corresponding to 8b and 8c.

10b and 10c.

Heat insulating plates 11 and 12 are attached to the lower surface of the fixed platen 1 and the upper surface of the movable platen 2, respectively, so as to block heat conduction from the hot plate 9 to the fixed platen 1 or the movable platen 2. It has become.

Next, a configuration showing one feature of the present invention will be explained with reference to FIG.

The mold clamping cylinder S shown in FIG. 2 is a double-acting hydraulic cylinder, and oil cylinders 15 and 14 for supplying and discharging pressure oil are provided on the primary side and the secondary side, respectively.

On oil date 15.14, the ninth primary and secondary pipes 17 supplying pressure oil from hydraulic pumps 15 and 16, respectively.
．． 18 are connected. A four-bottom, two-position directional control valve 19.degree. 20 is connected to each conduit 17, 18 to control the operation of the mold clamping cylinder 3.

Additionally, an oil port 15 and a directional control valve 19. and respective pipe lines 17a of the oil port 14 and the directional control valve 20.

Electromagnetic relief valve 2 that sets the oil pressure of 18a to a predetermined pressure
1. Connect 22.

In addition, in order to make the set pressure of each electromagnetic relief valve 21 and 22 more appropriate, pressure fluctuations that change depending on the load and the environmental conditions of the hydraulic circuit are fed back to the primary and secondary sides of the mold clamping cylinder 5 during operation. A pressure sensor 23 is provided to sequentially detect the pressure.

Next, pressure control in the hydraulic circuit of the present invention will be explained.

First, based on the piston diameters on the primary and secondary sides of the mold clamping cylinder, the set pressures of the electromagnetic relief valves 21 and 22 are set so that the primary and secondary pressures are balanced.

For example, due to the difference in piston diameter, electromagnetic IJ IJ-7
It is possible to set the pressure difference between the primary side and the secondary side to zero by setting the set pressure of the valve 22 to so kg/di and the set pressure of the electromagnetic relief valve 21 to 45 #IA-I/l.

Then, each position of the directional control valve 19.20 is set to P@, and the hydraulic pressure from the pump 15.14 is supplied into the mold clamping cylinder 3 through the pipe 17.18 to reduce the pressure difference between the primary side and the secondary side. Make it zero.

Here, the hydraulic pressure from the pump 16 is supplied while maintaining the back pressure which is the secondary side pressure, and the position of the directional control valve 20 is switched so that the excess pressure oil above this pressure returns to the tank, and the pump 16t − Put it in unloaded state.

In order to enable the mold clamping output by the ram Sm of the mold clamping cylinder to be operated at the required low pressure, the set pressure of the solenoid valve 21 is adjusted so that a predetermined pressure difference is generated.
7-Determined in relation to the set pressure of the valve 22.

As a result, the hydraulic pressure from the pump 15 is transferred to the electromagnetic relief valve 2.
From the oil port 13 to the mold clamping cylinder 5p'3 according to the set pressure of 1.
This makes it possible to maintain the desired low pressure output.

Therefore, the set pressure of the electromagnetic relief valve 22 is changed to the electromagnetic 171.
If the pressure value corresponds to the appropriate minimum setting pressure of the 7-f valve 21 and the differential pressure between the primary side and the secondary side of the mold clamping cylinder is zero, then the electromagnetic IJ and IJ-f valve 21 will be Due to the characteristics of the electromagnetic valve, the pressure can be changed continuously from the lowest set pressure to the highest set pressure within a range that effectively operates.

In this way, when press-molding the IO card, the clamping force by the ram 3a of the clamping cylinder 3 is applied at a low pressure until the adhesive resin is evenly melted. After the adhesive resin is uniformly melted, the card is pressed under high pressure and press-molded so that the thermoset adhesive resin does not protrude from between the card plates.

Next, the ram 3a of the mold clamping cylinder is lowered.

This K is performed by switching the position of the directional control valve 19 to the Q side and returning the primary side supply oil pressure to the tank. In this case, if the descending speed is fast, a throttle valve is provided to adjust it.

Furthermore, the pressure sensor 2s shown in FIG. 1 is used to sequentially detect the primary and secondary pressures of the mold clamping cylinder 3, and the pressure is fed back to the set pressure of the electromagnetic I717 valve 21.22. If a control circuit is provided for the pressure, it is possible to stabilize the pressure more appropriately.

Although the present invention utilizes hydraulic pressure, other pressure sources such as air pressure may be used to perform similar operations.

(Effects of the Invention) As is clear from the above explanation, the present invention uses a double-acting mold clamping cylinder in a hot press, and uses a double-acting mold clamping cylinder so that the pressure difference between the primary side and the secondary side is zero. The set pressure of a pair of electromagnetic relief valves was determined, and the pressure medium from the pump was controlled by a directional control valve, so the mold clamping output was reduced to O.
It can be arbitrarily controlled from ky/cd to the set maximum output.

This makes it possible to safely and reliably perform press molding that requires low-pressure output maintenance, especially for work-0 cards, and to prevent molding defects.

Additionally, in the past, hot presses with particularly large mold clamping output compared to the size of the hot plate required a separate cylinder exclusively for lowering, but according to the present invention, this is no longer necessary.
The directional control valve allows the ram to be lowered easily and quickly.

[Brief Description of the Drawings] Fig. 1 is a pressure control circuit diagram as an embodiment of the present invention, Fig. 2 is a partially sectional front view showing a hot press of the present embodiment, and Fig. 3 is the same as that in Fig. 2. Figures 4 and 5 are schematic cross-sectional views showing conventional single-acting cylinders, 1...Fixed platen 2...Movable platen 5...Mold clamping Cylinder 9...Hot plate 19.20...Directional control valve 21.22...Solenoid relief valve 1 Figure 1--Surface holder 2--Movable turtle 3-- 9...11 Busy 19.20... On the other side 1lI116F valve 21.22...
...11 Stone Relief Fang 4 Diagram Procedure Amendment 1. Display of the incident 1986 Special Application No. 231696 2
, Name of the invention Hot Press 3, Relationship with the case of the person making the amendment Name of the person making the amendment: Taki Seisakusho Co., Ltd. 7, Amendment (1) Amend the #4 detailed statement as shown in the attached sheet. (2) Amend the drawing as shown in the attached sheet. Description 1, Title of the invention Hot press 2, Claims (1) A pressed product is placed between a fixed plate and a third plate movably provided with respect to the fixed plate. A double-acting type #7 that is equipped with a hot plate to drive the 5f moving platen! With Janda. A 1114fii relief valve and a directional control valve are provided in the primary and secondary 1111 pipes of this mold clamping cylinder, respectively, to balance the primary and secondary pressures of the mold clamping cylinder. Hot press port (2) equipped with a low pressure drive 5U pressure control circuit that provides a constant mold clamping force based on the pressure difference (2) The set pressure of each electromagnetic relief valve is the pressure of both the primary and secondary sides of the mold clamping cylinder. The hot press according to claim 1, characterized in that the output of the mold clamping cylinder is regulated based on an output sensor that detects fluctuations. Akari In''IF no Jyo 11 (Contents g: t't''rt,) 3
, Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a hot press for molding printed wiring boards and the like by heat and pressure, and particularly for molding IC cards that require low-pressure output maintenance. Regarding hot press. (Prior Art) Conventionally, in a hot press, the ram 30 & of a single-acting mold clamping cylinder 30 shown in Fig. 4 is raised at a predetermined output (by the set pressure of an electromagnetic relief valve), and The adhesive resin is heated and pressurized to perform press molding, after which the ram descends under its own weight. Due to the characteristics of the electromagnetic relief valve, there is a limit to the setting of the minimum pressure in the pressure control of the electromagnetic relief valve used to control the hydraulic pressure for the mold clamping cylinder of the hot press. For this reason, when attempting to press the plate to be processed within the hot plate of the hot press at low pressure, accurate control could not be achieved. Especially in the case of a large-sized hot press, a large mold clamping force is required, and the mold clamping cylinder also has a large diameter in accordance with the mold clamping force. However, in this case, although a high mold clamping force can be obtained, if the ram diameter becomes large, the pressure inside the mold clamping cylinder must be set to a low pressure when trying to lower the mold clamping force using the electromagnetic relief valve. Control of mold clamping pressure using a valve could not provide accurate pressure control in such cases. For this purpose, there is one set of side cylinders provided with a plurality of mold clamping cylinders. This is a #C position in which high-speed, low-pressure mold closing is first performed with one side cylinder, and after the mold is closed, all cylinders including the main mold clamping cylinder are used to clamp the mold. (Problem to be Solved by the Invention) However, with the device that divides the mold clamping force described above, it is possible to control the output within the range of mold clamping force of 0.6 to 13 tons and 2B to 600 tons, for example. , it becomes impossible to control the output in the intermediate range of 13 to 28 tons. In addition, when increasing the ram diameter to obtain a high mold clamping force, it is not possible to maintain a low output, so the contact pressure can be varied over a wide range from OK 17 cm" or low output to the highest constant pressure. It was unsuitable for manufacturing molded products such as IC cards, which require continuous pressure control.Furthermore, in IC card molding, thermosetting adhesive resin was melted between extremely thin card plates in a heated bath. It is necessary to apply pressure at low pressure to uniformly melt the adhesive resin.Then, apply high pressure to clamp the mold.At this time, the heat-cured adhesive resin is pressed against the pressure blade of the ram according to the resistance of the adhesive. If it is not possible to stop the pressure, a problem will arise in which the adhesive resin will protrude from between the card plates.In view of these circumstances, the present invention is designed to first output low pressure when hot-pressing a pressed product such as an IC card. The purpose of the present invention is to provide a hot press that enables pressure control over a wide range by controlling the pressure of the pressed product, and after uniformly melting 11M of adhesive on the press-formed product, appropriate compression is performed at high pressure. (Means for Solving the Problems) In order to achieve the above object, the hot press of the present invention provides a press-formed product between a fixed platen and a movable platen movably provided with respect to the fixed platen. A double-acting mold clamping cylinder is provided with a hot plate for pressurizing and clamping, and further drives the movable platen. A *mvv-f valve is installed in the primary and secondary pipe lines of this mold clamping cylinder, respectively. and a directional control valve to balance the primary and secondary pressures of the mold clamping sill, and to obtain a predetermined mold clamping force from the pressure difference between the primary and secondary sides, and to be able to drive at low pressure. (Function) Because of this configuration, when performing hot press molding, the ts provided on the primary and secondary sides of the clamping cylinder are
Since the pressure is controlled by the differential pressure of a millimeter relief, the mold clamping force is maintained at the desired low output even if the set pressure of each electromagnetic relief valve is set to an appropriate pressure rather than a low pressure that is problematic on the % column. Moreover, the output can be controlled continuously from low pressure to high pressure. (Example) An example of the present invention will be described based on the drawings. In a hot press, a hot plate is heated by steam or electricity, and the temperature is raised to about 150 to 400°C. In Figure 2, 1 is a fixed plate and 2 is a movable plate. 3 is a mold clamping cylinder 7, which includes a fixed platen 1 and a mold clamping cylinder 3.
It is arranged to face the flange part at a predetermined distance vertically. The movable platen 2 is fixed to the tip of a ram 3a inserted into the mold clamping sill 3, and is movable toward and away from the fixed platen l. Four protrusions 6 that protrude in the horizontal direction are formed on the collar of the mold clamping cylinder 3. A stay 4 is provided upright on each protrusion 6, and each stay 4 is formed at the four corners of the movable platen 2. The fixed platen 1 is fixed to the upper end of the stay 4 through the through hole. 7 is a step-like step board set up in the mold clamping ring 30, and there are four of these depending on the number of stays 4. Seating portions 8a and 8b are provided by a step. 8c. Between the fixed platen 1 and the movable platen 1112, a plurality of hot plates are placed between the fixed platen 1 and the movable platen 1112 in order to place pressed products such as printed dispatch boards and IC cards, and press and tighten them. 9. . . . are provided, and brackets 1O to be placed on the stepped plates 7 are attached to each corner of the hot plate 904. The length of the bracket 10 is shortened from the upper heating plate 9 to the lower part, and the valley seat part is 8 m. Brackets 10a are mounted corresponding to 8b and 8eK. 10 b, 10 c. Heat insulating plates 11 and 12 are attached to the lower surface of the fixed platen 1 and the upper surface of the movable platen 2, respectively, so as to block heat transfer from the hot plate 9 to the fixed platen 1 or l'iTma2. It has become. Next, the jp of the present invention! 1. Regarding the configuration of the characteristic pipe parts, the first
This will be explained with reference to the figures. The mold clamping cylinder 3 shown in FIG. 2 is a double-acting hydraulic cylinder, and is provided with narrow ports 13 and 14 on the primary and secondary sides for supplying and discharging pressure oil, respectively. The narrow ports 13 and 14 are provided with secondary and secondary pipes 17 for supplying pressure oil from hydraulic pumps 15 and 16, respectively.
．． 18 are connected. Each of the pipes 17 and 18 has a pair of pipes 17 m long,
17 b, 18 m, 18 b are connected, and hydraulic pump 15.
A position directional control valve 19,20 is provided, furthermore a narrow opening 13.
, 14 @ side passages 17b, 18b are provided with electromagnetic relief valves 21.
．． 22 are provided. In addition, in order to make the set pressure of each electromagnetic +71J valve 21, 22 more appropriate, pressure fluctuations that change depending on the load and the environmental conditions of the hydraulic circuit are fed back to the model #1 during operation.
A pressure sensor 23 is provided to sequentially detect the pressure on the primary side and the secondary side of the 7/D 3. Next, pressure control in the inventive hydraulic circuit will be explained. First, based on the piston/diameter in the primary side and secondary side 11111 of the mold clamping cylinder, the electromagnetic valve 21
, 22 are set. Then, the solenoids P of the directional control valves 19 and 20 are energized to transfer the hydraulic pressure from the pumps 15 and 16 to the pipes 17 and 18, respectively.
It is supplied into the mold clamping cylinder 3 through the mold clamping cylinder 3. At this time, the required mold clamping force is obtained by setting the set pressure with the magnetic relief valves 21 and 22 to a predetermined pressure and making the pressure difference between the primary side and the secondary side 1:2 a predetermined value. As a result, the hydraulic pressure from the pump 15 is supplied from the narrow port 13 into the mold clamping cylinder 3 according to the set pressure of the 'tm relief valve 21, and the desired low pressure output can be maintained as a DI function. If the set pressure of the valve 22 is made to correspond to the appropriate minimum set pressure of the VT electromagnetic relief valve 1, the electromagnetic relief valve 21 will be able to adjust the pressure from the lowest set pressure to the lowest set pressure within the range in which it operates effectively due to the characteristics of the electromagnetic relief valve. It can be changed continuously and sequentially up to. A more specific example of the above pressure control will now be described. In FIG. 1, the diameter of the large diameter portion of the ram 3a is D.
A, the diameter at the small diameter part is Dll, the area of the ram 3a in the lower chamber A of the mold clamping cylinder 3 defined by the ram 3a into two chambers is 8A, and the upper chamber B
The area of the ram 3a is SBe, the set pressure of the electromagnetic relief valve 21 is PA, the set pressure of the electromagnetic relief valve 22 is pB, the output FA of the ram 31 in each chamber A, BK,
FB > and the clamping force FAB of the ram 3a against the hot plate 9
I decided to look for it. Here, as an example of a specific numerical value, the diameter DA of the ram 3a
Tomi 356■, DB Tomi 30.0-9 Set pressure PA of electromagnetic relief valve 21! 10 h/cm", 'ei Wi Milli Reef 22 setting pressure P B = 35 b/era"
shall be. Medium E force of ram in chamber A FA tIfJ side of ram 31 in chamber A"'5'g X (35,
6m)" = 995.4- Output of ram 3a FA = 8A@PA = 995.4cm" tt x (J)"-x (rV2)"-
Name (("%A (duck 4) 1) -/4 ((35,6cm)" - (30cIg1)")
= 288.56 Output of Kaisetsu Ram 3a F'B-8B@PB -288,5cM Engineering X 35KP/II''-10097
, 10 tons in 5Kf. (Ili) Clamping force of ram FAB 'AM'''A-'B = 10ton - 10ton = Oton In other words, in the present invention, the clamping force of the ram 3a against the hot plate 9 can be made zero. This zero clamping force can be maintained stably. Next, we will discuss an example in which this clamping force is gradually increased from zero. In this case, the difference between the outputs FA and FIm of the ram 3a is It is sufficient to gradually increase the pressure from zero.Specific K1-1. Set pressure of the electromagnetic relief valve 22 to PB" 35 in the same manner as above.
Kll/cm" and under the same conditions as described above, the set pressure PA of the magnetic relief valve 21 was set to 1.
b/cm". The table below shows the setting pressure PA of the electromagnetic relief valve 21 from 10 to 4/- to 15 to 4/invert "e 20 Ky1 stroke", 25
It shows the outputs FA and F' of the ram 3a and the clamping force FAB obtained when changing to Kp/y*snow. These calculation formulas are the same as above. As shown in the table, in the present invention, the clamping force can be changed arbitrarily from zero. 5. When press-molding the IC card. Until the adhesive resin is uniformly VC melted, the molding force by the 'fJ tightening scissor cylinder 3m 3a is applied at low pressure. After the adhesive resin has melted uniformly, it is pressed under high pressure and press-molded so that the thermoset adhesive resin does not protrude from between the card plates. Next, the ram 3a of the mold clamping cylinder is lowered. This is done by switching the position of the directional control valve 19 to Q1ill and returning the primary side supply oil pressure to the tank.In this case, if the descending speed is fast, a shutoff valve is installed Further, using the pressure sensor 23 shown in Fig. 11, the primary and secondary pressures of the mold clamping cylinder 3 are sequentially detected, and the pressure is fed back to the set pressure of the ta milli-relief 21.22. If a control circuit is provided so that the pressure is controlled, it is possible to stabilize the pressure properly.Also, although the present invention uses hydraulic pressure, it is possible to perform similar operation using other pressure sources such as total atmospheric pressure. Conventionally, hot presses with large mold clamping power in IP# compared to the size of the hot plate required a separate cylinder exclusively for lowering, but with the present invention, In this case, this is not necessary and the ram can be lowered easily and quickly using the directional control valve.In addition, the conventional Hot 7 Luss has a mold clamping force 1% larger than the size of the hot plate. , a separate cylinder exclusively for lowering was required, but this invention eliminates this need.
The ram can be lowered easily and quickly using the directional control valve. 4. Brief Description of the Drawings pA1 is an output control circuit diagram as an embodiment of the present invention. FIG. 2 is a partially sectional front view showing the hot press of this embodiment. Figure 'iAJ is a schematic sectional view showing a conventional single-acting cylinder. 1...Fixed platen 2...Movable unit 3...Mold clamping cylinder 9...Hot plate 10.20...Direction control valve 21 .22... Electromagnetic Relief Valve Key Applicant Co., Ltd. Name @ Urasakusho 1'F force of the drawing (no change in content) Engraving of the drawing in Figure 1 (no change in the content) In the drawing in Figure 2 Engraving (without any change in the matter) Procedural amendment April 11, 1986

Claims (2)

[Claims] (1) A hot plate for pressurizing the pressed product is provided between a fixed plate and a movable plate movably provided with respect to the fixed plate, and the movable plate is driven. A double-acting mold clamping cylinder, and an electromagnetic relief valve and a directional control valve are provided in the primary and secondary pipes of the clamping cylinder, respectively, to balance the primary and secondary pressures of the clamping cylinder. In addition, the hot press is equipped with a pressure control circuit that can be driven at low pressure to apply a predetermined mold clamping force based on the pressure difference between the primary side and the secondary side. (2) The set pressure of each electromagnetic relief valve is adjusted based on a pressure sensor that detects pressure fluctuations on the primary side and secondary side of the mold clamping cylinder, and the output of the mold clamping cylinder is controlled. Hot press according to scope 1.