Abstract:
An extrusion press and an extrusion control method obtains a uniformly-shaped extruded product by constantly applying a constant container sealing force between a container and a die even when an extrusion force varies during an extrusion process, improving product yield, and keeping a small energy consumption at the time of extrusion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority of Japanese Patent Application No. 2007-005388 filed on Jan. 15, 2007 and Japanese Patent Application No. 2007-139986 filed on May 28, 2007 and the contents are incorporated herein as reference and continued in the subject application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an extrusion press and an extrusion control method and, more particularly, to an extrusion press and an extrusion control method capable of improving the product yields by controlling a container sealing force that acts on the end surface of a die to be constant during the entire process of extrusion. 
     2. Description of the Related Art 
     A conventional extrusion press comprises an end platen linked to a tie rod and a main cylinder device and on the side of the end platen, a container is arranged, in which a billet is loaded, with a die being sandwiched in between, and on the side of the main cylinder device, a stem is provided to a crosshead to be driven integrally with a main ram that enters/exits from the main cylinder. Then, the billet loaded in the container is extruded under pressure by the stem using the extrusion force by the main cylinder device and thus a predetermined product is extruded and molded from a die. 
     In such an extrusion press, it is desirable that the container sealing force be constant during the entire extrusion process, however, the billet in the container gradually becomes shorter and shorter in the extrusion process, and therefore, normally the force required for extrusion when extrusion starts is larger than that when extrusion ends. That is, even if the extrusion resistance of a die (required extrusion force that acts on a die) is constant, the frictional resistance between the container inner wall and the billet becomes smaller as the length of the billet is reduced, and therefore, the extrusion force gradually reduces on the whole. 
     If the extrusion force changes during the extrusion process, the force that acts on the die of the extrusion press changes, and as a result the amount of deflection of the die is not constant during the extrusion process. Consequently, there is a problem that the product obtained by a conventional extrusion press is not uniform in thickness and shape in the longitudinal direction. 
     Further, the change in the extrusion force causes the container sealing force against the die to vary and there used to be a problem of the occurrence of a so-called bursting phenomenon, in which the billet bursts forth from a sealed part. 
     In the extrusion press disclosed in Japanese Unexamined Patent Publication (Kokai) No. 4-274821, a pressing means for pressing under pressure a container to the side of a die so as to seal between the container and the die is provided to a crosshead that links a main cylinder device and a main ram. Then, when the length of a billet becomes equal to or less than a predetermined length during extrusion process, the container is pressed under pressure with the pressing means and a container seal force is applied between the container and the die by the pressing pressure, and thereby, the burst of the billet is avoided (patent document 1). 
     However, with the technique disclosed in above-described patent document 1, the container sealing force applied to the end platen via the die is added to cause the extrusion force to act and it is possible to keep constant the displacement of the end platen and the die in the longitudinal direction of extrusion of a product and to obtain a uniform product, however, during the extrusion process, the container is pressed under pressure by the pressing means, and therefore, there is a problem that a maximum load pressure when extrusion starts acts on the main cylinder device and the amount of energy consumption increases during extrusion process.
     [Patent document 1] Japanese Unexamined Patent Publication (Kokai) No. 4-274821.   

     SUMMARY OF THE INVENTION 
     The present invention has been developed in order to solve the problem and an object thereof is to provide an extrusion press and an extrusion control method capable of: obtaining a uniformly-shaped product by constantly applying a constant container sealing force between a container and a die even when an extrusion force varies during extrusion process, improving the product yields, and keeping a small energy consumption at the time of extrusion. 
     In order to achieve the above-mentioned object, an extrusion press according to a first aspect of the present invention is characterized by comprising a container moving means for moving a container at an end platen and molding a product by extruding a billet loaded in the container from a die by a stem of a main cylinder device, wherein a hydraulic pressure of the main cylinder device is detected, a deviation between the detected hydraulic pressure and a reference pressure set in advance is mathematically processed, and the extrusion press comprises a control means, which is capable of sending an output to the container moving means to reduce a container sealing force when the deviation is plus with respect to the reference pressure, or to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     An extrusion press according to a second aspect of the present invention is characterized by comprising a container moving means for moving a container at an end platen and molding a product by extruding a billet loaded in the container from a die by a stem of a main cylinder device, wherein a container drive means that reduces a pressing force that acts on the end surface of the die is provided at the end platen, a hydraulic pressure of the main cylinder device is detected, a deviation between the detected hydraulic pressure and a reference pressure set in advance is mathematically processed, and wherein the extrusion press comprises a control means capable of sending an output to the container drive means to reduce a container sealing force when the deviation is plus with respect to the reference pressure and a control means capable of sending an output to the container moving means to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     An extrusion press according to a third aspect of the present invention is characterized in that the container drive means provided at the end platen to reduce a container sealing force that acts on an end surface of a die comprises a hydraulic cylinder in the invention of the second aspect. 
     An extrusion control method according to a fourth aspect of the present invention is characterized by detecting a hydraulic pressure of a main cylinder device in an extrusion process of an extrusion press, mathematically processing a deviation between the detected hydraulic pressure and a reference pressure set in advance, and performing a constant pressure extrusion by sending an output to a container moving means to reduce a container sealing force when the deviation is plus with respect to the reference pressure, or to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     An extrusion control method according to a fifth aspect of the present invention is characterized by detecting a hydraulic pressure of a main cylinder device in an extrusion process of an extrusion press, mathematically processing a deviation between the detected hydraulic pressure and a reference pressure set in advance, and performing a constant pressure extrusion by sending an output to a container drive means provided in a container to reduce a container sealing force when the deviation is plus with respect to the reference pressure, or by sending an output to a container moving means to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     An extrusion control method according to a sixth aspect of the present invention is characterized by detecting a hydraulic pressure of a main cylinder device in an extrusion process of an extrusion press, mathematically processing a deviation between the detected hydraulic pressure and a reference pressure set in advance, and performing a constant pressure extrusion by sending an output to a container drive means and a container moving means provided in a container to reduce a container sealing force when the deviation is plus with respect to the reference pressure, or by sending an output to the container moving means to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     An extrusion press according to a seventh aspect of the present invention is characterized by comprising a container moving means for moving a container at an end platen and molding a product by extruding a billet loaded in the container from a die by a stem driven by a main cylinder device, wherein the extrusion press comprises a deflection amount detection means that detects a deflection amount of the die, a deflection amount of the die during extrusion is detected, a deviation between the detected deflection amount and a reference deflection amount of the die set in advance is mathematically processed, and wherein the extrusion press comprises a control means, which is capable of sending an output to the container moving means to reduce a container sealing force when the deviation is minus, or to increase the container sealing force when the deviation is plus, so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     An extrusion press according to an eighth aspect of the present invention is characterized by comprising a container moving means at an end platen and molding a product by extruding a billet loaded in the container from a die by a stem driven by a main cylinder device, wherein the extrusion press comprises a container drive means that reduces a container sealing force that acts on the end surface of the die and is provided at the end platen and a deflection amount detection means that detects a deflection amount of the die, a deflection amount of the die during extrusion is detected, a deviation between the detected deflection amount and a reference deflection amount of the die set in advance is mathematically processed, and wherein the extrusion press comprises a control means capable of sending an output to the container drive means to reduce the container sealing force when the deviation is minus and a control means capable of sending an output to the container moving means to increase the container sealing force when the deviation is plus, so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     An extrusion press according to a ninth aspect of the present invention is characterized in that the container drive means provided at the end platen to reduce the container sealing force that acts on the end surface of the die comprises an electric servomotor and a ball screw converter including a screw shaft and a ball nut to convert a rotational motion of the output shaft of the electric servomotor into a linear motion, in the invention of the second or eighth aspect. 
     An extrusion press according to a tenth aspect of the present invention is characterized in that the container drive means provided at the end platen to reduce the container sealing force that acts on the end surface of the die comprises a hydraulic cylinder, in the invention of the eight aspect. 
     An extrusion control method for an extrusion press according to an eleventh aspect of the present invention is characterized by comprising a container moving means for moving a container at an end platen and molding a product by extruding a billet loaded in the container from a die by a stem driven by a main cylinder device and by comprising the steps of: detecting a deflection amount of the die during extrusion process of an extrusion press; mathematically processing a deviation between the detected deflection amount and a reference deflection amount set in advance; and performing a constant pressure extrusion by sending an output to the container moving means to reduce a container sealing force when the deviation is minus, or to increase the container sealing force when the deviation is plus, so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     An extrusion control method for an extrusion press according to a twelfth aspect of the present invention is characterized by comprising a container moving means for moving a container at an end platen and molding a product by extruding a billet loaded in the container from a die by a stem driven by a main cylinder device and by comprising the steps of: detecting a deflection amount of the die during extrusion process of an extrusion press; mathematically processing a deviation between the detected deflection amount and a reference deflection amount set in advance; and performing a constant pressure extrusion by sending an output to a container drive means to reduce a container sealing force when the deviation is minus, or by sending an output to the container moving means to increase the container sealing force when the deviation is plus, so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     An extrusion control method according to a thirteenth aspect of the present invention is characterized by comprising the steps of: detecting a deflection amount of the die during extrusion process of an extrusion press; mathematically processing a deviation between the detected deflection amount and a reference deflection amount set in advance; and performing a constant pressure by sending an output to a container moving means and a container drive means provided at an end platen to reduce a container sealing force when the deviation is minus, or by sending an output to the container moving means to increase the container sealing force when the deviation is plus, so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die, in the invention of the twelfth aspect. 
     ADVANTAGEOUS EFFECTS OF THE INVENTION 
     As described above, in the extrusion press according to the first aspect of the present invention, the hydraulic pressure of the main cylinder device is detected and a deviation between the detected hydraulic pressure and a reference pressure set in advance is mathematically processed. Then, the press comprises the control means, which sends an output to the container moving means to reduce the container sealing force when the deviation is plus with respect to the reference pressure, or to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. The reference pressure is set, in advance, in a range lower than a maximum extrusion load pressure and higher than a required extrusion load pressure that acts on the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of displacement and deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to increase the container sealing force of the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion press according to the second aspect of the present invention, the container drive means that reduces the container sealing force that acts on the end surface of the die is provided at the end platen, the hydraulic pressure of the main cylinder device is detected, and a deviation between the detected hydraulic pressure and the reference pressure set in advance is mathematically processed. Then, the press comprises the control means that sends an output to the container drive means to reduce the container sealing force when the deviation is plus with respect to the reference pressure and the control means that sends an output to the container moving means to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of displacement and deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to make constant the container sealing force that acts on the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion press according to the third aspect of the present invention, the drive means provided at the end platen of the extrusion press according to the second aspect to reduce the container sealing force that acts on the end surface of the die is comprises of a hydraulic cylinder. Due to this, it is possible to make constant the container sealing force that acts on the die without increasing the load pressure of the main cylinder device and, at the same time, to minimize the size of the drive means and make the extrusion press compact. 
     In the extrusion control method according to the fourth aspect of the present invention, the hydraulic pressure of the main cylinder device is detected in the extrusion process of the extrusion press. Then, a deviation between the detected hydraulic pressure and the reference pressure set in advance is mathematically processed, and an output is sent from the control means to the container moving means to reduce the container sealing force when the deviation is plus with respect to the reference pressure, or to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. The reference pressure is set, in advance, in a range lower than a maximum extrusion load pressure and higher than a required extrusion load pressure that acts on the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of displacement and deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to make constant the container sealing force that acts on the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion control method according to the fifth aspect of the present invention, the drive means that reduces the container sealing force that acts on the end surface of the die is provided in the container, the hydraulic pressure of the main cylinder device is detected, and a deviation between the detected hydraulic pressure and the reference pressure set in advance is mathematically processed. Then, an output is sent from a control means to the container drive means to reduce the container sealing force when the deviation is plus with respect to the reference pressure, or an output is sent from a control means to the container moving means to increase the container sealing force when the deviation is minus with respect to the reference pressure, so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of displacement and deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to apply a pressing force to the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion control method according to the sixth aspect of the present invention, the drive means that reduces the container sealing force that acts on the end surface of the die is provided in the container, the hydraulic pressure of the main cylinder device is detected, and a deviation between the detected hydraulic pressure and the reference pressure set in advance is mathematically processed. Then, an output is sent from the control means to the container moving means and drive means of the container to reduce the container sealing force when the deviation is plus with respect to the reference pressure, or an output is sent from the control means to the container moving means to increase the container sealing force when the deviation is minus with respect to the reference pressure so that a container sealing force corresponding to the reference pressure acts on the end surface of the die. 
     Due to this, it is possible to correct with high precision and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of displacement and deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to apply a pressing force to the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion press according to the seventh aspect of the present invention, the means to detect the deflection amount of the die is provided, a deflection amount of the die is detected, and a deviation between the detected deflection amount and the reference deflection amount set in advance is mathematically processed. Then, the press comprises the control means, which sends an output to the container moving means to increase the container sealing force when the deviation is plus, i.e., the deflection amount is larger than the reference deflection amount, or to reduce the container sealing force when the deviation is minus, that is, the deflection amount is smaller than the reference deflection amount, so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to increase the container sealing force that acts on the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion press according to the eighth aspect of the present invention, the container drive means to reduce the container sealing force and the means to detect the deflection amount of the die are provided, a deflection amount of the die is detected, and a deviation between the detected deflection amount and the reference deflection amount set in advance is mathematically processed. Then, the control means that sends an output to the container drive means to reduce the container sealing force when the deviation is minus, i.e., the deflection amount is smaller than the reference deflection amount and the control means that sends an output to the container moving means to increase the container sealing force when the deviation is plus, i.e., the deflection amount is larger than the reference deflection amount are provided so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to increase the container sealing force that acts on the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion press according to the ninth aspect of the present invention, the container drive means provided at the end platen of the extrusion press according to the second or eight aspect to reduce the container sealing force that acts on the end surface of the die adopts a configuration that uses an electric servomotor and a ball screw converter comprised of a screw shaft and a ball nut to convert the rotational motion of the output shaft of the electric servomotor into a linear motion. 
     Due to this, the energy efficiency is improved and the container sealing force can be reduced with a small amount of energy consumption. 
     In the extrusion press according to the tenth aspect of the present invention, the container drive means provided at the end platen of the extrusion press according to the eight aspect to reduce the container sealing force that acts on the end surface of the die adopts a configuration that uses a hydraulic cylinder. 
     Due to this it is possible to minimize the size of the drive means and reduce the container sealing force. 
     In the extrusion control method according to the eleventh aspect of the present invention, a deflection amount of the die during extrusion process is detected and a deviation between the detected deflection amount and the reference deflection amount set in advance is mathematically processed. Then, an output is sent to the container moving means to increase the container sealing force when the deviation is plus, i.e., the deflection amount is larger than the reference deflection amount, or to reduce the container sealing force when the deviation is minus, i.e., the deflection amount is smaller than the reference deflection amount so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to increase the container sealing force that acts on the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion control method according to the twelfth aspect of the present invention, a deflection amount of the die during extrusion process is detected and a deviation between the detected deflection amount and the reference deflection amount set in advance is mathematically processed. Then, an output is sent to the container moving means provided at the end platen to reduce the container sealing force when the deviation is minus, i.e., the deflection amount is smaller than the reference deflection amount, or an output is sent to the container moving means to increase the container sealing force when the deviation is plus, i.e., the deflection amount is larger than the reference deflection amount so that a container sealing force corresponding to the reference deflection amount acts on the end surface of the die. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of displacement and deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to increase the container sealing force that acts on the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
     In the extrusion control method according to the thirteenth aspect of the present invention, when the deviation is minus, that is, the deflection amount is smaller than the reference deflection amount, an output is sent to the container drive means and the container moving means provided at the end platen to reduce the container sealing force in the extrusion control method of the twelfth aspect. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts on the die during the entire extrusion process. Because of this, it is possible to keep constant the amount of deflection of the die and the thickness and shape of the product become uniform in the longitudinal direction, and therefore, the product yields are improved. In addition, it is possible to increase the container sealing force that acts on the die without increasing the load pressure of the main cylinder device, and therefore, it is unlikely that the amount of energy consumption is increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of an extrusion press according to an embodiment of the present invention. 
         FIG. 2  is a characteristic chart of an extrusion force of the present invention. 
         FIG. 3  is a section view of an extrusion press according to another embodiment of the present invention. 
         FIG. 4  is a section view of an extrusion press according to another embodiment. 
         FIG. 5  is a section view of an extrusion press according to still another embodiment. 
         FIG. 6  is a section view of an extrusion press according to another embodiment of the present invention. 
         FIG. 7  is a characteristic chart of an extrusion force of the present invention. 
         FIG. 8  is a section view of an extrusion press according to another embodiment of the present invention. 
         FIG. 9  is a section view of an extrusion press according to another embodiment. 
         FIG. 10  is a section view of an extrusion press according to still another embodiment. 
         FIG. 11  shows a die deflection detection device,  FIG. 11(   a ) showing its section view, and  FIG. 11(   b ) showing a diagram along arrow A. 
     
    
    
     The present invention may be fully understood by the description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of an extrusion press and an extrusion control method according to the present invention are explained below in detail with reference to the drawings. 
       FIG. 1  is a section view of an extrusion press according to an embodiment. As shown schematically, in the extrusion press, an end platen  10  and a main cylinder device  12  are arranged in opposition to each other and both are linked by a plurality of tie rods  14 . On the inner surface of the end platen  10 , a container  18  is arranged with a die  16  in which an extrusion hole is formed being sandwiched in between, and a billet  20  is loaded in the container  18  and a product with a section in accordance with a die hole  16 A is extruded and molded by extruding under pressure the billet  20  toward the die  16 . 
     The main cylinder device  12 , that generates an extrusion force incorporates a main ram  12 B in a main cylinder  12 A and the main ram  12 B can be moved under pressure toward the container  18 . To the front end part of the main ram  12 B, an extrusion stem  24  is attached in a state of projecting toward the container  18  via a crosshead  22  so as to be arranged concentrically with a billet load hole  18 A of the container  18 . Because of this, when the main cylinder device  12  is driven to advance the crosshead  22 , the extrusion stem  24  is inserted into the billet load hole  18 A of the container  18 , and therefore, pressure is applied to the rear end surface of the loaded billet  20 , and thus a product  20 A is extruded. 
     To the main cylinder  12 A, a side cylinder device  26  is attached in parallel with the extrusion axial center and its cylinder rod  26 A is linked to the crosshead  22 . Due to this, the configuration is such that the extrusion stem  24  is initially moved to the position close to the container  18  as a preparation process of the extrusion process and the operation of extrusion under pressure is performed using both the main cylinder device  12  and the side cylinder device  26 . 
     To the end platen  10 , a container shift cylinder device  28 , as a moving means capable of freely moving the container  18  back and forth in the direction of the extrusion axis line, is attached, and its cylinder rod  28 A is linked to a container holder  19 . Due to this, the configuration is such that a sealed state is brought about as the preparation process of extrusion by causing the end surface of the die  16  to come into contact with the end surface of the container  18  and in the completion process, the end surface of the die  16  is separated from the end surface of the container  18  and thus a gap through which the remaining material of the billet  20  is discharged is secured. 
     The configuration of a drive hydraulic circuit of the main cylinder device  12  and a drive hydraulic circuit of the container shift cylinder device  28  is explained with reference to  FIG. 1 . 
     First, a hydraulic circuit  32  that drives the main cylinder device  12  comprises a hydraulic pump  30  of variable displacement type and the hydraulic pressure discharged therefrom is supplied to the main cylinder device  12  and the side cylinder device  26  via a hydraulic passage. To the hydraulic passage, a pressure sensor  34  that detects a hydraulic pressure is attached and thereby a detected hydraulic pressure is output to a controller  36 . 
     A drive circuit  42  of the container shift cylinder device  28  is provided with a hydraulic pump  38  that supplies pressurized hydraulic oil to the container shift cylinder device  28 . When pressurized hydraulic oil is supplied from the pump  38  to the rod side of the cylinder via the hydraulic passage, the cylinder rod  28 A is pulled in and driven and thus a container sealing force is caused to occur. It is designed so that when pressurized hydraulic oil is supplied to the head side of the cylinder, a hydraulic pressure that drives the cylinder rod  28 A to project is caused to occur. The hydraulic circuit  42  is provided with a proportional electromagnetic relief valve  44  that adjusts the hydraulic pressure to be supplied to the container shift cylinder device  28  and the pressure control is performed via an amplifier  48  in accordance with the set instruction value by a control signal from the controller  36 , which is output in accordance with the hydraulic pressure detected by the pressure sensor  34  of the drive hydraulic circuit  32  of the main cylinder device  12 . 
     As described above, during the extrusion process, extrusion is performed by the main cylinder device  12  and the side cylinder device  26 , and an extrusion force (F) at the time of extrusion is expressed by the sum of a required extrusion force (Fa) that acts on the die  16  and a frictional force (Fb) between the billet  20  and the inner wall of the container  18 . As shown in  FIG. 2 , the extrusion force (F) and the frictional force (Fb) between the billet  20  and the inner wall of the container  18  become maximum when extrusion starts and as the extrusion process advances and the length of the billet  20  reduces, the frictional force (Fb) is reduced, and therefore, the extrusion force (F) is reduced as a result. 
     The required extrusion force (Fa) that acts on the die  16  is substantially uniform and if the temperature condition of the billet is the same, it rarely happens that the required extrusion force varies. 
     As shown in  FIG. 2 , a reference pressure P 1  capable of maintaining a predetermined container sealing force also in the final step of the extrusion process and controlling constant the container sealing force is set lower than a maximum load pressure P 0  and higher than a required load pressure P 2  that acts on the die. In this case, in the first half of the extrusion process in which the extrusion load pressure that changes from P 0  to P 2  is in a range higher than the reference pressure P 1 , the container sealing force acts excessively on the die and in the second half of the extrusion process in which the extrusion load force is in a range lower than the reference pressure P 1 , the container sealing force that acts on the die is deficient. 
     If, therefore, pressurized hydraulic oil based on the mathematically processed deviation is supplied to the head side of the container shift cylinder device  28  and caused to act so that the container  18  is pressed back from the die to reduce the container sealing force, it is possible to keep constant the container sealing force, in the range where the container sealing force acts excessively on the die and the load pressure is higher than the reference pressure P 1 . 
     On the other hand, in the range where the container sealing force acts deficiently on the die and the load pressure is lower than the reference pressure P 1 , if the pressurized hydraulic oil based on the mathematically processed deviation is supplied to the rod side of the container shift cylinder device  28  and caused to act so that the container  18  is pressed under pressure against the die to increase the container sealing force, it is possible to keep constant the container sealing force. 
     As described above, the controller  36  controls so that the container shift cylinder device  28 , which is a moving means of the container, is caused to generate a correction force, and thus it is possible to correct and keep constant the container sealing force, and therefore, to keep constant the amount of displacement and deflection of the die. 
     The controller  36  inputs a detection signal detected by the pressure sensor  34  and stores the reference pressure P 1 , which serves as a value for comparison with the detected pressures, in its built-in memory. The configuration is such that the detected pressures are input successively in the extrusion process and the detected pressure that is input and the reference pressure P 1  are compared and mathematically processed. 
     Then, a difference in pressure (δP) between them is calculated and when the difference in pressure is higher than the reference pressure P 1 , it means that the container sealing force acts excessively, and therefore, a pressure value Pc 1  required to generate a correction force in accordance with the amount of excess and to be supplied to the head side of the container shift cylinder device  28  is calculated. The pressure value Pc 1  can be calculated by multiplying the total section area of the main cylinder device  12  and the side cylinder device  26  by the detected difference in pressure (δP) and dividing the product by the section area of the container shift cylinder device  28 . Then, voltage conversion processing corresponding to the calculated pressure value Pc 1  is performed and its result is output to the amplifier  48  as an output signal, and thus the proportional electromagnetic relief valve  44  is controlled. 
     Due to this, it is possible to correct and keep constant the excessively acting container sealing force. 
     On the other hand, when the detected difference in pressure (δP) is lower than the reference pressure P 1 , it means that the container sealing force is deficient, and therefore, a pressure value Pc 2  required to generate a correction force in accordance with the amount of deficiency and to be supplied to the rod side of the container shift cylinder device  28  is calculated. The pressure value Pc 2  can be calculated by multiplying the total section area of the main cylinder device  12  and the side cylinder device  26  by the detected difference in pressure (δP) and dividing the product by the section area on the rod side of the container shift cylinder device  28 . Then, voltage conversion processing corresponding to the calculated pressure value Pc 2  is performed and its result is output to the amplifier  48  as an output signal, and thus the proportional electromagnetic relief valve  44  is controlled. 
     Due to this, it is possible to correct and keep constant the deficient container sealing force. 
       FIG. 3  is a section view of an extrusion press according to another embodiment. As shown schematically, the basic configuration is substantially the same as the extrusion press shown in  FIG. 1  described above and only configurational parts that are different are explained and other configurational parts should be referred to the explanation of  FIG. 1  described above. The same symbols are given to the same parts as those in  FIG. 1 . 
     In  FIG. 3 , between the end platen  10  and the container  18 , a plurality of container drive means  50  arranged so as to surround the die  16  are provided. The drive means  50  is attached fixedly to the end platen  10  and is basically configured to include an electric servomotor  50 A, which is a drive source, and a ball screw converter SOB that converts the rotational motion of the output shaft of the electric servomotor  50 A into a linear motion, including a screw shaft and a ball nut. The drive means  50  is attached so that the direction in which the screw shaft extends is in parallel with the extrusion axis line of the extrusion press and is designed so that the tip end of the screw shaft can come into contact with the end surface of the container  18  and a correction force can be generated by pressing under pressure the container  18  using the drive of the electric servomotor  50 A. 
     In  FIG. 3 , the configuration is such that the container drive means  50  is attached to the end platen  10 , the container  18  is pressed back by the screw shaft, and thus the container sealing force is reduced, however, a configuration may be accepted, in which the container drive means  50  is provided on the container side and the end platen  10  is pressed under pressure, and thus the container  18  is pressed under pressure. 
     The configuration of the drive hydraulic circuit of the main cylinder device  12  and the drive hydraulic circuit of the container shift cylinder device  28  is explained with reference to  FIG. 3 . 
     First, the hydraulic circuit  32  that drives the main cylinder device  12  comprises the hydraulic pump  30  of variable displacement type and the hydraulic pressure discharged therefrom is supplied to the main cylinder device  12  and the side cylinder device  26  via a hydraulic passage. To the hydraulic passage, the pressure sensor  34  that detects a hydraulic pressure is attached and the detected hydraulic pressure is output to the controller  36 . 
     A drive circuit  43  of the container shift cylinder device  28  comprises the hydraulic pump  38  that supplies pressurized hydraulic oil to the container shift cylinder device  28 . It is designed so that when pressurized hydraulic oil is supplied from the pump  38  to the rod side of the cylinder via the hydraulic passage, the cylinder rod  28 A is pulled in and driven and thus a container sealing force is generated. When pressurized hydraulic oil is supplied to the head side of the cylinder, a hydraulic pressure is generated, which causes to project and drive the cylinder rod  28 A. The hydraulic circuit  43  is provided with the proportional electromagnetic relief valve  44  that adjusts the hydraulic pressure to be supplied to the rod side of the container shift cylinder device  28 , and pressure is controlled via the amplifier  48  in accordance with the set instruction value by a control signal from the controller  36 , which is output in accordance with the hydraulic pressure detected by the pressure sensor  34  in the drive hydraulic circuit of the main cylinder device  12 . 
     Then, as shown in  FIG. 2 , the container sealing force reference pressure P 1  capable of maintaining a predetermined container sealing force also in the final step of the extrusion process and controlling constant the container sealing force is set lower than the maximum load pressure P 0  and higher than the required extrusion load pressure P 2  that acts on the die. In this case, in the first half of the extrusion process in which the extrusion load pressure that changes from P 0  to P 2  is in a range higher than the reference pressure P 1 , the container sealing force acts excessively and in the second half of the extrusion process in which the extrusion load force is in a range lower than the reference pressure P 1 , the container sealing force is deficient. 
     If, therefore, a correction value based on the mathematically processed deviation is output to the electric servomotor  50 A of the drive means  50  and caused to act so that the container  18  is pressed back from the die to reduce the container sealing force, it is possible to correct and keep constant the container sealing force, in the range where the container sealing force acts excessively and the load pressure is higher than the reference pressure P 1 . 
     On the other hand, in the range where the container sealing force acts deficiently and the load pressure is lower than the reference pressure P 1 , if the pressurized hydraulic oil based on the mathematically processed deviation is supplied to the rod side of the container shift cylinder device  28  and caused to act so that the container  18  is pressed under pressure against the die to increase the container sealing force, it is possible to correct and keep constant the container sealing force. 
     As described above, the controller  36  controls so that the container shift cylinder device  28 , which is a moving means of the container, generates a correction force, and thus it is possible to keep constant the container sealing force, and therefore, to keep constant the amount of displacement and deflection of the die. 
     The controller  36  inputs a detection signal by the pressure sensor  34  and stores the reference pressure P 1 , which serves as a value for comparison with a detected pressure, in a built-in memory. The configuration is such that the detected pressures are input successively in the extrusion process and the input detected pressure and the reference pressure P 1  are compared and mathematically processed. 
     Then, the difference in pressure (δP) between them is calculated and when the difference in pressure is higher than the reference pressure P 1 , it means that the container sealing force acts excessively, and therefore, a torque value required to generate a correction force in accordance with the amount of excess and to be output to the electric servomotor  50 A of the drive device  50  is calculated. The torque value can be obtained by mathematically processing the load calculated by multiplying the total section area of the main cylinder device  12  and the side cylinder device  26  by the detected difference in pressure (δP) and dividing the product by the section area of the container shift cylinder device  28 . Then, conversion processing corresponding to the mathematically processed and calculated torque value is performed and its result is output to the amplifier  49  as an output signal, and thus the electric servomotor  50 A is controlled. 
     Due to this, it is possible to correct and keep constant the excessively acting container sealing force. 
     On the other hand, when the detected difference in pressure (δP) is lower than the reference pressure P 1 , it means that the container sealing force is deficient, and therefore, the pressure value Pc 2  required to generate a correction force in accordance with the amount of deficiency and to be supplied to the rod side of the container shift cylinder device  28  is calculated. The pressure value Pc 2  can be calculated by multiplying the total section area of the main cylinder device  12  and the side cylinder device  26  by the detected difference in pressure (δP) and dividing the product by the section area on the rod side of the container shift cylinder device  28 . Then, voltage conversion processing corresponding to the calculated pressure value Pc 2  is performed and its result is output to the amplifier  48  as an output signal, and thus the proportional electromagnetic relief valve  44  is controlled. 
     Due to this, it is possible to correct and keep constant the deficient container sealing force. 
       FIG. 4  is a section view of an extrusion press showing another aspect, in which the drive means  50  of the container  18  is used as a hydraulic cylinder in the aspect in  FIG. 3 . In  FIG. 4 , between the end platen  10  and the container  18 , a hydraulic cylinder  50 C is provided as the plurality of the drive means  50  of the container  18  arranged so as to surround the die  16 . The hydraulic cylinder  50 C comprises a drive hydraulic circuit  45  and is attached so that the direction in which a ram SOD extends is in parallel with the extrusion axis line of the extrusion press, and the tip end of the ram  50 D can come into contact with the end surface of the container  18  and the container  18  is pressed under pressure by the drive of the hydraulic cylinder  50 C to generate a correction force. 
     This differs from that in  FIG. 3  in the following points. That is, when the container sealing force is reduced, the controller  36  inputs a detection signal by the pressure sensor  34  and stores the reference pressure P 1 , which is a value used in comparison with a detected pressure, in the built-in memory. The configuration is such that the detected pressures are input successively in the extrusion process and the detected pressure that is input and the reference pressure P 1  are compared and mathematically processed. 
     Then, the difference in pressure (δP) between them is calculated and when the difference in pressure is higher than the reference pressure P 1 , it means that the container sealing force acts excessively, and therefore, a pressure value Pc 3  required to generate a correction force in accordance with the amount of excess and to be supplied to the hydraulic cylinder  50 C is calculated. The pressure value Pc 3  can be calculated by multiplying the total section area of the main cylinder device  12  and the side cylinder device  26  by the detected difference in pressure (δP) and dividing the product by the section area of the hydraulic cylinder  50 C. Then, voltage conversion processing corresponding to the calculated pressure value Pc 3  is performed and its result is output to the amplifier  48  as an output signal, and thus the proportional electromagnetic relief valve  44  is controlled. 
       FIG. 5  is a section view of an extrusion press according to still another embodiment, and its configuration adopts both aspects in  FIG. 1  and  FIG. 2 . A configuration is shown, in which when the container sealing force is reduced, an output is sent to the moving means and the drive means of the container, and the amount of control to be output to the proportional electromagnetic relief valve  44  that controls a hydraulic pressure to be supplied to the head side of the container shift cylinder device  28  and the electric servomotor  50 A is output to the amplifiers  48 ,  49 , respectively, by the controller  36  in accordance with a reference determined in advance, and thus the container sealing force is corrected. The correction to increase the container sealing force makes use of the means to apply a predetermined pressure to the rod  12 A side of the container shift cylinder device  28  described above. 
     As explained above, the hydraulic pressure of the main cylinder device  12  during the extrusion process is detected and compared with the reference pressure P 1  set in advance and then mathematically processed, and correction is made so as to reduce the container sealing force when the deviation is plus with respect to the reference value, or to increase the container sealing force when the deviation is minus with respect to the reference value, and therefore, it is possible to keep constant the container sealing force in the extrusion process. As a result, it is possible to keep constant the amount of displacement and deflection of the die, and therefore, to make uniform the thickness and shape of the extruded product  20 A in the longitudinal direction, and to considerably improve the product yields. 
     In addition, it is possible to make constant the pressing force of the die without increasing the load pressure of the main cylinder device when correcting and keeping constant the container sealing force, and therefore, energy efficiency can be improved and the amount of energy consumption can be reduced. 
     Further, there is an excellent effect that the container sealing force can be kept constant during the extrusion process and can be kept to a desired container sealing force, and the occurrence of burr caused by the bursting phenomenon from the sealing surface can be effectively prevented. 
     The amount of deformation and deflection of the end platen that is added when the correction force is caused to act on the container sealing force becomes small because the load is spread to the end platen not from the die sealing end surface but via the container shift cylinder device and the moment (force moment) that acts on the end platen is improved to be smaller, and therefore, the influence on the die works in a better manner. 
       FIG. 6  is a section view of an extrusion press according to an embodiment. As shown in  FIG. 6 , in the extrusion press, the end platen  10  and the main cylinder device  12  are arranged in opposition to each other and both are linked by a plurality of tie rods  14 . On the inner surface of the end platen  10 , the container  18  is arranged with the die unit  16  in which an extrusion hole is formed being sandwiched between the end platen  10  and the container  18 , and the billet  20  is loaded in the container  18  and a product with a section in accordance with the die hole  16 A is extruded and molded by extruding under pressure the billet  20  toward the die unit  16 . 
     The main cylinder device  12  that generates an extrusion force incorporates the main ram  12 B in the main cylinder  12 A and the main ram  12 B can be moved under pressure toward the container  18 . To the front end part of the main ram  18 B, the extrusion stem  24  is attached in a state of projecting toward the container  18  via the crosshead  22  so as to be arranged concentrically with the billet load hole  18 A of the container  18 . Because of this, when the main cylinder device  12  is driven to advance the crosshead  22 , the extrusion stem  24  is inserted into the billet load hole  18 A of the container  18 , and therefore, pressure is applied to the rear end surface of the loaded billet  20 , and thus the product  20 A is extruded. 
     To the main cylinder  12 A, the side cylinder device  26  is attached in parallel with the extrusion axial center and its cylinder rod  26 A is linked to the crosshead  22 . Due to this, the configuration is such that the extrusion stem  24  is initially moved to the position close to the container  18  as a preparation process of the extrusion process and the operation of extrusion under pressure is performed using both the main cylinder device  12  and the side cylinder device  26 . 
     To the end platen  10 , the container shift cylinder device  28 , as a moving means capable of freely moving the container  18  back and forth in the direction of the extrusion axis line, is attached, and its cylinder rod  28 A is linked to the container holder  19 . Due to this, the configuration is such that a sealed state is brought about as the preparation process of extrusion by causing the end surface of the die unit  16  to come into contact with the end surface of the container  18  and in the completion process of extrusion, the end surface of the die unit  16  is separated from the end surface of the container  18  and thus a gap through which the remaining material of the billet  20  is discharged is secured. 
     Then, the configuration is such that a die deflection detection device  60  is provided on the end surface on the product discharge side of the die unit  16  arranged on the inner surface of the end platen  10 , and the amount of deflection of the die that deforms by the extrusion force during the extrusion process is detected. 
     The configuration of a drive hydraulic circuit of the main cylinder device  12  and a drive hydraulic circuit of the container shift cylinder device  28  is explained with reference to  FIG. 6 . 
     First, the hydraulic circuit  32  that drives the main cylinder device  12  comprises the hydraulic pump  30  of variable displacement type, and the hydraulic pressure discharged therefrom is supplied to the main cylinder device  12  and the side cylinder device  26  via a hydraulic passage. 
     The drive circuit  42  of the container shift cylinder device  28  is provided with the hydraulic pump  38  that supplies pressurized hydraulic oil to the container shift cylinder device  28 . When pressurized hydraulic oil is supplied from the pump  38  to the rod side of the container shift cylinder via the hydraulic passage, the cylinder rod  28 A is pulled in and driven and thus a container sealing force is caused to occur. It is designed so that when pressurized hydraulic oil is supplied to the head side of the container shift cylinder, the cylinder rod  28 A is caused to project and the container  18  is separated from the die unit  16 . The hydraulic circuit  42  is provided with the proportional electromagnetic relief valve  44  that adjusts the hydraulic pressure to be supplied to the container shift cylinder device  28  and the pressure control is performed via the amplifier  48  in accordance with the set instruction value based on a control signal that is output from the controller  36  in accordance with the amount of deflection of the die detected by a die deflection sensor  62  of the die deflection detection device  60 . 
     Then, the control means of the container moving means comprises the controller  36  and the amplifier  48 . 
     As described above, the extrusion process is performed by the main cylinder device  12  and the side cylinder device  26 . Then, the extrusion force (F) during the extrusion process is expressed by the sum of the required extrusion force (Fa) that acts on the die unit  16  and the frictional force (Fb) between the billet  20  and the inner wall of the container  18 . As shown in  FIG. 7 , the extrusion force (F) and the frictional force (Fb) between the billet  20  and the inner wall of the container  18  become maximum when extrusion starts and because of the reduction in the frictional force (Fb) accompanying the reduction in length of the billet  20  as the extrusion process advances, the extrusion force (F) is reduced. 
     The required extrusion force (Fa) that acts on the die unit  16  is substantially uniform and if the temperature condition of the billet  20  is the same, it rarely happens that the required extrusion force varies. 
     As shown in  FIG. 7 , a deflection amount δ 1  of the die capable of ensuring a predetermined container sealing force also in the final step of the extrusion process and serving as a reference to keep constant the container sealing force is set smaller than a maximum load deflection amount δ 2  and larger than a required load deflection amount δ 0  that acts on the die. In this case, in the first half of the extrusion process in which the deflection amount that changes from δ 0  to δ 2  is in a range smaller than the reference deflection amount δ 1 , the container sealing force acts excessively on the die and in the second half of the extrusion process in which the deflection amount is in a range larger than the reference deflection amount δ 1 , the container sealing force that acts on the die is deficient. 
     If, therefore, a hydraulic pressure calculated by mathematically processing the deviation of the defection amount is supplied to the head side of the container shift cylinder device  28  and thereby the container  18  is moved in the direction in which the container  18  is pressed back from the die unit  16  to reduce the container sealing force, it is possible to correct and keep constant the container sealing force, in the first half of the extrusion process in which the container sealing force acts excessively on the die and the deflection amount of the die is smaller than the reference value. 
     On the other hand, in the second half of the extrusion process in which the container sealing force acts deficiently on the die and the deflection amount is larger than the reference value, if a hydraulic pressure calculated by mathematically processing the deviation of the deflection amount is supplied to the rod side of the container shift cylinder device  28  and thereby the container  18  is moved in the direction in which the container  18  is pressed under pressure from the die unit  16  to increase the container sealing force, it is possible to correct and keep constant the container sealing force. 
     As described above, the controller  36  controls the hydraulic pressure to cause the container shift cylinder device  28 , which is a moving means of the container  18 , to generate a correction force, and thus it is possible to keep constant the container sealing force, and therefore, to maintain constant the deflection amount of the die. 
     The controller  36  is input with a detection signal from the die deflection sensor  62  of the die deflection detection device  60  via an amplifier and stores the reference deflection amount δ 1 , which serves as a value for comparison with a detected deflection amount, in its built-in memory. 
     Then, the configuration is such that the detected deflection amounts are input successively in the extrusion process and the input deflection amount and the reference deflection amount δ 1  are compared and mathematically processed, and a deviation between them is mathematically processed and when the deviation is minus, that is, the deflection amount is smaller than the reference deflection amount δ 1 , it means that the container sealing force acts excessively, and therefore, the pressure value Pc 1  of the hydraulic oil required to generate a correction force in accordance with the amount of excess and to be supplied to the head side of the container shift cylinder device  28  is calculated. 
     The pressure value Pc 1  can be obtained by storing in advance the relationship between the extrusion force and the die deflection amount in the controller  36 , calculating the extrusion force from the mathematically processed deviation, and at the same time, dividing the calculated extrusion force by the section area of the container shift cylinder device  28 . Next, voltage conversion processing corresponding to the calculated pressure value Pc 1  is performed and its result is output to the amplifier  48 , and thus the proportional electromagnetic relief valve  44  is controlled. Due to this, it is possible to correct and make constant the container sealing force that acts excessively on the die. 
     On the other hand, when the mathematically processed deviation is plus, i.e., the deflection amount is larger than the reference deflection amount δ 1 , it means that the container sealing force is deficient, and therefore, the hydraulic pressure value Pc 2  required to generate a correction force in accordance with the amount of deficiency and to be supplied to the rod side of the container shift cylinder device  28  is calculated. 
     The pressure value Pc 2  can be obtained by calculating using the relationship between the stored extrusion force and the die deflection amount and dividing the calculated extrusion force by the section area on the rod side of the container shift cylinder device  28 . Next, voltage conversion processing corresponding to the calculated pressure value Pc 2  is performed and its result is output to the amplifier  48 , and thus the proportional electromagnetic relief valve  44  is controlled. Due to this, it is possible to correct and make constant the deficient container sealing force that acts on the die. 
       FIG. 8  is a section view of an extrusion press according to another embodiment. As shown schematically, the basic configuration is substantially the same as the extrusion press in  FIG. 6  described above, and only different constitutional parts are explained and other configurational parts should be referred to the explanation of  FIG. 6  described above. The same symbols are given to the same parts as those in  FIG. 6 . 
     In  FIG. 8 , between the end platen  10  and the container  18 , a plurality of drive means  50  of the container  18  arranged so as to surround the die unit  16  are provided. The drive means  50  is attached fixedly to the end platen  10  and its basic configuration includes the electric servomotor  50 A, which is a drive source, and the ball screw converter  50 B that converts the rotational motion of the output shaft of the electric servomotor  50 A into a linear motion, including a screw shaft and ball nut. The drive means  50  is attached so that the direction in which the screw shaft extends is parallel with the extrusion axis line of the extrusion press and is designed so that the tip end of the screw shaft can come into contact with the end surface of the container  18  and a correction force can be generated by pressing under pressure the container  18  using the drive of the electric servomotor  50 A. 
     In  FIG. 8 , the configuration is such that the drive means  50  of the container  18  is attached to the end platen  10 , the container  18  is pressed back by the screw shaft, and thus the container sealing force is reduced, however, a configuration may be accepted, in which the drive means  50  of the container  18  is provided on the container  18  side and the end platen  10  is pressed under pressure, and thus the container  18  is pressed back. 
     The configuration of the drive hydraulic circuit of the main cylinder device  12  and the drive hydraulic circuit of the container shift cylinder device  28  is explained with reference to  FIG. 8 . 
     First, the hydraulic circuit  32  that drives the main cylinder drive  12  comprises the hydraulic pump  30  of variable displacement type and the hydraulic pressure discharged therefrom is supplied to the main cylinder device  12  and the side cylinder device  26  via a hydraulic passage. 
     The drive circuit  43  of the container shift cylinder device  28  comprises the hydraulic pump  38  that supplies pressurized hydraulic oil to the container shift cylinder device  28 . It is designed so that when pressurized hydraulic oil is supplied from the hydraulic pump  38  to the rod side of the container shift cylinder via a hydraulic passage, the cylinder rod  28 A is pulled in and driven, and thus a container sealing force is generated. The hydraulic circuit  43  is provided with the proportional electromagnetic relief valve  44  that adjusts the hydraulic pressure to be supplied to the container shift cylinder rod side, and pressure control is performed via the amplifier  48  in accordance with the set instruction value by the control signal from the controller  36 , which is output in accordance with the deflection amount of the die detected by the die deflection sensor provided in the die deflection detection device  60 . 
     Then, the deflection amount δ 1  of the die capable of securing a predetermined container sealing force also in the final step of the extrusion process and serving as a reference to keep constant the container sealing force is set smaller than the maximum load deflection amount δ 2  and larger than the required load deflection amount δ 0  that acts on the die. In this case, in the first half of the extrusion process in which the deflection amount that changes from P 0  to P 2  is in a range smaller than the reference deflection amount δ 1 , the container sealing force acts excessively on the die and in the second half of the extrusion process in which the deflection amount is larger than the reference deflection amount δ 1 , the container sealing force that acts on the die is deficient. 
     If, therefore, a correction value based on the mathematically processed deviation is output to the electric servomotor  50 A of the drive means  50  and caused to act so that the container  18  is pressed back from the die unit  16  to reduce the container sealing force, it is possible to correct and keep constant the container sealing force in the first half of the extrusion process in which the container sealing force acts excessively on the die and the deflection amount of the die is smaller than the reference value. 
     On the other hand, in the second half of the extrusion process in which the container sealing force is deficient and the deflection amount that acts on the die is larger than the reference value, it is possible to correct and keep constant the container sealing force by supplying the hydraulic pressure mathematically processed and calculated from the deviation of the deflection amount to the rod side of the container shift cylinder device  28  and moving the container  18  from the die unit  16  in the direction of pressing under pressure to increase the container sealing force. 
     As described above, the container sealing force is kept constant, and therefore, the deflection amount of the die is kept constant by causing the container shift cylinder device  28 , which is a moving means of the container  18 , and the container drive device  50  to generate a correction force. 
     The controller  36  inputs a detection signal from the die deflection sensor  62  of the die deflection detection device  60  via an amplifier and stores the reference deflection amount δ 1 , which serves as a value for comparison with a detected deflection amount, in a built-in memory. Then, the configuration is such that the deflection amounts detected in the extrusion process are input successively and the input deflection amount and the reference deflection amount δ 1  are compared and mathematically processed. 
     When the mathematically processed deviation is minus, i.e., when the deflection amount is smaller than the reference deflection amount δ 1 , it means that the container sealing force acts excessively, and therefore, a torque value required to generate a correction force in accordance with the amount of excess and to be output to the electric servomotor  50 A of the container drive device  50  is calculated. The torque value is obtained by storing in advance the relationship between the extrusion force and the die deflection amount in the controller  36  and calculating the extrusion force from the mathematically processed deviation. Then, conversion processing corresponding to the mathematically processed torque value is performed and its result is output to the amplifier  49  as an output signal, and thus the electric servomotor  50 A is controlled. 
     Due to this, it is possible to correct and keep constant the container sealing force that acts excessively on the die. 
     On the other hand, when the mathematically processed deviation is plus, i.e., when the deflection amount is larger than the reference deflection δ 1 , it means that the container sealing force is deficient, and therefore, the hydraulic pressure value Pc 2  required to generate a correction force in accordance with the amount of deficiency and to be supplied to the rod side of the container shift cylinder device  28  is calculated. 
     The pressure value Pc 2  is obtained by calculating the extrusion force using the stored relationship between the extrusion force and the die deflection amount and dividing the calculated extrusion force by the section area on the rod side of the container shift cylinder device  28 . Next, voltage conversion processing corresponding to the calculated pressure value Pc 2  is performed and its result is output to the amplifier  48 , and thus the proportional electromagnetic relief valve  44  is controlled. Due to this, it is possible to correct and keep constant the deficient container sealing force that acts on the die. 
     Then, the control means of the container drive means  50  is configured by the controller  36  and the amplifier  49  described above. 
       FIG. 9  is a section view of an extrusion press showing another aspect with a configuration in which a hydraulic cylinder is used as the container drive means  50  in the aspect in  FIG. 8 . In  FIG. 9 , between the end platen  10  and the container  18 , the hydraulic cylinder  50 C is provided as the plurality of the container drive means  50  arranged so as to surround the die unit  16 . The container shift cylinder device  28  and the hydraulic circuit  45  for driving the hydraulic cylinder  50 C are provided, the hydraulic cylinder  50 C is attached so that the direction in which the ram  50 D extends is in parallel with the extrusion axis line of the extrusion press, the tip end of the ram  50 D can come into contact with the end surface of the container  18  and the container  18  is pressed under pressure by the drive of the hydraulic cylinder  50 C to generate a correction force. The control means of the drive means  50  in  FIG. 9  comprises the controller  36  and the amplifier  48 . 
     The action is different from that in  FIG. 8  in the following points. That is, when the container sealing force is reduced, the controller  36  is input with a detection signal from the die deflection sensor  62  of the die deflection detection device  60  via an amplifier and stores the reference deflection amount δ 1 , which is a value used for comparison with a detected deflection amount, in the built-in memory. Then, the configuration is such that the deflection amounts detected in the extrusion process are input successively and the input deflection amount and the reference deflection amount δ 1  are compared and mathematically processed. 
     When the mathematically processed deviation is minus, that is, when the deflection amount is smaller than the reference deflection amount δ 1 , it means that the container sealing force acts excessively, and therefore, the hydraulic pressure value Pc 3  required to generate a correction force in accordance with the amount of excess and to be supplied to the hydraulic cylinder  50 C is calculated. The pressure value Pc 3  can be calculated by storing in advance the relationship between the extrusion force and the die deflection amount in the controller  36 , then obtaining the extrusion force from the mathematically processed deviation, and dividing the extrusion force by the total section area of the main cylinder device  12  and the side cylinder device  26 . 
     Then, voltage conversion processing corresponding to the calculated pressure value Pc 3  is performed and its result is output to the amplifier  48  as an output signal, and thus the proportional electromagnetic relief valve  44  is controlled. 
       FIG. 10  shows a section view of an extrusion press according to still another embodiment and its configuration adopts both aspects in  FIG. 6  and  FIG. 7 . The configuration is such that an output is sent to the moving means and the drive means of the container when reducing the container sealing force, and the amount of control to be output to the proportional electromagnetic relief valve  44  that controls the hydraulic pressure to be supplied to the head side of the container shift cylinder device  28  and the electric servomotor  50 C is output to the amplifiers  48 ,  19 , respectively, by the controller  36  in accordance with the reference determined in advance, and thus the container sealing force is corrected. The correction to increase the container sealing force makes use of the means to apply a predetermined hydraulic pressure to the rod side of the container shift cylinder device  28  described above. 
       FIG. 11  is a section view showing essential parts of the die deflection detection device  60 . In  FIG. 11 , reference number  16  denotes a die unit and the die unit basically comprises a die  16 B, a die backer  16 C, a die ring  16 D, and a die bolster  16 E supported by the end platen  10 . The container is sealed by pressing under pressure the container  18  against the end platen  10  with the container shift cylinder device  28  and pressing under pressure the die  16 B against the end platen  10  by a container liner, through the die backer  16 C and the die bolster  16 E. 
     After the container is sealed, the container  18  is loaded with a billet and the rear end surface of the billet is pressurized toward the die  16 B side with a stem and a product is extruded from the die hole  16 A. 
     When an extrusion force acts on the die unit  16 , the die unit  16  deforms and deflects in the direction of extrusion accordingly. Then, the amount of deflection of the die unit  16  reduces in inverse proportion to the magnitude of the extrusion force that acts on the die unit  16 . 
     The die deflection detection device  60  basically comprises a product guide  61  provided in a product discharge hole in the center of the end platen  10  to prevent deformation due to an extrusion force and a plurality of die deflection detection sensors  62  attached at the tip end part of the product guide  61 . It is preferable to use a non-contact type displacement sensor, such as an eddy-current type, an optical type, and an ultrasonic type, as the die deflection detection sensor  62 . In the present embodiment, the configuration is such that the four die deflection detection sensors  62  are used and the deflection of the die  16 B is detected by the deflection of the die bolster  16 E, and the respective deflection amounts are input to the controller  36  and the average of the input values is used as a detected amount. 
     Although the configuration is such that a non-contact type displacement sensor is used as the die deflection sensor  62 , a configuration may be adopted, in which a plurality of non-contact type displacement sensors and a sensor that detects the magnitude of an acting force are used. 
     As explained above, the deflection amount of a die during extrusion process is detected and compared with a reference deflection amount set in advance and then mathematically processed, and when the deviation is smaller than the reference value, correction is made so as to reduce the container sealing force and when the deviation is larger than the reference value, correction is made so as to increase the container sealing force, and therefore, it is possible to keep constant the container sealing force in the extrusion process. 
     As a result, it is possible to keep constant the amount of deflection of the die unit  16 , and therefore, to make uniform the thickness and shape of the extruded product  20 A in the longitudinal direction, and to considerably increase the product yields. 
     In addition, it is possible to make constant the container sealing force that acts on the die unit  16  without increasing the load pressure of the main cylinder device  12  when correcting and keeping constant the container sealing force, and therefore, energy efficiency is improved and the amount of energy consumption can be reduced. 
     Furthermore, there is an excellent effect that the container sealing force can be kept constant during the extrusion process and can be kept to a desired container sealing force, and the occurrence of a burr caused by the bursting phenomenon from the sealing surface can be effectively prevented. 
     The amount of deformation and deflection of the end platen that is added when the correction force is caused to act on the container sealing force becomes small because the load is propagated to the end platen not from the die sealing end surface but via the container shift cylinder device and the moment that acts on the end platen is improved to be smaller, and therefore, the influence on the die unit works in a further better manner. 
     While the invention has been described by reference to specific embodiments chosen for the purposes of illustration, it should be apparent that numerous modifications could be made thereto, by those skilled in the art, without departing from the basic concept and scope of the invention.