Patent Publication Number: US-2006012073-A1

Title: Extrusion molding apparatus and extrusion molding method

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an extrusion molding apparatus and an extrusion molding method for molding an easily deformable extrusion molded body such as ceramic honeycomb structure.  
      2. Description of the Related Art  
      As a catalyst carrier used, for example, in an exhaust purifying apparatus for an automobile vehicle, as shown in  FIG. 13 , a ceramic molded body  8 , of a honeycomb structure, is used. In the body partition walls  81  for partitioning a multiplicity of cells  88  communicating in axial direction, are arranged in honeycomb shape. Such a ceramic molded body  8  is generally manufactured by continuously extruding ceramic material consisting of a kneaded clay-like material and, after cutting the extruded material into unit lengths, drying and firing the extruded product.  
      In recent years, as improvements in product performance are required, it is strongly required to manufacture the above described molded body  8  with thinner partition walls  81 . However, as the walls become thinner, the rigidity of the molded body immediately after extrusion is significantly decreased especially in the direction perpendicular to the axial direction, and in some cases, the molded body may deform due to its own weight and may not provide a successful product. This problem becomes particularly evident and pronounced in the case of honeycomb structure with ultra-thin walled partition where the thickness of partition walls is as small as 125 μm or less.  
      Demand for a ceramic molded body of honeycomb structure as described above is now increasing not only as a catalyst carrier in an exhaust gas purifying system in an automobile, but also as a substrate for collecting diesel particulates in an automobile vehicle. A ceramic molded body for collecting diesel particulates is constructed by plugging cells on both end faces in a checkered pattern and by composing the partition walls with a porous material so as to able to function as a filter.  
      When used as a substrate for collecting diesel particulates, a significantly larger body size is required for the ceramic molded body than is required when used simply as a catalyst carrier. For example, a volume capacity of about 2 liters is generally required for a passenger car, and volume capacity of about 6 liters to 15 liters is required for trucks of medium to large sizes. Thus, an increase in the weight is significant for a substrate for collecting diesel particulates due to the increases in volume and diameter, as well as an increase in thickness of partition walls, up to 250 to 350 μm, in order to satisfactorily filter and collect diesel particulates. Therefore, it becomes highly probable that the molded body immediately after extrusion may deform due to its own weight.  
      In order to resolve this problem, a method is proposed in horizontal extrusion process for producing a hexagonal honeycomb structure by extrusion in horizontal direction, in which the extrusion process is implemented such that the c-axis parallel to two sides of each hexagon is directed nearly in vertical direction (see Japanese Unexamined Patent Publication No. 2000-167818). This method, although effective, cannot be considered to be satisfactory as a further increase in size and a further reduction of wall thickness is needed.  
      In vertical extrusion process in which extrusion process is implemented in a vertically downward direction, it is difficult to support the outer circumferential surface during extrusion. The operation of supporting at the front end and cutting in unit length also becomes complicated, and efficiency is thereby lowered.  
      The problems associated with the lowering of rigidity of extrusion molded body are not limited to extrusion molding of ceramic molded body of honeycomb structure as described above, but are common to all molding of soft extrusion molded bodies that can deform due to the weight.  
      It is an object of the present invention to resolve the above problem associated with the prior art and to provide an extrusion molding apparatus and an extrusion molding method which, when molding a soft extrusion molded body with low rigidity in the direction perpendicular to the extruding direction, prevents such deformation and permits a sound extrusion molded body to be obtained.  
     SUMMARY OF THE INVENTION  
      In accordance with a first invention, there is provided an extrusion molding apparatus comprising a screw extruder which kneads the raw material for molding and extrudes the kneaded material from a molding die to form an extrusion molded body, and a conveying apparatus for supporting and conveying, in the extrusion direction, said extrusion molded body continuously extruded from the screw extruder: 
          characterized in that the inclination angle θ between the extrusion axis and the horizontal axis of said screw extruder is in the range of 15° to 85°,     and that said conveying apparatus is constructed such that the reception stage for supporting said extrusion molded body extruded along said extrusion axis on outer circumferential surface, is moved generally in parallel to said extrusion axis.        

      In the extrusion molding apparatus according to the present invention, the screw extruder is disposed obliquely such that the inclination angle θ is in the above specified range, and the reception stage of said conveying apparatus is provided movably in oblique direction along said extrusion axis. Thus, the conveying apparatus supports and moves forward the extrusion molded body continuously extruded from said screw extruder on outer circumferential surface with said reception stage. Thus, as compared to conventional horizontal extrusion process in which extrusion is performed along a horizontal axis, the deformation force exerted to the extrusion molded body can be decreased and deformation can be prevented.  
      Specifically, the deformation force for deforming the extrusion molded body is mainly produced as a reaction to the weight when the extrusion molded body is supported at an outer circumferential surface by the reception stage etc. With the extrusion molding apparatus of the invention, by providing the inclination angle θ, the reaction from the reception stage can be decreased as compared to conventional horizontal extrusion process. Therefore, even if the extruded molded body is a soft molding that may collapse due to its own weight when placed with its axis in horizontal direction, the extrusion molded body can be conveyed without deformation using the extrusion molding apparatus of the invention.  
      The extrusion molded body is supported by the reception stage on the outer circumferential surface. Thus, when the extrusion molded body continuously extruded is cut in unit length, the extrusion molded body continues to be supported on the outer circumferential surface, so that cutting process can be performed stably.  
      Therefore, in accordance with the present invention, an extrusion molding apparatus can be provided which permits, even when a soft extrusion molded body having low rigidity in the direction perpendicular to the extrusion direction is molded, such deformation to be prevented and a sound extrusion molded body to be obtained.  
      In accordance with a second invention, there is provided an extrusion molding method for molding an extrusion molded body using an extrusion molding apparatus comprising a screw extruder which kneads the raw material for molding and extrudes the kneaded material from a molding die to form an extrusion molded body, and a conveying apparatus for supporting and conveying in extrusion direction said extrusion molded body continuously extruded from the screw extruder: 
          characterized in that the screw extruder is tilted such that the inclination angle θ between the extrusion axis and the horizontal axis is in the range of 15° to 85°, and that said conveying apparatus supports said extrusion molded body extruded along said extrusion axis on outer circumferential surface by a reception stage, and moves it generally in parallel to said extrusion axis.        

      In the extrusion molding method according to the present invention, a screw extruder disposed obliquely such that the inclination angle θ is in the range specified above, and a conveying apparatus provided with a reception stage capable of being moved obliquely along the extrusion axis, are used. Thus, the extrusion molded body extruded continuously from the screw extruder is supported on the outer circumferential surface and is moved forward by the reception stage.  
      Thus, the deformation force exerted on the extrusion molded body can be decreased as compared to prior art, and deformation can be prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an explanatory view showing the construction of an extrusion molding apparatus in Example 1;  
       FIG. 2  is an explanatory view showing the interconnection between the conveying apparatus and a secondary conveying apparatus in Example 1 as seen in the direction of arrow X in  FIG. 1 ;  
       FIG. 3  is an explanatory view showing the process in the midway of extrusion molding in Example 1;  
       FIG. 4  is an explanatory view showing extrusion molded body after cutting in Example 1;  
       FIG. 5  is an explanatory view showing the cut unit molded body abutting against the end surface reception stage;  
       FIG. 6  is an explanatory view showing the construction of an extrusion molding apparatus in Example 2;  
       FIG. 7  is an explanatory view showing the construction of an extrusion molding apparatus in Example 3;  
       FIG. 8  is an explanatory view showing a rotated downender of the extrusion molding apparatus in Example 3;  
       FIG. 9  is an explanatory view showing the construction of the upstream portion of the extrusion molding apparatus in Example 1 to 3;  
       FIG. 10  is an explanatory view showing the construction of an extrusion molding apparatus in Comparative example 1;  
       FIG. 11  is an explanatory view showing the sectional shape of the extrusion molded body in Example 1;  
       FIG. 12  is an explanatory view showing the sectional shape of the extrusion molded body in Comparative example 1; and  
       FIG. 13  is an explanatory view showing a honeycomb molded body in a prior example. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In the above-described first and second inventions, the inclination angle θ is in the range of 15° to 85°. If the inclination angle θ is less than 15°, the effect of providing such an inclination angle cannot be sufficiently obtained. If the inclination angle exceeds 85°, the reaction when the extrusion molded body is supported on the outer circumferential surface is too small to obtain a stable support.  
      Thus, preferably, the inclination angle θ is in the range of 30° to 75°.  
      In the above-described first invention, the conveying apparatus comprises a conveyor with a conveying surface for placing the reception stage provided generally in parallel to the extrusion axis, and the conveyor is provided with a plurality of stoppers, for supporting the reception stage on the front end-face thereof in the moving direction, preferably constructed such that the reception stages successively supplied to the conveyor are successively supported by the stoppers to be moved forward. In this case, a plurality of reception stages can be successively moved forward at predetermined intervals, and the extrusion molded bodies can be stably supported.  
      The conveying apparatus also comprises a cutting device for cutting the extrusion molded body moving forward on the conveying apparatus in a specified length to form unit molded body, and one or plural reception stages are preferably disposed for each unit molded body. In this case, the extrusion molded body can be cut in unit lengths while being supported by one or plural reception stages so that stable cutting operation can be realized.  
      When the conveying apparatus comprises the above-described conveyor, the conveyor is preferably constructed such that conveying speed on the downstream side can be different from the conveying speed on the upstream side. With such construction, it is possible to separate the unit molded body cut by the cutting device from the lengthy extrusion molded body being extruded. It is also easy to slow down the conveying speed for changing to another direction. This increases the conveying capability for the unit molded bodies and facilitates a change in conveying direction.  
      It is also preferable that the conveying apparatus be interconnected with a secondary conveying apparatus for conveying the unit molded body in a direction different from the extrusion axis as it is supported at the axial end-face by the end-face reception stage. In this case, the unit molded body can be supported in an axial direction in which it is relatively rigid, and can be stably conveyed in a desired direction. Support by the end-face reception stage may be used in conjunction with support by the prior reception stage. Alternatively, support by the prior reception stage may be terminated and the unit molded body may be supported only by the end-face reception stage.  
      It is also preferable that a downender be disposed between the conveying apparatus and the secondary conveying apparatus for turning the axis of the unit molded body that is abutted against the end-face reception stage in generally vertical direction with the end-face reception stage facing downward. In this case, presence of the downender facilitates turning of the axis of the unit molded body in vertical direction.  
      It is also preferable that the extrusion molded body be a ceramic molded body using ceramic material as molding material. An extrusion molded body using ceramic material is very liable to be deformed immediately after extrusion. Therefore, above-described operative effect of the invention is particularly evident in such a case.  
      As the ceramic material, various raw materials, such as cordielite raw material that produces cordielite after firing, mullite raw material that produces mullite after firing, alumina raw material, silicon carbide raw material, silicon nitride raw material, etc can be used.  
      The extrusion molded body is preferably a honeycomb structure having partition walls arranged in a polygonal lattice pattern so as to provide a multiplicity of cells. When such a honeycomb structure is molded, it is required to maintain the lattice shape. As the partition wall becomes thinner, the wall is likely to be deformed, and therefore, the operative effect described above becomes more effective.  
      In the honeycomb structure as described above, the thickness of partition walls is preferably 125 μm or less. In this case, when it is used as a catalyst carrier in an exhaust gas purifying apparatus in an automobile, it can rapidly activate the carried catalyst and can improve the performance of the exhaust gas purifying apparatus. When the thickness of partition walls is preferably 125 μm or less, the structure is easily deformed, so that the operative effect of the first and the second inventions as described above becomes more effective. The lower bound of the thickness of partition walls is about 35 μm, based on the fluidity of clay material and extrusion pressure in the process of extruding clay-like ceramic material from a molding die, and constraints such as the strength of the molding die to withstand the pressure.  
      As the polygonal lattice, various forms are available such as triangular lattice, rectangular lattice, hexagonal lattice, and the like.  
      The honeycomb structure is preferably 300 mm or more in diameter. In this case, when it is used as a substrate for collecting diesel particulates in an automobile, a sufficient function for collecting particulates can be achieved. When such a honeycomb structure is to be molded, it is required to maintain the lattice shape. As the structure becomes larger, the partition walls are more likely to be deformed. In particular, when the diameter is 300 mm or more, the lattice is easily deformed, and therefore, the operative effect of the first and the second inventions becomes more effective.  
     EXAMPLE 1  
      An extrusion molding apparatus and an extrusion molding method according to an Example of the present invention will be described below with reference to FIGS.  1  to  5 .  
      The extrusion molding apparatus  1  of the present Example comprises, as shown in  FIG. 1 , a screw extruder  12  that kneads the molding raw material  80  and extrudes an extrusion molded body  8  from a molding die  11 , and a conveying apparatus  3  that supports the extrusion molded body  8  continuously extruded from the screw extruder  12 , and conveys same in extrusion direction.  
      The screw extruder  12  has an inclination angle θ, between the extrusion axis A and the horizontal axis H, in the range of 15° to 85°. The conveying apparatus  3  is constructed so as to move a reception stage  31 , which supports the extrusion molded body  8  extruded along the extrusion axis A on the outer circumferential surface, generally in parallel to the extrusion axis A.  
      This will be described in more detail below.  
      The screw extruder  12  constituting the extrusion molding apparatus  1  of the present Example has, as shown in  FIG. 1 , an extrusion screw  122  built into a tubular casing  121 , and has a molding die  11  provided via a resistance tube  125  at its distal end. The screw extruder  12  may be composed of plural screw extruders.  
      In the present Example, the extrusion axis A of the screw extruder, that is, the center axis of the screw extruder  12  and the molding die  11 , is inclined relative to the horizontal axis H. The inclination angle θ is set to 45° in the present Example.  
      The conveying apparatus  3  is provided in the lower portion in front of the screw extruder  12 . The conveying apparatus  3  of the present Example has a conveyor  32 , as shown in  FIG. 1 , provided with the conveying surface  310  for placing a reception stage  31  generally in parallel to the extrusion axis A. In the present Example, a roller conveyor is adopted as the conveyor  32 , and is constructed so as to move the reception stage  31  progressively forward by means of plural driving rollers  325 . The conveyor  32  is constructed such that conveying speed can be partially varied and, as will be described later, is actually set such that the conveying speed can be varied depending on the position of a cut unit molded body  8   a.    
      Also, as shown in the same Figure, the conveying apparatus  3  has a cutting device  39  for cutting the extrusion molded body  8  moved on the conveyor  32  into a unit molded body  8   a  ( FIG. 4 ). The conveying apparatus  3  is constructed such that one reception stage  31  is disposed for each unit molded body. The above-described cutting device  39  is one using a wire that is moved in cutting direction while the wire is run in an axial direction.  
      The reception stage  31  of the present Example is of generally rectangular parallelepiped in shape having a receiving surface (not shown) formed on top face by boring in circular arc along the outer circumferential shape of the cylindrical extrusion molded body.  
      The upstream end of the conveyor  32  is disposed with a gap to the molding die  11  at the front end of the screw extruder  12 . In this gap, a reception stage supplying apparatus  4  is provided for supplying the reception stages  31  successively. The reception stage supply apparatus  4  has a reception stage holding section  41  movable in up/down direction, and the reception stage holding section  41  comprises a roller  42  for moving forward the placed reception stage  31 . The reception stage supplying apparatus  4  successively elevates the reception stage  31  that is fed through a reception stage supplying route (not shown), and abuts it to the outer circumferential surface of the extrusion molded body  8  without imparting a shock and, then, the roller  42  moves the reception stage  31  forward with the advancing extrusion molded body  8 , and transfers it to the conveyor  32 .  
      As shown in  FIGS. 1 and 2 , the conveying apparatus  3  is interconnected with a secondary conveying apparatus  5  that conveys the unit molded body  8   a  in a conveying direction B different from the extrusion axis A with the unit molded body  8   a  (see  FIG. 2 , FIGS.  3  to  5 ) supported at the axial front end-face  801  by an end-face reception stage  33 .  
      The secondary conveying apparatus  5  is constructed, as shown in  FIG. 2 , as a combination of two conveyors so as to convey the unit molded body  8   a  in a horizontal conveying direction B perpendicular to the extrusion axis A that is the conveying direction of the conveying apparatus  3 .  
      Thus, the secondary conveying apparatus  5  comprises a first conveyor  51  that receives the reception stage  31  conveyed by the conveying apparatus  3  as it is and changes the conveying direction and a second conveyor  52  that receives a flat plate-shaped end-face reception stage  33  successively supplied by an end-face reception stage supplying apparatus (not shown) and supports and moves it forward in the conveying direction B. The conveying surfaces  511 ,  521  are disposed, as shown in  FIG. 2 , so as to be perpendicular to each other, and move in synchronism in the conveying direction B.  
      Next, the method of carrying out extrusion molding by using the extrusion molding apparatus  1  having the above-described construction will be described.  
      The extrusion molded body  8  molded in the present Example is a ceramic molding using a ceramic material as the raw material for molding, as shown in the above-described  FIG. 13 , that is a honeycomb structure having partition walls  81  arranged in the shape of hexagonal lattice to provide a multiplicity of cells in a cylinder-shaped skin section  82 . The honeycomb structure in the shape of hexagonal lattice is more likely to be deformed as compared to honeycomb structure in the shape of triangular lattice or rectangular lattice. It is to be understood that the partition walls  81  can be modified to triangular lattice, rectangular lattice, or another polygonal lattice.  
      The thickness of the partition wall  81  of the extrusion molded body  8  in the present Example is as small as 60 μm.  
      When molding the extrusion molded body  8 , a ceramic material was first provided as the raw material  80  for molding the extrusion molded body  8 , as shown in  FIG. 1 . The ceramic material used was powder to be formed into cordielite and was mixed with water in a clay-like form.  
      This raw material  80  for molding is kneaded and moved forward by the above described screw extruder  12  to be extruded from the molding die  11 .  
      The extrusion molded body  8  is first supported, as shown in  FIG. 3 , on the lower portion of the outer circumferential surface by the reception stage  31  supplied from the reception stage supplying apparatus  4 . The extrusion molded body  8  and the reception stage  31  moves forward synchronously, and the reception stage  31  is transferred to the conveyor  32 . Then, supported by the reception stage  31  moving on the conveyor  32 , the extrusion molded body  8  moves forward at a constant speed.  
      Then, as shown in  FIG. 4 , every time the extrusion molded body  8  moves forward a predetermined distance, the above-described cutting device  39  is used to cut a unit molded body  8   a  of predetermined length. At this time, the cut unit molded body  8   a  is placed on one reception stage  31 . The conveyor  32  of the present Example is constructed such that, immediately after cutting, speed on the downstream side is increased as compared to that on the upstream side. Therefore, a gap is provided between the rear end-face  802  of the unit molded body  8   a  and the front end  805  of the uncut extrusion molded body  8 , and this gap increases as the unit molded body  8   a  moves forward.  
      And as shown in  FIG. 5 , before the unit molded body  8   a  abuts against the end-face reception stage  33 , the conveying speed on the downstream side can be lowered such that the unit molded body  8   a  abuts against the end-face reception stage  33  with substantially no shock. Thereafter, as shown in  FIG. 2 , while supported both by the end-face reception stage  33  and by the reception stage  31 , the unit molded body  8   a  is conveyed in the conveying direction B by the first conveyor  51  and the second conveyor  52  of the secondary conveying apparatus  5 .  
      Next, the operative effect of the present Example will be described.  
      In the present Example, as described above, an extrusion molding apparatus  1  is used in which the screw extruder  12  is disposed obliquely such that the inclination angle θ takes a specified value, and the reception stage  31  of the conveying apparatus  3  can move obliquely along the extrusion axis A. The extrusion molded body  8  continuously extruded from the screw extruder  12  is supported on the outer circumferential surface by the reception stage  31  and moves forward in this state. In this way, the reaction force imparted from the reception stage to the extrusion molded body  8  can be decreased as compared to the case of conventional horizontal extrusion process in which extrusion molding is performed along horizontal axis. Therefore, a deforming force imparted to the extrusion molded body  8  can be reduced and deformation can be prevented.  
      The extrusion molded body  8  is conveyed with the outer circumferential surface supported by the reception stage  31 . Therefore, when the extrusion molded body  8  that is extruded continuously is cut into unit lengths, the molded body can be maintained at least in the state supported on the outer circumferential surface so that stable cutting operation can be achieved. Thereafter, in the present Example, when the unit molded body  8   a  is conveyed in the direction different from the extrusion direction, the unit molded body  8   a  is supported both by the reception stage  31  and by the end-face reception stage  33 , so that it can be conveyed more stably.  
      In the case where an extrusion molded body  8  for collecting diesel particulates is to be obtained using the extrusion molding apparatus  1  of the present Example, although the construction of the apparatus needs not be modified, the diameter of the molding die  11  of the screw extruder  12  is preferably set to 1.15 times or more of the diameter of the extrusion molded body to be obtained.  
     EXAMPLE 2  
      In the present Example, as shown in  FIG. 6 , the construction of the conveying apparatus  3  is modified from the extrusion molding apparatus  1  in Example 1.  
      Thus, the conveying apparatus  6  of the present Example adopts belt conveyors  61 ,  62  in place of the above-described conveyor  32  consisting of roller conveyors. Each of the belt conveyors  61 ,  62  has conveying surface  611 ,  621  for placing the reception stage  31  provided generally in parallel to the extrusion axis A. Plural stoppers  612 ,  622  are provided on the conveying surfaces  611 ,  621  for supporting the reception stage  31  at the front end-face in moving direction, and are constructed such that the reception stages  31  successively supplied to the conveyor can be successively supported by the stoppers  612 ,  622 , and can be moved forward.  
      The belt conveyor  61  on the upstream side and the belt conveyor  62  on the downstream side are constructed so as to be able to change conveying speed. More specifically, the belt conveyor  61  on the upstream side is kept at a constant speed, and the belt conveyor  62  on the downstream side is constructed such that it is accelerated when the reception stage  31  loading the unit molded body after cutting is transferred, and is decelerated before the reception stage  31  loading the unit molded body thereon is transferred to the conveying equipment on the downstream side.  
      The other constructions are the same as in Example 1, and same operative effect as in Example 1 can be obtained.  
     EXAMPLE 3  
      In the present Example, as shown in  FIGS. 7 and 8 , the construction of the conveying apparatus  3  in Example 1 is altered.  
      Thus, the conveying apparatus  7  in the present Example adopts, in place of the conveyor  32  consisting of simple roller conveyors as described above, a conveyor  71  having a downender  75  interconnected at the lowest stage.  
      The downender  75  exhibits L-shape in section with a first surface  751  and the second surface  752  disposed generally perpendicular to each other, and is constructed rotatably between the position in which the conveying plane of the first surface  751  is in parallel to the extrusion axis A ( FIG. 7 ) and the position in which the second surface  752  is horizontal ( FIG. 8 ).  
      In the present Example, a secondary conveying apparatus  76  having conveying direction C in horizontal direction is connected downstream of the downender  75 . In the state in which the second surface  752  of the downender  75  is horizontal, the conveying plane is coplanar with the conveying plane of the secondary conveying apparatus  76 .  
      The other constructions are the same as in Example 1.  
      In the present Example, the end-face reception stage  33  having the cut unit molded body abutted at the front surface is supported by a reception stage transfer apparatus  335  and is led to the first surface  751  of the down ender  75 . Immediately after the end-face reception stage  33  abuts against the second surface  752 , the down ender  75  rotates so as to bring the second surface  752  into horizontal state, whereby the second surface  752  is interconnected with the secondary conveying apparatus  76 . In this state, by moving the end-face reception stage  33  forward, the unit molded body  8   a  leaves the reception stage  31  and, supported by the end-face reception stage  33  in only the axial direction, is conveyed. On the other hand, the reception stage  31  is removed from the downender  75  by an unshown reception stage conveying apparatus.  
      Thus, in the present Example, the unit molded body  8   a  after cutting can be conveyed with its axis directed vertically and supported only on the lower end-face. Therefore, the unit molded body  8   a  can be conveyed more stably, and the effect on the prevention of deformation of the unit molded body  8   a  can be further increased. Otherwise, same operative effect can be obtained as in Example 1.  
      The extrusion molding apparatus  1  in Example 1 to 3 has a portion for supplying the molding raw material  80  in clay-like state on the upstream side of the screw extruder  12 . This portion will be described below with reference to  FIG. 9 .  
      As shown in  FIG. 9 , the upstream side of the screw extruder  12  comprises a molding raw material loading section  13 , a coarse kneader  14 , a fine kneader  15  in this order from upstream side. In the above construction, powder mixture consisting of ceramic material powder containing specified amount of water mixed with organic compound such as a binder, a lubricant, etc., is loaded into a loading port  131  of the molding raw material loading section, and the powder mixture is continuously kneaded in the course of passage through the coarse kneader  14  and the fine kneader  15  and is converted to clay-like state.  
      Then, the air incorporated into the clay-like raw material during the kneading is degassed in a vacuum degassing chamber  16  provided in the rear portion of the fine kneader  15 , and the clay is fed into the screw extruder  12  in a completely degassed and packed state.  
      Kneading is performed in two stage of coarse kneading and fine kneading in the present Example. Depending upon the properties of the raw material, single stage kneading or multiple stage kneading may be used.  
      Although the kneaders are arranged horizontally in the present Example, they may be arranged vertically.  
      A plural vacuum degassing chambers may be provided, one after each kneader.  
     COMPARATIVE EXAMPLE 1  
      In the present Comparative example, extrusion molding is performed using an extrusion molding apparatus  9  comprising a screw extruder  912  with extrusion axis D in horizontal direction and a conveying apparatus  93 , as comparative example compared to Example 1.  
      Here, an observation was made as to whether or not the deformation took place during conveyance of the extrusion molded body molded in Example 1 and the extrusion molded body molded in Comparative example 1.  
       FIG. 11  is a sectional view showing the sectional shape of the partition wall  81  of the extrusion molded body molded in Example 1.  FIG. 12  is a sectional view showing the sectional shape of the partition wall  81  of the extrusion molded body molded in Comparative example 1.  
      As can be seen from these Figures, it is difficult, at least in the case of ultra-thin walled honeycomb structure with thickness of the partition wall  81  of 125 μm, to mold by the horizontal extrusion molding method in which extrusion direction is horizontal (Comparative example 1) without giving rise to deformation during conveyance. This deformation can be prevented by tilting the extrusion axis A at an inclination angle relative to horizontal axis as described above (Example 1).