Extrusion-molding machine, extrusion-molding method, and method for manufacturing honeycomb structured body

A method for manufacturing a honeycomb structured body comprising:

• obtaining a wet mixture containing inorganic powder by wet-mixing;
• extrusion molding the wet mixture for molding thereof to manufacture a pillar-shaped honeycomb molded body having a number of cells, each penetrating in a longitudinal direction, placed in parallel with one another with a cell wall therebetween;
• and
• firing said honeycomb molded body to manufacture a honeycomb structured body made of a honeycomb fired body,
• wherein
• said extrusion-molding is carried out using an extrusion-molding machine comprising a screw having a blade portion for extruding a molding material with a high-hardness coat layer formed at least on said blade portion, the high-hardness coat layer having a Vickers hardness of about 1000 HV or more measured based on JIS Z 2244, the screw disposed in a tightly-closed space, and a die disposed in a tip portion of said extrusion-molding machine, said tip portion of said extrusion-molding machine being a tip portion of said screw, by mixing said wet mixture that has a moisture content of at least about 10% by weight and at most about 20% by weight while maintaining said space in a reduced-pressure atmosphere that is lower than the atmospheric pressure by at least about 50 kPa and at most about 100 kPa, and at the same time continuously extruding said wet mixture through said die placed at the outlet of said space,
• silicon carbide powder is used as said inorganic powder,
• said high-hardness coat layer has a surface roughness Ra of about 10 μm or less,
• said high-hardness coat layer has a porosity of about 0.3% or less,
• a maximum dimension of recess portions on the surface of said high-hardness coat layer is at least about 1 μm and at most about 50 μm,
• said extrusion-molding machine comprises two to four screw mixers each provided with said screw and said die,
• said extrusion-molding machine comprises a plurality of the screws and the same number of the dies as said screws, and a wet mixture, which has been mixed by one of the screws and then continuously extruded through one of the dies, is again mixed by another screw and continuously extruded through another die,
• said screw mixers comprise an upper-stage screw mixer and a lower-stage screw mixer,
• an upper-stage die in which a number of through holes are formed is attached to a tip portion of said upper-stage screw mixer,
• a vacuum chamber is provided at a portion of said upper-stage die through which the wet mixture is extruded, and the inside thereof is maintained in a reduced-pressure state close to vacuum,
• said extrusion-molding machine comprises an upper-stage cutter, serving as a cutting member, which is placed inside said vacuum chamber near said upper-stage die, and
• a cutting edge of said upper-stage cutter is located inside said vacuum chamber so that said cutting edge is allowed to reciprocally move up and down near said upper-stage die so that the wet mixture that has been extruded in a stick shape or in a thick noodle shape from said upper-stage die is cut into fine lumps by said cutting member, and a number of small lumps thus cut fall into said lower-stage screw mixer located right below.