Extrusion-molding machine and extrusion-molding method

Abstract

An extrusion-molding machine includes a screw, a die and a high-hardness coat layer. The screw has a blade portion to extrude a molding material. The screw is disposed in a tightly-closed space which is maintained in a reduced-pressure atmosphere. The die molds an extruded molding material. The high-hardness coat layer is provided at least on the blade portion.

1 . An extrusion-molding machine comprising:
 a screw having a blade portion to extrude a molding material, the screw being disposed in a tightly-closed space which is maintained in a reduced-pressure atmosphere;   a die to mold an extruded molding material; and   a high-hardness coat layer provided at least on the blade portion.   
     
     
         2 . The extrusion-molding machine according to  claim 1 ,
 wherein   a main component of said high-hardness coat layer comprises tungsten carbide.   
     
     
         3 . The extrusion-molding machine according to  claim 1 ,
 wherein   said high-hardness coat layer has a surface roughness Ra of about 10 μm or less.   
     
     
         4 . The extrusion-molding machine according to  claim 1 ,
 wherein   said high-hardness coat layer has a porosity of about 0.3% or less.   
     
     
         5 . The extrusion-molding machine according to  claim 1 ,
 wherein   a maximum dimension of recess portions on a surface of said high-hardness coat layer is at least about 1 μm and at most about 50 μm.   
     
     
         6 . The extrusion-molding machine according to  claim 2 ,
 wherein   nickel is used as a binder to provide said high-hardness coat layer.   
     
     
         7 . The extrusion-molding machine according to  claim 1 ,
 wherein   said high-hardness coat layer has a thickness of at least about 300 μm and at most about 1200 μm.   
     
     
         8 . The extrusion-molding machine according to  claim 1 ,
 wherein   said high-hardness coat layer has a Vickers hardness of about 2000 HV or more.   
     
     
         9 . The extrusion-molding machine according to  claim 1 ,
 wherein   said space has an inner pressure that is lower than an atmospheric pressure by at least about 50 kPa and at most about 100 kPa.   
     
     
         10 . The extrusion-molding machine according to  claim 1 ,
 comprising:   a plurality of the screws; and   a same number of the dies as said screws,   wherein   after the molding material is extruded by one of the screws through one of the dies, the resulting molding material is again extruded by another screw through another die.   
     
     
         11 . The extrusion-molding machine according to  claim 10 ,
 further comprising:   a cutting member used for cutting the molding material extruded by said one of the screws through said one of the dies.   
     
     
         12 . The extrusion-molding machine according to  claim 10 ,
 further comprising   two to four screw mixers each provided with said screw and said die.   
     
     
         13 . An extrusion-molding method comprising:
 mixing a wet mixture containing inorganic powder serving as a molding material;   continuously extruding said wet mixture through a die of an extrusion-molding machine including a screw having a blade portion to extrude the molding material, the die being placed at an outlet of a tightly-closed space in which screw is disposed;   maintaining a reduced-pressure atmosphere in said space; and   providing a high-hardness coat layer at least on said blade portion.   
     
     
         14 . The extrusion-molding method according to  claim 13 ,
 wherein   a main component of said high-hardness coat layer comprises tungsten carbide.   
     
     
         15 . The extrusion-molding method according to  claim 13 ,
 wherein   said high-hardness coat layer has a surface roughness Ra of about 10 μm or less.   
     
     
         16 . The extrusion-molding method according to  claim 13 ,
 wherein   said high-hardness coat layer has a porosity of about 0.3% or less.   
     
     
         17 . The extrusion-molding method according to  claim 13 ,
 wherein   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.   
     
     
         18 . The extrusion-molding method according to  claim 14 ,
 wherein   nickel is used as a binder to provide said high-hardness coat layer.   
     
     
         19 . The extrusion-molding method according to  claim 13 ,
 wherein   said high-hardness coat layer has a thickness of at least about 300 μm and at most about 1200 μm.   
     
     
         20 . The extrusion-molding method according to  claim 13 ,
 wherein   said high-hardness coat layer has a Vickers hardness of about 2000 HV or more.   
     
     
         21 . The extrusion-molding method according to  claim 13 ,
 wherein   said space has an inner pressure that is lower than an atmospheric pressure by at least about 50 kPa and at most about 100 kPa.   
     
     
         22 . The extrusion-molding method according to  claim 13 ,
 wherein   said wet mixture has a moisture content of at least about 10% by weight and at most about 20% by weight.   
     
     
         23 . The extrusion-molding method according to  claim 13 ,
 wherein   a period of time from charging of said wet mixture into said extrusion-molding machine till extrusion of the wet mixture is at least about 50 minutes and at most about 90 minutes.   
     
     
         24 . The extrusion-molding method according to  claim 13 , wherein
 said extrusion-molding machine includes a plurality of the screws and a 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.   
     
     
         25 . The extrusion-molding method according to  claim 24 ,
 wherein   said extrusion-molding machine further includes a cutting member used for cutting the molding material extruded by said one of the screws through said one of the dies.   
     
     
         26 . The extrusion-molding method according to  claim 24 ,
 wherein   said extrusion-molding machine further includes two to four screw mixers each provided with said screw and said die.