This invention relates to a method of extruding a ceramic material suitable for extrusion-forming of ceramic bodies, particularly ceramic honeycomb structures and an apparatus for use in the method.
In the past, in order to form ceramic bodies by extrusion-forming, a ceramic material is formed by means of a vacuum auger machine into circular cylinders or columnar bodies which are then supplied to an extrusion-forming apparatus such as a plunger molding machine to obtain ceramic bodies formed in predetermined shapes. The vacuum auger machine comprises a vacuum kneading section for kneading the ceramic material to obtain ceramic batches for forming ceramic bodies, a columnar body forming section for forming columnar bodies and a batch transferring section which transfers the ceramic batches obtained in the vacuum kneading section to the columnar body forming section by means of augers.
In such a hitherto used extrusion-forming method, ceramic batches obtained from the vacuum auger machine are directly extruded and formed by the extrusion-forming apparatus into desired shapes. In other words, even if laminations occur in the ceramic batches in being transferred by augers, the ceramic batches including the laminations are extruded to be formed without being rejected. As a result, when formed columnar bodies of the ceramic batches including such laminations are directly extruded by the plunger molding machine to obtain formed bodies in desired shapes, local deformations as defects would occur in the bodies after forming by the plunger molding machine or after firing the formed bodies. These defects are particularly acute in forming ceramic honeycomb structures whose grids are locally deformed, for example, waved in longitudinal directions of through-apertures or to form trapezoid cells deviated from, for example, square cells. As a result, when a catalyst is carried by such a honeycomb structure having the defects, through-apertures of the structure are often clogged in use.
U.S. Pat. No. 3,888,963 discloses a batch flow unifying device arranged immediately before a forming die of an extrusion-forming apparatus to eliminate unevenness in centers and outer circumferences of batches to be supplied to the forming die, in order to obtain uniformly formed bodies. However, it only serves to eliminate unevennesses in batches in a cylinder and does not solve the problem of the laminations above described.