Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Temperature control
Reexamination Certificate
2002-07-01
2003-11-25
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Temperature control
C425S378100, C425S380000, C425S467000
Reexamination Certificate
active
06652257
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of, and an apparatus for, producing ceramic moldings such as ceramic honeycomb structures.
2. Description of the Related Art
A ceramic honeycomb structure
8
having a large number of cells
88
partitioned by partitions
81
, as shown in
FIG. 12
of the accompanying drawings, has been used as a catalyst support of an exhaust gas purification device of an automobile. Ceramic moldings having a ceramic honeycomb structure are generally produced through extrusion molding.
A production apparatus
9
for ceramic moldings according to the prior art includes a screw type extruder
91
and a mold
93
fitted to the distal end of the extruder
91
through a resistance pipe
92
as shown in
FIG. 13. A
ceramic material
80
, that is pressure-fed from the extruder
91
into the resistance pipe
92
with the revolution of an extrusion screw
911
, is extruded from the mold
93
as a ceramic molding having a desired shape. The extrusion screw
911
is so disposed as to continue into a de-airing chamber
912
that is evacuated to a vacuum. The ceramic material
80
fed into the deairing chamber
912
by a push-in screw
913
is supplied to the extrusion screw
911
by a pair of right and left push-in rollers
914
.
When a ceramic molding has a complicated shape such as a honeycomb structure, the resulting shape is greatly affected by variance of the slit hole shape of the mold
93
, variance of the viscosity (variance of temperature) of the ceramic material
80
, and so forth. The viscosity of the ceramic material
80
, in particular, changes depending on season, time zone, etc, invites variance of the flow rate of the material, and exerts great influences on the shape of the ceramic molding.
To cope with such problems, Japanese Unexamined Patent Publication (Kokai) No. 9-277234 (prior art technology 1), for example, proposes to furnish a guide ring, that constitutes a mold, with a temperature controller for regulating the temperature of the ceramic material immediately before molding. This temperature controller can finely regulate a molding rate of the portion that serves as an outer skin of the honeycomb structure, and is believed to be capable of preventing molding defects.
Japanese Unexamined Patent Publication (Koukai) No. 53-21209 proposes to set the outer peripheral temperature of the ceramic material to a temperature by at least 10° C. higher than its center temperature between the extrusion screw and the mold (prior art technology 2). This technology is believed capable of molding continuously an excellent ceramic honeycomb structure.
Regarding the honeycomb structure, however, a demand has been increasing in recent years for reducing the thickness of partitions so as to improve its cell density. To reduce the thickness of the partitions, the extrusion resistance of the mold
93
becomes much greater than in the conventional apparatuses. The increase of the extrusion resistance makes the influences of variance of the viscosity of the ceramic material, and so forth, on the molding shape greater than ever.
Therefore, even if variance of the viscosity (temperature) of the ceramic material has not been the problem in the molding operation of the honeycomb structure having a conventional size, this variance exerts great influence on the molding shape when a honeycomb structure having a reduced thickness is produced. Consequently, it is difficult in this case to produce a honeycomb structure having an excellent shape at a high production yield.
When those ceramic moldings which are difficult to mold, such as a honeycomb body having a reduced thickness, are molded, even the methods of the prior art technologies 1 and 2 cannot smoothly produce the ceramic moldings having an excellent shape because their shape correcting effect is too small.
An explanation will be given more concretely. In the method of the prior art technology 1, the portion for regulating the temperature of the ceramic material is only the guide ring portion of the mold. Therefore, this method can regulate the temperature of only a limited outermost surface portion. If the shape defect of the molding is very serious, the method cannot easily correct the shape.
In the method of the prior art technology 2, the temperature control is limited to a certain specific condition, and only heating is available. It is therefore extremely difficult by this method to correct the shape of moldings in such a fashion as to follow accurately slight changes of the temperature, the moisture content, the grain size, etc, of the ceramic material.
SUMMARY OF THE INVENTION
In view of these problems of the prior art, it is therefore an object of the present invention to provide a method of, and an apparatus for, producing ceramic moldings that can smoothly execute a molding operation even for those moldings, the molding of which is believed to be difficult, while suppressing molding defects.
In a method of producing a ceramic molding having a desired shape by using a production apparatus including a screw type extruder and a mold connected to the distal end of the extruder through a resistance pipe, and by extruding a ceramic material, that is pressure-fed from the extruder into the resistance pipe, from the mold, the present invention provides a method of producing a ceramic molding characterized in that the ceramic material pressure-fed from the extruder into the resistance pipe is heated or cooled from round the periphery of the resistance pipe in order to control the shape of the ceramic molding extruded from the mold.
In other words, the ceramic material positioned inside the resistance pipe is positively heated or cooled in order to improve the shape of the ceramic molding.
Various means can employed as the heating or cooling means, such as means for circulating a heat medium round the resistance pipe, means for disposing a heating device such a heater round the resistance pipe, means for disposing a cooling device such as a cooler round the periphery of the resistance pipe, and so forth. The heating or cooling means can be controlled either manually or automatically in accordance with the shape of the ceramic molding.
The ceramic molding may be a honeycomb structure having a large number of cells. The ceramic honeycomb structure is relatively difficult to form. However, when the excellent molding method described above is employed, smooth molding can be easily carried out while suppressing molding detects. Particularly when the honeycomb structure has a cell density of 300 to 1,500 cells/inch
2
or a cell partition thickness of 0.035 to 0.125 mm, or when the cell density is 300 to 1,500 cells/inch
2
and the cell partition thickness is 0.035 to 0.125 mm, the function and effect of the production method described above becomes remarkable. The cell shape may be various shapes such as square, triangular, hexagonal, and so forth.
In the present invention, heating or cooling of the ceramic material is preferably carried out by circulating a heat medium, that is heated or cooled, round the resistance pipe, and by changing at least one of the circulation flow rate of the heat medium and its temperature. In this case, heating or cooling can be controlled easily.
In the present invention, the heat medium is preferably caused to circulate along a spiral flow passage round the resistance pipe. In this case, heat transfer can be achieved efficiently from the heat medium to the ceramic material inside the resistance pipe.
In the present invention, the heat medium is preferably circulated from the side of the mold towards the extruder on the periphery of the resistance pipe. When the heat medium is circulated spirally, for example, the heat medium is gradually moved from the mold side towards the extruder side while being wound round the resistance pipe. In this way, the temperature control of the ceramic material can be conducted more uniformly.
It is further preferred in the present invention to measure the temperature of the ceramic mold, that is extruded fr
Katou Hiromi
Matsui Nobutoshi
Yamaguchi Satoru
Denso Corporation
Leyson Joseph
Mackey James P.
Nixon & Vanderhye PC
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