Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Feed control of material en route to shaping area
Reexamination Certificate
1999-02-03
2001-03-27
Pyon, Harold (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Feed control of material en route to shaping area
C264S019000, C425S193000
Reexamination Certificate
active
06206671
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to, but is not restricted to, a pressure molding apparatus suitable for forming a dental crown by heating and pressurizing a ceramic raw material, such as glass-ceramics.
DESCRIPTION OF THE PRIOR ART
As is well known among people skilled in the art, a mold assembly composed of a mold body and a pressure piston is used to mold a ceramic raw material, such as glass-ceramics, into a dental crown. In the mold body, a molding cavity, a raw material charging cavity, and a sprue are formed. The raw material charging cavity is open upwards, and the sprue extends downward from the raw material charging cavity to the molding cavity. The raw material charging cavity of the mold body is charged with a raw material to be molded, i.e., a ceramic material such as glass-ceramics. Then, a lower portion of the pressure piston is inserted into the raw material charging cavity. An upper portion of the pressure piston protrudes upward from the mold body. Then, the mold assembly is accommodated into a heating space of a furnace in a pressure molding apparatus to heat the raw material to a suitable temperature. At the same time, a load is imposed on the pressure piston to pressurize the raw material. As a result, the raw material charged into the raw material charging cavity is flowed into the molding cavity through the sprue to mold it into a required form. Usually, the amount of the raw material charged is larger than the capacity of the molding cavity. Thus, the resulting dental crown is accompanied by an additional portion located in the sprue and the raw material charging cavity of the mold body. Such an additional portion is later removed from the dental crown by machining. Imposition of the load on the pressure piston is performed by a pneumatic cylinder mechanism.
The ceramic softened by heating has a relatively high viscosity of, say, about 10
4
to 10
6
poises. Such a raw material needs to be flowed, as required, against resistance due to the escape of air from the molding cavity (the mold body is usually formed of a porous material, and air in the molding cavity escapes through the mold body itself). For this purpose, it is necessary to apply a pressure of, say, about 5 kg/cm
2
to the pressure piston. To impose a load on the pressure piston fully stably, a considerably large, high performance pneumatic cylinder mechanism is needed. Hence, a molding apparatus has to be considerably bulky and expensive. The use of a relatively small, low performance pneumatic piston mechanism may often result in a stick-slip phenomenon (a phenomenon in which when the load is imposed on the pressure piston to flow the raw material, descent of the pressure piston is stopped accidentally, thereby terminating the flow of the raw material). The stick-slip phenomenon would make the raw material flow into the molding cavity insufficient and form flow mark on the molded dental crown.
SUMMARY OF THE INVENTION
A main object of the present invention is to provide a novel and improved pressure molding apparatus which does not require a large, expensive pneumatic cylinder mechanism, can thus be produced in a small size and at a low cost, and nonetheless can impose a completely stable load on a pressure piston.
Another object of the invention is to provide a novel and improved pressure molding apparatus which can bring a mold assembly to a required position fully easily, when accommodating the mold assembly into a heating space of a furnace.
The inventors of the present invention have conducted in-depth studies, and found that the main object can be attained by selectively applying the weight of weight means to a pressure piston, instead of using a pneumatic cylinder mechanism.
That is, the present invention provides, as a pressure molding apparatus for attaining the main object, a pressure molding apparatus comprising:
a furnace defining a heating space for accommodating a mold assembly including a mold body charged with a raw material to be molded, and a pressure piston for pressurizing the raw material;
heating means for heating the heating space; and
load imposing means for imposing a load on the pressure piston to mold the raw material, wherein
the load imposing means includes at least one weight means and weight supporting means, and the weight supporting means is selectively set in a load-free state in which the weight supporting means supports the weight means so that the weight of the weight means is not imposed on the pressure piston, and a load imposed state in which the weight supporting means releases the support of the weight means so that the weight of the weight means is imposed on the pressure piston.
Preferably, the load imposing means includes first weight means and second weight means, and the weight supporting means is selectively set in the load-free state in which the weight supporting means supports both the first weight means and the second weight means so that none of the weights of the first weight means and the second weight means are imposed on the pressure piston, a low load imposed state in which the weight supporting means releases the support of the first weight means so that the weight of the first weight means is imposed on the pressure piston, and a high load imposed state in which the weight supporting means releases the support of both the first weight means and the second weight means so that the weights of the first and second weight means are imposed on the pressure piston. Preferred embodiments are as follows: The furnace has a floor wall defining a lower surface of the heating space, and a ceiling wall defining an upper surface of the heating space; the mold assembly is laid on the floor wall; the pressure piston is stretched outward upwardly from the mold body; the first weight means is placed above the pressure piston and stretched through the ceiling wall; the second weight means is placed above the first weight means; the weight supporting means includes a supporting member, and hoisting and lowering means for hoisting and lowering the supporting member; when the supporting member is brought to a hoisted position, the second weight means supports the first weight means, and the supporting member supports the second weight means, and supports the first weight means via the second weight means; when the supporting member is lowered beyond a low load imposed position, the first weight means contacts the pressure piston, so that the support of the first weight means by the second weight means is released, whereby the load of the first weight means is imposed on the pressure piston; when the supporting member is further lowered beyond a high load imposed position, the second weight means contacts the first weight means, so that the support of the second weight means by the supporting member is released, whereby the load of the first weight means is imposed on the pressure piston, and the load of the second weight means is also imposed on the pressure piston via the first weight means. The second weight means includes a bracket member having an opening formed in a bottom wall; the first weight means includes a rod extending in an up-and-down direction through the opening; an engagingly stopping flange positioned above the bottom wall of the bracket member, and a contact flange positioned below the bottom wall of the bracket member are disposed on the rod; the bottom wall of the bracket member supports the engagingly stopping flange, whereby the second weight means supports the first weight means; and the bottom wall of the bracket member contacts the contact flange, whereby the load of the second weight means is imposed on the pressure piston via the first weight means. A contact member is disposed on the bracket member, and the supporting member supports the second weight means by contacting a lower surface of the contact member. In an embodiment for attaining the other object, the furnace includes a floor wall defining a lower surface of the heating space, and a furnace floor plate removably mounted on the floor wall, and position
Kobayashi Yutaka
Mogami Atsushi
Ohno Hideki
Sekino Masato
Tsuchiya Masatoshi
Luk Emmanuel
Pyon Harold
Smith , Gambrell & Russell, LLP
Tokuyama Corporation
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