Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – Molding of thermosetting or cross-linking stock
Reexamination Certificate
1999-05-12
2001-08-28
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
Molding of thermosetting or cross-linking stock
C264S328150, C425S549000
Reexamination Certificate
active
06280175
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a rubber injection molding nozzle used mainly for injection molding of rubber products such as rubber vibration insulators for automobiles, and an injection molding machine and a molding method.
BACKGROUND OF THE INVENTION
Relatively small rubber products, such as rubber vibration insulators or the like for automobiles, are manufactured by injection molding in general. In most cases, a preplasticizing type of injection molding machine or inline screw injection molding machine is used.
A preplasticizing type of injection molding machine A, as shown in
FIG. 14
, comprises a plasticizing mechanism
70
for plasticizing a molding material, or rubber (unvulcanized rubber) and feeding it to the front portion of an injection cylinder
61
, and an injection device
60
for injecting rubber being fed into a mold
40
and pressing it, such machines being classified into the plunger preplasticizing type and the screw preplasticizing type according to how rubber is pressed in.
An injection molding machine B of the inline screw type, as shown in
FIG. 15
, which is also referred to as the reciprocating screw type, has an injection device
60
provided with a screw
62
for plasticizing and measuring a molding material, or rubber, said screw
62
also performing the function of a plunger to inject the rubber resided in the front portion of an injection cylinder
61
into a mold
40
to fill the latter therewith.
Each of these injection molding machines is provided with a rubber injection molding nozzle
51
at the front end of the injection cylinder
61
of the injection device
60
.
This nozzle
51
, as shown in
FIG. 16
, has an injection channel
55
extending, through the nozzle
51
, from the side of an attaching portion
52
at which the nozzle is attached to said injection cylinder
61
, to the front end
51
a.
The nozzle
51
also has an orifice
56
which is disposed somewhere between the inlet
53
at the attaching side
52
of said channel
55
and the outlet
54
at the front end or which is disposed at the front end. This orifice
56
serves to increase the flow velocity of the rubber by reducing the channel diameter. Thereby, the heated rubber extruded from the cylinder
61
flows through said channel
55
, having its flow velocity increased by the effect of constricting by said orifice
56
, so that it is injected at high speed from the outlet
54
at the front end into the sprue
41
of the mold
40
.
In this connection, in the industry using such rubber products produced by injection molding, particularly the automobile parts industry, cost reduction is urgent requirement and measures to meet this requirement are being investigated. As a means therefor, it could be contemplated to enhance internal heat generation of the rubber passing through the nozzle so as to increase the temperature of the rubber being injected, thus shortening the vulcanization time in the mold.
However, in the conventional nozzle
51
shown in
FIG. 13
used in injection molding of rubber vibration insulator for automobile, the cross sectional shape of said orifice
56
is a simple circle, so that although more or less heat generation is brought about by passage of the rubber through said orifice
56
, the effect of the vulcanization time reduction due to such heat generation is small.
In particular, the peripheral portion of the rubber passing through the orifice
56
receives a force of friction against the interior wall face of the orifice and the shearing stress in the rubber thereby increases; thus, the temperature of generated heat, though increased to some extent, is not very high in the innermost portion, which means that there are differences in temperature within the rubber being injected. Therefore, in order to ensure thorough vulcanization within the rubber, it is necessary to set the vulcanization time on the basis of this low temperature rubber portion, presenting a problem that the vulcanization time is correspondingly prolonged.
SUMMARY OF THE INVENTION
The present invention provides a rubber injection molding nozzle which has an injection channel extending therethrough, characterized in that at least one portion of said injection channel constitutes an orifice having a non-circular cross section, said orifice having a flattened cross sectional shape such that it is elongate in one direction and such that at least at around major axial ends, a dimension measured orthogonal to its major axis gradually decreases as either of said major axial ends is approached.
When this injection molding nozzle is used to injection-mold a rubber article, a molding material, or rubber, passes through said injection channel, it being noted that at said orifice, the surface area is greater than at a circular cross section having the same cross sectional area. Therefore, the area of contact of the rubber passing through this portion is increased, thus increasing the frictional force acting on the rubber and the shearing stress produced in the rubber. As a result, the effect of the internal heat generation of the rubber itself is enhanced, thus achieving effective temperature rise due to the internal heat generation of the entire rubber. Thereby, the vulcanization time can be shortened.
In said rubber injection molding nozzle, said orifice having a non-circular cross section may be disposed between the ends of said injection channel.
In this case, when the molding material, or rubber, passes through said orifice, shearing stresses are produced in the rubber to heat the rubber internally. In addition to this, because of this orifice having a non-circular cross section, the area of contact of the rubber increases as compared with an orifice of circular cross section having the same cross sectional area, so that the frictional force acting on the rubber is increased, thus further increasing the shearing stresses produced in the rubber. As a result, the effect of the internal heat generation of the rubber itself is further enhanced, so that the temperature rise due to the internal heat generation extends deep into the innermost portion, thus minimizing the difference in temperature within the rubber and maximizing the vulcanization time reduction effect. For example, even when the vulcanization time is set on the basis of the portion of lowest temperature so as to ensure thorough vulcanization of the entire rubber, the vulcanization time can be greatly reduced, thereby achieving the cost reduction of rubber products.
Also in the case where the orifice having a non-circular cross section constitutes the outlet end of said injection channel, the effect of the internal heat generation of the rubber itself, as in the case described above, is further enhanced, so that the temperature rise due to the internal heat generation extends deep into the innermost portion, thus greatly reducing the vulcanization time.
Further, said orifice of flattened shape may be such that the interior wall face of said orifice may form substantially an acute-angled corner at around the opposite major axial ends in the cross section. In otherwise, said orifice may have a flattened substantially elliptic cross section.
In the case of this shape, the passage of the molding material, or rubber, through said orifice results in a shearing stress being produced in the rubber, thus internally heating the rubber itself, of course, and since said orifice is of said flattened shape, for example, substantially elliptic, the peripheral length of the interior wall face is increased as compared with an orifice of circular cross section having the same cross sectional area, so that the area of contact between the rubber passing through the orifice and said interior wall face is increased and is the shearing force produced in the rubber. Further, because of the shape in which the opposed interior wall faces gradually approach each other at the opposite major axial ends, the frictional force produced in the rubber also increases, thus enhancing the effect of the internal heat generation of the rubber itsel
Kamada Tsuneo
Kogami Kanya
Saki Tomihiro
Watanabe Toshihiro
Heitbrink Tim
Jordan and Hamburg LLP
Toyo Tire & Rubber Co., Ltd.
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