Metal founding – Means to shape metallic material – Pressure shaping means
Reexamination Certificate
2001-02-07
2003-05-06
Dunn, Tom (Department: 1725)
Metal founding
Means to shape metallic material
Pressure shaping means
C164S341000, C164S338100, C373S156000, C219S521000
Reexamination Certificate
active
06557620
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to an attachment apparatus for a heater for attaching the heater, which is configured in an almost circular shape in its side view and cut at a circumferential portion thereof to form opposite circumferential end portions, to the external peripheral portion of a heated member of a cylindrical or column shape. In particular, the invention relates to an attachment apparatus for a heater suitable to be provided at the external peripheral portion of a heat cylinder of an injection molding machine for metal.
2. Related Art
Metal molded items made of magnesium alloy, aluminum alloy etc., for example, are also formed by the injection molding. The injection molding machine for metal used for such injection molding is configured, as is well known, by a heat cylinder, a screw provided within an inner hole of the heat cylinder so as to be able to be driven in the axial direction and the rotational direction, and a screw driving device for driving the screw etc. An injection nozzle is provided at the front portion of the heat cylinder. Each of the heat cylinder and the injection nozzle is provided at its outer peripheral portion with a plurality of electric heaters, that is, heaters which are adapted to control the temperature independently. Thus, at the time of measuring an amount, as is well known, the metal material supplied to the heat cylinder is melted by the heat mainly supplied from the heater, then accumulated at the front portion of the heat cylinder and subject to the amount measurement.
As shown in (a) of
FIG. 2
, such a heater
30
is configured in an almost circular shape in its side view by a heat portion
33
formed by the combination of an insulator
31
made of ceramic, mica etc. and a nichrome wire
32
, and a heater outer cover
34
for protecting the heat portion
33
. The heater is cut at a portion to have abutment portions
35
,
35
′. As also shown in (b) of
FIG. 2
, the attachment apparatus for the heater
30
is formed by a pair of attachment metal members
36
,
36
′, a pair of rod-shaped members
37
,
37
′ and a bolt
38
etc. The pair of attachment metal members
36
,
36
′ are bent in ring shapes and fixed in the vicinity of the abutment portions
35
,
35
′ of the heater
30
by the welding, respectively. The rod-shaped member
37
′ is provided with a through hole through which the shaft portion of the bolt
38
is passed and the other rod-shaped member
37
is provided with female screw or internal threads to be engaged with the bolt
38
. The heater
30
is attached to the external peripheral portion of a heated member of a cylindrical or column shape, for example, a heat cylinder
40
in the following manner by using the aforesaid attachment metal members
36
,
36
′. That is, the heater
30
is attached to the external peripheral portion of the heat cylinder
40
, and then the pair of the rod-shaped members
37
,
37
′ are inserted into the ring-shaped bent portions of the attachment metal members
36
,
36
′, respectively. Then, the shaft portion of the bolt
38
is inserted into the through hole of the other rod-shaped member
37
′ and the bolt
38
is screwed into the threads of the one rod-shaped member
37
. Thus, the abutment portions
35
,
35
′ are attracted to each other and so the heater
30
is adhesively attached to the external peripheral portion of the heat cylinder
40
.
Although not shown in the drawings, the heater is also attached to the heat cylinder by using a marketed commodity called as a catch clip or a snap fastener in place of the aforesaid attachment apparatus.
Although the heater
30
can be attached to the heat cylinder
40
by using each of the aforesaid attachment apparatus and the marketed commodity called as the catch clip or the snap fastener, there arises many problems. For example, there may arise a case that the heater
30
can not be removed in order to replace it for a new one. That is, in the case of heating the heat cylinder
40
of the injection molding machine for metal to 550° C. by using the heater
30
which normal usage temperature is set at 550° C., the temperature of the heater
30
itself may not be limited to 550° C. and the temperature of the heater outer cover
34
may increase to a temperature higher about 200 to 400° C. than 550° C. which is the heating temperature of the heat cylinder
40
. In particular, when the heater outer cover
34
is heated in a state that heat reserving material is wound around the outside of the heater outer cover in order to prevent the heat radiation, the temperature of the heater outer cover
34
further increases. Thus, it is experienced in the heat cylinder of the injection molding machine for metal that since the bolt is heated to such a high temperature, the bolt
38
is burnt, whereby the heater
30
can not be removed for replacing it for a new one unless the attachment apparatus of the heater
30
is broken. Although it is considered that such a burning phenomenon can be prevented when burning prevention material such as high-temperature heat-resistant grease etc. is coated on the bolt
38
, it is experienced that the burning prevention material does not attain any effect in the heat cylinder of the injection molding machine for metal. Further, the grease itself may be burnt and hardened depending on an amount of the grease coated to thereby obstruct the removal of the bolt
38
.
Furthermore, since the degree of adhesion of the heat portion
33
of the heater
30
to the heat cylinder
40
reduces, there arises various problems. That is, the heater outer cover
34
is generally formed by stainless steel and the heater outer cover
34
is pulled by the bolt
38
of the attachment apparatus, so that the heat portion
33
is adhered to the heat cylinder
40
. Such a pulling force can be adjusted depending on the fastening force of the bolt
38
. As for the heat cylinder
40
of the injection molding machine for metal, the bolt is fastened so that a high tension of about 70 to 100N is applied to the heater outer cover. When the heater
33
is made conductive in a state where such a high tension acts on the heater outer cover, the heater outer cover
34
increases in its temperature and expands earlier than the heat cylinder since the heat capacity of the heater outer cover
34
is smaller than that of the heat cylinder
40
. Although the heat cylinder
40
also increases in its temperature with the lapse of the time, since the heat cylinder
40
is larger in its volume than the heater outer cover
34
, the heat cylinder is larger in its amount of the expansion than the heater outer cover and hence the heater outer cover
34
further expands. In other words, the heater outer cover
34
expands due to the creep phenomenon caused by the time difference of the thermal expansion between the heat cylinder and the heater outer cover, so that the setting fastening force can not be maintained. As a result, the heat portion reduces in its degree of the adhesion to the heat cylinder and there appears gaps partially between the heat cylinder and the heater outer cover. When the degree of the adhesion reduces in this manner, the heat transmission coefficient between the heat cylinder and the heat portion reduces. Further, when there appears gaps partially between the heat cylinder and the heat portion, the heat transmission efficiency therebetween varies or becomes uneven partially, which results in the cause of the “bending phenomenon” of the heat cylinder
40
and adversely affects the heat cylinder
40
due to the thermal stress. Furthermore, an amount of heat transmitted from the heat portion
33
to the heat cylinder
40
reduces due to the gaps, whereby the temperature of the heat portion
33
increases partially to an excessive value. Thus, the life time of the nichrome wire
32
becomes shorter since the oxidization of the nichrome wire
32
proceeds. Further, the nichrome wire
32
melts due to the excessive temperature, which re
Dunn Tom
Lin I.-H.
Sughrue & Mion, PLLC
The Japan Steel Works Ltd.
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