This invention relates to hot tip bushing means for a synthetic resin injection molding machine.
It is known that the hot tip bushing of this sort is used by inserting it in a mold sprue of the injection molding machine. And, fused resin from a runner is injected into a cavity or the resin cooled and solidified in a gate is heated and melted intermittently, subsequently injected intermittently into the cavity.
FIGS. 1 to 4 show respective views of the conventional hot tip bushing means, in which FIG. 1 is a side view thereof, FIG. 2 is a section view taken on line II--II of FIG. 1, FIG. 3 is a rear view of FIG. 2 and FIG. 4 is an expanded section view of the conventional hot tip bushing means which is disposed in a mold.
In 1982 the present Applicant filed a Japanese patent application No. 57-69184 relating to this conventional hot tip bushing means.
An example of the conventional hot tip bushing means will now be described with reference to FIGS. 1 and 4.
Symbol Bo denotes a hot tip bushing comprising a conical tip 1, a cylindrical body 2 in the middle and a disc type flange 3 in the rear.
Numeral 4 denotes a concave flow path formed axially along the conical tip 1 and the cylindrical body 2. The number of the concave passage 4 is optional, but in this example two concave flow paths 4, 4 are communicated with two paths 5, 5 which are united into one passage 15 at an opening 5a of the disc type flange 3.
The hot tip bushing Bo is made of a heat insulating metal, e.g. a stainless steel or the like. In addition, an external surface thereof is insulated thermally with an oxide layer treatment.
In the interior of the hot tip bushing Bo are disposed a heater 6 for heating locally a pointed end 1a of the conical tip 1 and a second heater 7 for heating a cylindrical body 2.
The heater 6 is communicated with a lead wire 6a, while the second heater 7 is done with a lead wire 7a. The two lead wires 6a, 7a are connected to a power source (not illustrated) from a side hole 8 of the disc type flange 3. Each of the heaters 6, 7 is earthed by connecting to the bushing Bo.
Under the aforesaid structure, as shown in FIG. 4 the hot tip bushing Bo is inserted into a sprue So of a mold M by way of a runner bush 9. Thus, both the hot tip bushing Bo and a manifold 14 are sealed together by a plurality of O-rings 13 by communicating the fused resin flow passage 15 of the manifold 14 with the opening 5a of the disc type flange 3.
Accordingly, there is formed an outer flow path 11 between the sprue So and the hot tip bushing Bo, wherein the disc type flange 3 is fit to the sprue So and contacted with the runner bush 9 on a side wall 10 of the flange 3. Thus, the pointed end 1a of the conical tip 1 is positioned so as to oppose to a gate 17 of a cavity 16.
In the case the fused resin is injected into the mold by way of a nozzle of the injection molding machine, it flows in the two paths 5, 5 by way of the resin flow passage 15 and flows unitedly at the gate 17 by way of the concave flow paths 4, 4 and the outer flow path 11.
The aforesaid conventional hot tip bushing means has the following inconveniences and disadvantages:
(1) The flow passage 15 is bifurcated and deflected at the opening 5a and divided into the two flow paths 5, 5 and the two concave paths 4, 4. In the middle stage the outer flow path 11 is of a tubular flow form. Accordingly, when feeding the fused resin under the application of pressure, a certain resistance from the wall surfaces of the flow paths is imposed upon the fused resin, so that the pressure loss becomes larger.
(2) Since the fused resin which flows in the paths 5, 5, 4, 4, and 11 is heated by the built-in heaters 6, 7 within the hot tip bushing Bo, the fused resin may be solidified and stuck to the inner surface of the sprue So. Namely, due to the inner heating system such a phenomenon is caused on the inner surface of the sprue So far from the heaters 6, 7. As a result, flow of the fused resin gets worse and the pressure loss is increased.
(3) The position of the pointed end 1a of the conical tip 1 is determined by contacting a side wall 10 of the disc type flange 3 with the runner bush 9. Namely, the disc type flange 3 is fit to the sprue So, so that the position of the hot tip bushing Bo is determined in the rear thereof. Accordingly, the conical tip 1 is susceptible to be vibrated, thereby its exact centering relative to the gate 17 gets difficult.
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