JPS6337232Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Background and Purpose of the Invention] The present invention relates to an extruder for cylindrical plastic sheaths for electric wires, cables, etc.

In an extruder used for this purpose, a core nozzle, which is normally placed inside the crosshead, is coaxially arranged within the crosshead 3 with a nozzle 1 provided at the tip of the crosshead 3, as shown in Fig. 1. The plastic material is injected and extruded through an annular gap 4 formed between the outer surface of the core 2 and the inner surfaces of the crosshead and the base 1, which are spaced apart from each other.

By the way, in such an extruder, when the inner diameter of the sheath to be extruded is small, the annular gap 4 between the core metal 2 and the mouthpiece 1 is set in a large taper shape with a large angle as shown in the figure. However, as the inner diameter of the sheath increases, the angle of the gap 4 becomes smaller, and finally, as shown in FIG. 2, it becomes an extremely small tapered shape with almost no angle.

When the slope of the taper is large as shown in Figure 1, pressure is applied to the supplied plastic material and a sheath of equal thickness is extruded, but when there is almost no taper as shown in Figure 2, No pressure is applied to the plastic material that has flowed in, and in this state, local uneven thickness may occur in the extruded sheath as shown in FIG.

Such uneven thickness not only causes electrical weaknesses in the cable, but also poses problems in terms of material strength.

In order to solve this problem, it may be possible to increase the thickness of the sheath itself, but this would result in an increase in the outer diameter of the cable, which is not desirable.

In view of these conventional problems, the present invention aims to provide an extruder that can extrude even a sheath with a large inner diameter without causing local thickness unevenness.

[Summary of the idea]

In order to achieve this objective, the present invention forms annular protrusions at different positions on the tapered inner surface of the cap and the tapered outer surface of the core metal, which face each other to define an annular gap that serves as a flow path for the plastic material. The projections are arranged so as to face each other at a distance, and the gap is formed in a meandering manner so as to wave in the radial direction.

〔Example〕

FIG. 4 shows an embodiment of the extruder according to the present invention, in which the basic shapes of the mouthpiece 1 and the core metal 2 are the same as those in FIG. 2, but an annular gap 4 is defined as a flow path for the plastic material. On the tapered inner surface of the cap 1 and the tapered outer surface of the core metal 2, which face each other and are separated from each other, three annular protrusions 5 each having an arcuate cross section are provided on the cap side.
The protuberances are formed one by one from different positions on the core metal side and are spaced apart and facing each other, and the gap 4 in the tapered portion is formed in a meandering shape so as to wave in the radial direction. It is what it is.

Since the annular gap 4 has a meandering shape as described above, the annular protrusions 5, 5, etc., which are the main cause of meandering, become an obstacle to the flow of the plastic material, and sufficient pressure is applied on the inflow side of the plastic material. In addition, the flow of the plastic material is only changed in the radial direction under the same conditions around the entire circumference of the core bar 2, so no local flow disturbance occurs, and as a result, a sheath with a uniform thickness and an undisturbed shape can be extruded. can.

In order to confirm the thickness unevenness rate of the extruder of this example mentioned above, when applying a vinyl coating to a pipe with a diameter of 140 mm, the thickness unevenness rate of the coating (maximum thickness of coating - minimum thickness) / (maximum thickness + minimum thickness) ) In the conventional extruder shown in Fig. 2, it is 30 to 45%, but in this example,
15 to 20%, and it was recognized that the effect of preventing uneven thickness was sufficiently achieved.

[Effect of idea]

As explained above, according to the present invention, the intended purpose of providing an extruder that can extrude even a sheath with a large inner diameter without causing local thickness deviation is more than achieved.

In addition, in the extruder of the present invention, in order to prevent uneven thickness, there is a part that resists the flow of plastic material.
Annular protrusions are formed at different positions on the opposing surfaces of the base and the core, and are spaced apart from each other to form annular protrusions, thereby creating a meandering gap that waves in the radial direction. There is no partial discontinuity in the gap that serves as the flow path for the material, and all parts of the entire circumference receive the same flow resistance. Therefore, disturbances in the sheath shape due to partial flow disturbances are prevented, and the sheath shape becomes uneven. It is possible to manufacture a high quality sheath with meat prevention.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional explanatory diagram showing the state of taper application of the extruder core cap when the sheath inner diameter is small, Figure 2 is a cross-sectional explanatory diagram showing the taper application state when the sheath inner diameter is large, and Figure 3 is the same as the above figure. FIG. 4 is an explanatory cross-sectional view showing the uneven thickness of a sheath manufactured by an extruder, and FIG. 4 is an explanatory cross-sectional view showing an embodiment of the extruder of the present invention. 1... Cap, 2... Core metal, 3... Crosshead, 4... Annular gap serving as a flow path for plastic material, 5... Annular protrusion.

Claims (1)

[Scope of utility model registration request] In an extruder for extruding plastic sheaths for discarded electric wires, cables, etc., the plastic is extruded through an annular gap formed between a cap provided at a crosshead and a core metal, and the plastic sheath is extruded through an annular gap formed between a cap provided at a crosshead and a core metal. Annular protrusions are formed on the tapered inner surface and the tapered outer surface of the metal core at different positions and are spaced apart from each other, and these protrusions form the gap in a meandering manner so as to wave in the radial direction. A plastic sheath extrusion machine for electric wires, cables, etc.