JPH04103327A - Mold for extrusion - Google Patents

Abstract

PURPOSE:To prevent a spider mark from being formed on a molded item while the advantages of a spider die is provided by extending a supporter integral with an outer die to the downstream side in a direction of extrusion, providing supporting shaft extending from the lower part of said supporter along the axis thereof toward the upstream side and fixing an inner die to the upstream side end of said supporting shaft. CONSTITUTION:By fixing an inner die 20(main inner die 23 of the die 20) to the upstream side end of a supporting shaft 40, the inner die 20 is disposed within an outer die 10. If an extruder is connected to the upstream side ends(left end) of the dies 10, 20 to deliver molten rubber Aa containing cut fiber therefrom, a molded item Ab formed into a cylindrical shape is extruded to the downstream side through the gap between both dies 10, 20. Since no spider is provided between the dies 10, 20 no spider mark is formed on the item Ab, which is preferable in consideration of the fact that spider marks, in general, is greatly produced when cut fibers are contained. Since the molten rubber Aa flows axially symmetrically along a straight line, uniformity in circumferential quality is excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an extrusion mold for obtaining a pipe-shaped molded product from a material such as rubber or plastic.

[Prior art] Extrusion molding is a molding method in which molten material (rubber or plastic) is kneaded and discharged from an extruder into a mold, the material is given a desired shape in the mold, and then cooled and cut. be. To obtain a pipe-shaped product by extrusion molding, a mold is used that combines an outer die and an inner die concentrically (on the same axis) to create a ring-shaped gap (in a cross section perpendicular to the axis). be done. Typical examples of such molds include spider dies and cross-hatching dies, which are made by leaving a gap in the outer die (or equivalent tube or ring) and inserting the inner die ( or the equivalent mandrel or shaft).
There is a difference in the following points.

b) Spider die: As shown in Figure 2, the inner die 20' is held on the outer die 10'' by spiders (spokes) 61 provided at several locations at intervals in the circumferential direction. The die 20' is formed by integrating a mandrel 21', a center shaft 22', and a main inner die 23', of which the outer side of the mandrel 21' is held by the outer die 10' via a spider 61. The molten material Aa passes between these several spiders 61.

Mouth) Lad die to cross: As shown in Figure 3, melt material A
The inner die 20' is fixed to the outer die 10' at a position closer to the base than the part through which Aa passes, and there is no gap in the fixed part through which the material Aa passes. In the figure, the extruder (
The material Aa discharged from the main inner die 23' on the downstream side does not pass through the fixed part of the center shaft 22' to the outer die 10'.

An example of a special mold is disclosed in Japanese Unexamined Patent Publication No. 48-73463. The multilayer circular die disclosed in the same publication makes it possible to adjust the concentricity of each die by combining the inner and outer dies (cores) so that they can swing around a spherical part provided in the center, and eliminates the spider described above. However, from the viewpoint of the holding position of each die and the inflow route of the material, it can be seen as a type of rad die to the above-mentioned cross.

[Problem to be solved by the invention] The conventional molds described above have the following problems.

B) Spider die When the molten material passes through one part of the spider, it is divided there, so spider marks (stripes that are clearly visible in appearance and have a different thickness and material than other parts) that are equal to the number of spokes are likely to occur on the molded product. . However, other than that, since the molten material always flows uniformly in the circumferential direction from the extruder along the same axis, it is possible to obtain a molded product with excellent uniformity in thickness and various physical properties.

Cross radial die: No spider mark is produced, but a weld line (at the joining part of the flowing end of the material,
After all, some parts are slightly inferior in appearance and strength). Furthermore, since the flow of the material is not uniform in the circumferential direction, it is difficult to expect uniformity in the quality of the molded product.

Furthermore, the mold disclosed in the above-mentioned publication has the same problems as the cross-to-rad die, and is also disadvantageous in that it has a complicated structure and the manufacturing cost of the spherical portion is high.

An object of the present invention is to provide an extrusion mold that has the advantages of a spider die but does not produce spider marks on molded products.

[Means for Solving the Problems] The extrusion mold of the present invention extends a support (for example, a support frame or a tie rod) that is integrated with the outer die toward the downstream side in the extrusion direction, and extends the above-mentioned support from the downstream portion of the support. A support shaft (a shaft or a shaft for supporting the inner die) is provided upstream along the axis, and the inner die is attached to the upstream end of the support shaft. Since the support is integrated with the outer die, it is placed outside the path through which the molded product is extruded, and one support shaft is provided along the axis of the die to attach the inner die, that is, the pipe-shaped molded product. It is installed inside (hollow part).

Further, as in claim 2, a gas path may be formed inside the support shaft to connect the downstream portion and the outer peripheral portion thereof.

[Function] In the mold of the present invention, the inner die is connected to the outer die through a support shaft formed meticulously on the downstream side and a support tool formed outside the spindle and also on the downstream side. combined. That is, the inner die is held by the outer die via a supporting shaft and a support that extend downstream, instead of via a spider like the spider die. therefore,
Since the molten material is not divided by spiders, etc., no spider marks occur on the molded product.

In addition, in the mold of this invention, the gap between the inner and outer dies is not closed at the upstream end even though the inner and outer dies are connected.
There is no need to change the flow direction of the molten material as in the rad die. Since the molten material thereby forms a symmetrical flow around one axis, a molded product with no weld lines and excellent uniformity in thickness, physical and chemical properties, etc. can be obtained.

In addition, in this mold, the support provided outside the molded product and the support shaft located inside the molded product are connected at the downstream part, so the pipe-shaped molding extends beyond the connection point. It is not possible to push out the product continuously. However, it is difficult to obtain a molded product (cut to each length) that does not exceed the distance from the exit of the inner and outer dies to this connection point, or to cut the molded product in the axial direction to reach the connection point. It is possible to obtain sheet-like products continuously.

In the mold according to claim 2, if a gas such as air (at room temperature) is sent from the downstream portion of the support shaft to the outer peripheral portion through the gas path (that is, toward the inner surface of the vibrator-shaped molded product), the molding is performed by the pressure. It is possible to prevent shrinkage of the product and to cool the molded product using the temperature difference. In this way, the half-molten molded product that has just come out of the inner and outer dies is quickly cooled down without losing its shape, making it easier to perform the cutting and slitting process described above.

[Example] FIG. 1 shows an example of the present invention. The illustrated mold is used to extrude a rubber pipe with a diameter of several hundred millimeters by connecting an extruder (not shown) to the left end portion of the figure. The rubber material is a composite material reinforced with short fibers.

This mold is attached with a raccoon cutter 50 that cuts the molded pipe in the axial direction at one point on the circumferential surface to form a sheet. The reason why a pipe is first formed to obtain a sort product is that it is desirable that the material is uniform across the width direction (circumferential direction before cutting), including the orientation of short fibers. When directly molding a sheet, deviations in material tend to occur between the width edges and the center.

Since a pipe is to be formed, the illustrated mold has an inner die 20 coaxially located inside an outer die 10 with an annular gap therebetween. Needless to say, molten rubber A passes through this gap.
a is formed into a pipe.

In this mold, the outer die 0 is a combination of a holding cylinder 11 and a main outer die 12, and the inner die 20 is a combination of a mandrel 21, a center shaft 22, and a main inner die 23.

In order to hold the inner die 20 at a predetermined position with a gap with respect to the outer die 10, this mold is designed as follows. That is, a) the support 30 extending downstream in the extrusion direction (right side in the figure; hereinafter, upstream and downstream refer to those along the extrusion direction) was assembled so as to be integrated with the outer die 10. Support tool 30
is a flange 31 sandwiched and fixed between the holding cylinder of the outer die 10 and the main outer die 12, a plurality of (two in this example) tie rods 32 extending downstream from the flange 31, and the tie rods 32. It consists of a flange 33 attached to the downstream end of the.

b) A flange 33 provided at the downstream end of the support 30
A support shaft 40 was fixed at the center of the shaft facing upstream. The support shaft 40 is arranged between the tie rods 32 so that its axial center overlaps the outer die 10 and the like (an extension line). In addition, two small holes (gas paths) 41a and 41b are formed inside the support shaft 40 by connecting its outer peripheral surface and the downstream end, and these holes are connected to the flange 33 at the downstream end of the support shaft 40. It was connected to small tubes 42a and 42b that penetrated through the tube. Further, on the outer circumferential surface of the support shaft 40, a packing seat 43 and a packing 44 extending all around the circumference were attached as shown in the figure at a position downstream of the openings of the gas passages 41a and 41b. However, Patsukin 44
does not require strict sealing.

C) By fixing the inner die 20 (the main inner die 23 thereof) to the upstream end of the support shaft 40, the inner die 20 was arranged inside the outer die 10 as described above. The main inner die 23 and center shaft 22 of the inner die 20 are assembled to the outer die 10 etc. from the right side of the figure together with the support shaft 40 and the flange 33, but the mandrel 21 is assembled onto the shaft 22 from the left side of the figure. Can be installed. Note that the gap t1 and t between the main outer die 12 and the main inner die 23, etc.
For the purpose of finely adjusting 2.t3, a washer 45 is inserted between the support shaft 40 and the main inner die 23 so that the thickness can be changed.

Now, for such a mold, outer die lG and inner die 20
When an extruder is connected to the upstream end (left end of the figure) of the extruder and molten rubber Aa containing short fibers is discharged from the extruder, both dies 10
・The pipe-shaped molded product Ab is pushed out downstream through the gap between 20 and 20 mm. Since there is no spider between both dies 10 and 20, there is no spider mark on this molded product Ab. This is particularly advantageous considering that spider marks are generally more pronounced when short fibers are included. Furthermore, since the molten rubber Aa flows along a straight line, so to speak, axially symmetrically, the molded product Ab has excellent uniformity of quality all around.

The molded product Ab exiting the inner and outer dies 10 and 20 is in a semi-molten state at a high temperature, and is likely to shrink if left in its natural state.
In addition, because it is easy to deform when subjected to external force, this mold blows air into the inner surface of the molded product to prevent natural shrinkage and deformation, and at the same time speed up cooling. That is, molded product Ab, inner die 20 (23),
Room-temperature air is blown into the space formed by the support shaft 40 and the packing 44 through the small tube 42a and the small hole 41a, while the air is blown into the space formed by the supporting shaft 40 and the packing 44 through the small tube 42a and the small hole 41a.
Appropriate exhaustion is performed through 2b to apply an appropriate pressure to the inner surface of the molded product Ab and to create an air flow.

The above-mentioned cutter 50 functions on the molded product Ab that has been cooled and shaped in this manner, and cuts the molded product Ab in the axial direction to form a rubber sheet Ac. The cut sheets Ac are fed out as shown in the figure (imaginary lines) without being obstructed by the tie rods 32 or the flanges 33, and are continuously produced.

[Effects of the Invention] According to the extrusion mold of the present invention, the quality of the molded product is particularly excellent in uniformity, and spider marks do not occur on the molded product. That is, the advantages of the conventional spider die are not lost, and the disadvantages thereof are improved.

It is also preferable that there are no special components that require high costs.

In particular, in the case of the extrusion mold of claim 2, the molded product can be quickly cooled while adjusting the shape and dimensions.

Further, therefore, the next process such as cutting can be carried out immediately on the molded product.

[Brief explanation of the drawing]

FIG. 1 is an axial cross-sectional view of an extrusion mold that is an embodiment of the present invention. On the other hand, FIGS. 2 and 3 are similar cross-sectional views showing conventional extrusion molds, respectively. 10...outer die, 20...inner die, 30 river support,
4o... Support shaft, 41a/41b... Small hole (gas path)
.

Claims (1)

[Scope of Claims] 1. An extrusion mold comprising an outer die and an inner die inside thereof on the same axis in order to obtain a pipe-shaped molded product, the die comprising a support integrated with the outer die. It is characterized by extending downstream in the extrusion direction, providing a support shaft from the downstream part of the support tool upstream along the axis, and attaching the inner die to the upstream end of the support shaft. Extrusion mold. 2. The extrusion mold according to claim 1, wherein a gas path is formed inside the support shaft to connect the downstream portion and the outer peripheral portion thereof.