JPH08309827A - Segment screw - Google Patents

Abstract

PURPOSE: To eliminate the gap between segment pieces even if a thermal expansion difference occurs at the pieces and a screw shaft. CONSTITUTION: A compression coiled spring-like elastic member 4 and a plurality of segment pieces 2a, 2b,..., 2n are sequentially assembled with the shaft part 1b of a screw shaft 1, and the member 4 is sandwiched between the flange 1a of the shaft 1 and the piece 2a of the nearest side to the root side to be held. A cap 3 is engaged with the end of the part 1b to prevent the member 4 and the pieces 2a, 2b,..., 2n from being removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is provided in the barrel of an extruder or an injection molding machine (hereinafter referred to as "extruder or the like"),
The present invention relates to a screw that melts and kneads while moving a molding material by its rotation, and particularly to a segment screw that can be divided into a plurality of constituent elements.

[0002]

2. Description of the Related Art Molding with an extruder or the like is performed by supplying a molding material such as ceramic powder mixed with a resin, a metal, or a binder into a barrel equipped with a screw and melting the molding material in the barrel. It is performed by pushing it into a die or injecting it into a die from a nozzle provided at the tip of the barrel. The screw has three functions: a function of feeding a molding material from a hopper, a function of plasticizing and melting the fed molding material, and a function of measuring a certain amount of melt so as to be extruded. Therefore, the screw has a different groove shape or the like in each of the portions that perform these functions. Furthermore, the optimum groove shape and the like differ depending on the molding method and molding material, and segment screws that can be divided into a plurality of constituent elements have been widely used for the purpose of diversifying the screw. As shown in FIG. 7, the conventional segment screw has a plurality of segment pieces 102a, 102b, ..., 102 each having a spiral groove of a predetermined shape.
n is non-rotatably incorporated into the screw shaft 101 serving as the core material. A screw hole is formed at the tip of the screw shaft 101, and the screw portion of the cap 103 is screwed into the screw hole. Each segment piece 102a, 10
, 102n are sandwiched between the flange portion 101a of the screw shaft 101 and the cap 103 by the tightening force of the cap 103, and are in close contact with each other.

[0003]

However, in the above-described conventional segment screw, a gap may be generated between the segment pieces while the molding machine is repeatedly operated and stopped. When a gap is formed between the segment pieces, the molten molding material enters from there and causes a problem of corroding the screw shaft and the end surface of the segment piece.

The gap between the segment pieces is caused by
The probable causes are as follows. When the operation of the extruder or the like is started, the segment screw is heated from the outside, so that the segment piece is heated first and thermally expanded in the axial direction. Due to the thermal expansion of the segment piece, a larger tightening force is applied to the threaded portion between the screw shaft and the cap than before the thermal expansion of the segment piece. When the entire segment screw is heated, the screw shaft also expands in the axial direction,
The tightening force of the screwed portion between the screw shaft and the cap is restored.

Although the screwing portion between the screw shaft and the cap is designed so that such a load can be absorbed within the elastic deformation, a load is repeatedly applied to the screw portion of the cap. Elongation due to plastic deformation,
Looseness of cap occurs. Therefore, when the entire segment screw is heated, conversely, the tightening force of the segment pieces is weakened, which causes a gap between the segment pieces.

When the molding material enters through the gaps between the segment pieces, the molding material is deteriorated due to stagnation, and when it is returned to the barrel again, the molding material is discolored or as a "burn" of the molded product. As a result, the quality of the molded product is deteriorated. In addition, the deteriorated molding material causes corrosion of the screw shaft, making it difficult to pull out the segment piece.

Therefore, the present invention has an object to provide a segment screw which prevents a molding material from entering by preventing a gap from being generated between the segment pieces even if a thermal expansion difference occurs between the segment piece and the screw shaft. And

[0008]

In order to achieve the above object, the segment screw of the present invention is rotatably provided in a barrel of an extruder or the like, and is incorporated in a screw shaft having a flange portion formed at a base portion thereof. Multiple segment pieces,
In a segment screw having a cap screwed to the tip end of the screw shaft in order to hold each segment piece by sandwiching it with the flange portion, the segment piece closest to the root among the segment pieces. And an elastic member that is deformable in the axial direction of the screw shaft are provided between the elastic member and the flange portion.

The elastic member may be made of a shape memory alloy.

[0010]

According to the present invention constructed as described above, the segment screw is heated by the outer cylinder portion and the heater when the operation of the extruder or the like is started, and at this time, each segment piece is heated first and thermally expanded in the axial direction. As a result, the elastic member is compressed in the axial direction. When the heating further progresses and the entire segment screw is heated, the screw shaft also thermally expands in the axial direction. When the screw shaft is thermally expanded, the elastic member compressed in the axial direction is restored to its original state, and the segment pieces are kept in close contact with each other. As a result, the molding material does not penetrate between the segment pieces.

Further, in the case where the elastic member is made of a shape memory alloy, since the elastic member is located upstream of each segment piece with respect to the flow direction of the molding material, the heating of the elastic member is performed by the heating of each segment piece. Will also be delayed. Therefore, when the segment piece is heated, the elastic member is compressed by the thermal expansion of the segment piece and plastically deforms. Then, when the entire segment screw is heated, the elastic member starts to restore and urges the segment piece toward the cap side. By utilizing this temperature difference, that is, by selecting the one whose transformation point of the shape memory alloy is directly below the forming temperature, when the segment piece is heated first, the elastic member is compressed by the thermal expansion of the segment piece. Plastically deforms. Then, when the entire segment screw is heated and the elastic member is also heated, the elastic member starts to restore and urges the segment piece toward the cap side. in this way,
When only the segment piece is heated, the elastic member is plastically deformed and the urging force of the elastic member does not act on the segment piece, so the load applied to the screwed portion between the screw shaft and the cap is reduced, and No stretching or loosening of parts occurs.

[0012]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of the segment screw of the present invention. As shown in FIG. 1, the segment screw of the present embodiment is arranged in a barrel 11 of an extruder or the like, and has a screw shaft 1 serving as a core, an elastic member 4 incorporated in the screw shaft 1 and a predetermined shape. A plurality of segment pieces 2a, 2b in which spiral grooves of
... 2n and a cap 3 screwed to the tip of the screw shaft 1.

The screw shaft 1 includes a shaft portion 1b in which the elastic member 4 and the segment pieces 2a, 2b, ... 2n are incorporated, and a flange portion 1a formed at the base of the shaft portion 1b.
Have and. The shaft portion 1b of the screw shaft 1 has a polygonal prism shape. Each segment piece 2a, 2b, ..., 2
The shape of the hole of n through which the shaft portion 1b penetrates also matches the outer peripheral shape of the shaft portion 1b, and each segment piece 2a, 2b ,.
.., 2n are installed so as not to rotate with respect to the screw shaft 1. Therefore, as the screw shaft 1 rotates, the segment pieces 2a, 2b, ..., 2n rotate together with the screw shaft 1. A screw hole is formed at the tip of the screw shaft 1. The threaded portion of the cap 3 is screwed into this threaded hole to prevent the elastic member 4 and the segment pieces 2a, 2b, ..., 2n from coming off.

As shown in FIGS. 1 and 2, the elastic member 4 is a compression coil spring member and is made of an elastic material such as metal. Further, the elastic member 4 is incorporated into the shaft portion 1b and abutted on the flange portion 1a prior to the incorporation of the segment pieces 2a, 2b, ..., 2n. When the elastic member 4 is assembled, the setting is the segment piece 2a,
2n are compressed to such an extent that a surface pressure is generated between the 2n, 2n, and 2n, and a temperature difference between the segment pieces 2a, 2b, ..., 2n and the screw shaft 1 is 150. The amount of shrinkage enough to absorb the amount of thermal expansion of about ° C is left, and the restoring force at the time of maximum compression is set to be equal to or less than the yield stress of the cap 3.

Based on the above structure, when the extruder or the like is started, the segment screw is heated from the outside, so that the segment pieces 2a, 2b, ..., 2n are heated first and thermally expanded in the axial direction. At this time, since the length of the shaft portion 1b of the screw shaft 1 does not change, thermal expansion of each segment piece 2a, 2b, ..., 2n causes each segment piece 2a to be expanded as shown in FIG. Two
2b compresses the elastic member 4 against the biasing force of the elastic member 4.

When the entire segment screw is heated, the screw shaft 1 also gradually expands in the axial direction. When the screw shaft 1 thermally expands, the shaft portion 1b of the screw shaft 1 also expands, but the elastic member 4 is restored by the amount of expansion of the shaft portion 1b,
Since the state returns to that shown in FIG. 1, as a result, each segment piece 2a, 2b, ...
Is kept urged toward. That is, the difference between the cumulative thermal expansion amount of each segment piece 2a, 2b, ..., 2n and the thermal expansion amount of the screw shaft 1 is absorbed by the elastic deformation of the elastic member 4, and each segment piece 2a, 2b,
... 2n are always in close contact with each other with a certain force or more.

Therefore, each segment piece 2a, 2b,
... No gap is generated between 2n, and the entry of the molding material into the inside of the segment screw is prevented. This allows
Screw shaft 1 and each segment piece 2a, 2b, ...
・ Corrosion of 2n gap is prevented. Further, “burn” due to the retention of the molding material in the gaps between the segment pieces 2a, 2b, ..., 2n is prevented, and the quality of the molding material becomes stable.

When the entire segment screw is heated, the elastic member 4 is restored in the axial direction as described above, and as shown in FIG. 1, a gap is generated in the elastic member 4 in the axial direction. The shaft portion 1b of the screw shaft 1 is exposed. However, the hopper 12 for supplying the molding material into the barrel 11 is located on the downstream side of the most proximal segment piece 2a of the screw shaft 1 with respect to the flow direction of the molding material due to the rotation of the segment screw. Since this is also the case with the conventional segment screw, intrusion of the molding material into the gap of the elastic member 4 hardly occurs, and there is no problem.

In the present embodiment, an example in which a compression coil spring type member as shown in FIG. 2 is used as the elastic member 4 is shown. However, for example, the bottom parts of two disc springs as shown in FIG. Each of the segment pieces 2a, 2 such as an elastic member 24 having a shape in which they are overlapped with each other, a cylindrical elastic member 34 as shown in FIG.
Any form may be used as long as it can urge b, ..., 2n toward the cap 3 side. In particular, in the elastic member 24 shown in FIG. 4 and the elastic member 34 shown in FIG. 5, both end surfaces cover the end surface of the flange portion 1a and the end surface of the segment piece 2a closest to the root, so that the shaft portion 1b. Intrusion of the molding material into the mold is reliably prevented.

The material of the elastic member 4 is not particularly limited, and a shape memory alloy can be used. When a shape memory alloy is used as the elastic member 4, the shape at high temperature is the shape when no load is applied when the shape memory alloy is not used as the elastic member 4.

The behavior when a shape memory alloy is used as the elastic member 4 will be described below. When the molding machine is operated, as described above, each segment piece 2a, 2b, ...
.... 2n is heated first, but among them, the segment pieces 2b, ..., 2 on the downstream side of the hopper 12
n is heated first, and on the upstream side, heating is delayed as it goes upstream. That is, the elastic member 4 is heated after all the segment pieces 2a, 2b, ..., 2n are heated. By utilizing this temperature difference, that is, by selecting a shape memory alloy whose transformation point is directly below the forming temperature, each segment piece 2a is heated when only the segment pieces 2a, 2b, ..., 2n are heated. Two
The elastic member 4 is compressed and plastically deformed by thermal expansion b, ..., 2n.

When the entire segment screw is heated, the screw shaft 1 and the elastic member 4 are heated, the screw shaft 1 is thermally expanded in the axial direction, and at the same time, the elastic member 4 is heated.
Is also heated and begins to restore to its original state. As a result, the difference between the cumulative thermal expansion amount of each segment piece 2a, 2b, ..., 2n and the thermal expansion amount of the screw shaft 1 is absorbed by the expansion due to the restoration of the elastic member 4, and each segment piece 2a, 2n.
Since b, ..., 2n are in close contact with each other,
There is no gap between the segment pieces 2a, 2b, ..., 2n.

As described above, by using the shape memory alloy as the elastic member 4, each segment piece 2a, 2
Since the elastic member 4 is plastically deformed during thermal expansion of b, ..., 2n, it is possible to reduce the load applied to the threaded portion between the cap 3 and the screw shaft 1. As a result, extension and loosening of the screwed portion are prevented, and the reliability of the fastening between the cap 3 and the screw shaft 1 is improved.

Further, by utilizing the characteristics of the shape memory alloy, the elastic member 4 is connected to the segment pieces 2a, 2b ,.
It can also be used as an actuator when removing n from the screw shaft 1. Below, when the shape memory alloy is used as the elastic member 4, the segment pieces 2a, 2
An example of a method of removing b, ..., 2n will be described with reference to FIG.

After the operation of the extruder and the like is finished and each part is cooled, the segment screw is pulled out from the barrel 11 (see FIG. 1). At this time, as shown in FIG. 6A, the elastic member 4 is in a stretched state. Next, the segment piece 2a closest to the root is pressed against the flange portion 1a. Then, as shown in FIG. 6B, the elastic member 4 is plastically deformed and compressed, and a gap is formed between the segment piece 2a closest to the root and the segment piece 2b adjacent thereto. As described above, since the segment piece 2a closest to the root is located upstream of the hopper 12 (see FIG. 1), the amount of the molding material attached is small and the segment piece 2a can be easily moved.

After forming the gap, as shown in FIG. 6C, the spacer 15 is inserted into this gap and the elastic member 4 is heated by a burner or the like. Then, as shown in FIG. 6 (d), the elastic member 4 is restored, and each segment piece 2a, 2
.., 2n and the spacer 15 are moved to the right in the figure. In actual work, each segment piece 2
A, 2b, ..., 2n must be heated in the same manner as during operation. Then, after cooling the elastic member 4, the segment piece 2a closest to the root is again pressed against the flange portion 1a side to compress the elastic member 4, and the above operation is repeated while adding the spacer 15 to repeat the segment piece 2b ,.・ Gradually move 2n to the right and remove it. Finally, the segment piece 2a closest to the root is pulled out by hand.

As described above, by utilizing the expansion and contraction of the elastic member 4 by heating and cooling, it is possible to easily remove the segment pieces 2a, 2b, ..., 2n without requiring a large force. In this method, particularly, the molding material adheres to the surface of the boundary portion of the segment pieces 2b, ..., 2n downstream of the hopper 12, and a large force is applied to pull out these segment pieces 2b ,. Is effective when is needed.

[0029]

As described above, the segment screw according to the present invention is provided with the segment piece on the most root side among the segment pieces and the flange portion of the screw shaft.
Since the elastic member that is deformable in the axial direction of the screw shaft is provided, even if a difference in thermal expansion occurs between each segment piece and the screw shaft, each segment piece can be kept in close contact with each other. As a result, the molding material does not enter between the segment pieces, so that corrosion of the screw shaft and deterioration of the quality of the molding material can be prevented.

Further, since the elastic member is made of a shape memory alloy, in addition to the above effect, when only the segment piece is heated, the urging force of the elastic member does not act on the segment piece, and the screw shaft and the cap are not affected. Since the load applied to the screw-engaged portion with and is reduced, it is possible to prevent the screw-engaged portion from being stretched or loosened. Furthermore, heating of shape memory alloy
By utilizing expansion and contraction due to cooling, the elastic member can also be used as an actuator for extracting the segment piece.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a segment screw of the present invention.

FIG. 2 is a perspective view of an elastic member of the segment screw shown in FIG.

FIG. 3 is a view showing a state when each segment piece is thermally expanded in the segment screw shown in FIG.

FIG. 4 is a perspective view showing another example of the shape of the elastic member.

FIG. 5 is a perspective view showing still another example of the shape of the elastic member.

FIG. 6 shows a case where a shape memory alloy is used as an elastic member,
It is a figure for demonstrating an example of the extraction method of a segment piece.

FIG. 7 is a schematic configuration diagram of a conventional segment screw.

[Explanation of symbols]

 1 Screw Shaft 1a Flange 1b Shaft 2a, 2b, ..., 2n Segment Piece 3 Caps 4, 24, 34 Elastic Member 11 Barrel 12 Hopper 15 Spacer

Claims (2)

[Claims] 1. A plurality of segment pieces incorporated in a screw shaft (1) rotatably provided in a barrel (11) of an extruder or an injection molding machine and having a flange portion (1a) formed at a root portion. 2n) and each of the segment pieces (2a, 2b, ..., 2n) are sandwiched between the flange portion (1a) to hold the screw shaft (1). ), A segment screw having a cap (3) screwed onto the tip of the segment piece (2a, 2b, ..., 2n).
An elastic member (4) that is deformable in the axial direction of the screw shaft (1) is provided between the most proximal segment piece (2a) and the flange portion (1a). Segment screw to be. 2. The segment screw according to claim 1, wherein the elastic member (4) is made of a shape memory alloy.