JPH02108505A - Extrusion molding of tube - Google Patents

Abstract

PURPOSE:To contrive to heighten the airtightness of tip part and to improve the yield by products by a method in which while a rounding mold is rotated at a prescribed speed, the air-extraction from the rounding mold is achieved at the position spaced apart from its rotating axis. CONSTITUTION:Body 13 is continuously sent into the nozzle 12 of the extruding machine with a core by a screw, and is molded into a tubular shape. When a molded object is extruded form the nozzle 12, the molded object 14 is cut at the exit of the nozzle 12. While the rounding mold 15 molding the bowllike tip of a protective tube with the core 11, is continuously set at the tip of the nozzle 12, the rounding mold 15 is rotated around the axis of the nozzle 12 in the range of 5-20rpm, and the body 13 containing air is discharged from the air-extracting hole 15a spaced apart from the rotation axis of the rounding mold 15. Then, while the body 13 is sent therein by the screw, the rounding mold 15 is synchronously moved with this sending speed and is separated from the nozzle 12, and then the tube part 16b connected to the bowl part 16a is extrusion-molded. Consequently, the bubble or flow line on the tip of the molded object is reduced, and the airtightness of the tip part is improved, whereby the yield of the product is heightened.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for extruding a tube.

[Prior Art] Conventionally, in extrusion molding of alumina protection tubes for thermocouples, for example, in order to form the bowl-shaped tip of the protection tube, an extrusion molding machine having a core 1 is used as shown in FIG. A rounding die 3 is connected to the tip of the base 2, and a rounding die 4 whose main component is alumina is formed.
The material is fed into a rounding mold 3 through a die 2 and molded.

In the figure, 3a is an air vent hole provided at the center of the bottom of the rounding mold 3.

[Problems to be Solved by the Invention] However, the tube produced by the conventional extrusion molding method has poor airtightness at the tip and a low yield.

The cause of such leakage failure at the tip is that when forming the tip, the diameter of the vibrator-shaped piece 4 is rapidly reduced by the rounding die 3, which causes air to be drawn in, leaving pores and causing flow lines. This is because (a trace of being sent) is created.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for extrusion molding a tube, which can improve the airtightness of the tip and thereby improve the yield of the product.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a method for extruding a tube tip portion onto a tip portion of a mouthpiece having a core using a rounding die at a speed of 5 to 20 rpm. In this method, the rounding mold is rotated at a distance from the axis of rotation, and the air is removed from the rounding mold at a position away from the rotation axis.

[Function] In the above means, the clay whose diameter is reduced from a pipe shape to a bowl shape by a rounding mold tends to have uneven axial velocity at each position in the circumferential direction. Rotation imparts a velocity component in the circumferential direction, and the axial velocity at each position in the circumferential direction becomes almost uniform, sufficiently reaching the bottom of the mold. It is ejected at a position away from the axis.

If the rotation speed of the rounding mold is less than 5 rpm, it will not be possible to impart a velocity component in the circumferential direction to the clay, and productivity will not improve, and if it exceeds 20 rpm, the pipe and arm portions of the clay will is separated.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 5.

First, 100 parts of alumina powder (average particle size: 1.1 M layer), 0.3 parts of magnesium carbonate (average particle size: 1.0 μm), and 100 parts of ion-exchanged water were placed in a ball mill, and mixed and pulverized for 48 hours. The resulting slip was heated at a temperature of 110°C for 2
It was dried for 4 hours and used as an alumina raw material.

Next, methyl cellulose (
5M-4000 (manufactured by Shin-Etsu Chemical Co., Ltd.), 2 parts of glycerin, 1 part of propylene glycol, and 12 parts of ion-exchanged water were added and kneaded for 30 minutes in a kneader to obtain a clay containing alumina as a main component.

Next, using the above clay, extrusion molding was performed as described below to obtain molded bodies, and each molded body was held at a temperature of 1740°C for 2 hours to obtain an outer diameter of 13 mm, an inner diameter of 9III11, and a length of 980 m.
An alumina protection tube of 1.5 m was obtained.

EXAMPLE As shown in FIG. 1, a molded body 13 is continuously fed into the mouthpiece 12 of an extrusion molding machine having a core 11 using a screw (not shown) to form it into a pipe shape. At the point when 14 was pushed out, the screw was stopped.

Next, as shown in FIG. 2, after cutting the molded body 14 at the outlet of the mouthpiece 12, a rounding mold 15, which together with the core 11 forms the bowl-shaped tip of the protective tube, is inserted into the mouth of the mouthpiece 12. As shown in FIG. 3, a rounding mold 15 is connected to the tip.
- An air vent hole 15 that rotates at 8 rpm around the axis of the base 12 and is provided in the rounding die 15 at a distance from the axis of rotation.
The screw and the rounding mold 15 were stopped after the screw 13 had rotated three times since it started coming out from a.

In the above process, the crosspiece 13 whose diameter is reduced from a pipe shape to a bowl shape by the rounding die 15 is given a velocity component in the circumferential direction by the rotation of the rounding die 15, and has an axial velocity at each position in the circumferential direction. becomes almost uniform, reducing air entrainment,
The clay 13 that has sufficiently reached the bottom of the mold and is mixed with air is discharged from the air vent hole 15a located away from the rotational axis of the rounding mold 15.

After forming the arm portion 16a at the tip as described above, as shown in FIG. 12, and a pipe portion 16b connected to the arm portion 18a was extruded. pipe part 1
During extrusion molding of the core 6b, since the core 11 is provided with ventilation holes (not shown), no deformation occurs. Thereafter, as shown in FIG. 5, the pipe portion 16b is cut at the outlet of the cap 12 to obtain a molded body 16.
The steps shown in FIGS. 5 to 5 were repeated to obtain molded bodies 16 that would become alumina protective tubes one after another.

Comparative Example In the example, the arm portion was molded at the point where the rounding die 15 was not rotated and the mold 13 protruded 10 cm from the air vent hole 15a, and the other steps were the same as in the example to obtain a molded body. Ta.

Twenty alumina protection tubes each made of molded bodies according to the above examples, comparative examples, and conventional examples were manufactured, and JIS R
When an airtightness test was conducted as specified in ``Nonmetallic Protection Tube for 14θ1r Thermocouple'', the number of non-defective products was 20 in the Example, 18 in the Comparative Example, and 16 in the Conventional Example.

Therefore, it can be seen that the molded bodies according to the examples described above have excellent airtightness and a high product yield.

[Effects of the Invention] As described above, according to the present invention, the clay whose diameter is reduced from a pipe shape to a bowl shape by a rounding mold tends to have uneven axial velocity at each position in the circumferential direction. However, due to the rotation of the rounding mold, a velocity component in the circumferential direction is given, and the axial velocity at each position in the circumferential direction becomes almost uniform and reaches the bottom of the mold. Since it is discharged at a position away from the rotation axis of the rounding mold, pores, flow lines, etc. at the tip of the molded product are reduced, and the airtightness of the tip is improved.
Product yield increases.

[Brief explanation of drawings]

1, 2, 3, 4, and 5 are cross-sectional views showing each step of the extrusion molding method for a protective tube according to an embodiment of the present invention, and FIG. 6 is a step of the conventional method. FIG. 11... Core, 12... Cap, 13... Clay, 1
5... Rounding mold, 15a... Air vent hole, 16...
・Molded body, 16a...ridge part, 16b...vibrator part Applicant: Toshiba Ceramics Co., Ltd. Agent Patent attorney: Yujibe Taka

Claims (1)

[Claims] (1) When extruding the tip of a tube using a rounding die connected to the tip of a nozzle having a core, the rounding die is
A method for extruding a tube, which rotates at 0 rpm and vents air from the rounding die at a position away from the axis of rotation.