JPH08332667A - Production of tubular member - Google Patents

Abstract

PURPOSE: To produce a resin tubular member reduced in residual stress and having no flaw dimensionally and physically. CONSTITUTION: A molten resin is extruded into a tubular resin passage 8 from a mold 3 having a plurality of pins 9 having fluid passages 11 axially provided therein and, by the presence of the pins 9, a cooling medium such as cooling air is sent in the through-hole 15 axially formed to the tubular member from the outside from a cooling medium introducing passage 13 and a fluid passage 11 to cool the tubular member from the through-hole 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a tubular body made of a synthetic resin, in which a plurality of through holes in the axial direction of the tube are juxtaposed in a tube wall.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a synthetic resin tubular body, a die having an annular resin passage is attached to the tip of an extruder, and the resin melted and kneaded by the extruder is extruded into a tubular form from the die. It is customary to send it to the cooling molding process. In this cooling molding step, the tubular body passes through the tip surface of the mold or a sizing die attached to a cooling device such as a water tank, and is cooled and shaped while being subjected to dimensional restrictions.

In this cooling molding step, since the shape is formed by cooling from the outer surface or the inner surface, the cooling rate is different between the inner and outer surface layers and the inner layer, and contraction / solidification is started. It is known that the residual stress is accumulated inside the tubular body because the time points for doing so shift. For example,
The publication "ANTE" of the research center of DuPont Canada
C ", 1989 edition: 546-549," A study of residual stress distribution in plastic pipe and profile extrusion molding (Prediction of ResidualStress Di
stribution in Plastic Pipe and Profile Extrusion)
", But this is pointed out.

[0004]

Due to this residual stress,
The formed tubular body may have non-uniform dimensions, and the tube ends are particularly prone to deformation, which makes it difficult to connect the tubular bodies to each other and to connect the tubular body and the joint. Also,
When an external force such as an external pressure or an internal pressure is applied during use, there is also a problem that the pipe is likely to be flat or cracked when the direction of the external force and the direction of the residual stress match.

Several methods have been developed to solve this problem. For example, in Japanese Examined Patent Publication No. 25129/1992, when a tubular body extruded from a mold is introduced into a cooling / solidifying step, only the surface layer is first cooled to a predetermined temperature without being rapidly cooled, and then air-cooled. A technique is disclosed in which liquid cooling is repeated a plurality of times to gradually and completely cool the inner layer.

However, in this method, the slow cooling process is long, and it takes too much time to completely cool and solidify the tubular body, which not only slows down the production rate, but also shrinks and shrinks the surface layer and the inner layer. It is not a fundamental solution because the gap between the start of solidification cannot be resolved.

The present invention solves the above-mentioned drawbacks of the prior art,
An object of the present invention is to provide a production method by which a resin tubular body formed by extrusion has a small residual stress and is free from defects in terms of dimensions and physical properties.

[0008]

According to the method for manufacturing a tubular body of the present invention, "a plurality of pins having fluid passages in the inner axial direction are arranged at the outlet side of an annular resin passage at intervals. When the tubular body is extruded from the die, the cooling medium is introduced from the outside of the die into the fluid passage of the pin, and the cooling medium is fed into the through hole formed in the tubular body by the pin in the axial direction of the tubular body. The above-mentioned object is achieved by this.

As the resin used in the production method of the present invention, any resin generally used in extrusion molding can be mainly used, and examples thereof include olefin resins represented by polyethylene, polypropylene and polybutene, and poly resins. Fluorine-based resins such as tetrafluoroethylene and polyvinyl difluoride, and crystalline engineered plastics such as polyethylene terephthalate, nylon, polyphenylene sulfide, and polyether ether ketone.

Examples of the amorphous resin include polyvinyl chloride, polyvinylidene chloride, polycarbonate, polymethyl methacrylate, polyvinyl alcohol, polyether sulfide, polyether imide and polyimide.

Further, in addition to the resin as the main material, fillers such as glass chopped strands, calcium carbonate, balloon-shaped blast furnace ash, halogen-based, non-halogen-based, inorganic-based flame retardants, hindered amine-based, benzophenone-based, etc. Various additives such as UV absorbers, colorants, and plasticizers can be used as necessary.

As the basic structure of the mold used in the present invention, the same structure as the mold generally used for extrusion molding of tubular bodies is used. For example, the outer die and the core die are supported by a spider, and an annular cavity between them is used as a resin passage.

However, in the present invention, one of the important elements is to use a plurality of pins having a fluid passage formed in the axial or longitudinal direction on the outlet side of the resin passage. . As a means for fixing this pin in the resin passage, either an outer mold or a core mold may be used, but in consideration of introducing the cooling medium from outside the mold, when introducing from the core mold, a core mold, When introducing from the outer mold, it is preferable to fix each to the outer mold.

In the present invention, due to the presence of this pin, the extruded tubular body is necessarily formed with as many through holes as the number of pins in the axial direction of the tube. Regarding the number and size of the through holes, it is preferable to consider so as to satisfy all the restrictions described in the following items (1) to (4). The shape of the through hole is determined according to the cross-sectional shape of the pin and is not particularly limited, but it is preferably a round hole from the viewpoint of moldability, strength retention and the like.

[0015] The value obtained by dividing the through-hole method in the pipe wall thickness direction by the through-hole method in the pipe wall circumferential direction is 1/4 to 4. When it becomes smaller, the inner diameter of the through hole occupying the circumferential direction of the tube wall becomes larger, and when it becomes larger, the distance between the wall surface of the through hole and the surface of the tubular body becomes too small, and in any case, the strength of the entire tubular body decreases. ． The value obtained by dividing the product of the inner diameter of the through hole in the circumferential direction of the pipe wall and the number of through holes by the total value of the intervals between the through holes should be 2 or less. When it becomes larger, the distance between the through holes in the circumferential direction becomes smaller than that in the method of the through hole in the circumferential direction of the tube wall, and the strength of the tubular body as a whole decreases. ． The number of through holes must be 3 or more. When the number of through holes is small, the effect of cooling the pipe wall is insufficient and the effect of reducing residual stress cannot be obtained.

.. The value obtained by dividing the through-hole method in the thickness direction of the pipe wall by the thickness of the pipe wall is 1/10 to 1/2. When it becomes smaller, the size of the through hole becomes smaller and the effect of reducing the residual stress cannot be obtained. When it becomes larger, the distance between the wall surface of the through hole and the surface of the tubular body becomes too small, and the strength of the entire tubular body lowers. ． The distance between the wall surface of the through hole and the surface of the tubular body closer to this,
The value divided by the thickness of the tube wall should be 1/8 or more. When it becomes smaller, the distance between the wall surface of the through hole and the surface of the tubular body becomes too small, and the strength of the entire tubular body decreases.

In the present invention, it is also an important factor to adopt a means of feeding the cooling medium into each of the through holes via the fluid passage provided in the pin. As the cooling medium source at this time, cooling air, cooling water, liquid nitrogen, liquid carbonic acid, or an organic solvent such as alcohol or acetone is used.

Further, it is preferable to provide a heat insulating material layer on the peripheral wall of the cooling medium introducing passage in the mold, the outer surface of the pin in the resin passage, the inner surface of the fluid passage, and the like. The form in which the cooling medium is fed may be an appropriate form depending on the cooling medium, such as blowing, pouring or spraying. The cooling medium sent into the through hole is removed when the tube is cut into a regular size in the final stage of forming the tubular body.

When the cooling method from the inside of the through hole of the tubular body is adopted in the present invention, cooling from the outer surface or the inner surface of the tubular body which has been conventionally carried out, for example, a cooled cylindrical shape is performed. Need a method of sliding the outer surface of the tubular body on the inner surface of the sizing die, or a method of sliding the inner surface of the tubular body on the outer surface of the mandrel that projects from the die tip and circulates the cooling medium inside. It may be carried out according to

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing only an essential part of an example of an apparatus suitable for carrying out the method for producing a tubular body of the present invention, and FIG. 2 shows a tubular body formed by using the same apparatus. It is a cross-sectional view showing a different example.

In FIG. 1, reference numeral 1 is a cylinder of an extruder in which a single screw 2 is arranged. 3 is a die attached to the front end of the cylinder 1, and is an outer die 4
And a core die 5, and a land portion 6 having a small diameter is provided on the outlet side of the outer die 4. The core die 5 is supported in the outer die 4 by a spider 7 fixed to the root thereof, thus forming an annular resin passage 8, and the structure up to this point is the same as the conventional die.

Inside the outlet side of the annular resin passage 8, a plurality of pins 9 are arranged at equal intervals, and a support portion 10 protruding from the inner wall of the outer die 4 into the resin passage 8 serves to External type 4
It is fixed to. A fluid passage 11 is provided in each pin 9 in the axial direction thereof, and the tip end opening 12 is flush with the end surface of the land portion 6 and the core die 5. Further, the rear parts are respectively bent to the outside, communicated with the cooling medium introducing passage 13 penetrating the outer mold 4 through the through holes in the supporting part 10, and to a cooling medium source (not shown) installed outside the mold. It is connected. Reference numeral 14 is a fluid passage 11, a through hole in the support portion 10 and a heat insulating material layer stretched on the inner wall of the cooling medium introduction passage 13.
Reference numeral 5 is a through hole formed in the tube wall of the tubular body P.

[0024]

According to the method for manufacturing a tubular body of the present invention, a plurality of pins having fluid passages through which the cooling medium can pass in the inner axial direction are arranged at the outlet side of the annular resin passages at intervals. Since the tubular body is extruded from the die, the tubular body having a through hole formed in the tube axial direction is continuously extruded, and the through hole communicates with the fluid passage of the pin.

Further, during the above-mentioned extrusion molding process, the cooling medium is fed from the outside of the mold into the through hole through the fluid passage of the pin, so that the tubular body extruded from the mold is cooled and cooled.
In the solidification step, cooling is also performed from the through holes, and cooling / solidification is started almost simultaneously over the entire tubular body. Therefore, the cooling rate of the entire tubular body is increased, the timing difference of the cooling and solidification between the surface layer and the inner layer of the tubular body and the difference in the cooling rate are almost eliminated, and the residual stress in the tubular body is not generated. It can be suppressed as much as possible.

[0026]

【Example】

[Examples 1 and 2] Using the above apparatus, a tubular body was extruded by the following molding materials and molding conditions. In addition to cooling from the inside of the pipe wall, a normal vacuum spray type outer diameter regulation system was adopted as a cooling sizing system. In addition, the screw diameter of the extruder 1 was 75φ, the number of pins was 16, and the cross-sectional shape of the pins was circular. Molding material: polyethylene (Mitsui Petrochemical Co., Ltd., 2015
M) Molding conditions: temperature conditions: cylinder = 220 ° C., mold =
Cooling air (temperature = 20 ° C., flow rate = 100 liters / hour) and atomized cooling water (temperature = 1
Examples 1 and 2 were used by using two types (5 ° C., flow rate = 100 liter / hour). The obtained tubular body has an outer diameter of 165 mm and an inner diameter of 139 m.
m, through-hole diameter = 6.5 mm, number of through-holes 16, positions of through-holes = equal spacing and center in the thickness direction of the tubular body.
The cross-sectional shape is shown in FIG.

Comparative Example 1 A tubular body was manufactured in the same manner as in Example 1 except that the cooling medium was not fed into the through hole and the inside of the through hole was in communication with the outside air.

[Comparative Example 2] A tubular body was produced in the same manner as in Example 1 except that a mold equipped with pins was not used.

The accumulated residual stress was measured for the tubular bodies obtained in the above Examples and Comparative Examples. In addition, the measuring method was calculated by inserting a cut in a plane passing through the tube axis into a sliced tubular body piece, cutting and measuring the amount of change in outer diameter, and substituting the numerical value into the following equation.

Σ _max = [± E (t) h] / [1-
ν ² ] × [D ₂ (t) -D ₁ ] / [D ₂ (t) D ₁ ] (Note) σ _max : maximum stress of the tubular body (Kgf / cm ² ) E (t): at time t Coefficient h of h: tubular wall thickness D ₁ : diameter before cutting D ₂ (t): diameter after cutting at time t ν: Poisson's ratio

As a result, in the cases of Examples 1 and 2, the values were 30 and 25 (Kgf / cm ² ) respectively, whereas in the cases of Comparative Examples 1 and 2, 50 and 60 (Kgf) respectively.
/ cm ² ) and it is clear that the effect of reducing residual stress is remarkable.

In the above embodiment, the through holes have a circular shape, but various shapes can be obtained as described above depending on the shape of the pin. An example thereof is shown in FIG. In the figure, 16 is a rectangular through hole.

[0033]

As described above, the tubular body manufacturing method of the present invention employs a method of cooling from the through-holes formed in the tubular body in the step of cooling and solidifying the tubular body in the extrusion molding.
The cooling rate becomes faster, and the production rate can be improved. Further, the difference in the cooling rate at each portion in the thickness direction of the tubular body and the deviation of the timing of the start of cooling / solidification are reduced, and the occurrence of residual stress in the tubular body can be suppressed as much as possible. Therefore, a product having excellent dimensional stability can be manufactured.

Further, since the tubular body obtained by the manufacturing method of the present invention has the through hole formed in the axial direction of the pipe, the weight of the tubular body can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of only a main part showing an example of an apparatus suitable for carrying out the method for manufacturing a tubular body of the present invention.

FIG. 2 is a cross-sectional view showing different examples of tubular bodies manufactured by the same apparatus.

[Explanation of symbols]

 P Tubular body 3 Mold 4 Outer type 5 Core type 6 Land portion 7 Spider 8 Annular resin passage 9 Pin 11 Fluid passage 13 Cooling medium introduction passage 15, 16 Through hole

Claims (1)

[Claims] 1. When extruding a tubular body from a die having a plurality of pins having fluid passages in the inner axial direction at the outlet side of an annular resin passage with a space provided therebetween, the tubular body is pressed from outside the die. A method for manufacturing a tubular body, comprising introducing a cooling medium into a fluid passage of the pin, and feeding the cooling medium into a through hole formed in the tubular body in the tube axial direction by the pin.