JPH05220816A - Manufacture of corrugated pipe made of synthetic resin - Google Patents

Abstract

PURPOSE:To equalize the distribution of wall thickness by forming a parison for satisfying the extrusion speed of the parison, the speed of travel of a mold and the specific conditions of the push of the overall length of the outer peripheries of a recessed section and a projecting section when a corrugated pipe is manufactured by using the molding die, in which the recessed sections and the projecting sections are formed alternately. CONSTITUTION:A parison 26 extruded from an extruder 24 is introduced into a cylindrical molding tunnel 18 parted by continuously connecting half molding dies 16, in which recessed sections 12 and projecting sections 14 are formed alternately, and changing the molding dies into a caterpillar. Compressed air is blown into the parison 26, and the parison 26 is pushed and extended toward the molding surfaces of the molding dies 16, thus continuously forming a corrugated pipe 28. In such manufacture, a synthetic resin having a 100% modulus value at 190 deg.C of 0.5kgf/cm<2> or more is extrusion-molded so as to satisfy the conditions of 0.9>=B/(AXC)>=0.6. A represents the overall length of the outer peripheries of the recessed sections and the projecting sections per unit length, B the extrusion speed of the parison and C the speed of travel of the mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a synthetic resin corrugated pipe used for protecting underground cables.
More specifically, the present invention provides 100 at 190 ° C.
A corrugated pipe made of a synthetic resin having a so-called inferior molding processability, such as a resin having a% modulus value of 0.5 kgf / cm ² or more, a high resin viscosity at the time of melting and a high tensile strength at the time of molding, such as a hard polyvinyl chloride resin The present invention relates to a method for producing a corrugated pipe made of synthetic resin, which is improved so that the cross-section wall thickness in the longitudinal direction of the pipe is uniformly formed when the pipe is continuously produced.

[0002]

2. Description of the Related Art Synthetic resin corrugated pipes have heretofore been generally produced by continuously molding synthetic resin corrugated pipes using a molding machine and an extruder as shown in FIG. -1
It is manufactured by the method as described in Japanese Patent No. 6835. The molding machine 10 shown in FIG. 1 has a semi-cylindrical molding die 16 shown in FIG. 2 having a half-cylindrical molding surface in which concave portions 12 and protrusions 14 are alternately formed inside.
2 are continuously connected to each other without a gap to form an endless track in an annular shape as a whole, and the forming surfaces are opposed to each other over a certain distance to form a cylindrical forming tunnel 18.
It is equipped with a series of endless track mold dies 20 and is driven by rollers 22 to move in the direction of the arrow.

The parison (a tube of molten resin) 26 extruded from the extruder 24 is introduced into the molding tunnel 18 and at the same time, compressed air is blown into the parison, so that a difference between the inside and outside of the parison is generated. A pressure is generated, and the differential pressure causes the pipe-shaped material of the molten resin to be spread toward the molding surface of the molding die, whereby the synthetic resin corrugated pipe 28 is continuously molded. The extrusion speed of the parison 26 extruded from the extruder 24 is the same as the speed of the endless track molding die 20 that continuously swirls. As an alternative to blowing compressed air, for example, Japanese Patent Publication No. 55
As described in Japanese Patent No. 23738, etc., a through hole communicating with a vacuum pump is provided in a mold, and a vacuum is suctioned between the parison extruded into the mold and the mold, whereby A method is known in which a differential pressure is generated between the outer side and the parison, and the parison is suctioned to the molding surface of the molding die to continuously manufacture the corrugated pipe made of synthetic resin.

[0004]

However, the above-mentioned conventional method for manufacturing a corrugated pipe made of synthetic resin has the following problems. The problem is that in the synthetic resin corrugated pipe 28 manufactured by the conventional method, the wall thickness distribution in the longitudinal cross section thereof is as shown in FIG.
2 is thin at the peak portion 30 of the pipe and thick at the valley portion 32 of the pipe formed by the protrusion of the molding die, and the wall thickness is uneven between the peak portion and the valley portion. Was to be. Further, the wall thickness is as shown in FIG.
From the mountain to the mountain portion 30 changes continuously according to the volume,
Generally, it tends to decrease. This change in wall thickness is more remarkable as the pitch p of the corrugated pipe (one cycle of the wave, for example, the distance between valleys in the corrugated pipe) is smaller and the height h of the peak is higher. ..

If the ridge portion 30 is thin, the mechanical strength (tensile strength, compressive strength, etc.) of the ridge portion decreases, and the mechanical strength and impact strength of the entire corrugated pipe decrease. Therefore, the corrugated pipe is easily damaged by an impact applied by a pickaxe or the like at the time of laying, which is a practical problem. When manufacturing a corrugated pipe made of synthetic resin by the conventional manufacturing method, in order to increase the strength of the thin ridge portion, increase the average wall thickness of the entire pipe to reduce the thin ridge portion. I had no choice but to take measures to increase the wall thickness. But,
In such a solution, the weight of the pipe (the amount of material per unit length of the pipe) is increased to increase the manufacturing cost of the pipe,
In addition, the weight of the pipe was increased and workability during laying was deteriorated.
Therefore, this was not an economical solution.

On the other hand, polyethylene has been generally used as a material resin for synthetic resin corrugated pipes. However, since polyethylene corrugated pipes lack mechanical strength, they are used for protecting underground cables. Has higher mechanical strength,
For example, 1 at 190 ° C made of rigid polyvinyl chloride
A corrugated pipe made of a synthetic resin having a 00% modulus value of 0.5 kgf / cm ² or more is required, and it has been desired to provide it at a low price. The 100% modulus value at 190 ° C means that the elongation percentage of the test piece is 1 at 190 ° C.
It is a value obtained by dividing the load when it reaches 00% by the original cross-sectional area of the test piece. A material having a large value has high rigidity, but is inferior in moldability. By the way, polyethylene is 190 ° C
Then, it is in a molten state.

In the case of polyethylene, which has a low melting point and can be molded at a temperature above the melting point of the resin, it has a low melt viscosity during molding and a low tensile strength. Therefore, while molding is relatively easy, when a rigid polyvinyl chloride is manufactured by a conventional manufacturing method, it is necessary to perform the molding process at a temperature below the melting point because the melting point is high. High viscosity and high tensile strength. Therefore, the molding process was very difficult, and the cross-sectional wall thickness of the corrugated pipe made of hard polyvinyl chloride was more uneven and uneven than that of polyethylene. The poor moldability of rigid polyvinyl chloride means that the rigid polyvinyl chloride has softened at the molding temperature (for example, at a resin temperature of about 200 ° C that normally comes out of an extruder), but is not in a molten state. It is also clear from the fact that it retains a clear shape and that it is possible to measure tensile strength at this temperature.

Attempts to ensure good moldability by raising the processing temperature to reduce the viscosity have been unsuccessful because the polyvinyl chloride resin thermally decomposes when the temperature is raised. Particularly, in the case of rigid polyvinyl chloride, it is very difficult to raise the processing temperature because the thermal decomposition temperature is low. As described above, in the conventional method for manufacturing a corrugated flexible tube made of synthetic resin, it is difficult to manufacture a corrugated tube made of synthetic resin having high rigidity such as hard polyvinyl chloride and having a uniform wall thickness distribution. In view of the existing situation, an object of the present invention is to make a corrugated pipe which is made of synthetic resin having a 100% modulus value at 190 ° C of 0.5 kgf / cm ² or more and has a uniform cross-section wall thickness distribution and high strength. Is to provide a method of manufacturing.

[0009]

The above object of the present invention is achieved by the following method for producing a corrugated pipe made of synthetic resin according to the present invention. The method, while moving the mold die having a cylindrical molding surface in which concave portions and protrusions are alternately formed in a certain direction, pushes the parison onto the molding surface of the die to make contact with the mold surface, In a method for producing a corrugated pipe made of synthetic resin, which comprises a step of pressing the parison against a molding surface by a pressure difference generated between the inside and outside of the parison to form a corrugated pipe, a 100% modulus at 190 ° C. Value is 0.5
In order to manufacture corrugated pipes made of synthetic resin of kgf / cm ² or more,
The following conditions, Is a method for manufacturing a corrugated pipe made of synthetic resin, which is characterized in that extrusion molding is performed. In addition, A is the total extension of the outer peripheral edges of the recesses and protrusions formed on the molding surface per 1 m in the longitudinal direction in the longitudinal section of the molding die (the total length of the thick line in FIG. Is displayed in m, B is the parison extrusion speed in m / min, and C is the mold moving speed in m / min.

As a result of extensive studies on the relationship between the extrusion speed of the parison and the moving speed of the molding die, the present inventors have found out the following. The reason why the cross-sectional wall thickness of the synthetic resin corrugated pipe manufactured by the conventional manufacturing method is uneven is that the extrusion speed of the parison extruded from the extruder at the time of molding processing and the continuous track mold that continuously swirls Since the speed of the mold is the same, and as a result, the wall thickness of the crest portion of the corrugated pipe formed by the recessed portion of the mold is formed because the parison is significantly stretched and formed (see (The blow ratio is large in this case), but the valley portion of the corrugated pipe formed by the protruding portion of the molding die becomes thicker because the rate of expansion is smaller than that of the crest portion.
In the present invention, the parison is obtained by melting and plasticizing a resin and then extruding the resin into a pipe shape by an ordinary known extruder. Next, the post-extrusion parison is introduced into a molding machine, subjected to corrugation processing, and molded into a corrugated tube having flexibility.

As a result of repeated experiments based on the above findings, the present invention has a 100% modulus value at 190 ° C. of 0.5 kgf / When molding a resin having a cm ² or more, the value of B / (A × C) is 0.6 to
We have found the fact that good shaping is possible only in the range of 0.9. When the value of B / (A × C) is 0.9 or more, molding becomes easy, but a parison of a necessary amount or more is extruded, and a surplus portion is formed in the molded corrugated pipe.
The surplus part impairs the flexibility of the corrugated pipe, and when the pipe is bent, the stress is concentrated in this part due to the folds in the surplus part and the corrugated pipe is destroyed. Therefore, the product with excess meat is rejected. On the other hand, the above B / (A ×
If the value of C) is less than 0.5, a part of the obtained corrugated pipe which cannot be molded occurs. In particular, a part where the parison cannot reach is formed in a part of the concave part of the molding die, and therefore a part where the parison is not formed is formed. This tendency is remarkable for resins such as hard polyvinyl chloride, which has a high viscosity during molding.

The preferable value of B / (A × C) is from 0.6 to
Within the range of 0.8, the moldability is very good and there is no excess of meat. Further, if the thickness of the parison coming out of the extruder is too thick, a large pressure is required for molding, and molding may not be possible. Therefore, it is preferable to mold using a parison with a wall thickness of 10 mm or less. .. Incidentally, what is not specified in the above description in the implementation of the method for producing a synthetic resin corrugated pipe according to the present invention is the same as the case in the above-mentioned conventional method for producing a synthetic resin corrugated pipe. Hereinafter, the present invention will be described in more detail based on examples with reference to the accompanying drawings.

[0013]

Example 1 A 100% modulus value at 190 ° C. of 4.0 kgf /
Using a commercially available different-direction twin-screw extruder and a molding machine in which a hard polyvinyl chloride resin composition of cm ² is selected as a resin material and the value of B / (A × C) is set to 0.7 , While extruding the parison by the usual method, the corrugation process for molding the ridges and valleys of the corrugated pipe by the concave portion and the projecting portion of the molding die, respectively, is performed. A tube was made. With respect to the corrugated pipe obtained in Example 1, the wall thicknesses of the valley and the peak were measured, and the results are shown in Table 1. Example 2 A hard polyvinyl chloride corrugated pipe of Example product 2 was prepared and measured in the same manner as in Example 1 except that the value of B / (A × C) was set to 0.8. The results obtained are shown in Table 1.

[0014]

[Table 1]

Comparative Examples 1 to 3 In Comparative Example 1, the value of B / (A × C) was set to 1.0, and in Comparative Example 2, the value of B / (A × C) was set to 0.4. The same hard polyvinyl chloride resin composition as in 1 was corrugated to produce corrugated pipes of Comparative example products 1 and 2, and the thickness distribution of the obtained flexible pipes of comparative example products 1 and 2 was measured. The results are shown in Table 1. As Comparative Example 3, a synthetic resin having a 100% modulus value at 190 ° C. of 0.5 was selected as a material, and the value of B / (A × C) was set to 0.3, and the same as in Example 1. The corrugated pipe of Comparative Example product 3 was produced by corrugation processing, and the wall thickness distribution of the obtained corrugated pipe of Comparative Example product 3 was measured. The results are shown in Table 1.

As a result of measuring the cross-sectional wall thickness distribution of corrugated pipes formed by changing the value of B / (A × C) variously, Example product 1
As shown in Table 1, the corrugated tubes of Nos. 2 and 2 had very uniform wall thickness distribution. On the other hand, in Comparative Example 1, B / (A
Since the value of xC) was 1.0, which was larger than the upper limit of the range specified in the present invention, the parison in excess of the required amount was extruded to generate a meat excess portion, and the obtained corrugated pipe was made into a defective product. Comparative example 2
Then, since the value of B / (A × C) is 0.4, which is smaller than the lower limit of the range specified in the present invention, a part of the peak portion of the corrugated pipe obtained is not formed, and The corrugated tube of Comparative Example Product 2 was made defective. In Comparative Example 3, the 100% modulus value at 190 ° C. is 0.5, which is smaller than that in Example 1, but the value of B / (A × C) is 0.3, which is lower than the lower limit of the range specified in the present invention. Because of the small size, a portion of the peak portion of the corrugated pipe obtained in the same manner as in Comparative Example 2 was not molded, and the corrugated pipe of Comparative Example Product 3 obtained was made a defective product.

[0017]

According to the present invention, by setting the ratio of the moving speed of the molding die to the extrusion speed of the parison within a specific range, it is difficult to carry out the molding at 190 ° C. which was difficult by the conventional method.
Of 100% modulus value of 0.5kgf / cm ² or more made of high-rigidity synthetic resin and uniform in cross-section wall thickness in the longitudinal direction of the pipe, that is, the wall thickness of valley and peak is almost equal. The attached tube can be efficiently manufactured without producing defective products. The synthetic resin corrugated pipe produced by the method according to the present invention is imparted with good balance of physical properties such as mechanical strength and impact resistance, and is particularly important for imparting flexibility to the pipe. Has a uniform cross-section wall thickness in the longitudinal direction. Therefore, the existing pipelines can be easily avoided and flexible and stretchable to withstand uneven settlement, lightweight and easy to handle, earth canopy, sufficient strength to withstand the load (repetition) by vehicles, and construction work. It has shock resistance and the like that the pipe will not be broken by the impact load of a pickaxe or the like received at the time of, and is most suitable as a protective pipe for protecting the power cable for underground cables.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a parison extruder and a molding machine.

FIG. 2 is a longitudinal cross-sectional explanatory view of a half mold.

FIG. 3 is a partial cross-sectional explanatory view of a synthetic resin corrugated pipe in a longitudinal direction.

[Explanation of symbols]

 10 Molding Machine 12 Recessed Part 14 Projection Part 16 Mold Die 18 Forming Tunnel 20 Endless Track Mold 22 Roller 24 Extruder 26 Parison (Tube of Molten Resin) 28 Synthetic Resin Corrugated Pipe 30 Pipe Crest 32 Pipe Valley

Claims (1)

[Claims] 1. A parison is pushed onto and brought into contact with the mold molding surface while moving in a certain direction a mold mold having a cylindrical molding surface in which concave portions and projecting portions are alternately formed. A method for producing a corrugated pipe made of synthetic resin, comprising the step of pressing the parison against the die molding surface by a pressure difference generated between the inside and the outside of the parison to form a corrugated pipe. % Modulus value is 0.5kgf /
cm ² or more synthetic resin under the following conditions (Here, A is the total extension of the outer peripheral edges of the recessed portions and the protrusions formed on the mold molding surface per 1 m in the longitudinal direction in the longitudinal section of the molding die.
, B shows the extrusion speed of the parison in m / min, and C shows the moving speed of the mold in m / min. ) Extrusion molding is carried out by a method for producing a corrugated pipe made of a synthetic resin.