JP3294923B2 - Manufacturing method of synthetic resin tube - Google Patents

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 synthetic resin tube by extrusion molding.

[0002]

2. Description of the Related Art In general, when a synthetic resin tube is manufactured by extrusion, a tubular molten resin is caused to flow out of an extrusion die, and the molten tube is immersed in a cooling water tank to be cooled from the outer surface of the molten tube. That is being done.

Conventionally, when performing this extrusion molding, an auxiliary mandrel provided with an annular auxiliary ring or a tapered auxiliary mandrel is protruded from a mandrel of an extrusion die.
With this auxiliary mandrel, the shape and the like of the inner surface of the molten tube are maintained (for example, see Japanese Patent Publication No. 63-7929).

[0004] In addition, cooling with a refrigerant is also performed from the inner surface of the molten tube body to improve the cooling efficiency and prevent molding distortion in the thickness direction of the tube. See JP-A-48-89971). Further, a shield plate is provided on the inner surface of the molten tube, and the refrigerant used for cooling the inside of the tube is recovered after cooling (see Japanese Patent Application Laid-Open No. 4-135731).

[0005]

However, when the inner surface shape of the molten tube is maintained or shaped by the above-mentioned conventional auxiliary mandrel, the molten tube becomes excessively cooled while passing through the auxiliary mandrel. If this occurs, the hardened tube will closely adhere to the auxiliary mandrel, causing a large resistance. As a result, tension is applied to the pipe body between the auxiliary mandrel and the take-off machine, which causes problems such as the formation of a distorted pipe body, the resin clogging the auxiliary mandrel, and the breakage of the pipe body. Occurs.

Further, when cooling with a refrigerant from the inner surface of the molten tube, the used refrigerant remains on the inner surface of the tube. Is easily attached and rusted, which causes inconvenience in terms of equipment maintenance and the like. Further, the cooling balance is different between the upper part of the tube where the refrigerant is hardly in contact and the bottom part of the tube where the refrigerant is likely to accumulate, causing distortion in the circumferential direction of the tube.

Further, when the cooling medium is recovered by the shielding plate, it is difficult to completely recover the cooling medium. Therefore, the above-described inconveniences such as rusting of the cutting machine and collapse of the cooling balance occur. In addition, the shield plate becomes a resistance when it is taken off by the take-off machine, and tension is applied to the tube body to cause distortion in the axial direction, or the resin is clogged in the shield plate and the tube body is cut. This will cause inconvenience.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of manufacturing a synthetic resin tube capable of efficiently and surely manufacturing a product having excellent product accuracy.

[0009]

According to the present invention, there is provided a method for manufacturing a synthetic resin tube, which comprises the steps of: discharging a tubular molten resin from an extrusion die; A method for manufacturing a synthetic resin tube comprising a step of holding and shaping with an auxiliary mandrel protruding from a mold mandrel , wherein a refrigerant passes through an outer peripheral surface of the auxiliary mandrel.
A spiral pleat is formed by the excess cooling pipe, and the inner surface of the molten tube is held and shaped through the pleat.
At the same time, cooling is performed from the inner surface of the molten tube .

[0010]

According to the present invention, by holding and shaping the inner surface of the melting tube through the spiral fold, the melting tube is not constrained simultaneously in the circumferential direction but is constrained in a spiral shape. The time resistance will be reduced. Also, cooling piping
The inner surface of the molten tube is cooled indirectly by the refrigerant passing through
Will be rejected.

[0011]

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

FIG . 1 schematically shows a synthetic resin pipe manufacturing apparatus 1 used in the present invention.

As shown in FIG . 1 , the manufacturing apparatus 1 includes a cooling pipe 40 spirally wound around an outer peripheral portion of an auxiliary mandrel 4 to form a fold 41, and a refrigerant pipe 22 guided inside the extrusion die 2. The cooling pipe 40 is connected to the cooling pipe 40 to circulate the refrigerant. The cooling pipe 40 cools the inside of the pipe 3 and the cooling water tank 5 cools the pipe 3 outside . . However, the extrusion die 2 and the auxiliary mandrel 4
The auxiliary mandrel 4 cooled by the refrigerant passing through the cooling pipe 40 does not cool the extrusion die 2.

[0014]

Examples 1-3, Comparative Examples 1-3 Stabilizers and processing aids were added to vinyl chloride resin and melt-kneaded with a twin screw extruder.
The production apparatus 1 shown in 1, molding the rigid polyvinyl chloride tube having an inner diameter of 50 mm, was observed production situation. The cooling pipe 40 was made of copper having a diameter of 5 mm, the pitch A was 10 mm, and the number of strips was one. The length L of the auxiliary mandrel 4 was 300 mm. Further, the pipe inner surface temperature is measured by measuring the internal temperature of the pipe body 3 after passing through the auxiliary mandrel 4 with a thermocouple, and the cooling water temperature is determined at the position of the refrigerant pipe 20 led out of the extrusion die 2 after passing through the cooling pipe 40. It was measured. Further, the take-up speed of the tube 3 was changed in three stages according to the amount of extrusion of the tube 3.

[0015] Thus by cutting the rigid polyvinyl chloride pipe was prepared in the annular length 10 cm, as shown in FIG. 3, a test piece of C-shaped cut with the cutting width D of 20mm in the circumferential direction No. 30 was formed. And the cutting width D of this opening portion
Was measured, and the effect of residual strain was examined.

Further, for comparison, as shown in FIG. 2
And the auxiliary mandrel 7 with 15 pitches A of 30 mm
A hard polyvinyl chloride pipe was manufactured in the same manner for the manufacturing apparatus 10 provided with the auxiliary ring 71, and the cutting width D of the opening was measured. Table 1 shows the results.

[0017]

[Table 1]

[0018] Consequently, in the embodiment according to the present invention, the temperature of the inner surface of the tubular body 3 in comparison with the comparative example is cooled to less than half, sufficient cooling effect was confirmed that the obtained. Further, the cutting width D of the opening is supported by this cooling effect, and it was confirmed that the lower the inner surface temperature of the tube was, the closer to the theoretical cutting width of 20 mm, and that the product was excellent in that the residual strain was small. .

[0019]

As described above, according to the present invention, the resistance at the time of taking-off can be reduced, so that a product having no molding distortion and excellent in product accuracy can be manufactured.
In addition, it is possible to prevent the resin from being clogged or cut during the manufacturing process, and it is possible to efficiently and reliably manufacture these products having excellent product accuracy. Also cooling
Inner surface of the molten tube indirectly by refrigerant passing through the pipe
Can be cooled, handling of the refrigerant after cooling
To manufacture products efficiently without having to
it can. In addition, it is indirect cooling, and the refrigerant
Rusting of the cutting machine or
Distortion can be prevented, and equipment
Produce stable products while improving maintainability
It is possible to do.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing an example of an apparatus for manufacturing a synthetic resin tube.

FIG. 2 is a partial sectional view showing a conventional synthetic resin pipe manufacturing apparatus.

FIG. 3 is a sectional view showing a test piece.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 2 Extrusion die 21 Mandrel 3 Tube 4 Auxiliary mandrel 40 Cooling pipe 41 Pleasing part

Claims (1)

(57) [Claims] 1. A synthetic resin comprising a step of discharging a tubular molten resin from an extrusion die and holding and shaping the inner surface of the molten tube with an auxiliary mandrel projecting from a mandrel of the extrusion die. A method of manufacturing a pipe, wherein a cooling pipe through which a refrigerant can pass is provided on an outer peripheral surface of an auxiliary mandrel.
A spiral fold is formed by this, and the inner surface of the fusion tube is held and shaped through the fold, and at the same time, the fusion tube is formed.
A method for producing a synthetic resin tube, wherein cooling is performed from the inner surface of the tube.