JP2001310389A - Heat-expandable vinyl chloride resin pipe for steel pipe lined with vinyl chloride and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vinyl chloride resin pipe for a steel pipe lined with a vinyl chloride which has enough restoring expansion in the diameter direction when the shape of the pipe is restored and the thickness of which can hardly be changed when the pipe is stretched in the axial direction and a method for producing the vinyl chloride pipe easily. SOLUTION: In the heat-expandable vinyl chloride pipe for the steel pipe lined with the vinyl chloride which is produced by being cooled to a temperature between the softening temperature of the vinyl chloride and the softening temperature plus 40 deg.C before the vinyl chloride pipe of a high temperature which is discharged from a mold is introduced into a shaping/cooling mold, the thickness of the pipe wall is larger than the thickness of the vinyl chloride immediately after being discharged from the mold, and the length of the vinyl chloride pipe after being lined is larger than that of the pipe before being lined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an object to provide a heat-expandable vinyl chloride pipe used for a vinyl chloride-lined steel pipe obtained by bonding a steel pipe by heat-expanding the vinyl chloride pipe, and a method for producing the same. It is a thing.

[0002]

2. Description of the Related Art A vinyl chloride-lined steel pipe is manufactured by extruding a vinyl chloride pipe which is expanded by heating for an inner pipe and applying an adhesive to the outer surface and / or the inner surface of the steel pipe or both. And heat it sequentially from one end to the other end or from the center to both ends from the outside of the steel pipe by a known method such as a hot blast stove, infrared heating furnace, or high-frequency heating furnace to restore and expand the PVC pipe. A method is known in which the vinyl chloride pipe is adhered to the inside of the steel pipe while the air between the steel pipe and the vinyl chloride pipe is drawn toward the pipe end.

As a method for producing a vinyl chloride pipe used in this method, as shown in Japanese Patent Application Laid-Open No. Hei 10-235716, an uncured resin pipe immediately after being extruded from an extrusion die is used. Once expanded by passing through a core for diameter expansion that is larger than the diameter of the end of the mandrel, which is provided adjacent to the end of the mandrel, heat-expanding is performed on the cured resin tube by forming while reducing the diameter. The production method to be applied is known.

In this method, a portion passing through the core for diameter expansion is heated by a heater, and the temperature of the resin tube passing therethrough is heated to substantially the same temperature as when the resin tube exits the mold.
Cooling and curing with a forming tube while taking up at a speed higher than the extrusion speed. Therefore, the vinyl chloride tube obtained by this method is thinned in the diameter direction by being pulled in the drawing direction, and is hardened in a state of being stretched in the axial direction. For this reason, when the shape is restored by heating, there is a problem that while the shape is sufficiently restored and expanded in the diameter direction, a large shrinkage occurs in the axial direction and the wall thickness is increased.

That is, when a vinyl chloride-lined steel pipe is manufactured using the vinyl chloride pipe obtained by this method, the amount of shrinkage in the axial direction is predicted in addition to the radial expansion of the vinyl chloride pipe due to heating, and the amount of shrinkage is predicted in advance. A PVC pipe longer than the length of the steel pipe was prepared, and after heating lining, the excess PVC pipe at the pipe end was cut off. However, the amount of shrinkage varies depending on the variation in the inner diameter of the steel pipe, that is, the variation in the expansion diameter of the vinyl chloride pipe, and the variation in the original shrinkage characteristics of the vinyl chloride pipe. .

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a vinyl chloride tube which has a sufficient restoring expansion in the diameter direction when its shape is restored by heating, and which extends in the axial direction and whose wall thickness hardly changes. Another object of the present invention is to provide a method for easily producing the same. Further, as another object, it is possible to use a polyvinyl chloride pipe having a length substantially the same as a steel pipe used in the production of a lining pipe. It is possible to reduce the number of PVC pipes that must be cut and removed from the pipe end later, thereby reducing waste of raw materials and at the same time contributing to the reduction of vinyl chloride resin waste. Since the length of the PVC pipe that extends can be minimized, the risk of air residue between the steel pipe and the PVC pipe at the pipe end is reduced. Made but also have the purpose.

[0007]

According to a first aspect of the present invention, there is provided a heat-expandable vinyl chloride pipe for a vinyl chloride-lined steel pipe (Invention 1). This is a vinyl chloride pipe used for a vinyl chloride lining steel pipe obtained by inserting a vinyl chloride pipe coated with, applying heat and expanding the vinyl chloride pipe to the inner surface of the steel pipe, and the thickness of the pipe wall is discharged from the mold. A heat-expandable vinyl chloride pipe for a vinyl chloride-lined steel pipe, characterized in that the thickness is greater than the thickness of the high-temperature vinyl chloride pipe immediately after the pipe is formed, and the length of the vinyl chloride pipe after the lining is longer than the length before the lining.

According to a second aspect of the present invention, there is provided a method for producing a heat-expandable vinyl chloride pipe for a vinyl chloride-lined steel pipe (invention 2), wherein the high-temperature vinyl chloride pipe discharged from the mold is introduced into a shaping cooling mold. A method for producing a heat-expandable vinyl chloride pipe for a vinyl chloride-lined steel pipe according to Invention 1, wherein the surface temperature of the vinyl chloride pipe is adjusted to a temperature equal to or higher than the softening temperature of the vinyl chloride resin and equal to or lower than + 40 ° C.

In the heat-expandable vinyl chloride pipe according to the present invention, the thickness of the pipe wall is larger than the thickness immediately after the vinyl chloride resin is discharged from the mold, and the length of the vinyl chloride pipe after the lining is equal to that before the lining. Because it is longer than the length, when expanded in the diameter direction by heating, when only the polyvinyl chloride pipe is heated without entering the steel pipe, the diameter increases, the axial direction shrinks, and the wall thickness decreases, but when it is put in the steel pipe When the diameter of the steel pipe does not increase any more because the steel pipe is obstructed, it will extend in the length direction by the thickness. The softening temperature in the present invention is defined by JIS
K 7206 refers to the Vicat softening temperature according to the Vicat softening temperature test method.

For example, when the gap between the steel pipe and the vinyl chloride pipe is set so as to reach the inner diameter of the steel pipe at an expansion rate of about 4%, when the heating is performed at a temperature higher than the expansion rate of 4%, the extra peripheral length becomes thicker. Although it increases in the direction and the axial direction, it hardly increases in the thickness direction structurally, and only extends in the axial direction.

In the production of a heat-expandable vinyl chloride tube,
In a conventional production method, a high-temperature vinyl chloride pipe (hereinafter, referred to as a parison) immediately after being discharged from a mold is cooled by blowing air with a blower or the like after leaving the mold. The surface temperature sometimes exceeded the softening temperature of the vinyl chloride resin + 40 degrees. Therefore, even if the shape at the temperature of the parison is memorized, the resin temperature is still sufficiently high. It is greatly elongated, and when heated, the shrinkage in the axial direction increases, and the shrinkage greatly in the axial direction.

On the other hand, in the production of the vinyl chloride pipe of the present invention, before the parison is introduced into the cooling shaping mold (hereinafter, referred to as forming tube), the parison is at or above the softening temperature of the vinyl chloride resin and + 40 ° C. Since the vinyl chloride pipe is cooled below, the length of the vinyl chloride pipe is small due to the take-up, and the wall of the pipe becomes thicker by the extent that the length does not increase when the diameter is reduced by the forming tube. Can be suppressed.

The surface temperature of the parison after cooling must be equal to or higher than the softening temperature of the vinyl chloride resin and equal to or lower than the softening temperature + 40 degrees. If the softening temperature of the vinyl chloride resin is higher than +40 degrees, the entire pipe is greatly stretched by the stretching effect of the take-off machine, and large shrinkage occurs when heated during lining. Further, if the temperature is lower than the softening temperature, although stretching does not occur, there is a possibility that the pipe wall is not deformed and wrinkled when the diameter is reduced by the forming tube.

The cooling method is not particularly limited, and includes, for example, a method using a spot cooler, a method using an internal cooling jacket, a method using internal air cooling, a method using internal spray cooling, a method using external spray cooling, and the like.

In practice, as an example, in the case of a heat-expandable vinyl chloride tube manufactured by a conventional method, the diameter expansion is 10% and the axial shrinkage is 7 to 10 when heated to the parison temperature.
%, But in the case of the one manufactured by the manufacturing method of the present invention, it can be expected that the expansion of the diameter is 10% and the shrinkage in the axial direction is 0.5 to 2%.

(Function) As described above, the heat-expandable vinyl chloride pipe of the present invention has a wall thickness greater than that of a parison, so that when the shape is restored by heating, the steel pipe is When the expansion in the radial direction due to is suppressed, it expands in the axial direction by the thickness.

In the invention 2, the surface temperature of the parison is reduced before the parison discharged from the mold is introduced into the forming tube in order to cause the vinyl chloride tube to exhibit the above-mentioned action at the time of heating. Since the cooling is performed at a temperature higher than the softening temperature and lower than the softening temperature of + 40 ° C., a heat-expandable vinyl chloride tube having the above-mentioned action can be obtained.

[0018]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows an example of an apparatus for producing a heat-expandable vinyl chloride pipe for a vinyl chloride-lined steel pipe according to the present invention.

The surface of the parison discharged from the mold 2 attached to the extruder 1 is cooled by the pre-cooling device 3 before being introduced into the forming tube 4 having an inner diameter smaller than the outer diameter of the parison. The PVC pipe that has exited the forming tube 3 passes through the cooling water 5 tank, is taken by the take-up machine 6, is cut into a predetermined length by the cutting machine 7, and becomes a heat-expandable PVC pipe P.

The surface temperature of the vinyl chloride pipe cooled by the pre-cooling device 3 is set to be higher than the softening temperature of the vinyl chloride resin and lower than the softening temperature +40 degrees. At this time, the surface temperature of the tube is lowered, but the temperature inside the tube wall of the tube is still higher than the softening temperature, so when the PVC tube is pulled in, it is tuned to a speed slightly higher than the extrusion speed of the parison. At the set take-off speed, the surface of the vinyl chloride tube does not extend, and only the inside of the tube wall flows. Therefore, when the diameter is reduced by the forming tube 4, the stretching in the length direction is suppressed, and the wall thickness is increased accordingly.

The vinyl chloride tube thus obtained is
When re-heated to return to the shape of the parison before cooling, it expands in the radial direction, but shrinks less in the length direction, and at the same time, returns to its shape so that the wall thickness becomes thinner, but it is put in a steel pipe. When the expansion in the radial direction is hindered, the thickness in the thickness direction does not decrease any further, but expands in the axial direction by an amount corresponding to the amount of resin, and the elongation length is larger than the contraction length, so that the whole is heated. It will elongate.

(Embodiment) Using the manufacturing machine shown in FIG. 1, the surface of the vinyl chloride tube was gradually cooled with a spot cooler so that the surface temperature of the vinyl chloride tube immediately before being introduced into the forming tube was 110 ° C. Was taken out by a drawing machine while being pre-cooled, and cut into a predetermined length to obtain a heat-expandable vinyl chloride tube. The thickness of the parison ejected from the mold was 2.55 mm, while the thickness of the vinyl chloride tube exiting the forming tube was 2.65 mm.

The obtained heat-expandable vinyl chloride tube (outer diameter 2
04mm, wall thickness 2.65mm, length 5500mm) is coated with a polyester-based adhesive on the outer surface, and the outer diameter is 216.3m
m, a wall thickness of 3.8 mm and a length of 5500 mm into a steel pipe, and heated from the center of the pipe toward both ends of the pipe using a V-type heating furnace at a heating temperature of ℃ to heat and expand the PVC pipe. It was bonded to a steel pipe to form a vinyl chloride-lined steel pipe.

The final length of the vinyl chloride tube after lining was 5530 mm, and the tube was elongated by 30 mm by heating. A total of 30m at both ends to make the product
m vinyl chloride tube was cut off.

Comparative Example A heat-expandable vinyl chloride tube was obtained in the same manner as in the example except that the surface temperature of the vinyl chloride tube immediately before being introduced into the forming tube was 140 ° C. The wall thickness of the obtained tube was 2.45 mm.

The obtained heat-expandable vinyl chloride tube (outer diameter 2
A vinyl chloride-lined steel pipe was formed in the same manner as in Example except that the thickness was 0.4 mm, the wall thickness was 2.45 mm, and the length was 5800 mm. The final length of the vinyl chloride tube after lining was 5600 mm, and the tube shrunk by 200 mm by heating. In order to make a product, a total of 10
A 0 mm vinyl chloride tube was cut and removed.

[0027]

As described above, by using the heat-expandable vinyl chloride pipe of the present invention, it is possible to use a short-sized vinyl chloride pipe at the time of manufacturing a lining pipe, and at the same time to contribute to the reduction of vinyl chloride resin waste. In addition to this, the possibility that air remains between the steel pipe and the vinyl chloride pipe at the pipe end is reduced.

In addition, the method of manufacturing the same simply adds a simple pre-cooling device to the same extruder as in the prior art, so that it is possible to easily manufacture a heat-expandable vinyl chloride tube having the above-mentioned effect.

[Brief description of the drawings]

FIG. 1 is an example of an apparatus for manufacturing a heat-expandable vinyl chloride pipe for a vinyl chloride-lined steel pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Extruder 2 Die 3 Pre-cooling device 4 Die for cooling shaping (forming tube) 5 Cooling water tank 6 Take-off machine 7 Cutting machine P Heat-expandable vinyl chloride pipe

Claims (2)

[Claims] 1. A vinyl chloride pipe used for a vinyl chloride-lined steel pipe obtained by inserting a vinyl chloride pipe coated with an adhesive on the outer surface into a steel pipe, heating the vinyl chloride pipe and bonding it to the inner face of the steel pipe. The thickness of the pipe wall is larger than the thickness of the high-temperature PVC pipe immediately after being discharged from the mold, and the length of the PVC pipe after lining is longer than the length before lining. Heat-expandable PVC pipe for PVC-lined steel pipe. 2. Before the high-temperature polyvinyl chloride pipe discharged from the mold is introduced into the shaping cooling mold, the surface temperature of the vinyl chloride pipe is set to a temperature not lower than the softening temperature of the vinyl chloride resin and not higher than + 40 ° C. The method for producing a heat-expandable vinyl chloride pipe for a vinyl chloride-lined steel pipe according to claim 1, wherein the adjustment is performed.