JPS6262730A - Manufacture of thermally recoverable tube - Google Patents

Abstract

PURPOSE:To easily obtain a thermally recoverable tube with no axial contraction by a method wherein a crosslinked plastic tube, round the outer peripheral surface of which a string-shaped heat-shrinkable body is helically wound at a desired pitch, is heated in a state that a slight inner pressure is applied to it. CONSTITUTION:Firstly, a crosslinking plastic tube 1 under the state that the slight inner pressure is applied to it is helically wound with a string-shaped heat-shrinkable body. Secondly, the resultant tube 1 under the state that both ends of its are open is introduced in a heating oven 9 in order to heat up to a temperature exceeding the crystalline melting point of the tube. Thirdly, in a state that the tube 1 is softened, the string-shaped body 2 starts to shrink itself so as to deform the helical pattern of the tube in contact with the body radically in a large way in order to form a helically and radically diminished portion. At the same time, the portion corresponding to the crest is radially pulled so as to diminish the redius and, after that, cooled with water at a pre-cooling device 10. Fourthly, immediately after being pre-cooling, the resultant tube together with the string-shaped body is introduced in a cooling water tank 3 in order to be cooled and solidified. Fifthly, the solidified tube is continuously taken up and housed on a take-up reel 15. Finally, by removing the string-shaped body, a thermally recoverable tube formed in a helically wavy shape is obtained. The radial contraction of the tube at its heat recovery is very small.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a heat-recoverable tube suitable for use in preventing and repairing internal corrosion of piping, particularly in water, gas, and chemical industrial plants, and for rehabilitation. It is related to.

(Conventional technology) Existing pipes used in water, gas, and chemical industry plants have deteriorated over time, causing deposits such as rust to accumulate on the inner surface of the pipes, leading to a decrease in flow rate, or due to aging of the pipes as a whole. Accidents such as leakage of water, gas, and chemicals sometimes occur, and depending on the type of chemicals mentioned above, they sometimes become major social problems.

In the case of water and gas pipes mentioned above, roads are often excavated and existing pipes replaced with new pipes, or repaired and rehabilitated, but such excavation is difficult due to recent traffic conditions, and Han University There are problems such as high costs, and there is an increasing need to repair and replace buried pipes in their original state. As a method for coating the inner surface of a buried pipe with anti-corrosion coating, a method has generally been proposed in which a thermal expansion tube is inserted into the buried pipe, expanded and brought into close contact with the inner surface of the pipe.

(Problem to be solved by the invention) Generally, in order to impart such thermal expandability to a tube, a cross-linked plastic tube is stretched in the axial direction at a temperature near the crystal melting point.
On the other hand, this is done by shrinking the tube in the radial direction, but in this case, it is difficult to achieve the desired diameter reduction unless a fairly large displacement is applied in the axial direction of the tube.On the other hand, the shrinkage in the axial direction becomes large during heat recovery. It has drawbacks such as reduced dimensional stability and poor adhesion to the inner surface of the tube.

In addition, particularly when working with long tubes, the large friction between the inner surface of the pipe and the outer surface of the tube makes it difficult to draw the tube, and the tube is easily damaged. Since such a tube utilizes the ability to expand in the radial direction due to contraction in the axial direction as described above, the recovery force in the axial direction is sufficiently large compared to its own weight and the frictional force with the pipe, and furthermore, Unless the previously set shrinkage allowance is forced into the piping path by some method, sufficient adhesion to the inner surface of the pipe cannot be expected, and this will cause a great deal of damage to the uniformity of the inner surface coating and workability in narrow spaces. There was a problem.

(Means for Solving the Problem) The inventors of the present invention have made extensive studies to eliminate the conventional drawbacks of such heat-expandable tubes, and as a result, they have found that it is extremely easy to insert and draw them into a piping path, and that they can be easily inserted and pulled into a piping path, and that they can be easily We have discovered a method for manufacturing a heat-recoverable tube that has minimal shrinkage in the direction of the tube and can extremely easily cover the inner surface of the tube in close contact with the inner surface of the tube. The cross-linked plastic tube is heated under a slight internal pressure that allows the cross-linked plastic tube to maintain its shape when heated to heat-shrink the heat-shrinkable string, and the cross-linked plastic This method of manufacturing a heat-recoverable tube is characterized by forming a spiral diameter-reduced portion displaced in the radial direction in the tube, and then removing the heat-shrinkable string-like body.

In the present invention, the crosslinkable crystalline polymer for obtaining the crosslinked plastic tube is one of commonly used polyolefin resins such as polyethylene, polyethylene, ethylene-vinyl acetate copolymer, and ethylene-ethylene acrylate copolymer. , or a mixture of two or more thereof, and a mixture of such a crystalline polymer and an amorphous thermoplastic resin or rubber can also be used.

Then, a tube made of such a crosslinkable polymer or a two-layer tube in which these polymers are used as an insulating outer layer and a conductive inner layer made of a similar crosslinkable polymer mixed with a conductive substance such as carbon black is obtained, and this is A crosslinked plastic tube may be obtained by crosslinking by any one of silane crosslinking, electron beam crosslinking, or chemical crosslinking.

In these cases, the degree of crosslinking is 10% to 80% in terms of gel fraction.
is desirable.

Next, the heat-shrinkable string-like body is selected from the same materials as the crosslinkable polymer, extruded into a string-like body, cross-linked in the same manner as above, and then heated to a temperature near the crystal melting point. It is made by stretching in the longitudinal direction at a desired stretching ratio and then cooling and solidifying it in that state to impart heat shrinkability. The cross-sectional shape of this heat-shrinkable string-like body may be any shape, such as circular, oval, square, or rectangular, and is not particularly limited.

The degree of crosslinking is preferably the same as or higher than the above crosslinked plastic tube in terms of shrinkage stress during heat shrinkage, and the shrinkage rate in the axial direction is determined by When the spiral winding pitch of the string-like body is large, it is necessary to increase the displacement of the troughs in order to obtain the desired diameter reduction effect on the crests by shrinking the helical waveform into the troughs. It is necessary to increase the shrinkage rate of the shaped body. Conversely, when the helical winding pitch is small, the desired diameter reduction effect on the peaks can be obtained even if the displacement of the helical waveform toward the valleys is not so large, so there is no need to increase the shrinkage rate so much. A particularly preferable shrinkage rate of the heat-shrinkable string in the axial direction is 20% to 80%.

Here, the spiral winding of the heat-shrinkable string around the outer circumferential surface of the cross-linked plastic tube may be done in advance in a separate process, or may be done while simultaneously being wrapped one time during heat forming.
Either method can be adopted.

The pitch at the time of winding is preferably 20% or more and 70% or less of the outer diameter of the cross-linked plastic tube, but it should be adjusted appropriately in relation to the shrinkage rate in the axial direction so that the diameter can be reduced into a spiral waveform. It is preferable to select O. FIG. 1 is an explanatory diagram of one embodiment of the method of the present invention. A supply reel (Fig. 2) containing a long winding of a heat-shrinkable string (2) spirally wound around a cross-linked plastic tube (1) to which internal pressure has been applied in advance (Fig. 2). 6), and both ends of the cross-linked plastic tube (1) are kept open so that the inside pressure is equal to the atmospheric pressure, and the tube is pulled out through the guide roll (7). (The speed of II7 is synchronized and the tube is introduced into the heating furnace (9) at a constant speed so that it is heated to a temperature above the desired crystal melting point. The cross-linked plastic tube (1) is softened. In this state, the heat-shrinkable string-like body (2) starts to contract, and the spiral portion of the tube that is in contact with it is largely displaced in the radial direction to form a spiral diameter-reduced portion. The corresponding part is dragged in the radial direction due to the large displacement of the trough and is reduced in diameter. is cooled and solidified.Next, Gytrol (In(1)
2'), and is continuously wound up and stored in a take-up reel (reel). Fig. 3 shows a helical diameter-reduced portion whose diameter is reduced by the above-mentioned contracted string-like body (2). If the tube (3) is shown and the string-like body is removed, the fourth
As shown in the figure, a helically corrugated heat-recoverable tube according to the present invention is obtained. In this case, the outer diameter of the cross-linked plastic tube (1) is the same as or slightly larger than the inner diameter of the pipe that is the opposite of the inner coating, and after diameter reduction, the outer diameter of the crest of the spiral waveform is larger than the inner diameter of the pipe. It is preferable to appropriately set the shrinkage rate and winding pitch of the heat-shrinkable string so that the heat-shrinkable string becomes slightly smaller.

(Function) In the present invention, a heat-shrinkable string is spirally wound at a desired pitch around the outer peripheral surface of a cross-linked plastic tube to which a slight internal pressure is applied, and this is heated to form the heat-shrinkable string. Since the string-like body is heat-shrinked, the cross-linked plastic tube does not undergo any significant shrinkage in its axial direction.

Therefore, the shrinkage of the tube in the axial direction during heat recovery is extremely small.

(Example) The present invention will be explained in more detail with reference to Examples below.

Example 1 A tube with an outer diameter of 53 mm and a wall thickness of 2.0 mm was extruded from silane-modified low-density polyethylene and treated with hot water in a conventional manner to obtain a cross-linked polyethylene tube with a gel fraction of 75%. Next, a string-like body with an oval cross section is extruded from the same material, cross-linked in the same manner as above, and stretched in the axial direction (magnification: 1
．． 7) A heat-shrinkable string-like body with an oval cross section and an outer diameter of 3×4IW1 was obtained. This heat-shrinkable string-like body was pre-wound spirally at a pitch of 25 m around the outer circumferential surface of the cross-linked tube, and the cross-linked tube was continuously heated in a heating furnace at 150°C with an internal pressure of 0.05 kg/ffl applied. Shape while heating,
The tube was immediately solidified by water cooling and reduced in diameter into a spiral waveform. Next, by removing the heat-shrinked string-like body, a heat-recoverable tube with a helical pitch of 25 ugliness, an outer diameter of about 33 ridges at the troughs, and an outer diameter of about 49 corners at the peaks are uniformly displaced and reduced in diameter over the entire length. Don't get it. This heat-recoverable tube has a length of 50 mm.
When the tube was cut into pieces of 0 sn and heated at 150° C. for 20 minutes, the crosslinked tube had an outer diameter of 53 mm and a length of 500 mm, resulting in a crosslinked tube that did not shrink in the axial direction.

Example 2 A 1.5 m thick insulating outer layer made of the same material as in Example 1, and a 0.5 mm thick conductive inner layer blended with conductive carbon black (15% by weight) of the same material to impart conductivity. A tube with a thickness of 2.0 mm and an outer diameter of 53 mm was extruded and subjected to the same crosslinking treatment to obtain a crosslinked tube with a gel fraction of 75%. The same heat-shrinkable string material as in Example 1 was wound around the outer periphery of this cross-linked tube in a spiral shape at a pitch of 20 mm, and was continuously molded under the same heating conditions, solidified by water cooling, and heat-shrinked into a spiral wave shape. Got the tube. The string-like body was removed to obtain a heat-recoverable tube whose diameter was reduced evenly between the outer diameter of the troughs of the helical waveform of about 32 and the outer diameter of the peaks of about 48. . This heat-recoverable tube was cut into lengths of 50 (1 m) and heat-treated in the same manner to obtain a completely heat-recovered crosslinked tube with no shrinkage in the axial direction.

(Effects of the Invention) As described above, the present invention provides a method of spirally winding a heat-shrinkable string at a desired pitch around the outer peripheral surface of a crosslinked plastic tube.
This is heated with a slight internal pressure applied inside the cross-linked plastic tube to heat-shrink the heat-shrinkable string-like body, thereby forming a spiral diameter-reduced portion displaced in the radial direction in the cross-linked plastic tube. This has the effect that it is very easy to obtain a heat-recoverable tube without axial shrinkage, which is given thermal expandability by displacement and diameter contraction in only the radial direction of the tube due to the heat-shrinkage stress of the string-like body.

The surface of the tube has a spiral waveform, which significantly reduces the frictional resistance with the inner surface of the tube, making it easier to pull long products into narrow spaces, and significantly improving the coverage of the inner surface of the pipe during heat recovery. The effects of its industrial use are extremely large.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the manufacturing process of the heat-recoverable tube of the present invention;
Figure 2 is an explanatory diagram of a cross-linked plastic tube made of a heat-shrinkable string wound spirally, Figure 3 is an explanatory diagram of a tube formed into a spiral waveform, and Figure 4 is an illustration of the final heat-recoverable tube. It is an explanatory diagram. 1...Crosslinked plastic tube, 2...Heat-shrinkable string-like body, 3...Spiral corrugated tube.

Claims (3)

[Claims] (1) A heat-shrinkable string is spirally wound around the outer peripheral surface of a cross-linked plastic tube at a desired pitch, and heated while applying a slight internal pressure to the cross-linked plastic tube. 1. A method for manufacturing a heat-recoverable tube, comprising heating and shrinking a string-like body to form a radially displaced spiral diameter-reduced portion in the crosslinked plastic tube, and then removing the heat-shrinkable string-like body. (2) Heat recovery properties as set forth in claim 1, wherein the heat-shrinkable string-like body is made of cross-linked plastic, and has a gel fraction of 10% or more and a shrinkage rate of 20% or more. Method of manufacturing tubes. (3) When winding the heat-shrinkable string body spirally around the outer circumferential surface of the cross-linked plastic tube, the winding pitch is set to 20% or more of the outer diameter of the cross-linked plastic tube;
2. The method of manufacturing a heat-recoverable tube according to claim 1, wherein the length is 0% or less.