JPH10146890A - Production of heat-shrinkable tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize the irregularity of residual stress at the time of stretching into a star shape. SOLUTION: A heat-shrinkable tube material 21 stretched into a star shape in order to obtain a high shrinkage factor is reheated in such a state that a mandrel 25 is loosely inserted into the heat-shrinkable tube material 21 to be shrunk to be closely brought into contact with the outer periphery of the mandrel 25 and allowed to stand at predetermined temp. for a definite time to uniformize residual stress at a time of the molding into the star shape. When the tapered mandrel 25 is inserted to be reheated, a tapered heat-shrinkable tube 21 can be formed to become easy to detach from the mandrel 25 and the mandrel and the tube are fitted in a telescopic state to enhance space efficiency.

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 heat-shrinkable tube having a high shrinkage rate and having no irregularities on the surface when thermally shrunk.

[0002]

2. Description of the Related Art One application of a heat-shrinkable tube is, for example, coating a conductor connection portion of a rubber-plastic insulated cable 1 whose cross section is shown in FIG. This insulated cable 1
Outside the center conductor 2, the inner semiconductive layer 3 and the insulator 4
And the outer semiconductive layer 5 are formed concentrically in this order. In such a rubber-plastic insulated cable 1, when laying a long line, the cable length is restricted in manufacturing, transportation, and laying.
Cables need to be connected on site.

As shown in FIG. 12, the cables are connected on site by removing the coatings on the ends of both cables 1 and 1 to be connected, exposing the conductors 2 and abutting the end faces of each other. After the conductor connection sleeve 6 is put on the outer circumferences of the two conductors 2 in a compressed state and connected by compression, an inner semiconductive layer similar to the cable 1 is formed outside the conductor connection sleeve 6. As a method therefor, there is a method in which the semiconductive tube 7 for inner conduction is covered, or an uncrosslinked semiconductive tape is wound to a predetermined thickness, and this is heated and molded.

Further, an insulating tape made of an uncrosslinked thermoplastic resin is wrapped around the inner conductive semiconductive tube 7 in multiple layers to form an insulating layer 8 as a substitute for the insulator 4 of the cable 1. An outer semiconductive tube 9 instead of the outer semiconductive layer 5 is provided on the outer side. In this case, similarly to the inner semiconductive layer, a rubber-based heat-shrinkable tube for surface shaping is used. Is used. The inner conductive semiconductive tube 7 and the outer conductive semiconductive tube 9 are previously covered on the outer periphery of one of the cables 1 at the time of cable connection, and the conductor connection sleeve 6 is crimped. The outer conductive semiconductive tube 9 is moved to the outside of the insulating layer 8 after the insulating layer 8 is formed, and is contracted by being moved to the outside of the connection sleeve 6 and contracted to adhere to the outer periphery. Close to the outer periphery.

[0005] Therefore, it is necessary to use a material having a high shrinkage rate, but it has been considered difficult to manufacture a semiconductive plastic resin having a shrinkage rate of 60% or more.

As a method for expanding the diameter of the heat-shrinkable tube material, a high-pressure gas is injected into the tube material while the tube material for the heat-shrinkable tube is heated to expand the tube material, and the expanded state is cooled and expanded. A method of fixing to a diameter state is conceivable. However, in the method of injecting high-pressure gas, when the thickness of the tube material is not uniform and there is uneven thickness, the thin portion expands first, and the thick portion does not expand. As a result of the increased wall thickness, when the diameter expansion ratio was increased, the tube was broken during the diameter expansion, so that a tube with a high shrinkage ratio could not be manufactured.

Therefore, the present applicant has already filed an application for a manufacturing method capable of manufacturing a relatively long heat-shrinkable tube which can expand the diameter almost uniformly even if there is slight unevenness of the wall thickness. No. 6-290434).

The present invention relates to a method for manufacturing a heat-shrinkable tube which is reduced in diameter by being heated to a predetermined temperature or higher. A tube material having a circular cross section is placed on the outer periphery of a heating mandrel so as to be in close contact with the tube. At three or more points on the outer peripheral side of the material that divide the circumference substantially equally, the expansion control restricts the movement of the contact point by contacting the outer surface of the tube when the tube expands in the expanding direction. A member is provided, and in a state where the tube material is in contact with the diameter expansion regulating member, a portion of the tube material deviating from the diameter expansion restriction member is radially extended by the diameter expanding means while being heated by the heating mandrel. Then, after forming into a so-called star shape, the state of the star shape cooled and extended is fixed.

FIG. 13 shows an example of a star-shaped heat-shrinkable tube manufactured by the above-mentioned manufacturing method. This heat-shrinkable tube 11 has six star-shaped protrusions 11a projecting in the radial direction. In this case, the expansion ratio of the heat-shrinkable tube material with respect to the circumference of the heat-shrinkable tube material before the expansion is increased, and accordingly, the shrinkage ratio of the heat-shrinkable tube 11 after the expansion is increased as the expansion ratio is increased.

FIG. 14 shows a portion in which the heat-shrinkable tube has the largest shrinkage when the heat-shrinkable tube manufactured by the above-described manufacturing method is used for coating the connection portion of the cross-linked polyethylene insulated cable 12, that is, the cable 12 has the highest shrinkage. FIG. 5 is a cross-sectional view showing both side portions of the connection portion of FIG. That is, the star-shaped heat-shrinkable tube 11 is loosely fitted on one of the outer circumferences of two cable terminals for cable connection in advance (the state shown by the two-dot chain line in FIG. 14). The work of connecting the conductor 12a and the like is performed. After connecting and insulating the conductors 12a, the heat-shrinkable tube 11 is moved to the outer periphery of the connection portion. At this time, since the outer diameter of the connecting portion is larger than the outer diameter of the cable, the diameter of the heat-shrinkable tube 11 is increased by extending the bellows-like protruding portion 11a in the circumferential direction, so that the outer circumference of the connecting portion is expanded. Put on.

When the heat-shrinkable tube 11 is uniformly heated by a heating means such as a gas burner in a state where the connection portion of the cable 12 and the portion adjacent to the connection portion are covered by the heat-shrinkable tube 11,
Shrinks and adheres closely to the outer periphery of the connection portion, and further shrinks to adhere closely to the outer periphery of the cable of an adjacent portion having a smaller diameter than the connection portion (see FIG. 12). Thus, the connection portion and its adjacent portion are air-tight. To complete the connection work.

[0012]

However, in the above-described conventional heat-shrinkable tube having a high shrinkage ratio, when heated and shrunk, the groove 11 which is continuous in the axial direction is formed on the tube surface.
b had occurred. When the heat-shrinkable tube material 12 is extended in a star shape, the concave groove 11b
2 is formed at a contact portion with a diameter-increasing restricting member which is in contact with a plurality of positions on the outer peripheral surface and restricts movement in the diameter-increasing direction. Therefore, since the elongation of the portion of the heat-shrinkable tube material 11 that has been in contact with the diameter-increasing regulating member is limited, a difference occurs in internal stress between the heat-shrinkable tube member 11 and the portion that is not in contact with the heat-shrinkable tube member 11. It appears that the difference appears as a difference in residual stress.

Therefore, when the heat-shrinkable tube 11 is shrunk to its shrinkage limit, that is, to the state before the diameter expansion, the concave groove 11b disappears, but when used, it is used without shrinking to the shrinkage limit. A concave groove 11b is generated. Therefore, conventionally, the heat shrink tube 1
After contracting 1, the edge of the groove 11b formed on the surface must be cut to eliminate the step, and there is a problem that this cutting work is troublesome.

The present invention has been made in view of the above circumstances, and is intended to produce a heat-shrinkable tube which has a high shrinkage ratio upon heat shrinkage and which can obtain a smooth outer peripheral surface without forming a concave groove on the tube surface. It is intended to provide a way.

[0015]

As a means for solving the above-mentioned problems, the present invention provides a method for manufacturing a heat-shrinkable tube which is reduced in diameter by being heated to a predetermined temperature or higher. While heating the heat-shrinkable tubing, the heat-shrinkable tubing is extended radially at the three or more points that divide the circumference of the heat-shrinkable tubing while restricting the movement in the radially expanding direction. After being cooled, the stretched state is once fixed by cooling, and further, a mandrel having a circumferential length slightly shorter than the inner circumferential length of the heat-shrinkable tube material is inserted inside the stretched heat-shrinkable tube material. Then, in this state, the heat-shrinkable tube material is heated again, left at a predetermined temperature for a certain time, cooled, and then removed from the mandrel.

In the method for manufacturing a heat-shrinkable tube, a mandrel having a tapered shape whose diameter gradually increases from one end to the other end may be used.

Therefore, as described above, the heat-shrinkable tubing material having a circular cross section is heated, and the heat-shrinkable tubing material is restricted from moving in the radially expanding direction at three or more points equally dividing the circumference. When the unregulated portions are each extended in the radial direction, the heat-shrinkable tubing is formed in a so-called star shape. Next, once cooled,
The star-shaped heat-shrinkable tube material was expanded in the diameter-expanding direction, and a mandrel having a circumference slightly shorter than the inner circumferential length of the heat-shrinkable tube material was inserted inside the heat-shrinkable tube material. It fits with a gap between the inner surface of the heat-shrinkable tube material.

When the heat-shrinkable tubing material is reheated to a predetermined temperature in a state where the heat-shrinkable tubing material is fitted with a gap outside the mandrel, the heat-shrinkable tubing material fixed in the expanded state is Since the tube material thermally shrinks in a state where it is not restrained at all, the dispersion of the residual stress in each portion of the tube when the tube material is extended in a star shape is averaged. Therefore, a heat-shrinkable cable having a circular cross section, a high shrinkage rate and a substantially uniform residual stress can be obtained by cooling the heat-shrinkable tubing material that has contracted and adhered to the surface of the mandrel and then removed from the mandrel.

Further, in the method for producing a heat-shrinkable tube, when the expanded heat-shrinkable tube material is reheated,
If the heat-shrinkable tube is formed on the outside of a tapered mandrel whose diameter gradually increases from one end to the other end and heated, the heat-shrinkable tube can be formed in a tapered shape, and can be easily removed from the mandrel. Further, since the obtained heat-shrinkable tube has a taper, it can be fitted in a nested manner, and the space efficiency at the time of stocking, transporting or working is improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a heat-shrinkable tube according to the present invention will be described below with reference to FIGS.

FIG. 4 shows a state in which a heat-shrinkable tube material 21 as a material is attached to a manufacturing apparatus 20 used for manufacturing a heat-shrinkable tube by the manufacturing method of the present invention. A heat pipe type heating mandrel 22 having a heat-shrinkable tube material 21 provided on the outside thereof, and respective ridge portions (movement restricting portions) 23b at positions where the outer circumference of the heating mandrel 22 is equally divided into six. An expansion guide member 23 arranged in a star-shaped cross section with the six aluminum alloy angle members 23a formed so as to cover the outer periphery of the expansion guide member 23 and provided concentrically with the heating mandrel 22. , Heat shrink tubing 2
1, and an expansion control pipe 24 for preventing adhesion of dust and the like. Further, the expansion guide member 23 and the expansion restriction pipe 24 are provided detachably.

The heating mandrel 22 is provided with a wick (not shown) on the inner peripheral surface of a container made of a metal pipe made of copper or copper alloy having excellent heat conductivity.
A heat pipe function is provided by enclosing only a condensable working fluid therein, and one end thereof is a heating / cooling unit that receives heat during heating and cools during cooling.

When the heat shrinkable tubing 21 is extended by the manufacturing apparatus 20, the heating mandrel 22 is inserted inside the heat shrinkable tubing 21.
When the heating / cooling portion of the heating mandrel 22 is heated after being disposed at the center surrounded by the expansion guide member 23, the entire heating mandrel 22 is uniformly heated by the soaking characteristics of the heat pipe. The heat-shrinkable tube material 21 covered on the outside of the mandrel 22 is heated.

When the heat-shrinkable tube material 21 reaches the melting softening point, the air compressed by the compressor is removed from the surface of the heating mandrel 22 and the heat-shrinkable tube material 2.
1 and press-fitted into the heat-shrinkable tubing 21
Begins to expand. At this time, since the ridge portions 23b of the six angle members 23a constituting the expansion guide member 23 are arranged close to the position where the outer periphery of the heat-shrinkable tube member 21 is substantially equally divided by six, the heat that expands is formed. Shrink tube material 2
1 is in contact with the ridge line portion 23b and is supported in a state where its outer peripheral surface is divided into approximately six equal parts in the circumferential direction.

[0025] Therefore, since the heat-shrinkable tubing material 21 expands in each of the six equally divided parts, the six equally-divided parts almost uniformly expand even if the thickness of the heat-shrinkable tube material 21 is uneven (FIG. 5).

The heat-shrinkable tube material 21 that further expands is guided by the adjacent angle members 23a, 23a, and expands in a wedge shape, and expands until it comes into contact with the inner peripheral surface of the expansion control pipe 24. Is formed into a star shape having a peak 21a.

At the time of molding into a predetermined star shape, the pressure inside the heat shrinkable tube 21 is kept constant by the compressor, and the heating / cooling portion of the heating mandrel 22 is positioned upward by a blower or the like with the heating mandrel 22 positioned above. Cooling is performed by blowing cold air to fix the shape of the star-shaped heat-shrinkable tube 21.

After sufficient cooling, the internal pressure of the heat-shrinkable tube 21 is reduced, the expansion control pipe 24 and the expansion guide member 23 are removed, and the heating mandrel 22 is taken out. 2
If 1 is removed, a heat-shrinkable tube material 21 formed in a star-shaped cross section having six peaks and having an extended outer peripheral length is obtained (see FIG. 1).

Next, a heat-shrinkable tubing material 21 fixed in the extended state is placed in a mandrel having a circular cross section with a slightly shorter circumferential length than the inner circumferential length of the star-shaped heat-shrinkable tubing material 21. Then, the heat-shrinkable tube material 21 is heated again in this state and left at a predetermined temperature for a certain time.

At this time, as a means for heating the heat-shrinkable tube material 21, a cylindrical mandrel 25 covered with the heat-shrinkable tube material 21 is put in a heating furnace or a thermostat, or There is a method in which a sheet-shaped heater is wound around the outside and heating is performed from the outside, a method in which a heater is built in the mandrel 25 and heating is performed from the inside, a method in which the mandrel itself is heated as a heat pipe, and the like. It can be heated simultaneously from inside and outside.

When the star-shaped heat-shrinkable tube material 21 is reheated to a predetermined temperature, it shrinks and comes into close contact with the outer periphery of the mandrel 25. At this time, since the heat-shrinkable tubing 21 is loosely fitted on the outer periphery of the mandrel 25 and is not restrained at all, the entire heat-shrinkable tubing 21 is stretched when contracted, and stress unevenness is averaged. , And mandrel 2
5 is left at a predetermined temperature for a certain period of time in a state in which the residual stress is kept in close contact with the outer periphery of 5, thereby uniformizing the residual stress.

After a certain period of time, the heat-shrinkable tube material 21 is cooled and fixed in shape in a state of being closely attached to the outer periphery of the mandrel 25.
By removing 1 from the mandrel 25, a heat-shrinkable tube 26 with uniform residual stress and a circular cross section as shown in FIG. 6 is obtained.

In the heat-shrinkable tube 26 manufactured by the method of this embodiment, the heat-shrinkable tube material 21 is heated, expanded once, and then re-heated to uniform the residual stress. When the whole shrinks evenly,
No groove or the like due to a partial difference in the amount of shrinkage occurs, and the surface shrinks smoothly.

Therefore, if the connection portion of the cable is covered by using the heat-shrinkable tube 26 manufactured by the method of this embodiment, the connection portion of the cable and the cable portion continuous on both sides thereof are airtight due to the high shrinkage. , And can be covered in a smooth state with no grooves or the like on the surface.

In the above-described embodiment, the case where the cylindrical mandrel 25 having a constant thickness is inserted into the expanded heat-shrinkable tube member 21 formed in a star shape and reheated is described. However, as shown in FIG. 9, the tapered section gradually increases in diameter from the upper end to the lower end, and the circumference of the large diameter portion is slightly shorter than the inner circumference of the star-shaped heat-shrinkable tube material 21. If the circular mandrel 35 is inserted and reheated, the residual stress is made uniform, and at the same time, it contracts and comes into close contact with the outer periphery of the tapered mandrel 35. Therefore, after cooling in this state, if it is detached from the mandrel 35, as shown in FIGS. 8 and 9, a tapered heat-shrinkable tube 36 having a circular cross section whose diameter gradually increases from one end to the other end is obtained.

Therefore, when the heat-shrinkable tubing material 21 that has been expanded into a star shape using the tapered mandrel 35 is reheated, even if the heat-shrinkable tubing material 21 that shrinks adheres to the mandrel 35, the heat-shrinkable tubing material 21 does not shrink. Just moving the tube 36 slightly from the large-diameter side to the small-diameter side causes the entire heat-shrinkable tube 36 to be peeled off from the surface of the mandrel 35, so that the heat-shrinkable tube 36 has a smaller diameter than when the cylindrical mandrel 25 is used. Can be easily removed.

Further, since the plurality of heat-shrinkable tubes 36 can be nested by forming the heat-shrinkable tubes 36 in a tapered shape, a large number of heat-shrinkable tubes 36 can be accommodated in a space slightly longer than the length of one heat-shrinkable tube 36. Since the shrinkable tubes 36 can be stacked and stored, and the space efficiency is excellent, the transfer efficiency is improved as compared with the cylindrical heat shrinkable tubes 26, and the cylindrical heat shrinkable tube is stored in the same space when stocking. Many times the volume of the shrink tube 26 can be stored.

When the heat-shrinkable tube 36 is applied to, for example, a heat-shrinkable tube for covering the connection portion 37a of the power cable 37, the heat-shrinkable tube 36 must be connected before the power cables 37 are connected to each other. 2 including spare
It is necessary to insert the heat-shrinkable tubes 36, 36 into the outer periphery of the power cable 37 in advance, but if the heat-shrinkable tubes 36 are formed in a tapered shape as shown in FIG. The heat shrinkable tubes 36, 36 can be nested. Therefore, the space occupied can be reduced as compared with the case where the cylindrical heat-shrinkable tube 26 is used, and the workability can be improved.

When the heat-shrinkable tube 36 is applied to the inner conductive semiconductive tube and the outer conductive semiconductive tube of the power cable 37, the power cables 37, 37
Before connecting the conductors at both ends of the power cable 37, two heat-shrinkable tubes 36, 36 serving as an inner conductive semiconductive tube and an outer conductive semiconductive tube are loosely inserted into the outer periphery of one power cable 37. If it is necessary to form the semiconductive tube for inner conduction and the semiconductive tube for outer conduction in a tapered shape, it can be nested and loosely inserted around the cable. improves.

In the above embodiment, the case where the heat-shrinkable tube is formed in a star-shaped cross section having six peaks has been described, but a star-shaped cross section having seven or more peaks, or four or three peaks has been described. When formed in a heat-shrinkable tube having a star-shaped cross section having a plurality of peaks, substantially the same operation and effect as in this embodiment can be obtained. In addition, even when the lengths of the star-shaped peaks are not the same and a plurality of peaks having different lengths are formed, substantially the same operation and effect can be obtained.

Further, in the above embodiment, in the manufacturing apparatus 20 for the heat-shrinkable tube 26, the back surface (the 2nd angle) of the aluminum alloy angle member 23a constituting the expansion guide member 23 arranged in a star-shaped cross section. If a sheet-shaped heater or the like is provided on the surface between the sides) to heat each of the angle members 23a, when the heat-shrinkable tube material 21 is stretched and formed into a star shape, the heat-shrinkable tube material 21 is formed. Since the fluidity of the material in contact with these angle members 23a is increased, the entire heat-shrinkable tube material 21 can be almost uniformly extended, and a heat-shrinkable tube having a uniform wall thickness can be manufactured. .

[0042]

As described above, according to the method for manufacturing a heat-shrinkable tube of the present invention, the circumference of the heat-shrinkable tube is extended inside the star-shaped heat-shrinkable tube from the inner circumference of the heat-shrinkable tube. Insert a slightly shorter mandrel and reheat the heat-shrinkable tubing in this state, so that the heat-shrinkable tubing heated to a specified temperature or more shrinks until it adheres to the surface of the mandrel, and remains at a specified temperature even after it adheres During the standing time, unevenness of the residual stress when the star is extended is averaged, so that a heat-shrinkable tube having a uniform residual stress can be manufactured.

When the expanded heat-shrinkable tube material is reheated, if the tapered mandrel is used, the heat-shrinkable tube can be formed in a tapered shape, and can be easily removed from the mandrel. In addition, the taper of the heat-shrinkable tubes can be used to fit in a nested manner, so that the space efficiency during stocking or transportation can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional front view showing an example of a heat-shrinkable tube manufactured by a manufacturing method of the present invention.

FIG. 2 is a cross-sectional front view showing a state where a mandrel is inserted into the heat shrinkable tube of FIG.

FIG. 3 is a cross-sectional front view showing a state after reheating the heat-shrinkable tube of FIG. 1 with a mandrel inserted.

FIG. 4 is a cross-sectional front view showing a state where a heat-shrinkable tube material is set in a manufacturing apparatus.

FIG. 5 is a sectional front view showing an expansion process of the heat-shrinkable tube material.

FIG. 6 is a sectional front view of a heat-shrinkable tube completed by reheating.

FIG. 7 is a sectional side view showing a state in which a cylindrical mandrel is inserted and reheated.

FIG. 8 is a plan view showing a tapered heat-shrinkable tube.

FIG. 9 is a sectional side view showing a state where a tapered mandrel is inserted and reheated.

FIG. 10 is an explanatory diagram showing a case where a tapered heat-shrinkable tube is used for covering a cable connection portion.

FIG. 11 is a sectional view of a rubber / plastic insulated cable.

FIG. 12 is a partial cross-sectional side view showing a connection portion of a rubber / plastic insulated cable.

FIG. 13 is a cross-sectional front view showing a conventional star-shaped heat-shrinkable tube.

FIG. 14 is a sectional front view showing a state in which a conventional star-shaped heat-shrinkable tube is heat-shrinked.

[Explanation of symbols]

20: Manufacturing equipment 21: Heat-shrinkable tube material, 23a
... Angle material, 25 ... Cylindrical mandrel, 26 ...
... heat shrinkable tube (completed product), 35 ... tapered mandrel, 36 ... tapered heat shrinkable tube (completed product), 37 ... cable, 37a ... connection part.

Claims (2)

[Claims] In a method for manufacturing a heat-shrinkable tube which is reduced in diameter by being heated to a predetermined temperature or higher, a heat-shrinkable tube having a circular cross section is heated, and the circumference of the heat-shrinkable tube is equalized. At three or more points, the unregulated part is extended in the radial direction while restricting the movement in the radial direction, and then cooled and fixed in the extended state, and then further extended. A mandrel having a circumference slightly shorter than the inner circumference of the heat-shrinkable tubing was inserted inside the heat-shrinkable tubing, and the heat-shrinkable tubing was heated again in this state and left at a predetermined temperature for a predetermined time. Then, after cooling, it is detached from the mandrel. 2. The method according to claim 1, wherein the mandrel has a tapered shape whose diameter gradually increases from one end to the other end.