JPS6147694B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-shrinkable tube, particularly a thick heat-shrinkable tube.

Various methods have been devised and put into practical use for manufacturing heat-shrinkable tubes using cross-linked plastic tubes as raw materials. Because of their small size, they are generally easily manufactured in series. On the other hand, in the case of thick molded heat-shrinkable tubes with a diameter of several centimeters or more, the variation in lengthwise expansion and contraction that occurs during heat-shrinking during use is large, which poses a practical problem.
Generally, they are manufactured in standard lengths of about 1 to 5 m.

The methods for manufacturing thick heat-shrinkable tubes from such material tubes can be roughly divided into two methods: multiple rods are inserted into the tube, heated uniformly, and then each rod is moved in a radial direction to expand the diameter. The mechanical stretching method involves forming a polygonal column tube, inserting it onto a guide pipe of a predetermined size, and reheating and shrinking it to form a predetermined heat-shrinkable tube. The tube is inserted into a guide pipe with the same dimensions, one end is closed, a gas injection valve is attached to the other end, pressurized gas is injected into the tube, the tube is brought into close contact with the inner surface of the guide pipe, and the tube is cooled and solidified. There is a gas pressure expansion method that molds a shrink tube. However, in the former case, no consideration is given to controlling the expansion/contraction change in the length direction, and therefore, there is a drawback that the change in the length direction is large and the variation is large when heat shrinking is used. It was hot. Also, even in the latter case,
Due to variations in material thickness and heating temperature, or variations in the frictional force during the expansion process between the guide pipe and the tube that regulates expansion, the degree of expansion of the tube may vary, resulting in variations in the circumferential and longitudinal directions. This tends to result in non-uniform elongation.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to eliminate the above-mentioned drawbacks of the prior art and, in particular, to provide a method for manufacturing a heat-shrinkable tube that can reliably control dimensional changes in the longitudinal direction during use.

The gist of the present invention is to use a cross-linked plastic tube with known shrinkage characteristics obtained by expanding uniformly into a polygonal or circular shape as a material, to cover the repair pipe, and to continuously measure the length. At the same time, the tube is rotated to uniformly heat and shrink with a heater, and when the change in the length direction of the tube reaches a predetermined value, uniform rapid cooling is performed from the inside and outside of the tube. Embodiments of the present invention will be described below with reference to the drawings by manufacturing a heat-shrinkable tube that always has predetermined shrinkage characteristics within a range of conditions.

FIG. 1 is a diagram for explaining the preparation of a sample and its basic characteristics in order to understand the basic characteristics of a material tube before manufacturing a heat-shrinkable tube according to an embodiment of the present invention. teeth,
Generally, a material tube formed by extrusion molding is cut to a predetermined length L, and the inner diameter of this sample is indicated by D, and the wall thickness is indicated by T. Since the sample in this initial state has orientation in the length L direction,
In order to prevent variations in the results obtained in the subsequent process, preliminary processing is performed to eliminate the distortion by heat aging. Then, Fig. 1b
As shown in , sample B has an inner diameter d stretched to about 2 to 4 times the inner diameter D, which is the stretching region during actual manufacturing, without changing the length l ₁ (i.e., l ₁ = L),
As shown in Fig. 1c, the inner diameter d is similarly set to 2 to 4
A sample C is prepared which has been stretched to about twice the same size. At this time, the length l ₂ of the sample C becomes shorter than the length L. Further, in the conventional manufacturing method, the diameter-enlarged tube is generally located between sample B and sample C.

The relationship between the change in the length direction and the residual shrinkage rate when heat-shrinking samples B and C was found.
The results shown in FIG. 1d were obtained. In the figure, the length expansion/contraction ratio on the vertical axis is based on the lengths l ₁ and l ₂ before heat shrinkage, respectively. On the other hand, the residual shrinkage rate on the horizontal axis means the degree to which the inner diameter d returns to the inner diameter D during heat shrinkage, and when it is 0%, it means that the inner diameter d has become equal to the inner diameter D and has been completely shrunk. Residual shrinkage rate 100
% means the state before contraction.

From this result, sample B has a residual shrinkage rate of 100% and 0%.
The length l ₁ becomes equal to the length L, but it becomes smaller than the length L in the middle. This is due to the fact that longitudinal strain is introduced during stretching. On the other hand, the length l ₂ of sample C increases in inverse proportion to the contraction of the inner diameter d, and finally becomes equal to the length L. This is due to stretching while releasing strain in the longitudinal direction. Heat-shrinkable tubes produced by conventional manufacturing methods generally have characteristics that are between those of Sample B and Sample C, and have large individual variations.

In this way, if something with large variations is created in the pre-stretching stage, it is extremely difficult to correct it in the subsequent process. First of all, it is important to create a however,
It is generally difficult to make something equivalent to Sample C because frictional force is generated between the tube and the device during the process of stretching the tube during manufacturing. It is practical to prepare the original pre-expanded tube by a method of manufacturing one with characteristics similar to those. FIG. 2 illustrates, based on the conditions under which an expansion tube with little variation was obtained, a modification process to satisfy practical requirements. In the figure, z ₁ and z ₂ are the range of residual shrinkage ratio, n ₁
is the allowable shrinkage rate at z ₁ and n ₂ is the allowable elongation rate at z ₂ .

As a result, a suitable tube has a length change characteristic as shown by P, which means that, for example, a tube corresponding to the above-mentioned stretched sample B can be moved in the length direction while keeping the inner diameter the same. About△
It is necessary to correct it so that the distortion corresponding to 1 is released. Here, as is well known, heat shrinkable tubes have other important basic properties such as shrinkage force, crack resistance, heat deterioration resistance, etc., and the above conditions are not necessarily satisfied only. Consideration should be given to comprehensively considering the selection of materials, devising connection structures, rationalization of standards, etc.

FIG. 3 is a diagram showing an outline of equipment used to manufacture a heat-shrinkable tube having such characteristics. In the figure, 1 is a base, 2 is a correction pipe, 3 is an auxiliary pipe connected to both ends of the correction pipe 2 with flanges, 4 is a bearing that supports each auxiliary pipe 3, and 5 is provided on the outer periphery of the auxiliary pipe 3. A main gear, 6 a drive gear that rotates the main gear 5, 7 a motor that rotates the drive gear 6, 8 a rotary coupling, and 9 a heater for heating the tube inserted onto the correction pipe 2. , 10 is a cooler for forcedly cooling the tube on the heated correction pipe, 11 and 12 are differential transformers, 1
3 is a controller that controls heating or cooling in response to signals from the differential transformers 11 and 12, and 14 is a pre-expansion tube.

FIG. 4 is a diagram showing the relative positional relationship between the correction pipe 2 and the pre-stretch tube 14 and the heater 9 and the cooler 10. Preferably, a lubricant 15 is interposed so as to do so. Also, the third
In the figure, V ₁ , V ₂ , V ₃ indicate electromagnetic valves,
Valve V ₁ is for the heating material of the heater, valves V ₂ and V ₃
is the opening/closing valve for cooling water to the cooler. FIG. 5 is a diagram showing the structure of the correction pipe 2 and the auxiliary pipe 3. The correction pipe 2 is composed of a main pipe 2a and a Teflon coat layer 2b coated thereon, and the correction pipe 2 and the auxiliary pipe 3 are connected to each other. is an O-ring 3b between each corresponding flange 2c and 3a.
are connected by bolts 3c. Here, the modification pipe 2 is used by replacing it with one having a predetermined outer diameter that corresponds to the size of the plastic expansion tube.

A method of manufacturing a heat-shrinkable tube according to the present invention using such equipment will be described below.

A plastic stretch tube 14 is prepared which is stretched into a circular or polygonal cross-sectional shape and treated as described above so that the change in the length direction during the shrinkage process is known and the variation in the change is controlled within a narrow range. The extension tube 14 having such characteristics is placed over the surface treated with a lubricant 15 such as silicone oil or hot melt on the repair pipe 2 taken out by loosening each bolt 3c (Fig. 5), and 2 is returned to its original position and fixed with a bolt 3c (see FIG. 3). The movable stylus 11a and 12a of the pair of differential transformers 11 and 12 are brought into contact with each opposing end of the extension tube 14, and the motor 7 is started to connect the correction pipe via the drive gear 6, main gear 5 and auxiliary pipe 3. 2 is rotated, and the heater 9 is ignited to uniformly heat the extension tube 14. At this time, the heater 9 is preferably equipped with suitable heating control means so as not to overheat the tube.

The tube 14 contracts as the heating temperature rises and comes into close contact with the surface of the repair pipe 2, but when it is further heated to a specified temperature or higher, the longitudinal strain of the tube gradually disappears. For example, if the tube is similar to sample B mentioned above,
Its length is contracted. This change is caused by the movable stylus 11
a, 12a, it is measured by the differential transformers 11, 12 and transmitted to the controller 13, and when the amount of change reaches a predetermined regulation value, the controller 13 sends out a control signal _S1 to control the electromagnetic valve of the heater. Close V ₁ and extinguish the fire. In response to the closing actuation of the valve V ₁ , the controller 13 sends a control signal S ₂ to open the solenoid valves V ₂ and V ₃ of the cooler, thereby spraying cooling water from the cooler 10 onto the heated tube. At the same time, cooling water is forced to flow through the auxiliary pipe 3 and into the correction pipe 2 for forced cooling. This allows the tube 14 to be cooled uniformly and quickly from both its inner and outer surfaces.
It is fixed in a state where the longitudinal dimension changes at the specified value. This dimensional change is measured by the differential transformers 11 and 12, and the motor 7 is stopped to stop the rotation of the correction pipe 2, and the valves V ₂ and V ₃ are closed to stop the spraying and flow of cooling water. control signals are transmitted from the controller 13. Thus, as described above, by removing the repair pipe and extracting the solidified tube, a heat-shrinkable tube as a product is manufactured.

Here, the final heating temperature of the tube mentioned above is about 180°C, and a temperature drop of about 100°C is required to solidify the tube.
Even if forced cooling is performed from the inner and outer surfaces of the tube, it cannot be avoided that a certain amount of time is required, and this may cause slight variations in the shrinkage characteristics. Therefore, as shown in FIG. 6, the gripping fittings 16 for fixing the tube 14 on the repair pipe 2 are used to fix both ends of the tube, respectively, when the change in the length direction of the tube reaches a specified value. Alternatively, the length can be fixed by mechanical fixing means such as fixing two points of the tube by interconnecting a pair of gripping fittings 16 with a bar (not shown) having a length equal to or longer than the required tube length. It should be noted that regulating the change in direction can further reduce the variation in shrinkage characteristics.

As described above, according to the present invention, the material tube is pre-stretched, it is inserted into the repair pipe,
The required conditions are achieved by uniformly heating the tube to shrink it, continuously automatically measuring changes in the length direction of the tube, and when the tube reaches the optimum length, forced cooling from the inside and outside of the tube. The heat shrinkable tube can be modified to have suitable shrinkage characteristics, and the heat shrinkable tube can always be easily and reliably produced in accordance with the actual situation.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the characteristics required of the heat-shrinkable tube manufactured according to the present invention. FIG. 2 is a diagram for explaining the characteristics required of an actual tube based on the results shown in FIG. FIG. 3 is a plan layout diagram showing an outline of equipment applied to the manufacturing method according to the present invention. FIG. 4 is a schematic sectional view taken along the line of FIG. 3. FIG. 5 is an axial cross-sectional view of the modified and auxiliary pipe shown in FIG. 3; FIG. 6 is a diagram showing means for fixing the tube applicable in the present invention. 2... Correction pipe, 3... Auxiliary pipe, 5...
Main gear, 6... Drive gear, 7... Motor, 9...
... Heater, 10 ... Cooler, 11, 12 ... Differential transformer, 13 ... Controller, 14 ... Extension tube.

Claims (1)

[Claims] 1. A cross-linked plastic pre-stretched tube with known shrinkage characteristics is prepared as a material, the tube is inserted onto a modified pipe having a predetermined outer diameter, and the tube is heated uniformly while being rotated, and the length of the tube is adjusted. The change in the length direction of the tube is continuously and automatically measured, and when the value detected by the continuous automatic measurement becomes substantially the same as the predetermined amount of change in the length direction of the tube, the heating to the tube is stopped and the tube length is changed. 1. A method for manufacturing a heat-shrinkable tube, which comprises forming a heat-shrinkable tube whose shrinkage characteristics have been substantially modified by predetermined shrinkage characteristics by solidifying the tube by forcedly cooling the tube simultaneously from the inner and outer sides.