Title of Invention

"METHOD OF EXPANDING DIAMETER OF ELASTIC TUBE."

Abstract

A method of diametrally expanding an elastic tube, which comprises the steps of inserting a distal end portion of an expansion member into an elastic tube, the expansion member being provided at a surface thereof with a solidified layer of a low melting point material and also provided at a rear end thereof with a hole for housing a hollow supporting body therein, and the distal end portion of the expansion member being tapered, a tip end of which having a diameter which is equal to or smaller than an inner diameter of the elastic tube, moving the elastic tube over the solidified layer to diametrally expand the elastic tube, and allowing the expanded elastic tube to be rested on the hollow supporting body while withdrawing gradually the hollow supporting body from the hole.

Full Text

TITLE OF THE INVENTION METHOD OF EXPANDING DIAMETER OF ELASTIC TUBE BACKGROUND OF THE INVENTION This invention relates to a method of expanding the diameter of an elastic tube, and in particular to a method of expanding the diameter of an elastic tube which is adapted to be employed for enclosing the joint portion for instance of electric wire, cable, pipe, etc. In recent years, there has been developed, for the purpose of protecting, insulatively enclosing or repairing a joint portion of electric wire, cable, pipe, etc., a method of employing a self-shrinkable elastic tube which is capable of covering the joint portion without necessitating the application of heat in place of the conventional method of using a heat-shrinkable tube. This self-shrinkable elastic tube is made of a rubber-like elastic material and is normally supported in advance on a tubular rigid supporting body whereby the inner diameter of the elastic tube is kept in an expanded state. In the employment of the self-shrinkable elastic tube, the self-shrinkable elastic tube is inserted over a joint portion of power cable for instance while it is kept in an expanded state as mentioned above, and then the supporting body is withdrawn from the self-shrinkable elastic tube, thereby allowing the self-shrinkable elastic tube to be shrunk diametrally, thus obtaining the joint portion which is hermetically covered by the elastic tube. There has been conventionally proposed the following method as a means to expand the diameter of such an elastic tube. Namely, first of all, an elongated bag-like expandable hollow body twice as long as that of the self-shrinkable elastic tube is prepared. Then, the fore half portion of this expandable hollow body is inserted into the self-shrinkable elastic tube, and then the expandable hollow body is entirely expanded by means of a pressurized air whereby diametrally expanding the self-shrinkable elastic tube. Thereafter, a supporting body disposed on the side of the rear half portion of the expandable hollow body is forcibly introduced into the fore half portion of the expandable hollow body where the self-shrinkable elastic tube is disposed. Then, the pressurized air in the expandable hollow body is withdrawn thereby allowing the expandable hollow body to shrink. As a result, a self-shrinkable elastic tube rested on the supporting body with the self-shrinkable elastic tube being kept expanded can be obtained (Japanese Patent Unexamined Publication S/63-74624). However, this conventional method is accompanied with the problem that since a bag-like expandable hollow body is rendered to be interposed between a supporting body and a self-shrinkable elastic tube in the process of resting the self-shrinkable elastic tube on the supporting body in this method, the hollow body is ultimately left strongly sandwiched between the supporting body and the self-shrinkable elastic tube. As a result, it is very difficult to remove the supporting body from the self-shrinkable elastic tube at the occasion of mounting the self-shrinkable elastic tube on the joint portion of a power cable for instance. With a view to overcome the aforementioned problem, the present inventors have proposed a method of expanding the diameter of an elastic tube as disclosed in Japanese Patent Unexamined Publication H/9-109257. Namely, according to this method, a tapered expansion member (a tool for expanding the elastic tube), at least the surface of which being constituted by a solidified body of a low melting point material and a tip end of which being configured to have a diameter equal to or smaller than the inner diameter of the elastic tube, is employed. At first, the tip end of this expansion member is inserted into the elastic tube, and then the elastic tube is allowed to slip over the low frictional surface of a melted low melting point material, thus expanding the elastic tube. FIGS. 1A and 1B illustrate a method of manufacturing the expansion member to be employed in the method of expanding the diameter of the elastic tube, while FIGS. 2A to 2E illustrate a method of expanding the diameter of the elastic tube by making use of the expansion member, which is set forth in Japanese Patent Unexamined Publication H/9-109257. As shown in FIG. 1A, the expansion member 1 is placed in a cylindrical container 2 having a conical tip end. In the manufacture of this expansion member 1, a hollow supporting body 14 is temporarily held within the container 2, and then a low melting point material 3, typically water, is poured into the container 2. Thereafter, the container 2 is kept in a tank which is cooled to a solidification temperature of the low melting point material 3, whereby the low melting point material 3 is solidified forming the expansion member 1. FIG. IB illustrates the expansion member 1 which has been taken out of the container 2. This expansion member 1 is configured to the same shape as that of the interior of the container 2, and hence constituted by a conical distal end portion 4 and a cylindrical barrel portion 5 having the same diameter as that of the maximum diameter of the conical tip portion 4. Since this expansion member 1 is made of the low melting point material 3, the surface thereof melts under normal temperatures, thus making the surface slippery. The process of expanding the elastic tube 6 by making use of the expansion member 1 shown in FIG. IB will be explained with reference to FIGS. 2A to 2E. First of all, as shown in FIG. 2A, the elastic tube 6 is inserted over the distal end portion 4 of the expansion member 1. Then, the elastic tube 6 is shifted from the distal end portion 4 up to the cylindrical barrel portion 5 of the expansion member 1. In this case, since the surface of the expansion member 1 is made slippery by the melting thereof, the elastic tube 6 can be easily moved from the distal end portion 4 to the cylindrical barrel portion 5 as shown in FIGS. 2B, 2C and 2D with a weak force. Subsequently, the low melting point material 3 is allowed to melt and eliminated ultimately by exposing the expansion member 1 to a temperature higher than the melting point of the low melting point material 3. As a result, the elastic tube 6 which is rested on the hollow supporting body 14 with the diameter of the elastic tube 6 being kept expanded as shown in FIG. 2E can be obtained. By the way, the method of moving the elastic tube 6 from the conical distal end portion 4 to the cylindrical barrel portion 5 can be performed by either pushing or pulling the elastic tube 6. The method illustrated above is advantageous in that since the friction between the elastic tube and the solidified body is very small, the expansion of the elastic tube can be performed with a relatively weak force. However, this method is accompanied with a problem that since it is required to manufacture the solidified body individually and the resultant solidified body, which is relatively large in size, is required to be eliminated through melting, it takes a long period of time in the solidification of the expansion member. BRIEF SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method of expanding the diameter of a self-shrinkable elastic tube, which makes it possible to easily perform the diametral expanding operation of a self-shrinkable elastic tube. Namely, this invention provides a method of diametrally expanding an elastic tube, which comprises the steps of: inserting a distal end portion of an expansion member into an elastic tube; the expansion member being provided at a surface thereof with a solidified layer of a low melting point material and also provided at a rear end thereof with a hole for housing a hollow supporting body therein; and the distal end portion of the expansion member being tapered, a tip end of which having a diameter which is equal to or smaller than an inner diameter of the elastic tube; moving the elastic tube over the solidified layer to diametrally expand the elastic tube, the surface of the solidified layer being made into a low frictional surface due to a melting of the low melting point material; and allowing the expanded elastic tube to be rested on the hollow supporting body while withdrawing gradually the hollow supporting body from the hole. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIGS. 1A and IB show respectively a cross-sectional view of an expansion member to be employed in a conventional method of expanding the diameter of an elastic tube; FIGS. 2A to 2E show respectively a cross-sectional view illustrating the process of expanding the diameter of an elastic tube according to the conventional method; FIG. 3 is a cross-sectional view showing an expansion member to be employed in the method of expanding the diameter of an elastic tube according to this invention; FIG. 4 is a cross-sectional view showing an expansion member to be employed in the method of expanding the diameter of an elastic tube according to this invention; and FIGS. 5A to 5F show respectively a cross-sectional view illustrating the process of expanding the diameter of an elastic tube according to this invention. DETAILED DESCRIPTION OF THE INVENTION The method according to this invention is featured in that an expansion member provided at only the surface thereof with a solidified layer of a low melting point material and also provided at a rear end thereof with a hole for housing a hollow supporting body therein is employed; and that the process of expanding an elastic tube is performed by the steps of; inserting a distal end portion of an expansion member into an elastic tube; moving the elastic tube over the surface of solidified layer which is melted thus turning it into a low frictional surface thereby expanding the elastic tube; and withdrawing gradually the hollow supporting body from the hole in simultaneous with the movement of the expanded elastic tube whereby allowing the expanded elastic tube to be rested on the hollow supporting body. As for the low melting point material useful in this invention, there is not any particular limitation as long as it can be melted within the range of temperature which would not dissolve or denature the materials constituting the elastic tube or the hollow supporting body. The melting point of this low melting point material should preferably be -60°C or more if the elastic tube is formed of silicone rubber. Because if the melting point of this low melting point material is less than -60°C, the elastic modulus of silicone rubber would become less than 1 MPa and hence silicone rubber can hardly be deformed. Preferable examples of the low melting point material are those which are liquid at normal temperatures, specifically water (melting point: 0°C), glycerin (melting point: 17°C), ethylene glycol (melting point: -11.5°C), etc. Most preferable example of the low melting point material is water, which can be easily solidified into ice. For example, an expansion member can be manufactured by solidifying water at a temperature of 0°C to -20°C, and then employed by allowing the ice to melt whereby rendering the surface to become low in friction, thus allowing an elastic tube to be easily slid on the surface of the expansion member in the diametral expanding process of the elastic tube. This is one of most important features of this invention. The tapered angle of the tapered portion of the expansion member according to this invention should preferably be in the range of 5 to 30 degrees, i.e. 10 to 60 in apex angle. The tip portion of the expansion member where the diameter thereof is not larger than the inner diameter of the elastic tube may not be tapered but may be flat-ended. In other words, the shape of the tip portion of the expansion member may be optionally selected as long as it can be inserted into the elastic tube. The diameter of the tip portion of the expansion member is required to be approximately equal to or smaller than the inner diameter of the elastic tube before the elastic tube is expanded. The expression of "approximately equal to" should be understood to a case where the diameter is slightly larger than the inner diameter of the elastic tube. Because, due to the elasticity of the elastic tube, it is possible to insert the tip end portion of the expansion member into the elastic tube even if the diameter of the tip end of the expansion member is slightly larger than the inner diameter of the elastic tube. If the angle of the tapered portion of the expansion member is too large, a large force would be required in expanding the diameter of the elastic tube. Moreover, if the angle of the tapered portion of the expansion member is too large, the difference in angle between the tapered portion and the horizontal portion becomes too large so that an excessively large force would be required at the moment of transferring the elastic tube from the tapered portion to the horizontal portion. Therefore, the boundary portion between the tapered portion and the horizontal portion should preferably be as smooth as possible so as to facilitate the movement of the elastic tube over the expansion member. As explained above, it is possible according to this invention to minimize the frictional force even if the hoop stress of the elastic tube is increased in the expansion in diameter of the elastic tube. Therefore, the tensile stress in the axial direction can be minimized, and hence there is little possibility that the elastic tube is fractured in this process of expanding the elastic tube. Further, since the hollow supporting body is housed in the hole in advance, and since the elastic tube is transferred from a portion of larger diameter to a portion of smaller diameter in the transfer thereof onto the supporting body, the transfer of the elastic tube onto the supporting body can be smoothly performed with a small force. Additionally, since the solidified body consisting of the low melting point material can be repeatedly employed during the melting period thereof, the working efficiency can also be improved. This invention will be further explained with reference to the drawings. FIG. 3 illustrates the expansion member to be employed in this invention. This expansion member 11 is constituted by a core member 12 of small wall thickness and a solidified layer 13 formed on the outer surface of the core member 12. Namely, since the solidified body of a low melting point material is formed into a thin layer, the quantity of the solidified body can be minimized. As for the material for the core member 12, a material which cannot be denatured or does not exhibit brittleness in the temperature range of from the melting point of the solidified body to the working temperature, such as metal, plastics and wood can be employed. FIG. 4 shows an example wherein the space in the core member 12 of the expansion member 11 shown in FIG. 3 is utilized for housing the hollow supporting body 14. Namely, the rear portion of the core member 12 is elongated as compared with the ordinary expansion member, thus making it possible to house the hollow supporting body 14 for carrying a diametrally expanded elastic tube 16 in the hole 15 formed in the core member 12. FIGS. 5A to 5E illustrate the process of diametrally expanding the elastic tube 16 by making use of the expansion member 11 shown in FIGS. 3 and 4. First of all, the elastic tube 16 is engaged with the cone-shaped tip end portion of the expansion member 11. Then, the elastic tube 16 is advanced from the conical distal end portion 13a up to the barrel portion 13b. Since the surface of the expansion member 11 is slightly melted and made slippery as explained above, the elastic tube 16 can be easily moved with a small force from the distal end portion 13a to the barrel portion 13b as shown in FIG. 5B, FIG. 5C and FIG. 5D. As a result, the elastic tube 16 is diametrally expanded. Then, as shown in FIG. 5E, a hollow supporting body 14 is housed at rear portion of the expansion member 11, and at the same time, the elastic tube 16 is further moved to the rear portion of the expansion member 11. At the same time, the hollow supporting body 14 is gradually withdrawn from the hole 15, whereby allowing the elastic tube 16 to be rested on the surface of the hollow supporting body 14. In this manner, a self-shrinkable elastic tube 16 which is supported on the hollow supporting body 14 as shown in FIG. 5E can be easily manufactured. As explained above, since the elastic tube is transferred onto the hollow supporting body by taking advantage of the low frictional melted surface of the expansion member, the tensile stress in the axial direction at the occasion of the transferring the elastic tube can be minimized, thus minimizing any possibility of fracturing the elastic tube. Accordingly, it is possible to perform a diametral expansion in a maximum extent irrespective of the wall thickness and diameter of the elastic tube. It is also possible to efficiently transfer a diametrally expanded elastic tube onto a hollow supporting body in a single processing step. Further, the method of this invention is advantageous in that it utilizes water which is cheap in price available easily and easy in handling, and also utilizes a cheap housing for hollow supporting body. Of course, there is not any intervening material between the hollow supporting body and the elastic tube as in the case of the conventional method. Furthermore, since the solidified layer of low melting point material is formed only on the surface of the expansion member in the method of this invention, the time required for the solidification of low melting point material can be minimized. We Claim : 1. A method of diametrally expanding an elastic tube, which comprises the step of: - inserting a distal end portion of an expansion member into an elastic tube, - moving said elastic tube over the solidified layer of low melting point material provided at the surface of said expansion member to diametrally expand the elastic tube, the surface of said solidified layer being made into a low frictional surface due to a melting of said low melting point material and - allowing said expanded elastic tube to be rested on hollow supporting body while withdrawing gradually said hollow supporting body from a hole provided at the rear end of said expansion member for housing said hollow supporting body. 2. The method as claimed in claim 1, wherein said low melting point material is selected from the group consisting of water, glycerin and ethylene glycol. 3. The method as claimed in claim 1, wherein an apex angle of the tapered portion of said expansion member is 10 to 60 degrees. 4. A method of expanding diameter of elastic tube, substantially as herein before described with reference to the accompanying drawings.

Documents:

537-del-1998-abstract.pdf

537-del-1998-claims.pdf

537-del-1998-correspondence-others.pdf

537-del-1998-correspondence-po.pdf

537-del-1998-description (complete).pdf

537-del-1998-drawings.pdf

537-del-1998-form-1.pdf

537-del-1998-form-19.pdf

537-del-1998-form-2.pdf

537-del-1998-form-3.pdf

537-del-1998-form-4.pdf

537-del-1998-pa.pdf