Abstract:
A method for manufacturing sealing tool comprising a socket ( 3 ) and a head ( 4 ) at one end and the other end of a linear element ( 2 ) respectively and a protrusion ( 11 ) for locking the head ( 4 ) in a head-insertion hole ( 10 ) of the socket ( 3 ), which comprises the steps in the mentioned sequence of fixing a core ball ( 13 ) and either the socket ( 3 ) or the head ( 4 ) to the linear element ( 2 ), cutting the linear element ( 2 ) at a point close to the core ball ( 13 ), pulling the linear element ( 2 ) to bring the core ball ( 13 ) to be set in a cavity ( 27 ) and filing a synthetic resin in the cavity ( 27 ) in a manner such that the core ball ( 13 ) and the socket ( 3 ) engageable with the head ( 4 ) are integrally formed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for manufacturing a sealing tool which has a socket at one end of its linear element and a head at its other end, and also which is provided with a protrusion for engaging the head into a head-insertion hole of the socket. 
     2. Description of the Prior Art 
     Conventionally, when manufacturing a sealing tool which has respectively a socket at one end of its thread strip and a head at the other end and also which is provided with a protrusion for engaging the head in a head-insertion hole of the socket, a part of the thread strip traversing in a socket-molding cavity, i.e. the thread strip positioned in the socket hole has been cut off though a cut-off portion of a piston-type movable mold (see Japanese patent application Kokai publication No. 60-2458). 
     However, if the thread strip traversing in the socket hole remains therein without cutting off, the remaining part of the thread strip acts as an obstacle, making it impossible to insert the head into the socket hole. 
     Moreover, according to this prior art, after the thread strip to which the socket and the head are fixed is once wound around a bobbin, while rewinding the thread strip from the bobbin the thread strip is cut off between the socket and the head in order to manufacture the seating tool, thus taking much time to resultantly make it impossible to manufacture the sealing tool efficiently. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the above problems, it is an object of the present invention to provide a method for manufacturing a sealing tool with a high quality of which the linear element does not protrude into the head-insertion hole. 
     The method for manufacturing such a sealing tool according to the invention that has respectively a socket at one end of its linear element and a head at the other end and also that is provided with a protrusion for engaging the head in a head-insertion hole of the socket comprises the steps of: fixing a core ball and either one of the above-mentioned socket or the above-mentioned head to the above-mentioned linear element; cutting off the above-mentioned linear element at a position near the above-mentioned core ball; setting the above-mentioned core ball into a cavity while drawing out the above-mentioned linear element; filling synthetic resin into the above-mentioned cavity, to double-mold a member connectable with another member molded together with the above-mentioned core ball in such a manner that the former member may include the above-mentioned core ball. 
     Thus, after fixing the core ball and either one of the socket and the head to the linear element, that linear element is cut off at a position near the core ball to grip the core ball with a gripping portion of a carrier robot etc. in order to set the core ball in the cavity while drawing the linear element out of a reel etc. Then, synthetic resin may be filled in the cavity to double-mold a member (e.g., a socket in the case where the core ball and the head are formed together) connectable with another member molded together with the core ball so as to include the core ball, thus preventing the linear element from protruding into the head-insertion hole. As a result, it is possible to manufacture a high-quality sealing tool efficiently. 
     Moreover, according to the present invention, by fixing a plurality of core balls at one end of a linear element, the core ball positioned at the top can act as a member for stopping the other core balls from being extracted, thus preventing them from falling out. 
     Further also, according to the present invention, by utilizing the core ball as a gripped portion of a linear element draw-out means, the core ball can be automatically transported into a cavity for molding the socket or the head. 
     This core ball has a function of carrying the linear element to a predetermined position by using a gripping portion of a carrier robot etc., a function of fixing a tip of the linear element in the mold cavity, and a function of fixing a piece made of synthetic-resin at the end of the linear element to fill the cavity with necessary resin in order to mold, so-called double-mold, a predetermined molding product. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a sealing tool molded according to a method of the present invention; 
     FIG. 2 is a cross-sectional view taken along line A-A′ of FIG. 1; 
     FIG. 3 is a front view of the sealing tool of FIG. 1; 
     FIG. 4 is a cross-sectional view taken along line B-B′ of FIG. 2; 
     FIG. 5 is a cross-sectional view taken along line C-C′ of FIG. 2; 
     FIG. 6 is a cross-sectional view taken along line D-D′ of FIG. 2; 
     FIG. 7 is an illustration showing a state where a linear element is set in a first metal mod; 
     FIG. 8 is an illustration showing a head and a core ball which are injection-molded; 
     FIG. 9 is an illustration showing a state where the head and the core ball are fixed in a rosary-ball shape to the linear element; 
     FIG. 10 is an illustration showing a state where the ball is set in a second mold and the linear element, in the first mold; and 
     FIG. 11 is an illustration showing a state where the socket, the head, and the core ball are injection-molded. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following will describe embodiments of the invention with reference to the drawings. 
     As shown in FIG. 1, a sealing tool  1  has respectively a socket  3  at one end of its linear element  2  elongated like a thread strip and a head  4  at the other end. 
     The head  4  comprises: a tip  5  having a gill-shaped or wrapper-shaped engage claw  8 ; a pharynx  6  having a mountain- or fork-shaped cross section; and a round-bar shaped barrel  7 . 
     As shown in FIG. 2, the socket  3  has a head-insertion hole  10  in the home-base shaped body  9 . An annular protrusion  11  having a smaller diameter than the head-insertion hole  10  is provided at the middle thereof. This head-insertion hole  10  is provided in such a direction as to intersect the linear element  2 . 
     The engage claw  8  of the head  4 , when passing through the protrusion  11  in the head-insertion hole  10 , narrows at the free end  8   a  thereof in an arrow (a) direction (see FIG.  5 ). However, when passing the protrusion  11 , it returns to the initial state thereof, thus preventing the head  4  from going out of the head-insertion hole  10  of the socket  3 . 
     In this sealing tool  1 , a core ball  13  fixed to the tip of the linear element  2  is included or integrated in the socket body  9 , so that the tip of the linear element  2  does not protrude into the head-insertion hole  10  of the socket  3 , particularly into the protrusion  11 . The core ball  13  may come in a single discrete type or a sequential type comprising two or more of the core balls. In the case of a sequential type, a core ball at the top is utilized as a core-ball stopping member  13   b , thus preventing the inner core balls  13   a  from falling out. 
     Preferably, the head  4 , the socket  3 , and the core ball  13  are made of, e.g., such thermoplastic synthetic resin as polyester, nylon. 
     The linear element  2 , on the other hand, is preferably made of a thread strip formed with such a fiber as a natural fiber or synthetic fiber, a metal fine wire formed with such metal as steel or stainless steel, an elastic thread formed with heat-resistant rubber, or a mono-linear element formed with such thermoplastic synthetic resin as polyester or nylon. 
     The following will describe a method for manufacturing the above mentioned sealing tool. 
     As shown in FIG. 7, the linear element  2  as drawed out of a reel (not shown) is set under tension into a straight groove  23  formed on a junction face  22  of a multi-division type first mold  21 , then thermoplastic synthetic resin is injected into both a head-molding cavity  24  and a core-ball molding cavity  25 . With this, as shown in FIG. 8, the head  4  and the sequential two core balls  13  are molded simultaneously. 
     As shown in FIG. 9, when the linear element  2  is taken out of the first mold  21 , the head  4  and the core balls  13  are securely fixed to the linear element  2 , so that the core balls  13  is gripped with a gripping portion  30  of a carrier robot and the linear element  2  is cut off with a cutter or any other cutting means (not shown) between the core ball  13  and the head  4  (see an arrow E). In this case, it is important to cut the linear element  2  at the position where it comes close to the core balls as much as possible and the tip of the linear element  2  may not protrude out of the core balls  13 . 
     Next, while drawing out the linear element  2  from the reel (not shown) by moving in an F arrow direction the gripping portion  30  of the carrier robot which grips the core balls  13 , as shown in FIG. 10, the core balls  13  are set in a socket-molding cavity  27  of the second mold  26  and, at the same time, the linear element  2  connected to the core balls  13  is set under tension into the groove  23  of the first mold  21 . 
     Since a spacing L between the first mold  21  and the second mold  26  is adjusted at a predetermined dimension beforehand, after the core balls  13  are set in the socket-molding cavity  27  of the second mold  26 , when the linear element  2  is set under tension in the groove  23  of the first mold  21 , a distance between the socket  3  and the head  4  can be set at a predetermined dimension. 
     Next, thermoplastic synthetic resin is injected respectively into the above-mentioned cavities  24 ,  25 , and  27 , then molding the socket  3 , the head  4 , and the core balls  13  as shown in FIG.  11 . Note here that by pushing up a piston  28  incorporated in the second mold  27 , the socket  3  can be easily taken out of the second mold  26 . 
     By repeating the above operations of FIGS. 9 through 11, such a sealing tool  1  as shown in FIG. 1 can be molded efficiently. 
     According to the present invention, for example after molding the core ball  13  and the socket  3  with core-ball and socket molding molds the core balls  13  is set into a head-molding mold, thus the sealing tool  1  which includes the core balls  13  in the head  4  is capable of molding. 
     Moreover, the socket  3  and the head  4  may, different from the above-mentioned shapes, be formed flat overall as a hook, providing one portion strip with a hole having a protrusion and the other portion strip with an engagement claw for coupling with the protrusion. In short, when the engagement claw provided at one portion strip would be coupled with the protrusion in the hole of the other portion strip, it may not be released preferably. 
     As described above, according to the present invention, after core balls and either one of a socket or a head are fixed to a linear element, the linear element is cut at a position where it comes close to the core ball, to set the core balls in a cavity while drawing the linear element out of a reel etc. by gripping the core balls gripped with a gripping portion of a carrier robot etc. and then fill the cavity with synthetic resin, to double-mold a member (e.g., a socket in the case where the core balls and the head are molded simultaneously) connectable with another member molded together with the core balls so that the former member may include the core balls, thus preventing the linear element from protruding into the head-insertion hole. Consequently, it is possible to manufacture a high-quality sealing tool efficiently. 
     Moreover, according to the present invention, a plurality of core balls are fixed to the one end of the linear element and the core ball at the top may act as a member for stopping the other core balls from being extracted, thus preventing them from falling out. 
     Further also, according to the present invention, the core ball is utilized as a gripped portion of a linear element-draw-out means, thus making it possible to automatically move the core ball into the socket- or head-molding cavity.