Abstract:
A silver contact fixing structure for conductive blades aims at providing a retaining force on a silver contact so that the silver contact is more secure and does not break loose when subject to striking. The silver contact is built in a fastening section formed on a conductive blade. The fastening section has at least two fixing zones connecting to each other and a bucking end adjacent to the fixing zones to increase the retaining force between the silver contact and the conductive blade so that the silver contact does not break loose easily thereby increasing the service life thereof.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a silver contact fixing structure for conductive blades and particularly to a technique that employs a novel conductive blade structure and a silver contact fixing method to enhance the strength of silver contacts. 
   BACKGROUND OF THE INVENTION 
   Conventional techniques for fabricating silver contacts often encounter some problems, notably: 
   Silver contacts are usually used in switches to establish conductive connection. When in use, the silver contact receives a strike from a connection leg to form a connection contact with the switch. The conventional silver contact is generally wedged in a housing space. When subject to striking over a prolonged period, the silver contact is prone to break loose from the conductive blade. 
   To remedy the foregoing problem, a technique has been disclosed to improve the fabrication of silver contacts in R.O.C. patent publication No. 448454 entitled “Method for fastening silver contacts of conductive blades”. It punches a fastening hole on a conductive blade that is concave on the upper side and convex on the lower side. Extra material of the conductive blade is extruded to form an extended wedging flange. The fastening hole has screw threads formed therein to provide a horizontal friction force so that the silver contact is less likely to break off. Finally, the top section of the silver wire is formed in a protrusive bucking flange through an upper mold, and a lower mold is deployed to ram the wedging flange towards the fastening hole so that the silver wire is filled and wedged securely in the fastening hole. The aforesaid technique can fix the silver contact more securely without breaking loose. However, in the design of switches, the interval between the movable contact and the closed circuit contact has to comply with safety regulations (for instance the interval under European safety regulations is 3 mm). The protrusive bucking flange will affect the distance between the movable contact and the closed circuit contact. Hence, the relative positions of the elements in the switch have to be rearranged. 
   Referring to  FIG. 1 , to resolve the problems set forth above, some people proposed an injection forming approach to embed the silver contact when the conductive blade is formed by injection. Such a design does not create the bucking flange, and the positions of the elements in the switch do not need to be rearranged. However, embedding by injection forming requires fabrication of new molds to suit the different contact sizes of various switches. Manufacturing processes cannot be modularized. As a result, manufacturing cost is higher. 
   SUMMARY OF THE INVENTION 
   The primary object of the invention is to solve the aforesaid problems. The invention provides a method and structure for fixing silver contacts more securely. The conductive blade has a fastening section corresponding to where a silver contact is located. The fastening section has at least two fixing zones formed on a corresponding vertical surface connected to each other, and a bucking end abutting the juncture of the fixing zones so that a silver wire may be pressed and filled in the fastening section to form the silver contact. Thus, a retaining force is provided when the connection leg strikes the silver contact. Moreover, the horizontal cross section of the fastening section may be formed in a non-circular and irregular shape to make the silver contact less likely to break loose. 
   Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a cross section of a conventional silver contact. 
       FIG. 2  is a perspective view of a first embodiment of the conductive blade of the present invention. 
       FIGS. 3A through 3F  are schematic views of the fabrication process of the first embodiment of the invention. 
       FIG. 4  is a perspective view of a second embodiment of the conductive blade of the present invention. 
       FIG. 5  is a top view of the second embodiment of the present invention. 
       FIGS. 6A through 6F  are schematic views of the fabrication process of the second embodiment of the invention. 
       FIG. 7  is a cross section of a third embodiment of the present invention. 
       FIG. 8  is a cross section of a fourth embodiment of the present invention. 
       FIGS. 9A ,  9 B and  9 C are cross sections of a fifth embodiment of the present invention. 
       FIG. 10  is a cross section of a sixth embodiment of the present invention. 
       FIG. 11  is a cross section of a seventh embodiment of the present invention. 
       FIG. 12  is a cross section of an eighth embodiment of the present invention. 
       FIG. 13  is a block diagram of the fabrication process for the first embodiment through to the eighth embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Please refer to  FIGS. 2 ,  3 -A through  3 -F, and  13  for a conductive blade  10  of a first embodiment of the invention. It has a fastening section  11  corresponding to where a silver contact  17  is located. The fastening section  11  has a first fixing zone  15  and a second fixing zone  19  on a vertical surface corresponding to the conductive blade  10  that connects to each other. The first fixing zone  15  is greater than the second fixing zone  19  and forms a bucking end  121  at their juncture. A silver wire  16  is pressed and filled in the fastening section  11  to form a silver contact  17 , which has the same shape as the fastening section  11 . The bucking end  121  provides a retaining function to increase the retaining strength. Fabrication of the conductive blade  10  includes the following steps in the order of A: stamping a blank; B: stamping the blank for a second time; and C: planting the silver wire. 
   Step A: stamping a blank. Form the first fixing zone  15  on the conductive blade  10  by stamping through a punching end  201  of a first upper mold  20 . The punching end  201  is a cylinder with a lower tapered end. The first fixing zone  15  has a bucking end  51  formed on the peripheral side of one end thereof in a chamfered angle. 
   Step B: stamping the blank for a second time. Form the second fixing zone  19  on the conductive blade  10  by stamping through a second upper mold  22 . The first fixing zone  15  is bigger than the second fixing zone  19 . The bucking end  121  is located on the peripheral side of one end of the first fixing zone  15  in a chamfered angle. 
   Step C: planting the silver wire. Place the conductive blade  10  on a first lower mold  21 ; press and fill the silver wire  16  in the fastening section  11  to become the silver contact  17  which has the same shape of the fastening section  11 . The bucking end  121  strengthens the retaining ability. 
   Refer to  FIGS. 4 ,  5 ,  6 A through  6 F for a second embodiment of the silver contact  17   a  of the invention. The conductive blade  10   a  is substantially constructed as the first embodiment. However, the first fixing zone  15   a  is formed in a saw shape. The process for fabricating the silver contact  17   a  includes the following steps in the order of A: stamping a blank; B: stamping the blank for a second time; and C: planting the silver wire. 
   Step A: stamping a blank. Form the first fixing zone  15   a  on the conductive blade  10   a  by stamping through a first upper mold  20   a . The punching end  201   a  of the first upper mold  20   a  has an extended angle  18   a  with a lower tapered end formed in a saw shape. 
   Step B: stamping the blank for a second time through a second upper mold  22   a  smaller than the first upper mold  20   a  to form a second fixing zone  19   a  on the conductive blade  10   a  that is smaller than the first fixing zone  15   a . The second upper mold  22   a  is a cylinder. 
   Step C: planting the silver wire. Place the conductive blade  10   a  on a first lower mold  21 ; place the silver wire  16  in the fastening section  11   a  which consists of the first fixing zone  15   a  and the second fixing zone  19   a ; press and fill the silver wire  16  in the fastening section  11   a  through a third upper mold  23  to finish the fabrication of the silver contact  17   a  of the second embodiment. The first fixing zone  15  has a bucking end  121  formed on the peripheral side of one end in a chamfered angle. 
   Refer to  FIGS. 7 and 8  for the conductive blades  10   b  and  10   c  of a third and a fourth embodiment of the invention. They are formed in a shape substantially similar to the second embodiment. The fabrication step A for stamping a blank and the step B for stamping the blank for a second time and the step C for planting the silver wire (not shown in the drawings) set forth above are also applied. However, in the third embodiment, the first fixing zone  15   b  is a conical trough with a tapered lower end and the second fixing zone  19   b  is a circular trough with a saw type inner wall. In the fourth embodiment, the first and the second fixing zones  15   c  and  19   c  are formed in a saw type, and the first fixing zone  15   c  is a conical trough with a tapered lower end. 
   Refer to  FIGS. 9A ,  9 B,  9 C and  13  for a fifth embodiment of the invention. The fastening section includes first, second and third fixing zones  15   d ,  19   d  and  14   d . The fabrication process includes A: stamping a blank; B: stamping the blank for a second time; and C: planting the silver wire. 
   Step A: stamping a blank. A first upper mold  20   d  and a second lower mold  24  are used to stamp a conductive blade  10   d  on the upper side and the lower side to form the first and third fixing zones  15   d  and  14   d.    
   Step B: stamping the blank for a second time. From a second fixing zone  19   d  on the conductive blade  10   d  through a second upper mold  22   d  that is smaller than the first and third fixing zones  15   d  and  14   d . The first and the third fixing zones  15   d  and  14   d  are conical troughs with a tapered end adjacent to the horizontal center of the conductive blade  10   d . The first fixing zone  15   d  also has a saw type peripheral wall. 
   Step C: planting the silver wire (not shown in the drawings). The silver wire is placed in a fastening section  11   d  formed by the first, second and third fixing zones  15   d ,  19   d  and  14   d , and is pressed and filled in the fastening section  11   d  through a third upper mold (not shown in the drawings). 
   Refer to  FIGS. 10 ,  11  and  12  for a sixth embodiment ( FIG. 10 ), seventh embodiment ( FIG. 11 ) and eighth embodiment ( FIG. 12 ). The fabrication processes are substantially the same as those previously discussed. The sixth embodiment includes a first, second and third fixing zone  15   e ,  19   e  and  14   e . Only the second fixing zone  19   e  ( FIG. 10 ) is formed in a saw type. The seventh embodiment includes a first, second and third fixing zone  15   f ,  19   f  and  14   f . Only the third fixing zone  14   f  ( FIG. 11 ) is formed in a saw type. The eighth embodiment ( FIG. 12 ) includes a first, second and third fixing zone  15   g ,  19   g  and  14   g , and all of them are formed in a saw type. 
   While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments that do not depart from the spirit and scope of the invention.