Abstract:
Since all points on a spherical surface are equidistant from the center of its sphere, the occurrence of interference during mold release can be prevented by releasing the half sphere along the normal direction of a plane passing through the center of the sphere. In this invention, the upper and lower molds of the ball chain each has a protruding configuration having a spherical surface, and the upper and lower molds are released along an inclined direction, thus preventing the interference between the protruding configuration and the finished product during mold release. Such mold releasing method also can solve the difficulties in production and can improve the effect of the spacers for separating the steel balls.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a ball chain that is used in a rolling mechanism for preventing the steel balls from colliding with each other, and more particularly to a method for making such a ball chain.  
         [0003]     1. Description of the Prior Art  
         [0004]      FIG. 1  is a front view of showing a conventional ball chain,  FIG. 2  is a cross sectional view of the ball chain taken along the line A-A′ of  FIG. 1 . The ball chain  1  comprises a plurality of spacers  11 , and a connecting member  12  is connected at either side of the spacers  11 , so that the spacers  11  are connected in a string. Each two neighboring spacers  11  define a space for holding a steel ball  2 , and each spacer  11  defines a concave  111 ,  112  in either side thereof for mating with the steel ball  2 , so that a plurality of steel balls  2  can freely roll within the spaces defined by the spacers  11  without impacting each other. A ball chain is generally designed to have tens of spacers  11 , and the spacers  11  are connected in a string by the ball chain. For easy description, however, only four spacers  11  are illustrated in the figures. The ball chain manufactured by the method may comprise three or four or more spacers  11 , and the method of making it is the same.  
         [0005]     A conventional method of making a ball chain is to use a plurality of steel ball as a core in an injection molding process, and with the aid of an upper and a lower molds, the ball chain is formed by injection molding, after that, a ball chain is obtained by releasing the upper and lower molds. At this moment, the steel balls serving as a core are still in contact with the ball chain. And finally, it should try to make the steel balls lose contact with the ball chain (as disclosed in JP Pat. No. 552,217). Due to using steel balls as a core, plus a ball chain usually comprises tens of spacers, that is, tens of spacers all need to serve as mold cores, the conventional method of making ball chain requires too many molds, and the resultant production is too complicated.  
         [0006]     After that, proposals were made to make ball chain by using separate upper mold and lower mold, and to separate the upper mold from the ball chain by force during mold releasing process. However, due to the interference strength between the mold and the ball chain is very great, it will lead to a server deformation of the chain during the mold releasing process (the finished product is lengthened). If increasing the interference of the steel balls with respect to the spacers and reducing the interference strength between the mold and the ball chain, it will adversely affect the rolling motion of the steel balls.  
         [0007]     The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.  
       SUMMARY OF THE INVENTION  
       [0008]     The primary objective of the present invention is to provide a method of making a ball chain, which can solve the difficulties in production and can improve the effect of spacers for separating the steel balls.  
         [0009]     Since all points on a spherical surface are equidistant from the center of its sphere, the occurrence of interference can be prevented during mold release by releasing the half sphere along the normal direction of a plane passing through the center of the sphere.  
         [0010]     The ball chain comprises a plurality of spacers, and a connecting member connected at either side of the respective spacers for connecting the spacers together in a string fashion, each two neighboring spacers define a space for holding a steel ball, and each spacer defines a concave in either side thereof for mating with the steel ball, so that a plurality of steel balls can freely roll within the space defined by the spacers without impacting one another. A method of making a ball chain in accordance with the present invention comprises the steps of:  
         [0011]     forming an upper mold and a lower mold by injection molding process;  
         [0012]     closing the upper mold and the lower mold, wherein the upper mold has an abutting configuration for mating with an upper surface of the connecting member and a protruding configuration for mating with the concave in one side of the spacer, and the lower mold has an abutting configuration for mating with a lower surface of the connecting member and a protruding configuration for mating with the concave in another side of the spacer;  
         [0013]     injecting material into the cavity defined between the upper and lower molds, wherein the material can be plastic, rubber, or the other polymer; and  
         [0014]     releasing the upper and lower molds along a direction inclined with respect to the connecting member.  
         [0015]     Since all points on a spherical surface are equidistant from the center of its sphere, the occurrence of interference can be prevented during mold release by releasing the half sphere along the normal direction of a plane passing through the center of the sphere. And the two half molds (upper and lower molds) of the present invention are released along the normal direction of a plane passing through the center of the sphere, such mold releasing method can solve the difficulties in production and can improve the effect of spacer for separating the steel balls.  
         [0016]     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiments in accordance with the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a front view of showing a ball chain;  
         [0018]      FIG. 2  is a cross sectional view of the ball chain taken along the line A-A′ of  FIG. 1 ;  
         [0019]      FIG. 3  is an illustrative view of showing a ball chain made by the method in accordance with the present invention, and an upper mold and a lower mold for making the ball chain;  
         [0020]      FIG. 4  is an illustrative cross sectional view of showing that the upper and lower molds are closed together;  
         [0021]      FIG. 5  is an illustrative cross sectional view of showing that the upper and lower molds are being released from each other;  
         [0022]      FIG. 6  shows the relationship between the inclined angle θ  1  and the wrap angle;  
         [0023]      FIG. 7  shows a first embodiment of the present invention wherein the method of manufacturing a ball chain is applied to form ribs on the protruding configuration;  
         [0024]      FIG. 8  shows a second embodiment of the present invention wherein the method of manufacturing a ball chain is applied to form ribs on the protruding configuration;  
         [0025]      FIG. 9  shows another embodiment of the present invention in which protrusions are formed on the protruding configuration;  
         [0026]      FIG. 10  is a cross sectional view taken along the line B-B′ of  FIG. 9 ; and  
         [0027]      FIG. 11  shows another embodiment of the present invention in which protrusions are formed on the protruding configuration. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     The foregoing, and additional objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof, taken in conjunction with the accompanying drawings.  
         [0029]      FIG. 3  is an illustrative view of showing a ball chain  1  made by the method in accordance with the present invention, and an upper mold  4  and a lower mold  5  for making the ball chain  1 . The ball chain  1  in  FIG. 3  comprises a plurality of spacers  11  (for easy description, only four spacer  11  are illustrated, but in fact, a ball chain may comprises tens of spacers  11 ), and a connecting member  12  connected at either side of the respective spacers  11  for connecting the spacers  11  together in a string fashion. Each two neighboring spacers  11  define a space for holding a steel ball (not shown), and each spacer  11  defines a concave  111 ,  112  in either side thereof for mating with the steel ball  2 , so that a plurality of steel balls  2  can freely roll within the spaces defined by the spacers  11  without impacting each other. The concave  111  and  112  is of a spherical surface. The upper mold  4  has an abutting configuration  41  for mating with the configuration of the upper surface of the connecting member  12 , and a protruding configuration  42  for mating with a concave  111  of the spacers  11 . Likewise, the lower mold  5  has an abutting configuration  51  for mating with the configuration of the lower surface of the connecting member  12 , and a protruding configuration  52  for mating with another concave  112  of the spacers  11 . The spacer-configuration  43  of the upper mold  4  and the spacer-configuration  53  of the lower mold  5  in the drawing cooperate with each other to define a configuration of the outer diameter of the spacers  11 . A land area  44  of the upper mold  4  and a land area  54  of the lower mold  5  will come into contact with each other when the two molds are closed. During mold release, the upper mold  4  is released from the lower mold  5  along an inclined angle θ  1 , thus preventing the occurrence of interference during mold release. A plurality of holes  55  are defined in the lower mold  5 , and a plurality of lifting pins  56  are received in the holes  55  for separating the chain  1  from the lower mold  5 .  
         [0030]      FIG. 4  is an illustrative cross sectional view of showing that the upper and lower molds are closed together. After the upper and lower molds  4  and  5  are closed, the spacer-configuration  43 , the protruding configuration  42  of the upper mold  4  and the spacer-configuration  53 , the protruding configuration  52  of the upper mold  5  will cooperate together to define a cavity having the shape of the spacer  11 , for forming the spacers  11  of the ball chain  1 . The ball chain in accordance with the method of the present invention is formed by injection molding process, and the required mold tool includes the upper mold  4  and the lower mold  5 . In operation, the upper mold  4  and the lower mold  5  are closed (as shown in  FIG. 4 ), and then material is injected into the cavity defined between the upper and lower molds  4  and  5 . Finally, the upper and lower molds are released from each other in such a manner that the upper mold  4  and the lower mold  5  are released along a direction inclined with respect to the connecting member  12 .  FIG. 5  is an illustrative cross sectional view of showing that the upper and lower molds are being released from each other, wherein the upper mold  4  and the lower mold  5  are released along an inclined angle θ  1 , the inclined angle θ  1  is smaller than 60 degrees, so that the spacer  11  can wrap as large as 60 degrees portion of the steel ball. The inclined angle θ  1  is optimally 45 degrees, and at this moment, the portion of the steel ball to be wrapped by the spacer  11  will be as great as 90 degrees. After releasing the upper and lower molds  4  and  5  from each other, the ball chain  1  can be released from the lower mold  5  by pushing the lifting pins  56  out of the holes  55 , and thus a ball chain  1  is finished.  
         [0031]      FIG. 6  shows the relationship between the inclined angle θ  1  and the wrap angle (the wrap angle means the portion of the steel ball to be wrapped by the spacer, for example, the circumferential angle of steel ball is 360 degrees, and if the wrap angle is 60 degrees, that means one sixth portion of the steel ball will be wrapped by the spacer). When the protruding configuration  42  of the upper mold  4  shown in  FIG. 5  is released along the inclined angle θ  1 , in order to prevent the protruding configuration  42  from interfering with the formed spacer  11 , the wrap angle θ  2  should be greater than the greatest half angle θ  3 , and the greatest half angle θ  3  equals to 90 degrees minus the inclined angle θ  1 . If the inclined angle θ  1  is greater than 60 degrees, the greatest half angle θ  3  will be 30 degrees, and the wrap angle θ  2  will not be greater than  60  degrees. If the inclined angle θ  1  is 45 degrees, the greatest half angle θ  3  will be 45 degrees, and the wrap angle θ  2  will be as great as 90 degrees. If the inclined angle θ  1  is 60 degrees, approximately 60 degrees portion of each side of the steel ball will be confined, just like that two symmetrical sides of a hexagon are confined. Such arrangement already has a pretty good separating effect. If the inclined angle θ  1  is 45 degrees, the wrap angle θ  2  will be as great as 90 degrees, and approximately half periphery of the steel ball will be in contact with the spacer  11 , and at this moment, the effect of confining the steel ball will be the best.  
         [0032]     Still using the method of releasing mold along the inclined angle θ  1 , the protruding configurations  42  and  52  also can be defined with some ribs or protrusions.  FIGS. 7-11  show some other embodiments of the present invention. As shown in  FIG. 7 , a plurality of ribs  421 ,  521  are formed on the protruding configurations  42  and  52 , so that, after injection molding, a plurality of oil grooves  1111 ,  1121  will be formed in the concaves  111  and  112  of the spacer  11  for reserving a small amount of lubricant and reducing the resistance of the concaves  111  and  112  with respect to the steel balls. Since the forming direction of the ribs  421 ,  521  are the same as the inclined angle θ  1 , the occurrence of interference can be prevented during mold release. For easy illustration, the ribs  421 ,  521  in  FIG. 7  extend horizontally, but in fact, they also can extend in longitudinal direction or in other directions.  
         [0033]     In the embodiment of  FIG. 8 , a plurality of ribs  422 ,  522  are formed on the protruding configurations  42  and  52 , so that, after injection molding, a plurality of oil grooves  1112 ,  1122  will be formed in the concaves  111  and  112  of the spacer  11  for reserving a small amount of lubricant and reducing the resistance of the concaves  111  and  112  with respect to the steel balls. Since the forming direction of the ribs  421 ,  521  are the same as the inclined angle θ  1 , the occurrence of interference of the upper mold  4  with the upper mold  5  can be prevented during mold release.  
         [0034]     In addition, for facilitating the flow of lubricant through the respective steel balls, a through hole can be defined in each of the spacers  11 . As shown in the embodiments of  FIGS. 9 and 10 , a protrusion  423  and  523  is formed on the protruding configurations  42  and  52 . The protrusions  423  and  523  will contact each other to define a rectangular space when the upper and lower molds  4  and  5  are closed, thus a through square passage  113  will be formed in the spacer  11  after injection molding, and the passage  113  facilitates the flow of lubricant through the respective steel balls. For preventing the occurrence of interference between the protrusions  423  and  523  during mold release, the releasing angle θ  4  should not be smaller than the inclined angle θ  1 . The releasing angle θ  4  refers to an angle of the abutting surface of the two protrusions  423 ,  523  with respect to the connecting member  12 .  
         [0035]     The embodiment shown in  FIG. 11  is also designed to form a through passage in the spacer  11  for facilitating the flow of the lubricant through the steel balls. In  FIG. 11 , a protrusion  424  and  524  is formed on the protruding configurations  42  and  52 , the protrusions  424  and  524  can be pyramid-shaped or conical-shaped. The protrusions  424  and  524  will contact each other to define a conical passage  114  when the upper and lower molds  4  and  5  are closed, and the passage  114  facilitates the flow of lubricant through the respective steel balls. For preventing the occurrence of interference of the protrusions  423  and  523  with the ball chain  1  during mold release, the half cone angle θ  5  should not be greater than the inclined angle θ  1 .  
         [0036]     While we have shown and described various embodiments in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.