Abstract:
A tire blade system for curing tires including a tire mold defining at least one slot, the slot defining a first recess and a second recess spaced by a bridge, the walls of the first and second recess being straight; a blade including a body exposed within the tire mold and an attachment assembly received in the slot, the attachment assembly including a first and a second prong spaced by a notch; and wherein the first prong includes a engaging edge and the second prong including an undercut edge, and when the blade is inserted into the slot, the engaging edge deflects the bridge toward the undercut edge to resiliently hold the blade in the slot.

Description:
The present invention generally relates to tire mold systems. In particular, the present invention relates to a blade attached within a tire mold to form a sipe. Most particularly, the present invention relates to a self-locking tire blade system including a blade having an attachment assembly that fits into a receiver formed in a tire mold, where the attachment assembly includes a surface that deforms the receiver upon insertion to secure the blade within the mold. 
     BACKGROUND OF THE INVENTION 
     Tire molds often incorporate blades to form slots or grooves in the tread of a tire. These slots and grooves are typically referred to as sipes. The blades are typically thin metal strips of various lengths. The strips are typically straight but may include one or more bends and/or arcs depending on the shape of the sipe to be formed by the blade. 
     To mount the blade within a machined tire mold, slots are machined into the tire mold and the blade is inserted into the slots. Typically, the slot has a uniform depth and extends the entire length of the blade to provide the greatest amount of surface area for application of an adhesive, such as epoxy, to hold the blade within the slot. Since a single tire mold may include hundreds of slots, the time required to machine the slots is significant. Also, the labor involved in applying an adhesive to each blade before insertion is extensive. To that end, a self-locking blade has been recently developed to secure the blade within a slot without the need for the time consuming step of applying epoxy to the blade. The self-locking blade includes self-locking structures that expand outwardly to create an interference fit within the mold. To that end, grooves are formed in the tire mold to receive the self-locking structures. To allow the self-locking structure to expand, these grooves are undercut such that they have a trapezoidal profile with a base that is wider than the top opening of the groove, and sidewalls that slope inwardly from the base to the opening. 
     The self-locking structures include tendons that extend downward from the base of the blade. The tendons generally have a split configuration with a center portion that joins the split halves of the tendon and extends downward from the tendons. The tendons initially have a width less than the top opening within the groove to allow them to be easily inserted. To secure the blade, the blade is tapped with a hammer to collapse the center portion forcing it inward between the split halves. The collapsing center portion forces the split halves outward to fill the undercut portions of the groove. 
     While this blade improved over the prior method of securing blades with epoxy, the machining of the undercut grooves requires a five axis machine. Forming this undercut becomes even more difficult when using electric discharge machining (EDM). The use of EDM is attractive because of the speed with which slots may be formed using this technique. Therefore, a self-locking blade that does not require formation of an undercut groove within the tire mold is desirable. 
     Tire molds may also be constructed by casting the mold. In this process, the blades are attached by forming the mold around the blade. To that end, during the casting process, the blades are held in a pattern, and then molten mold material flows around the base of the blade. Taking advantage of this process, blades used in cast molds include notches on the side of the blade base below the top surface of the mold so that the molten material flows into these notches and positively stops the blade from being pulled out. It will be appreciated that this type of blade cannot be used in a machined slot. Therefore, it is desirable to have a self-locking blade that can be used in both a machined mold and a cast mold. 
     SUMMARY OF THE INVENTION 
     The present invention generally provides a tire blade that defines a notch in which a bridge within the tire mold is received. One side of the notch defines an undercut and the opposite side is adapted to engage the bridge and deform the bridge into the undercut portion of the notch. 
     The present invention also provides a method of attaching a blade within a slot including the steps of providing a blade having a notch with an undercut on one side of the notch; forcing a portion of the mold into the undercut portion of the notch by inserting the blade into the slot. 
     The present invention also provides a tire blade system including a tire mold defining at least one slot, the slot defining a first recess and a second recess spaced by a bridge, the walls of the first and second recess being straight; a blade including a body exposed within the tire mold and an attachment assembly received in the slot, the attachment assembly including a first and a second prong spaced by a notch; and wherein the first prong includes a engaging edge and the second prong including an undercut edge, and when the blade is inserted into the slot, the engaging edge deflects the bridge toward the undercut edge to hold the blade in the slot. 
     The present invention also provides a blade for attachment to a tire mold including a body; a first prong and a second prong extending from a bottom edge of the body and defining a notch therebetween, the first prong including an engaging edge, facing the second prong and the second prong including an undercut edge, facing the first prong, the engaging edge and the undercut edge being generally parallel and oriented other than perpendicular to the bottom edge. 
     The present invention also provides a self-locking tire blade system including a tire blade having an attachment assembly extending from a base of the tire blade, wherein the attachment assembly includes at least one prong, a tire mold having a receiver, the receiver defining a recess corresponding to the prong, and wherein the attachment assembly has a surface adapted to deform the receiver upon insertion to create an interference fit between the tire blade and the tire mold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view of a tire blade according to the concepts of the present invention; 
         FIG. 2  is an enlarged front elevational view of the area indicated in  FIG. 1  to show details of an attachment assembly formed on the blade; 
         FIG. 3  is a partially schematic front assembly view depicting insertion of the blade into a slot formed in a tire mold according to the concepts of the present invention; 
         FIG. 3A  is a top plan view of a slot according to the concepts of the present invention; 
         FIG. 3B  is an enlarged view of a portion of the slot depicted in  FIG. 3A ; 
         FIG. 4A  is a perspective view of a tire blade system including a blade having a pair of attachment assemblies being inserted into a slot having corresponding receivers with rounded corners; 
         FIG. 4B  is a perspective view similar to  FIG. 4A , depicting the receivers after the blade has been inserted, where the corners of the receiver have been deformed by the square corners of the blade; 
         FIG. 5A  is a front elevational view of a tire blade system, partially sectioned to show details of the insertion of the blade into the slot formed in the tire mold, where the outer prongs have been rounded to facilitate insertion; and 
         FIG. 5B  is a front elevational view similar to  FIG. 5A  showing the blade inserted. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A tire mold blade according to the concepts of the present invention is generally referred to by the number  10  in the accompanying drawings. Referring to  FIG. 1 , blade  10  is generally a thin member that is attached to a tire mold M. Blade  10  may be formed of a variety of materials including, for example, and without limitation, steel, stainless steel, aluminum, and Inconel®. It will be appreciated that other materials may be used as long as they are capable of withstanding the tire molding process. 
     Blade  10  includes a body  12  that is exposed within tire mold M to form a sipe within the finished tire. To attach blade  10 , an attachment assembly, generally indicated by the number  20  is provided at the base  14  of blade  10 . As best shown in  FIG. 2 , attachment assembly  20  may include at least one prong  22  that extends outward from base  14  of blade  10  toward tire mold M. As shown, attachment assembly may include a pair of prongs  22 , where the first and second prongs define a notch  24  for receiving a bridge formed in tire mold M, as will be described more completely below. Prongs  22  may have any shape including for example, the rectangular shape shown. Also, the outward edge of prong  22  may be square. In general prongs  22  have a width less than the length of blade  10 . 
     As shown in  FIG. 1 , blade  10  may include more than one attachment assembly  20 . Since longer blades are subjected to forces over a larger area and are able to accommodate more attachment assemblies  20 , the number of attachment assemblies  20  used typically will be determined by the length of the blade. In the example shown, two attachment assemblies  20  are located at opposite ends of a blade  10 . To attach blade  10  to mold M, blade  10  is inserted within a slot  30  formed in mold M. 
     In accordance with the concepts of the present invention the tire mold system includes a slot  30  formed within mold M that holds blade  10 . To that end, slot  30  includes a receiver, generally indicated by the number  31  that receives the attachment assembly  20 . Receiver  31  generally conforms to attachment assembly  20 . For example as shown in  FIGS. 3-3B , receiver  31  includes a pair of recesses  32  that receive a pair of prongs  22  separated by a protruding bridge  34 . If blade  10  includes multiple attachment assemblies  20 , slot  30  may be formed with corresponding receivers  31 , as shown in  FIGS. 3 and 3A . To provide additional Support slot  30  may include a shallow recess  33  for receiving a portion of base  14  that lies adjacent to the attachment assemblies  20 . For example, with attachment assemblies  20  located at the ends of blade  10 , the center section of the blade&#39;s base  14  may be received in a central recess  33 . Advantageously, since attachment assemblies  20  hold the blade, recess  33  does not have to be machined to the full depth of receivers  31  to provide the necessary support. This saves considerable time, material, and tool wear in machining slots  30 . 
     The outer walls  36  of receiver  31  may be cut straight, meaning without an undercut. For example, as shown, the walls may be perpendicular to the top surface of mold M. When compared to the undercut walls found in the prior art, using straight cut walls greatly reduces the complexity of machining slot  30  and allows the use of electronic discharge machining (EDM). 
     In general, attachment assembly  20  creates an interference fit with receiver  31  by locally deforming receiver  31 . To that end, attachment assembly  20  includes at least one surface adapted to deform receiver  31  upon insertion of blade  10  in a slot  30 . In one embodiment of the invention, the cross-section of attachment assembly  20  is made larger than the cross-section of the corresponding receiver  31  to create an interference fit. For example, as shown in  FIGS. 3B-4B , the corners  27  of attachment assembly  20  are made square, while the corners  37  of receiver  31  are rounded ( FIG. 3B ). By rounding one or more corners  37 , the cross-section of attachment assembly  20  having square corners  27  is larger than its corresponding receiver  31 . By applying a radius R to at least one of the corners  37  of recesses  32 , when the blade  10  is inserted, prongs  22  deform the corners  37  of recesses  32 .  FIG. 4A  shows the radiused corners  37  of receivers  31  before blade  10  is inserted, and  FIG. 4B  shows the resulting deformation after insertion. The difference in cross section between attachment assembly  20  and receiver  31  creates an interference fit that helps hold blade  10  against pulling forces within mold M. This method of attaching blade  10  may be used as a separate method of attaching blade  10  or in combination with the engaging edge method described below. 
     Alternatively, attachment assemblies  20  may create an interference fit with mold M by deforming a bridge  34  within mold M. For example, as best shown in  FIG. 2 , an engaging edge  38  on prong  22 A may be provided on one side of notch  24 , and an undercut edge  40  may be provided on a second prong  22 B on the opposite side of notch  24 . It will be understood that the undercut is formed by opening undercut edge  40  interiorly of the mouth  25  of notch  24 . In effect the material of the undercut prong  22 B forms an overhanging portion at the mouth that interferes with outward movement of blade  10  relative to mold M after it is attached, as described more completely below. 
     Engaging edge  38  is adapted to force bridge  34  toward undercut edge  40  as blade  10  is inserted into slot  30 . Any shape suitable for forcing bridge  34  toward undercut edge  40  may be used. In the example shown, engaging edge  38  slopes inward at an angle α, relative to bottom face  41  of prong  22 , as it extends inward toward floor  42  of notch  24 . Likewise, undercut edge  40  may have any shape so long as it opens inward of the edge  44  formed at the juncture of bottom face  41  and undercut edge  40  of prong  22 . In this way, as the bridge  34  is pushed into the open area (seen between the dashed line and surface  40  in  FIG. 2 ), it is partially trapped by the outer edge  44  of prong  22 . In the example shown, undercut edge  40  slopes at an angle β, relative to bottom face  41  of prong  22 . Angle β may be equal to angle α such that the engaging edge  38  and undercut edge  40  are parallel. These angles, however, do not have to be equal, and may vary relative to each other. As depicted by the dashed lines in  FIG. 2 , in this example, undercut edge  40  opens notch  24  laterally the same extent that engaging edge protrudes into notch  24 . It has been found that increasing the angle of engaging edge  38  and undercut edge  40  increases the force needed to pull the blade  10  from slot  30 . Suitable angles, i.e. those resulting in pull out forces within the range typically experienced in tire molds, included absolute angles from greater than zero degrees to about 7.5 degrees. It is expected that angles above 7.5 degrees would result in higher pull out forces, and thus would be suitable as well. Consequently, any angle other than perpendicular, measured relative to the bottom face  41 , is believed to be suitable. 
     The outer edges  43  of prongs  22  are cut straight or perpendicular to bottom face  41  to facilitate insertion of prongs  22  into straight cut recesses  32 . As mentioned above, using straight cut recesses  32  greatly reduces the complexity of machining mold M by avoiding the use of undercut slots in a machined mold. 
     It is believed that the attachment assembly  20  described above would be effective in a cast mold. When forming the cast mold, molten material would flow around prongs  22  and into the open space defined by undercut edge  40  such that the same interference fit between attachment prongs  22 A,  22 B and bridge  34  would be created during the molding process. Consequently, a blade  10  having such an attachment assembly  20  could be used in both a machined mold and a cast mold. 
     Optionally, as shown in  FIG. 5A , one or more edges of prongs  22  may be rounded or beveled to ease insertion of blade  10  into slot  30 . For example, the outside corner  45  formed between bottom face  41  and outer edge  43  of the outermost prongs  22  on blade  10  may be rounded to help locate blade  10  in slot  30  and facilitate its insertion. Blade  10  may be inserted in any known manner including simply pressing blade  10  inward until attachment assemblies  20  are seated within receivers  31  ( FIG. 5B ). If necessary, blade  10  may be tapped into slot  30  with a hammer or other suitable object, as is known in the art. Or when using blade  10  in a cast mold, blade  10  having an attachment assembly  20  is held in a pattern while molten molding material fills the mold. The molten material flows around attachment assembly  20  and is allowed to cool and harden. Once hardened, the pattern is removed and blade  10  is held within the completed mold. In both cases, the interference fit established by attachment assembly  20  holds blade  10  against the pulling forces created during the tire molding process. 
     It should be apparent that the invention as described provides comports with patent statutes by providing a new and useful self-locking tire blade system. It should further be understood that the preceding is merely a detailed description of a preferred embodiment of this invention and that various modifications and equivalents can be made without departing from the spirit or scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined by the appended claims and their equivalents.