Abstract:
A segmented tire mold having radially movable circumferentially spaced sliding center segments activated by sliding connections between an upper mold half and the segments in response to opening and closing of the mold.

Description:
This application is a 371 of PCT/US99/22799 filed Oct. 1, 1999. 
    
    
     TECHNICAL FIELD 
     This invention relates to segmented tire molds and especially to molds having center segments which are movable radially in response to opening and closing of the mold. 
     BACKGROUND OF THE INVENTION 
     Full segmented molds such as the mold shown and described in U.S. Pat. No. 5,585,064 provide for expanding and contracting segments, however, the segments are mounted on the top mold and must be lifted to retract the segments. In addition to the added power required to lift the segments, the wear on the parts is also a disadvantage of this type of mold. 
     Other segmented molds, such as the mold shown in Great Britain Patent GB 1,176,162 provide hinged segments with springs for retracting the hinge pins of the segment. The tilt type segmented molds of this type do not provide for loading an uncured tire without engaging the bridge work on the segments. This is especially objectional for molds with curved segmental boundary designs where the mold segments must be retracted in a direction perpendicular to the vertical axis of the segments. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a segmented mold having radially movable center segments which are mounted on the lower mold half. Each center segment has a slotted connection with a sloped surface of the upper mold half for retracting and then returning the segment to the registered position for molding a tire. The slot in the center segment is open at the top to permit opening of the mold without lifting of the segment. A spring holds the center segment in a radially outward position against a stop in the lower mold half which positions the slot for engagement with the upper mold half upon closing of the mold. 
     In accordance with one aspect of the invention there is provided a segmented tire mold having an upper mold half, a lower mold half and radially movable circumferentially spaced sliding segments characterized by: 
     a. each of the sliding segments being mounted on the lower mold half for radial movement, 
     b. a disengagable sliding connection between the upper mold half and each of the sliding segments for moving the segments radially of the mold between an open retracted position and a closed molding position. 
     In accordance with another aspect of the invention there is provided a method of vulcanizing a tire in a segmented tire mold having an upper mold half, a lower mold half and radially movable circumferentially spaced center segments in sliding engagement with the lower mold half and slidably engagable with the upper mold half upon closing of the mold characterized by: 
     a. opening the mold by lifting the upper mold half away from and out of sliding engagement with the center segments, 
     b. moving the center segments radially outward by the sliding engagement with the upper mold half, 
     c. limiting the movement of the center segments radially outward by stop means on the lower mold half, 
     d. placing an unvulcanized tire on the lower mold half, 
     e. lowering the upper mold half in sliding engagement with the center segments for moving the center segments radially inwards into engagement with the tire upon closing of the mold, 
     f. applying heat to the tire mold to vulcanize the tire, 
     g. lifting the upper mold half for sliding the center segments radially outward on the lower mold half, and 
     h. removing the tire from the tire mold. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a plan view of the lower mold half and the center segments embodying the invention. 
     FIG. 2 is a section of the mold embodying the invention taken along line  2 — 2  in FIG. 1 with parts being broken away to show the plunger and coil springs of the mold in the closed position. 
     FIG. 3 is a section like FIG. 2 showing the center segment in a partially retracted position. 
     FIG. 4 is a enlarged fragmentary sectional view of one of the centering pin connections between the lower mold half and the upper mold half taken along the plane of line  4 — 4  in FIG.  2 . 
     FIG. 5 is an enlarged fragmentary sectional view of the lower mold half taken along the line  5 — 5  in FIG. 1 showing the stop means and spring pin for a center segment in the fully retracted position. 
     FIG. 6 is an enlarged fragmentary sectional view of the sliding connection between the upper mold half and one of the center segments taken along line  6 — 6  in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, a segmental tire mold  10  is shown having a lower mold half  12 , an upper mold half  14  and radially movable center segments  16 . The lower mold half  12  and the upper mold half  14  have sidewall forming surfaces  18  and  20  respectively. The center segment  16  has tread forming surfaces  22 , which are movable radially for disengaging the mold  10  from the tire after vulcanization. 
     Each of the center segments  16  is slidably mounted on a T-bar  24 , fastened to the lower mold half  12  by bolts  26  or other suitable means. Each T-bar  24  extends radially of the mold  10  and slides in a slot  27  extending radially of the mold. 
     Each of the center segments  16  also have recesses  36  with end flanges  28  for plungers  30  mounted in sleeves  32  mounted on the lower mold half  12  and urged radially outward by coil springs  34  located between the recessed surface  36  in the lower mold half  12  and a flange  38  on the plunger  30 . The coil springs  34  hold the center segments  16  in the fully retracted position after mold half  12  is pulled away from the center segments  16 . 
     Referring to FIG. 6, a slot  40  is provided in a sloped surface  42  of the center segment  16  and has grooves  44  for receiving rollers  46  mounted on a shaft  48 , supported by a bar member  50  which is bolted to the upper mold half  14  by a bolt  51 . The slot  40  extends from a base surface  52  to a top edge  54  of the center segment  16 . With this construction, lifting of the upper mold half  14  from the position shown in FIG. 2 to the position shown in FIG. 3 provides for travel of the rollers  46  upward through the grooves  44  pulling the center segments  16  radially outward to the position shown in FIG.  3 . 
     Referring to FIG. 5, stop means, such as bolts  56  are located on the lower mold half  12  at spaced apart positions for limiting the radially outward movement of the center segments  16  beyond the partially open position shown in FIG. 3 to a position where the upper mold half  14  is lifted away from the lower mold half  12  and center segment  16  removing the rollers  46  from the grooves  44 . The bolts  56  hold the center segments  16  in the position shown in FIG. 5 by springs  36  so that when the upper mold half  14  is lowered onto the center segment  16 , the rollers  46  will be in alignment with and enter the grooves  40  for closing the mold  10 . 
     Referring to FIG. 4, centering pins  58  are mounted in the lower mold half  12  at circumferentially spaced positions for registering in holes  60  in the upper mold half  14  when the upper mold is lowered into position over the center segment  16  and lower mold half  12 . 
     The upper mold half  14  has shoulder forming surfaces  62  adjacent the sidewall forming surfaces  20  and the lower mold half  12  has shoulder forming surfaces  64  adjacent the sidewall forming surfaces  18 . Positioned between the shoulder forming surfaces  62  and  64  are the tread forming surfaces  22  on the center segments  16 . 
     In addition to the lower mold half  12 , upper mold half  12  and center segments  16 , the segmental tire mold  10  also includes means for heating the molds and lifting and lowering the upper mold half  14 . These services are well known in the art and are included in this disclosure, although not shown in the drawings or described herein. 
     In operation the segment tire mold  10  is opened by lifting the upper mold half  14  away from the center segments  16  and lower mold half  12  causing the center segments  16  to retract to a partially open position shown in FIG.  3 . The springs  36  move the segments  16  to the fully open position shown in FIG. 5. A green unvulcanized tire is then lowered into the lower mold half  12  and the upper mold half  14  lowered so that the centering pins  58  shown in FIG. 4 are registered in the centering pin holes  60 . The grooves  44  in the center segments are then in position for receiving the rollers  46  of the segment bars  50  in the slots  40  of the center segments  16 . Further lowering of the upper mold half  14  from the position shown in FIG. 3 to the position shown in FIG. 2 causes the tread forming surfaces  22  of the center segments  16  to move radially inward into the position shown in FIG.  2 . During the closing of the mold  10 , the springs  34  are compressed by movement of the flange  28  radially inward against the plungers  30 . The segmental tire mold  10  is then in position for molding the tire upon the application of heat for a predetermined period of time. 
     After the tire is vulcanized, the mold  10  is opened by raising the upper mold half  14 . This results in radially outward movement of the center segments  16  due to the action of each T-bar  24  in each slot  27  of each center segment. As the upper mold half  14  is lifted, the rollers  46  attached to the upper mold half engage the surfaces of the slot  40  in the center segments  16  urging them radially outward out of engagement with the cured tire tread. The upper mold half  14  may then be lifted away from the center segment  16  and lower mold half  12  for removal of the tire.