Abstract:
A tire mold heat transfer system in which heat pipes are enclosed in tubular passages in the tire mold to transfer heat to heated positions adjacent the tread and sidewall forming sections of the mold.

Description:
TECHNICAL FIELD 
     This invention relates to tire molds and especially to tire molds having heat pipes incorporated for providing improved heating of the tread and sidewall forming surfaces. 
     BACKGROUND OF THE INVENTION 
     Tire molds of steel or aluminum have been heated by steam heated platens or by placing the molds in steam domes. Thermal conduction through steel or aluminum has been relied upon to transfer heat to the tread and sidewall forming surfaces. Also, the cure time has been extended by the temperature recovery time following a loading or unloading cycle. Problems have also been encountered in providing temperature uniformity at positions on the mold-tire interfaces. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to utilizing a heat transfer system containing elongated sealed metal heat transferring heat pipes incorporated in the tire mold for transmitting heat to the mold surfaces. In accordance with this system, the heat is transmitted directly from the heat source such as a platen or a steam dome to the tread area of the mold. With a platen-heated mold, the heat pipes are positioned in the tread mold segments so as to transmit the heat from the platen directly to positions adjacent the tread forming surfaces of the mold. With the steam dome tire presses, the heat is transmitted by heat pipes directly from the steam dome to the heating positions adjacent the tread and sidewall forming surfaces of the mold. 
     In accordance with one aspect of the invention, there is provided a generally cylindrical tire mold having a radially inner tread forming surface, characterized by tubes extending from openings in the mold to heating positions adjacent the tread forming surface and heat pipe means positioned in the tubes for selectively transferring heat to the tire mold at the heating positions. 
     In accordance with another aspect of this invention there is provided a tire mold an upper cylindrical mold half and a lower cylindrical mold half with each mold half having a cylindrical groove spaced from the tread forming surface, the heat pipe means comprising a coiled heat pipe disposed in the groove and the tubes being formed in the groove by heat conducting material filling the voids around the heat pipe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross sectional view of a tire mold embodying the invention mounted in a tire press having a heating platen with parts being broken away showing two heat pipes in position for transferring heat to the tread forming surface. 
     FIG. 2 is a bottom view of one of the segments of the tire mold shown in FIG.  1 . 
     FIG. 3 is a sectional view like FIG. 1 of the segment shown in FIGS. 1 and 2 taken along the plane of line  3 — 3  in FIG.  2 . 
     FIG. 4 is a sectional view like FIG. 1 taken along the plane of line  4 — 4  in FIG.  2 . 
     FIG. 5 is a view in perspective of another tire mold half embodying the invention showing the ends of the heat pipes exposed to the steam in a steam dome press. 
     FIG. 6 is a cross sectional view of the mold half shown in FIG.  5 . 
     FIGS. 7 and 8 are sectional views of the mold half shown in FIG. 6 taken along the plane of line  7 — 7  and  8 — 8 . 
     FIG. 9 is a view in perspective of another embodiment of the invention wherein the heat pipe is coiled and positioned in a circumferential groove for transferring heat from the platen to the tread forming surfaces showing the coiled heat pipe. 
     FIG. 10 is a fragmentary sectional view of a tire mold half with the coiled heat pipe of FIG. 9 embedded in the circumferential groove of the mold half and showing the platen for heating the coiled at the end of the pipes. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a schematic view of a portion of a tire press  10  embodying the invention is shown with an upper press platen  12  and a lower press platen  14  mounted for a relative vertical movement in a manner well known in the art. Mounted on the upper press platen  12  is the upper mold section  16  which includes a full circle mold back  18  and a plurality of radially movable mold segments  20  in sliding engagement with the mold back. Mounted on the mold segments  20  are radially inner tread mold segments  21  having radially inner tread forming surfaces  22 . An upper sidewall surface  24  is provided on the upper mold section  16  and a lower sidewall surface  26  is provided on a lower mold section  28  which is in abutting relation with the lower platen  14  for heating the lower mold section. Also in abutting relation with the lower mold section  28  and platen  14  are the mold segments  20  slidably movable in a radial direction on a heat-conducting surface  30  as shown in FIGS. 1-4. This heat conducting surface  30  is in engagement with a heated surface  32  of the heated platen  14  shown in FIG.  1 . 
     The sectional view of the mold segment  20  in FIG. 1 is taken along lines  1 — 1  in FIG.  2  and illustrates the positions of the radially inner tubes  34  and the radially outer tubes  36  extending vertically through each of the segments  20  and having openings  38  and  40  facing the heat conducting surface  30  of the mold segment  20 . Additional side tubes  42  and  44  may be provided at the sides of the segments  20  and extend partway into the mold segments as shown in FIG.  3 . The center of each of the segments  20  is provided with grooves for sliding engagement with the upper mold section  16 . 
     Inserted in each of the tubes  34 ,  36 ,  42  and  44  are heat pipes  46  extending from the heat conducting surface  30  of the lower mold section  28  to tread heating positions  48 . Each of the heat pipes  46  may be of a type embodying an elongated, sealed metal heat transferring container for a liquid working fluid having a liner of wick material and an open core extending from a first end of the container to the second end of the container wherein the working fluid may be vaporized at the first end and the vapor transferred to the second end where it is condensed and then returned to the first end by capillary action through the liner. The second end of the container may include a substantial length of the container where heat transfer takes place due to the temperature differential between that portion of the container and the mold portion to be heated. 
     In the embodiment shown in FIGS. 1-4, the first sidewall surface  24  and lower sidewall surface of the mold are heated by the upper platen  12  and lower platen  14 . The radially inner tread forming surfaces  22  are heated by the transfer of heat from the heated surface  32  of the lower press platen  14  which is in contact with the heat conducting surface  30  of the mold segments  20  and in contact with the heated ends of the heat pipes  46  in the side tubes  42  and  44  and the central tubes  50  and  52  located in the inner tubes  34  and outer tubes  36  of the mold segments. As shown in FIGS. 1 and 2, the heat pipes  50  in the radially inner tubes  34  are longer than the heat pipes  52  in the outer tubes  36  for transmitting heat to the outer extremities of the mold segment  20 . 
     In operation, when the upper press platen  12  and the lower press platen  14  are heated, the upper sidewall surface  24  and lower sidewall surface  26  are heated by conduction. The tread forming surfaces of the mold segments  20  are heated by conduction from the heated surfaces of the upper press platen  12  and the lower platen  14 . This is supplemented by the heat transmitted through the heat pipes  46  in contact with the heated surface  32  of the lower mold section  28 . It has been found that with the supplementary heating by the heat pipes  46 , there is substantial reduction in heating time for curing tires and also the temperature recovery time following loading and unloading is substantially improved. 
     With reference to FIGS. 5,  6 ,  7 , and  8 , a mold half  54  of a steam dome press is shown with heat pipes  56  in tubes  58  extending from a radially outer surface  60  to heating positions  62  in the proximity of the tread forming surfaces  64 . In the embodiment shown the mold has grooves  66  and ribs  68  for forming the tread. The tubes  58  are positioned so as to extend into the ribs  68  for transmitting heat through the heat pipes  66  from the radially outer surface  60  of the mold half which is exposed to the steam in the steam dome to the tread forming surface  64 . As shown in FIGS.  6 , 7 , and  8 , the tubes  58  are also positioned at spaced apart positions axially of the mold half  54  for transmitting heat through the heat pipes  56  to different positions axially of the mold half. 
     Referring to FIGS. 9, and  10  a sectional view of a platen heated mold half  70  is shown having a circumferential groove  72  extending axially in close proximity to the tread forming surface  74 . The groove  72  may also have a radially inner extension  76  in close proximity to the sidewall  78 . A coiled heat pipe  80 . shown in FIG. 9 is positioned in the circumferential groove  72  and extension  76  with voids  82  filled with a thermally conductive solder or past to provide tubes for supporting the coils and conducting the heat to the mold. A heating platen  84  is positioned adjacent the mold half  70  and the bottom coils of the heat pipe  80 . 
     In operation the coiled heat pipe  80  is heated by the platen  84  and heat transmitted through the coiled heat pipe to the tread forming surface  74  of the mold half  70 . 
     A similar construction for an upper mold half and upper platen with a coiled upper heat pipe may be provided for the upper half of the tire mold. The heat pipe  80  in the lower mold half and upper mold half then approach one another in terms of heat transport capacity. Each has a slight slope along its length with the upper pipe working against gravity and the lower pipe  80  working with gravity. This can be compensated by using different pitch windings for the upper and lower mold halves. This arrangement produces a favorable uniformity about the mold axial centerline with all pipes on a properly sized heat pipe surface being within a few degrees of temperature of one another. With a single spiral wound heat pipe per mold half, the number of components is minimized and the probability of failure is reduced. 
     While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes may be made therein without departing from the spirit or scope of the invention.