Abstract:
Making a tire mold having a plurality of complete tire mold segments ( 20 ) of epoxy resin mold material formed in the chambers ( 18 ) of segmental shoes ( 10 ) and having reinforced stand alone ribs ( 56 ) formed in recesses in the tread models mounted in the shoes. The shoes ( 10 ) and models ( 50 ) are reusable and have standard shoe split diameters and chord lengths to reduce the time necessary to make the molds. The models ( 50 ) are of resilient material and are also reusable.

Description:
TECHNICAL FIELD 
     This invention relates to methods and mold constructions for making molds of plastics, such as epoxy resin. These molds may be made by pouring uncured, liquid plastic epoxy resin over models in segmented shoes. The present invention is especially directed to the forming of epoxy resin molds for molding tires which have recesses in the tread surface which are formed by stand alone ribs in the surfaces of the molds. The segmented shoes are reusable and may be prefabricated with standard shoe split diameters and chord lengths to reduce the time necessary to make subsequent molds. Alignment and sealing of the shoe parts is provided. 
     BACKGROUND ART 
     As shown in U.S. Pat. No. 4,858,881, it has been proposed to make partial tire molds of epoxy or other resin to repair tire sidewalls. It has also been proposed to reinforce plastic articles with glass fibers, as shown in U.S. Pat. No. 4, 692,291. U.S. Pat. No. 5,449,483 uses modular shoe containers for making metal shells with a resin backing. 
     The transfer of metal blades from slits in a matrix of rubber to a mold shell is described in U.S. Pat. No. 2,275,582. The matrix is covered by an electro-formed metal shell which bonds to the blades so that upon removal of the matrix the blades become part of the metal mold shell. The mold shell must then be machined to become part of a tire mold. 
     DISCLOSURE OF INVENTION 
     In accordance with the method of this invention, a model of a segment of a tire having a tread configuration with recesses such as grooves, slots and slits in the model surface is mounted in a shoe having a chamber for receiving a plastic, such as uncured, liquid epoxy resin, to form a complete segment of the tire mold. Before filling the chamber with the uncured epoxy resin , the model is sprayed with a grease type spray release agent which does not react with the epoxy resin to retard its curing. 
     In one embodiment of this invention a mixture of fiberglass and epoxy is sprayed on the surface of the model and into the recesses in the model surface to provide reinforced stand alone ribs in the tread molding surface of the epoxy resin mold after curing and removal of the mold from the model. In another embodiment, the mixture of uncured epoxy resin and fiberglass is formed in a semi-liquid putty-like consistency, and instead of spraying, this material is packed against the surface of the model to fill the recesses in the model surface. After the recesses are filled by packing the mixture of epoxy resin and fiberglass and allowing it to cure the chamber in the shoe is completely filled by pouring uncured liquid epoxy resin mold material into the chamber of the shoe to form a complete mold segment. This liquid epoxy resin mold material is then cured. 
     In another embodiment, a slurry of liquid epoxy resin and fiberglass is poured directly over the model and the chamber filled after which pressure is applied to force the slurry into the recesses in the model surface and to form stand-alone ribs in the mold surface. 
     In a further embodiment, single or laminated metal blades are inserted in the slits of the model after the model has been sprayed with a release agent. The blades may be glued to the model with an appropriate adhesive for bonding metal to elastomeric materials. The model is then mounted in a shoe container and filled with a liquid epoxy resin mold material which bonds to the surface of the blades. The epoxy resin mold material is cured and then cooled. When the model is removed, the solidified epoxy resin mold material contained in the shoe is pulled away from the model. The blades remain in the epoxy tread mold and reinforce the ribs and make them capable of withstanding the stress and strain from the tire molding process. 
     The model is preferably a resilient elastomeric material facilitating insertion of the blades into the slits of the model and removal of the blades from the slits in the model after pouring of the epoxy resin mold material. The model can then be used again to form another tread mold segment. 
     The process of this invention provides steel or aluminum parts to make the epoxy resin tread mold segment and to hold the segments during tire curing. Parts of different sizes have been needed to make molds of different tire sizes. In order to make the molds quickly, the parts have been prefabricated. In accordance with this invention, the number of different size parts has been reduced by prefabricating them in different sizes using two dimensional standards. One dimensional standard is the mold split diameter which is the diameter at which the sidewall plates meet the tread segments. The other dimensional standard is the chord angle and the sequence of the slide block parts which are used in the mold mechanism. 
     The shoes of this invention may also be used more than once by providing a U-shaped cavity with radial sides permitting easy removal of the epoxy mold tread segment from the cavity after curing while at the same time the tread segment mold part is secured without requiring lips on the edges. This is accomplished while providing sealing of the shoe cavity and holding the model bracket in alignment with the shoe. 
     In accordance with one aspect of the invention, there is provided a method of providing reinforced stand-alone ribs in the molding surface of a mold of epoxy resin mold material for molding an article having recesses in the surface comprising: 
     (a) making a model of elastomeric material having recesses in the surface of the model; 
     (b) applying a release agent to the surface of the model characterized by; 
     (c) inserting metal blades in the recesses; 
     (d) placing the model in a shoe container chamber having the shape of a complete mold part; 
     (e) filling the shoe container chamber with an epoxy mold material to form a complete mold part; 
     (f) curing the epoxy mold material in the container while it is cured to form the mold part; and 
     (g) separating the mold part from the model with the metal blades adhering to the mold part and being pulled out of the recesses in the surface of the model. 
     In accordance with another aspect of this invention, there is provided a method of providing reinforced stand-alone ribs in the surface of a plastic mold for molding an article having recesses in the surface of the article comprising 
     (a) making a model of elastomeric material having recesses in the surface of the article; 
     (b) applying a release agent to the surface of the model characterized by; 
     (c) spraying the surface with uncured epoxy resin mold material containing reinforcing material to fill the recesses; 
     (d) placing the model in a shoe container chamber having the shape of a complete mold part; 
     (e) filling the shoe container chamber with the uncured epoxy resin mold material to form a complete mold part; 
     (f) retaining the epoxy resin mold material in the container chamber while it is cured to form the mold part; and 
     (g) separating the mold part from the model with the epoxy resin mold material in the recesses being pulled out of the recesses in the model in the form of stand alone ribs. 
     In accordance with a further aspect of this invention, there is provided a method of providing reinforced stand alone ribs in the surface of a plastic mold for molding an article having recesses in the surface of the article comprising 
     (a) making a model of elastomeric material having recesses in the surface of the model; 
     (b) applying a release agent to the surface of the model characterized by; 
     (c) packing plastic mold material containing reinforcing material against the surface and into the recesses of the model; 
     (d) placing the model in a shoe container chamber having the shape of a complete mold part; 
     (e) filling the shoe container with a plastic mold material to form a complete mold part; 
     (f) retaining the plastic mold material in the container while it is cured; and 
     (g) separating the mold part from the model with the plastic mold material containing the reinforcing material in the recesses being pulled out of the recesses in the model in the form of reinforced stand alone ribs. 
     In accordance with a still further aspect of the invention there is provided a tire mold comprising: 
     (a) a plurality of mold segments of epoxy resin mold material; 
     (b) each of the segments having a radially inner tread molding surface with ribs for molding recesses in the tread surface characterized by; 
     (c) the tread molding surface having stand alone ribs of a mixture of epoxy mold material and reinforcing material; and 
     (d) each of the mold segments being completely shaped to mold a segment of a tire tread in the tire mold. 
     In accordance with another aspect of the invention there is provided a complete tire mold comprising: 
     (a) a plurality of mold segments of epoxy resin mold material; 
     (b) each of the segments having a radially inner tread molding surface with metal blades adhered to the segment for forming recesses in a tire made by the mold. 
     (c) a segmental shoe of metal encasing each of the mold segments of epoxy resin material comprising; 
     (d) radially extending shoe side plates providing a U-shaped cross section in a radial plane containing the axis of the mold whereby after use of the segmental shoe, the epoxy mold material may be removed from the chamber of the segmental shoe of metal so that the shoe may be used again; 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a segmental shoe for a tire mold embodying the invention. 
     FIG. 2 is a sectional view taken along line  2 — 2  in FIG.  1 . 
     FIG. 3 is a schematic sectional view of part of a tire press with the segmental shoe mounted in the press. 
     FIG. 4 is a schematic plan view of the segmental shoes in accordance with FIGS. 1 and 2 assembled to form a 360° tread molding surface showing the different cord angles and circumferential lengths of the segments. 
     FIG. 5 is a detailed exploded view of one of the segmental shoes shown in FIG.  1 . 
     FIG. 6 is a sectional view of the model on the center bracket shown in FIG. 6 taken along line  6 — 6  in FIG. 7 showing the metal blades and strips positioned in the recesses. 
     FIG. 7 is a plan view of the model taken along the line  7 — 7  in FIG.  6 . 
     FIG. 8 is an enlarged plan view of two forms of nested multiple blades for inserting in recesses in the model where the recesses are wider than the thickness of a single blade. 
     FIG. 9 is a sectional view of the model enclosed in the shoe with the epoxy resin being sprayed under pressure into the recesses in the model surface. 
     FIG. 10 is a sectional view of the model on the center bracket being sprayed with the epoxy resin to fill the recesses in the mold surface. 
     FIG. 11 is a sectional view of the model on the center bracket with the epoxy resin 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, a segmental shoe  10  for a tire mold is shown. This segmental shoe  10  and eight other shoes are assembled in a tread ring  12  as shown in FIG.  4 . Each shoe  10  consists of shoe side members  14  connected by an outer tread forming member  16 . Inside the segmental shoe  10  is a chamber  18  containing a tread mold segment  20  of epoxy mold material having a tread molding surface  22 . The segmental shoe  10  may be mounted in a tire press  24 , a part of which is schematically shown in FIG.  3  and is movable radially into and out of a molding position as shown in FIG.  3 . Stand alone rib members, such as steel blades  26  and epoxy ribs reinforced by steel strip members  28  extend outwardly from the tread molding surface  22  to provide slits and larger slots in the tire tread. 
     Segmental shoes  10  of different sizes have been needed to make the tread mold segments  20  for different tire sizes. This has required prefabrication, and accordingly it is desirable that the inventory of segmental shoes be kept to a minimum. As shown in FIGS. 2 and 4, the number of parts has been reduced by prefabricating the shoes in different sizes using two dimensional standards. One dimensional standard is the mold split diameter D. The other dimensional standard is the chord angle A shown in FIGS. 1 and 4. Mold split diameters D which have been found to be desirable for reducing the number of segmental shoes are 19.770 inches (50.216 cm), 20.420 inches (51.87 cm), 21.420 inches (54.41 cm), 21.030 inches (53.42 cm), 22.140 inches (56.24 cm) and 22.840 inches (58.01 cm). 
     As shown in FIG. 4, chord angles and the chord sequence which have been found to provide standardized parts and also reduce the tire noise due to sequenced molds are in the following sequence: 
     34.400 degrees 
     40.000 degrees 
     45.600 degrees 
     40.000 degrees 
     34.400 degrees 
     40.000 degrees 
     45.600 degrees 
     40.000 degrees 
     40.000 degrees 
     Referring to FIG. 5, segmental shoe  10 , end brackets  30  and  31 , center bracket  34  and end plate  36  are shown in an exploded condition. Bolts  38  are provided for threaded engagement with corresponding threaded holes in the segmental shoe  10  and end bracket  30 , end bracket  31  and center bracket  34 . Bolts  40  are provided for threaded engagement with threaded holes in the end brackets  30  and  31  and the shoe side members  14 . Alignment pins  42  extend through holes in the end brackets  30  and  31  into holes in the shoe side members  14 . Sealing means, such as O-ring chord material  44  mounted in O-ring grooves  46 , provide a seal for the chamber  18  inside the segmental shoe  10 . Inlet holes  48  in the end plate  36  are provided for communicating the epoxy or other plastic material in liquid form into the chamber  18 . 
     Referring to FIGS. 6 and 7, fragmentary views of the segmental shoe  10  with a model such as model blank  50  fastened to the center bracket  34  are shown. The model blank  50  may be made in a plaster back set-up mold, in which the shape of the tire crown is formed by sweeping the plaster back. The end brackets  30  and  31  are placed over the center cavity in the plaster back and an elastomer, such as silicone, is poured in the cavity. The end brackets  30  and  31  are removable to provide clearance for carving the model blank at the shoulder. The model blank  50  shown in FIGS. 6 and 7 has a tread carved with recesses, such as slits  52  and wider slots  54 , to provide stand alone ribs in the tread molding surface  22  of the mold segment  20 . 
     Referring to FIGS. 2,  3  and  6 , the metal blades  26  forming part of the tread molding surface  22  are placed in the slits  52  of the model blank  50 . Also the steel strip members  28  are placed in the slots  54  of the model blank prior to assembling the segmental shoe  10 . The steel strip members  28  may be glued to the model blank  50  in the slots  54  by a suitable adhesive for bonding metal to elastomers. The segmental shoe chamber  18  is then filled with a plastic, such as epoxy, which may contain aluminum pellets and the epoxy material is permitted to cure. In this embodiment the epoxy tread mold segment  20  is cured at room temperature for 24 hours and then heated to a higher temperature, such as 200° F. (93° C.), 300° F. (149° C.) and 400° F. (205° C.) for four to five hours. The segmented shoe  10  is then disassembled and the tread mold segment shown in FIGS. 2 and 3 is ready for mounting in the tire press  24  as shown in FIG.  3 . The steel blades  26  are pulled out of the model blank  50  and the steel blades  26  extend into the stand alone ribs  56  of the tread molding surface  22  as shown in FIG.  2  and are also pulled out of the slots  54  in the model blank  50  with the stand alone ribs  56 . The adhesive holds the steel strip members  28  in place during the application of the plastic material and aluminum pellets. Then after curing, the steel strip members  28  may be pulled away from the model blank  50  and any remaining adhesive removed from the steel strip members. The model blank  50  may be used again simply by adding the steel blades  26  and the steel strip members  28 . 
     As shown in FIGS. 1 and 2, bolts  58  and  60 , having locking collars  62  and  64 , extend through the tread forming member and are imbedded in the epoxy material  66 . The side surface  67  of the chamber  18  are preferably parallel so that after use, the bolts  58  and  60  may be released and the epoxy mold  66  removed from the chamber  18  whereupon the metal parts can be used again for making another mold segment. 
     Referring to FIG. 8, steel blades  26 ′ and  26 ″ are shown, which are adapted to fill slits  52  or slots  54 , having similar shapes. The blades  26 ′ and  26 ″ may be laminated to fill wider slits if desired. It has been found, however, that it is not always necessary to fill the slots  54 , but simply to place the steel strip members  28  in the slots where they provide sufficient reinforcement for the epoxy stand alone ribs. 
     Referring to FIG. 9, a segmental shoe  69  is assembled with a center bracket  70  and end brackets  72  and  74 . A model blank  76  is mounted on the center bracket  70 , and has a carved tread mold forming surface  78  with recesses  80  to form stand alone ribs. In accordance with this embodiment, an epoxy material containing a reinforcing material, such as chopped fiberglass, is communicated into the chamber  82  of the segmental shoe and sufficient pressure applied to force the reinforced epoxy material into the recesses  80 . The epoxy is cured in a manner similar to that set forth hereinabove for the embodiment of FIGS. 1-8, whereupon the model blank  76  is removed and the segmental shoe  68  may be mounted in a tire press. 
     Referring to FIG. 10, a model blank  84  is shown mounted on a center bracket  86  and end brackets  88  and  90 . In this embodiment, the epoxy mold material  92  reinforced with a suitable material, such as fiberglass, is sprayed on the tread mold forming surface  94  under pressure to fill the recessed  96  in the model blank  84  to provide the stand alone ribs of reinforced epoxy material. After application of the reinforced epoxy material  92  to the tread molding surface  94 , the center bracket  86  and end brackets  88  and  90  are mounted in the segmental shoe and the end plates  36  bolted and sealed whereupon the chamber  38  is filled and the tread mold segment completed as described hereinabove for the embodiment shown in FIG.  9 . 
     Referring to FIG. 11, a further modification is shown in which a model blank  98  is mounted on a center bracket  100  and end brackets  102  and  104 . The recesses  106  are then filled with epoxy containing reinforcing material, such as chopped fiberglass, by packing the material into the recesses  106 . The center bracket  100  and end brackets  102  and  104  are then assembled in the mold segment as described hereinabove for the embodiments of FIGS. 9 and 10 for completing the tread mold segment.