Patent Publication Number: US-2009218017-A1

Title: Tire, a Mold for Vulcanizing the Tire, a Method of Fabricating the Mold, and a Mold Matrix

Description:
RELATED APPLICATION 
     This application claims the priority of French patent application Ser. No. 07/60285 filed Dec. 21, 2007, the entire content of which is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to the technical field of tires. 
     Below, the term axis is used with respect to a tire to designate its axis of revolution. This axis defines an axial direction of the mold, as considered when the tire is in the mold. 
     BACKGROUND OF THE INVENTION 
     A tire generally has a tread forming a body of revolution about the axis of the tire. The tread includes in particular a tread design that provides the tire with good grip. 
     Wear of the tread leads to the tread design wearing away and thus to a drop in the grip performance of the tire. 
     This applies in particular to a tire for a heavy good type vehicle, and it is known to embed channels in the rubber that forms the tread, which channels serve in particular to limit the loss of grip of the tire when the tread wears. Wear of the rubber constituting the tread leads to the channels showing on the surface of the tread. These flush channels form grooves that can replace, at least in part, the initial tread design that has worn away. 
     In the state of the art, and in particular from document WO 03/029031, a tire is known that includes molded channels in the tread. Each channel extends parallel to the axis of rotation of the tire. 
     Nevertheless, when the tread wears away, not all of the channels become flush simultaneously over the entire tread, which means that grip is lost in a manner that is non-uniform. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the invention is to provide a tire in which grip is relatively uniform after the tread has worn. 
     To this end, one aspect of the invention is directed to a tire including a tread having at least one molded channel formed therein, the molded channel being interrupted by at least one furrow of the tread, extending along a curved path and presenting at least two curvatures about two radii that are not coplanar. 
     Such a tire enables uniform grip to be obtained after the tread has worn. Since the channel follows a curved path, arrangements are made to ensure that the curve is substantially parallel to the curved crown of the tire such that the channel can be caused to show on simultaneously over the entire tread as it wears away. Thus, loss of grip is limited in a manner that is relatively uniform over the entire tread. 
     According to optional characteristics of the tire of the invention:
         The path of the molded channel is substantially parallel to an outside surface of the tread in a radial section plane of the tire. As explained above, such a channel is particularly effective for a tire that is subjected to wear that is substantially uniform over the entire tread.   The tread includes a plurality of channels that are spaced apart radially and circumferentially.       

     In an embodiment of the tire of the invention, the molded channel extends axially over the entire width of the tread. 
     In another embodiment of the tire of the invention, the molded channel extends axially over a fraction of the width of the tread. 
     To understand the description below, the term “liner” is used to designate the part that presents the final mold shape that is to impart its shape to the tire. The liner thus has a shape that is the negative of the shape of the final tire. The term “matrix” is used to designate the part that serves to mold the mold liner. The matrix thus has a shape that is the positive of the tire shape and the negative of the liner shape. 
     Another aspect of the invention is directed to a mold for vulcanizing a tire, comprising:
         a molding member for molding a molded channel in a tire tread; and   a liner carrying a molding surface for molding a portion of the tire tread, the liner including at least one fillet for molding a furrow in the tread; the fillet including at least one guide channel for guiding the molding member, the guide channel extending through the fillet.       

     Each guide channel enables the molding member to be guided, in particular enables it to follow a curved path. 
     According to optional characteristics of the mold of the invention:
         The molding member is substantially filamentary in shape and, after being inserted into the guide channel, it extends substantially parallel to a surface of the liner for molding an outside surface of the tread of the tire.   The fillet includes at least two radially spaced-apart guide channels.   The molding member is substantially filamentary in shape and, after being inserted in the guide channel, presents at least two curvatures about two radii that are not coplanar.       

     Advantageously, at least one end of the guide channel is defined by a flared inner edge, preferably without any sharp portions. 
     Inserting the molding member in the guide channel is thus made easier. Since the inside edge is flared, the molding member is guided to the inside of the guide channel. 
     Optionally, the guide channel is formed by an liner arranged in the fillet. 
     The use of an insert enables the guide channel to be calibrated accurately relative to the molding member. Such calibration would be more difficult to obtain if the guide channel were formed directly in the fillets, e.g. by drilling. Thus, during vulcanization of the tire, the accurate calibration serves to prevent rubber from passing between the guide channel and the molding member, which would lead to an unsightly rubber sleeve being formed. By suitably selecting the material for the insert, it is possible to reduce the wear caused by the molding member moving on each baking cycle, thereby correspondingly delaying the appearance of clearance that could lead to rubber sleeves being formed. 
     At this stage, it should be observed that it is entirely possible to make a mold having guide channels made directly in the fillets or in the blades of the mold. Nevertheless, as mentioned above, it should be observed that the guide channels would wear very quickly because of the nature of the materials generally employed for fabricating the mold liner. 
     According to an optional characteristic of the mold of the invention, the molding member for molding the channel is coated in an non-stick coating. 
     The non-stick coating serves to limit the axial forces exerted on the mold while unmolding the vulcanized tire. The molding member needs to be moved axially so as to allow the vulcanized tire to be unmolded. The non-stick coating serves to reduce friction between the channel molded in the rubber and the molding member being moved therealong. 
     The non-stick coating also serves to make the outer section of the molding member more uniform. The bare molding member generally presents a section that is irregular, such that during molding of the tire, rubber might infiltrate between the guide channel and the bare molding member, thereby forming an unsightly rubber sleeve. Sleeve formation can be avoided by virtue of the coating. 
     Preferably, the molding member for molding the channel is coated in a coating comprising a compound of the polyetheretherketone type. 
     In addition, a coating that comprises a polyetheretherketone type compound presents properties of being inert at high temperatures, thereby avoiding deterioration thereof and avoiding pollution of the tire rubber while the tire is being vulcanized. 
     According to another optional characteristic of the mold of the invention, for a liner including at least first and second axially spaced-apart fillets, the molding member extends through first and second successive guide channels that are arranged respectively in the first and second fillets common to the molding member. 
     Advantageously, considering the path followed by the molding member through the first and second guide channels, the outlet of the first guide channel points so as to direct the molding member towards the inlet of the second guide channel. 
     Thus, putting the molding member into place in the guide channels is made simpler. While the molding member is being inserted into the first and second guide channels, the molding member can penetrate into the second guide channel without it being necessary for the user to intervene to guide the member between the first and second guide channels. 
     Optionally, the length of the path between the first and second successive guide channels is no more than 40 millimeters (mm). 
     This characteristic makes it possible to prevent the molding member from sagging under the effect of rubber pressure while the tire is being molded. In addition, by reducing the distance between the first and second successive guide channels, the curvature that is imparted to the molding member can be increased. 
     Another aspect of the invention is directed to a method of fabricating a so-called final liner having a molding surface for molding a portion of a tire tread, the final liner including at least one molding fillet for molding a furrow in the tread, the method being of the type in which the final liner is molded on a so-called final matrix, the final matrix including at least one so-called final insert for forming a housing in the fillet of the final liner for receiving a member forming a guide channel for guiding a molding member for molding a channel in the tread. 
     According to optional characteristics of the method of the invention:
         The final insert is formed by the member forming the guide channel.   The final matrix is made of a material that is inert relative to the molten material of the final liner.   The final matrix is made of a material comprising sand and/or plaster. The use of a material comprising sand or plaster makes it easy to unmold the final liner. Such a material is easily fragmented and, furthermore, is inexpensive and suitable for recycling.       

     Optionally, prior to molding the final liner on the final matrix, the following steps are performed:
         molding an intermediate liner of shape substantially similar to that of the final liner on an intermediate matrix of shape substantially similar to the final matrix;   ensuring the intermediate matrix includes at least one intermediate insert for forming a housing in a fillet of the intermediate liner for receiving the final liner; and   molding the final matrix on the intermediate liner.       

     Advantageously, the intermediate liner is molded out of a material having shape memory, preferably an elastomer material, e.g. comprising silicone. 
     The shape memory material enables the intermediate liner to be cut easily. Furthermore, the intermediate liner as molded in this way can be reused. 
     According to an optional characteristic of the method of the invention, the intermediate matrix comprises:
         at least one removable block comprising two mutually separable portions, each including a housing for positioning the intermediate insert; and   a base including at least one housing for positioning the removable block.       

     Since the block is removable, the intermediate liner can be separated from the base. Furthermore, since the removable block comprises two mutually separable portions, it can be separated from the intermediate insert molded in the fillet of the intermediate liner without it being necessary to fragment the intermediate matrix, so it is therefore reusable. 
     In addition, the housing for the intermediate insert, enabling the intermediate insert to be positioned axially in the fillet of the intermediate matrix, may be formed accurately in each of the separable portions, independently of fabricating the base. 
     Advantageously, the intermediate matrix is made of a plastics material, preferably by molding or by machining. 
     By way of example, the plastics material makes the base easy to machine accurately, in particular concerning the housing for positioning the removable block. In addition, the plastics material is generally compatible with the material of the intermediate liner. 
     According to an optional characteristic of the method of the invention, at least one substantially transverse cut is made in a fillet of the intermediate liner, preferably a skew cut, said cut terminating in a housing for an intermediate insert so as to enable the final insert to be withdrawn by being moved through the cut. 
     Cutting the intermediate fillet and using shape memory material makes it possible to separate the intermediate liner from the final matrix without fragmenting the intermediate liner, where that would run the risk of damaging the final matrix. 
     Advantageously, after molding the intermediate liner on the intermediate matrix, and before molding the final matrix on the intermediate liner, the intermediate insert is replaced by the final insert. 
     After the intermediate insert has been replaced by the final insert, the skew cut in the fillet of the intermediate matrix makes it possible to reposition the cut portions of the fillet of the intermediate liner accurately relative to each other. 
     By replacing the intermediate insert with the final insert, the method of fabricating the mold is simplified. It is possible to use intermediate inserts that are of a standard length while using final inserts that present different lengths that are appropriate depending on their locations within the fillet of the final matrix. 
     Optionally, the intermediate insert and/or the final insert includes a collar for holding it axially relative to the fillet of the intermediate and/or final liner. 
     The final insert generally presents an axial dimension that is sufficient to project on either side from the fillet through which it passes. While molding the tire, the collar enables the final insert to be held in a position that is accurate relative to the fillet so as to avoid untimely axial shifting of the final insert relative to the fillet, since that could give rise to an unsightly draft being formed in the molded rubber on one side of the fillet, and to an exaggerated undercut being formed on the other side of the fillet. 
     Preferably, the intermediate insert and the final insert both have respective collars. Since the intermediate insert is positioned axially in the fillet of the intermediate liner by means of the positioning housing formed in the moving block, the collar serves to position the final insert identically in the fillet of the final liner. 
     Another aspect of the invention is directed to a matrix for molding a liner having at least one molding surface for molding a portion of a tread of a tired, the matrix comprising:
         at least one removable block comprising two mutually separable portions each including a housing for positioning an insert for forming, in the fillet of the liner, a housing for a member for forming a guide channel for a molding member for molding a molded channel in the tread; and   a base including at least one housing for positioning the removable block.       

    
    
     
       DETAILED DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood on reading the following description given purely by way of non-limiting example and made with reference to the accompanying drawings, in which: 
         FIG. 1  is a section view in a radial plane of a tire in a first embodiment of the invention; 
         FIG. 2  is a section view in a radial plane of a mold liner including molding members enabling the  FIG. 1  tire to be fabricated; 
         FIG. 3  is a section view in a radial plane showing an intermediate matrix of the  FIG. 2  liner, comprising a base and removable blocks; 
         FIG. 4  is a section view in a radial plane showing the  FIG. 3  intermediate matrix with an intermediate liner molded thereon; 
         FIG. 5  is a section view in a radial plane of the  FIG. 4  intermediate liner together with removable blocks after the base has been withdrawn; 
         FIG. 6  is an enlarged view of  FIG. 5  showing removable blocks of the intermediate liner in a separation position relative to the intermediate liner; 
         FIG. 7  is a perspective view of a fillet of the intermediate liner; 
         FIG. 8  is an axial section view of a final insert forming a guide channel for the molding member; 
         FIG. 9  is a section view in a radial plane of the intermediate liner of  FIGS. 4 to 6 , on which a final matrix is molded; 
         FIG. 10  is a section view in a radial plane of the final matrix after the intermediate liner has been withdrawn; 
         FIG. 11  is a section view in a radial plane of the final matrix overmolded with a final liner; 
         FIG. 12  is a plan view of a mold liner in a second embodiment of the invention, showing the molding members in the guide channels; and 
         FIG. 13  is a plan view of a mold liner in a third embodiment of the invention, showing the molding members in the guide channels. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a tire constituting a first embodiment of the invention and given overall reference  10 . 
     The tire  10  includes a tread  12 . The tread  12  includes an outside surface  14  that is to come into contact with the road, and two shoulders  16  and  18 . In addition, the tread  12  includes furrows  20   a - d  and incisions  21   a - b  formed in the rubber of the tread  12 . The furrows  20   a - d  and the incisions  21   a - b  are axially spaced apart from one another and they are distributed over the entire axial dimension of the tread  12 . 
     Two channels  22  and  24  are formed in the tread  12 . The two channels  22  and  24  are regularly spaced apart. In addition, each channel  22  or  24  extends over the entire axial dimension of the tread  12 , from the shoulder  16  to the shoulder  18 , and it is interrupted by the furrows  20   a - b  and the incisions  21   a - b . For the needs of the present description, there are two channels in the radial direction. Nevertheless, it is possible without departing from the teaching of the invention to provide one channel or more channels that are radially spaced apart. Similarly, the channels may also be spaced apart in a circumferentially-determined distribution. 
     Furthermore, in the radial plane of the tire shown in  FIG. 1 , each channel  22 ,  24  extends along a curved path substantially parallel to the outside surface  14 .  FIG. 2  shows a mold  26  suitable for fabricating the tire  10  of  FIG. 1 . 
     The mold  26  has a liner  28  carrying a molding surface  30  for molding a portion of the tread  12  of the tire  10 . The mold  26  also has molding members  32  and  34  for molding the channels  22  and  24  respectively. 
     The liner  28  has a plurality of radially spaced apart fillets  36   a - d  that are for molding the furrows  20   a - d . The liner  28  also has two blades  37   a - b  for unmolding the incisions  21   a - b . The surface  30  includes a molding surface  38  for molding the outside surface  14  of the tire  10 . 
     The fillets  36   a - b  and blades  37   a - b  include respectively, firstly successive channels  36   a   1 ,  36   b   1 ,  36   c   1 ,  36   d   1 ,  37   a   1 , and  37   b   1  for guiding the member  32 , and secondly successive channels  36   a   2 ,  36   b   2 ,  36   c   2 ,  36   d   2 ,  37   a   2 , and  37   b   2  for guiding the member  34 . Each guide channel extends through a fillet or a blade. Guide channels passing through the same fillet or the same blade are spaced apart radially. In addition, the length of the path between two successive channels is no more than 40 mm. 
     Each guide channel  37   a   1 - a   2 ,  37   b   1 - b   2  is formed by a cylindrical ring  39 . Each guide channel  36   a   1 - a   2 ,  36   b   1 - b   2 ,  36   c   1 - c   2 , and  36   d   1 - d   2  is formed by an insert  40 , referred to as a final insert, and shown in greater detail in  FIG. 8 . Each insert  40  has two ends  42  and  44  defined by respective inside edges  46  and  48 . The section of the insert may be circular, as suggested in  FIG. 8 , or of arbitrary shape depending on the shape it is desired to impart to the channels. Each inside edge  46 ,  48  is flared and has no sharp portions. Each insert  40  also includes a collar  50  for holding it axially relative to the corresponding fillet  36   a - d.    
     Each molding member  32  or  34  is substantially filamentary in shape and is generally in the form of a flexible needle. The member  32  is common to the successive channels  36   a   1 ,  36   b   1 ,  36   c   1 , and  36   d   1  and it extends substantially parallel to the surface  30  through said channels  36   a   1 ,  36   b   1 ,  36   c   1 , and  36   d   1 . Similarly, the member  34  is common to the channels  36   a   2 ,  36   b   2 ,  36   c   2 , and  36   d   2 , and it extends substantially parallel to the surface  30  through the channels  36   a   2 ,  36   b   2 ,  36   c   2 , and  36   d   2 . 
     With reference to the path of the member  32  through the channels  36   a   1  to  36   d   1 , the outlets of the channels  36   a   1 ,  36   b   1 ,  36   c   1  point in such directions as to direct the member  32  towards the inlets of the channels  36   b   1 ,  36   c   1 ,  36   d   1  respectively. The inlets and outlets of the channels  36   a   2  to  36   d   2  are arranged,  mutatis mutandis , like the inlets and outlets of the channels  36   a   1  to  36   d   1 . 
     In addition, each molding member  32  and  34  is provided with an non-stick coating so as to facilitate extraction of said molding member from the tread after the tire has itself been extracted. Specifically, a coating comprising a compound of the polyetheretherketone type has been found to be effective. 
     The mold  26  can be fabricated by implementing a method of the invention, the main steps of which are described below with reference to  FIGS. 3 to 10 . 
       FIGS. 3 and 4  show an intermediate matrix  52 . This intermediate matrix  52  comprises removable blocks  54   a - d  and a base  56 . The base  56  includes housings  58   a - d  for positioning the removable blocks  54   a - d . The base  56  also has housings  60   a - d  for positioning the blades  37   a - b , respectively. 
     Each removable block  54   a - d  comprises two portions  62   a - d  and  64   a - d  that are mutually separable. The block  54   a  has two housings  66   a   1  and  66   a   2  for positioning two intermediate inserts  70 . Specifically, each portion  62   a  and  64   a  includes part of each of the housings  66   a   1 ,  66   a   2 . Each block  54   b - d  includes two housings with references that can be deduced,  mutatis mutandis , from the references of the block  54   a . In the example shown, all of the intermediate inserts  70  are identical. 
     Like the final insert, each intermediate insert  70  includes an axial retention collar  50 . Each intermediate insert  70  presents an outside shape similar to that to the final insert  40 . However, an intermediate insert  70  is solid whereas a final insert  40  is tubular. 
     The intermediate matrix  52  comprising the base  56  and the removable blocks  54   a - d  is made of a soft plastics material by molding, or preferably by machining. 
     In addition, as shown in  FIG. 4 , an intermediate liner  72  is molded on the intermediate matrix  52 . The intermediate liner  72  is of a shape substantially similar to that of the final liner  28  shown in  FIG. 2 . 
     In the example shown, the intermediate liner  72  is molded of a material having shape memory. Specifically, the material commonly used is of the elastomer type and may comprise silicone. 
     Each intermediate insert  70  forms a respective housing  76   a   1 - a   2 ,  76   b   1 - b   2 ,  76   c   1 - c   2 , or  76   d   1 - d   2  respectively in each of the filets  74   a - d  of the intermediate liner  72  for the purpose of receiving a corresponding final insert  40 . 
     Thereafter, as shown in  FIG. 5 , the intermediate liner  72  is withdrawn from the base  56 . 
     Then, as shown in  FIG. 6 , the two portions  62   a - d  and  64   a - d  are separated so as to release each intermediate insert  70  from its corresponding housing  66 . 
     Thereafter, substantially transverse skew cuts  78  are made in each fillet  74   a - d  of the intermediate liner  72 . 
     After the above step, each intermediate insert  70  is replaced by the corresponding final insert  40 . 
     Thus, as shown in  FIG. 7 , where there can be seen only the intermediate fillet  74   a , it can be seen that the cut  78  leads to the housings  76   a   1  and  76   a   2  for the final insert  40  in such a manner as to enable these inserts  40  to be withdrawn by moving through the cut  78 . 
     In a variant, the intermediate insert  40  could be replaced by the final insert  70  after cutting the fillets  74   a - d.    
     Thereafter, the blades  37   a - b  provided with the guide rings  39  in the intermediate liner  72  are replaced. 
     Thereafter, as shown in  FIG. 9 , the final matrix  80  is molded on the intermediate liner  72 . In order to avoid the material of the final matrix  80  penetrating into the guide channels formed by the insert  40 , the guide channels are plugged temporarily. The final matrix  80  includes the final insert  40 . 
     With reference to  FIG. 10 , the final matrix  80  is of a shape that is substantially similar to the intermediate matrix  52 . The final matrix  80  is made of a material that is inert relative to the molten material of the final liner  28 . This material preferably comprises sand and/or plaster. 
     Thereafter, the intermediate liner  72  of the final matrix  80  is withdrawn as shown in  FIG. 10 . The cuts  78  enable the fillets  74   a - d  of the intermediate liner  72  to be separated from the inserts  40 . The intermediate liner  72  is then ready for subsequent use in molding a new final matrix. It is then appropriate to reintroduce inserts  40  into the housings  76   a   1 - a   2 ,  76   b   1 - b   2 ,  76   c   1 - c   2 , and  76   d   1 - d   2 . 
     Finally, as shown in  FIG. 11 , the final liner  28  is molded on the final matrix  80 . The final liner  28  is molded out of a metal, and in this example out of aluminum. 
     Each insert  40  forms, in each fillet  36   a - d  of the final liner  28 , a housing  82   a   1 - a   2 ,  82   b   1 - b   2 ,  82   c   1 - c   2 , and  82   d   1 - d   2 , for a member forming the corresponding guide channels  36   a   1 - a   2 ,  36   b   1 - b   2 ,  36   c   1 - c   2  or  36   d   1 - d   2 . Specifically, the members forming the guide channels  36   a   1 - a   2 ,  36   b   1 - b   2 ,  36   c   1 - c   2 , and  36   d   1 - d   2 , are the final inserts  40 . 
     Finally, the final matrix  80  is fragmented so as to release the final liner  28 , and the inserts  40  are opened. 
       FIG. 12  shows a liner  28  of a mold  26  in a second embodiment of the invention. In  FIG. 12 , elements that are analogous to elements in the above-described figures are designated by references that are identical. 
     For reasons of clarity, only some of the guide channels  36   a - d  are shown. 
     Unlike the mold of the first embodiment, each molding member  32  presents at least two curvatures with two radii that are not coplanar. Thus, each member  32  extends along a path that is curved when projected onto a radial plane, and along a path that is curved when projected flat onto the liner  28 . In addition, each member  32  extends over a fraction only of the axial size of the liner  28 . 
     In order to facilitate inserting molding members  32  into the mold  26 , each molding member  32  is preshaped. 
       FIG. 13  shows a liner  28  of a mold  26  in a third embodiment of the invention. In  FIG. 13 , elements analogous to elements of the above-described figures are designated that are identical. 
     Unlike the first embodiment, each molding member  32 ,  34  presents two curvatures with respective radii that are not coplanar. In addition, when projected flat onto the liner  28 , each member  32  and  34  presents a point of inflection. 
     From the above, it is entirely possible to cause the flexible molding member to follow a path that presents one or more variations in curvature depending on the positions of the blocks of rubber placed on the tread. This advantage expands the options available when designing the tire by reducing the limits imposed by methods of the prior art.