Abstract:
A method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a loading and shaping process is disclosed. A tire press comprises a lower mold, an upper mold, and a center mechanism. The center mechanism has an upper clamping mechanism for securing the upper periphery of a bladder and a lower clamping mechanism for securing the lower periphery of the bladder. A center mechanism tube has a center rod positioned therein. A piston is disposed within the center mechanism tube. The piston provides reciprocating motion to the center rod. A position sensor mechanism is operatively associated with the center mechanism. The method comprises the steps of establishing a first baseline height by first applying a set force to the center rod of the bladder securement mechanism to determine the stretch of the bladder; repeatedly curing tires with said bladder up to a certain number of cures; establishing a successive baseline height; and, comparing the first and successive baseline heights and if the difference is less than a predetermined stretch height tolerance, continuing curing tires. If the difference between the first and successive baseline heights is outside of an acceptable stretch tolerance, the bladder must be corrected, either through replacement or by adjusting the height that the center rod reaches during the loading process.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    This invention pertains to applications for bladder securement mechanisms for a tire press utilizing a position sensor mechanism, and more specifically to a method of utilizing an adjustable height bladder securement mechanism to effect advantageous tire shaping during the curing process.  
           [0003]    2. Description of the Related Art  
           [0004]    Tire presses and methods for making tires are well known in the art. FIG. 2 shows a green tire  12  undergoing a curing process in a tire press  10 . The green tire  12  is placed within a cavity defined by a lower mold  14  and an upper mold  16 . The lower mold  14  is fixedly installed on a base frame  18 . The upper mold  16  can be closed and opened in relation to the lower mold  14 . In FIG. 2, the tire press  10  is shown in the closed position.  
           [0005]    A bladder securement mechanism  40 , some aspects of which are currently known in the art, is illustrated in FIG. 1. The bladder securement mechanism  40  is commonly referred to as a “center mechanism.” In the bladder securement mechanism  40 , a center mechanism tube  42  is supported by a guide cylinder  44 , which is fixed on the base frame  18 . The upper end (or first end)  32  of a bladder  30  is held by an upper clamping mechanism  70 , which is attached to the upper end  48  of a center mechanism rod  46 . The center mechanism rod  46  is positioned on a piston  50  of the center mechanism tube  42 . A lower clamping mechanism  80 , which holds the lower end (or second end)  34  of the bladder  30 , is attached to the upper end of the center mechanism tube  42  through a hub  51 . A pressurized fluid is supplied by way of a first port  52  formed in the lower part of the center mechanism tube  42  to a portion below the piston  50 . The pressurized fluid is also supplied from a second port  54  through a pipe  56  to a portion on the top of the piston  50 . The pipe  56  passes through the piston  50  and is inserted into the center mechanism rod  46 .  
           [0006]    The piston  50  and the center mechanism rod  46  move upward together. When the bladder  30  is deformed around the lower clamping mechanism  80 , a heated pressurized medium such as steam is supplied through a fluid supply tube  58  via a through hole on the hub side into the bladder  30 . Then the bladder  30  comes tightly into contact with the inner side of the green tire  12 .  
           [0007]    A floating piston  60  is adapted to contact the hub  51  and is slidably attached to the center mechanism rod  46 . A stacking spacer  62  is positioned above the floating piston  60 , and a stretch height spacer  64  is positioned below the floating piston  60  but above the piston  50 . The stacking spacer  62  and the stretch height spacer  64  are exchangeably attached to the outside of the center mechanism rod  46 . The stacking spacer  62  sets the lower limit position of the upper clamping mechanism  70  so that the upper clamping mechanism  70  is set to a shaping height corresponding to the tire size. The stretch height spacer  64  limits the upper clamping mechanism&#39;s  70  upward movement.  
           [0008]    While suited for their intended purpose, present center mechanism designs of the tire curing presses have several disadvantages, which will now be described. The art does not address the bladder compounds, their resiliency, their thickness, or other variations that happen as the bladders age due to usage. As such, over time, bladders cease to maintain their original shape and size.  
           [0009]    Further, as different sized tires are cured, the top clamp ring of the upper clamping mechanism must be repositioned to accommodate each tire size. This requires spacers of different lengths to be changed on the center mechanism. These spacers are cumbersome to change as different sized tires are cured. In addition, valuable production time is wasted. Also, since the spacers are generally fabricated from standard pipe, their lengths are not as precise as desired. Further, the spacers are subject to wear and tear over time, which leads to further imprecision and, thereby, possible imprecision in the tire.  
           [0010]    Another problem with traditional spacers is that adjustment of the top ring is extremely limited during the curing process because the top clamping ring cannot advance towards the bottom ring once it has contacted the spacer. Still yet, another disadvantage of utilizing spacers is that the tire press only has two positions: open and closed. There is no mechanism for fine precision to ensure the green tire will cure correctly without any flaws or inaccuracies.  
           [0011]    Present center mechanisms are limited in performance due to the restrictive nature of the spacers. For example, bladders utilized during the curing process must be discarded once their structural integrity has been degraded and/or the bladder has stretched to such a length that they cannot be used. Currently, there is no precise method of determining when the bladder has reached the end of its life. There is an economic incentive to use bladders for their full life cycle, so that bladders are changed less often.  
           [0012]    Once bladders have been utilized over a certain number of curing cycles, they have been permanently stretched beyond their original length. As such, when the bladder securement mechanism is lowered to position the bladder against the green tire, there is excess bladder to position. However, since there are no controls used on most bladder securement mechanism designs, the bladder cannot be precisely controlled during the shaping process.  
           [0013]    Also, during the curing process, an operator is “blind” as to the position of the upper clamping mechanism during the curing process. There is now way for the operator to finely tune the position of the top clamp ring of the upper clamping mechanism to ensure the cured tire will be free of defects.  
           [0014]    Therefore, a need exists in the art for a center mechanism that operates without a spacer and that overcomes the foregoing difficulties and others. The present invention is contemplated to overcome these disadvantages by utilizing a linear position sensor with the bladder securement mechanism, such that the upper clamping mechanism may be moved at any time during the loading and shaping process. Having the ability to move the upper clamping mechanism offers safety and bladder insertion advantages.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention is a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process. A tire press comprises a lower mold, an upper mold, and a center mechanism. The center mechanism has an upper clamping mechanism for securing at least a portion of the upper periphery of a bladder and a lower clamping mechanism for securing at least a portion of the lower periphery of the bladder. A center mechanism tube has a center rod positioned therein. A piston is disposed within the center mechanism tube. The piston provides reciprocating motion to the center rod. A position sensor mechanism is operatively associated with the center mechanism. The method comprises the steps of applying a force to a displacement mechanism, namely, the center rod. Then, the stretch of the bladder is determined, and a first baseline height is established. Tires are repeatedly cured. Next, the bladder is checked, which may be done either manually or automatically. A force is reapplied to the displacement mechanism. It is then determined if the stretch of the bladder is within a permitted stretch tolerance. If the stretch of the bladder is within a permitted tolerance, tires continue to be cured. If the stretch of the bladder is not within a permitted tolerance, the bladder is corrected by either discarding the bladder or by applying more force to the displacement mechanism to increase the height of the center rod in order to stretch the bladder in a vertical direction. Next, a second baseline height is established. The first and second baseline heights are compared, and if the difference is within a permitted tolerance, tires are repeatedly cured. Accordingly, it is an object of the present invention to provide a method for utilizing a position sensor mechanism in conjunction with a bladder securement mechanism to advantageously shape a tire.  
           [0016]    Another object of the present invention is to provide a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process, wherein the bladder securement mechanism further comprises a proportionate speed control mechanism for moving the upper clamping mechanism at a velocity independent from the tire press, namely, the upper mold. The method further comprises the steps of extending the bladder to a predetermined height; positioning a green tire on the lower mold; lowering the upper clamping mechanism at a predetermined velocity, the velocity being dependent upon the bladder height; pressurizing the bladder such that it comes into contact with the tire; closing the press; curing the tire; and, opening the press.  
           [0017]    Yet, another object of the present invention is to provide a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process, wherein the velocity of the bladder securement mechanism is variable.  
           [0018]    Still, another object of the present invention is to provide a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process further comprising the step of decreasing the velocity of the bladder securement mechanism when the upper clamping mechanism reaches a predetermined distance from the upper mold.  
           [0019]    Further yet, another object of the present invention is to provide a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process further comprising the step of manipulating the upper clamping mechanism in a vertical direction at any time during the curing process.  
           [0020]    Still, another object of the present invention is to provide a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process, wherein the predetermined number of cures varies.  
           [0021]    Another object of the present invention is to provide a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process further comprising the step of translating the movement of the bladder securement mechanism and the upper clamping mechanism into a pictorial representation.  
           [0022]    Still, another object of the present invention is to provide a method of utilizing an adjustable height bladder securement mechanism to effect advantageous bladder movement during a curing process further comprising the step of discarding the bladder after its height exceeds a predetermined stretch limit or useful life.  
           [0023]    Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and herein:  
         [0025]    [0025]FIG. 1 is a cross sectional view of a bladder securement mechanism for a tire press known in the art.  
         [0026]    [0026]FIG. 2 is a cross sectional view of a tire press utilized with the present invention.  
         [0027]    [0027]FIG. 3 is a cross sectional view of a bladder securement mechanism utilizing a position sensor mechanism.  
         [0028]    [0028]FIG. 4 is an enlarged view of the piston and magnet of FIG. 3.  
         [0029]    [0029]FIG. 5 is a top view of FIG. 3.  
         [0030]    [0030]FIG. 6 is an elevational view of the tire press and a schematic drawing of the controller. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting the same, FIGS.  2 - 6  illustrate a tire press  10  and a bladder securement mechanism  40  having a position sensor mechanism  100  operatively associated therewith. It should be understood that the present invention may be used with any tire press known in the art, such as a dome press or a platen press. The tire press illustrated in the FIGURES operates with a bladder securement mechanism, and serves as one possible example.  
         [0032]    Turning to FIG. 2, the tire press  10  is shown in a closed position. The top of the bladder securement mechanism  40  is also illustrated. The tire press  10  comprises a lower mold  14  and an upper mold  16  defining a cavity therein when the upper mold  16  contacts the lower mold  14 . The lower mold  14  is fixedly installed on a base frame  18 . The upper mold  16  can be opened and closed relative to the lower mold  14 . A tread ring  15  is positioned between the lower mold  14  and the upper mold  16 . It should be understood that the inventive method described herein may be utilized with a segmented mold  15  as shown in FIG. 2, or simply with a two piece mold design encompassing upper and lower mold halves  14 ,  16 . A green tire  12  is snugly received within the lower mold  14 , the upper mold  16 , and the tread ring  15 . A bladder  30  is in tight contact with the inner face  13  of the green tire  12 , thereby shaping the tire  12 . In order to prevent tire defects, the bladder  30  should not have any bulges or ripples when it contacts the green tire  12 . The contact between the bladder  30  and the green tire  12  should be smooth and continuous.  
         [0033]    Still viewing FIG. 2, the tire press  10  also comprises a platen support  20  positioned above the upper mold  16 . A press beam  22  extends upwardly from the platen support  20 , and an upper adjusting screw  24  is positioned within the press beam  22 . A mold actuating ring  26 , which may be a segmented mold actuating ring, is operatively connected to the upper mold  16 . The mold actuating ring  26  and the press beam  22  define a first void  28  having a volume V 1 . The actuating ring  26  and an upper clamping mechanism  70  define a second void  29  having a volume V 2 . The first and second voids  28 ,  29  are adapted to contain excess pressure released from the tire  12  during the curing process.  
         [0034]    Turning to FIGS. 2 and 3, the bladder securement mechanism  40  comprises the upper clamping mechanism  70 , which includes an upper mold ring  72 , a top bladder clamp ring  74 , and a top bladder lock ring  76 . The top bladder clamp ring  74  and the top bladder lock ring  76 , which are fastened together, secure the upper periphery  32  of the bladder  30 . A lower clamping mechanism  80  secures the lower periphery of the bladder  34 . The lower clamping mechanism  80  comprises a lower mold ring  82  attached to a lower bladder clamp ring  84 . As is well known in the art, the lower mold ring  82  forms the bead of the tire  12  with the bladder  30 . The lower mold ring  82  is also utilized to strip the tire  12  from the mold after the curing cycle.  
         [0035]    As shown in FIGS. 2 and 3, the bladder securement mechanism  40  further comprises a cylindrical center mechanism guide  44  securely attached to the base frame  18 . The center mechanism guide  44  surrounds an upper portion of a center mechanism tube  42 . The center mechanism guide  44  provides support and maintains the alignment of the center mechanism tube  42  as it rises and lowers in a vertical direction during the tire curing process. A center mechanism hub  51  attaches to the center mechanism tube  42  and is threadably secured to the lower bladder clamp ring  84 . Positioned within the center mechanism tube  42  is a center mechanism rod  46 , having a first end  48  and a second end  49 . The first end  48  is fixedly attached to the top clamp ring  74  through a post clamp  53 . The second end  49  of the center mechanism rod  46  is connected to a piston  50 . Tubes  58 ,  59  are connected to the center mechanism hub  51 . The tubes  58 ,  59  facilitate the pressurization and depressurization of the bladder  30  during the curing cycle.  
         [0036]    The center mechanism rod  46  is lifted together with the piston  50  when a working fluid, such as water or oil, is supplied to a first space portion  66  located beneath the piston  50 , thereby lifting the upper periphery  32  of the bladder  30 , which is held by the upper clamping mechanism  70 . Conversely, when the working fluid is supplied to a second space portion  68  within the center mechanism rod  46 , the center mechanism rod  46  travels downward with the piston  50 , thereby lowering the upper periphery  32  of the bladder  30 .  
         [0037]    In order to limit the height of the upper clamping mechanism  70 , a position sensor mechanism  100  is utilized in conjunction with the bladder securement mechanism  40 . As such, the stretch height spacer, the stacking spacer, and the floating piston may be eliminated. What is meant by the term “position sensor mechanism” is any mechanism, whether electrical and/or mechanical, that controls the movement of the upper clamping mechanism and/or the lower clamping mechanism such that the bladder may be repeatedly stretched to determine its current stretch height. It should be noted that the position sensor mechanism  100  described herein serves as one possible example of the mechanism which enables movement of the upper (or lower) clamping mechanism. As best seen in FIGS. 3 and 4, the piston  50  may be welded to the second end  49  of the center mechanism rod  46 . Of course, the piston  50  may be secured to the second end  49  of the center mechanism rod  46  through any other means chosen in accordance with sound engineering judgment. The position sensor mechanism  100  comprises a floating magnet  102 , a linear sensing rod  104 , and a signal generating unit  106 . The floating magnet  102  is fixedly attached to the piston  50  through a snap ring  108 . The floating magnet  102  is laterally spaced from the linear sensing rod  104  as it travels vertically with the piston  50  through the center mechanism rod  46 . A cable  110  takes mechanical positioning magnetically induced signals from the signal generating unit  106  and passes them through to a remote electronics module  112 , which is associated with a control system  114  (“controller”), shown schematically in FIG. 6. When the working fluid is introduced through tube  52  and into the first space portion  66  below the piston  50 , the magnet  102  is lifted with the piston  50 , and the linear sensing rod  104  senses the position of the magnet  102 , which is detected by the signal generating unit  106  as a travel amount of the piston  50 . The travel amount of the piston  50  is transmitted to the controller  114 . Based upon the travel amount of the piston  50 , the controller  114  controls the vertical movement of the top clamp ring  74 . The height of the bladder  30 , which corresponds to the tire size, is set to the lower limit position of the top clamp ring  74 .  
         [0038]    Through the position sensor mechanism  100 , the top clamp ring  74  may be moved and adjusted in a vertical direction during the curing process so that the bladder  30  properly contacts the green tire  12  to prevent defects from forming during the curing cycle. It is also contemplated to be within the scope of the present invention to translate the movement of the bladder securement mechanism  40  into a pictorial representation on a monitor  118  of the control system  114 . This enables the tire press operator to easily see the position of the bladder securement mechanism  40  after the tire press is closed, especially the placement of the top clamp ring  74 , and to provide any required adjustments.  
         [0039]    With reference to FIGS. 3 and 6, a proportionate speed control mechanism  120  is operatively associated with the bladder securement mechanism  40  and is in communication with the controller  114 . The proportionate speed control mechanism  120  may take the form of any electronic control system that provides for programmable height control of the top clamp ring  74 . For example, the proportionate speed control mechanism  120  may be a programmable logic controller (PLC).  
         [0040]    As previously stated, the proportionate speed control mechanism  120  provides height control of the upper clamping mechanism  70 , namely, through the top clamp ring  74 . The proportionate speed control mechanism  120  enables the operator to control the top clamp ring  74  velocity independent from the tire press  10 , and more specifically, the velocity of the upper mold  16 . Because the top clamp ring  74  may move independently from the upper mold  16 , the bladder  30  can be better positioned against the green tire  12 . The velocity at which the top clamp ring  74  is moved is dependent upon the current height of the bladder  30 . As the bladder  30  becomes stretched after numerous curing cycles, more care is needed when lowering the top clamp ring  74  to ensure that the bladder  30  properly contacts the green tire  12 . For example, it may be desirable to lower the top clamp ring  74  quickly at first, but as the top clamp ring  74  reaches a predetermined distance from the upper mold  16 , the top clamp ring  74  may be decreased in order to avoid bulges in the bladder  30 .  
         [0041]    Continuing to view FIG. 3, an interfacing system  130  facilitates lifting the entire center mechanism  40  upward for tire removal. Kinematics  132 , which enables the lifting of the bladder securement mechanism  40 , are depicted in phantom lines. The kinematics  132  are well known in the art and will not be further described herein.  
         [0042]    Next, the mode of operation of the tire press  10  and its bladder securement mechanism  40  described above will be explained. The bladder  30  is tensioned in an extended state with the center mechanism tube  42  placed in the bottom position and with the center mechanism rod  46  placed in the top position. Then the green tire  12  is inserted onto the lower mold  14 . After the insertion of the tire  12 , the piston  50  and the center mechanism rod  46  are lowered to move the top clamp ring  74  downward until the bladder  30  conforms to the inner surface of the tire  12  while being curved and deformed. The velocity of the top clamp ring  74  is controlled through the proportionate speed control mechanism  120 . The linear sensing rod  104  senses the travel amount of the piston  50  by the magnet  102 , thereby monitoring the fall of the top clamp ring  74  and a signal of the travel amount is generated to the controller  114 . The controller  114  controls the supply of the working fluid to the center mechanism tube  42  to lower the top clamp ring  74  so that the lower limit position of the top clamp ring  74  is set to the shaping height corresponding to the tire size.  
         [0043]    A heated, pressurized medium, such as steam, is injected into the bladder  30  through tube  58  to fully expand the bladder  30  for shaping. The bladder  30  comes into close contact with the inner surface of the tire  12 . Subsequently, the upper mold  16  is closed to the lower mold  14  for curing the green tire  12 .  
         [0044]    After the cure, the upper mold  16  is opened and made to retreat to allow the center mechanism tube  42  to move upward together with the center mechanism rod  46 , and then the tire  12  is separated and raised off the lower mold  14 . The center mechanism rod  46  is moved upward while the center mechanism tube  42  is moved downward, thus pulling out the bladder  30  from the inner surface of the tire  12  with which the bladder  30  is in close contact. Next, this post-cure tire  12  is removed upwardly by means of a tire unloader or other means (not shown), being discharged out of the tire press  10 .  
         [0045]    As is well known in the art, bladders  30  have a finite life cycle, and they need to be changed regularly to ensure proper tire formation. A defect in the bladder  30  could result in a deformed tire, which is not suitable for use. It is desirable for tire manufacturers to have minimal defective tires in order to maintain low overhead costs. One way to help minimize overhead costs is to utilize the bladder  30  for as many cures as possible without compromising the quality of the tire. This is accomplished through the position sensor mechanism  100  previously described.  
         [0046]    In order to maximize the life cycle of the bladder, the following steps are taken. First, a force is applied to the center rod  46  of the bladder securement mechanism  40  to determine how far the bladder  30  should stretch in a vertical direction. Once properly stretched in the vertical direction, a first baseline height of the bladder  30  is established by determining the distance moved by the piston  50 . The distance is generated into a signal and sent to the controller  114 . This distance is recorded as the first baseline height. Since bladders  30  vary in their geometric dimensions, including diameter, height and thickness, the first baseline height will depend on the particular bladder  30  chosen for the tire size that is being cured in the tire press. Further, because of the variance in bladders  30 , pressures needed to move the center rod  46  or the displacement mechanism will vary. As such, a generalized pressure cannot be determined since it depends on each and every application.  
         [0047]    Tires are repeatedly cured for either a number of predetermined cycles or for a number or random cycles. Next, the bladder  30  should be checked to ensure that it is within the permitted stretch tolerance. Checking may either be manual or automatic. Checking manually may be through an operator&#39;s observation. Alternatively, an automatic check may be based with the controls in the controller  114 . A set force is reapplied to a displacement mechanism, namely, the center rod  46 , either manually or automatically. It should be understood that the displacement mechanism may be any mechanical, electrical or electromechanical device or system that enables the bladder  30  to be placed in tension. It is then determined whether or not the stretch of the bladder  30  is within a permitted stretch tolerance. This may be through a device that reads a diameter of the bladder  30 , such as a light beam (not shown) or an electric eye (not shown). If the bladder  30  is within a permitted tolerance, tires may continue to be cured. Further, if the bladder  30  is not within a permitted tolerance, the bladder  30  is corrected. Until now, correction was performed by discarding the bladder  30  and replacing it. This may still be an appropriate course of action if the bladder  30  has reached the end of its life cycle. However, correction may be performed by placing an increased force on the displacement mechanism to increase the vertical height of the bladder  30 . When an increased force is applied to the displacement mechanism or center rod  46 , a successive baseline height is established. The successive baseline height and the first baseline height are compared, and if the difference between the two heights is within a permitted tolerance, the bladder  30  may be used for a continued number of cures (random or predetermined). After a number of tires have been cured, another successive baseline height is recorded in the same manner previously described. By following this method, the full life of the bladder  30  is utilized before it is discarded.  
         [0048]    As the difference between the first and second baseline readings increases, the number of predetermined curing cycles should decrease. Further, it should be noted that correcting the bladder  30  and checking the bladder  30  may be done in any combination of manual or automatic operations described above.  
         [0049]    The invention has been described with reference to preferred embodiment. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alternations in so far as they come within the scope of the appended claims or the equivalence thereof.  
         [0050]    Having thus described the invention, it is now claimed: