Abstract:
A method and apparatus for rapid heating of calender rolls  350, 352  for a calendering apparatus  200  is disclosed. At a heating area  800,  the rolls  350, 352  are preheated, reheated, or maintained at any temperature prior to the rolls  350, 352  being placed into the calendering apparatus  300.  The preferred method of heating is by induction heating. The rolls  350, 352  may be delivered to the heating apparatus  802  from an initial storage area  420  or the calendering apparatus  300.  The rolls  350, 352  are transported by an overhead transfer mechanism  400.  The disclosed method and apparatus greatly facilitate formation of multi-layered laminates and is particularly useful in the tire building art.

Description:
TECHNICAL FIELD  
         [0001]    The disclosed invention relates to a unique method and apparatus for heating calender rolls in a calender roll system where the rolls are readily changeable. The disclosed heating is particularly suitable in the method for forming tire components of predetermined cross sections.  
         BACKGROUND ART  
         [0002]    Conventional heating methods for calender rolls include hot water steam heating and electrical resistance heating. However, with such conventional heating methods, the heating of the entire roll requires a substantial length of time.  
           [0003]    Induction heating of rolls is also known in the art. With induction heating, heating of the roll can be both selective and rapid. Induction heaters are typically classified by the frequency of the induced current. Low-frequency heaters usually induce power frequency current in the charge. A medium-frequency induction heater induces currents of frequencies between 180 and 540 hertz while a high-frequency heater induces currents of frequencies from 1000 hertz and upwards.  
           [0004]    U.S. Pat. No. 5,571,066 discloses heating the ends of a calendering roll. An external electro-magnetic induction system heats the entire working surface of the roll while an internal electric-resistance heating system heats the roll from internally. In normal operation, only the external heating system is active. The internal heating system must be used to bring the roll up to the required operating temperature.  
           [0005]    U.S. Pat. No. 5,123,340 discloses induction heating of softcalender and supercalender rolls. The rolls are provided with a thermally conductive coating.  
           [0006]    U.S. Pat. No. 5,111,564 discloses two induction heating coils at the opposing ends of a roll. The induction heating compliments the hydraulic heating of the median portion of the roll.  
           [0007]    U.S. Pat. No. 5,074,019 discloses the use of high frequency induction heating coils inside and outside of a calender roll. A number of coils are uniformly distributed the length of the entire roll. For uniform heating, a corresponding bank of induction heating coils is may be arranged along the outside length of the roll.  
           [0008]    Almost all of the above mentioned prior art patents are concerned with increasing the roll diameter by a miniscule amount to effect a papermaking process. The prior art references fail to teach heating of a calendering roll at a separate location from the calendering process wherein at least one of the calender rolls is occasionally replaced with another roll for operation within the calendering process.  
           [0009]    U.S. Pat. Nos. 5,513,560 and 5,762,740, both incorporated herein by reference, disclose a quick change over method and apparatus for a calendering apparatus  200 . The disclosed apparatus  200  is used to form a laminate from a series of tire components, forming a tire casing. Each calender assembly  302  includes two calender rolls  350 ,  352 , as seen in FIG. 7. The rolls  350 ,  352  are delivered to the assembly  302  by an overhead moveable transfer mechanism  400 .  
           [0010]    During operation of the calendering process, the calender rolls  350 ,  352  can be internally heated or cooled. The heating means  335  has a resistive heating element which enters through an opening in the hubs  314  or  316 . The internal heating elements  335  are employed when the material being processed can be more efficiently applied in a heated environment.  
           [0011]    While heating means are sufficient to internally heat the rolls  350 ,  352 , greater efficiency of the calendering process is achieved when the rolls  350 ,  352  are heated prior to the roll delivery into the calender assembly  302 .  
           [0012]    The present invention is directed toward an improvement in the quick change over calendering apparatus. Prior to placement of the rolls  350 ,  352  in a calender assembly  302 , the rolls  350 ,  352  are heated at a heating station. Heating the rolls  350 ,  352  prior to placement in the calender assembly  302  permits rapid start-up of the calendering operation, instead of waiting for the rolls to be heated by the formally disclosed internal heating means. The internal heating means may be used to maintain the roll temperature.  
           [0013]    At the heating station, induction heating is the preferred method of heating. Induction heating provides almost instantaneous heating of the rolls, and is a more efficient method of heating.  
         SUMMARY OF THE INVENTION  
         [0014]    This invention is an improved method of calendering a material. The material is calendered by at least one calender roll, the roll operating at a predetermined operating temperature. The calender rolls are replaced from time to time with another roll. Prior to placing the new roll into its calendering position within the calendering apparatus, the replacement roll is heated, using a heat source, from a temperature lower than the operating temperature. The preferred predetermined operating temperature ranges from 180° to 260° F.  
           [0015]    The material may be calendered by a pair of associated rolls and replaced by another pair of associated rolls.  
           [0016]    The preferred method of heating the calender rolls is by induction heating. The induction heating coil is preferably operated at a frequency range of 7 to 11 kHz.  
           [0017]    The disclosed method of heating the calender rolls may also be used to reheat rolls which have been removed from the calendering position within the calendering apparatus.  
           [0018]    The disclosed heating station also permits the rolls that are being heated prior to placement within the calendering apparatus, or rolls that are being reheated, to be held at any temperature for a period of time. When holding the roll for a period of time after heating the roll, the roll temperature may be constant after reaching the desired temperature or may be variable if the roll is heated to a temperature greater than the operating temperature and allowed to cool to the operating temperature during the holding period. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0019]    The invention will be described by way of example and with reference to the accompanying drawings in which:  
         [0020]    [0020]FIG. 1 illustrates an overview of the quick changeover calender apparatus;  
         [0021]    [0021]FIG. 2 illustrates a single heating stage;  
         [0022]    [0022]FIG. 3 illustrates a heating stage with a pair of calender rolls thereon;  
         [0023]    [0023]FIG. 4 is a cross-sectional view of FIG. 3;  
         [0024]    [0024]FIG. 5 illustrates the induction heating coil;  
         [0025]    [0025]FIG. 6 illustrates the induction heating coil, without the main bracing;  
         [0026]    [0026]FIG. 7 illustrates a calender assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    [0027]FIG. 1 illustrates an overview of the quick changeover calender apparatus. As disclosed in U.S. Pat. Nos. 5,513,560 and 5,762,740, the apparatus  200  is used to form a laminate from a series of components, the method being particularly useful for forming a tire casing from a plurality of tire components. The tire casing forming apparatus  200  is a plurality of calender apparatuses  300 . Each calender assembly  302  includes two calender rolls  350 ,  352 . At each calender apparatus  300 , the laminate is calendered to a predetermined configuration by the calender rolls  350 ,  352 . The calender rolls  350 ,  352  are delivered to the assembly  302  by an overhead moveable transfer mechanism  400  from an initial roll staging area  420 . The transfer mechanism  400  enables the rolls  350 ,  352  to be removed from the calender apparatus  300  and exchanged with other calender rolls with different profile configurations when it is desired to form laminates with different predetermined configurations of either the overall laminate configuration or individual components of the laminate. For a greater discussion of the differing profiles of the calender rolls  350 ,  352 , the calendering apparatus  300  and the overhead transfer mechanism  400 , reference is made to U.S. Pat. Nos. 5,513,560 and 5,762,740.  
         [0028]    During formation of the laminate from a series of components, the formation process may benefit from the calender rolls  350 ,  352  being heated. The calender rolls  350 ,  352  may be internally heated, as previously noted. The previously disclosed method and apparatus is improved by the inclusion of the heating area  800 , located between the roll staging area  420  and the tire component forming apparatus  200 .  
         [0029]    The heating area  800  is a plurality of heating stages  802 , each station preferably corresponding to a calender apparatus  300  in the tire component forming apparatus  200 . There may be fewer heating stages if at a certain location in the calendering process it is determined that external heating of the roll surface is not desired. The series of heating stages  802  may be joined by a frame extending from the first heating stage to the last stage (not illustrated).  
         [0030]    A single heating stage  802 , without the calender rolls  350 ,  352  to be heated thereupon, is illustrated in FIG. 2. The heating stage  802  has a frame structure  804 . Traversing the heating stage  802  is a drive roll  806 . The drive roll  806  is driven by the motor  808 . At opposing sides of the stage  802  are a pair of idle rolls  810 . Each idle roll  810  is mounted to permit free rotation of the roll  810 . Between each idle roll  810  and the drive roll  806  is a heating means  812 . The heating means  812  extend substantially the length of the stage  802 , generally corresponding to the length of the idle rolls  810 . The heating means  812  preferably employ induction heating coils  814  which extend substantially the full length of the heating means  812 .  
         [0031]    The calender rolls  350 ,  352  are delivered to the heating stage  802  by the overhead moveable transfer mechanism  400 . The rolls  350 ,  352  may be paired together with at least one pair of plows  320  laterally positioned at predetermined locations radially above the pair of calender rolls  350 ,  352 . See FIG. 3. Each plow  320  has a pair of rigid members  324  contoured to precisely fit above and between the two rolls  350 ,  352 . The plows  320  secure and provide lateral support to the rolls  350 ,  352  while preventing an overflow of calendered material while forming the tire casing at the tire component forming apparatus  300 .  
         [0032]    When the calender rolls  350 ,  352  are placed onto the heating stage  802 , each roll  350 ,  352  contacts the drive roll  806  and one idle roll  810 , as illustrated in FIG. 4. As the drive roll  806  rotates in the direction illustrated by the direction arrow, each calender roll  350 ,  352  rotates in the opposing direction, as indicated. Due to the point of contact, the idle rolls  810  rotate in the same direction as the drive roll  806 , as indicated.  
         [0033]    The calender rolls  350 ,  352  are in close proximity to the heating means  812 . The heating source  812  may be positioned within the frame  804  at an inclination angle, as illustrated, in order to provide for the close proximity of the heating source  812  to the rolls  350 ,  352 . Each roll  350 ,  352  is associated with a single heating source  812 .  
         [0034]    The preferred final temperatures of the rolls  350 ,  352  is from about 140° to about 260° F. (60° to 126° C.). The initial temperature of the rolls  350 ,  352  may vary from a room temperature to the final temperature; that is the initial roll temperatures 60 to 260° F. (15° to 126° C.). While the majority of the rolls being heated in the heating stage  802  will be at about room temperature the rolls may also be delivered to the heating stage  802  from the tire component forming apparatus  300  to reheat, adjust, or maintain the temperature of the rolls.  
         [0035]    Temperature sensors are mounted on the heating frame  804  near the rolls  350 ,  352  to determine the roll temperature. This data is provided to a controller (not illustrated) to factor into the heating cycle of the heating means and the roll speed. The surface speed of the rolls  350 ,  352  also plays a role in the heating process. The speed at which each roll  350 ,  352 ,  806 ,  810  turns determines the amount of time that a portion of the roll  350 ,  352  dwells in the heating field generated by the heating means  812 . For this reason, a roll speed feedback device is also employed to provide the speed data to the controller.  
         [0036]    The type of heating that may be employed include induction heating, dielectric, and radiant heating means. Dielectric heating may be accomplished by forming the rolls  350 ,  352  from a nominally insulating material and subjecting the rolls  350 ,  352  to an alternating electrical field. The dielectric heater operates at a frequency above 10 megahertz.  
         [0037]    As noted above, the preferred method of heating is by induction heating coils  814 . As the rolls  350 ,  352  are rotated, the surface of each roll  350 ,  352  will continually pass through the induction field generated by the associated induction coil  814 . For induction heating, the gap between each heating means  812  and the associated roll  350  or  352 , at the smallest distance, ranges from {fraction (1/16)}″ to ½″ (1.58 to 12.70 mm), with a preferred spacing of {fraction (5/32)}″ (3.97 mm). If the gap is too great, the heating efficiency of the induction coils  814  is reduced.  
         [0038]    The preferred induction heating means  812  are more fully illustrated in FIGS. 5 and 6. The induction coil  814  is of the type conventionally known as a split return pancake coil due to its single sided heating and preferably formed from square copper tubing. The induction coil  814  is supported by a set of support bracings  816 . Each bracing  816  includes a main bracing  818  and an angle bracing  820 . Brackets  822  may also be employed for mounting. The induction coil  814  is secured to the angle bracing  820  by a plurality of brass fittings  824 . Other conventional mounting means may be employed. The primary requirement is that the mounting means be made of nonconductive insulating materials.  
         [0039]    The coil  814  is mounted on a pair of copper plates  826 . Each copper plate  826  is L-shaped. The small leg  828  of the L-shaped plate has means  830  for mounting onto the power supply. The long leg  832  of the L-shaped plate has means  834  to secure the two plates together. In between the two plates is a TEFLON separator  836 . The separator  836  acts to keep the positive and negatively charged plates  826  separate. The plates  826  and separator  836  are secured by nylon nut and bolt fittings.  
         [0040]    Extending from the underside of the coil  814 , adjacent each copper plate  826 , is the inlet  838  for the a coolant, typically distilled water, but other conventional coolants may be used, which travels through the induction coil  814 . The coolant travels in both directions along the center leg  840  of the coil, splits at the opposing ends  842 ,  844 , and back along the outside legs  846 ,  848  of the coil. The coolant exits through the tong-shaped tube  850  and exits though the outlet leg  852 . Similar to the coil  814 , the tong-shaped tube  850 , as well as the inlet  838  and outlet  852  are copper tubing. Preferably, the inlet  838  and outlet  852  are round tubing as illustrated, but may also be square tubing. During operation of the induction coil  814 , because the induction coil  814  is internally cooled with the recirculating coolant, the coil  814  does not see appreciable heat buildup.  
         [0041]    The current flow through the induction coil  814  travels in an opposing path through the coil  814 . The current flows through one copper plate  826 , along the outside coil legs  846 ,  848 , joins at a first coil end  842  or  844 , down the center leg  840 , splits at the opposing end  844  or  842 , and through the remaining legs  846 ,  848 , and into the other copper plate  826 . Because the current passing through the coil is alternating (AC), the path of the current reverses itself each cycle.  
         [0042]    To force the current flowing along the center leg  840  of the coil  814  to generate a greater induction field above the coil  814 , a plurality of flux concentrators  854  are stacked along the undersides of the center leg. The concentrators  854  are illustrated only in one portion of the coil  814 ; however, concentrators  854  are placed along the full length of the coil  814 . The concentrators  854  increase the heating efficiency of the disclosed system. The concentrators  854 , of a conventionally known material, are thin, u-shaped members. The concentrators  854  fill the spaces between the extending pegs  856  spaced along the center leg  840 . For increased efficiency of induction field, at approximately every ¼″ (approx. 6.35 mm), an insulation piece, with the same shape as the flux concentrators, is placed amongst the flux concentrators  854 . The insulation pieces break up any current attempting to travel through the flux concentrators  854 . Without the insulation, the concentrators  854  would tend to unnecessarily heat up, using energy that could otherwise be transmitted to the rolls  350 ,  352 .  
         [0043]    For protection, a cover  858  may be applied to the top of the heating means  812 , as illustrated in FIG. 4. The cover  858  is secured to the bracings  820 .  
         [0044]    The power wattage and its frequency is varied by the controllers, in order to vary the frequency and wattage provided to the coils. The wattage controls the amount of heat being generated in the rolls  350 ,  352 . The frequency of the power to the coil  814  controls the depth of the heat generation. At relatively high frequencies, most of the heat will be induced at or near the outside surface of the rolls  350 ,  352 . At lower frequencies, the heat will penetrate deeper in the rolls  350 ,  352 . Typically, the use of higher frequencies provide more efficient heating to the rolls  350 ,  352 . For this reason, the disclosed system operates at relatively high frequencies with a narrow air gap between the roll and coil face.  
         [0045]    For the disclosed invention, the frequency is within the range of 1 kHz to 20 kHz, preferably 7-11 kHz. If the frequency employed is too low, an audible noise highly disturbing to persons nearby is generated. During operation of the induction coil  814 , at the preferred frequency range for the induction coil  814 , the roll  350  or  352  is heated to a limited depth of the roll  350  or  352 . The remainder of the roll  350  or  352  is heated by means of traditional conduction as the heat that was induced conducts deeper into the roll  350  or  352 . The combination of the induction heating and the conduction heating optimizes the energy consumption of the heating station  802  and takes advantage of the roll material.  
         [0046]    With the disclosed induction heating means, the entire mass of a 1300 lb. (2866 kg) roll may be heated from a room temperature of approximately 70° F. (21° C.) to about 200° F. (93° C.) in about 3 minutes. This is a very rapid heating compared to the internal heaters previously disclosed; internal heating of the same 1300 lb. roll to the same temperature would take approximately 20 minutes.  
         [0047]    Employing the heating stages  802  disclosed herein provides for improved efficiency of the calendering process and also permits greater flexibility in the calendering process. By placing rolls  350 ,  352  into the calendering apparatuses, the calendering process may begin as soon as the rolls  350 ,  352  are secured instead of waiting for the internal heaters  335  to bring the rolls  350 ,  352  up to the desired operating temperatures. Once the heated rolls  350 ,  352  are placed into the calendering apparatus  302 , in accordance with the present invention, the internal heaters  335  may be used to maintain the roll temperature.  
         [0048]    The heating stage  802  also allows for faster changeovers in the laminate specifications or repairs to the calendering apparatus  302 . When it is desired to change the laminate specifications, rolls with a different defined profile may be delivered to the heating station  802  and heated to either the desired operating temperature or greater than the desired temperature. If the temperature is greater than the operating temperature, the roll may then be held while it cools to the desired temperature. This may be desired, for example, if for some reason the plurality of calendering apparatus  302  are changed out serially, instead of in parallel. With a serial changeover, all of the rolls  350 ,  352  may be heated and then held, with the last roll to be changed out heated to a greater temperature since it may have a longer hold period before being put into the associated calendering apparatus.  
         [0049]    Also, as stated, if repairs are needed to the calendering apparatus  302 , or a material change is to be accomplished, the rolls  350 ,  352  may be transferred back to the heating stage  804  and then heated/reheated and then held at the operating temperature while the desired repair or material change is carried out. Other circumstances may occur which may precipitate placing the rolls  350 ,  352  into the heating stage  804  for reheating or maintaining a temperature. For whatever circumstances may arise, the ability to have the rolls  350 ,  352  at a temperature that allows for almost instantaneous operation of the calendering apparatus  302  once all of the desired rolls  350 ,  352  are in place increases the efficiency of the apparatus  200 , leading to less down time of the process, and reduced manufacturing costs.