Abstract:
A heat transfer roll for producing sheet material, particularly material having a cross-section whose thickness varies across the width of a sheet being formed, includes a journal on which the roll is rotatably supported, and at least two cooling channels at the surface of the roll that can be supplied with various fluids at various flow rates and temperatures. Fluid in the first and second channels flows at predetermined longitudinal positions at the roll surface. The first channel includes cylindrical spiral portions and the second channel includes a circular cylindrical channel located between the spiral portions. A diverter provides hydraulic flow continuity across the second flow channel to first and second portions of the first flow channel. Risers carry fluid radially outward to the flow channels at the outer surface of the roll.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to the field of process rolls, more particularly it pertains to heat transfer rolls for use in the production and processing of sheets of material, such as paper, plastic and rubber. 
   2. Description of the Prior Art 
   The principal techniques for manufacturing wide sheets of polymer, such as plastic, or of paper are an extrusion process and a cast film process. The flat sheet extrusion process is used to produce plastic sheet by pressing molten polymer material between two or more rolls that serve to flatten the material into a continuous sheet having a desired thickness. The material passes around and between multiple rolls during production and processing of the sheet. Often a pull roll is used to keep tension in the extruded flat sheet as it exits the final roll. The sheet is then continuously rolled on a core, or it is cut and stacked in flat sheets. 
   U.S. Pat. No. 5,567,448 describes a heat transfer roll for use in forming flat sheet material by an extrusion process. The roll includes a core, a shell surrounding the core and a duct, through which fluid for controlling the temperature of the sheet flows from the core to the shell. The roll extrudes sheet having a uniform thickness across its width and provides one cooling fluid flow passageway. The roll has no provision for multiple fluid channels and cannot accommodate variable sheet thickness or a variable heat content of sheet material across the width. 
   Various techniques have been employed to control the temperature on the surface of a roll used to form sheets of paper or plastic. For example, U.S. Pat. No. 4,233,011 describes a roll having a cylindrical core, a tubular shell surrounding the core, and a heating strip carried on the core. Temperature sensors located on the core are used to produce a signal employed by an electrical regulating circuit that controls the application of electric power supplied to the heating strip. The heating strip is regulated so that a predetermined temperature difference between the heated and unheated sides of the core is maintained. The purpose of maintaining this temperature difference on the core is to produce thermal displacement or arching of the core. That displacement is transmitted to the shell. U.S. Pat. No. 5,103,542 describes a fluid distribution system for a variable-crown roll that includes a stationary central axis and a revolving shell surrounding the axis. The fluid distribution system includes a system of ducts in which pressurized fluid enters isolated areas on the roll. The fluid distribution system includes axial ducts and transverse bores that direct fluid to hydraulic loading elements to compensate for stresses resulting during processing. Neither of these patent references describes the use of multiple temperature channels on a forming roll. 
   Rolls for forming sheet material have conventionally included an annular passage located between a core and a shell surrounding the core. Fluid for cooling the sheet material flows in the annular passage along a spiral path bounded by partition strips that extend radially between the core and the inner surface of the outer shell. U.S. Pat. Nos. 3,548,929 and 3,676,910 describe rolls having a spiral fluid flow channel. The &#39;910 patent describes a machine for forming T-shaped fins that include a sealing gasket, the fins being used as a spiral seal between the core and outer shell of a fluid heat exchanger type roll. The &#39;929 patent describes use of a continuous partition strip arranged in a spiral and located in an annular space between the core and outer shell of the roll. The partition strip is formed of a composite structure that can withstand the chemical and thermal action of certain fluids used for heat transfer purposes that tend to corrode or decompose partitions made of rubber and plastic. 
   The process for producing long, wide, thin sheet material of plastic, paper and similar materials by the cast film processing includes use of an extruder that delivers molten material in a fluid state to a die. The die has a profiled opening or orifice that forms the surface contour of the sheet as the molten polymer passes through the die orifice to form an elongated sheet width. The sheet may have relatively thick areas spaced across the elongated width and extending continuously along the length of the sheet. 
   Accordingly, the rate of cooling of the cast sheet product varies across the sheet, that rate being longer in the areas of thick sheet and shorter in the areas of thin sheet. There is need for a heat transfer roll that accommodates the cooling requirement differences across the sheet width by providing multiple cooling channels located within the roll and located appropriately to correspond to the location of thick and thin sheet areas. 
   SUMMARY OF THE INVENTION 
   In one of its embodiments, the present invention provides a heat transfer roll on which molten sheet material is cooled, the roll including a first cylindrical shell; a second cylindrical shell surrounding the first shell, and defining a cylindrical annular space therebetween, said space having an axial length and a periphery; a first flow channel located in said space, extending along a first portion of the axial length and around the periphery of said space, having a first inlet and a first outlet; and a second flow channel located in said space, extending along a second portion of the axial length and around the periphery of said space, having a second inlet and a second outlet. 
   In another of its embodiments this invention contemplates a method for forming a long sheet of material having a cross-section with a width and a thickness, the thickness having a relatively thin area and a relatively thick area, the thin area extending across a first portion of the width, and the thick area extending across a second portion of the width, or vice versa. The method comprising the steps of passing molten material through a die having an orifice with a shape complementary to the cross-section of sheet being produced; placing said passed sheet on a roll having a surface exposed to a first flow channel and a second flow channel; locating the sheet on the roll such that the lateral location of the thin area corresponds to the lateral location of the first flow channel, and such that the lateral location of the thick area corresponds to the lateral location of the second flow channel; supplying fluid from a first fluid source to the first flow channel; and supplying fluid from a second fluid source to the second flow channel. 
   As previously described, a molten sheet having varied thickness cross-sectional profiles will have different solidification times at the thinner and thicker portions of the sheet. As a result, cooling of the molten material at one rate causes degradation and varied shrinkage as portions solidified across the profile as different times. By increasing the cooling rate of the thicker profiles so that it substantially matches the time of solidification of the thinner profiles, the quality of the product is improved. Therefore, a multiple thermal channel roll according to the present invention allows a wider operating range of thicker verses thinner sheet profiles due to the wider cooling ranges between the thermal channels. 
   Further, because thicker portions of the molten sheet material can be cooled faster by appropriate choice of coolant and other process variables, a roll having multiple coolant temperature channels according to the present invention permits the process line speed to be increased compared to the speed using a conventional forming roll. 
   It is still another advantage of this invention that different cooling fluids can be used in each fluid flow channel to maximize the heat transfer from the sheet material to the coolant in the several cooling channels on the roll. It is yet another advantage that both heating and cooling channels can be used when producing sheet material of composite materials having substantially different thermal properties. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     It is to be understood that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the instant invention, for which reference should be made to the claims appended hereto. Other features, objects and advantages of this invention will become clear from the following more detailed description made with reference to the drawings in which: 
       FIG. 1  is a diagram representing process steps for producing thin sheet by the cast film process employing a roll having multiple thermal channels according to the present invention; 
       FIG. 2  a front elevation view taken at plane  2 — 2  of  FIG. 1  showing a non-uniform cross-sectional contour profile on a sheet leaving a die; 
       FIG. 3  is a side elevation view taken at plane  3 — 3  of  FIG. 1 ; 
       FIG. 4  is a cross section taken through a central longitudinal axis of a process roll according to the present invention; and 
       FIG. 5  is a view looking radially inward toward the inner shell with the outer shell removed and the cylindrical surface of the outer shell projected into a horizontal plane. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Turning first to  FIG. 1 ,  2  and  3 , the process equipment and machinery for producing long, wide, thin sheet material of plastic, paper and similar materials by cast film processing includes an extruder, shown generally at  10 , which receives stock, such as polymer through a bin  12 . The extruder delivers molten material in a fluid state through a conduit  14  to a die  16 . The die has a profiled orifice  18  that forms the surface contour and cross-sectional profile of the sheet as the molten polymer passes through the die orifice. The shape of the die orifice  18  is the complement of the surface contour and cross-sectional profile of the sheet being produced. The sheet may have relatively thick areas  20 , shown in  FIG. 2  in the form of projections, spaced mutually across the width and extending continuously along the length of the sheet, the projections being separated by thin, flat areas  21 , which also extend continuously along the length of the sheet. 
   The sheet material leaves the die  16  and passes over a heat transfer roll  30 , supported for rotation at each axial end on journals  32 ,  34 . An air knife may be used to force the sheet closely against the heat transfer roll  30 . The sheet is cooled on the outer surface of roll  30  and cut into lengths by a secondary process before final assembly or subsequent processing. 
     FIG. 4  illustrates the roll  30 , according to the present invention, for use in forming sheet material having thicknesses, heat content properties, and cooling rate requirements that vary across the width of the sheet. The roll includes left-hand and right-hand journals,  32 ,  34 , which are formed in a known manner to be received in conventional bearings or pillow blocks, on which the roll is supported for rotation about a central axis  36 . Preferably each journal  32 ,  34  includes a keyway  38 , through which power is transmitted from an external source to rotate the roll about axis  36 . At the right-hand end of the roll, a circular end plate  40  is secured to the right-hand journal  34  by a welded connection  42 . At the left-hand side of the roll, another circular end plate  44  is secured by a circular weld  46  to the outer surface of the left-hand journal  32 . 
   Located within the right-hand journal  34 , at the fluid inlet side of the roll  30 , is a siphon tube  48 , which is connected through a rotary union  50  to a first source conduit  52 , which is hydraulically connected to a first source of fluid liquid  54 , i.e., chilled or heated fluid. Surrounding the siphon tube  48  and located in an annular passageway between the outer wall of the right-hand journal  34  and the wall of siphon tube  48  is a fluid journal-passage  56 , which is similarly connected through the rotary union  50  to a second source conduit  58  connected to a second fluid source  60  holding heat transfer fluid or liquid. 
   Located within the left-hand journal  32 , at the fluid outlet side of the roll  30 , is a siphon tube  62 , which is hydraulically connected through a rotary union  64  to a conduit  66 , through which fluid is returned to the first fluid source  54 . Surrounding the siphon tube  62  and located in an annular passageway between the outer wall of journal  32  and the wall of siphon tube  62  is a fluid journal-passage  68 , which is similarly connected through the rotary union  64  to a conduit  70 , through which fluid is returned to the second fluid source  60 . 
   A first siphon plug  72  forms a bulkhead that blocks and closes the end of the fluid journal-passage  56  in the right-hand journal  34 . Similarly, a second siphon plug  74  closes the end of the fluid journal-passage  68  in the left-hand journal  32 . 
   A first tube  76  is fixed by a weld  78  to the inner end of the right-hand journal  34 , and a second tube  80  is fixed by a weld  82  to the inner end of said left-hand journal  32 . The ends of tubes  76 ,  80  are mutually connected by a center weld  84 . The siphon tube  48  is hydraulically connected to the tube  76 , which is blocked by a third siphon plug  86 , but tube  76  is blocked by the first siphon plug  72  from communication with the annular journal-passage  56 . The tube  80  is in direct fluid communication with the siphon tube passage  62 , but tube  80  is blocked by the second siphon plug  74  from communication with annular journal-passage  68 . 
   Extending radially outward from the axis  36  and fixed to the right-hand journal  34  is a first riser pipe  88 , which is in fluid communication with annular journal-passage  56 . Similarly, a second riser pipe  90  is fixed to said left-hand journal  32  and extends radially outward from axis  36 . The second riser pipe  90  is in fluid communication with the annular journal-passage  68 . 
   Located at the radially outer end of the riser pipes  88 ,  90  is an inner shell  92  providing a circular cylindrical outer surface  94 . The inner shell  92  is sealed and joined by a weld  96  to end plate  40 , and inner shell  92  is sealed and joined to end plate  44  by a weld  98 . 
   Spaced radially from the cylindrical surface  94  of the inner shell  92  is an outer shell  100 , which has an outer circular cylindrical surface  102 , joined and sealed at the inlet and outlet sides of the roll to the end plates  40 ,  44  by welds  104 ,  106 . Located within the cylindrical annular space  107  between the inner shell  92  and outer shell  100  are spiral-shaped seals  108 . 
   Located approximately midway between the riser pipes  88 ,  90  is a diverter  110  in a form of tube communicating with a spiral channel having portions  112 ,  114  located at opposite axial sides of the diverter  110 . Communication between the spiral portions  112 , 114  is blocked by circular seals  116 ,  118 , which extend around the circumference of the inner shell  92 . The diverter pipe  110  is fixed to the inner shell  92  and is supported on the shell by a hanger flange  120 . 
   An annular channel portion  130  located between seals  116 ,  118  is hydraulically connected and supplied with fluid from the first fluid source  54  through the first tube  76  and a third riser pipe  132 . The annular channel portion  130  is hydraulically connected also to the second tube  80  by a fourth riser pipe  134 . 
   In this way, the roll  30  contains first and second flow channels, each channel hydraulically connected to one of the fluid sources  54 ,  60 . The first flow channel for carrying coolant from the inlet side to the outlet side of roll  30  is supplied from the second fluid source  60 , through conduit  58 , rotary union  50 , journal-passage  56 , and first riser pipe  88  to the spiral channel portion  112  located in annular space  107 , between inner shell  92  and outer shell  100 . Diverter  110  carries fluid around the annular channel portion  130 , bounded by circular seals  116  and  118 , to the spiral channel portion  114 . The second riser pipe  90  carries fluid from spiral portion  114  to the journal-passage  68  located between the inner wall of the left-hand journal  32  and the outer wall of siphon tube  62 , through rotary union  64 , and conduit  70  for return to fluid source  60 . 
   The second fluid flow channel for carrying coolant from the inlet side to the outlet side of roll  30  is supplied from the first fluid source  54 , through conduit  52 , rotary union  50 , siphon tube  48 , tube  76 , and the third riser pipe  132  to the annular channel portion  130  located in the annular-space  107  between the circular seals  116 ,  118 . The fourth riser pipe  134  carries hydraulic fluid from the annular channel portion  130 , through tube  80 , siphon tube  62 , rotary union  64 , and conduit  66  for return to fluid source  54 . 
   In this embodiment, the roll defines a first outer cooling channel having a first spiral portion  112  that extends longitudinally on the outer cylindrical surface  102  of the outer shell  100  between end plate  40  and seal  116 , and having a second spiral portion  114  located on the outer cylindrical surface  102  of outer shell  100  and extending longitudinally between circular seal  118  and the end plate  44 . The roll also includes an annular cooling channel portion  130  in its center, located on the outer circular surface  102  of outer shell  100  extending longitudinally between circular seals  116  and  118 . 
   The radially outer end of the first riser pipe  88  communicates with the spiral portion  112  of the first flow channel through an inlet  146 , through which fluid enters the spiral portion  112  of the first flow channel. The radially outer end of the second riser pipe  90  communicates with the spiral portion  114  of the first flow channel through an outlet  148 , through which fluid exits the spiral portion  114  of the first flow channel. Fluid flow continuity between the spiral portions  112 ,  114  is provided by the diverter  110 , which has an inlet  122  through which fluid exits spiral portion  112  and enters diverter  110 , and an outlet  124  through which fluid leaves diverter  110  and enters spiral portion  114 . 
   Similarly, the radially outer end of the third riser pipe  132  communicates with the second flow channel, being the cylindrically annular channel portion  130 , via an inlet  150 , through which fluid enters the annular channel portion  130 . The radially outer end of the fourth riser pipe  134  also communicates with the annular channel portion  130  of the second flow channel via an outlet  152 , through which fluid exits the annular channel portion  130  and enters riser pipe  134 . Fluid flow continuity between riser pipes  132  and  134  is provided by channel portion  130 . 
     FIG. 5  shows an embodiment of a multi-channel arrangement with spiral seal  108  and circular seals  116 ,  118 , viewed radially inward with outer shell  100  removed and the cylindrical outer surface of the inner shell  92  of the roll  30  in a horizontal plane. The spiral channel portion  112  of the first flow channel extends longitudinally along axis  36  from the inner surface of end plate  40  to seal  116 . Spiral portion  112 , which is located in the annular space between the outer shell  100  and inner shell  92 , entirely encircle the inner shell  92  several times.  FIG. 5  shows spiral portion  112  extending four times around the circumference of the roll  30 . 
   Spiral seal  108  abuts end plate  40  and travels angularly about and axially along the outer surface of inner shell  92  in a spiral path. The radially outer end of seal  108  contacts the inner surface of the outer shell  100 , thereby sealing the outer surface of inner shell  92  and the inner surface of outer shell  100  against fluid flow across seal  108 , and directing flow along the length of seal  108 . Therefore, fluid entering channel portion  112  from inlet  146  flows along a spiral path bounded by shells  92 ,  100  and seal  108 , to inlet  122 , where the fluid enters diverter  100 . Fluid in the first flow channel then leaves diverter  100  through outlet  124 , enters the spiral channel portion  114 , and flows along channel portion  114  to the outlet  148 . Fluid in the first flow channel would then leave the roll through the second riser pipe  90  and journal-passage  68 , rotary union  60  and conduit  70 . 
   Preferably, but not always, the axial pitch of the spiral about the axis  36  in the spiral portion  112  decreases angularly from the inlet  146  as the seal  108  extends away from end plate  40  toward circular seal  116 . After then passing through diverter  110 , fluid enters the spiral portion  114 . Similarly, as seal  108  moves away from the circular seal  118 , in the spiral portion  114 , the axial pitch of the spiral gets smaller and the width of the channel increases, so that resonance time of the fluid passing therethrough increases. In this way, the resonance time of the cooling fluid increases as the fluid moves through channel portions  112 ,  114  from inlet  146  to outlet  148 , so as to maintain uniform cooling of the sheet across its width. 
   Circular seals  116 ,  118  are supported on the outer surface of inner shell  92  and travel along the circumference of the outer surface of inner shell  92  in a circular path. The radially outer end of seals  116 ,  118  contact the inner surface of the outer shell  100 , thereby sealing those surfaces of the shells against fluid flow across seals  116 ,  118 , and directing flow in the annular channel portion  130  along the length of those seals. 
   In the vicinity of the diverter inlet  122  and outlet  124 , the inlet  150  of the third riser pipe  132  and outlet  152  of the fourth riser pipe  134  are sealed mutually by transverse seal  156 . In this way, fluid entering the annular flow channel portion  130  through the inlet  150  from riser pipe  132  flows about axis  36  and along the annular space bounded by seals  116 ,  118 , the outer surface of inner shell  92  and the inner surface of outer shell  100 , to the outlet  152  at riser pipe  134 . Then fluid in this second fluid flow channel enters tube  80  and exits the roll through the siphon tube  62  in the journal  32 , rotary union  64  and conduit  66 . 
   Continuing to focus in the vicinity of the diverter inlet  122  and outlet  124 , seal  108  either continues uninterrupted past seals  116 ,  118 , or seals  116 ,  118  continue uninterrupted past seal  108 . In either case, transverse seal  156  prevents direct communication between the inlet  150  and outlet  152  of riser pipes  132 ,  134 , and seal  108  continues its spiral path angularly about and axially along axis  36  from the diverter outlet  124  to the outlet  148  of riser pipe  90 . 
   Although the first flow channel shown in  FIG. 4  has been described as having only two spiral flow portions  112 ,  114 , separated by the second flow channel having one annular flow channel portion  130 , there may be any suitable number of first flow channel portions and second flow channel portions as shown in FIG.  5 . Accordingly any number of diverters  110  and riser pipes  88 ,  90 ,  132 ,  134  that are needed to accommodate the fluid cooling requirements of the surface profile or contour of the sheet being produced by the process can be added to the roll. For example,  FIG. 5  shows six spiral flow channel portions  112 ,  114 ,  160 ,  161 ,  162 ,  163  of the first fluid flow channel, each separated by one of five secondary fluid flow channels having portions  130 ,  164 ,  165 ,  166 ,  167 . 
   Also, the direction of fluid flow in either or both of the spiral fluid flow channel portions  112 ,  114  and the annular channel portion  130  can be reversed so that fluid flows clockwise in one channel and counterclockwise in another channel when viewed from a lateral side of the roll. Each flow channel can also contain a different fluid. The linear flow rate of fluid and mass flow rates of fluid in each channel may differ mutually. Further, the flow channels can be provided with turbulators and other such devices for increasing the degree of turbulent fluid flow through the channels in order to increase the rate of heat transfer through the various portions of the outer shell wall. 
   Furthermore, the first and second flow channels need not be cylindrical spirals and annular, as described here, but may have any suitable form and combination. The axial width of the various portions of the first flow channel may be mutually equal or they may differ from one another to optimize heat transfer. Similarly, the axial width of the second flow channel portions may differ mutually and in relation to the widths of the first flow channel portions in accordance with the cooling requirements of the sheet being produced. 
   Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts and method steps may be made to suit requirements without departing from the spirit and scope of the invention.