Abstract:
A method for preheating a permeable, thermoformable material having first and second sides includes supplying heated fluid to a fluid distribution system; regulating flow of the fluid such that fluid having a first temperature flows at a first velocity, and fluid having a second temperature less than the first temperature flows at a second velocity greater than the first velocity; introducing the fluid onto the first side of the material; and developing a suction on the second side of the material sufficient to draw the fluid through the material thereby convectively heating the material; wherein the flow of the fluid is regulated so as to transfer substantially uniform energy flux to the material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a method for heating a permeable, thermoformable material using heated fluid to convectively heat the material, wherein flow of the fluid is regulated such that relatively cooler portions of the fluid travel more quickly than hotter portions of the fluid. 
     2. Background Art 
     A prior method of heating a thermoformable material, including thermoset and thermoplastic materials, involves contact heating. The contact heating method includes placing the material in direct contact with a heat source, such as thermally regulated upper and lower platens. Heat is then transferred principally by conduction from the outer surface to the inner core of the material. Because such materials are typically poor conductors of heat, however, this method requires a significant amount of time to sufficiently heat the materials. 
     Another method of heating a thermoformable material involves radiant heating. This method involves placing the material near a radiant heat source, such as electric coils or ceramic heaters. The outer portions of the material, however, tend to selectively absorb the radiant energy, and core heating is again accomplished primarily by conduction. Consequently, this method also requires a significant amount of time to sufficiently heat the material. 
     U.S. Pat. No. 6,036,896, which is assigned to the assignee of the present invention, discloses a method of heating a permeable, thermoformable material using convective heating. The method involves supplying heated fluid to a fluid distribution system and homogenizing t he fluid such that the fluid has a substantially uniform velocity and temperature. The method further involves drawing the fluid through the material and passing the fluid through a flow regulating device so as to maintain the homogeneity of the fluid as the fluid exits the material. 
     SUMMARY OF THE INVENTION 
     Under the invention, a method for preheating a permeable, thermoformable material having first and second sides includes positioning the material proximate an outlet of a fluid distribution system such that a first section of the material is disposed further away from the outlet than a second section of the material; supplying heated fluid through the outlet; regulating flow of the fluid; introducing the fluid onto the first side of the material; and developing a suction on the second side of the material sufficient to draw the fluid through the material thereby convectively heating the material; wherein the flow of the fluid is regulated such that a first portion of the fluid having a first velocity and a first temperature passes through the first section of the material, and a second portion of the fluid having a second velocity less than the first velocity and a second temperature greater than the first temperature passes through the second section of the material, such that substantially uniform energy flux is transferred from the first and second portions of the fluid to the first and second sections, respectively, of the material. 
     Advantageously, substantially uniform energy flux may be transferred from the first and second portions of fluid to the first and second sections, respectively, of the material during initial or transient flow conditions, as well as during later steady state flow conditions. As a result, the material may be efficiently and effectively heated without necessarily requiring steady state flow conditions to be reached. Thus, heating cycle times can be reduced. 
     Further under the invention, a method for preheating a permeable, thermoformable material having first and second sides includes supplying heated fluid to a fluid distribution system; regulating flow of the fluid such that fluid having a first temperature flows at a first velocity, and fluid having a second temperature less than the first temperature flows at a second velocity greater than the first velocity; introducing the fluid onto the first side of the material; and developing a suction on the second side of the material sufficient to draw the fluid through the material thereby convectively heating the material; wherein the flow of the fluid is regulated so as to transfer substantially uniform energy flux to the material. 
     More specifically, a method for preheating a permeable, thermoformable material having first and second sides includes positioning the material in a housing having a fluid inlet such that a first section of the material is disposed further away from the inlet than a second section of the material; supplying heated fluid to the inlet; passing the fluid through a first flow regulating device having first and second openings such that a first portion of fluid passes through the first opening and a second portion of fluid passes through the second opening, wherein the first opening is disposed further away from the outlet than the second opening, and wherein the first opening is larger than the second opening, such that after passing through the first flow regulating device the first portion of fluid has an average first temperature and an average first velocity, and the second portion of fluid has an average second temperature greater than the average first temperature and an average second velocity less than the average first velocity; passing the fluid through a second flow regulating device disposed downstream of the first flow regulating device so as to homogenize each of the first and second portions of the fluid; introducing the fluid onto the first side of the material; developing a suction on the second side of the material sufficient to draw the fluid through the material such that the first portion of the fluid passes through the first section of the material and the second portion of the fluid passes through the second section of the material, thereby transferring substantially uniform energy flux from the first and second portions of the fluid to the first and second sections, respectively, of the material; and passing the fluid through a third flow regulating device disposed downstream of the material so as to maintain the homogeneity of each of the first and second portions of the fluid. 
     These and other objects, features and advantages of the invention are readily apparent from the following detailed description of the preferred embodiments for carrying out the invention, when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic diagram of an apparatus for heating permeable, thermoformable materials according to the invention, wherein dampers of the apparatus are shown properly positioned so as to route heated fluid through a fluid bypass subsystem of the apparatus; 
     FIG. 2 is a schematic diagram of the apparatus with the dampers properly positioned so as to route heated fluid through a processing chamber of the apparatus; and 
     FIG. 3 is a fragmentary perspective view of the processing chamber showing a plurality of flow regulating devices. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings, the preferred embodiments of the invention will now be described. FIG. 1 shows a schematic view of an apparatus according to the invention for preheating permeable, thermoformable materials such as a laminate assembly  12 . Laminate assembly  12  may include, for example, a formable layer  14 , an adhesive layer  16  and a cover member  18 . Alternatively, the apparatus  10  may be used to heat any suitable permeable material. 
     The apparatus  10  comprises an insulated main housing  20 , a source of heated fluid such as a burner chamber  22 , a fluid distribution system  24  in fluid communication with the burner chamber  22 , a processing chamber  26  in fluid communication with the fluid distribution system  24 , and a fluid return system  28  connected between the processing chamber  26  and the burner chamber  22  for returning fluid to the burner chamber  22 , as explained below in greater detail. 
     In the embodiment shown in FIG. 1, the burner chamber  22  is disposed in the main housing  20 , and includes a burner chamber housing  30  and a burner arrangement  31  for heating air or other fluid in the burner chamber housing  30 . The burner arrangement  31  includes a burner  32 , which may be any suitable burner such as a natural gas burner or a propane burner. The burner arrangement  31  also includes a combustion blower  33  for providing fresh air, or other fluid, to the burner chamber housing  30 . Alternatively, the apparatus  10  may include any suitable source of heated fluid such as a steam source. Furthermore, the apparatus may include multiple sources of heated fluid. 
     The fluid distribution system  24  is also disposed within the housing  20  and includes a supply blower  34  disposed in a blower chamber  36 . The fluid distribution system  24  further includes a supply duct  38  disposed between the blower chamber  36  and the processing chamber  26 , and the supply duct  38  has an outlet  39  for supplying heated fluid to the processing chamber  26 . A supply damper  40  is disposed in the supply duct  38  for regulating flow of fluid through the supply duct  38 . The supply damper  40  is moveable between a closed position, shown in FIG. 1, and a open position shown in FIG.  2 . 
     The fluid distribution system  24  also preferably includes a fluid bypass subsystem  41  for routing fluid back to the burner chamber  22  without releasing the fluid into the processing chamber  26 . The fluid bypass subsystem  41  may include, for example, a bypass duct  42  and a bypass damper  43  for regulating flow of fluid through the bypass duct  42 . The bypass damper  43  is moveable between an open position shown in FIG. 1, and a closed position shown in FIG.  2 . 
     Alternatively, the fluid distribution system  24  may have any suitable configuration sufficient to route heated fluid to the processing chamber  26 , or other location configured to receive the laminate assembly  12 . 
     Referring to FIGS. 1 through 3, the processing chamber  26  includes a processing chamber housing  44  having an inlet  46  and an outlet  48 . The processing chamber  26  also includes one or more flow regulating devices for regulating the flow of fluid as the fluid passes through the processing chamber housing  44 , such that relatively cooler portions of the fluid may travel more quickly through the laminate assembly  12  than hotter portions of the fluid. As a result, substantially uniform energy flux, which is proportional to fluid temperature times fluid velocity, may be transferred to substantially all portions of the laminate assembly  12 , as explained below in detail. Furthermore, energy flux may be represented as Watts per square meter times time in seconds. 
     In the embodiment shown in FIGS. 1 through 3, for example, the processing chamber  26  includes first, second, third and fourth flow regulating devices  50 ,  52 ,  54  and  56 , respectively. The first and fourth flow regulating devices  50  and  56 , respectively, preferably include baffle arrangements having a plurality of openings for regulating the flow of fluid. For example, the first and fourth flow regulating devices  50  and  56 , respectively, may each include first and second openings  58  and  60 , respectively. Each first opening  58  is disposed further away from the inlet  46  than a corresponding second opening  60 , and the first openings  58  are generally larger than the second openings  60 . As shown in FIG. 3, for instance, the second openings  60  may each have a constant width W, whereas the first openings  58  may each have a width that expands from 2W at one end to 3W at the opposite end. 
     The first and fourth flow regulating devices  50  and  56  may each also have additional openings  62  disposed between the first and second openings  58  and  60 , respectively. The additional openings  62  disposed progressively closer to a particular first opening  58  are preferably progressively larger than the associated second opening  60 . However, adjacent additional openings  62  may be the same size. Furthermore, the openings  58 ,  60  and  62  of the first flow regulating device  50  are preferably, but not necessarily, aligned with the openings  58 ,  60  and  62  of the fourth flow regulating device  56 . 
     As another example, if the inlet  46  is centrally located on the top of the processing chamber housing  44 , the first and fourth flow regulating devices  50  and  56 , respectively, may each be provided with one or more relatively small central openings, and a plurality of additional or outer openings that are progressively larger toward the perimeter of each of the first and fourth flow regulating devices  50  and  56 , respectively. 
     The second flow regulating device  52  is preferably configured to mix the fluid so as to homogenize one or more portions of the fluid upstream of the laminate assembly  12 , as explained below in greater detail. The third flow regulating device  54  is preferably configured to maintain the homogeneity of the one or more portions of fluid downstream of the laminate assembly  12 , as explained below in detail. In one embodiment of the apparatus  10 , the second and third flow regulating devices  52  and  54 , respectively, each include a mesh, such as a fine wire mesh or a TEFLON® coated fiberglass mesh. Alternatively, the second and third flow regulating devices  52  and  54 , respectively, may each include any suitable flow regulating device, such as a perforated sheet or panel. 
     The second and third flow regulating devices  52  and  54 , respectively, may also function as retaining members for retaining the laminate assembly  12  within the processing chamber  26 . For example, the second and third flow regulating devices  52  and  54 , respectively, may be slidably mounted to the processing chamber housing  44  so that the second and third flow regulating devices  52  and  54 , respectively, may be removed partially or fully from the processing chamber housing  44 , and separated so as to receive the laminate assembly  12  therebetween. As another example, the second and third flow regulating devices  52  and  54 , respectively, may each be configured as a conveyor belt for automatically loading and unloading the laminate assembly  12 , or other material, in the processing chamber  26 . Alternatively, the apparatus  10  may be provided with any suitable member or members for retaining the laminate assembly  12  within the processing chamber  26 . Furthermore, the second and third flow regulating devices  52  and  54 , respectively, may be positioned in the processing chamber housing  44  such that the second and third flow regulating devices  52  and  54 , respectively, are spaced away from the laminate assembly  12  when the laminate assembly  12  is positioned in the processing chamber housing  44 . 
     Advantageously, all of the flow regulating devices  50 - 56  may be removably mounted within or to the processing chamber housing  44 , so that each of the flow regulating devices  50 - 56  can be modified, eliminated or replaced with another component depending on the application. 
     Referring to FIG. 2, the fluid return system  28  includes a return duct  64  that collects fluid from the processing chamber  26  and routes the fluid back to the burner chamber  22 . With such a configuration, the supply blower  34  is able to reduce pressure within the return duct  64  relative to the pressure in the supply duct  38 . For example, the supply blower  34  may achieve a gauge pressure within the return duct  64  of about 0 to −5 pounds per square inch (psi) or 0 to −3.446×10 4  Pascal, and a gauge pressure in the supply duct  38  of about 0 to 5 psi (0 to 3.446×10 4  Pascal). As a result, a pressure gradient of about 0 to 10 psi (0 to 6.892×10 4  Pascal) may be developed across the laminate assembly  12  for drawing fluid through the laminate assembly  12 . 
     The fluid return system  28  also includes a return damper  66  disposed in the return duct  64  for regulating flow through the return duct  64 . The return damper  66  is moveable between an closed position shown in FIG. 1, and an open position shown in FIG.  2 . 
     The fluid return system  28  may also include an exhaust duct  68  connected to an exhaust blower  70  for removing fluid from the apparatus  10 . Furthermore, an exhaust damper  72  is disposed in the exhaust duct  68  for regulating flow of fluid through the exhaust duct  68 . The exhaust damper  72  is moveable between an open position shown in FIG. 1 and a closed position (not shown). 
     The apparatus  10  may also include a control system  73  that controls operation of the burner  32 , blowers  33 ,  34  and  70 , and dampers  40 ,  43 ,  66  and  72 . The control system  73  may also control fluid temperature in the processing chamber  26  by periodically monitoring the fluid temperature, and regulating the amount of energy, such as fuel, provided to the burner  32  in order to achieve a desired temperature. 
     Referring to FIGS. 1 through 3, a method according to the invention for heating a permeable material, such as the laminate assembly  12 , will now be described. First, the blowers  33 ,  34  and  70  are activated with the supply damper  40  in the open position, the bypass damper  43  in the closed position or partially open, the return damper  66  in the open position and the exhaust damper  72  in the open position, so as to purge combustible vapors, if any, from the apparatus  10 . During the purge cycle, proper air flow through the ducts  38 ,  42 ,  64  and  68  may also be confirmed. At the end of the purge cycle, the burner  32  is activated to establish a pilot flame. After the pilot flame is confirmed as being stable, such as by viewing the pilot flame through a looking glass, the burner  32  establishes a process capable flame so as to heat fluid, such as air, in the burner chamber  22 . 
     Next, a process temperature is selected using the control system  73 . Operation of the apparatus  10  is then continued so as to achieve the process temperature at least momentarily in the processing chamber  26 . Next, referring to FIG. 1, the supply damper  40  is moved to the closed position, the bypass damper  43  is moved to the open position and the return damper  66  is moved to the closed position, so as to route heated air through the fluid bypass subsystem  41 . The laminate assembly  12  may then be positioned between the second and third flow regulating devices  52  and  54 , respectively, and within the processing chamber housing  44  such that a first section  74  of the laminate assembly  12  is disposed further away from the outlet  39  than a second section  76  of the laminate assembly  12 . 
     The formable layer  14  of the laminate assembly  12  may be any permeable material that is thermoformable when sufficiently heated. Such materials include thermoformable rigid urethane (TRU) and polyethylene terephthalate (PET), with fibrous, non-woven PET being the preferred material for headliner applications. The adhesive layer  16  may comprise any permeable thermosetting or thermoplastic adhesive. The cover member  18  preferably comprises non-woven PET for headliner applications, but it may comprise any suitable permeable cover material such as cloth or carpet. Alternatively, the cover member  18  and/or the adhesive layer  16  may be eliminated if not required for a particular application. Furthermore, multiple formable layers  14  and/or adhesive layers  16  may be utilized depending on the application. 
     Next, referring to FIG. 2, the supply damper  40  is moved to the open position, the bypass damper  43  is moved to the closed position and the return damper  66  is moved to the open position, so as to route heated air through the supply duct  38 . The heated air then passes from the outlet  39  through the inlet  46  of the processing chamber housing  44 . At the inlet  46 , the heated air may have a temperature in the range of, for example, 240 to 260° C. Next, the heated air passes through the first flow regulating device  50 . 
     Still referring to FIG. 2, a first portion of air traveling along a first flow line  78 , from the outlet  39  to the first opening  58 , must travel further than a second portion of air traveling along a second flow line  80 , from the outlet  39  to the second opening  60 . As a result, the first portion of air will likely be cooler than the second portion of air at the first flow regulating device  50 . For example, the first portion of air may have an average first temperature in the range of about  180  to 190° C., while the second portion of air may have an average second temperature in the range of about 200 to 210° C. It is to be understood that average temperatures may vary depending on such factors as desired process temperature, size of processing chamber  26 , and relative positions of the outlet  39  and the first flow regulating device  50 . 
     Advantageously, because of the relative sizes of the first and second openings  58  and  60 , respectively, the first flow regulating device  50  provides minimum flow resistance to the first portion of air, while providing somewhat greater flow resistance to the second portion of air. Consequently, after passing through the first flow regulating device  50 , the average velocity of the first portion of air is preferably greater than the average velocity of the second portion of air. For example, the first portion of air may have an average first velocity in the range of 0.28 to 0.30 meters per second, while the second portion of air may have an average second velocity in the range of 0.24 to 0.26 meters per second. Alternatively, the first flow regulating device  50 , as well as other components of the apparatus  10 , may be configured to achieve any suitable flow velocities. 
     The first flow regulating device  50  is also preferably configured to regulate flow of additional portions of air that pass through the additional openings  62 , such that additional portions of air that pass through additional openings  62  disposed progressively further away from the second opening  60  will have progressively greater average velocities than the second portion of air. Furthermore, the first flow regulating device  50  is preferably provided with a sufficient number of additional openings  62  such that changes in velocity may occur gradually along a transverse plane downstream of the first flow regulating device  50 . Moreover, additional portions of air that pass through adjacent additional openings  62  may have the same average velocity downstream of the first flow regulating device  50 . 
     Next, the heated air passes through the second flow regulating device  52 , which homogenizes each portion of the heated air so as to reduce temperature and velocity variations within each portion of air. The second flow regulating device  52  also induces mixing of adjacent portions of air such that changes in temperature and velocity may occur gradually along a transverse plane downstream of the second flow regulating device  52 . The heated air is then drawn through the laminate assembly  12  so as to heat the laminate assembly  12 . The third and fourth flow regulating devices  54  and  56 , respectively, preferably maintain the homogeneity of each portion of the heated air as the heated air exits the laminate assembly  12 , in order to ensure optimum air flow through the entire laminate assembly  12 . 
     Advantageously, the method and apparatus  10  of the invention enable uniform energy flux to be transferred from the heated air, or other heated fluid, to the laminate assembly  12 . More specifically, the flow regulating devices  50 - 56  are configured to regulate flow velocity, as described above, so that the first and second portions of air may respectively transfer substantially the same energy flux to the first and second sections  74  and  76 , respectively, of the laminate assembly  12 . Similarly, the flow regulating devices  50 - 56  are configured to regulate flow velocity such that the additional portions of air traveling between the first and second portions of air may each transfer substantially the same energy flux to a particular additional section of the laminate assembly  12 . As a result, substantially uniform energy flux may be transferred from the air to the laminate assembly  12 . 
     Furthermore, each portion of air, including each additional portion of air, preferably delivers substantially uniform energy flux to a particular section of the laminate assembly  12  during initial or transient flow conditions, as well as during later steady state flow conditions. As a result, the laminate assembly  12  may be efficiently and effectively heated without necessarily requiring steady state flow conditions to be reached. Thus, heating cycle times can be reduced. Alternatively, heating of the laminate assembly  12  may continue during steady state flow conditions. 
     Once sufficiently heated, the laminate assembly  12  may then be thermoformed in any suitable manner. For example, the laminate assembly  12  may be positioned between two or more mold sections, and the mold sections may be forced together so as to form a part, such as a headliner, floor carpet system, or package tray for a motor vehicle. 
     Under the method of the invention, a relatively large piece of material, such as a piece of material to be used as a headliner for a motor vehicle, may be efficiently and effectively heated to a substantially uniform temperature. Furthermore, because the method involves selectively regulating velocity of the heated air or other heated fluid, the method may be practiced using a single heated fluid source and without requiring expensive manifold arrangements to distribute fluid over large areas. However, such manifold arrangements may be used if desired. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.