Patent Publication Number: US-2002000050-A1

Title: Apparatus for and process of drying articles

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001] This application claims the priority of German Patent Application Serial No. 100 08 750.7, filed Feb. 24, 2000, the subject matter of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002] The present invention relates, in general, to an apparatus for and process of drying articles.  
       [0003] It is known to transport articles, e.g. pieces of furniture coated with varnish, lacquer or paint or bricks, painted sheets etc., by means of a conveyor belt through a tunnel, in which drying air is circulated. Once moved through the tunnel, the articles can be used for further processing at the other end of the tunnel. As relatively high transport speeds are increasingly demanded, the drying times in the tunnel dryer become either short, or the tunnel dryer has to be desired sufficiently long to provide suitable drying times, which means that the overall costs become prohibitively high.  
       [0004] German Pat. No. DE 36 32 740 describes a dryer for the treatment of articles coated with e.g. varnish, lacquer, paint, etc, which includes in the drying chamber a transport system of the paternoster type. The transport system includes several tray-like carriers for support of the articles. The carriers are moved by a chain incrementally upwards, to the side and subsequently downwards. In the lower region, the carriers are moved laterally back again so that each carrier moves through a drying cycle. This conventional dryer suffers shortcomings because drying air flows between individual carriers so that a desired temperature distribution of the circulating drying air cannot be established. Rather heat accumulates in the upper region of the drying chamber so that depending on the maximum temperature a certain temperature profile is formed across the height of the drying chamber. However, oftentimes there is a need for drying in the lower region of the drying chamber at a lower temperature in order to effect a drying action through the entire article and thus to prevent a mere surface drying. Only afterwards is it desired to apply a high temperature for realizing a drying action so as to effect a hardening. This conventional dryer is unsuitable to implement a temperature control in this manner. Another problem is wear of the employed chain guides of the paternoster mechanism and a resultant need for regular maintenance work that requires a shutdown of the entire apparatus. This is cumbersome and expensive as far as overall operating costs are concerned.  
       [0005] It would therefore be desirable and advantageous to provide an improved process and apparatus, obviating prior art shortcomings and effective to realize long retention times of the articles in the drying chamber while yet allowing a transport of the articles in a simple manner, without requiring significant maintenance work.  
       SUMMARY OF THE INVENTION  
       [0006] According to one aspect, the present invention provides for a drying process including a drying chamber in which drying air is circulated and in which the articles to be dried are fed onto a first carrier element which is then moved step-by-step in a vertical direction, while a second carrier element with an article to be dried is stacked directly underneath or above the first carrier element, and the stack of carrier elements is then moved stepwise in a vertical direction.  
       [0007] By stacking the carrier elements through either positioning a carrier element upon or underneath a carrier element of a stack of carrier elements and moving the stack incrementally in vertical direction, the need for mechanical conveyors such as chains, belts or other transport devices that require regular maintenance works, is eliminated. The carrier elements can easily be stacked, thereby reducing the complexity of the transport mechanism. Further, as a consequence of a stacked arrangement of the carrier elements, there is no spacing between the carrier elements for escape of warm drying air so that the apparatus operates energy-efficient and allows a desired temperature profile in the drying chamber.  
       [0008] In accordance with a preferred embodiment of the present invention, the second carrier element is moved underneath the first carrier element and the stack of carrier elements is elevated by a lifting device. Such a stack configuration in the drying chamber allows supply of articles to be dried in the lower zone and a subsequent movement of the carrier elements upwards so that the lower zone of the stack can be utilized as pre-heating phase with a temperature that is cooler than in the upper zone. To ensure a uniform height of the stack of carrier elements, an uppermost carrier element of the stack is removed to the side each time the stack is elevated. Suitably, the uppermost carrier element is deposited on a neighboring second stack of carrier elements so that the carrier elements advance through a drying cycle.  
       [0009] To implement such a drying cycle of the carrier elements while yet using minimum transport elements, the lifting device can be so configured to move a lowermost carrier element from the neighboring second stack underneath the first stack, with dry articles being removed from this carrier element and new articles to be dried being fed. Subsequently, the carrier element is stacked again underneath the lowermost carrier element of the first stack. The lifting device can thereby effectively be used to move and rearrange carrier elements between the neighboring stacks.  
       [0010] According to another aspect of the present invention, a drying apparatus includes a drying chamber, an aerating mechanism for circulating warm drying air in the drying chamber, a stack of superimposed carrier elements accommodated in the drying chamber and adapted for receiving articles to be dried, a lifting device for moving the stack of carrier elements in a vertical direction, and a transport device configured for feeding articles to be dried to the carrier elements and receiving dried articles from the carrier elements.  
       [0011] When stacking the carrier elements with the articles to be dried in the drying chamber and moving the stack of carrier elements by the lifting device in a vertical direction, the use of circulating transport chains or similar power-transmitting devices can be eliminated. As a result, maintenance works are reduced to a minimum, and the aeration of the articles with a desired temperature profile can be enhanced in view of the stacked superimposed arrangement of the carrier elements that leaves at most only small openings between the carrier elements.  
       [0012] According to another feature of the present invention, the stack of carrier elements is secured in position by a catch mechanism. An example of such a catch mechanism includes catches that engage in complementary recesses or other latching configurations of the carrier elements. As the stack of carrier elements may have a fairly substantial weight, the catch mechanism is so configured to engage the stack of carrier elements at least at four locations to better distribute the weight force. The catches may be moveable linearly towards and away from the carrier elements, or each catch may include a swing mechanism.  
       [0013] According to another feature of the present invention, each of the carrier elements has sidewalls in parallel relationship to a feed direction of articles to be dried, with the carrier elements stacked directly on the sidewalls. In this manner, a sealed conduction of the drying air is realized in parallel relationship to the sidewalls so that a targeted air stream can migrate into the hollow space between two carrier elements. As a result, the temperature profile in the stack can be accurately controlled. It is possible, to subdivide the stack of carrier elements in aeration zones with different temperature.  
       [0014] According to another feature of the present invention, a second stack of carrier elements is accommodated in the drying chamber in neighboring relationship to the first stack of carrier elements, whereby the single carrier elements move through a drying cycle through the drying chamber. In this way, the articles can be retained in the drying chamber over a long period while at the same time the demand for space is minimized. Suitably, the drying chamber may include in an upper area of the first and second stack of carrier elements a gantry for transferring an uppermost carrier element from one stack onto an uppermost carrier element of the other stack of carrier elements.  
       [0015] According to another feature of the present invention, a lowermost carrier element of one stack can be transferred to a position underneath a lowermost carrier element of the other stack through synchronized operation of the lifting device and the catch mechanism. Thus, the individual carrier elements can be moved in increments, without any need for complicated conveying devices.  
       [0016] Suitably, the sidewalls of the carrier elements are heat-insulated.  
       [0017] According to another feature of the present invention, each of the carrier elements has centering elements on one side and pockets on an opposite side to allow engagement to a superimposed one of the carrier elements and attachment of an subjacent one of the carrier elements. In this way, great stacking heights without additional guide elements can be realized. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0018] Other features and advantages of the present invention will be more readily apparent upon reading the following description of preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
     [0019]FIG. 1 is a schematic sectional side view of a first embodiment of a drying apparatus according to the present invention;  
     [0020]FIG. 2 is a front view of the drying apparatus of FIG. 1;  
     [0021]FIG. 3 is a top view of the drying apparatus of FIG. 1;  
     [0022]FIG. 4 is a detailed illustration of a carrier element for use in the drying apparatus of FIG. 1;  
     [0023]FIG. 5 is a sectional side view of the carrier element of FIG. 4;  
     [0024]FIG. 6 is a cutaway view, on an enlarged scale, of one variation of a catching mechanism for latching onto a carrier element;  
     [0025]FIG. 7 is a cutaway view, on an enlarged scale, of another variation of a catching mechanism for latching onto a carrier element;  
     [0026]FIG. 8A is a schematic side view of a second embodiment of a drying apparatus according to the present invention;  
     [0027]FIG. 8B is a top view of the drying apparatus of FIG. 8A; and  
     [0028]FIG. 9 is a schematic side view of a third embodiment of a drying apparatus according to the present invention.  
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     [0029] Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals.  
     [0030] Turning now to the drawing, and in particular to FIG. 1, there is shown a schematic sectional side view of a first embodiment of a drying apparatus according to the present invention, generally designated by reference numeral  1 . The drying apparatus  1  includes a drying chamber  1   a  which accommodates a first stack  26  of a plurality of superimposed carrier elements  5  and a second stack  27  of a plurality of superimposed carrier elements  5  in side-by-side disposition, as shown in FIG. 2. Disposed anteriorly of the drying chamber  1   a  is a feed unit in the form of a transport band  2  for supply of articles  3  to be dried. On the opposite side of the drying chamber  1   a  is a transport unit  4  for moving dried articles  3  away to a subsequent, not shown, processing station.  
     [0031] Positioned upon the bottom of the drying chamber  1   a  is a lifting device in the form of a lifting platform  6  which can be adjusted in a vertical direction, indicated by double arrow  60 , by a pantographic linkage  7 . The lifting platform  6  is supported on rollers  28  which are guided in rails  29  so as to allow a travel of the lifting platform  6  in a direction of double arrow  70  between the stacks  26 ,  27 . Thence, the lifting platform  6  can be positioned underneath each of the stacks  26 ,  27  to lift or lower the entire stacks, respectively, as will be described furtherbelow.  
     [0032] As shown in FIG. 4, each carrier element  5  includes a conveyor belt  33  which should be made of a material that is capable to withstand temperatures of preferably up to 200° C. Suitably materials for the conveyor belt  33  include textile material, plastic, sheet metal or a link chain. The conveyor belt  33  is trained about a belt-reversing roller  34  and a spring-mounted tension roller  35  spaced from one another in a direction transversely to a transport direction of the articles  3 , indicated by arrow  90 . The belt-reversing roller  34  is driven via a gear  43  by a, not shown, drive mechanism and rotatably supported in parallel sidewalls  31  which are sized to extend beyond the conveyor belt  33 , as shown in FIG. 5. The tension roller  35  is also rotatably supported by the sidewalls  31 . Disposed underneath the conveyor belt  33  is a table-like backing  37  which has a sliding surface to support the conveyor belt  33  and thereby prevent a sagging thereof. Additional support rollers  36  are provided in a central location below the conveyor belt  33 .  
     [0033] Each of the stacks  26 ,  27  is held in place in the drying chamber  1   a  by a separate catch mechanism which includes at least four catches  8  configured for latching onto the carrier element  5  that is in lowermost position at a given time. As shown in FIG. 6, each sidewall  31  of the carrier elements  5  is connected integrally with a bottom  42 , with a recess  5   a  formed at a junction between the sidewall  31  and the bottom  42  for engagement of a one of the catches  8 . Of course, the number of recesses  5   a  of each carrier element  5  corresponds to the number of catches  8 , i.e. in the nonlimiting example of FIG. 1 four catches  8  engage in four recesses  5   a . The catches  8  are each swingably mounted for rotation about a pivot axis  38  so that the catches  8  can disengage from the respective carrier element when the stack of carrier elements is slightly elevated by the lifting platform  6 . As an alternative, the catches may also be configured for linear movement to the outside.  
     [0034] The vertical extension of the sidewalls  31  is so sized that the space between the bottom  42  of the carrier elements  5  and the conveyor belt  33  of the subjacent carrier element  5  is sufficient for receiving articles  3  to be dried. As shown in FIG. 5, each carrier element  5  has conical centering pins  32 , which project out from the sidewalls  31 , and pockets  39  are formed in the bottom  42 . Thus, through engagement of the centering pins  32  of one carrier element  5  in pockets  39  of a superimposed carrier element  5 , an exact positioning of the carrier elements  5  in superimposed disposition can be realized.  
     [0035] Disposed in the upper region of the drying chamber  1  is a gantry  10  which is mounted to and movable along a guide rail  11  by rollers  22 . The gantry  10  includes four grippers  9  by which an uppermost one of the carrier elements  5  of the first stack  26  can be lifted and moved sideways, as another carrier element  5  is moved by the lifting unit  6  underneath a lowermost carrier element  5  of the stack  26 . In the nonlimiting example of FIG. 1 with two stacks  26 ,  27 , the grippers  9  move an uppermost one of the carrier elements  5  of the first stack  26  sideways to deposit this carrier element  5  atop the uppermost one of the carrier elements  5  of the stack  27 , as indicated in FIG. 2 by dashdot line, while the lifting platform  6  moves sideways underneath the stack  26  to transfer the lowermost carrier element  5  to a position underneath the stack  26 .  
     [0036] Persons skilled in the art will understand that the provision of four grippers  9  is done by way of example only, as the arrangement of more than four grippers is certainly conceivable and covered within the scope of the present invention.  
     [0037] The drying chamber  1   a  is aerated by a first fan  12  in the upper zone of the stack  26  and by a second fan  14  in the lower zone of the stack  26 . The fans  12 ,  14  are each equipped with a, not shown, filter and a, not shown, heater, e.g., heat exchanger or heating coil so that pure air can be used for drying the articles  3 . A subdivision of the stack  26  into drying zones with different temperature can be implemented through provision of a baffle  13  positioned downstream of and interacting with the fan  12  and a baffle  15  positioned downstream of and interacting with the fan  14  so that the airstream through the hollows between the carrier elements  5  can be accurately controlled as a function of the temperature, the volume stream and the flow speed. Disposed on the opposite side of the drying chamber  1   a  is an upper aeration chamber  16  and a lower aeration chamber  18  which connect, respectively, in vent channels  19 ,  20  that terminate in a chimney  21 .  
     [0038] Aeration of the second stack  27  is executed in a similar manner with an upper fan  24  and a lower fan  25  (FIG. 5) and a chimney  41  arranged on the opposite side (FIG. 3). The stacks  26 ,  27  are separated from one another by a partition  40  to thereby provide a total of four aeration zones in which a predetermined temperature can be set. Of course, the size and number of the aeration zones as well as the aeration parameter can be selected in any suitable manner and suited to the situation at hand, e.g. size of the drying chamber.  
     [0039] As an alternative to the aeration system shown in FIGS.  1  to  3 , it is also possible to aerate the carrier elements  5  with the articles  3  to be dried through an energy-efficient counterflow process whereby hot air is introduced in an upper region of the stack  26  and conducted through the hollows between the upper carrier elements  5  and subsequently guided through a baffle to a subjacent region. The drying air cools down hereby so that less heat is provided in the lower region of the stack  26 . The cooled air is subsequently conveyed via a chimney to the outside. Aeration of the second stack  27  can be carried out in a same direction as the movement of the carrier elements  5  so that higher temperatures are provided in the upper area, whereas the stack  27  is cooled in the lower region. Thus, the carrier elements  5  are not exposed to excessive heat when receiving new articles  3  to be dried.  
     [0040] The operation of the drying apparatus is as follows: The lowermost carrier element  5  of the stack  27 , carrying dried articles  3 , is lifted by the lifting platform  6  to allow disengagement of the catches  8  which swing outwards. The stack  27  can now be lowered by a distance corresponding to the height of a carrier element  5 . The catches  8  are then returned into engagement with the carrier element  5  immediately above the lowermost carrier element  5  to thereby securely hold the stack  27  in place. The lowermost carrier element  5  rests on the lifting platform  6  which moves sideways underneath the stack  26 . The dried articles  5  are withdrawn from the carrier element  5  via the conveyor belt of the transport unit  4 , and new articles  5  are supplied from conveyor belt  2  of the transport unit  2  onto the now empty carrier element  5 . Of course, the conveyor belt  33  is in alignment with the conveyor belts of the transport units  2 ,  4 . The lifting platform  6  underneath the stack  26  moves upwards to slightly elevate the stack  26  and thereby allow disengagement of the catches  8  from the previously lowermost carrier element  5  of the stack  26 . The catches  8  are moved outwards, and the lifting platform  6  moves further upwards by a carrier element  5 . The catches  8  move again into engagement with the now lowermost carrier element  5  to hold the stack  26  in place. The movement of the lifting platform  6  is synchronized with a movement of the gantry  10 . Thus, as the lifting platform  6  raises the stack  26 , the uppermost carrier element of the stack  26  is moved sideways and placed on top of the uppermost carrier element  5  of the stack  27 . Thus, the carrier elements  5  move incrementally or step-by-step through the drying chamber  1   a  in a drying cycle to implement a sufficient drying action.  
     [0041] The conveyor belt  33  of the carrier elements  5  is so operated as to run only when the carrier element  5  occupies the lowermost position in the stack  26 , at which point the conveyor belt  33  is in alignment with the conveyor belts of the transport units  2 ,  4 . After the catches  8  of the stack  26  engage again the lowermost carrier element in stack  26 , the lifting platform  6  is lowered and returned to a position underneath the stack  27  and the gantry  10  is returned to a position above the uppermost carrier element  5  of the stack to repeat the cycle.  
     [0042] Although the preceding description of the drying apparatus is directed to a configuration with two stacks  26 ,  27 , the concept of the present invention as outlined here is also applicable when using only a single stack of carrier elements  5  whereby an uppermost carrier element  5  is moved away by the grippers  9  of the gantry  10  and another carrier element  5  on the lifting platform  6 , after loaded with new articles to be dried, is attached to the previously lowermost carrier element  5 .  
     [0043] Turning now to FIG. 7, there is shown a variation of a catch mechanism for interaction with a modified configuration of the sidewall  31  of the carrier elements  5 . The sidewall  31  of each carrier element  5  has a C-shaped configuration and defines an upper arm  48 , and the catch mechanism has a catch  80  which is configured to engage below the arm  48  and swingably mounted in a frame  47  for rotation about a pivot axis  46 . A downward deflection of the catch  80  is restricted by a stop  45  mounted interiorly of the frame  47 . At operation, when a stack of carrier elements  5 , e.g. stack  26 , is lowered, the upper arm  48  of the lowermost carrier element  5  impacts upon the catch  80  which, in turn, impacts upon the stop  45 . Suitably, a, not shown, spring may pre-load the catch  80  in clockwise direction to ensure that the catch  80  is biased in a direction of engagement.  
     [0044] Although not shown in the drawing, a plurality of such catches  80  may be provided along the sidewall  31  to evenly distribute the load. The catches  80  operate as a ratchet mechanism that allows a movement of the stack upwards while preventing a downward movement of the stack.  
     [0045] When using two stacks  26 ,  27  for the drying apparatus, the other stack, e.g. stack  27 , the catch mechanism may be configured in such a manner that the catches  80  are disengaged from a carrier element long enough to allow lowering of the stack  27  by a carrier element  5 . As an alternative, the catch mechanism may also have a controller for controlling the movement of the catches  80 .  
     [0046] To realize an energy-efficient configuration, the sidewalls  31  may be lined with an insulation.  
     [0047] In the foregoing embodiments of a drying apparatus according to the present invention, the use of a catch mechanism has been described for holding the stacks  26 ,  27  in position. Persons skilled in the art will understand that other mechanisms may be possible without departing from the spirit of the present invention. Also, the lifting platform  6  may certainly be replaced by a hydraulic mechanism, positioned under each of the stacks  26 ,  27  to upwardly move the carrier elements  5 . The lateral transfer may also be provided by an additional transport mechanism.  
     [0048] In FIG. 1, the transport unit  2 ,  4  are shown in linear alignment. It is, however, also possible to arrange the transport unit  4  next to the stack  27  to commence the further transport from this stack  27 , so that the transport unit  4  may then be arranged at the same side as the transport unit  2 . Moreover, the transport units  2 ,  4  may be arranged in superimposed disposition in a common frame.  
     [0049] Persons skilled in the art will also understand that the unloading position and loading position of a carrier element  5  may be implemented practically at any location upon the stacks  26 ,  27 . For example, when loading the stack  26  from below, the dry articles  3  can be withdrawn from the respective carrier element  5  from below or any location thereabove. The direction of movement of the carrier elements  5  may also be reversed, for example, when requiring only short drying times.  
     [0050] Turning now to FIGS. 8A and 8B, there are shown a second embodiment of a drying apparatus according to the present invention. Parts corresponding with those in FIG. 1 are denoted by identical reference numerals and not explained again. In this embodiment, the carrier elements  5  are devoid of a separate transport unit as the transport of the articles  3  is implemented within the drying chamber  1   a  via a belt conveyor  50  which projects through slots in the carrier element  5  that is in the lowermost position at any given time. The articles  3  to be dried are conveyed initially by the transport unit  2  into the drying chamber  1   a  and transferred onto the belt conveyor  50  which projects through the carrier element at the lowermost position of the stack  26 . Subsequently, the entire stack  26  is elevated by a vertically adjustable lifting device  52  about the height of a carrier element  5 . At the same time the belt conveyor  50  is lowered and the lowermost carrier element  5  of neighboring stack  27  is transferred from a conveyor belt  51  below the stack  27  (FIG. 3) onto the belt conveyor  50  for pickup of new articles to be dried, while the uppermost carrier element on stack  26  is transferred onto the stack  27 , e.g., by the grippers of the gantry  10  in the transport direction of the articles  3 . Thus, the required width of the drying apparatus is significantly reduced. Although not shown in the drawing, the slots of the carrier elements  5  may be closed by, e.g., sheets, once the carrier elements  5  have left the belt conveyors  50 ,  51  to thereby enhance the control of the air circulation. The carrier elements  5  in the stack  27  are moved downwards by the lifting device  62 , after the lifting device has moved underneath the stack  27 , until reaching the belt conveyor  51  for transfer of dried articles  3  to the transport unit  4 .  
     [0051] Turning now to FIG. 9, there is shown a third embodiment of a drying apparatus according to the present invention. In this embodiment, provision is made for the arrangement of receiving elements  55  located upstream of the drying chamber  1   a  between the transport unit  2  and the articles  3  to be dried. Subsequently, the articles  3  are moved together with the receiving element  55  to a carrier element  5  for movement with the stacks  26 ,  27  in the drying cycle. A lower lifting device in the form of a lift truck  56  is hereby used for travel underneath between the stacks  26 ,  27  and respective lifting of the stacks  26 ,  27  in a manner as described above and in conjunction with the upper gantry  10 , not shown here. The receiving elements  55  may be provided as flexible band with a rod  57  at the leading end and the trailing end for movement of the receiving elements  55 . For example, the receiving element  55  may be transported to a carrier element  5  by a hydraulic mechanism, acting on the leading rod. After leaving the drying cycle, the receiving elements  55  are returned by, not shown, conveyors to the transport unit  2 , so as to advance in a loop, as schematically indicated in FIG. 9 by the arrows.  
     [0052] While the invention has been illustrated and described as embodied in an apparatus for and process of drying articles, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
     [0053] What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims: