Abstract:
A vacuum drying apparatus and method to dry and cure paint is disclosed. The method provides a substantially particle free environment that shortens drying time, reduces cost and improves surface finish. The apparatus includes an enclosed drying tunnel that is maintained at a reduced pressure relative to ambient conditions. Heat lamps with the drying tunnel aid in curing and provide the desired particle free environment.

Description:
REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 10/755,571 filed on Jan. 12, 2004 now U.S. Pat. No. 7,658,017. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to the field of painting and more specifically to a method and device for drying and curing paint. 
     Automobile assembly plants use a clean room atmosphere for drying and curing paint applied to automotive components. Such clean room environments entail high maintenance and operational costs. Further, such clean room drying processes still produces defects in the paint that require costly repairs in order to provide an acceptable level of quality. 
     Accordingly, it is desirable to develop an improved method and device for effectively drying and curing a coating applied to an article. 
     BRIEF SUMMARY OF THE INVENTION 
     An example method and device according to this invention includes an enclosure maintained at a desired vacuum pressure for curing an applied coating such as paint. 
     The example method consists of drying a coating applied to a painted article, utilizing the steps of placing the painted article in an enclosure, controlling a first pressure within the enclosure such that the first pressure within the enclosure is lower than a second pressure outside the enclosure, and maintaining the first pressure within the enclosure to provide a desired condition of the coating applied to the painted article. 
     An example device according to this invention includes an enclosure with an inlet airlock and an outlet airlock. A painted article enters the inlet airlock and is sealed from an external environment. A vacuum is then generated within the inlet airlock that is equal to a vacuum pressure within the enclosure. Once the inlet airlock and the enclosure are of the same pressure, the painted article enters the enclosure and remains within the enclosure for a desired duration until the applied coating is cured as desired. The painted article is then removed through the outlet airlock back to ambient conditions. 
     The vacuum pressure within the enclosure removes undesirable particles and dust while also providing an environment that speeds the curing of the paint on the painted article. 
     Accordingly, the method and device according to this invention provides substantial improvements in paint quality and process efficiency. 
     Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention. 
         FIG. 1  is a schematic diagram illustrating the operation of a portion of the invention. 
         FIG. 2  is a schematic diagram illustrating the operation of a portion of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Detailed descriptions of an example embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually an appropriately detailed system, structure or manner. 
     As shown in enclosed  FIG. 1 , an example vacuum paint drying apparatus  10  comprises a vacuum chamber  12  having an entry air lock  14 , a drying tunnel  16  and an exit air lock  18 . Radiant heat sources in the form of infrared or ultraviolet heat lamps  20  are arranged within the air locks  14  and  18 , as well as along the drying tunnel  16 . The air locks and drying tunnel  16  each have respective conveyors  22 ,  24  and  26  that transport items, such as automobile bodies  28 , through the apparatus. Air locks  14  and  18  each include a high capacity vacuum pump  30  and  32 , respectively, for rapidly pumping the air locks  14 ,  18  to a desired atmospheric pressure. The drying tunnel  16  includes a set of vacuum pumps  38  for maintaining a desired vacuum pressure within the drying tunnel  16 . 
     In operation, the drying tunnel  16  is maintained below atmospheric pressure by vacuum pump sets schematically shown at  38  and the air locks  14  and  18  that isolate and seal the drying tunnel  16  from the ambient surrounding environment. The entry air lock  14  is initially at atmospheric pressure and open to the ambient surrounding environment. A freshly painted automobile body  28  enters the entry air lock  14  on conveyor  22 , the air lock  14  is sealed from the ambient surrounding environment, the lamp  20  is turned on and the air lock  14  is pumped down to a desired pressure by the vacuum pump  30 . 
     When the desired pressure in the entry air lock  14  is equal to the pressure in the drying tunnel  16 , the air lock  14  is opened to the drying tunnel  16  and the automobile or other painted article is transferred from the conveyor  22  to the conveyor  24 . Conveyor  24  moves the automobile body  28  through the drying tunnel  16 , exposing the automobile body  28  to lamps  20  in a vacuum to dry and cure the paint. 
     When the automobile body  28  reaches the end of the drying tunnel  16 , the exit air lock  18  is sealed from the ambient surrounding environment and pumped down using vacuum pump  32  to a pressure equal to the pressure within the drying tunnel  16 . The exit lock  18  is opened to the drying tunnel  16  and the body  28  is transferred to the exit conveyor  26 . The exit air lock  18  is then sealed from the drying tunnel  16  and vented to atmosphere through vent valve  36 . When the pressure is equal to the ambient surrounding environment, the exit air lock  18  is opened to the ambient and the automobile body  28 , painted and dried, is discharged from the vacuum drying apparatus  10 . While the automobile body  28  is traversing the drying tunnel  16 , the entry air lock  14  is isolated from the drying tunnel  16  and vented to atmosphere through vent valve  34 . Once the pressure within the entry air lock  14  is equal to atmospheric, the entry air lock  14  is opened to the ambient to admit another automobile body  28 . The process described above is then repeated, and the automobile bodies  28  are vacuum and heat dried in a continuous process. Note that drying takes place in both the entry air lock  14  and within the drying tunnel  16 . 
       FIG. 2  shows another vacuum drying assembly  40  utilized in a batch mode drying operation. The vacuum drying assembly  40  includes a vacuum chamber  42  with doors  44  and  46  on either end. A conveyor  48  moves items such as automobile bodies  28 , or other painted articles into and out of the chamber  42 . The chamber  42  has radiant heat sources  20 , a high capacity vacuum pump  50  and vent valve  52 . 
     In operation, the chamber  42  is initially at atmospheric pressure with the door  44  opened to admit a freshly painted automobile body  28 . The door  44  is then closed and the chamber  42  is pumped down by vacuum pump  50 . The radiant heat sources  20  are turned on and the paint is dried to a desired level upon exposure to the heat and vacuum. When the drying is complete to the desired level, the chamber  42  is vented to atmosphere through vent valve  52 . When the pressure within the chamber  42  is equal to atmospheric pressure, the door  46  is opened and the painted and dried automobile body  28  is removed from the chamber via conveyor  48 . 
     This method and apparatus for drying and curing painted articles such as automobile bodies, is substantially cleaner as the disclosed inventive method provides an atmosphere substantially dust and particle free. Maintenance of the drying tunnel  16  and the air locks  14  and  18  is substantially less than that of a clean room type paint chamber. Further, the cycle time for curing painted articles within the drying chamber  16  is substantially shorter than current paint drying processes utilizing clean room drying tunnels, and therefore provides a faster drying time. Additionally, the disclosed inventive process provides an improved surface finish that results from the substantially particle free drying environment. Further, it should be understood that although paint is described in the disclosed example embodiment other coatings, such as primers, rust inhibitors, clear coats, and other substances applied to articles will benefit from the novel aspects of the disclosed inventive method and device. 
     While the invention has been described in connection with a preferred embodiment, it is not intended to limit the scope of the invention to the particular form set forth, but on the contrary, it is intended to cover such alternatives, modification, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.