Abstract:
A paint circulation system ( 10 ) for automotive coating applications presents a paint supply source ( 18 ) and a pump ( 20 ) for pumping the paint. A circulation line ( 16 ) is fluidly communicated with the paint supply source ( 18 ) and circulates the paint at an operational pressure. A relief line ( 28 ) has a pressure relief device ( 30 ) adaptable for withstanding a predetermined pressure of the paint and to circulate the paint through the relief line ( 28 ) as the operational pressure exceeds the predetermined flow pressure. A pressure control mechanism is operatively communicated with the circulation line ( 16 ) and the relief line ( 28 ). The pressure control mechanism senses the operational pressure to continuously circulate the paint in the relief line ( 28 ) in response to a difference between the operational pressure and the predetermined pressure before the operational pressure exceeds the predetermined pressure thereby preventing the pressure relief device ( 30 ) from actuating.

Description:
RELATED APPLICATION  
       [0001]     This application claims priority to and all the benefits of U.S. Provisional Patent Application Ser. No. 60/533,660 filed on Dec. 31, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to paint circulation systems used in automotive industry, and in particular, to a pressure control device for a paint circulation system.  
       BACKGROUND OF THE INVENTION  
       [0003]     A production paint application process where paint is applied to a substrate, such as, for example a vehicle body moving through a paint booth, requires paint to be transferred from a paint reservoir to a paint applicator disposed in the paint booth. Due to the complex nature of most paint application facilities, wherein the paint booth is located, the reservoir is located a substantial distance from the paint applicator that atomizes and applies paint to the substrate of each vehicle body.  
         [0004]     The layers of paint applied to each vehicle body generally include a spray primer surfacer, a spray base coat, and a clear coat. Each of these paints, and in particular, the spray primer surfacer and the base coat are necessarily maintained in continuous circulation to prevent the solids suspended in these paints from settling, which is known to cause paint defects that are visible in the painted products. Furthermore, colored primer surfaces and base coats generally include high percentages of pigment which are known to settle when these paints are not maintained in continuous circulation.  
         [0005]     To transfer these paints from the paint reservoir to each paint applicator, the circulation system is installed in each paint facility, which may stretch across an expanse of hundreds of meters. These paint circulation systems include paint lines through which the paint is continuously circulated between the paint reservoir and a color changer, located just prior to each applicator, by a circulation pump. The paint lines generally include several valves intended to stop circulation through the paint line for maintenance operations. For example, most paint circulation systems include a bag filter that must be periodically replaced. To remove a typical bag filter, valves are located both upstream and downstream of the filter, each of which is closed during a filter change operation. This prevents paint from spilling during the filter change operation which would require hazardous waste cleanup.  
         [0006]     It is necessary to terminate operation of the circulation pump prior to closing a valve downstream of the pump to prevent damaging of the pump or seals which prevent paint from leaking from the paint circulation system. For example, if the paint is prevented from circulating while the pump continues to operate pressure will build up in the paint line causing damage to various seals both inside and external to the pump, which again could cause paint to spill requiring a hazardous waste cleanup. To prevent this type of damage from occurring, a rupture disc type pressure relief is generally installed in a bypass loop of the paint circulation system, which is triggered at a predetermined pressure not when paint is prevented from circulating due to, for example, a closed valve. Once the rupture disc has ruptured, it must be replaced prior to reactivating the paint circulation pump and reinitiating production through the paint facility. This is known to be a laborious and slow process which results in significant amounts of lost production through the paint application facility.  
         [0007]     Therefore, it would be desirable to provide a secondary relief to the paint circulation system that is triggered upon a predetermined pressure buildup within the paint circulation system thereby preventing the rupture disc from rupturing.  
       SUMMARY OF THE INVENTION  
       [0008]     A closed loop paint circulation system provides continuously circulating paint between a paint reservoir and a paint applicator for use in a production paint facility. A circulation line fluidly communicates the paint at a desired operational pressure between the paint reservoir and the paint applicator. A relief line is cooperably seperable from the circulation line by a relief device that opens for reducing the operational pressure of the paint circulating through the circulation line when the operational pressure increases beyond a predetermined value. A secondary pressure relief device is cooperable with the first pressure relief device where the second pressure relief device actuates in response to a difference between the predetermined pressure and the operational pressure to prevent the first relief device from opening.  
         [0009]     The first pressure relief device, generally a rupture disc, as stated above, requires a significant amount of maintenance upon opening, i.e., rupturing, to prevent pressure buildup within the paint circulation line from causing damage to the paint circulation pump and various seals. Providing a second pressure relief device that opens at a pressure just below the predetermined pressure that causes the rupture disc to rupture allows pressure relief to be introduced to the paint circulation system without the requisite maintenance and the associated manufacturing down time set forth above. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:  
         [0011]      FIG. 1  is a schematic view of an inventive paint circulation system for supplying paint to a paint applicator and an associated pressure control device. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring to  FIG. 1 , wherein like numerals indicate like or corresponding parts, an inventive closed loop paint circulation system is generally shown at  10 . The paint circulation system  10  supplies paint to at least one paint booth  12  where the paint is applied to a product, such as, for example, a vehicle body  14 . In a typical automobile assembly plant paint is maintained in constant circulation through long circulation line  16  stretching between a paint reservoir  18  and one or more paint spray booths  12  by a pump  20 . The vehicle body  14  is transported through the paint spray booth  12  by conveying equipment (not shown) where the paint is applied to the vehicle body  14  and subsequently cured in a paint oven (not shown) as is known to those skilled in the art. The paint may be applied by human operators or mechanically by automated equipment  22  such as rotary atomizers. The equipment  22  is generally disposed inside the walls of the paint booth  12  and is robotically operated, as again, is known to those skilled in the art.  
         [0013]     The circulation line  16  fluidly communicates with the paint reservoir  18  defining a first fluid circulation circuit, generally indicated at  24 , wherein the paint is circulated at a generally constant pressure, i.e. operational flow pressure. Various manually operated valves  26  are disposed in the circulation line  16  as will be described further below. These valves  26  are generally closed during maintenance operations. The pump  20  is located downstream of the paint reservoir  18  and provides circulation pressure to the paint circulation system  10  by delivering the paint from the paint reservoir  18 . Those skilled in the art will appreciate that various types of pumps may be used with present inventive concept and which do not limit the inventive concept.  
         [0014]     A relief line of the present invention is generally indicated at  28 . The relief line  28  fluidly communicates with the circulation line  16  and is separable by a pressure relief device, such as, for example a rupture disc  30 . The rupture disc  30  ruptures or opens when the operational flow pressure of the paint circulating through the circulation line  16  increases beyond a predetermined value. Typically, if a vessel&#39;s internal pressure rises to the predetermined value, the rupture disc  30  bursts, providing an instantaneous, unobstructed full relief by allowing the paint to circulate through the relief line  28 . Preferably, the rupture disc  30  is certified for 300 PSI or other predetermined value known to prevent damage to the paint circulation system  10 . A sight tube  32  is disposed in the relief line  28  to provide verification that the rupture disc  30  is opened or as the paint is circulating through the relief line  28 .  
         [0015]     A second pressure relief mechanism is cooperable with the rupture disc  30  and operates in response to the difference between the predetermined flow pressure and the operational flow pressure thereby preventing the rupture disc  30  from opening or rupturing. The second pressure relief mechanism includes a pressure control sensor/transmitter  34  for sensing the differences in the operational flow pressure preferably located between the pump  20  and the first of the valves  26  positioned downstream of the pump  20 . A pressure relief valve  36  of the second pressure relief mechanism is fluidly communicated with the relief line  28  and is operated in response to the pressure control sensor/transmitter  34 . Preferably, the pressure relief valve  36  is 1½″ stainless steel three pieces pneumatically actuated pressure relief ball valve located in a tee branch downstream of the pump  20 . Other types of mechanical valves known to those skilled in the art and may be used as desired and should not limit the inventive concept.  
         [0016]     As further illustrated in  FIG. 1 , an actuating device is cooperable with the pressure relief valve  36  for operating the pressure relief valve  36  in the second pressure relief device in response to pressure difference between the operational flow pressure and the predetermined flow pressure. The actuating device includes an actuator  40  for pneumatically opening and closing the pressure relief valve  36  and a solenoid valve  42  for energizing the actuator  40 . The actuator  40  is designed to hold the pressure relief valve  36  in a closed position by generally 40 PSI of compressed air. Those skilled in the pneumatic art will appreciate that various additional sources of compressed air may be fluidly communicated with the inventive system  10 . Furthermore, sensor actuated valves may also be used to adjust response time if required. Preferably, the solenoid valve  42  is rated for explosion proof use and is designed for continuous operation at 24 volt DC. A pressure regulator  44  is cooperable with the actuator  40  for regulating amount of pressure supplied from one of the aforementioned sources of compresses air that normally supplies compressed air at 90 PSI.  
         [0017]     Generally, two of the manually operated valves  26  are disposed in the circulation line  16  on opposite sides in a given components, such as a filter bag  46 . These valves  26  are designed to shut down flow of the paint in case of emergency, maintenance, such as, changing a filter bag  46 , positioned downstream the relief line  28 . A back pressure regulator  48  is disposed at the circulation line  16  to monitor the operational flow pressure required for circulating the paint in the circulation line  16  and for maintaining the operational flow restrictions. Those skilled in the art will appreciate that various types of the back pressure regulator  48  may be used with present inventive concept and which do not limit the inventive concept.  
         [0018]     A controller  50  is operably connected to the pressure control sensor/transmitter  34  and the solenoid valve  42 . Preferably, the controller  50  includes a computer having an input/output interface, a central processor unit, a random access memory, i.e. RAM, and a read only memory, i.e. ROM. The input interface is electrically connected with the pressure control sensor/transmitter  34  and the solenoid valve  42  for operating the second pressure relief mechanism in response to the difference between the operational flow pressure and the predetermined flow pressure before the operational flow pressure exceeds the predetermined flow pressure to prevent the rupture disc  30  from opening. Preferably, the flow pressure that initiates the opening sequence for the pressure relief valve  36  is far enough below the predetermined flow pressure that opens the rupture disc  30  to allow enough time for the controller  50  to open the pressure relief valve  36 .  
         [0019]     In a normal operating mode of the paint circulation system  10 , the paint is circulated through the circulation line  16  under the operational flow pressure of approximately 200 PSI and is delivered to the paint applicator  22  disposed in the paint booth  12  to be applied to the vehicle body  14 . When the operational flow pressure exceeds 200 PSI due to an inadvertent pressure relief valve  36  closure or if the paint circulation system  10  becomes blocked, and before the operational flow pressure reaches the predetermined flow pressure of, for example 300 PSI, the pressure sensor/transmitter  34  will detect a high flow pressure conditions to either speed-up or slow down the pump  20 . For example, if the operational flow pressure exceeds but before the operational flow pressure reaches the predetermined flow pressure, the pressure sensor/transmitter  34  will detect the difference in the operational flow pressure thereby signaling the controller  50  this difference. The controller  50  then signals the solenoid valve  42  that is operatively connected to the pressure relief valve  36 . The solenoid valve  42  is de-energized through the signal received from the controller  50  as the pressure sensor/transmitter  34  responds to the difference between the predetermined flow pressure and the operational flow pressure in the paint circulation system  10 . The solenoid valve  42  cooperable with the actuator  40  assists the actuator  40  thereby venting out compressed air from the actuator  40  cooperable with the pressure relief valve  36 . The loss of compressed air pressure operates as the actuator spring return to mechanically open the pressure relief valve  36  to allow the paint circulation in the relief line  28 . The pressure relief valve  36  is opened as soon as the operational flow pressure exceeds its operational value but before the operational flow pressure reaches the predetermined flow pressure. An alarm (not shown) is operatively communicated with the circulation line  16  and is actuated to warn maintenance crew about the inadvertent valve closure or if the paint circulation system  10  becomes blocked. The alarm is actuated as soon as the pressure relief valve  36  is opened in response to the difference between the operational flow pressure and the predetermined flow pressure.  
         [0020]     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.