Abstract:
A process and system for continuous flow-through dip-coating of a workpiece requires the introduction of the workpiece in a porous coating basket at a first side of a coating chamber and the removal of the coated workpiece in the coating basket from a second side of the coating compartment different from the first side. This enables the commingling of coated and uncoated workpieces to be avoided and allows for a higher throughput in the coating process.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flow-through dip-spin coating process and system for applying a coating onto a workpiece. 
     2. Description of the Prior Art 
     Coatings are typically applied to workpieces in order to give the workpiece a desired property such as improved corrosion resistance, an improved appearance, improved lubricating properties and/or improved adhesive properties. Since coatings are less expensive than going to an upgrade of material like stainless steel from a basic carbon steel, coating processes have become very popular in the industry. 
     One method of applying a coating that is very popular is known as dip-spin coating. In this type of process, a mesh or porous basket filled with workpieces, such as fasteners, clamps, springs, O-rings, U-bolts, nails and screws, is immersed in a coating solution for a desired period of time. The basket is then removed from the coating solution and spun to eliminate excess coating solution by centrifugal force. The coated workpieces are then removed from the basket and sent to a curing stage where the coatings are hardened on the workpieces. 
     Dip-spin processes are most advantageous for small parts which can be coated in bulk and achieves precise, highly repeatable results, with transfer efficiencies as high as 98%. Additionally, dip-spin processes solve many environmental problems and allow many different types of coatings to be applied in an efficient and cost effective manner. 
     Conventional dip-spin coating processes have problems in that it is easy to get the coated and uncoated workpieces confused since the coated workpieces exit from the coating booth from the same side in which they entered as uncoated workpieces. Additionally, due to the care necessary to avoid the commingling of the coated and uncoated workpieces, the throughput of the coating process is not as fast as desired in that it is difficult to operate as a continuous process. 
     SUMMARY OF THE INVENTION 
     Through extensive research to find a dip-coating process and system which avoids the problems outlined above, the present inventors have discovered the present invention. That is, the present invention has as an object to provide a dip-spin coating process and system in which commingling of coated workpieces with uncoated workpieces is avoided. 
     The present invention has as another object to provide a dip-spin coating process which has a high throughput and can be operated in a continuous fashion. 
     These and other objects are achieved by providing a dip-spin coating process in which the uncoated workpieces enter a coating chamber in a basket through a first side and, after a dip-spin coating step, exit the coating chamber in the basket through a second side of the coating chamber different from the first side. The coated parts can be removed from the basket at a location which is remote from the location at which the uncoated parts are loaded into the basket and since the uncoated parts enter through a first side of the coating chamber and the coated parts exit from a second side of the coating chamber different from the first side, continuous operation of the dip-spin coating process is possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a top view of the dip-spin coating process of the present invention, 
         FIG. 2  is a side view of a dip-spin coating system of the present invention, 
         FIGS. 3A and 3B  illustrate a telescoping conveyor feeding workpieces into a basket in a normal and tilt mode, 
         FIG. 4  illustrates a hydraulic lift and tilt apparatus which holds the coating basket during the introduction of uncoated workpieces into the coating basket, 
         FIGS. 5A and 5B  illustrate a plan view and a front view of a coating basket used in the present invention, 
         FIG. 6  is a rear view of the dip-spin coating chamber, and 
         FIGS. 7A and 7B  are front and end elevations of a basket unloader used in the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a plan view of the dip-spin coating system  1  of the present invention. A bin loader  2  takes uncoated workpieces  8  and delivers them into a porous coating basket  7  supported on a pallet  10 . The workpieces can be metallic, ceramic or plastic parts such as fasteners, clamps, springs, O-rings, U-bolts, nails and screws. 
     As shown in  FIG. 4 , the porous coating basket  7  and the pallet  10  are locked into a hydraulic lift and tilt mechanism  11  prior to the introduction of the workpieces  8  therein from the bin loader  2 . The hydraulic lift and tilt mechanism is provided below floor level and supports the porous coating basket  7  at approximately floor level during the loading of the workpieces therein. A load cell can be used to monitor the weight of the workpieces  8  introduced into the porous coating basket  7 . The hydraulic lift and tilt mechanism can tilt the porous coating basket  7  to a desired angle to aid in the introduction of the workpieces therein. Additionally, the hydraulic lift and tilt mechanism  11  comprises a powered turntable  12  which can rotate the porous coating basket  7  in a desired direction to help insure that the workpieces are evenly distributed therein. The rotational speed of the powered turntable  12  can be varied depending on the properties of the workpieces  8 . 
     As shown in  FIGS. 3A and 3B , a telescoping conveyor feeder  3  can be used to introduce the workpieces directly into the porous coating basket  7 , if the workpieces are of such a nature that introducing them directly into the porous coating basket from the bin loader  2  would damage them. After the workpieces  8  are loaded into the porous coating basket  7 , the hydraulic lift and tilt mechanism  11  raises the loaded coating basket and the pallet to the level of a first conveyor  13  and a chain conveyor  14  provided on the hydraulic lift and tilt mechanism transfers the loaded coated basket and the pallet onto the first conveyor  13 . 
     The first conveyor  13  is preferably a chain conveyor and carries the pallet  10  having the porous coating basket  7  containing the workpieces  8  therein through a first side  15  of a dip-spin coating chamber  5 . Upon reaching a predetermined position in the dip-spin coating chamber  5 , a coating basket cover  16  locks onto the porous coating basket  7  containing the uncoated workpieces  8 . The coating basket cover  16  is connected to a drive unit  17  for rotating and tilting the coating basket and supports the porous coating basket  7  as the pallet  10  is transferred by a second conveyor  22  out of the coating chamber  5  through a second side thereof  24  which is different from the first side  15  of the coating compartment. The second conveyor  22  is a bi-directional conveyor and can transfer the pallet  10  to and from the dip-spin coating chamber  5 . 
     As shown in  FIGS. 2 and 6 , a coating tank  18  containing a coating solution  20  is positioned below the porous coating basket  7  containing the workpieces  8  in the dip-spin coating chamber  5 . A coating tank lift  21  raises the coating tank  18  to a height where the coating solution  20  is brought into contact with the workpieces  8  in the porous coating basket  7 . The coating solution  20  can be solvent- or water-based and comprise corrosion resistant, lubricant or adhesive compositions. The workpieces  8  are immersed in the coating solution  20  for a predetermined period of time sufficient to apply a desired coating onto the workpiece  8 . 
     When the predetermined immersion time of the workpieces  8  in the coating solution  20  has elapsed, the coating tank  18  is lowered to a position where the workpieces  8  in the porous coating basket  7  are no longer contained in the coating solution  20  but at least a part of the porous coating basket  7  is still positioned within the coating tank  18 . The drive unit  17  for rotating and tilting the coating basket is capable of supporting the coating basket in a vertical position or an inclined position as shown in  FIGS. 2 and 6 . A spin cycle is then initiated in which the porous coating basket is rotated at a sufficient speed to remove excess coating solution from the workpieces  8  by centrifugal force. The excess coating solution exits the porous coating basket  7  and impinges against the walls of the coating tank  18  and drains back into the coating solution  20  contained in the coating tank. 
     The drive unit  17  for rotating and tilting the coating basket can position the coating basket  7  in the coating tank  18  at up to a 45° angular tilt in the coating solution and can rotate the basket at a speed of from 0-20 RPM in the coating. The work basket then can shift back to the vertical position and accelerate up to 425 RPM. 275-425 RPM is the preferred range. After all of the excess coating solution has been removed from the workpieces  8 , the coating tank  18  is lowered further so that the porous coating basket  7  is no longer contained therein and the second conveyor  22  then brings the pallet  10  back into the coating chamber  5  through the second side  24  thereof. 
     In the dip-spin coating chamber  5 , the porous coating basket  7  containing the coated workpieces  8  is then placed on the pallet  10  and the coating basket cover  16  removed therefrom. The second conveyor  22  then transports the coating basket  7  containing the coated workpieces  8  through the second side  24  of the coating chamber  5  to a third conveyor  23 . Air bladders (not shown) support the second conveyor  22  over the third conveyor  23 . When the loaded basket  7  reaches a desired position over the third conveyor  23 , the air bladder deflates so that the height of the second conveyor  22  becomes lower than that of the third conveyor  23  and the loaded coated basket  7  provided on the pallet  10  is now supported by the third conveyor  23 . 
     The third conveyor  23  in the illustrated embodiment of  FIG. 1  comprises powered bi-directional rollers which are capable of rotating in two different directions. The third conveyor  23  transports the pallet  10  with the loaded porous coating basket  7  containing the coated workpieces  8  to a basket unloading station  6 . There the loaded coated basket  7  is removed from the pallet  10  and, as shown in  FIGS. 1 and 7 , placed in a basket unloader  25  and locked therein. The basket unloader  25  is capable of pivoting the loaded coating basket  7  through an angle of 180° while rotating the coating basket in order to aid in the discharge of the coated workpieces therefrom. After the coated workpieces  8  have been discharged from the porous coating basket  7 , the basket unloader  25  is unlocked to allow the empty porous coating basket  7  to be removed therefrom and repositioned on the pallet  10  provided on the third conveyor  23 . 
     The third conveyor  23  then transports the pallet  10  and the empty porous coating basket  7  to a location where a fourth conveyor  26  is provided. The fourth conveyor  26 , like the second conveyor  22 , is supported by air bladders (not shown) which are inflated and deflated to raise and lower the fourth conveyor  26 . Once the pallet  10  and the empty porous coating basket  7  are positioned above the fourth conveyor  26 , the air bladder is inflated to raise the height of the fourth conveyor  26  above that of the third conveyor  23  so that the pallet  10  and the empty porous coating basket  7  are supported thereon. The fourth conveyor  26  is preferably a chain conveyor. 
     The fourth conveyor  26  transports the pallet  10  and the empty porous coating basket  7  to a fifth conveyor  27  which carries the empty porous coating basket  7  and the pallet  10  to an empty coating basket loading/unloading station  28 . The fifth conveyor  27  is shown as being powered rollers in  FIG. 1  and, if desired, an optional in-line basket cleaning station comprising spray nozzles and a cleaning solution can be provided over the fifth conveyor. 
     At the empty coating basket loading/unloading station  28 , a sixth conveyor  30  is provided to receive the empty porous coating basket  7  and the pallet  10  from the fifth conveyor  27 . The sixth conveyor  30  is also supported by an air bladder (not shown) which is deflated and inflated to lower and raise the sixth conveyor  30 . As shown in  FIG. 2 , the sixth conveyor  30  is provided on a scissor lifting and lowering device  29  which can be lowered and raised to allow the removal and replacement of the empty porous coating basket  7  and/or the pallet  10  therefrom. When the air bladder is inflated, the height of the sixth conveyor  30  is above that of a seventh conveyor  31  and the sixth conveyor  30  receives the pallet  10  and the empty porous coating basket  7  from the fifth conveyor  27 . Upon the pallet  10  and the empty porous coating basket  7  reaching a desired position over the seventh conveyor  31 , the air bladder supporting the sixth conveyor  30  is deflated bringing the pallet  10  and the empty porous coating basket  7  into contact with the seventh conveyor  31 . 
     As shown in  FIG. 1 , the seventh conveyor  31  can be powered rollers which are used to convey the pallet  10  and the empty porous coating basket  7  to a location where the pallet  10  and the empty porous coating basket  7  are provided on the hydraulic lift and tilt mechanism  11 , where they are then locked into place and ready to receive uncoated workpieces  8  from the bin loader  2  and/or telescoping conveyor feeder  3  and be introduced into the dip-spin coating compartment  5 . 
     While the invention has been described above with a specific example, the present invention is not limited thereby and various changes and modifications may be apparent to those of ordinary skill in the art. Since changes and modifications are to be understood as being included within the scope of the present invention as defined by the impending claims, unless they department therefrom.