Coating processes – Solid particles or fibers applied – Fluidized bed utilized
Reexamination Certificate
2001-10-18
2003-03-25
Parker, Fred J. (Department: 1762)
Coating processes
Solid particles or fibers applied
Fluidized bed utilized
C427S470000, C427S486000, C427S203000, C427S386000, C427S388100
Reexamination Certificate
active
06537610
ABSTRACT:
BACKGROUND
The present invention directed to a coating process for a dual-layer coating on a suspension component for an automobile; and more particularly, for suspension spring components.
Steel suspension components for use with automobile suspension systems are typically coated with a protective coating to protect the components from corrosion and other environmental damage. Because these components are typically subject to impact damage caused by flying stones and gravel,the automotive industry is beginning to utilize dual-layer coating systems for such suspension components, where the first layer is a zinc-rich coating that has a self-healing property when the coating is broken or damaged and an outer layer of a thermoplastic material that protects the inner layer from chipping and damage caused by objects thrown up from the road. The inner, zinc-rich layer is typically approximately 2.00 to approximately 3.00 mils and the outer coat thermoplastic layer is typically approximately 13.0 to approximately 17.0 mils. See U.S. Pat. No. 5,981,086 for more detailed information regarding the dual-coat materials.
Traditionally, the zinc-rich layer has been applied to the steel suspension component utilizing an electrostatic spray application (involving the steps of charging the zinc-rich powder with a low amp, very high voltage charge, placing the steel components on a grounded conveyor, and then spraying the components with the charged powder such that the charged powder is evenly and uniformly attracted to, and hence, applied to the grounded steel component). After the electrostatic spray application, the component is conventionally placed in an oven so that the layer of zinc-rich powder is baked onto the steel component (i.e. is cured). It is then envisioned that the outer, thermoplastic layer will be applied in a similar manner.
A problem confronted by the industry with this dual-coat process is that the thermoplastic powder is not sufficiently conductive (not electrostatic), and hence, utilizing an electrostatic coating operation for the outer, thermoplastic layer has been very problematic. The coating industry has, thus, resorted to different types of dual-layer coatings and has experimented with different types of methods for coating the outer layer. The primary problem with these alternate methods for applying the outer, thermoplastic coat is that they require a labor-intensive, manual application and are therefore very expensive to perform.
The application problems are increased with automotive components having more complex shapes, such as coil-springs. Prior-art attempts for obtaining an adequate thickness and uniformity of the thermoplastic layer on both the inner and outer diameter surfaces of the coil-spring have included over-heating the coil-spring prior to a spray application of the thermoplastic powder in an attempt to make the thermoplastic powder attract to and adhere to the inner and outer diameter surfaces of the coil-spring (i.e., relying more on the heat of the coil-spring to attract the thermoplastic powder than the electro-static properties). A problem with this attempt is that such over-heating causes the zinc-rich layer to become over-cured, which, in-turn, substantially reduces the amount of adhesion or bonding between the zinc-rich layer and the thermoplastic layer in the finished product. Additionally, in an attempt to obtain adequate thickness and uniformity on the inner diameter surfaces of the coil-spring, the outer diameter surfaces tend to become overloaded with the thermoplastic material. This increases consumption of the thermoplastic powder (increases cost) and presents possible fit problems with mating components during automobile assembly.
Accordingly, there is a need for a high-volume process for applying the dual-layer coating described above to steel suspension components that does not necessitate the use of an error-prone electrostatic spray application for the outer, thermoplastic layer of the dual-layer coating.
SUMMARY OF THE INVENTION
The present invention involves a process for applying a dual-layer protective coating to metallic suspension components of an automobile that involves the steps of applying a first coat of the zinc-rich coating powder utilizing the conventional electrostatic application process; partially curing the layer of zinc-rich coating that has been applied to the steel component such that the zinc-rich coating is gelled; immersing the component with the first layer of gelled zinc-rich coating in a fluidized bed of the thermoplastic powder so that a relative uniform layer of the thermoplastic coating powder is applied over the first coat of gelled zinc-rich coating; and finally curing the outer layer of thermoplastic powder coating and the inner layer of the zinc-rich coating.
In an exemplary embodiment, the fluidized bed of the thermoplastic powder is heated to bring the fluidized bed of thermoplastic powder within a predetermined temperature difference from the temperature of the component with just prior to the component being immersed within the fluidized bed of thermoplastic powder. In an even more detailed embodiment, the temperature of the component prior to being immersed within the thermoplastic powder and the temperature of the fluidized of thermoplastic are monitored prior to immersing the component within the fluidized bed of thermoplastic powder; and further, the heat of the fluidized bed of thermoplastic powder may be adjusted if the difference between the component and the fluidized thermoplastic deviate from the predetermined potential.
In yet a further detailed embodiment, excess thermoplastic powder is removed from the components subsequent to immersing the components within the fluidized bed of thermoplastic powder by the step of directing a stream of air or gas against the excess powder carried on the components.
Therefore, it is a first aspect of the present invention to provide a method for applying a protective coating to a steel component of a vehicle that includes the steps of: applying a first coat of epoxy-based, protective powder to the component; partially curing the first coat; heating a fluidized bed of thermoplastic powder; immersing the component with the partially cured first coat into the heated fluidized bed of thermoplastic powder so as to apply a second coat of the thermoplastic powder over the first coat; withdrawing the component from the fluidized bed; and finally curing the first and second coats. In a detailed embodiment the fluidized bed of thermoplastic powder is heated to bring the fluidized bed of thermoplastic powder within a predetermined temperature difference from the temperature of the component at a time just prior to the immersing step. In a further detailed embodiment, the method further includes the steps of: monitoring the temperature difference between the fluidized bed of thermoplastic powder and the component at the time just prior to the immersing step; and responsive to the monitoring step, adjusting at least one of the temperature of the fluidized bed of thermoplastic powder and the temperature of the component at the time just prior to the immersing step. In yet a further detailed embodiment, the adjusting step is performed automatically; or, alternatively, the adjusting step is performed, at least in part, manually.
In an alternate detailed embodiment of the first aspect of the present invention, the predetermined temperature difference is approximately 60° F. to approximately 75° F. In another alternate detailed embodiment of the first aspect of the present invention, the temperature of the component at the time just prior to the immersing step is approximately 140° F. to approximately 230° F. and the temperature of the fluidized bed of thermoplastic powder is approximately 90° F. to approximately 180° F. In a further detailed embodiment, the temperature of the component at the time just prior to the immersing step is approximately 200° F. to n approximately 210° F. and the temperature of the fluidized bed of thermoplastic powder is approximately
Conn Jason
Harmon Jamie
Springer Paul W.
Wolf Robert
Parker Fred J.
Springco Metal Coating, Inc.
Taft Stettinius & Hollister LLP
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