Innovations In Job Shop Coating Applications
Contrary to routine coating procedures where all parameters are known entities, occasionally a customer will ask us to innovate a new procedure for a unique coating application. In one specific case, the application concerned the phosphorous bronze material used in a Cathode Ray Tube (CRT) for the Tempest Military Program. Phosphorous bronze was selected as the screen material due to its capability to reduce CRT emissions. Ekco/Glaco was asked to use black teflon® coating on the phosphorous bronze 180 mesh screen with no bridging or plugging of any of the screen openings. Paint could not be used because the coating requirement was to eliminate peeling, chipping, cracking, and scratching prior to assembly.
The end use of the application was for the coated screen to be laminated between two pieces of glass on the bezel of an electromagnetic interference EMD CRT panel to improve visual clarity. The purpose of the Teflon® or coating was for contrast enhancement of a visual CRT screen created for a dark room environment.
Upon receiving the customer's approval, we proceeded with the following sequence to insure the desired quality and performance:
- A metal frame was constructed to hold the phosphorous screen securely taut, without allowing any distortion whatsoever of the screen.
- The black teflon® material was then modified to greatly reduce the possibility of bridging or plugging of screen openings. Numerous modifications tried prior to obtaining the proper material application characteristics.
- To enhance coating adhesion, special surface preparation methods were developed to remove particles from the screen prior to coating the phosphorous bronze surface.
- It was essential to coat the screen immediately after preparation in order to prevent oxidation.
Unfortunately, the screen was still plugged in numerous areas, even after the above procedures were repeated several times. Therefore it was necessary to go a few steps further.
First, a wooden box was fabricated to accommodate two 150 watt lamps to generate sufficient heat to quickly evaporate the coating solvents. This resulted in an extremely thin film that virtually eliminated the plugging problem after the coating was applied. To alleviate operator eye strain from the bright incandescent lights, a dark plastic amber lens was fabricated to go over the boxed screen. In addition to solving the problem of eye strain, the amber lens gave the operator a clearer view of the screen during the coating process.
Any bridging (plugging) that occurred at this point was gently blown out with a controlled air jet, resulting in a 100% bridge-free screen. The coated screen was then oven-baked at the proper time and temperature. Finally, to avoid damage in transit egg crate type packaging was designed.
Though this process was used successfully on a production basis through 1989, we have since produced even newer technology for production of EMI panels.
Ekco/Glaco Inc. specializes in the preparation and application of powder coatings, protective coatings and release coatings. They are also a licensed DuPont application for teflon® coatings.
Teflon® is a registered trademark of DuPont
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