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These are high performance coatings and they have many properties that are different from standard epoxy and polyester powder coatings. Extra attention to proper pre-treatment, application and curing is required to ensure good performance. We recommend thoroughly testing this material on your substrate with your application procedure before using.
Metal Types: These coatings are generally appropriate for steel, cast aluminium and Type I aluminized steel. Various grades of substrate are available, and some substrates have their own temperature limits. The user should test the coating using their substrate and pre-treatment method before production use. In accelerated salt fog testing, these coatings have limited performance over steel substrates. For extended outdoor use, aluminium or aluminized steel is highly recommended or contact a sales representative for more information.
Pre-treatment: High temperature coatings require cleaner substrates to create good adhesion. Proper pre-treatment is essential to the performance of these coatings, and the goal of the following recommendations is to provide a clean, dry surface for the powder to bond to.
Chemical Pre-treatment: Alkaline cleaner under high pressure followed by thorough de-ionized water rinse. Force dry and coat as soon as possible to avoid rust.
Do not use phosphate on steel substrates because the phosphate layer will fail at high temperatures. We do not recommend using any pre-treatment method that leaves a coating or sealer on the surface. Several other cleaners including Alumiprep 33 from Henkel has been used in the laboratory with good results. Again, the user should test the coating using their substrate and pre-treatment method before production use. Keep records of application procedures including pre-treatment, coating thickness, cure time and temperatures.
Mechanical Pre-treatment: Clean abrasive media blast is highly recommended. This provides both a clean surface and a good profile that promotes coating adhesion. After blasting any dust can be removed with air. Do not hand wipe with any solution after blasting.
Pre-treatment Precautions: Hand wiping with any kind of solvent or thinner will impair adhesion and lead to coating failure. Use only pressurized alkaline cleaning systems or abrasive media blasting. Phosphated steel and some other pre-treatments have their own temperature limits and are not suitable for high temperature applications.
Fluidisation: This type of material is highly electro-statically active. During transit, vibration may cause small, very soft electrostatic agglomerations of powder. Some users have described the appearance as “lumpy.” This is normal and is easily corrected by conditioning the powder prior to use. Filter the powder through a clean, grounded screen with a coarse mesh (such as window screen material). Then fluidise the material for several minutes before spraying. If the agglomerations are difficult to disperse, it is likely that the material has gotten too hot in transit or storage and has sintered. In many cases, especially with textured finishes, this is easily corrected. Again, condition the powder by sifting through a grounded screen and discard the larger agglomerations.
Use only a fluidising hopper, not a box feeder. This material may not feed well through a box feeder, and a vibratory feeder can actually pack the material down and may cause it to sinter.
Application: Use electrostatic application to room temperature substrate at 1.0 to 3.0 mils. Thicker applications are not recommended as they can cause out-gassing and adhesion problems. Preheating the substrate will make it very difficult to put on the proper film thickness. Reduced voltage will help ensure film thickness uniformity. 65kv has been used in the laboratory with good results.
Silicone resins have lower melting points than other powders. They will begin to become tacky at less than 100°F. We recommend an application area temperature of no more than 75°F.
Curing: Silicone powder coatings require more energy to fully cure. Without a full cure, the film will have less flexibility and be prone to cracking, chipping and corrosion.
The minimum cure cycle is 450°F (230°C) for 20 minutes with the substrate up to temperature. Some applications will achieve better cure results with increased time and temperature. These are high heat resistant coatings, so there is no chance of over baking them at450°F to 500°F. Generally, the longer and hotter the cure you can provide (within reasonable limits), the better.
Cleanup: Some poorly formulated silicone powder coatings have created a persistent myth that all silicone powders are terribly contaminating. Our high temp products contain a modified silicone molecule that is very different from that of cleaners and lubricants that cause serious contamination. We estimate that the potential for contamination with these coatings is similar to using a high flow urethane. We recommend a good cleanup immediately after use. It is also a good idea to test for compatibility with other products and then plan to run a textured coating immediately after, just in case.
Clean up with cold water only. Warm water will only melt the powder and make it more difficult to remove.
Storage: Silicone products are more temperature sensitive to heat and humidity than standard powder chemistries. They should be stored and used at temperatures below 75 F (24 C). Recommended shelf life after receipt is six months under carefully controlled conditions.Troubleshooting: The most common causes of coating failure are inadequate pre-treatment and/or curing. When fully cured on clean substrate, these coatings will provide excellent performance up to rated temperatures. Higher gloss coatings may lose some gloss at the top end of their temperature range. For applications at the top end of the temperature range, we recommend starting with a low gloss or flat finish to minimize colour change.
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