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| Electrocoating, which is also referred to as electro deposition, electrophoretic deposition, CED Coating, CED Painting or electropainting, is an organic finishing process that uniformly applies thin-film primers and one-coat finishes to metallic substrates. Electrocoating resembles electroplating in that it utilizes an electrical current to deposit a coating onto substrates. However, electrocoating deposits water born paint onto substrates rather than metal ions.
The overall process consists of four main process steps: Pre-treating, Electrocoating, Rinsing, and Baking.
The electrocoating process may be anodic or cathodic, depending on the charge applied the substrate. Although the processes are virtually the same, properties of the resultant coating are dissimilar. Anodic systems, which were the first to be used for electrocoating, apply paint to positively charged substrates. The negatively charged pigment and resin particles deposit onto the substrate (anode). One disadvantage of this process is that substrate metals dissolve and become incorporated into the coating, which affects surface properties. Cathodic electrocoating deposits paint onto negatively charged substrates and offers several advantages over anodic electrocoating. For example, metal dissolution of the substrate does not occur, cathodic electrocoating has the ability to deposit over contaminants, corrosion resistance is improved, and a better color consistency occurs over welded areas.
The electrocoat process can be divided into four distinct steps:
1. Pretreatment
2. CED/Electrocoat Bath
3. Post Rinses
4. Baking
The pretreatment zone cleans and phosphates the metal to prepare the surface for electrocoating. Cleaning and phosphating are essential to achieving the performance requirements desired by today’s end user of the product. A high quality zinc phosphate system using the immersion method is primarily used where steel and iron parts are to be coated.
The electrocoat bath and ancillary equipment zone is where the coating is applied and the process control equipment operates. The electrocoat bath consists of 80-90% deionized water and 10-20% paint solids. The deionized water acts as the carrier for the paint solids which are under constant agitation. The solids consist of resin and pigment. Resin is the backbone of the final paint film and provides corrosion protection, durability and toughness. Pigments are used to provide color and gloss.
The post rinses provide both quality and conservation. During the electrocoat process, paint is applied to a part at a certain film thickness, regulated by the amount of voltage applied. Once the coating reaches the desired film thickness, the part insulates and the coating process slows down. As the part exits the bath, paint solids cling to the surface and have to be rinsed off to maintain efficiency and aesthetics. The excess paint solids are called “drag out” or “cream coat.” These excess paint solids are returned to the tank to create a coating application efficiency above 95%.
The bake oven receives the parts after they exit the post rinses. The bake oven cross links and cures the paint film to assure maximum performance properties. The minimum bake schedule is 20 minutes with the part temperature at 375°F for most electrocoat technologies. However, there is also a “low temperature cure” electrocoat material. This material has a minimum cure of 20 minutes at a part temperature of 180°F so that many assemblies containing seals, bushings, bearings, or oil can use the electrocoat process.
CED Coating or Cathodic Electro Deposited Coating is used to coat a surface of an object. This type of coating is electronically applied and it offers the highest level of corrosion resistance. Owing to its high degree of durability, it is widely used to coat automobile parts and components. But, first the preparation of metal surface needs to be done, so that it can be painted properly. This process is similar to the process of "laying of foundation".
The requirement of pre-treatment before CED Coating on automobile products is due to the following:
• Cleaning of the surface for oil, physical contamination & rust
• Making such a surface condition that has higher degree of paint-adhesion
• Minimize or eliminate any chance of reaction of paint with the base metal
• Provide added benefit of high level of corrosion resistance
• Highest level of rust resistance
• Allows coating of highly recessed areas
• Provide ability to coat complex shapes with unmatched preciseness
• Transfer efficiency of over 95%, reduced paint wastage
• CED paint does not sag during curing and doesn't wash off in enclosed areas due to hot vapours.
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Office & Works:
Kamal Envirotech Pvt. Ltd.
Plot No. F-193, F-194, EPIP RIICO Industrial Area
Neemrana, Alwar-301705, Rajasthan, GSTIN:08AAACK0711H1Z0
Phone:+91-9810043891
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