 Electrocoating is a method of giving a metal an organic finish by using electrical current to deposit the paint. The process works on the simple principle of Opposites Attract. An Electrocoat System applies a DC charge to a metal part immersed in a bath of oppositely charged paint particles. The paint particles are drawn to the metal part and paint is deposited on the part, forming an even, continuous film over every surface, in every crevice and corner, until the coating reaches the desired thickness. At that thickness, the film insulates the part and the attraction of paint particle stops and electrocoating is complete.
Types of Electrocoat
 Electrocoating could be protective, decorative and may combine the properties of both depending upon the end use. Depending upon the polarity of the charge, electrocoating is classified as either: Anodic, or Cathodic.
In Anodic Electrocoating, the part to be coated is the anode with a positive electrical charge, which attracts negatively charged paint particles in paint bath. In the anodic process, small amounts of metal ions migrate into the paint film, which limit the performance properties of these systems. Their main use is for products in interior or moderately aggressive exterior environments. Anodic coatings are economical and offers excellent color and gloss control.
 The Cathodic process is just the opposite of anodic process. In Cathodic Electrocoating, the part to be coated is given a negative charge, attracting the positively charged paint particle. The reversing of anodic polarities greatly reduces the amount of ions entering the cured paint film and thus enhances the properties of cathodic electrocoated products. Cathodic electrocoatings are high performance coatings with excellent corrosion resistance and can withstand the harshness of exterior environment.
Anodic and cathodic coatings can be done by using both epoxies and acrylics.
The Cutting Edge of Electrocoating
Electrocoating offers some significant advantages over powder coating and liquid spray systems. They may be divided into two categories: Environmental and Techno-economic.
Environmental
Electrocoat Technologies are eco-friendly because:
• Most Electrocoat formulations are heavy metal free with little or no Hazardous Air Pollutants (HAPS) and very low levels of organic solvents
• Since these are water based coatings, they have very low Volatile Organic Compounds (VOC). They range from 0.012 kg per litre up to 0.360 kg per litre with most products below 0.120 kg per litre
• As solvent levels of electrocoat products have dropped over the year, so has the Biochemical Oxygen Demand (BOD) and COD (Chemical Oxygen Demand).
• There is practically no solid waste
• Most electrocoat materials are not considered "Red Label"
• They are formulated as water based materials, hence there is no fire hazard
• Electrocoat is a clean system not requiring any disposable suits, respirators, and other paraphernalia to protect workers from airborne hazards.
Techno-Economic
 Electrocoat System also has the techno-economic edge over powder coating and liquid spray system. The important ones include:
• High Corrosion Protection Property: Cathodic epoxy electrocoating is highly corrosion resistant. A 20-micron dry film thickness can withstand as much as 1000 hours salt spray test in accordance to test conditions laid down in ASTM B117 standard.
• Uniform Coating: The ability to give very even coating with variances ranging to only 1-2 microns.
• Coating of Complex Parts: Electrocoat system has the versatility to coat highly recessed and complex surfaces, which are not amenable to powder coating or liquid spray system.
• Higher Transfer Efficiency: Closed loop rinsing allows transfer efficiency of more than 95% with dramatically reduced wastewater streams.
• Very Low Incidence of Rejects: Since most of the key process parameters are electronically controlled, human errors play a very little role and hence the rejection rate could be as low as zero. As a corollary to it, no special skills are required for handling the plant and production.
• Much Higher Productivity: No other paint system can match the throughput capacity of an electrocoat system. For example, if product remains the same, an electrocoat system can give at least three-times more production with less manpower during the same period.
• Much Better Quality: Electrocoat films are controlled by voltage adjustments. Once the metal is insulated, deposition stops. There is no other organic coating system that can be controlled with the film uniformity as it is in electrocoating system.
• Ease in Handling: Even the uncured paint is dry enough to allow human touch and careful handling.
The Limitations
Electrocoating has some limitations as well. They include:
• It can be done only on metals
• Only one color is economically viable in one set-up/line
• It demands special care to prevent air entrapment during paint deposition process in paint bath
• It is more energy intensive process than powder coating and liquid spray for the simple reason that the circulation pump to agitate the paint bath have to run 24 hours, irrespective whether there is production or not
• It cannot cover the surface defects of parts to be electrocoated, and
• Its initial capital cost is higher in comparison to powder coating and liquid spray systems.
Article courtesy: Coatec India, Chandigarh. Tel: 0172-5063438. Fax: 91-172-5063439. Mobile: 098889-95352. Email: info@coatecindia.com
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