Cathodic Electrocoating

Cathodic Electrocoating

Cathodic Electro Deposited coating is used extensively in the automotive industry. In this process, the component after phosphate pretreatment is dipped in the bath of E-coat chemicals and given an electric charge. The coating gets deposited on the component and then it is removed from the bath, washed and then baked.

A complete E-coat system consists of the following

• Pre-treatment line
• E-coat line
• Material handling system
• Oven

This technology gives an organic finish on metal part/component by electrically depositing paint on it.It also requires the following auxiliary equipment:

• Hot water generator
• RO water system
• DI water system
• Laboratory
• Effluent treatment plant

Pre treatment:

• Pre treatment line will consist of the following stages:Knock off degreasing
• Degreasing
• Water rinse
• Water rinse
• Activation
• Phosphating
• Water rinse
• Recirculated DI water rinse
• DI water rinse

It will also have circulation, heating, filtration etc, wherever required.

• The Ecoat line will consist of the following stages:Ecoat
• Permeate rinse 1
• Permeate rinse 2
• DI water rinse
• It will also have prefiltration, ultrafiltration, chiller, rectifier and anolyte system.

Material Handling

For the SME segment the programmable hoist type system is the most economical. This is also popularly called the transporter system or the transporter wagon. The products duly loaded on the jig are carried from one tank to the other in a pre-programmed sequence and pre-defined time. For mass produced similar products, conveyor system is more suitable. 

Baking oven

The oven can be electric, diesel or gas fired. The diesel or gas fired ovens are with stainless steel heat exchanger or direct fired. Forced convection is a must for the oven. The auxiliary equipment is available from a large number of sources.

To be able to design a system, the following information is required:

1. Size of the component
2. Surface area of the component
3. Weight of the component
4. Number of components to be coated per hour
5. Number of working hours per day
6. In some cases, simply the tank size, the expected surface area per batch, weight per batch and the number of batches per hour is also enough.

Depending upon a component's coating requirement, Coatec recommends appropriate technologies. Some technology areas of proficiency with Coatec are outlined in this section.

This technology gives a metal part or a component with an organic finish by electrically depositing paint on it. This works on the simple principle of 'Opposites Attract'.

The Cathodic Epoxy Electrocoating process is outlined in brief detail here.

• A DC charge is applied to a metal component immersed in a bath comprising of oppositely charged paint particles.
• The paint particles deposit on the component to a point where the coating reaches the desired thickness and an even, continuous film is formed over every surface, crevice and corner.
• On attaining desired thickness, the film insulates, resulting in stopping of attraction between paint particle and the component, thus completing the process.
• Depending upon the end use, you can choose either protective, decorative or a combination type of electrocoating

Types of Electrocoat 

Anodic and Cathodic 

ANODIC: For Excellent Colour and Gloss control, combined with economy

• The component to be coated works as an anode with a positive electrical charge attracting negatively charged paint particles in the paint bath.
• Small amounts of metal ions migrate into the paint film, thus limiting the performance properties.
• Anodic Coating finds it's main use in products meant for interiors or moderately aggressive exterior environments.

CATHODIC: High Performance Coatings with excellent corrosion resistance

• The part to be coated is given a negative charge, which attracts positively charged paint particles.
• The reversing of anodic polarities greatly reduces the number of ions entering the cured paint film and this enhances the performance properties of cathodic electrocoated products.
• Cathodic electrocoating are high performance coatings and can withstand the harshness of exterior environment.

Anodic and cathodic coatings can be done by using both epoxies and acrylics.

ELECTROCOATING VS POWDER COATING AND LIQUID SPRAYS

• ENVIRONMENTAL ADVANTAGEEco-friendly
• Free of heavy metal with little or no Hazardous Air Pollutants (HAPS) and very low levels of organic solvents.
• Being water based coatings, they have very low Volatile Organic Compounds (VOC),ranging from 0.012 kg per litre up to 0.360 kg per litre with most products below 0.120 kg per litre.
• Practically no solid waste
• No fire hazard.
• Electrocoat is a clean system not requiring any disposable suits, respirators, and other safety equipment to protect workers from airborne hazards.
• TECHNO-ECONOMIC ADVANTAGECathodic epoxy electrocoating is highly corrosion resistant. A 20-micron dry film thickness can withstand as much as 1000 hours salt spray test.
• Uniform Coating: Electrocoating has 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: The process being a closed loop process allows transfer efficiency of more than 95%, with much reduced waste water streams.
• Very Low Incidence of Rejects: Being electronically controlled, human errors play a very little role thus minimizing rejection rates which could be as low as zero.
• No special skills required for handling the plant and production.
• Higher Productivity: No other paint system can match the through-put capacity of an electrocoat system.
• Quality Edge: As Electrocoat films are controlled by voltage adjustments the deposition stops, once the metal is insulated. No other organic coating system can be controlled with the film uniformity as in Electrocoating system.
• Ease in Handling: Even the uncured paint is dry enough to allow human touch and careful handling.