What is Electro Coating?
E-coating is an immersion wet paint finishing process that uses electrical current to attract the paint product to a metal surface. This process is also referred to as paint deposition. The E-coat process is a dipping (immersion) system very similar to what is used in metal plating except the finish uses organic paint particles not metal particles in the immersion baths.[Back to top.]
How does E-Coating work?
Electro coating applications use paint particles suspended in a fluid bath. An opposite charged part is lowered into the paint bath and the paint particles are drawn to the metal part. The paint particles build up on all surfaces of the metal part to form an even, continuous, low-profile film over the entire surface. This process continues until the desired film thickness is reached. Film thickness is regulated by the amount of voltage differential applied. The higher the voltage, the thicker the film build.
Working on the principle that opposites attract, an e-coat system applies an electrical charge to either the metal part, or the fluid in the immersion tank. The paint is than attracted by one or the other being grounded. The process can be performed either way, however there are benefits of having the part grounded (-) and a charge applied to the solution (+) vs. having the parts (+) positively charged and the tank solution holding a (-) negative charge. Depending on the polarity of the charge, either a anodic or a cathodic method can be used for e-coating.[Back to top.]
In anodic systems, the part is the anode, positively charged. It attracts the negatively charged paint particles in the paint bath. Small amounts of metal ions migrate from the part into the paint film, limiting the performance properties of these systems. The metal ions contaminate the coating. This process is not widely used due to the degraded corrosion resistance and durability. Allows for a lower cure temperature.
In cathodic systems, the product or part is negatively charged, which attracts the positively charged paint particles. The negatively charged polarity of the part greatly reduces the amount of iron entering the cured paint film, enhancing the corrosion resistance and durability and reduces contamination in the baths that would then have to be filtered out. . Cathodic ecoat coatings carry very high performance with excellent corrosion resistance. If you are going to e-coat, this is the best method.
E-coat solids deposit initially in the areas closest to the counter electrode and, as these areas become insulated to current, solids are deposited in more recessed bare metal areas to provide complete coverage. This phenomenon is known as throwing power and is a critical aspect of the electro coat process. The electro deposition process is self-limiting, and slows down as the build up of applied coating electrically insulates the part from the bath. The e-coat paint covers and protects the entire part or product so that even corners, edges and recessed areas are completely protected. Ecoat does not protect inside tubes. As a rule, E-coating will only cover the inside of a part 2 times the width of the opening. Much like the Ventury effect in powder coating, the paint material does not attract inside an enclosed area.
Electro coating is used on many products you own! In fact, today, approximately 99% of all new cars manufactured are E coated then top coated with the color of choice. A Cathodic Epoxy E Coat Primer is what protects your car from rusting.
Cathodic epoxy electrocoatings are the benchmark for corrosion resistance. Widely used in the automotive and automotive parts industries, they provide superior salt spray, humidity, and cyclic corrosion resistance. However, the cathodic epoxy technologies generally have low resistance to UV light, requiring a topcoat to protect the epoxy primer from sunlight. All automakers use cathodic epoxy e coat for under hood applications, and as a prime/topcoat. Cathodic acrylic electrocoatings are used as a one-coat finish. It is typically used in applications where both UV durability and corrosion resistance on ferrous substrates are desired. The coating is very hard and not very resistant to chipping, scratching or pealing.
Cathodic acrylic electrocoatings are used as a one-coat finish. It is typically used in applications where both UV durability and corrosion resistance on ferrous substrates are desired. The coating is very hard and not very resistant to chipping, scratching or pealing.[Back to top.]
E Coating Benefits:
- Superior Corrosion Resistance
- Uniform, even coat
- Environmentally Friendly
- E Coating is environmentally friendly. Many manufacturers use e-coat because the electrocoat process produces little or no HAPS (Hazardous Air pollutants), VOCs (Volatile Organic Compounds), and is RoHS, OSHA and EPA compliant. Efficiency
- Virtually all unused paint is recovered. Most lines have 2 but some have 3 post rinses to remove any residual paint buildup. The post rinses are than filtered and any paint collected in the rinse stages is re-introduced back into the application bath. Most e-coat systems are automated, the amount of paint applied to a product can be precisely controlled, yielding minimal waste unlike powder or paint overspray.
- Line density.
- Each line is different, but with the correct engineering it is possible to coat as many parts or products that can be hung at once. This is based on total square footage to be coated at one time. Depending on the size of the tank, the correct number of anodes must be installed in order for the tank to cover the maximum amount of surface area required. As long as parts to not touch, the entire tank can be filled with parts. Racking is very important for overall line efficiency.
- The ability to provide very good inter-coat adhesion with most topcoats allows this process to be used as a primer for almost all ferrous applications.
- E-coat makes products last longer.
- Manufacturers choose electrocoating to provide their products with a durable, lasting finish that will stand up to outdoor environments such as water and sunlight or indoor environments such as chemicals used in your laundry room. Electrocoat is a technology used worldwide to achieve high-quality, low-cost finishes at a level of efficiency and environmental compliance no other finishing method approaches. The performance advantages, along with reduced finishing costs, have made it a growing technology that will continue long into the future as new uses and technologies are developed.
- Construction and maintenance of an ecoat line is very expensive.
- With the paint being suspended in the bath, it has to be constantly agitated, if power is lost, a pump fails, and the paint is allowed to settle, it is junk. The replacement of the paint material and clean up of the system can cost 10’s of thousands to complete.
- Color changes are next to impossible.
- This is not the correct method for doing one or two parts a specific color. The system is set up for one paint product to run constantly. Several filters and settings would have to change and the process of doing so is measured in days not hours. Because of the sheer volume of material to fill the baths, changing material is very costly.
- UV protection.
- Epoxy e-coats are very susceptible to sunlight. The UV light will break down the coating causing it to fail. This can be overcome with a topcoat of paint.
- Because e-coat is immersive, coaters are always concerned with trapping air in sealed corners or carrying over solution in non-draining voids in parts .
- Mil Spec MIL-P-53084
How many steps are in the e-coat process?
The total number of steps can vary from line to line depending on the most important part of the entire process, PRETREATMENT and CLEANING. For the purpose of listing all the different steps throughout the process Hartford Finishing’s line will be used as a reference, but keep in mind not all e-coat lines include all these stages.