So, you want to learn about E-Coating? You’ve come to the right place!
Sometimes referred to as electrocoating, electrophoretic painting or electropainting, e-coating is a high-tech process in which metal components are covered in a protective finish by submersing them in a chemical bath and applying an electrical current.
Once a part is submerged into a specially designed e-coat paint tank, the paint particles are positively charged with electricity. The positively charged paint particles are then forced to the part, which is grounded. Once the coated part emerges from the e-coating tank, the process results in uniform paint thickness on the part. This process means it can endure the harshest conditions, ensuring a long-lasting finish that stands the test of time.
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Steps in the E-Coating Process
1. Pretreatment
The e-coating process begins with cleaning and pretreatment of the parts to prepare them for painting. The cleaning process removes soils that would otherwise cause surface blemishes. Pretreatment promotes good paint adhesion and contributes to coating performance. Cleaning and pretreatment also protect the e-coat tank from contamination.This process typically includes cleaning, rinsing, activating (if a zinc phosphate coating will be used), phosphating, rinsing, passivating and a final rinse with D.I. / RO water before entering the e-coat tank.
2. Cleaning
The first step in the pretreatment process is the removal of dirt, oils and other soils that will interfere with development of a good quality phosphate coating, good paint adhesion or cause surface defects. The cleaner used will depend on the soil to be removed and the substrate. While alkaline cleaners are the most common, the pH will depend on the condition of the part.
Proper cleaning of parts requires a combination of spray and immersion stages. The spray stage provides mechanical scrubbing of the parts. Immersion is able to reach areas of the part that may be inaccessible to the spray.
3. First Rinsing
The immersion rinse stage following the cleaner is ambient city water. This rinse is used to remove any residual alkaline cleaner or soils before phosphating.
4. Activating (For Zinc Phosphate)
Immersion conditioning rinses provide sites on the part surface that promote the formation of Zinc crystals in the Zinc Phosphate Pretreatment bath.
This stage is used to increase the number of phosphate crystals, decrease the size of the crystals and generally improve the phosphate coating.
5. Phosphating
Applying a zinc coating is the most critical part of the pretreatment process. This makes the part ideal for paint bonding and improves corrosion resistance.The crystal size of the phosphate coating impacts paint bonding capacity and corrosion resistance. A large crystal structure is more porous, has poorer corrosion resistance and requires more coating to achieve a complete film. A fine-grained, tight, uniform coating will provide the best performance.The composition of the bath, the temperature, exposure time and the previous cleaning process will affect the phosphate composition and crystalline phase.
6. Second Rinsing
The rinse stage following the phosphate is city water.
7. Passivating Rinse / Seal
The non-chrome rinse neutralizes any residual water-soluble salts to prevent humidity blistering, fills in any voids that are present in the Zinc Phosphate layer and promotes corrosion protection.
8. D.I. / R.O Water Rinse
This rinse uses low conductivity water to make sure contaminates are not carried into the e-coat tank.
9. Part Wetting / Drying
The e-coat process will work with wet parts or dry parts. The choice to dry or not to dry is a system consideration. If a dry off oven is used, it should be about 5 minutes long, operating at 275 to 350°F. A correctly designed dry-off oven will utilize air during the drying process. The duct work should discharge directly onto the parts with sufficient velocity to break up the moisture for easier drying.
If a dry-off oven is used, the parts must be cooled to room temperature before they enter the e-coat bath. Wet parts shorten processing times, reduce capital equipment cost and reduce operation costs.
Proper cleaning and pretreatment will promote robust performance.
A Brief History of E-Coating
The e-coating process was used in the early 1900s to apply latex to cloth to make rubber gloves.
With e-coating, the substrate is immersed in a bath that may consist of paint, epoxy or other water-based solution. An electric current is then used to attract the particles that are suspended in the liquid solution and deposit them onto the surface of the substrate.
Low-E coating removal machines are equipped with two operating heads with grinding wheels. Thanks to special sensors, the machine detects the low-e coating: the grinding process is accurate, facilitating the subsequent application of the frame.
Low-E coatings have been developed to minimize the amount of ultraviolet and infrared light that can pass through glass without compromising the amount of visible light that is transmitted. When heat or light energy is absorbed by glass, it is either shifted away by moving air or re-radiated by the glass surface.
A low E coating in combination with a tint is often referred to as “solar glass”, and can have a solar heat gain coefficient (g-value) of as low as 0.14 – meaning 86% of solar thermal energy is reflected away from your home.
The thermal transmittance (U-Value) of Low E glass performs equally well, regardless of whether it is on surface 2 (the cavity surface of the outer pane) or surface 3 (the cavity surface of the inner pane). But surface 3 is recommended as it does impact the optical effects and is the industry standard.
Zinc plating is cost-effective, readily available, and can be applied to a wide range of metal substrates. However, it may not offer the same level of coverage as Ecoating, Ecoat, EP Coating and is less effective in protecting recessed or hard-to-reach areas.
The coating is highly resistant to many chemicals, solvents and detergents. E-Coat should provide six months to one year plus shelf life and wear. There are some design limitations to remember when thinking of E-Coat. Many materials cannot withstand the heat during the baking process.
The coating is thin, non-toxic and virtually colorless. Low-E glass benefits are immense as it works to minimize the amount of ultraviolet and infrared light that can pass through the glass by reflecting it away.
Intended Application: Anodizing may be better for corrosion and wear resistance, while e-coating may be better for achieving a specific color or texture.
In 2005, glass manufacturers introduced the modern, state-of-the-art low-e coatings, which feature three layers of silver and multiple layers of dielectric material in over 12 layer stacks as thin as 300 nanometers.
E-Coat is an electrically-applied paint coating. E-coating was developed originally for the automotive industry because it is economical and provides superior coverage, adhesion, and corrosion resistance. It coats any metal (aluminum, zinc, brass, steel) that conducts electricity.
To achieve an optimum effect and reduce voids exposing bare metal, a general recommendation is that powder coating is applied at a minimum film thickness of 2.5 – 3.0 mils.
How long do Low-E windows last? Windows coated in Low-E glass can last anywhere from 10-15 years. Of course, proper maintenance can add years to the lifetime of your windows. We also find that the effectiveness of hard-coat Low-E glass lasts longer in most climates.
While e-coating can provide many of the same benefits, powder coating results in a thicker more durabe finish. In addition, most e-coats are not UV stable, so powder coating lends increased protection to products that face exposure to the elements.
E-coating is an environmentally friendly process, using few-to-zero HAPS (Hazardous Air Pollutants), low VOCs (Volatile Organic Compounds), and it is OSHA-, RoHS- and EPA-approved.
Introduction: My name is Lidia Grady, I am a thankful, fine, glamorous, lucky, lively, pleasant, shiny person who loves writing and wants to share my knowledge and understanding with you.
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