E-coating is a form of electrophoretic deposition (EPD). Like powder coating, this is a metal finishing process, that involves applying a coating to a substrate to enhance and protect it.
There are differences to powder coating, however, in both the process and the finish it provides.
Although both e-coating and powder coating are forms of electrophoretic deposition, e-coating is the closer of the two in technique to electroplating. It involves submerging a substrate in a bath containing a water-based solution such as epoxy or paint.
You then pass a current through the liquid solution. This attracts the particles suspended in the liquid to the surface of the substrate. This process continues until you reach the desired level of thickness for your coating. You can regulate this by increasing or decreasing the voltage level of the current passing through the solution.
Once you have coated the substrate, you cure it in an oven. This promotes the cross-linking of the polymers in the coating.
In contrast to e-coating, powder coating is a dry coating process for metal finishing. You apply a dry powder to the surface you wish to coat, through an electrostatically-charged spray gun.
The powder is a precise combination of different ingredients, including pigments, resins and curing agents. Charging the powder causes it to adhere to the surface. As with e-coating, to complete the process you baked the powder-coated surface in an oven. This causes the particles to melt and fuse together, creating an even, tough outer shell.
Typically, e-coat metal finishing thicknesses range from around 15 microns to 30 microns.
Thickness depends on the end-function of the substrate you are coating.
At the further ends of the thickness scale, you can apply clear, acrylic undercoats at 10 microns or under; but you can extend thicknesses up to around 40 microns for surfaces where tough environmental conditions apply.
The applications parameters for e-coating are wide and you can vary them according to the thickness of coating you wish to achieve.
The process variables that enable you to do this are:
When you have a given percentage of solids and bath temperature, you can vary the voltage of the current to determine how much coating you deposit. The higher the voltage, the thicker the e-coating.
On the other hand, if you are working with a set voltage, you can increase the solids or the bath temperature to increase the thickness of the e-coating.
There can also be secondary factors that influence thickness, such as dwell time, immersion time or pH.
The cost for applying an e-coating finish will vary according to several factors:
There are also options to apply second layers or topcoats to optimise the performance of the coating.
This type of electrocoat system can coat any metals or objects, as long as they have sufficient electoral conductivity, within the 0–400v range.
This conductivity is essential in ensuring the metal finishing process will work, attracting the particles in the solution to the substrate.
With stainless steel, however, the main issue in successfully applying a coating is in its pre-treatment.
Common pre-treatment processes involve the use of alkaline cleaners, to thoroughly remove oil and grease. When it comes to hard metals like stainless steel, the alkalinity in the cleaner solution must be strong enough to remove the kinds of oils typically used in manufacturing parts.
After cleaning, but before applying the e-coat, stainless steel surfaces also require an additional layer, known as a conversion coating.
This promotes adhesion and chemical compatibility. The conversion layer is often a zinc phosphate layer.
When coating stainless steel, choosing the right conversion coating system is essential to the metal finishing process. Typical phosphate layers do not work well with stainless steel.
The reason for this is that stainless steel is designed to resist chemicals, and these properties may also make it difficult for the conversion layer to adhere to the surface.
One solution is to apply the e-coat direct to the metal. But to do this, you must ensure a high level of pre-treatment cleaning, usually with a light mechanical blast or peen.
You can apply a topcoat over an e-coat. In fact, you can apply a powder coating on top of an e-coated surface.
This allows you to make best use of the different advantages that each process provides:
With e-coating, you have excellent control of coating thickness, and a thorough distribution of the coating, including on hard-to-reach areas
Powder coating delivers coatings that are aesthetically attractive, long-lasting and sustainable, and you have a huge colour range to choose from.
Essentially, there is room for both processes, as they deliver different finishes, but will also work together.
Consider the type of finish you require, and what the end-application of your part, product or surface will be.
For more information about powder coating, or a quote, please contact us.