February 03rd, 2021
When it comes to electrophoretic deposition, or as it is often referred to: e-coating, your components can make all the difference between a perfect finish and having to rework the job. In this blog, we take a closer look at the potential problems that can arise during the electrophoretic deposition (EPD) coating stage of manufacture, and discuss how simply changing your plain bearings can eliminate the two main potential issues: lack of coating and paint flake.
Electrophoretic deposition (also known as EPD, electrocoating, e-coating, e-painting and so on) is the process of coating metal parts. It’s widely used in the automotive sector as the initial chassis coat. It works by submerging the components or assemblies to be painted into an electro paint bath, then applying a charge through this.
It’s a quick and effective way of coating an entire surface, works with a range of materials and can be used for applications from vehicles and vehicle components to appliances and furniture as prime examples. EPD is easy to control, it enables manufacturers to apply a uniform corrosion protective coat to a set thickness.
However, as engineers are aware, this process is not without its challenges, and one of these is the effect of debris from the electrophoretic deposition stage becoming embedded in the surface and impacting on the finish, this can be known as paint flake.
The old saying, “If it can go wrong, it will go wrong” is unfortunately very apt when it comes to e-painting.
For example, there are no fewer than 40 potential defects during the process of painting a vehicle. The odds are against everything going (literally) smoothly, with the electrophoretic deposition coating stage being especially vulnerable.
The main defects in e-painting are:
• Paint flakes can cause contamination. These form debris which if unchecked, will be coated during the e-coating process and remain as unsightly particles. As well as the obvious cosmetic problem, these defects can compromise the protective aspect of the coating.
• Craters in the finish are caused by of a lack of conductivity at a hinge or pivot point. They can also be caused by problems with electrical discharge.
• Boiling damage is another conductivity related problem. This occurs when the bearing or assembly is wrong, and there’s electrical discharge in the bearing area.
If any of these defects occur, the surface should be sanded and repaired: an additional cost and delay.
We’ll take a closer look into how defects can occur during e-coating. Good electrical conductivity is essential for all stages during the initial e-painting.
Conductive pivot points or “earthing” straps are used to provide electrical connection between links/joints to ensure the current flows over the whole assembly. The e-paint coats every surface, and sticks in the gaps in the pivot/hinge points. When the joints are rotated the paint cracks, which can create debris or flakes which are visible on the final coat.
Because conventional plain bearings are completely conductive, the paint will adhere to the bearing in the electrophoretic coating stage. This means that the paint will cross the gap between the joints and the main body, this is known as a “paint bridge”, the result is paint flakes off as soon as the joint is moved. If the conductivity between the assembly is interrupted, this can cause craters or boiling. If this occurs it can result in a poor paint finish and potential corrosion through lack of full coating so complete conductivity through the assembly is a must.
This video demonstrates how rotational movement after the pivot/hinge has been painted can lead to paint flakes when paint bridges are broken.
Saint-Gobain and the family of NORGLIDE® Bearings have a number of materials that are able to support with the e-coating process. The type of material used in this application will depend on the load and the required co-efficient of friction of the link/joint. Our NORGLIDE® materials have been created for non-conductive bearings yet the innovative design allows for the free flow of electricity throughout the whole assembly which then eliminates the potential for paint bridges that create quality issues to the fresh paint. Using NORGLIDE® Bearings removes the potential additional costs for earthing straps thus saving money.
During the manufacturing process, our bearings are formed with raised notches. The non-conductive layer of the notches is then skived off to create conductive points, which will allow current to flow through the hinge. The bearings provide conductivity while maintaining an electrically insulating top layer, causing paint separation within the pivot points.
Corrosion occurs when metal surfaces become exposed. This happens when paint flakes away or metal is not covered correctly, the exposed metal surface will corrode over time. NORGLIDE® Bearings provide the essential conductivity through metal-to-metal contact created by the conductive points and, thanks to a PTFE layer, they also have non-conductive areas which prevents the paint adhering to it, eliminating paint flakes.
E-painting, as stated above, can be used in all different applications and industries, whether you need a bearing for rotational or linear applications NORGLIDE® can be used in an e-coating process. They produce the same result of a non-conductive bearing acting as a “conductive bearing” and removes the need for conductive straps and conductive bearings that can create quality issues like paint bridging.
Saint-Gobain Bearings is a company that has technical engineering locations in all of the major manufacturing countries globally where our engineers are able to support, advise and help your design and manufacturing engineers to ensure that you receive the optimum performance.
When it comes to E.P.D. NORGLIDE® PTFE Bearing solutions with this unique design utilising the non-conductive/conductive bearing is the difference between a perfect finish and rework.