February 03rd, 2021
In this blog we will explain how choosing the right bearings in the automotive hinge can help to reduce some of the paint defects created during e-coating, thereby reducing rework. By choosing the right bearing for your hinge, you can improve quality, ramp up productivity and drive down costs.
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.
Great paintwork is vital - Colour and paint provide the vehicle with an appearance that promotes brand recognition and thus good sales figures. And much more: strong, long-lasting resistance to unavoidable mechanical, chemical and physical “attacks” during the car’s service life is absolutely essential.
Painting defects can cause severe rework during the coating process and even corrosion over the life of the vehicle. Problems can emerge in the painting process that lead to debris and the need for rework. This has a direct impact on output and cost.
Such rework can lead to:
This results in increased overall cost of running the line. Thats why “Paint work should always be right first time”.
There are more than 40 defects and problems that can occur while automotive coatings are being applied or soon after, especially during the bakes. These defects hurt appearance and may compromise the protective ability of the coating. When they occur they must be sanded and repaired, which can lead to additional defects. The best way to fix defects is to prevent them occurring!
Several paint defects (embedded particles, pinholes and runs and sags) can occur at pivot points. These specific defects can be caused by contamination and dirt. Boiling and cratering are other defects that can occur at pivot points. These can be caused by problems associated with conductivity.
During the painting process, every exposed surface gets coated this includes the bearing and bearing flange edge because they are fully conductive. Robots open and close all of the vehicle’s panels that operate on a pivot point: tail gates, hoods, doors etc. during the painting process, this causes previous paint layers to flake off as the hinge runs against the bearing, and the bearing against the rivet. This causes debris to disperse and fall.
The construction of the hinge can lead to contamination during painting.
When the pivot point is moved, irregular PTFE flakes can form. These then settle on the surfaces around the hinge pivot. The particles then get coated with paint during the painting process and remain visible under the paint surface.
Defects can also occur due to conductivity-related issues such as craters. Craters can be caused because of a lack of conductivity at a hinge or pivot point or because of electrical discharge issues.
Boiling can also be caused by conductivity issues. If the bearing or assembly is wrong and there’s electrical discharge in the bearing area, boiling damage can occur.
A good electrical conductivity is required to guarantee an undisturbed painting process of the car body. Conductive pivot points are generally needed if no other conductive connection is assembled to the exterior part of the chassis (side door/trunk/hood). Conductive points provide the electrical connection between hinge parts (pivot points on naked car body) to ensure current is flowing over the whole car body. Otherwise craters or insufficient painting can occur.
Common paint will stick on every conductive surface. If the complete bearing is conductive, paint will stick in the gap of the pivot points.
NORGLIDE® Bearings significantly reduce paint defects associated with using fully conductive hinge bearings. A NORGLIDE® Bearing is made with non-conductive material and added conductivity notches to allow paint to flow but not stick. This in turn results in:
This is the composition of your traditional type Metal-Polymer PTFE bearing. The steel backing topped with bronze particles coated with thin (Max. 40µm) PTFE conductive tape. As it’s completely conductive, a paint layer builds up at the pivot point during the painting process. This can flake off creating loose paint debris when the hinge is moved.
NORGLIDE® Bearings, on the other hand, are constructed of a strong steel backing with a thick layer of non-conductive PTFE tape (250µm). Because of this thick non-conductive PTFE layer, there is no excess build-up of paint around pivot points, reducing the likelihood of problematic paint.
NORGLIDE® Bearings also offer a solution to the problem of PTFE flakes. Even with high pressure on the bearing flange and cylinder, the thick PTFE compound might deform but will not crack. This means that no PTFE compound flakes will be created, reducing contamination, paint debris and crack-off.
During our manufacturing process the bushing is formed with raised notches that will later be removed by our forming machine. The non-conductive layer at the notches is then removed to create conductive points to allow current flow through the hinge. NORGLIDE® Bearings provide excellent paintability through tailor-made conductivity while simultaneously maintaining an electrically insulating top layer to create paint separation within the pivot points.
Electrical resistance values of pivot points should be less than 1000 Ω to achieve a satisfactory painting result. A hinge using NORGLIDE® Bearings with notches can achieve less than 1 Ω.
The notches of NORGLIDE® Bearings provide conductivity through metal to metal contact between the hinge halves which is necessary in the vehicle painting process. The non-conductive top layer of NORGLIDE® Bearings separates the paint from either side of the hinge halves. When the part is rotated the paint doesn’t flake off which means in the upcoming coating stages the chance of embedded paint debris and thus rework will be reduced.
With conventional bearings, paint damage around the pivot point leads to corrosion over time. With NORGLIDE® Bearings, the excellent painting quality around the pivot points further postpones a potential corrosion effect and increases corrosion resistance over the life of the vehicle.
In this white paper we explore in more detail the automotive e-coating process and the problems that occur. We put our innovative NORGLIDE® Bearing to the test to prove the effectiveness of reducing paint bridges at pivot points and present the results.
Saint-Gobain 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 and high quality.
When it comes to E.P.D. NORGLIDE® PTFE Bearing solutions with this unique design utilizing the non-conductive/conductive bearing is the difference between a perfect finish and rework.