Case study paint line.

The paint line in this case study has two iron-phosphatizing stages followed by three rinse stages, the last being a D.I. water rinse, prior to the electrophoretic coating (e-coat) process. Parts are transported through the paint line by an overhead conveyor.

Oil and dirt.

The high volume of parts that is treated results in large amounts of oil and dirt being introduced into the first bath.

An aspect which is just as important, but often overlooked, is the effect of drag-out: depending on the parts there is more or less fluid on it when they go from one stage to the other. Obviously the fluid needs replenishing, but a much bigger problem is the oil and dirt that gets carried along through the paint line, up to the last rinse stage and even into the e-coat. Click on the photo to the right to see the baths in this case study.

Oil control.

It is essential to control the oil level in the first process step. The lower the oil concentration, the less is carried on to the next stage.

It is also essential to remove the oil from the process quickly. On the parts, the dirt and oil are not separated. Once removed from the parts, the dirt is still in the oil and if removed quickly enough, this dirt is removed with the oil. If the oil remains in the bath for a longer period of time, the chemistry will separate both and distribute oil and dirt through the medium completely.

Measures to remove the oil from the installation in this case study included:

• a static, conventional oil separator
• a floating skimmer, added later to try and remove oil from the surface
• manual removal of oil, with a vacuum cleaner, once every week

Despite these measures, the bath was showing much too high oil and dirt concentrations. The static oil separator required manual skimming of the accumulated oil. What was skimmed off was 90% cleaner; the oil never seemed to build up to a thick layer.

Suparator® oil control.

To control the oil, the installation was fitted with a Skim & Treat® system, based on an 86/240GR02 Suparator® separation system and a 91/2x50/104F Suparskim® floating skimmer.

The images to the right show what the bath looked like before the installation, right after the start up, and one day later. These pictures are taken with full production going on.

The 86/240 Suparator® separation system immediately started to accumulate and concentrate oil. Initially there was only foam visible on the surface, but gradually the build up of an oil layer underneath it could be observed.

The pictures to the right very clearly show how the Suparator® principle collects and concentrates the oil. Notice that there is no oil layer in the front of the unit. In the close-ups you can see how pure, viscous, oil creeps over the oil weir.

To keep the oil concentration low, it is essential that the amount of oil that is removed, matches the amount of oil that gets into the bath. For this installation the daily amount of oil that was carried in, was calculated at 10 liters. The first day 12 liters of pure oil were separated from the bath.

Notice how black the oil is; this is oil with the dirt still in it. It is also clearly visible, from the way it adheres to the wall of the bucket, that this is viscous oil with no surfactants or water.