As we all know, pretreatment and electrophoresis processes are vital for automobile coating. The apparent quality of electrophoresis would determine the finish coating quality, for instance glossiness and skinning. In order to ensure the apparent quality of electrophoresis coating, the filtration equipment are installed in the pretreatment degrease and water washing circulation loop, electrophoresis tank circulation loop, ultrafiltration washing for deionized circulation loop after electrophoresis, therefore the tank liquid and circulation loop liquid would be largely filtrate.
The following impurities exist in the pretreatment and electrophoresis processes: dust in automobile, scrap iron, weldments and sealant, other mechanical contaminant brought by fans and flights, coating scrap and spherical particles. However, the bulges would be very obvious after electrophoresis coating, also increasing the tri-plane roughness, thus making more labor work on the electrophoresis polishing. So, the impurities should be wiped out thoroughly by filtrating.
What’s more, the quality of filtration equipment also has a great influence on the efficiency of electrophoresis. The types of filter that are applied in the automobile coating industry are the following: centrifugal filters, bag filter, deiron filter, basket filter and cartridge filter. The deiron filter is considered as an optional by putting a high power of magnet into the basket filter or bag filter, thus absorbing the iron scraps maximally, also by this way increasing the bag’s serve time. Besides, oil contamination is a one of the major reason of shrinkage during coating, so eliminate the oils is greatly needed.
The types of filter bag applied in the automobile coating are as follows:
As the nylon NO material is not acid-resisting and the electrophoretic painting is faintly acid, the nylon NO is usually used as a filtration element for degrease and priming coat, but polypropylene is usually not applied in the electrophoretic system.
The filtration process has a great impact on the final electrophoretic quality. The dust in automobile, scrap iron, weldments and sealant should be removed in the pretreatment process. In the before, the 200um mesh nylon filter bag is applied in the pretreatment process, but some impurities couldn’t be fully eliminated, which gives a burden for filtrating the electrophoresis process and influence the apparent quality of electrophoresis coating. Later, the step-down filtration solution is applied to solve this problem. The filter bag mesh with 150um nylon, 100um nylon and 50um polypropylene are then used in the pre-degrease process, main degrease process and water washing process. The filtration efficiency has largely increased by applying that way, and with proven positive feedback.
| Process | Filter Element | Mesh/um | Replace Frequency/ day |
| Pre-degrease | Nylon NO | 150 | 5 |
| Main degrease | Nylon NO | 100 | 8 |
| Water spraying | PP | 50 | 15 |
| Water washing | Durable PP | 25 | 15 |
| Electrophoresis tank | Melt and blown PP, oil-absorption, absolute precision | 25 | 15 |
| electrophoresis UF inlet | Melt and blown PP, oil-absorption, absolute precision | 25 | 15 |
| UF 1#，2#，3# | Melt and blown PP | 25 | 22 |
| Deiron water 1#，2# | Melt and blown PP | 25 | 22 |
Several tips to notice in manufacturing - Requirements in filter seal
Absolute seal is needed for filter itself, interior and exterior of the equipment should be totally sealed, in case of any foreign impurities flow into clean liquid end. If not well sealed, the impurities in the electrophoresis tank would not be totally removed, and then the final apparent quality is affected after electrophoresis coating.
