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Electro Deposition

Ultra filtration provides a closed rinse system for electro deposition by removing paint particles and impurities from the rinse water using polymeric membranes with pore sizes small enough to retain organic molecules but allow water and smaller molecules to pass through. The ultra filtrate is then used to rinse parts emerging from the tank, creating a continuous rinse-filtration-rinse cycle that recovers over 95% of dragged out paint solids. Key factors in the ultra filtration rinsing system include maintaining a minimum flux rate of 20L/m2/hr and periodically purging a small amount of permeate to drain to control contaminant levels in the bath.

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284 views2 pages

Electro Deposition

Ultra filtration provides a closed rinse system for electro deposition by removing paint particles and impurities from the rinse water using polymeric membranes with pore sizes small enough to retain organic molecules but allow water and smaller molecules to pass through. The ultra filtrate is then used to rinse parts emerging from the tank, creating a continuous rinse-filtration-rinse cycle that recovers over 95% of dragged out paint solids. Key factors in the ultra filtration rinsing system include maintaining a minimum flux rate of 20L/m2/hr and periodically purging a small amount of permeate to drain to control contaminant levels in the bath.

Uploaded by

sagarzende
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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ELECTRO DEPOSITION

Ultra Filters : Ultra filters provide adequate ultrafiltrate to operate a closed rinse system efficiently. Ultrafiltration solves the following problem, Loss of excess paint (drag out ) in the rinse water. The concentration of foreign ions (drag in) in the paint tank, from the pre-treatment stage & thereby interfering with E.D. process, the environmental problem of paint particles in the discharge water i.e., purging of impurities from the paint tank by discharging the Ultrafiltrate to the waste.

UF Principle : UF is a pressure driven filtration process. Paint containing water & suspended / dissolved material is pumped across the membrane surface with pore size that are so small (20-100A0 ) that larger organic molecules are retained while water & smaller molecules can pass through' the membrane i.e., permeate, while the retained phase is called concentrate ( reteotate ) & is returned back to the bath. Polymeric Membranes: Ultra-filtration is accomplished by passing the electro-deposition paint over the polymeric membranes. The membrane will not allow the paint portion of the water & paint mixture to pass through its lattices. Ultra-filtration is purely a mechanical process in which the membrane must be specifically selected for the resin system. The net effect of this operation is to remove de-ionized water & any water-soluble ion which may have been introduced in the bath from the extraneous source. These polymeric membranes act as screens which discriminate between molecular & colloidal species on the basis of size, shape & chemical structure. Substances in the electro coating bath above a pre-selected molecular weight - coating particles, in particular-are removed at the membrane while the remaining water is

forced through it by hydrostatic pressure. Ultra-filter water is used to rinse the parts emerging from the tank, thus, creating a continuous rinse-filtration-rinse cycle. UF Rinsing system : The principle is as follows: The paint is pumped through the UF plant & a small portion leaves as the permeate while the majority of the feed to the UF plant is returned to the paint bath. Approximately 90% of the permeate goes to the rinsing stage while approximately 10% is diverted to the drain to lower the bath conductivity by maintaining correction-concentration in the bath paint. However the purge quantity is dictated by the bath conductivity ( i.e., the concentration of low molecular weight contaminants caused by phosphate drag in, bacterial growth etc., in the bath paint.) & evaluation of coating performance in the test laboratory. A typical example of CED bath contaminant level is given below: Traces of contaminants limit (parts per million ) 1. Na 2. Fe 3. Cr 4. Pb < 30 < 100 < 100 < 900-1400

The rinse water is fed back to the paint tank after rinsing off the dragged paint & thereby provides a means of recovery of dragout solids. The large electro coat plants are most often operated with a closed loop multistage rinsing system, where rinsing system consists of both dipping & spraying. In multistage rinsing process, more than 95% of the recovery efficiency can be achieved. The key to the successful UF rinsing system is the ultra-filtrate flux rate. A minimum capacity of 20lt/m2/hrs.is required. A typical example of multistage UF rinsing system is given below: S. no 1 2 3 4 Item Over tank ( UF spray ) 2 stage re-circulated UF rinse(spray/dip) Pure UF Spray D. M. Water Spray Volume reqd. Spray time

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