Problem
At Radson b.v., Zonhoven (Belgium), radiators are de-greased and phosphatised in an Eisenmann conveyor spray booth station before immersion painting. The conveyor line includes two active zones, each with a storage volume of 13,500 l, and completes a full rotation 18 times per hour. Approx. 6,000 m²/h surface are processed every day. The product used is a combination de-greasing and ferric phosphatising substance (pH value approx. 5.0 and average temperature approx. 40° C). The problem of the existing installation was the relatively short operating life of the processing liquid, which had to be completely replaced after about 3 weeks of two-shift operation. The reason for this short life were the tramp oils that were attracted (approx. 200 l/day) and the concentration of phosphate sludge (approx. 35 l/day).
Solution / Realization
In 1999, STA installed a combination bath maintenance system consisting of 4 S-15 centrifugal separators (2 in each active bath area) for separation of solids and a DPS-1050 tramp oil removal system at bath zone 1, each connected to the baths by the by passmethod.
Result
Up to 32 – 40 kg of compact, cake dry phosphate sludge is separated from both active zones per shift and approx. 80 – 100 l tramp oil is separated from the main phase, in used oil quality. When the baths were replaced at the end of December 1999 no significant sludge deposits were found in either of the active zones. The nozzle fittings in the spray booths were free from solid deposits, with the result that maintenance expenses were minimal. The bath replacement intervals could be extended from 3 weeks to their current length of 5 to 6 months, performed as part of the semi-annual preventive maintenance program. Some of the existing liquid is reused for priming the new baths.
This resulted in the following savings:
- Reduced personnel costs as cleaning costs are reduced considerably
- Savings over previous costs for bag filter inserts
- Reduced costs of sludge disposal due to lower weight of sludge (compact sludge with low residual moisture, see illustration)
- Reduced disposal costs resulting from bath rejection
- Low costs of chemicals and fresh water for new bath priming
The investment cost of approx. 107,000 € was recovered after 18 months.
Furthermore, the measure brought the following advantages:
- Better working hygiene due to continuous separation of harmful substances, such as mold, bacteria, sludge flocs and other residues
- Reduced annoyance caused by bad odors through constant aeration of the liquid
