METHOD FOR PREVENTING QUENCH STAIN OF TIN PLATING LINE

PURPOSE:To prevent the quench stain occurring in circulating water by executing back washing of a filter device in a short period of time to suppress the impurities in the cooling water in a quench tank at a specified level. CONSTITUTION:The automatic back washing type filter device 7 and a replenishing tank 11 for storing the overflow from the quench tank 2 are provided in circulating water piping systems C, D for cleaning to feed water to the quench tank 2 in the case of quenching of a steel plate 1 subjected to a reflow treatment in a tin plating line by immersing this steel plate into the quench tank 2. A motor-operated 3-way valve 8 and 5-way valve 10 are changed over for the purpose of back washing to replenish the overflow water from the replenishing tank 11 to the above-mentioned filter device 7 when the drop of the filter capacity is detected by a differential pressure gage 12. The impurities, such as tin hydroxide, deposited on filter media, are then back washed by the pump pressure of a filter pump 9, by which the filter media are rinsed. The back washing water is drained via the 5-way valve 10 to a drain gutter 13. The back washing is stopped by changing over the motor-operated 3-way valve 8 and 5-way valve 10 and the normal operation to supply the circulating water for cleaning is executed when the recovery of the filtration capacity is confirmed.