BUILD UP, CONTROL AND REPLENISHING:

Fill up the tank with DM water upto the operating level and start heating to maximum of 55 deg C. Add Passiphos - 683  at the rate of 250 to 500ml for every 100 litres of the bath so that bath acquires.  a) a pH of 4 to 4.5 and/or b) an acid pointage (concentration) of 4-6. If necessary (if the pH of the bath becomes below 4.0), while mixing the bath thoroughly, repeating the addition, until the target pH of 4.0-4.5 is achieved.

These parameters (pH and Total acid pointage), are established, maintained and controlled as follows:

a) pH of the bath: Check the pH of the bath by means of a pH meter or pH paper(narrow range) A fresh bath prepared as above will have pH between 4 and 4.5. and also it has to be maintained through out between 4 and 4.5.

If at any point of time, the pH is less than 4.0 (due to acidic carry over from preceding rinse bath), then add Rxsol Passivation Liquid  at the rate of 50 ml per 100 litres at a time, while mixing the bath thoroughly, repeat the addition, until the target pH of 4.0-4.5 is achieved.

If the pH goes beyond 4.5, then Passiphos - 683  is added at the rate of 500ml for every 1000 lit at a time, while mixing the bath thoroughly, repeat the addition, until the target pH of 4.0-4.5 is achieved. At any point of time, pH should never be allowed to exceed above 5.0 or depleted below 3.5.

Total Acid pointage: (concentration):

Total Acid pointage: (concentration): has to be determined by simple titration. as below

• Transfer 100 ml of Passivation bath solution to a 250 ml conical flask.
• Add 4 - 6 drops of phenolphthalein indicator solution.
• Titrate with 0.1 N sodium hydroxide solution until a permanent pink colour is reached.

The number of mls of alkali added is the total acid titration. This should be 4-6 and also has to be maintained in the range of 4 to 6 mls.

If at any point of time, the pointage is less than 4 (due to acidic carry over from preceding rinse bath), then add Rxsol Passivation Liquid at the rate of 50 ml per every 100 litres of bath size, at a time,while mixing the bath thoroughly, repeat the addition, until the target pointage of 4-6 is achieved.
 

If the pointage is above 6.0, then Passiphos - 683   is added at the rate of 500ml for every 1000 lit at a time, while mixing the bath thoroughly, repeat the addition, until the target pointage of 4-6 is achieved. (Normally, about 0.5 to 1.0 litre of Passiphos - 683   per 1000 litres bath of Passiphos - 683   will be needed for increasing pointage by 1 unit)