Alkalinity Loss in Cleaning Stage of Washer

Article From: Products Finishing,

Posted on: 12/1/2001

Question: We are experiencing significant drops in the alkalinity of our first stage cleaning bath in a seven-stage pretreatment line.

Question:

We are experiencing significant drops in the alkalinity of our first stage cleaning bath in a seven-stage pretreatment line. Tank size is 5,200 gal, and initial chemical charge is 150 gal of cleaner. We are losing as much as 8% in concentration in a period of 2-3 hr, adding as much as 45 gal/day of cleaner to keep the concentration at the 3% starting point. Besides dragout of stage one or leaking, what can be happening and how do we troubleshoot?L.S.

Answer:

This is a little difficult to answer without knowing more specifics regarding this pretreatment system. What has changed? How much has it changed by? Why is this coming up now? Did you previously add 10 gal of cleaner and now are adding 45 gal? Whenever troubleshooting, it is always very important to reconstruct the previous history as much as possible.

I also have to point out an inconsistency in the numbers you gave me. You mention a decrease in concentration of 8% in a matter of 2-3 hr. This equates to about 45 gal of cleaner concentrate. In the next sentence, it is stated that you add 45 gal/day of cleaner. Going through this volume of cleaner in 2-3 hr would be significant for any pretreatment system and would make me suspect a leak into a collection pit or some spray nozzles that are severely out of alignment. There are a couple of things you could do to check if this were the case. If you have an automatic fill valve on the tank, it should be disabled or bypassed when the liquid level gets low. Then measure the amount of volume loss versus time. If your are losing 8% in 2-3 hr, and assuming most of it was due to leakage and/or overspray, that would mean you would lose about 1,500 gal in this time. That would equate to about 500-750 gal/hr! That is not a mere leak and has to be accounted for somehow. That size of a leak ought to register in the wastewater treatment system. If it were largely due to nozzle misalignment, then it would likely be spraying into the rinse tank immediately following the cleaning stage. Cut any overflow from the rinse tank and see if you measure an appreciable increase in concentration of cleaner in the rinse stage and/or any significant increase in liquid volume.

On the other hand, if you are actually loosing 45 gal/day of cleaner, this does not seem quite as extraordinary. Given the size of the washer stage, I would assume you are pretreating relatively large pieces of metal with a significant surface area. If this were being done over a two- or three-shift operation, I would not be particularly surprised to see you go through that volume of cleaner, especially with a liquid concentrate as you appear to be using. A two- or three-shift operation doing large parts could result in the dragout of possibly several hundred gallons (depending on part geometry). This combined with the neutralizing effect of many lubricant components would be enough to lower the concentration of the cleaner by this much per day. My experience with liquid cleaners has been that they have several advantages including automatic addition capability as well as being easy to mix, but they often do not have the same longevity as a similar powdered cleaner. It is possible there are less "builders" in the liquid formulation. This lack of buffering and reserve alkalinity may also be contributing to the relatively rapid decrease in concentration.

 


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