Water quality needed for plating and rinsing

A. Hi. The only rule of thumb I have ever heard is 1000:1 dilution as a good starting point for many plating tanks and 500:1 for cleaning and prep rinse tanks. You are probably right that they are using more water than necessary since experience shows that most shops are able to reduce their flows after study, but actually you don't yet KNOW that they are even using enough water, let alone too much :-)

Unfortunately, you won't know for sure until long trial-and-error proves something. And even then, unless the owner is very hands-on, you still won't be able to track the rejects attributable to poor rinsing.

It's a very, very, thorny problem since you can't even learn much about barrel plating from running hull cells. But I would approach it the other way: people successfully run major production on barrel lines with 5 GPM total rinse water per line depending on the size of the barrels. So that might be the way to do it: set the water usage goal at 5 GPM.

But as for trying to limit the water flow in that "final rinse" that you mention, I cannot agree with trying to figure out what you can get away with in terms of shipping dirty parts to your customers :-)
... you should probably recirculate the final rinse through a de-ionizer instead.

Luck and regards,

A. Read Ted's work on rinsing at this site. Simply stated, additional rinses. Spray rinse addition does not do much good for barrels, but does not hurt. Controlling rinses with conductivity controls is one help used by many. Flow restriction that can not be tampered with is used by some, where the overuse of water is abused.

Recycle water with a RO unit is very cost effective. DI is less cost effective, but simpler. Also, better water quality equals better rinsing and less process tank contamination.

The best answer is to hire a consultant that is qualified for one day to survey the plant and offer recommendations.

Volumes have been written on this subject, and any short and simple answer from here, not knowing the real circumstances is not going to be of that much help. Sizing is important to cost effectiveness and the bottom line is everything.

A. Hi Vijay. I've never seen a quantitative answer to this question, even in "Water and Waste Control For the Plating Shop" ⇨
but if your water is hard, it doesn't ever hurt to deionize it.

A "rule of thumb" sometimes applied as a first cut to determine required rinse rates, is that you should dilute the solution between 500:1 and 1000:1. Good luck.

Regards,

A. Your tap water is probably much different than mine or that of other readers, Mr. Nadeem, so it is hard to say whether tap water is good enough. Thousands of shops use tap water, but many people also think that only deionized water should ever be used in a plating shop. Ignoring economics, the purer the water the better. An excellent discussion of the issues can be found in Kushner's "Water and Waste Control for the Plating Shop". Best of luck.

A. Hi Pat. This is discussed in pretty good detail in Kushner's "Water and Waste Control for the Plating Shop" where he cautions against such estimates, but quotes the work of Soderberg and Hogaboom. For a single guesstimate, 1 gallon per thousand square foot is as good as any other, but it's not very good :-)

Take a baking pan or similar rectangular object to your kitchen sink, wet it, and hold a bottom edge horizontal for a few seconds. Then tilt it and be surprised at how much water quickly runs off at the corner. This raises two points: one, always try to rack with a corner down instead of horizontally; two, such estimates are very very rough.

You may be interested in my old booklet which is on-line here: "20 Ways to Reduce Water Usage in Plating Shops". Good luck.

A. Ref book/russian/osnoby galvanostegy/year1957/page604. Dragout for simple forms/sheets/ around 50-100 ml/sq.meter.

Good luck

A. Dragout on a flat, vertically hung sheet will be approximately 0.9 to 1.5 gallons per 1,000 square feet.

The lower number corresponds to a drain time that is long enough for there to be no further dripping. The higher number corresponds to a minimum drain time that allows several seconds between drips.

Thanks to all for your help.

A. Hi Angelo. Personally I don't believe that is the source of the stains. There is D.I. water, as commonly used in plating shops for makeup and rinsing, and then there is ultrapure D.I. water, used in semiconductor electronics and such, that is corrosive. If you have just standard cation and anion cylinders, that would be the common usage. If that is followed by a mixed-bed exchanger designed for ultrapure water, yes, that can be corrosive.

Regards,

 Thank you, Ted,

We do use the DI for our makeup for sure. We use city water for the in-between rinses and then DI for a final rinse. It may be the Sulfur in the Mid Phos EN that is causing the stains as well. Just trying to cover all my bases.

A. Okay, good luck. You can also search the site for "electroless nickel stains" and find lots of input.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 2019