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Zinc plating defects (poor quality metal finishing)
Current question and answers:
November 25, 2020Q. We are supplying forged, machined and subsequently Zinc plated parts to our European customers. This part goes into automotive application. The supply quantity is around 1.5 million per annum.
We are testing one piece per batch for salt spray test (as per customer specs) before the shipment and did not find any issues during test time. But in a very few cases (approx.- 25 nos) a gray color patch mark is observed on face of the part.
These parts were wrapped in VCI bag and packed in corrugated box.
It is our experience that such cases are usually noticed during monsoon seasons, i.e., between July to September period.
We need expert advice for cause of the defect and preferred solutions.
Please suggest
Best regards
- RAJKOT INDIA
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November 2020
A. Hi Manjunath. I may be jumping to conclusions, but the corrosion pattern in the first picture looks to me like it echoes the shape of cardboard corrugations -- indicating (if it's true) that the parts were touching the cardboard box rather than actually being in a VCI bag. So the first thing I would suspect is that the packaging is not always done quite as carefully as we might hope, and occasional parts are exposed to moist cardboard boxes.
Luck & Regards,
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
March 30, 2021
A. Hi Subhasis,
1) use cardboard and pack a few pieces for 72 hours.
2) pack without cardboard some others for 72 hours.
Inspect all parts after 72 hours for black spots, if you have black spot on cardboard use, then a packaging problem; if not, there is not a cardboard problem for black spot, looks like some dripping on parts or touching.
- STERLING HEIGHTS, Michigan
Previous closely related Q&A's starting in:
July 14, 2009Q. OUR ORGANIZATION DEALS WITH VARIOUS TYPES OF ENCLOSURES MADE WITH SHEET METAL (LIKE COLD ROLLED CARBON STEEL SHEETS). I OFTEN FIND DEFECTS LIKE WHITE PATCHES, PLATED SURFACE GETS FADING FEW DAYS AFTER OPENING THE AIR TIGHT BOXES IN WHICH ENCLOSURES WERE KEPT, BLACK MARKS ON THE PLATED SURFACE, RUST FORMATION ON THE PLATED SURFACE.
THE ABOVE ARE SERIOUS PROBLEMS I am FACING IN MY ORGANIZATION.
CAN YOU PLEASE SUGGEST ME THE SOLUTION FOR THE ABOVE PROBLEMS?
CUSTOMER - BANGALORE, KARNATAKA, INDIA
July 17, 2009
A. Mr Subramanium
The defects cited by you constitute post and pre treatment faults that tend to show up after plating is over and some time has elapsed. Here is what you can do.
Set up an audit at your vendor after setting up an approved plating procedure.
OR
Change the Plating vendor.
Better still...
Use a consultant to set up the entire Plating process to avoid such problems.
As a buyer you can only conduct retrospective analysis and then arrive at conclusions of probable causes but a short walk down the plating line with a Plating Consultant and observation of work procedures will save you future agony.
Asif Nurie [dec.]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
August 25, 2009
A. Dear Mr Pal,
Are these problems prevalent during the monsoon period? Is your sheet metal of good grade steel? These two things need to be answered before looking at Plating.
Mr Nurie: your pitching so hard for a consultant makes me seriously want to look at an alternative career. Is business really that good?!?
September 1, 2009
A. This forum is supposed to give free advice. So let us straight go and attend to the problems.
Dear Pal,
You will have to make a visit to the plater and get the details of the supplier of plating chemicals. Call the representative of the supplier and tell him to guide the plater. Check the following:
1.Proper Cleanings are done.
2.Plating thickness is proper (For Zinc 8-12 microns)
3.Chromating is proper
4.See they have good volume of soft water.
5.Proper cleaning after plating and Chromating is a must.
6.Hot water last swill is preferable.
7.Hot air drying is a must.
8.Should not pack air tight immediately after drying. Leave it for 24 hours minimum.
9.Remember to put some moisture absorber like silica gel in the packing box.
Still if you cannot cope with the situation consult Mr. Vahanwala who sits in Bangalore! It seems Mr. Nurie is ready but he stays in Delhi!
Regards,
T.K. Mohan
plating process supplier - Mumbai, India
September 1, 2009
Now that we've heard from the buyer who is encountering the issue, and from a plating consultant, and from a plating shop, and from a supplier of the plating chemicals, every base has been covered :-)
The only summary point I would add is that either:
1). the work must go to a different, better plating shop, or
2). the plating shop must solve the problem, or
3). the buyer must visit the plating shop (whether alone or with a consultant or with a supplier rep) to see the problem and solve it.
Hints from 3rd parties can help you know what to look for, but actually 'walking the line' is usually key because the "story" and the reality usually vary greatly; oftentimes even the shop management is unaware of exactly what the line foreman or the operators are actually doing and which is causing the problem :-)
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey