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topic 52070

Pin holes problem in hard chrome plating



A discussion started in 2003 & continuing through 2017

(2003)

Q. My company is mainly involved in the injection of plastic parts for cars.
Recently, we are facing problems with our new chrome parts, the main problem we face is the surface of the parts have pin holes problem(very small holes that are hard to see until you chrome it).

We have already tried using a dehumidifier while producing the plastic parts, sanded the surface of the mold(doubt it is caused by the mold since the pin hole runs around the part), but we still couldn't solve the pin hole problem.

Does anyone here have any advise?
Secondly, I would like to know what type of mold material should I used when making the mold?
And typically the hardness should be in what range?

Thanks in advance.

Mew, Yu Tsing
Automotive - Shah Alam, Selangor, Malaysia


(2003)

A. To sand blast the mold is completely wrong way. The molds for injection of plastic parts that are to be chrome plated must have the very best mirror finish (preferably they would also have to be plated to avoid rust and reduce scratches). If the pinholes are present before the plating, then something is wrong with your injection parameters or resin. You didn't mention what type of plastic you run. If it is ABS, it has to be purchased as "plating grade". This plastic was designed for plating and for its preparation it will develop microscopic pinholes (locks). Proper plating procedure will level (fill) these microholes and produce a mirror finish.

Guillermo Marrufo
Monterrey, NL, Mexico



(2005)

Q. Dear Sir,

Attached please find herewith photographs of my plated parts. Picture 1 to 3 are plated by using proprietary hard chrome chemical volts 4 ampere per part 8 surface area .41 cm2.

35742

You can clearly see the following problem i.e. pin holes , submicron trenches, etc. These parts are electroclean and back etched Volts 7 time 3 minutes before plating. Further using soft start to avoid hydrogen embrittlement.

Picture four shows very uniform coating without above mentioned faults. I wish that my parts should also look it picture 4.

Your kind suggestion in this regards would be highly appreciated.

Yours Truly

Tayyab Kausar
- Pakistan


(2005)

? What is the substrate?

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


simultaneous (2005)

? Tayyab Saheb,

Information you have provided is not enough to comment specially when we are talking of functional coatings. Kindly mention chemistry, thickness, base metal etc.

Sorry I forgot trivalent chrome, impurities (both inorganic and suspended in bath if you know).

Regards

Qutub Saify
- Ajman, UAE


(2005)

Q. The material is mild Steel AISI 1020 case hardened.

With best wishes and regards

Tayyab Kausar [returning]
- Pakistan


simultaneous (2005)

Q. I am using Trivalent chrome solution and the manufacturer claim that it is fluoride free. The thickness of the coating is 2o micron. and the pictures are from the fresh bath not over 30 hours of plating time.

Looking forward to your valued comments.

With best wishes and regards

Tayyab Kausar [returning]
- Pakistan


(2005)

THERE ARE PROBLEMS BUT SOLUTIONS ARE ALSO available.
WE TRY TO ANSWER(WHAT WE HAVE OBSERVED) IN OUR OWN WAY, FOR SOME THEY MAY BE USEFUL FOR OTHERS OF NO USE.
1.REDUCE TIME IN ETCHING,UP TO 30 SECONDS
2.BASIS METAL PITTED.
3.IMPROVE SURFACE FINISH.
4.REDUCE USE OF MIST SUPPRESSORS
5.FILTER THE SOLUTION

ajay raina
Ajay Raina
Ludhiana, Punjab, India


simultaneous (2005)

You will not get a Hard Chrome deposit free of pores using Trivalent chrome. Try hexavalent.

Rudolf Kempf
- Haan, Germany


(2005)

Tayyab.
You say the chrome solution have been in production only for 30 hour. Have you electrolyzed the chrome solution before you used for production. I will recommend you do an analysis of the trivalent chrome in the solution.

Regards

anders sundman
Anders Sundman
3rd Generation in Plating
Consultant - Arvika, Sweden



(2005)

Q. Dear Sir,

Yes the solution was electrolyzed before putting into production.

Further I would like to thank all of you for sparing your valuable time for this problem and above of all I would thank everybody associated with finishing.com to provide such a wonderful platform for sharing problems and ideas.

Dear Ted,

Your kind valued comments regarding Pin holes etc are anxiously awaited.

With best wishes and regards,

Tayyab Kausar [returning]
- Lahore, Pakistan,


(2005)

A. Sorry, Tayyab, I don't have the hands-on experience that the other responders have. The only small piece of advice that I can pass on (and I hate to bore everyone with the same reply to so many chrome defect questions) is what some very experienced tech service people from Atotech always taught me: don't even start the head-scratching of trying to figure out what's wrong until you've gone through the shop and thrown away every piece of used sandpaper and used emery cloth that someone might possibly touch that shaft with.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



(2006)

Q. Dear sir,
I have some questions about my works listing below,
1. My business is hard chroming in piston grooves, to a thickness of 0.25mm to 0.35mm standard. when doing this I got a problem always that many pinholes and pits on the surface of the chromed area. what is the cause of this and how to avoid it?
(my component to be chromed is 26cm to 96 cm in diameter and heavy weight. ship engine piston crowns.)
2. After grinding to standard size the chrome thickness is showing slight variation in actual size in thickness. (e.g., actual thickness plated is 0.30 mm but the checking instrument shown only 0.23mm only.) what will be the problem,and how to avoid this?.
3. Any chrome thickness checking instruments can be measure the actual thickness (must be in portable size), please inform to me the product name.
Seeking a good answer,
Thanking you,

RAJAN.V.N.NAIR
HARD CHROME PLATING - Singapore


(2006)

A. 1. Pinholes may come from dust particles in your bath, previous porosity or improper surface cleaning. Improve filtration, inspect previous surface with magnifier lens and improve cleaning to obtain "water break free surface"
2. With a cylinder or flat block that is precision ground before and after chrome you can be sure what is the real chrome thickness. Then, calibrate the checking instrument.
3. There are many coating thickness instruments in the market (Defelsko and Electrophysik are just two brands that came to mind).
Good luck.

Guillermo Marrufo
Monterrey, NL, Mexico



To minimize searching and offer multiple viewpoints, we've combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



(2006)

Q. I'm a chemist in a hard chrome plating shop where we use a conventional bath. We mostly plate crankshafts. Once every two or three years or so, we're visited by a gremlin. Production can be really sailing in the plating shop, then with seemingly no warning, pinholes start showing up all over the place. There seems to be no connection to the bath chemistry - we have 15 tanks running "within parameters" - maybe seven or eight tanks will start showing problems. There seems to be no connection to the current density or surface prep (we clean our sand all the time) or rectifier ripple or anything I can think of. Can anyone tell me anything about this gremlin?

Thank you,

Peter H. Millican
- Denver, Colorado, USA


(2006)

A. It could be suspended trash from the bottom of the tank or it is more probable that you are getting magnetized parts that attract metal filings which cause trees which serve as robbers and then break off leaving the pit. Use a 10 power loop and look at the bottom of the holes. You will see a tree stump near the middle of most of the pits.

James Watts
- Navarre, Florida


(2006)

A. Hi
Just one possibility is the breakdown of UNSTABLE fume suppressants which are known to cause pitting.

asif_nurie
Asif Nurie
- New Delhi, India

With deep regret we
sadly advise that
Asif passed away

on Jan 24, 2016



(2006)

Q. We use a PFOS based wetting agent. Are those unstable? I'm curious about this, because although I've heard they'll (sulfonated fluorocarbons) be around until the sun goes nova, I've seen sulfate levels go up in the solutions and seen inert residues pooling on the surface of the baths. I claim they're inert because they're resistant to HNO3-HClO4 digestions.

Thanks,

Peter H. Millican [returning]
- Denver, Colorado, USA



To minimize searching and offer multiple viewpoints, we've combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



Micro Porosity of Substrate a Major Setback for Hard Chroming

May 23, 2008

Q. We are doing Hard Chrome Plating since last 2 decades with very much success regarding matters like thickness coating up to 1 to 1.5 mm, very good adhesion, hardness up to 65 hrc etc. My question is that usually in small job up to 40 mm dia. x 500 mm long the major problem sometime we face is of pin/blow holes on most of the jobs (particular lot) for a thickness of 0.4mm to 0.5mm even after repeating the process with slow current density the problem occurs. Our degreasing and surface preparation is very best in industry what might be the problem can you suggest me some tip/solutions or is it the material fault.

We regularly plate huge Roller requiring super finishing without pin holes, etc. only this particular job or small jobs creates problems once in a while.

We have facility of shot peening/blasting will this process help to close any micro porosity generated and increase adhension in substrate please suggest.

RATNESH VELINGKAR
DIRECTOR - MUMBAI, MAHARASHTRA, INDIA


May 26, 2008

A. Hi ,

there are many things that can cause pitting / pinholes .

poor base material

poor cleaning

if parts are sand blasted , ensure the blasting media is clean as any impurities could embed themselves in the substrate ( I had that problem recently - cleaned the sand and problem solved ) I noticed that if I soaked item that I was plating in HCl acid after blasting and prior to plating I had no pinholes . the acid dissolved the embedded impurities .

contaminated wax ( water or general dirt etc )

lack of agitation - some times tiny gas bubbles stick to the component and the chrome tries to plates around it -thats what I read in a book , which I found interesting because the general gassing caused by the plating should be enough to disperse the bubbles ?

may I suggest you take note of the positioning of the pinholes on 1 particular part - strip , and re-plate .
if you notice that the pinholes are in exactly the same place , then you will know if it is a problem with the base metal . if they pinhole in different positions , then that should prove that it is a cleaning , etching or plating problem .

hope this helps

Jay Smith
- Essex, UK



Trouble Shooting for the pinhole defect in chromium plating

August 30, 2008

We are running a small scale chrome plating shop.We are facing the pinhole defect during chrome plating. we checked the bath contents regularly and also subject to post heat treatment for avoiding Hydrogen embrittlement. but still we suffer with this problem. What would be the root cause ? whether Cr3+ ions con. is high or other reason ? Please kindly tell me.

Omprakash Premnath
regulator - Madurai, TamilNadu, India



To minimize searching and offer multiple viewpoints, we've combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



April 23, 2009

Q. Dear Sir!
I observe Pin holes just like dots after hard chrome plating in piston rod. I am not find out actual root cause, supplier told this is cause of raw material. Please sir provide me proper out cause from which this problem can be solved.

Crack observed just like net in plated area after hard chrome plating in piston rods.
Please sir give me proper guide line for this problem.

Hare Ram Yadav
Product designer - Gurgaon, Harayana, India


May 14, 2009

A. Are these rods hardened?
in case they are you need to do proper pretreatment

Prashant Soman
- Thane, Maharashtr , India


May 19, 2009

A. Do you have a:
Soak Clean.- Must to be aggressive
Electroclean.- 5 mins in it
Wash
Neutro .- Make it in the same way than electro and put some voltage
Wash
Wash
wash
Nickel/Chrome/
or Hard Chrome

Sergio Sama niego
Mexicali, Baja California, Mexico


August 29, 2009

A. 1.You need to check the material pin holes before plating.
2.Proper cleaning is required before plating
3.If part is hardened you need to do Hydrogen de-embrittlement after plating for 2 hours at 200 degrees.

Sudheer Babu
- Bangalore, India



August 22, 2010

Q. Dear sir,

I am a hard chrome plater using HEEF 25 rs and chromium tri oxide by Atotech. Adhesion is ok and chrome colour also bright but after plating 20 hrs above, can see pin hole so have to cover on it. delay time to complete the job; why can have pin hole? and what is the problem ?

Aye Hansoe
plater - Singapore


August 27, 2010

A. Hi Hansoe,
Lot of information is missing in your query.
1. Job material/size and its surface finish
2. Current density at which you are plating
3. Do you filter your solution?
4. Thickness of coating required

If possible send a picture it says a thousand words.

vikram dogra Vikram Dogra
- Chandigarh, India



November 26, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello
I have a hard chrome plating plant for hydraulic cylinder rods and I consistently encounter pin holes on the rods we plate...
I have had any number of suggestions of potential causes and they number to at least twenty...

The rods range from 2" to 6" x 40 inches in length
Rods are prepped in the cylindrical grinder (020" to 40" undersize) with 60 grit wheel then linished with 120 then 240 then 320 then wet and dryed with 400 grit
Rod are masked with plastic and duct taped with lead and aluminium tape
Rods are cleaned with solvent and the washed thoroughly with dish washing liquid
Rods are etched 2.5 amps per square in and then ramped up to 2.0 amps for square inch over two minutes - plated for forty five minutes then wet and dried to smooth out any roughness
Re introduced into chromic solution and then plated for twelve to twenty four hours dependant on amount undersize (2.0 amps per square inch = .002" per hour / 3.0 amps per square inch = 003" per hour).
Pin holes are predominantly at the end of the rods....but not limited to the end ..pin holes can be sparatic as well concentrated
Pin holes look like a tube sometimes / volcano on other occasions they have a raised straight line above them on occasions and not on other times
All different combinations of etching / plating / initial plating duration before wet and drying / low surface amperage plating
Potential corrective means have been ensuring extremely good surface finish, new emery paper, limiting etching time and so many more.....
Any assistance would be greatly appreciated as it gets extremely dis heartening when despite every effort pin holes are constantly occuring
The anodes have been removed and yellow lead chromate removed which in this instant was severely caked onto anode causing gassing
Any help will be greatly appreciated....

Gavin Dorington
Plating shop employee - Kalgoorlie / Western Australia



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