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Grinding hard chromium plating


An ongoing discussion from 2000 to 2014 and beyond about chrome plating cracking during grinding . . .


(2000)

Q. I am searching for information about machine grinding hard chrome. How many number of revolution/minute and how much shall I grind/minute. I like also know which type of grindstone is best?

Regards,

Anders Sundman
    surface finishing engineer
- Malmo, Sweden


(2000)

A. Dear Anders,

The most important thing about grinding hard chrome is not to develop any heat.

Use a grinding wheel with an open structure to make good cooling possible. Keep your grinding wheel sharp by dressing it more often than you normally would do.

The grinding speed should preferably be about 35 mtrs/sec.

Consequently, the number of r.p.m. depends on the diameter of the grinding wheel.

We have more detailed information on this subject available.

Kind regards,

Roel Jaarsma
- Netherlands

Electrodeposition of Chromium from Chromic Acid Solutions
by George Dubpernell



At what temperature does "Mud-flat" cracking occur?

(2000)

Q. Re: hard chrome plating/grinding: We get "rejected" parts from our grinding shop that must be stripped and re-plated due to "cracked chrome." We have read that when the base metal gets too hot during grinding, the chrome can crack and look like a dried up lake bed - which is referred to as mud-flat cracking.

Our question is - at what temperature this occurs? What is the "danger range" for how hot the basis metal needs to get for this to occur? Typical basis metals are high strength steels and stainless steels.

Nick Cortese
airline - Atlanta, Georgia USA


(2000)

A. Not that simple. It is the tiny area under the grinding wheel where the chrome reaches a high temperature and then immediately cools off as soon as the wheel moves.

Causes:

My experience is reason one and two, 99% of the time.

The machine shop gets paid for getting the parts out and they rush grinding. The fact that it recycles is the platers union problem, not the machinist union.

There is about 1 in a thousand chip cutter that will listen to a plater, even when presented articles stating fact. After all, machinists are highly talented and trained people. If you do not think so, just ask one.

Been there and done that. Talk with straight tongue. Every time we had a problem, I would check the grinders and sure enough, they forgot to order wheels and were using unsuitable substitutes. They also thought that a 0.005 grinding cut was fine, because it "worked" (for about 100 revolutions).

James Watts
- Navarre, Florida


(2000)

A. Excellent reply Mr. Watts! You've hit the nail squarely on the head. Improper grinding costs this country billions of dollars a year in excess tool wear and component failure, but woe to the engineer who tells the grinder operator that there is a problem.

A little additional information: I have personally measured temperature under a grinding wheel of up to 1200 °F, and suspect that my temperature measurements are low. These high temperatures can cause the metal to expand so much that it plastically deforms because it kept from expanding by the cool metal around it. Then when it cools, it tries to contract but cannot, and a tensile residual stress is the result. Since chrome is more brittle than most steels, it stands to reason that the chrome will crack long before the steel.

In the aircraft industry, great effort is often made to achieve low stress grinding. I know of one company that will deeply investigate for heat damage if they see a spark while grinding. Yes, that is "A" spark.

It might be worth your time to investigate CBN [

Ed. note: cubic boron nitride] wheels in addition to taking Mr. Watts advice to heart very seriously. Good Luck

Frederick Diekman
- Streamwood, Illinois, USA


(2004)

A. Mr. Diekman,

You mentioned CBN wheels and it just rings the bell with me. We have had a very positive experience grinding Molybdenum plasma-sprayed component by a vitrified CBN wheel. We used to apply a set of two wheel for this operation - an electroplated one to remove the bulk of the material and alumina wheels for finishing. We have been able to replace them both by a single vitrified CBN wheel with induced porosity. It grinds very cool and puts mush less stress on the component. It does not inflict metal burns, that were common before.

Gennady Gurinovich
abrasive wheel supplier - St. Peterburg



thrashing

(2004)

Q. I'm working in a plating department of a helicopter rework company as a technician. Over past few years we have frequent problem with chrome cracking-flaking, some refer this as "mud-flat" cracking. This occurs during grinding on .002"-.005" to base material which is mainly inconel 718 but not always (happened on steel also). Parts are being stripped and replated. All chemicals, cleaners are on optimum level, rinse water ionized and clean, parts vapor degreased. After plating chrome looks good, no visible cracks or any marks not even after NDT. If somebody could enlighten us with any info or suggestion would be greatly appreciated.

Miro Stankovic
Electroplating technician - New Westminster, British Columbia, Canada


(2004)

A. In my experience the mud cracking is due to poor adhesion, If the grinder has a incorrect wheel or is taking to much off on his grinding passes, you can get mud cracking but there is often a discoloration along with the mud cracking.

Chris Snyder
plater - Charlotte, North Carolina


(2004)

A. Hard Chrome is under very high tensile stress for almost all plating conditions and chemistries and has less than 1% elongation. This is responsible for the tendency to alleviate by either cracking or spalling. The grinding adds more stresses through cutting forces and heat. Some substrates also differ too much from chrome in thermal expansion coefficient, which adds another factor.

Guillermo Marrufo
Monterrey, NL, Mexico


(2004)

A. I had many a war over this subject. The problem is in the machine shop management. The machinists are doing one or more things wrong.

1. The wrong wheel. I cannot count the times that they ran out of the correct wheel and put on a wrong type, and then bitched like mad because the plating failed. There is an optimum grit material, grit size and binder to be used!
2. The wrong feed or speed, Faster is not better!
3. Too deep a cut. They would literally crush the surface of the wheel and the plating by trying to take a 0.002" cut.
4. Inadequate or the wrong cutting fluid.
5. Not dressing the wheel often enough.

Besides, everyone knows that if plating fails, it has to be the platers fault. It certainly could not be an engineering, or management problem! If you do not believe that, just ask them. (just like it was the platers fault when the part had chrome on it, but was 0.020 smaller than it started out)

James Watts
- Navarre, Florida

Chromium Plating
by Weiner & Walmsley


(2004)

thumbsup2I loved the parenthetical comment, James; you created an entire colorful scene for me in 25 words or less.

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

(2004)

A. Miro,

Read letter 12398, "Hard Chromium Plating of Nickel-Based Alloys" and 25160 "Hard nickel won't adhere to Inconel" about plating on Inconel 718. Be very careful when starting grinding on the high current density areas on the part.

Regards,

Anders Sundman
    surface finishing engineer
Sweden


(2004)

A. I have to agree with all of the responses. Working in the plating field for close to thirty years, especially in hard chrome, I have yet to see any of the Machinist Foreman that I have to deal with, say it was their fault. I was even told by the Director of Operations, that I didn't know what I was doing, must of been absent during that course. Slow is better, and use a lot of coolant, best of luck.

Charles H. Collins
- Watervliet, New York


March 19, 2011

A. What activation process are you using for Inconel? Are you going in the bath live? What amps per square inch are you plating at? How much grind stock are you putting on part? How much chrome are you putting on per hour?

Greg Mcvay
- Peoria Arizona United States


(2005)

Q. I'm getting cracks on some of my batch of hard chromed steel shafts. The shafts are machined and stress relieved then chrome plated to DEF-STAN 03-14 and finished with a final grind. The cracking does not appear to be raising the surface profile but ruins the sealing capabilities of the sliding seals in the mating part. The base metal is S144 stainless steel and the diameter is approx. 8 mm.

Can anyone suggest a cause?

Best Regards,

Chris Elliott
- Redditch, U.K.


(2005)

A. Hi Chris,

Have you measured the hardness on the part before the grinding?

How is your stress relive is that by baking in a oven or shoot peening? Or is it together in the same operation? (remember that it is different temperature in same operation or not).

How is the trivalent chrome content in your chrome solution.

How deep gets the grinding wheel for every cut? (remember when starting grinding that most take carefully not more than .0002 per cut.

Regards,

Anders Sundman
    surface finishing engineer
Sweden


(2005)

Q. Those are all good questions. Unfortunately the part is made by a subcontractor who swears they are doing everything by the book.

I haven't measured the hardness. I understand that the hardness of the underlying steel can affect the de-embrittlement heat treat but I'm not sure what process indicator measuring the chrome would give.

The stress relief is by heat treatment as dictated DEF STAN 03-14.

I don't know the trivalent chrome content. I expect that to be kept within tolerance by the plating sub-contractor.

The depth of cut is set by the machining sub-contractor. There has been heavy 'blueing' of the visible steel on these parts so I suspect the final grind operation has to little coolant or is too brutal.

Chris Elliott [returning]
- Redditch, U.K.


(2005)

A. I think you've answered your own question -- inappropriate grinding procedure.

Bill Reynolds
   consultant metallurgist
Ballarat, Victoria, Australia

It is this website's profoundly sad
duty to relate the news that Bill
passed away on Jan. 29, 2010.



(2005)

A. Chris,
I think you have your answer there by the grinding.

Regards,

Anders Sundman
    surface finishing engineer
Sweden



thrashing

(2005)

Q. Unlike the rest of you readers, I am a machinist that is having problems with chrome plating on aircraft parts. I have only been grinding these parts for about 10 weeks now. I have had no problem grinding .0005 per side or (.001 on diameter) at an RPM of 43 on a 4 inch diameter part. No cracking at all for 30 parts. Now all of a sudden the past 6 parts have all cracked on the surface. Using the same wheel the same dressing the same feed rates, etc. etc. Now what would cause this to happen? My plating engineer keeps saying I'm taking to much material per side. But this has worked just fine in the past... Any Answers?

Dan Smith
aircraft repair - Arizona


(2005)

A. The chrome plating could have become more stressed, but that is not likely unless the plater made a huge change in parameters, really huge change.
Cracking in chrome during grinding is normally-virtually always- caused by the wrong wheel or the grinder taking off too much at a pass. 0.0005 is about the max that you should take on a pass. You might also look at the coolant. Did it change in any way-point of application or flow rate or?

James Watts
- Navarre, Florida

(2005)

A. Dan,

Ask the plating engineering how hard is the material. I suppose the hardness in the material is 40-55 HRC. Have the part shoots peening before chrome plating, heat treatments before chrome plating, the sulphate content's in the chrome solution. Many thing can gets cracks in a hard chrome layer in a grinding operation.

Regards,

Anders Sundman
    surface finishing engineer
Sweden


(2005)

Q. We are having issues with "High Background" in FPI after chrome grind. We have attempted numerous fixes that have not yielded the elimination of the problem. It is not necessarily a rejectable condition however it keeps the inspectors from inspecting for real defects.

Has anyone seen this and what was done to eliminate it?

Thanks,

Scott Maitland
- Cleveland, Ohio



June 16, 2008

Q. I want to know some more about grinding hard chrome.

greg Alexander
- six mile, South Carolina


October 28, 2011

A. Chromium is a very good conductor of heat and therefore it is possible to create grinding burns, Tempered or untempered Martensite (white layer) creates cracks in base material and also in the chromium layer.
Regards,
Jos

Jos van Langh
- Helmond, Noord Brabant, Netherlands

June 10, 2013

A. We use I to K grade wheels with 45 to 60 grit, and grind 0.0002" max cut per pass, and only feed on at one end usually at tail stock. We also dress at 0.001" above final size and have [ed. note: haven't?] any problems with etch inspection.

Phill Morris
landing gears - Bolton, England



December 14, 2012

Q. Anybody consider it can be done by benchwork? Polishing using additive (Autosol) can cause peel off too?

Endro
- Bandung, Indonesia



Does BAC5032 allow 0.003" grinding depth per pass, or what does it mean?

August 6, 2013

Q. Dear All,
I have a question in regards to standard BAC5032.

"The grinding wheel shall be dressed frequently with a finish dress when the part surface is a maximum of 0.003 inch from the finish dimension."

Does this mean a maximum grinding depth of 0.003" per pass? Any insight would be greatly appreciated.

Thanks.

Tiger Wu
Landing Gears - Xiamen, Fujian, China
  ^- Privately contact this inquirer -^

Hard Chromium Plating


August 8, 2013

A. You absolutely cannot take 0.003 per pass on chrome, especially on aircraft parts.
What it is telling you is that when the grind dimension is within 0.003 of the final dimension that you must dress the wheel.
The correct grit and resin of the wheel makes a major difference in the finish. The wrong wheel and too aggressive grinding is begging for failed plating and it is not the plater's fault.

James Watts
- Navarre, Florida

August 9, 2013

A. I haven't read the Specification, and the context of that paragraph could shed more light, but to my understanding it does not imply any specific amount of material removal but to treat the last 3 mils gently. Good luck,
G. Marrufo-Mexico

Guillermo Marrufo
Monterrey, NL, Mexico
August 9, 2013

A. Hi Tiger,

I am not going to second-guess Boeing's meaning, you need to talk to your Boeing technical representative to get a technical decision on interpretation.

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom


August 28, 2013

A. The spec is saying that the wheel must be dressed .003" max above finished size. My company grinds chromed landing gear pistons and we dress .001" max above finished size, and we use .0002" max per cut.

Phill Morris
landing gear manufacturer - Runcorn England


August 12, 2013

thumbsup2Thank you all for your response.

Tiger Wu
Landing Gear - Xiamen, Fujian, China



November 29, 2013

Q. Hi, I'm new on this site but I got good references about it.

I am running a hard chrome process at a workshop and I have been having good results inside my working area; I mean we have to check every product we pass through the process with copper sulphate to have an idea of the chrome layer we made over the product.

But we have the inconvenience that our clients are checking the product as well with the same substance (copper sulphate) when it arrives at their business. Sometimes there are some cracks in the surface of the chromed product. We believe that the molds we are chroming have a lot of pores. And our rectifier is working perfectly; the chrome temp. ranges are from 48 °C to 56 °C
Our chrome and sulphates in our tank are 445.43 and 3.5 (respectively)

We want to know what are the causes of the cracks?

And another question. What is the difference between the flake chrome presentation and the chromium granulate presentation? We have been working a lot better with granulated hard chrome than the flaked chrome.
Thanks for your responses.

Esteban Gonzalez
- Matamoros, Tamaulipas, Mexico
  ^- Privately contact this inquirer -^



April 30, 2014appended

Q. After chrome plating a certain part, there is an on-going issue with a certain area having linear cracks after grinding. What may cause these cracks. On my end, the plating chemistry is excellent, filters are changed frequently, tank de-slugged, etc. The plating appears excellent prior to grinding. The machinist claims to be performing the correct procedures but the issue has been ongoing for a few months now on a particular area. The other three plated surfaces do not crack, which are plated in the same bath. Any suggestions?

claudine_meinhardt
Claudine Meinhardt
Chemist - San Antonio, Texas USA
  ^- Privately contact this inquirer -^


May 7, 2014

A. What is the parent metal? Hardness? Prebaked. Shot peened?
Plate thickness? Post plate bake cycle??

My cracking problems normally rested with the grinder operator. Their first passes were normally excessive. Feed and speed were sometimes cheated on. Depth of cut after the first pass normally was cheated on. Failure to true the wheel often enough.
The absolute biggest problem was the choice of the disk-grit size and resin. The last year, the failure was always related to using an unsuitable substitute wheel when they could not find the correct one.

Some companies allow a bit of mud flat cracking on certain areas.

James Watts
- navarre, Florida

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