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topic 1183

Pretreatment techniques and Hard Chrome Plating of Cast Iron and Chilled C.I.

Hard Chrome  
Plating pointer 

       
(1998)

Q. We are hard chrome plating chilled cast iron calender rolls (65 HRC hardness, 3% carbon) size 700 mm dia. * 2000 mm long that are used in PVC (polyvinyl chloride) film industry.

We sandblast the roll, scrub by hand with Pumice [linked by editor to product info at Amazon] powder, chrome plate in conventional chromic acid at 4 ASI initial forward strike (no reverse etch) and step down to 2 ASI, at 73-75 °C, intermediate grind to 100 micron, re-chrome to 200 micron finished thickness.At times during grinding deposit cracks,sometimes during service at 210 °C temperature. Deposit cracks. We operate at higher temperature to produce a less hard and low stress deposit. Due to lack of floor space we do not have cleaning tanks, or oven for stress relieving. If absolutely essential we can incorporate an oven and one cleaning tank. What do you recommend? Cast Iron dryers 1220 mm dia. * 2000 mm long, used in paper industry has pin holes which are not to be covered by chromium deposit. Which is the best option: acid copper/cyanide copper/dull nickel or any other undercoat/thermal spray/inserting steel pins in cast iron surface pin holes,from technical and commercial point of view?

Shaunak Shah
- India


weiner book
Chromium Plating

Weiner & Walmsley


Hard Chromium Plating

(1998)

A. I believe that steel plugs and nickel under-plate is the correct approach.

The eminently readable booklet, "Defects in Hard Chromium Deposits", by Chessin, Knill, and Seyb says that copper is suitable on ferrous substrates not subjected to severe pressure or stress. Nickel is recommended for other applications. The nickel bath should be brightener-free. Details on repair methods of the basis metal are also given.

This paper was presented during SUR/FIN 81. I understand that Atotech has an office in India, perhaps a copy of this paper is available from them.

pooky
tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania

(1998)

A. Hi, Shaunak. Also, in answer to your question about an oven, my response is 'yes, it is absolutely essential'. Any hard chrome plating shop that does items subject to hydrogen embrittlement needs an oven to bake the items for hydrogen relief. Good luck.

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


(1998)

Q. Dear Sir

We thank you very much for your prompt response.

90% of the steels we chrome plate have a tensile strength way below 1000 Newton/mm2, In most of these jobs chrome plating is carried out for wear resistance, hence there is no problem if stress relieving is omitted. However with chilled cast iron, when the roll is heated during service to 200° C or due to localised heat generation during grinding, hydrogen entrapped in the chrome plating may be responsible for cracking? Manufacturer of calender rolls caution that roll heating or cooling must be carried out at a rate not exceeding 0.5 to 1 deg. C per minute. Is this heating cycle adequate for carrying out stress relieving or chromium plating?

These calender rolls have 3% carbon, the end application dictates that the plating deposit must have good adhesion, no pin holes, good corrosion resistance, because there is no tensile load on the roll or no abrasive material coming in contact with the roll, high wear resistance of the chromium plating is not required.

Reverse etching is very good for finish ground jobs of low carbon steels because it cleans the job and being low carbon not much of the carbon comes to the surface and a good adhering deposit results. However with high carbon steels sand blasting accompanied with good cleaning may be a better technique to produce a good adherent deposit? What temperature, ASI, time, sequence do you suggest to produce a low stress chrome deposit? In case during intermediate grinding we notice pin holes, is there any solution to micro drill the hard chromium and plug. Any other solution?

Thanking you
Yours faithfully

Shaunak Shah
- India


(1998)

A. Sir,

On soft steel,the thicker the deposit, the more stress it will have relative to the bond strength. When you heat it, the chrome expands faster than the steel and cracks or peels.

Hydrogen embrittlement is a cracking of the substrate normally along grain boundaries and has nothing to do with the initial cracking of the chrome. After the chrome cracks, the crack will propagate into the base metal because of hydrogen embrittlement.

James Watts
- Navarre, Florida


(1998)

A. Plating a 1/1000 inch thick deposit of nickel is such an elegant solution to so many problems; pinholes, corrosion protection, adhesion, that it really doesn't pay to try to do without it.


Tom Pullizzi
Falls Township, Pennsylvania

similarly





similarly
(2000) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am having a problem with a hard chrome plating application. As a hard chrome job shop, we normally plate plastic injection molds and assembly machines. We have started plating cast iron rolls for a new customer and are unable to eliminate small voids or pits in the plating after a post grinding process. We feel the pits are from the porosity of the cast iron and not the bath chemistry. As I stated before, the part is a cast iron roll 7.500" dia. X 6.00" tall with a 6.200" i.d. (the grade of the cast iron is unknown). The O.D. is to be ground undersize, then hard chrome plated and reground to the finish dimension. The total thickness of the chrome after final grinding is approx. 0.004" p/s. I would normally burnish a part like this to close up the pores in the steel, but there are holes on the O.D. that would prevent the burnishing tool from working properly

Should iron castings that require a #16 micro inch finish be plated with another material, possibly a sulfamate nickel, then hard chrome plated?

Any suggestions would be appreciated.

Jeff

Jeff Hanaway
- Pennsylvania


(2004) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

A. Jeff we use chrome plated roll in our business of making coated paper. The nickel under coating is a good way to seal the cast iron surface from corrosion because chrome is porous. You might want to try nickel plating the cast iron first, about .001 per side, then chrome plate.

Scott M. Richardson
Coated Paper - Westbrook, Maine


(1999) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

! SIR,

I AM A MANUFACTURER OF CHILLED CAST IRON ROLLS. I HAVE COME ACROSS A LOT OF PEOPLE WHO HAVE UNSUCCESSFULLY TRIED TO PLATE CHILLED CAST IRON ROLLS. IF YOU FIND A FOOL PROOF SOLUTION, DO LET ME KNOW.

REGARDS,

VIKRANT SINGH GILL
New Delhi, India


 

Hi, Vikrant.

I don't think anyone has foolproof solutions, but Tom & Scott have presented a good case for specifying an under-layer of nickel plating. Good luck.

Regards,

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


(1996) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We are looking for a pretreatment method to hard chrome plate a roller made of chilled cast iron.

Any advise is highly appreciated

Herbert Fröhlich

A. Hi, Herbert. Chessin, Knill and Seyb report in the Feb. '83 issue of Plating & Surface Finishing: 'Free graphite in cast iron and some high carbon steels does not create a problem for the plater unless the metal is subjected to excessive etching procedures that cause the graphite to accumulate on the surface of the work, making it very difficult to cover with a chromium deposit.' I would read this to say that part of the solution is to minimize etching. Good luck.

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


(2001) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear sir:

We are working on coating the cast iron engine cylinder with the hard chrome and now we would like to know if there is a way that we can measure the adhesion of the coating. Thank you for your attention & your prompt response will be highly appreciated.

Sincerely yours,

hassan eivazy
- Iran, Tehran


June 2009

A. Hi, Hassan. There are a number of different adhesion tests, but the "modified Ollard test" is probably the "referee" method because you do an actual tensile pull test of the adhesion -- please see letter 18002 for diagrams and explanations. Good luck.

Regards,

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


July 23, 2009 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We have problems with hard chromium plating on cast iron parts. Please describe surface preparation and plating condition (current density, temp.) for hard chromium plating on these parts. Can we use metallic inter layer coating like nickel electroplating before hard chrome plating?

ali zaghar
plating shop - Cabol, Afghanistan


October 21, 2010 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Please suggest me what are the essential to do for hard chrome plating over the Gray cast iron cylinder, and how can I seal the minute pin holes. If it's sealed how can we we ensure it?

Ebrahim Ebrahim
reading the book - Chennai, Tamilnadu, India


  -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We do hard chrome plating for automobile industries. We are facing problem of plating peel-off on cast iron . We have attended to all types of pretreatment before plating. Any suggestions.

Regards,

Harish Krishna
- Bangalore, India


 

A. Dear Mr Krishna,

1)What kind of cast iron are you talking about? 2)When you say "all types of pretreatment" you don't specify You better describe exactly what you have tried so far.

Regards,

Christos Sigalas
- Athens, Greece


 

A. Krishna,

Can you explain what type of chrome solution you use. If you use a Sargent's chrome solution try to bake the part at 200° C, degrease for 2-3 hours before plating. That is to remove the hydrogen from the part. All casting materials have some hydrogen from the beginning.

Sincerely,

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



 

Q. HARD CHROME PLATING ON CAST IRON

WE ARE FACING PEELING PROBLEM ON PLATING CAST IRON. WE HAVE ATTENDED TO SULPHURIC ACID ETCHING, POLISHING, HOT WATER WASH, CAUSTIC SODA CATHODIC CLEANING, AND COLD WATER PRESSURE WASH. THE CAST IRON IS A ALLOY CASTING OF SILICON, MANGANESE AND CARBON. WE ARE USING CHROMIC ACID SULPHATE BATH. THE JOB IS VERY BIG AND CONNECTING CATHODE AND ANODE ARE THROUGH CABLES AND THIS TAKES ABOUT 30 MIN. COULD THIS BE ONE OF THE REASONS? KINDLY SUGGEST A PROPER PROCEDURE. WE KNOW THAT THE JOB SHOULD BE CLEAN AND FREE FROM OXIDE SCALES BUT PRACTICALLY THERE COULD BE AN HUMAN ERROR.

REGARDS,

Harish Krishna
- Bangalore, India



(2006) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Does anyone have a simple reliable way of pretreating nitrided cast iron prior to chrome plating.

Norman Evans
hard chrome plating - Springfield, Ohio


(2006)

A. A thorough cleaning (solvent and electro), light sand blast and immediate plating in a mixed catalyst or fluoride bath sounds to me like the easiest method. But you'll have better answers if you tell us what are you talking about. Shape, size, quantity, finish or smoothness required. Also, if you have tried something w/o success.

Guillermo Marrufo
Monterrey, NL, Mexico



July 18, 2012

Q. We are about to hard chrome plate cast iron cylinder liners of diesel engines. We successfully plate case hardened shafts and plate, but we need to know the best surface preparations for hard chrome plating cast iron.
The anode positioning specifications for 4" in .dia. cylinder is also a problem.

Any kind hearted help would be greatly helpful.

Hanifa Khan
- Dhaka, Bangladesh.

January 27, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,
I am working on the design of an 'Impression cylinder' of offset printing press. The problem before me is the Peeling Off of Hard chrome coating on the Cylinder.
Till now the usual coating method that we follow for similar situation is Electroplating of hard chrome. The substrate is G3 cast iron of nearly 190 mm dia. and 1030 mm length. Can you please suggest an alternate Coating method for me? Either a new coating material or a different method for chrome?

NIRMAL
- KANNNUR,KERALA STATE,INDIA


January 27, 2013

A. Hi Nirmal. We've appended your inquiry to an interesting discussion which I think will answer it for you. If not, please try to phrase your question in terms of the answers already given (like "we tried ... and it didn't work", or "we cannot nickel plate because ...", etc.)

Regards,

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



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