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Chrome Plating: White streaks on the ends of the rotogravure cylinder

February 13, 2012

Q. Morning Gentlemen,

I am new to this experts-exchange & hope to get find the right advice towards fixing my current problem.

Issue:- 'White streaks on the "2 ends" of the rotogravure cylinder'

58278

Current Setup:-
- Chrome Type : Hard chrome Tank (1500 mm x 300 mm x 300 mm)
- Acid Used - Atotech Chromic Acid (liquid)
- Supressant - Atotech Supressant
- Anode - Lead/Nickel
- Temperature - 50 °C

Things I have done to address this:-
- Checked the acid density -> Found it to be appropriate
- Cylinder edges -> The cylinder edges are clean & do not have any copper residue prior to the chrome plating process
- Anode -> Still fresh with no yellow shade
- Since this is a 1500 mm x 300 mm x 300 mm, ensure there is enough anode coverage "end to end"
- Tried chrome plating multiple cylinders at one go -> not a fix

This did not fix my issue. How do you think I can address the streak issue ?

Looking forward to your feedback &/or suggestions ...

David Jose
- Chennai, India

February 18, 2012

A. Hello,

this is called burning and you need to review your bath chemical parameters to your physical parameters.

Kind regards,

Dominik Michalek
- Melbourne, VIC, Australia


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February 19, 2012

Q. Thank you for your response!

Could this be an issue around the chemical density ...etc ... I checked & corrected the density. The issue continues to persist.

Can you provide me with some more specifics around how to address this problem ... ?

David Jose
- India


February 19, 2012

A. This is clear burning :
- check the anode / cathode distance (minimum 7 cm, best is 10 cm)
- check the cathode current density

Best regards ;)

Francois Pignon
- France


February 20, 2012

A. I am a strong proponent of conforming anodes where the anode cathode distance would be about 2 cm and the anode would be trimmed on the end until the burning stopped. Increased distance yields lower tank efficiency.
With tank anodes, a common fix would be to either use robbers or to use shields on the end to reduce the excessively high current density and get a normal bright plate. Some people use both.

Conforming anodes uses a close distance and gets a fantastically high plate rate that is bright. It does not burn on the end because trimming the ends of the anode increases the throw distance and uses the amperage where you want it to plate. Is it easy on large rolls-NO, but it is great after you develop the techniques. It uses a mesh mat anode so you get lots of solution flow.

James Watts
- Navarre, Florida

misc. plating stuff
For Sale cheap



February 21, 2012

A. My friend, did you say anode: LEAD/NICKEL?? I think that was a typo error...should have been lead/tin?
Anyways I would go with my friend Dominik.

vikram dogra Vikram Dogra
- Chandigarh, India

February 26, 2012

Thank you Francois, James & Vikram for your inputs.

Francois - I will try and correct the cathode/anode distance to be at 10 cms and let you know the results.

James - Could you please elaborate on the term "robbers" & "shields"? I would like to understand and try them out if it's giving good results.

Vikram - Thank you for highlighting this! Yes, it's lead/tin and not Nickel :)

David, Jose
- Chennai, India


March 6, 2012

A. Hi David,

Please let me know your cylinder data (face length and circumference) and as well which current and voltage is in use. Also, which method are you using (vertical or horizontal) for the chrome plating?
I would appreciate if you give us some more information about your bath specifications and analysis results.

Thanks,
Dominik

Dominik Michalek
- Melbourne, VIC, Australia


March 6, 2012

A. Hi David,

Me again. I just have seen that you try to chrome plate at 50 degrees. If your chemical balance is given (min. 270g/l CrO3 & 0.9% H2SO4) then I would suggest you increase your temperature to 58 degrees. I do not recommend to increase your distance to the anode by now since it can cause higher resistivity and therefore reducing your amperage which then will result in a poor coverage of engraved cells in the middle of the cylinder and causing possible printing problems (shorter run times, poor ink release to substrate, etc).

Good Luck,
Dominik

Dominik Michalek
- Melbourne, VIC, Australia


March 19, 2012

A. David,

On the picture there is the part burned to the right, but the 2 grey streaks are, I believe, coming from the material when they machine the part and weld it.

Regards

Anders Sundman
    surface finishing engineer
- Malmo, Sweden



April 7, 2012

A. Anders raises a good point. I am not sure that the part has been machined, but I agree the photograph is misleading. Assuming the streaks referred to in the original question are (is) the one at the end of the gravure, I would go along with the idea it is "burning" caused by a high current density that would be expected to be seen in such an array. I would suggest using a robber to reduce the effective current density at the ends of the gravure.

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


April 26, 2012

Q. I have a related question to ask about Chrome 6 plating.
Recently, we encountered our current setting is fluctuating during plating. The difference is -40 to +40 ampere from setting that we want to plate. The outcome is whitish and burned chrome plating layer and sometimes yellowish or not plated with chrome at all.

Is it related to sulphate content or other additive which is not in balance in the bath?
How about the mechanical factor like wiring, cable, connector and rectifier itself?

We have tried changing rectifier, controller, doing some dilution and adding in some additive, but still not effective. Please give some idea?

For your information, recently we have changed all the tin lead anodes for this bath.

Norddin
- Malaysia


April 26, 2012

A. Hi Nordin,
Need more info on your process. Chromic acid concentration, sulfuric acid concentration, operating temperature, current density used. New setup having problem or old line which having been running fine before? The last question need to be asked because hexavalent chromium plating need a low ripple rectification.

SK Cheah
- Penang, Malaysia


May 1, 2012

info: Hi Mr.Cheah,

Regarding your question --
chromic acid concentration is 245 g/l, sulphate 1.4g/l, operating temperaturec 39-40° C., current density use depends on part shape/character -- normally between CD 4-CD 8 with plating time 2.5 to 3.0 minutes.

Norddin
- Malaysia


First of two simultaneous responses -- May 4, 2012

A. Hi.
1. You need to make sure your rectifier is the low ripple type which is specially for chromium plating. Changing the rectifier with one that is conveniently available is not an option. It has to be a low ripple type design specially for chromium plating. Your amperes fluctuation is reflective of this problem.
2. Your sulfate level is low. Increase to 2.45 g/l making the ratio to your chromic acid 1 : 100 .
3. Your current density used is low. Your yellow or no chrome plating is due to this. Depending on operating temperature, current density should be 10 to 20 A/dm sq.
Good Luck.

SK Cheah
- Penang, Malaysia


Second of two simultaneous responses -- May 6, 2012

A. Dear Norudin,

Kindly check with your supplier chromic to sulphate ratio they recommend , it should be min 100 : 1 and secondly your temperature is also low , Min 50 plus .

Qutubuddin Saify
- Ajman UAE



May 5, 2012

Q. We have a problem with plating chrome over copper in rotogravure cylinder. After the cylinder is going to press and after 1 ton or less the chrome is going weak and the doctor blade makes scratches on the cylinder surface.

We use current density of 65 A/dm2

Dedda Dedda
plating shop employee - SA

May 10, 2012

A. Please first check hardness you are getting its looks like you getting below 800 vickers . Are you using conventional bath or its organic catalyst bath.

Qutubuddin Saify
- Ajman UAE


First of two simultaneous responses -- May 10, 2012

A. I work in ASI for chrome, so 65 ASD = about 650 ASF which = about 4 ASI. Normally this would be good, but if you are using stick anodes with a long distance from the part to the anode, You are generating a huge amount of heat. The 4 ASI would normally take in the low efficiency of the tank, but that depends hugely on the highest temp for the run.
It is not unheard of to have an efficiency of 10% which would normally mean a soft chrome plate.
Next, was the part baked after plating? Chrome starts to turn to jello at 600°F. Thermocouple several parts in different locations.

How thick is the copper plate, how thick is the chrome, what is the hardness of the parent metal??

James Watts
- Navarre, Florida

misc. plating stuff
For Sale cheap



Second of two simultaneous responses -- May 11, 2012

A. Try to lower your current density since you have a greater build up on radius of cylinders and edges of cells. If you have a chemical imbalance, your throwing power will suffer and leads to lower lifetime of cylinders. Also, micro-cracks which usually will provide the lubrication during the print will be greatly reduced. How's you temperature and chemical parameters?

Cheers

Dominik Michalek
- Melbourne, VIC

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