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topic 47682

Electropolishing and Chemical Etching Processes for Cobalt Chromium



A discussion started in 2002 & continuing through 2017

(2002)

Q. I am currently undertaking research investigating the use of electropolishing (used in CoCr metal denture manufacture) in enhancing the fit of ceramometal copings or substructures (Porcelain Fused to Metal substructures) after they have been subjected to extra expansion during the investing stage before casting the wax patterns in wilceram metal. Any information on like or similar research or related information on electropolishing will be deeply appreciated.

Tassy Pillay
- Umhlatuzana, Durban, South Africa


Electroplating Engineering Handbook


A. Hi Tassy.

Although I am not personally familiar with the specifics of electropolishing of CoCr alloys compared to other alloys, the Electroplating Engineering Handbook =>
has an excellent 20+ page chapter on Electropolishing which explains both the whys and the hows of the process.

Metal Finishing Information Service / Finishing Publications Ltd. in Stevenage, Herts, England has a specialty computerized literature search database for the metal finishing industry which can be accessed online, or is available on CD; they also can perform the literature search for you if you prefer.

Metal Coating Process Corp. is a specialist in electropolishing chemicals, training programs, and consulting, and can surely help you.

Good luck.

Regards,

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



(2003)

Q. Dear Sir,
I need a solution to electropolishing a Co-Cr alloy (51:20 chemistry value). A Glycol, Sulfuric Acid, HCl has been suggested, however does anyone know of any other suitable solutions and or more suitable ratio of given chemicals.
Which glycol is more suitable?
Can you guide me for sources?

Thanks in advance. Regards, Devesh

Devesh Kothwala-
Medical - SURAT, GUJARAT, INDIA


(2004)

Q. I need to know a couple of pieces of information about electropolishing. First can CoCr be electropolished and if so what kind of bath is needed. Secondly we currently electropolish stainless steel, if we put the CoCr in the same bath will there be any contamination between the parts? This is a big issue due to the customer we deal with. If you have any information about this situation please let me know.

Scott Hawkins
medical instruments - Dayton, Ohio



metalcoabanner

A. Hi Devesh. Again, I don't know the idiosyncrasies of Cobalt Chromium alloys, but there is an old U.S. Patent, No. 2,607,772 which explains a sulfuric-glycolic mix for electropolishing stainless steel which may be applicable for you: http://pdfpiw.uspto.gov/.piw?Docid=02607722

I believe that a local plating process distributor may be able to offer you a proven proprietary. Alternately you may wish to contact an electropolishing specialist which offer training, seminars, and specialized chemistry, like Metal Coating Process Corporation =>

Hi Scott. Surely Cobalt Chromium alloys can be electropolished. Obviously your second question about cross contamination is difficult to answer conclusively but considering the mechanism and polarity of the operation, I wouldn't foresee any contamination in the electropolishing step per se.

Best of luck.

Regards,

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



Does electropolishing of Cr-Co dentures effect the thickness, and how?

(2006)

Q. I'm studying dental technology and would like to know more to have less errors
Thanks

Nancy Almustafa
student- Jordan



A. Hi Nancy. Electropolishing selectively dissolves the asperities because the highest current density is there. If the surface was reasonably smooth before electropolishing, I think very little metal needs to be consumed to achieve the smoothing. Here's what Dean Ward had to say about that in the Electroplating Engineering Handbook:

47682

Regards,

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



Post cleaning of Co-Cr alloy type L605

(2006)

Q. Hello

I am working with a Co-Cr alloy, L605, which contains 15% Tungsten. After welding process of the alloy, followed by electropolishing treatment, I receive impurities with mushroom shape (approx. 5 µm size) on the surface of my alloy. I tried to remove it by Chemical etch, mechanical polishing, ultrasound, sandblasting, nothing was helping.

I would really like to have advice on what I should do? I think thermal treat can help, but don't know what temperature and time.

I will appreciate any help.
Thank you,

Shlomit Chapel
microprocessors - Italy


(2007)

A. The possible cause of this problem is bad preparation of the surface before electropolishing. After welding there were developed oxide layers of different thickness. In locations where oxide layer thickness is max (and oxide does not conduct electrical current), electropolishing does not take place, but electropolishing does go on around such locations. That is why you see creation of the mushroom shape.
You need to add etching step after welding and before electropolishing.

anna_berkovich
Anna Berkovich
Russamer Labs
supporting advertiser 
Pittsburgh, Pennsylvania
russamer labs banner


(2007)

thumbs up signThank you!

Shlomit Chapel [returning]
microprocessors - Italy



Etching solution for Co-Cr L605 Alloy

January 30, 2008

Q. Our company manufactures medical devices, coronary stents.
Now presently I am looking for stent Descaling Process (to remove the metal oxide created after Laser Cutting), Annealing (to refine the grain size, hardness and elongation), Electropolishing (for bright & rounded edges) and Etching (To develop the microporosity on the stent surface) processes for chromium cobalt L605 alloy.

Regarding Descaling, Annealing, Electropolishing, I have validated all processes as per our application but after polishing we need to do etching. Here I want to do microporous development after etching on the stent surface but so far I cannot achieve.

I had taken different composition of HCl, H2SO4, and DI water with different times & temperatures, and also FeCl3 10% 20% 30% 45% solution and given various times and temperatures but I cannot develop microporosity on the stent surface.

Please give me suggestion what can I do for further?

Thanks,

Regards,

Bhavesh Pastagia
- Surat, Gujarat, India


February 25, 2008

A. Hello,

Use an electrolytic etchant (10%, 2 sec, 3 mv) such as: oxalic, phosphoric, etc.

Jose Castellanos
- Minneapolis, Minnesota, USA



May 21, 2013

Q. Dear Sir,

I have found crack problem in Co-Cr L605 metal in coronary stents after Electropolishing, I have reduced laser power during cutting, variable focal points, gas pressure, but not reduced this crack problem in coronary stents.

Regards,

Brijesh Ranoliya
- Surat, Gujarat, india


May 28, 2013

adv.
Russamer Lab licenses electropolishing of the Cobalt Co-Cr stents to interested companies. Contact us for testing samples arrangements.

anna_berkovich
Anna Berkovich
Russamer Labs
Pittsburgh, Pennsylvania



What solutions to use to Electropolish Co-Cr Alloy (L605)

(2006)

Q. Hi!

Could you share your Co-Cr electropolishing solution recipe here?

Thanks

Adam Pietruszko
- Warsaw, Poland


(2007)

Q. Hello, I'm doing a M.S. thesis work on electropolishing Co-Cr alloy L605. I hope this question hasn't been asked yet. I don't know what solutions to use to EP L605. I read through the standard guide for electrolytic polishing of metallographic specimens by ASTM. It indicated a couple of acids that are used for SS, and other metals. But I was unable to find a specific acid for Co-Cr alloy L605. What are the appropriate solutions that I should be using to EP L605. Can I still use the solutions indicated with SS 316L and still have the same effect for L605?

Hokuto Aihara
San Jose State University - San Jose, California, USA


August 18, 2010

Q. Hi, I have the same question. I have looked and spoken to many people, but no one has been willing to help in this regard. Most people say it is proprietary and leave it at that. I also wanted to know what metal is generally used for the Cathode? Any feedback would be greatly appreciated.

Iain Kemp
- South Africa


December 4, 2013

A. Most electrolytes for Cr Co alloys are composed of:

85% EF 200 Ethylene Glycol,
10& Sulfuric Acid,
5% Hydrochloric acid. Brilliant Shine. Some corrosive fumes.
(The hydrochloric acid can be optional).

-OR-

85% EF 200,
15% Phosphoric acid (Shine varies from Brilliant to mat)

This particular formula has good effect on most CrCo alloys and has a 70 year history in industry.

Bruce Dean
Technical Product Manufacturer - Central Point, Oregon, USA



Electropolishing Solution for Platinum Chromium stents?

May 12, 2011

Q. I am currently involved in research and development of platinum chromium coronary stent. Can you suggest which acids and chemicals are involved in Descaling (Acid pre-cleaning process) and Electro-Polishing Process?

We are already engaged with Co-Cr l605 and SS 316L coronary stents.

I certainly appreciate your fast help.

Looking forward to hearing from you.

Regards,

Bhavesh Pastagia
Manufacturing Cardiovascular coronary stents & support devices - Surat, Gujarat, India



April 1, 2014

Q. In electropolishing CoCr, why not use Co in anodic and cathodic chemical reaction?

kinjal patel
- Ahmedabad,Gujarat, India


April 3, 2014

Hi Kinjal. Sorry, I don't understand you. Do you mean: "why not use Cobalt cathodes?" Please explain your situation. Thanks.

Regards,

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



Cathode and racking material for electropolishing of CoCr alloy?

April 18, 2014

Hello Sir,
I want to do electropolishing of CoCr L605 material.
Will you please suggest me the Material for Anode and Cathode?

Sanjay Patel
- Gandhinagar,Gujarat and India


May 3, 2014

A. Final finishing of Co-Cr stents faces the following challenges:

1. The surface must not be saturated by hydrogen, in order to prevent embrittlement;

2. Since Co-Cr stents are usually very thin, special holder design is required to distribute electrical current evenly;

3. Depending on the alloy composition there may be various hard-to remove molybdenum or other carbides, that do not disappear during electropolishing.

We work with cobalt-chrome material for almost 15 years, mostly with knee implants.

adv.
Our ultrapolishing method allows to remove all of the peaks of hard-to-remove carbides. However for such delicate stents the ultrapolishing method does not work.

Recently we developed two-step processing. During the first step the surface is smooth electrochemically --

47682-1
(image of the stent)

The second step dissolves all carbides on the stent surface.

47682-2
(SEM image)

anna_berkovich
Anna Berkovich
Russamer Labs
Pittsburgh, Pennsylvania


sidebar






sidebar
December 13, 2014

Q. I want to know etching solution composition for CoCr L605 Material.
Can you describe it?

Dhaval Kapadia
- surat, gujarat, india


December 16, 2014

Q. What is chemical etchant for Co-Cr alloy L605? Which electrolytes can be used for above?

shrikant thorat
- pune, india


kissofdeath
Kiss of Death

December, 2014

A. Hi Dhavel; hi, Shrikant.
Jose described it in good detail. Can you please phrase your question in terms of his previously posted answer to keep this interesting dialog moving forward? Have you tried his suggestion? Is there a reason you can't? Do you have further questions about it?
Ignoring previous responses and starting over is often the kiss of death to a thread :-)

Thanks & Regards,

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


sidebar2 December 16, 2014

Q. I need to know if Co-Cr stents are stuck with each other after annealing process due to heating, then what is the process to separate them?

Vickysh S Mevawala
- Vapi, Gujarat, INDIA


August 8, 2017

Hi sir,

I need to know about the sticking problem occurred after annealing process in CO Cr L605 alloy? How to get rid of it?

Is there any solution to separate the material?

Kindly guide me.

Vickysh Mevawala
- Surat, Gujarat, INDIA


October 2017

Hi Vickysh. This thread is about electropolishing rather than annealing, but please try your best to carefully detail your own exact situation rather than posting abstract questions. Are you saying that you properly performed an annealing process, but because the parts were bunched together, touching each other, they fused together? If these are stents or other medical or dental parts, I find it hard to believe that they will be salvageable if they have fused :-(

Luck and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



February 13, 2015

Q. What kind of surface texture is created after etching of Co-Cr alloy and why? Example, like formation of porosity on stent surface? What are research journals available for the etching of Co-Cr alloy?

shrikant thorat [returning]
- Karad,Maharashtra,India



March 11, 2015

Q. Dear Sir/Madam

Would you please let me know how can I measure the current density for various voltages during a given electropolishing process?

Thank you for your answer

Aref daneshfar
- Isfahan, Iran


March 2015

A. Hi Aref. The average current density is easy: it's just the current divided by the surface area of the parts. But the specific current density at different locations in the tank is quite a bit more difficult. There were immersible current density monitors available from companies like QCI but I'm not sure if anyone manufactures them anymore. You could try Material Testing Technology in Wheeling, Illinois. Stresstabs may help too.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



May 4, 2016

Q. Hi sir, I'm a biomedical engineer. Currently I work with electropolishing machine for Chrome - Cobalt alloy (L605 alloy). However, we can't get the good surface after polishing because we don't know the detail of polishing liquid. What kind of acid I should use? Sulfuric acid or Phosphoric acid and the concentration to get the best result? Can you give me some advice, thank you very much.

BAO NGUYEN
biomedical engineer - Ho Chi Minh City, Vietnam


May 2016

thumbs up signHi Bao! Bruce Dean already answered that question. Please ask for clarification, or describe in what way it didn't help.

We've suggested that you contact Metal Coating Process Corp. or Russamer Lab [a finishing.com supporting advertiser] if you'd like to purchase appropriate chemistry, or receive training, or retain consulting services; and if you want technical references on the subject, we listed books, computer databases, and patents covering it.

Good luck, and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



November 24, 2016

Q. Hi everyone. I work with electropolishing of CoCr alloy for medical implants. We work with a solution containing sulfuric acid (4%) and phosphoric (13%) besides others components. Do you have some suggestion to control the stability of the electropolishing solution? Or perhaps some other acid solution to deal with this specific alloy?

At some stage of the polishing (after 100 pieces polished) the CoCr alloy begins to show defects, even using the parameters that provide a good surface.

Lara Morais
medical - Goias, Brazil



December 13, 2016

Q.
We make CoCr stents which are then electro-polished using EP solution and machine supplied by ESMA, USA. The problem we see, at the rate of about 20% fallout, is pits and cavities on the surface of the stents.

We are not sure if the pits/cavities are the result of impurities within the CoCr raw material, or the result of something happening in the EP process or prior processes (which include acid descaling and heat treatment)

Would appreciate any help identifying the source and suggestions for what we could do to reduce the fall out. Thanks in advance ...

best, Anil

Anil K
- HYDERABAD, India


December 13, 2016

There are many ways to electropolish CoCr, the effectiveness depends on the exact alloy composition and alloy supplier. Another problem is that even after regular electropolishing, there are pits produced by undissolvable carbides. We remove them by final plasma-like electropolishing, with duration of few seconds.

adv.
Contact me for more information and testing possibility. I have attached SEM images before and after plasma treatment

47682-3a  47682-3b

anna_berkovich
Anna Berkovich
Russamer Labs
Pittsburgh, Pennsylvania


July 21, 2017

Q. In electropolishing process after completing the EP process on (CoCr coronary stent) we are getting defects on the stent like oxide, pits, etc. Excluding the suggestion of varying the parameter (i.e., current & time), can you kindly help me regarding these defects?

Manisha Kumari
employee - gandhinagar,gujarat,india.


July 2017

A. Hi Manisha. A solution which does not involve changing the current and time may or may not be possible. But please start by telling us the temperature and time that you are employing, and the solution that you are using. Thanks.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


August 26, 2017

Dental style Chrome Cobalt alloys can be, and have been, electropolished for over 70 years.

Pre-Made solutions can be obtained from ESMA Chemicals, Nobilium.com, Dentsply.com (Sirona Division), Dentaruim.com. For small quantities, try ESMAINC.COM Chemicals (about US $70 per gallon plus shipping). As well as making them yourself.

60% Ethylene Glycol
40% Phosphoric Acid (85%)

6 amps/sq ft DC

Bruce Dean
WDR Scientific - Central Point, Oregon USA


August 2017

thumbs up sign Thanks Bruce, but can you double check your units? I don't think you mean 6 Amps/sq ft; to me that sounds low by a factor of about 50 to 1. Thanks.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"


October 12, 2017

A. Co-Cr stents electropolishing is different from other parts electropolishing. Usually if electropolished by standard solution, the outer stents surface is electropolished well. However the inner surface is not polished property.

adv.
We have developed the unique technological process that electropolishes the inner and the outer surface equally on tiny cobalt stents. See image below:

47682-4

Also our electropolishing is not using hazardous ethylene glycol. We also develop special holders for each PARTICULAR stent design. We can do outsourcing or deliver processing and equipment.

anna_berkovich
Anna Berkovich
Russamer Labs
Pittsburgh, Pennsylvania



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