Methods for removal of W-, Ni- and V-coating
07-31-2008, 02:38 PM, (This post was last modified: 07-31-2008, 02:41 PM by kahrax.)
#1
Methods for removal of W-, Ni- and V-coating
Hi

As the topic suggests I am looking for ways to remove Tungsten, Nickel and Vanadium coatings. My starting point is an substrate with a layer of Tungsten and an intermediate layer of either Nickel or Vanadium.

The substrate used would be varying types of steel. For now I am not that interested in the effect on the substrate, but more the actual fact of removing the coatings.
Reply
08-01-2008, 09:06 AM,
#2
RE: Methods for removal of W-, Ni- and V-coating
Hi Kahrax,

Enstrip A/TL and Enstrip GT-317 can be used for stripping tungsten carbide if thats any use to you? For Nickel nitric acid works a treat. I don't know about vanadium thoughSad
Water jet stripping could be used as an alternative?

Jim
Reply
08-05-2008, 02:22 PM,
#3
RE: Methods for removal of W-, Ni- and V-coating
Hi Kahrax

Sign0016 to the Surface Engineering Forum.

Apart from mechanical removal like grit blasting, machining, water jet etc.

Nickel - nitric acid as TurbineRepair says or a commercial nickel strip salt used in plating industry. Not sure if effective on tungsten or vanadium though.

Tungsten - Electrolytic etching with sodium carbonate (20%) tartaric acid (5%) and water. coating acts as anode, 4-8 amps per square inch @6 v dc.

Can't find chemical stripper, though I know potassium ferricyanide/potassium hydroxide solution seem to etch vigorously.

Vanadium - seems very little info. Resistant to sulphuric and hydrochloric acids and molten caustic salts. Nitric acid might work if it does not passivate. Try methods as for tungsten.
Reply
08-08-2008, 08:30 AM,
#4
RE: Methods for removal of W-, Ni- and V-coating
is there anybody who is still capable of stripping parts circa 2m in length using the Enstrip process in the uk?

Cheers,

Pete
Reply
01-31-2011, 12:07 PM,
#5
RE: Methods for removal of W-, Ni- and V-coating
Dears,

The prescription what was mentioned (sodium carbonate (20%) tartaric acid (5%) ) seems too simple compared to the cost of the Enstrip 317 or other HVOF remover stuffs. Has enybody already tested this mix?
I'd like to have a contract with one of the local supplier (galvanizer company) to test this prescription. If you have any experience, please let me know!
The coating I'd like to strip is: WC+CrC+Ni alloy.
The electrolytic stripping methode is importan for me, because It seems that this is the easiest way to keep the shape of the substrate during stripping.

Thanks in advance for all experiences or advices!

Balint


(08-05-2008, 02:22 PM)Gordon Wrote: Hi Kahrax

Sign0016 to the Surface Engineering Forum.

Apart from mechanical removal like grit blasting, machining, water jet etc.

Nickel - nitric acid as TurbineRepair says or a commercial nickel strip salt used in plating industry. Not sure if effective on tungsten or vanadium though.

Tungsten - Electrolytic etching with sodium carbonate (20%) tartaric acid (5%) and water. coating acts as anode, 4-8 amps per square inch @6 v dc.

Can't find chemical stripper, though I know potassium ferricyanide/potassium hydroxide solution seem to etch vigorously.

Vanadium - seems very little info. Resistant to sulphuric and hydrochloric acids and molten caustic salts. Nitric acid might work if it does not passivate. Try methods as for tungsten.

Reply
02-04-2011, 06:23 PM,
#6
RE: Methods for removal of W-, Ni- and V-coating
Hi Balint

Sign0016 to the Surface Engineering Forum.

Quote:The prescription what was mentioned (sodium carbonate (20%) tartaric acid (5%) ) seems too simple compared to the cost of the Enstrip 317 or other HVOF remover stuffs. Has enybody already tested this mix?
I'd like to have a contract with one of the local supplier (galvanizer company) to test this prescription. If you have any experience, please let me know!
The coating I'd like to strip is: WC+CrC+Ni alloy.
The electrolytic stripping methode is importan for me, because It seems that this is the easiest way to keep the shape of the substrate during stripping.

Thanks in advance for all experiences or advices!

I've not tried this recipe personally, so I would very interested in how it works for your application. I think I mentioned this recipe a few times before in other threads, but as yet have had no feed back. Good luck, I hope it works well for you Smile
Reply
02-10-2011, 04:50 PM,
#7
RE: Methods for removal of W-, Ni- and V-coating
Hi Gordon!

Ok. I will let you mnow the result.

But, if anybody has any experience please, let me know!

Balint


(02-04-2011, 06:23 PM)Gordon Wrote: Hi Balint

Sign0016 to the Surface Engineering Forum.

Quote:The prescription what was mentioned (sodium carbonate (20%) tartaric acid (5%) ) seems too simple compared to the cost of the Enstrip 317 or other HVOF remover stuffs. Has enybody already tested this mix?
I'd like to have a contract with one of the local supplier (galvanizer company) to test this prescription. If you have any experience, please let me know!
The coating I'd like to strip is: WC+CrC+Ni alloy.
The electrolytic stripping methode is importan for me, because It seems that this is the easiest way to keep the shape of the substrate during stripping.

Thanks in advance for all experiences or advices!

I've not tried this recipe personally, so I would very interested in how it works for your application. I think I mentioned this recipe a few times before in other threads, but as yet have had no feed back. Good luck, I hope it works well for you Smile

Reply
02-23-2011, 05:44 PM,
#8
RE: Methods for removal of W-, Ni- and V-coating
Hello every1,

I want to try this out but I have a few queries

1. Area: When you mean 4Amps/ Sq.inch, do you mean the area of the coating or the area of the cathod?
2. Current density: if the area to be considered is that of the coating, then if the coating is 600Sq.Inch what current would be required? mathematically it would be 600x4 but that doesnot sound right.
3. What grade of NaCO3 and Tartaric would be required? AR/LR or would lower grades would work?
4. Would higher voltage (let say 24V) make any difference?

If i do go ahead, I shall surely post the results..

BR
Rik
Reply
02-24-2011, 07:40 PM,
#9
RE: Methods for removal of W-, Ni- and V-coating
Hi Rik

Yes, I think that was meant to be current density for coating area. After thinking about it, this does seem to be extremely high. I checked the original document

Quote:Bath: 20% sodium carbonate, 5% tartaric acid, 75% water
Temperature: 70 - 80 C

A stainless steel cathode is required. The coated part acts as the anode. This method requires a current density of 4-8 amperes per square inch (0.006 - 0.0013 amperes/square mm) at 6 volts d.c.

Coating removal rate for tungsten coatings is approximately 0.001" per 20 min. and 0.001" per 10 min.for tungsten carbide coatings.

I suspect that may be in error. Maybe it should be 0.4 - 0.8 amperes per sq.inch. Another recipe from same document says "power requirements are .6 amperes at 11 volts d.c." I can only assume a current density per sq.inch. So may be a decimal point error.

I think commercial lower grade chemicals would be fine.

"Would higher voltage (let say 24V) make any difference?" I'm not really sure if it would be beneficial.

I think maybe a little experimentation will be called for Smile Good luck.

(02-23-2011, 05:44 PM)rik Wrote: Hello every1,

I want to try this out but I have a few queries

1. Area: When you mean 4Amps/ Sq.inch, do you mean the area of the coating or the area of the cathod?
2. Current density: if the area to be considered is that of the coating, then if the coating is 600Sq.Inch what current would be required? mathematically it would be 600x4 but that doesnot sound right.
3. What grade of NaCO3 and Tartaric would be required? AR/LR or would lower grades would work?
4. Would higher voltage (let say 24V) make any difference?

If i do go ahead, I shall surely post the results..

BR
Rik

Reply
04-11-2011, 11:32 AM, (This post was last modified: 04-11-2011, 11:50 AM by rik.)
#10
RE: Methods for removal of W-, Ni- and V-coating
Hello Every one...
Took a couple of trials with whatever material and chemicals I could gather. Tried this on a WC-Co coated strip that had around 220microns of as sprayed coating. The first 100 microns just took about 25 minutes but as the soultion became merkier, the efficiency dropped drastically. The next check after about 60 minutes only showed a thickness reduction on 50 microns. Conclusion is that it does work but would need more trials to reach consistent results.

Coated area approximately 4 Sq.inch, Voltage: 7VDC, Current: 4 Amps. I prepared the solution on volume concentration of the chemicals. Would carry out more trials very soon. Shall keep you posted on this. I am yet to see if the emissions in this process or the byproduct is harmful.

NOTE: NaCO3 + Tartaric Acid + Water -> Very effervescent mixture . If you are about to try this, first mix the Sodium carbonate and Water and then add the tartaric acid in small amounts while constantly stirring the mixture.

BR

Rik
Reply
04-12-2011, 09:36 AM,
#11
RE: Methods for removal of W-, Ni- and V-coating
Hi Rik

Thanks for the feedback Smile
Reply
04-21-2011, 12:34 PM,
#12
RE: Methods for removal of W-, Ni- and V-coating
Dear Rik!

Great news. Thanks for the feedback.

Bálint
Reply
05-29-2014, 03:10 PM,
#13
RE: Methods for removal of W-, Ni- and V-coating
Is the stripping recipe based on volume or mass? In other words, does one use 20% sodium carbonate by volume or by weight?
Reply
05-29-2014, 04:12 PM,
#14
RE: Methods for removal of W-, Ni- and V-coating
Hi djewell

Good question Question , Recipe I have only gives % which is poor. I would assume by weight eg. 20g sodium carbonate, 5g tartaric acid and 75g or 75 cc water.

(05-29-2014, 03:10 PM)djewell Wrote: Is the stripping recipe based on volume or mass? In other words, does one use 20% sodium carbonate by volume or by weight?
Reply
06-04-2014, 02:41 PM,
#15
RE: Methods for removal of W-, Ni- and V-coating
(07-31-2008, 02:38 PM)kahrax Wrote: Hi

As the topic suggests I am looking for ways to remove Tungsten, Nickel and Vanadium coatings. My starting point is an substrate with a layer of Tungsten and an intermediate layer of either Nickel or Vanadium.

The substrate used would be varying types of steel. For now I am not that interested in the effect on the substrate, but more the actual fact of removing the coatings.

Use high purity of alumina grit with bigger mesh size & do pressure blasting using higher pressure.

Thanks
Reply
01-28-2015, 07:53 PM,
#16
RE: Methods for removal of W-, Ni- and V-coating
(04-11-2011, 11:32 AM)rik Wrote: Hello Every one...
Took a couple of trials with whatever material and chemicals I could gather. Tried this on a WC-Co coated strip that had around 220microns of as sprayed coating. The first 100 microns just took about 25 minutes but as the soultion became merkier, the efficiency dropped drastically. The next check after about 60 minutes only showed a thickness reduction on 50 microns. Conclusion is that it does work but would need more trials to reach consistent results.

Coated area approximately 4 Sq.inch, Voltage: 7VDC, Current: 4 Amps. I prepared the solution on volume concentration of the chemicals. Would carry out more trials very soon. Shall keep you posted on this. I am yet to see if the emissions in this process or the byproduct is harmful.

NOTE: NaCO3 + Tartaric Acid + Water -> Very effervescent mixture . If you are about to try this, first mix the Sodium carbonate and Water and then add the tartaric acid in small amounts while constantly stirring the mixture.

BR

Rik

Rik,
Do you hear your solution? Are you stripping the part at 120 or is it closer to 70-80 degrees? I am trying to find out if the solutions temp makes a big difference.
Thanks!
Reply




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