Wire drawing cracking problem
06-20-2016, 11:22 PM,
#1
Wire drawing cracking problem
Hi, good afternoon.

I need some points of view about a problems that I have.

In the company we repair wire drawing blocks with HVOF tungsten carbide. In some occasions the wear of the capstans that we work are to several so we need to fill the wear (0.130 in diameter) using TWAS carbon steel coating (0.06-0.15 %C ,1.40-1.85% Mn) and then we apply the WC-Co, previous a grinding process and the sandblast, obviously.
A cracking problem occurs intermittently only in the carbon steel filling coating, and there is not only a wire drawing problem, this problem can present in all the carbon steel filling pieces. We had the idea that the cracking problem came from the filling, but making a probe we discovered that no, the substrate (carbon steel coating) is ok, with no crack (DPI inspection). Thinking that the HVOF parameters and material were the root of the problem, we made some specimens to analyze in the lab, the results are ok, no cracking, the hardness 1058.73 ± 139.59 HV , the porosity less than 1% and a very good carbide distribution.
So, I have some theories, one is the materials thermal expansion, specially the filling material (carbon steel). I know that the residual stress induced in the coating process (TWAS) is considerable and could be that with the HVOF process temperature the piece achieve a stress relief modifying a little bit the dimensions affecting the carbide coating.
Using the material coating physical properties of the TAFA 9000 operation manual.
Coefficient of thermal expansion:
420 ss : 6.6x10-7 in/in (1000 F)
95Ni-5Al: 7x10-6 in/in (1000 F)
I thing that try to using 420 ss or Ni Al TWAS coatings replacing the Carbon steel, of a small coating (This depends of the wear) around 0.060 in diameter can solve the craking problem, this for the thermal expansion differences.
What do you thing about the problem, Do you thing that is a process problem? What do you thing about the filling material change?
I hope your points of views about my problem. I think that changing the filling material can solve the problem but, Do you have any experience with this kind of problem?

Thank you!

Héctor
Reply
06-21-2016, 10:03 PM,
#2
RE: Wire drawing cracking problem
(06-20-2016, 11:22 PM)Hector Monjardin Wrote: Hi, good afternoon.

I need some points of view about a problems that I have.

In the company we repair wire drawing blocks with HVOF tungsten carbide. In some occasions the wear of the capstans that we work are to several so we need to fill the wear (0.130 in diameter) using TWAS carbon steel coating (0.06-0.15 %C ,1.40-1.85% Mn) and then we apply the WC-Co, previous a grinding process and the sandblast, obviously.
A cracking problem occurs intermittently only in the carbon steel filling coating, and there is not only a wire drawing problem, this problem can present in all the carbon steel filling pieces. We had the idea that the cracking problem came from the filling, but making a probe we discovered that no, the substrate (carbon steel coating) is ok, with no crack (DPI inspection). Thinking that the HVOF parameters and material were the root of the problem, we made some specimens to analyze in the lab, the results are ok, no cracking, the hardness 1058.73 ± 139.59 HV , the porosity less than 1% and a very good carbide distribution.
So, I have some theories, one is the materials thermal expansion, specially the filling material (carbon steel). I know that the residual stress induced in the coating process (TWAS) is considerable and could be that with the HVOF process temperature the piece achieve a stress relief modifying a little bit the dimensions affecting the carbide coating.
Using the material coating physical properties of the TAFA 9000 operation manual.
Coefficient of thermal expansion:
420 ss : 6.6x10-7 in/in (1000 F)
95Ni-5Al: 7x10-6 in/in (1000 F)
I thing that try to using 420 ss or Ni Al TWAS coatings replacing the Carbon steel, of a small coating (This depends of the wear) around 0.060 in diameter can solve the craking problem, this for the thermal expansion differences.
What do you thing about the problem, Do you thing that is a process problem? What do you thing about the filling material change?
I hope your points of views about my problem. I think that changing the filling material can solve the problem but, Do you have any experience with this kind of problem?

Thank you!

Héctor

Hi hector
when you repair ,you should be sure that all old coating has faded away after grinding ,if not you will have cracks ,also you have to control the heat of steel to stop coating ,when you reach the limite supported by dilatation ,you can stop let the substrat colding and finish coating later ,I hope it could help
Reply
06-22-2016, 08:07 AM, (This post was last modified: 06-22-2016, 08:08 AM by sprayloud.)
#3
RE: Wire drawing cracking problem

There are a few threads with similar questions. You might find some answers there:
http://www.gordonengland.co.uk/sef/Threa...20-coating
http://www.gordonengland.co.uk/sef/Threa...lame-Spray
Reply
06-23-2016, 05:37 PM,
#4
RE: Wire drawing cracking problem
Thank you Corund!...
I'm working with that.

Regards
Reply




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