Thread galling
Thread galling
(OP)
I need some help on some galling issues. I desing instruments for medical devices, so the material is usually stainless steel. When I have thread mating instruments (both of same material), I have been told that differing the heat treat between the two parts will reduce the likelyhood of galling. For example, Part 1 will be 17-4PH (H900) and Part 2 will be 17-4PH (H1150). So these two parts are supposedly more gall resistent than 2 mating threads of both 17-4PH (H900).
A material science friend showed me this threshold galling data (below) that gives threshold galling values for the pairing of materials with the same heat treat, but this still leaves the question of mixing and matching heat treats unanwsered.
does anyone have some insight on this subject?
fyi, adding a lubricant isnt an option.
-----------
1st material
17-4PH heat treat to H900 (HRC-45)
2nd material
17-4PH heat treat to H900 (HRC-45)
Threshold Galling Stress (MPa)
69
------------
1st material
17-4PH heat treat to H1150 (HRC-34)
2nd material
17-4PH heat treat to H1150 (HRC-34)
Threshold Galling Stress (MPa)
34
--------------
thanks
dan.
A material science friend showed me this threshold galling data (below) that gives threshold galling values for the pairing of materials with the same heat treat, but this still leaves the question of mixing and matching heat treats unanwsered.
does anyone have some insight on this subject?
fyi, adding a lubricant isnt an option.
-----------
1st material
17-4PH heat treat to H900 (HRC-45)
2nd material
17-4PH heat treat to H900 (HRC-45)
Threshold Galling Stress (MPa)
69
------------
1st material
17-4PH heat treat to H1150 (HRC-34)
2nd material
17-4PH heat treat to H1150 (HRC-34)
Threshold Galling Stress (MPa)
34
--------------
thanks
dan.





RE: Thread galling
RE: Thread galling
http://nt
that reports:
"The nuts a r e usually s i l v e r plated t o overcome galling. Silver does not readily sublimate and acts. as. a lubricant and. antigalling agent"
Regards,
http://www.welding-advisers.com/
RE: Thread galling
bcd
RE: Thread galling
RE: Thread galling
(There must be one of them that is certified for medical devices.)
Nick
I love materials science!
RE: Thread galling
RE: Thread galling
Hi.
Yes, I agree with the others. Creating a hardness gap between metals by 20 (Rc) is very good. So is adding a coating for 'dry' lubrication.
Is this for an implantable device? Maybe it's short-term, direct tissue contact, re-usable? Or perhaps it's short-term, direct tissue contact, disposable? Your answers are most important in choosing a coating.
Like Nick says, PVD/PACVD/CVD may serve you well.
For more help, see:
<a href="http
Good luck!
William Gunnar
http://www.IndustrialCoatingsWorld.com
RE: Thread galling
RE: Thread galling
RE: Thread galling
V
RE: Thread galling
As it is a basic coating provided by pretty much any coatings provider, you will find it cheap in comparison to AlTiN.
You could also try out CVD Diamond-like Carbon (DLC), as it has a much lower coatings-steel coefficient of friction, but it will be a more expensive application and if the torque on the threads is high it may crack the coating due to its high hardness.
Finally, you could try tungsten disulphide (WS2); it may be more difficult to locate a vendor in the US than TiN coaters, but it works similarly to MoS2 but binds to the surface better, so you get a longer life. Also, this will cope with any potential substrate deformation better than any coating, as it is a very thin application and can migrate between surfaces.
Andy
RE: Thread galling
Hi, again.
Material choices with lower ductility are less likely to experience galling. This is because under higher loads, surface asperities are more prone to fracture-dislocation during interlock.
Conversely, high ductile materials are much more prone to plastic deformation. Therefore, galling is more likely to occur.
Assuming you've taken into account contact stress and finish, consider surface treatments, like nitriding, carburizing, hard face coatings and ion implantation. They can serve you well, assuming your thread configuration is compliant.
For more information, just see:
<a href="htt
Generally speaking, for austenitic stainless steels, consider Cr-Mn-N over Cr-N alloys. And for the heat treat hardenable stainless steels, higher threshold galling stress materials like PH martensite, under decreased aging temperature, are the way to go.
Preventing galling through a large difference in hardness is a misconception. Actually, alloys with good adhesive wear, like 440C (57 HRC) and S21800 (92 HRB) are excellent choices, regardless of the hardness of the other alloy.
Good luck!
William Gunnar
http://www.IndustrialCoatingsWorld.com
RE: Thread galling
In our world, we use silver plated nuts and bolts on the exhaust on our really expensive cars. They also work really well on axle CV's which are abused without end on a race car. The silver plated stuff never galls--problem solved.
Also, we have found that lousy machining leaves mirco-burrs which will gall in a heart-beat. Nicely machining your parts goes a long way to prevent galling. Perhaps you could try electro-polishing or cleaning up your threads somehow. Look at them under a microscope--you may not like what you see.
As for making parts with different hardnesses, I am not sure about that one. The hubs on an F1 and the wheel nuts are made from the same material--Steel (can't divulge the alloy) hardened to 55 Rockwell C. Talk about loading, slamming, banging, taking off an putting back on--there may be no equal. They avoid galling by truly beautiful machining practices.
David
www.kirkhammotorsports.com
RE: Thread galling
B
RE: Thread galling
Depending on the thread type and size, you may consider thread inserts such as Heli-coil.
RE: Thread galling