Galling - Stellite 6 self mated pair 2

[howkers]

The usual loaded pin galling pressure test runs at relatively low surface velocities. I am told by one of our valve suppliers that they had extensive difficulties with self-mated Stellite 6 in water when the operating speed of the valve was increased to slightly over 1 ft/sec. Below this it was OK.

This velocity doesn't seem particularly fast to me and I have always regarded Stellite 6 on Stellite 6 as an excellent anti-galling pair. None of the local metalurgists has heard of velocity being a factor in galling; however the valve man says it was definitely confirmed by extensive trials with different material pairs and velocities.

Does anyone else have any experience of surface velocity being an important variable in resisting galling in Stellite or other materials.

 

[PeterIgg]

We have typically used Stellite 6 running on Stellite 21 (Ball valves - 6 on the ball, 21 on the seat). However at higher temperatures we have experienced galling in this combination. More lately we have been using HVOF applied carbides, typically Tungsten carbide, and have had few problems to date but with improved performance. At this level of hardness (about 72 HRC) there appears to be no need to have a hardness differential.

Would be interested in other experiences.

 

[wustl]

When you have galling problems with Stellite alloys at high temperatures, you should consider using Tribaloy alloys, which are more stable at high temperatures.

 

[vonbixadmiral]

The traditional tests according ASTM G 98 (91) may be useful, but it is only qualitative for a generic overview.
The main parameters are or may be: "specific pressure onto the surfaces,velocity,materials,temperature"; the function has a certain complexity and you have to study more dedicated tests in order to get appropriate evaluations.
You have to prepare a matrix of various parameters and to define the importance. Consequently you have to define some tipical situations by an effective simulations.

 

[DowneastTech]

Just a suggestion. You might consider running stellite #6 against Colmonoy #5 this combination runs together remarkably well in all of the conditions I have used it in.

DowneastTech
Mechanical Engineer
Magnus R & D, Cypress, TX