threads seizing... ideas why?

[USAeng]

we have a 1 1/4-12 unf 1B and a 1 1/4-12 unf class not specified on drawing but with a pitch limit of 1.194/1.193

the material is 1144 steel and the temp is about 1000F

customer is complaining about parts not being able to be taken apart after in service for some time

Any ideas why these threads would be seizing? Thanks

My initial ideas are to explore different materials and to go to a course thread.

 

[USAeng]

Its basically a cap nut that fits over a nozzle that screws onto a pipe to give the nozzle a mechanical seal from the lapped surface of the nozzle to the lapped surface at the end of the pipe. The thread specs are above.

 

[USAeng]

it sprays oil but normally sits empty in those temps

 

[rmw]

I've always seen those oil gun nozzle caps as a hard SS material, and I don't remember what but somehow 410 popped into my mind. I've never seen them in CS. The gun tube, yes, CS.

rmw

 

[unclesyd]

If this is for an oil gun tip I concur with rwm in that everyone I've seen has been made from SS. On the one's we use the barrel and tip are made from SS. Most of the time the atomizer nozzle is also made from SS and a few made from CS.
All our tips are 316 SS with a few exceptions where a higher alloy is used along with a 304 nozzle. Th threads are 6 TPI.

One thing I did many years ago was to use a metal O-ring gasket between the tip and nozzle for sealing. This helped to prevent distortion due different CTE and differential heating. I would definately try to get away from mating two lapped surfaces under your operating conditions. By using the gasket we were able to tap the threads oversize and undercut the male threads

Just before I left I made 2 nozzles from Nitronic 60 because they are used in a make and break application for cleaning. I don't have any results as they only have about 500 hrs in operation due to rocess changes.

 

[USAeng]

a few pictures of the threads that were seized after being cut open... any ideas?

 

[USAeng]

another

 

[USAeng]

yet another

 

[USAeng]

here is one more

 

[desertfox]

Hi

Looks like thread galling to me.

desertfox