Appropriate Steel which survives durability cycles

[harid]

Hello Everyone,

I would like to know wat kinda steel will be good( in terms wear resistance due to pitting of 440 steel ball on coin band) for a inlet tube which needs coining to seal a 440 steel ball sitting on the Inner dia of tube. Problem is the assembly leaks after 20,000 durability cycles, I want the inlet tube coin band to last for 100K cycles.
Thank u all for any suggestions.
Harid

 

[metman]

1. The 440 is stainless steel?
2. Is the steel ball used to coin the tube?
3. Is the steel ball pitting or is the tube pitting?
4. What material is the tube?

Jesus is THE life,
Leonard

 

[alexit]

What is flowing in the tube that your stopping (air, oil, water, NaCl @ 850°C?)

 

[harid]

Ball is 440 Stainless steel, tube is 416 Stainless steel. Starter fluid or EEE fluid is flowing through the assembly. The steel ball is pitting the coin band on the tube and wearing it off causing leak increase with number of cycles of flow. Wear could also be because of vapor bubbles created,maybe imploding when the ball offsets or moves say 30microns from center causing huge pressure change in fraction of seconds causing wear of coin band. Please advice.

 

[alexit]

Continuing with stainless materials I would look to 52100 or perhaps a high-nitrogen stainless steel (like FAG material called Cronidur.) Both are used in the bearing industry for high mechanincal wear surfaces.

There could also be a chemical wear from the pressure issue as you stated, perhaps a material with different reactivity would improve life. Look to chemical compatibility of different materials with this fluid.

 

[harid]

Thanks for the replies, really appreciate it..
I am using the steel ball for coining with a coin force of 800lbf get a good seal band, my operating pressures are 400kpa max. Does 52100 steel withstand such coin force? How is the cost compared to 416 which is cheap. Basically this assembly has to work for gasoline fuel flowing through it. Its a regulator assembly.Please advice me further , do u really think chemical wear might be a cause?
Thanks a lot...
Harid

 

[israelkk]

You could use tungsten balls. However, I suspect the pre-coining process is the problem. When you are using the steel ball for coining to get a good seal band/ring you can not guarantee that the sealing ball will hit the coined area perfectly thereby, continuously enalarging the coined band. More than that, each time the ball hits the sealing area it distorts it and hit it off center creating multiple uncompleated partial round indentations which are in offset to the original perfect coined sealing ring/band.

One more problem is that even if it hits perfecly the sealing band will grow with each hit of the ball.

This is a commom problem with metal to metal bang bang sealing and there will always be some leak. On an on-off high speed pneumatic valve we used 440 ball on PH15-5 H900 or Custom 455 H-950 seat instead of 416. We had the same problem as you describe when we used pre-coining. We solved it in a different way than pre-coining.

Is the tube machined by you or is an off the shelf hydraulic tube? 416 is a free cutting stainless steel and as far as I know it is not supplied in tube form, it may come as hollow bar. Tubes are usually made of 316? Can you clarify on this?

Can you supply more data how the ball is guided to hit the coining band and how much is the ball travel until it hits the sealing area. Can you give the ball diameter and the sealing diameter?

 

[harid]

Thanks a lot for some good comments..
let me answer some of ur questions which might help u giving me solution for this problem.
Tube is machined by us and hardened to RC30, ball of dia 7mm is seated on 6mm ID tube and press is used to hit on the ball to create the pre-coin.
Coming to PH15-5 H900 or 455H-950 seat , could u please tell me cost comparison with 416 steel?
We also tried tunsten balls, but couldnt get away with leak.We also tried some harder steels with higher Rc values but we couldnt even pass initial leak before durability. 416 seems to work initial leak but not durability.
Could u please let me know how u solved ur problem without pre-coining?
Ur help and advice is greatly appreciated.
Thanks in advance

harid

 

[israelkk]

Before I be able to explain how we solved the problem I need to know how your assemly is built.
Is it a check valve?
Is the sealing ball is loaded by a spring or what other force presses it to the coined band?
How far is the ball from the sealing sit (coined band)? What are the forces that acts on the ball during sealing? Is the pressure coming from the tube (attempting to raise the ball) or helping the ball to seal?
What is the desired effective flow area when the ball is not sealing the tube?

 

[israelkk]

I looked again at your postings and understood that it is used in a regulator assembly. Is it used as a relief valve for excess pressure or is it the active regulating item? How much movement of the ball is really needed? Sometimes limiting the ball movement to the absolute minimum needed movement from the sealing face can do the job.

 

[harid]

Thanks for the replies..
It is a regulator. used as active regulating item.The sealing ball is loaded by spring. The ball sits on coin band. when fuel flows through it at 400kpa, ball lifts by approx 250microns.Also could u please give an idea of cost comparison of the materials u suggested with 416 steel.Could u please advice and also plz lemme know how u have tackled this problem?
Thank u
harid

 

[harid]

Hello friends,

Could u please help me with the question I posted... Israelkk could u please help me out..i would really appreciate it.

Thank you
Harid

 

[alexit]

I have no idea of your location or quantity but from my own rule of thumb:
416 =1x
52100 = 2-3x
High Nitrogen Steel = 10-20x

You must also special attention to heat treating of high nitrogen steels, this is art because the nitrogen pressure in the heat treat cannot add/subtract nitrogen from the material without damaging the properties making this so wear resistant.

If the above costs do not scare you, the high nitrogen steels were designed with the aircraft industry for very-high-speed and/or very-high-life applications. This material replaced the 52100 steels in many different applications.

One application I have heard mentioned is in the turbine where they use the jet fuel as bearing coolant.

 

[Metalguy]

52100 is not a stainless steel, so if water in your fluid is a possibility you may not want to use it.