Large thrust bearing - Material for thrust runner 1

[NZ Hydropower]

Hi,
I have a large, fluid film thrust bearing for a vertical shaft. Operating load is over 100 tonnes, and speed is several hundred rpm. I am considering making a replacement thrust runner for this bearing from mild steel plate, rather than by forging or casting, due to time constraints. I am concerned about the possibility of finding defects in the rolled plate, and the durability of the polished surface due to its relatively low hardness. I am looking for advice regarding choice of suitable materials and mechanical properties in this application, and any issues foreseen with the use of a rolled mild steel plate as stock.

Thanks in advance.

 

[HydroPE]

Hello macguyver21,

This is a replacement for a hydroelectric application, correct? Many of our hydro facilities have cast iron thrust runners that run on Babbitt shoes. The specific loading is somewhere around 100 to 200 psi (typically limited by Babbitt).

I believe mild steel plate would work fine. The bearing pressure is relatively low compared to steel. We reconditioned a thrust runner from the 1920's that was a soft steel with high specific loading (200 to 300 psi). The bearing surface was ground to 12-16 RMS. The unit has been running reliably ever since.

If there's uncertainty regarding the material, 4140HT is probably the way to go. Just be careful not to heat it beyond its serviceable temperature (based on temper).

Could you describe the original thrust collar/thrust runner? What's your timeline?


Best Regards,
HydroPE

 

[NZ Hydropower]

Thanks for your reply HydroPE. You are correct that this is a replacement part. We have settled on a forging made from AISI 1026/29 steel, with hardness 137-170 BHN. The forging will also be stress relieved. I have tentatively specified 16 Ra for the ground surface, with total runout of 0.8 thousandths on the running face. The forging seemed like the best option given I had concerns about potential quality problems with plate, and the relative softness of the plate we had available. The main attraction of using flame cut plate was a short lead-time.

 

[tbuelna]

What form of forging are you using? Is it a rolled ring, or a pancaked disc? Remember that your forging quality will be related to the raw material quality you start with. The purchase specifications of your forging should include requirements like max/min dimensions and form of raw material stock, upset/reduction ratios, grain characteristics, etc. Also be sure to allow for sufficient machine stock removal (>1/8") on all hot forged surfaces.

 

[NZ Hydropower]

Hi tbuelna. The forging will be made by ring rolling. I am relying on the expertise of the forging company to choose the correct reduction. I imagine the direction of grain flow will be pre-determined by the forging technique, in this case ring rolling. With regard to machining allowances, the forging supplier is proof machining the part for NDT with an allowance for finishing. Thanks for your input.

 

[tbuelna]

macguyver21-

Sounds like you're on the right path. If you need a metallurgy report for things like grain size, and you're not too particular, you can save some money by taking the samples from a prolongation rather than cutting up a forging. Let your vendor know this ahead of time so they can roll a ring with the extra length for the prolongation.

Good luck with your project.