Vacuum Bearings for TMP-50

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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hans_shokunin
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Re: Vacuum Bearings for TMP-50

Post by hans_shokunin »

Dennis P Brown wrote: Wed Sep 15, 2021 1:36 pm Maybe start a new one after this point.
I'm not sure what you mean. Do you mean the new thread?

Anyway, I moved on. After removing bottom segger ring and bunch of fine washers and sealing, I was able to pull the propellers out from the pump body. Then I realized that it didn't take that much force to pull the propellers off. Under it, there was another set of washers and sealing. Now I have the shaft assembly:
IMG_20210915_210848.jpg
There is a bushing where the bearings sit in. This bushing sits in the pump body this way (segger and washers already removed):
IMG_20210915_211046.jpg
The bushing has the bearings inside and covers on both the ends. They are press-locked and also seem glued in.
IMG_20210915_211417.jpg
I guess the next step is to order the puller and try to pull the entire assembly off the shaft. After that, I'm afraid that I will have to heat it up to make the glue brittle and then I may be able to disassemble it.

So it seems that there's plenty of room to make a mistake. Hope these photos help to anybody doing similar thing. Wish me luck :-)
John Futter
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Re: Vacuum Bearings for TMP-50

Post by John Futter »

I hope you have numbered the stator plates as to position

do not mix them up i used a pencil to leave numbers and left that on
John Futter
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Re: Vacuum Bearings for TMP-50

Post by John Futter »

I hope you have numbered the stator plates as to position

do not mix them up they look the same but aren't. i used a pencil to leave numbers and left that on
hans_shokunin
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Re: Vacuum Bearings for TMP-50

Post by hans_shokunin »

John, thank you for pointing that out. There seems to be two kinds of stator plates with different blade sizes and angles. I have stored them in reverse order, so hopefully I won't mix them up.

Next, I tried to push the shaft outside the housing. It didn't really take much force. One of the bearings came disassembled this way, so I have bunch of ceramic balls and the cage. Now I'm thinking how to get the outside rim of the bearing out from the housing. It seems to be catched firmly inside. Maybe glued in? Or inserted into the preheated housing? Who knows... it seems to be next battle :-)
IMG_20210916_112546.jpg
IMG_20210916_112546.jpg (59.99 KiB) Viewed 3956 times
Peter Schmelcher
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Re: Vacuum Bearings for TMP-50

Post by Peter Schmelcher »

I don’t see how from the pics the ball bearings are pre-loaded and they will be. Ball bearings get hot when spinning and the housing tube will behave as a heat sink to control dimensional growth between the parts. Hopefully some form of a spring was used for the pre-load and reassembly will be easy. If not keep the old ball bearing parts, make width measurements, and then somehow adjust or shim the new ball bearings effective width to replicate the original pre-load.
-Peter
hans_shokunin
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Re: Vacuum Bearings for TMP-50

Post by hans_shokunin »

There is a spring inside the tube, but I'm having trouble to get the outer ring of the old bearing out. It seems to be glued in or so. Maybe I should try inner bearing puller?
Peter Schmelcher
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Re: Vacuum Bearings for TMP-50

Post by Peter Schmelcher »

Well, that’s interesting.
For a spring to be an effective preload one of the 2 ball bearing outer races needs to slide in the tube (a non-binding slip fit on a very thin oil film). The odds are 50-50 but perhaps you opened the wrong end of the tube or the “glue” is corrosion. A copper or brass drift might come in handy to figure that out. I think I see some rust on the outside surface of the ball bearing tube assembly, which is mildly concerning. Oxalic acid will take oxygen away from rust should the sliding surfaces need some initial TLC before some very fine sandpaper or lapping to is used to restore the slip surface.
-Peter
hans_shokunin
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Re: Vacuum Bearings for TMP-50

Post by hans_shokunin »

Thank you Peter, you were right, there was a corrosion and it was holding it tight, so the preload didn't work at all. Some gasoline, ultrasonic cleaner and plenty of patience took care about it. The tube is symmetric inside and the spring preloads both the bearings.
IMG_20210918_154642.jpg
Peter Schmelcher
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Re: Vacuum Bearings for TMP-50

Post by Peter Schmelcher »

Both bearings floating is a bit odd because one of the two bearings must be precisely axial positioned so the rotor and stator fans blades don’t ever touch. It might be helpful for the next pump repair person to know the typical bearing pre-load spring force.

I would not have guessed that the disintegration of the bearing cage wouldn’t destroy the pump during spin down. Just curious how many ceramic balls were in the bearing?

I am guessing a $200 bearing is not in the budget. A ceramic bearing approx. $12 from China https://www.ebay.com/itm/124096028496 is allegedly ABEC7 and is available from many middleman sellers but without sufficient information to know how well it will work in a turbo pump. Over the years I have removed the rubber seal from many bearings. I use a cable tie end to lift the rubber seal followed by a flat blade screwdriver to pop off the seal but the important detail is don’t scratch any rolling surface.
hans_shokunin
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Re: Vacuum Bearings for TMP-50

Post by hans_shokunin »

There is a segger in the middle of the tube. From the side of the motor there sits additional washer on it. I will definitely doublecheck, but I think that this side of the assembly is pressed tight from the end cap. The end cap is locked with the rim of the tube being bent over.

I received the pump with the rotor completely stuck. During the loosening of the nut it got a bit loose and rotating it back and forth helped it spin again - but very, very noisy. After the bearings disassembly, it was full of rust and maybe another mess too. It seems that the bearings weren't actually that bad, maybe the preload function failure and aggressive and wet gases just made it bad. Unfortunately the cages were too fragile and were broken during the disassembly. Eight balls each. My theory is that the pump was working worse and worse and maybe got stuck not during the operation, but during the storage - because the turbine is in perfect order. However, plenty of rust everywhere in the bottom part.

Thank you for the link to particular bearing. My greatest concerns are about the oil vapor pressure. The bearings live in the output vacuum part, but it still requires to have some oil that doesn't get vaporized at operation temperature and is still able to act as a lubricant. For my foreline pump (rotary vane) I use double vacuum destilated oil, but I have no clue about the required viscosity for the TMP bearings. Most likely it's not the right one as it seems to be too dense.

I already asked Alpine to find the bearing for me and they pointed me to https://alpinebearing.com/ball-bearings/yca1650c-ghy72/. That's very close to those $200 for a pair. I also checked their lubricant Asonic GHY72, but even the smallest package is crazy expensive. Way more than $200!

At this point I'll try to check multiple bearing options. Let's see what I will find. Anyway all the alternatives are a bit risky - almost anything will work in the beginning, until it get stuck during the operation. Hopefully the Turbotronik will detect high consumption. And hopefully I will be able to detect topo high temperature of the TMP on time.
Peter Schmelcher
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Re: Vacuum Bearings for TMP-50

Post by Peter Schmelcher »

$200 for the correct set of pre greased bearings sounds very reasonable. A pair of the inexpensive bearings and 20ml of Kluber asonic ghy72 will run about $50. A chance at saving $150 is probably not worth your worry.
Many good tips are in the high-speed spindle bearing rebuild video. Clean is extremely important but honestly it is not all that difficult if you have good mechanical skills.

The TURBOTRONIK NT10 I have does not check very much. As I recall just the spin up time must be under 2minutes?? I think Jerry Biehler posted a schematic awhile back. Have fun.
Gustavo Cervantes
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Re: Vacuum Bearings for TMP-50

Post by Gustavo Cervantes »

Hello Hans,

Yes i was succesful, but i made a terrible work 😅 so i would not be showing such horrific things here.
The pump works great though, i just finished the dirver, im still programming it.
I opened another thread for that too.
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