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Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Make sure you have some expansion volume for the oil, or you'll get an expensive lesson in thermal expansion when the oil gets hot. An air bubble in the oil is not a good idea, for obvious reasons. The usual solution is to use some sort of flexible membrane as a part of the outer casing, or a rubber bulb in the oil, either filled with air and sealed off, or vented to the outside of the casing.
Also, I second what James is saying. The actual x-ray head is only one sub-assembly of a complete x-ray machine, and whether you've used a complete manufactured x-ray head or put one together out of parts out of other x-ray machines makes little difference in the big picture. Doing it the way you have done can be a very valuable learning exercise though.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Anders M. wrote ...
Make sure you have some expansion volume for the oil, or you'll get an expensive lesson in thermal expansion when the oil gets hot. An air bubble in the oil is not a good idea, for obvious reasons. The usual solution is to use some sort of flexible membrane as a part of the outer casing, or a rubber bulb in the oil, either filled with air and sealed off, or vented to the outside of the casing.
Yes, but make sure that any "rubber" or other flexible membrane that you use is compatible with oil. Natural rubber will deteriorate very quickly while in contact with oil. Most dental X-ray heads use "Buna-N" (aka, Nitrile) rubber, which can be in contact with oil for decades without deteriorating. Some heads utilize the actual housing for oil expansion/contraction which is made of a very thin steel sheetmetal, sort of like a can of Spam!
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Yes I'm trying to think of a way to solve the expansion issue, as of right now there is just an air bubble in there.
Another issue, oil is seeping out. Not leaking out (no puddles of oil), but just a thin film is seeping out. I think I need some thicker oil, this transformer oil is thinner than water, pretty much as thin as acetone.
Hmm, maybe I could drill a hole in the rubber stopper, then superglue pice of a nitrile glove over the hole. I found these purple gloves in the basement and they aren't very stretchy, so they are likely nitrile.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Alright so here's what I came up with.
Basically I'm sticking a gove's finger in the hole and gluing it in place. It should work...
I needed a thicker oil so I found some husqvarna premium bar and chain oil. The stuff is as thick as maple syrup and by using a 9kV NST I figured out that its dielectric strength is about 10kV per mm, therefore it should be an excellent oil for this x-ray head.
*Let it be known that husqvarna premium bar and chain oil has a dielectric strength of 10kV per mm, and costs only 5 bux a quart*
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Your plastic casing probably has enough flex to deal with expansion, although putting a sealed air filled rubber item inside is not a bad idea, maybe seal the end of a disposable plastic eye dropper or a small syringe?
Thick oil will wick out too if you have a leak. Did you seal the feedthroughs with silicone or epoxy on the inside?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Grenadier wrote ...
19kV, I made sure to space them apart enough. If not I can always glue a little piece of plastic in between them.
Perhaps you might want to do that before powering up for the first time. Once surface tracking has started, you might not notice it until the course of the tracks is too well established to get rid of.
Ionic surface contamination - perspiration, for example - helps set the scene for tracking breakdown.
Dielectric surface discharges are complex phenomena, so you mustn't think of your GND and HV terminals as though they were simply separated by air.
Powering up in complete darkness, and then looking for the presence of streamers once your eyes have adjusted, may help you identify spawning problems.
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Grenadier's big thread of Röntgen related shenanigans
