Making a Ceramic HV Bushing

[Steven Sesselmann]

Hi Guys,

I thought some of you might be interested in this little project of mine,
making a ceramic bushing or feedthrough. As I was unable to find a ready
made insulator, I decided to draw on my old skills (I used to be a dental
ceramist, many moons ago) and try to make one myself. Note, that this is
not a vacuum feedthrough, it is HV bushing for use with an oil filled
chamber.

Unfortunately I I do not yet know how it will perform, or how many volts it
can withstand before breaking down. I am hoping that it will be good for
100KV.

I took a few snapshots as I was making a complete mess of my
workroom.

Here are the instructions, how to do it.

http://www.beejewel.com.au/~steven/Bushing.html

Steven

[Donald McKinley]

Beautiful Work

Don

[DaveC]

Steven -

Wanted to also say that it looks very professional from its photo. Hope its performance is just as good. Very nice, indeed.

Dave Cooper

[Starfire]

Excellent work - are they available to others Steven?

[Steven Sesselmann]

John, I was not really thinking of starting another business, but if it works
well, who knows? In the mean time it is pretty easy for anyone to do. You
could make the model from anything, I chose to use wood, because I am
comfortable with that medium. The only purpose of the model is to make
the plaster mould, so you could make a model by gluing some round discs
to a pipe, or anything of that nature..

Steven

[HighVoltageFox]

Great. I was wondering what you will use to bond the ceramic to stainless steel. I have been looking for a cheap alterative for indium as a seal medium, but have come up with nothing so far.

,AH

[Steven Sesselmann]

Andrew, fortunately I do not need a vacuum feedthrough for my fusor
design, I am trying something a little different. My design has an oil filled
chamber into which the high voltage feedthrough is placed, so the
feedthrough has two grooves for rubber O-rings.

However, I can offer a little bit of advise on bonding ceramics to metal, as
I worked for many years as a dental technician making VMK porcelain
bonded to metal crowns.

For starters you would need to use pure alumina clay, and not simple
china clay. Alumina porcelain does not bond directly to metal, but bonds to
the metal oxide on the surface, which in turn bonds to the metal.

In order to get a good ceramic to metal bond, we used to sandblast the
metal, which was either a beryllium or platinum based, then we used to
run it through a furnace to get a thin layer of oxide on the metal. Following
this we would apply a thin wash of alumina ceramic across the surface
and fire it again, this thin wash would then create a strong metal-ceramic
bond, onto which the main porcelain body could be bonded. Ideally this
shuld be done in a vacuum furnace.

This is probably why the going price for these things are around $2500
each.

Steven

[JohnCuthbert]

It might be an interesting project to make the feedthroughs for a fusor, but I think there's a catch.
How much does a kiln cost?

[Steven Sesselmann]

John, ... no catch, the girls at the local hobby ceramics club, did all the
firing for me and charged me $20.00 for the use of the power only

If I hadn't stopped them, they would have painted flowers all of the darn
thing too!

Steven

[Richard Hull]

Kilns of the size to fire that insulator are in the $2000.00 to $3000.00 new range. I have seen good used ones at hamfests for under $500.00 They take up about a cubic metter of living space and demand 240 volts at 40 amps. Find someone with a massive kiln and use their services.

Richard Hull

[Starfire]

Well - with flowers it would have been different

[DaveC]

Some Middle and High Schools have ceramics classes, and so do most Jr and Community Colleges. The worst it could cost you is tuition for a course. And you would get some exposure to the other secrets, too. The high schools might... welcome the project as an educational/cultural broadening experience for the students. You might need to make one for the instructor to put on display.

Dave Cooper

[Frank Sanns]

Dave has it. Take a class. There are many around. Often they will fire an extra piece for you at no charge. I did this for a while with projects until I wanted to bring hydrogen gas into a hot kiln. That didn't go over so well so I ended up buying one for myself.

My kiln does not get used very much but when I have a project that needs temperatures upto 2,350 F and need great control, it goes into the kiln. The kiln I have has complete electronic propertioning control for heating and cooling. You dial in heating rate or rates, hold temp or temps and cooling rate or rates and stand back and let its program do the job and record the entire program of time vs temp for the run. See http://www.skutt.com/products/km-1027.html for more info. It cost around $1,100 if I remeber correctly but it works great and is very versitile. I currently have a hydrogen tank sitting near it (not too near) and a series of stainless steel lines that go into a high temperature reactor that is located inside the kiln. I have done reductions and various other chemistries in the kiln. You would be amazed how many surface and heat treatments you can do on metals. Of course it is a blast to use the kiln to slip cast items (i.e. cups, bowls, dishes, vases, pencil holders) and make them for the house. I get board with the same ole same ole paterns so sometimes it is to the kiln and some creative firing and glazing. Yes flowers and odd shapes and colors. It beats boring!

Buy a kiln, have fun, do science, and furnish the house all wiht the same unit.

Frank S |*~--~*|

[Richard Hull]

I have two small kilns. Both have about a 8X8X8 inch capacity. I do a lot of lost wax casting when needed and some custom alloying with higher temp metals. A good OLD amateur scientist is very versatile and has accumulated a lot of useful stuff by 60 years of age. You gain skills while young for the most part and gear, insturments and equipment later as you enter the work force and rise through the ranks. Children are usually a deal breaker unless you have a fantastic job or the wife slaves away at a job as well.

People seem to think I am somehow magically loaded with most everything I need. It only took 60 years of stumbling around the planet to get here. Fortunately, I had no crumb snatchers hung around my neck like the proverbial albatross.

Richard Hull

[Steven Sesselmann]

Richard, you konstantly surprise... lost wax casting, is there nothing you
can't do? Incidentally my day job is lost wax casting, so if you need any help
on that one, no problem.

Steven

[Steven Sesselmann]

Thanks Carl,

I am familiar with the use of wax for model making, that could work well. I simply used wood, as I had it in my garage.

It should be noted, that I run a Jewellery manufacturing business by day, so I have three of those furnaces to play with.

The hardest part of the project was to eliminate cracking between the ridges. I ended up having to reduce the height of the ridges.

I also made MkII version, where I rolled out a square from the clay, and then rolled it onto a ceramic rod, like a "swiss roll" cake.

I then allowed the roll to dry for a few days, and consequently machined it in a leith to the desired shape, before bisque firing it.

This in my opinion was easier than using the plaster mould.

Steven

[Steven Sesselmann]

Carl,

Yes, after rolling it tightly onto the 8mm ceramic tube, making sure that the rod sticks out a bit on both ends, I was able to mount it on the leith by the ends of the ceramic rod.

Turning on very low speed, the green clay cuts like butter.

After machining you need to wrap it in a towel and let it dry for at least a week, before firing.

Steven

[DaveC]

A potter's "wheel" comes to mind, too, as an alternate to a lathe.

For a vacuum tight ceramic, you will most likely need to do some type of compression while the cereamic is still wet, so that micro pores are collapsed as much a possible. The glazing also helps to seal, but it is primarily a surface seal.

Definitely a task requiring significant skill.

Dave Cooper

[Steven Sesselmann]

As Dave correctly pointed out, making a high vacuum feedthrough is a lot harder. I am working on a different fusor design, where the feedthrough is not connected directly into the vacuum chamber, so for me that was not an issue.

If you wanted to make a vacuum feedthrough, you would start with a rod of machinable glass ceramic, such as Macor. This product is a very dense pre fired glass ceramic, and can be machined to very fine tolerances on a leith using normal tools.

The problem with Macor, is that it almost costs as much as buying a finished feedthrough.

Steven

[Verp]

Has anyone looked into this; http://www.warmglass.com/ ?