manufacturing engineering structural ceramics?

[coppercone2]

If you have a decent kiln and a little shop, do you see it possible to manufacture decent engineering ceramics like stand offs?

The go-to solution for this is to use MACOR, but does anyone know if its like a serious ordeal to make decent quality stuff with good ingredients?

is it gonna be the same hydraulic press and mold bullshit requirement as ferrite?

[David Hess]

I am sure you could if you know how to do it.  Tektronix made their own ceramic parts like terminals in their own small shop.

[coppercone2]

Do you know if you can just extend the heat cycle to something really long and stupid to get similar results to pressing? Does it just not diffuse right if you don't have the right initial conditions? I could see myself paying alot to run a kiln for a long period of time but I don't see myself figuring out how to grind and lap nice molds to make small parts, partly because the fun is gone at that point if I am sitting in solidworks trying to make a hydraulic piston because I want some kind of custom standoff then having to make all this tooling, I was hoping there is a 'more expensive' process where I can use jewelry making techniques/stuff that works with plastics prototyping/3d printers. The rapid prototype thing is completely gone at that point, unless you:

1) get a program that makes a mold from your 3d model (if you even need one, I was hoping I can replicate things that are drilled out from metal, wood, wax or such in ceramic.)
2) get a 150,000$ CNC machine that can make the mold

Same for ferrites (in my other thread), you need to fucking press them. The hydraulic press jig requires pretty much a lot of expensive tools and knowledge compared to mixing some powders and making a spin dryer and even making a high end kiln (you go from cutting/welding/balancing to thick precision machining)

[KL27x]

Some ceramics require extreme consistency with very tight tolerances. Ceramics are mainly a sintered material. Cook too long, and you end up with areas of amorphous glass or crystals with inclusions instead of the desired material. Famous pottery manufacturers of old maintained strict conditions down to the attitude of the workers. And if the place were destroyed by war or natural disaster or the workers were lost, those materials and processes and proudcts were potentially lost. Even having the recipes written on a piece of paper and one person with overall knowledge, it would be very difficult to reproduce the conditions and workflow and culture that originally happened to strike and maintain that exact note. So yeah, if you heated it enough, it might melt into one chunk. But it probably wouldn't produce the same physical characteristics. The reason it is done the way it is is so that the stuff fuses in the right configuration in the right amount at the right time and without producing internal stresses.

For the home shop, I suspect exotic ceramics beyond basic pottery would be a hobby/passion/timesink. It could be enormous work to fine tune the mix and the kiln ramp for a specific size/shape mold, and to replicate that for another shape/size might be like starting over. If you aren't making thousands, that could be very unproductive. In some cases, it might be easier to shape/mill out parts from commercially available ceramics with diamond saws and bits.

[coppercone2]

is it really that bad? I know there is research in 3d printed ceramics for engineering purposes. I thought maybe kinda you could get something pretty close since people are 3d printing em

Some seem to have extreme difficulty, like boron carbide (i think) but I thought maybe there is some approachable ones.

[nanofrog]

You can get ceramic standoffs relatively inexpensively (2" long, #6-32 screw), so you're better off just buying what you need. Do note that the prices go up as you shorten the length (0.75" long, #6-32 screw).

[chris_leyson]

Why bother trying to manufacture ceramic when you can buy it, if you want make your own ceramic standoffs then good luck but it's a waste of time. Have you even thought about the end terminations, are you you going to manufacture all of the tooling to stamp them out and then make the tooling to crimp them because that's how they were made back in the day. So you got a kiln well make some pottery then.

[coppercone2]

I have thought of alot of different things.

[T3sl4co1l]

is it really that bad? I know there is research in 3d printed ceramics for engineering purposes. I thought maybe kinda you could get something pretty close since people are 3d printing em

Some seem to have extreme difficulty, like boron carbide (i think) but I thought maybe there is some approachable ones.

Yes, it is that bad, but it depends on what you are doing.

Pottery cycles are rated by cones, a cone being a triangular molded shape, which slumps and falls over at a well defined time*temperature, made with a precision formulation.

A cone is not a specific temperature.  It takes time for the components to react and dissolve, and the viscous part-glassy mix formed takes time to slump as well.  This makes designing a thermal profile not the easiest thing, but it also means the body being fired will respond in the same way as the cone does.

If you're doing simple stoneware, you can usually fire over a wide range of levels.  A cone 0 "bisque" firing is enough to stick the material together (it is hard and makes a "tink" sound when struck), but it isn't very strong and has a chalky feel.  Cone 10 is very typical for a dense, strong body, or maybe cone 6 with a lot of flux in the mix.  Pure clays typically melt around cone 30 (a peak temperature over 1800C I think).

The mix matters very much.  Porcelain achieves its fine translucent beauty thanks to a large glass content.  It must be fired very carefully, so that some crystalline matrix remains at peak temperature.  A little more and it slumps to a blob.  Too low and it's just any stoneware, with remaining porosity.

For electrical applications, you'd be most interested in porcelain and glazed stoneware for insulators, plain for spacers, and also steatite and cordierite for lower expansion applications (commonly used in wirewound resistors).  Mullite and alumina are a bit more challenging (high firing temperature), and probably not very necessary outside of very high temperature applications (good for making your own kiln hardware, though).

Shrinkage on firing will be typical for a given batch, assuming it's well mixed and de-aired.  Warpage occurs if heating is too fast or uneven.  Dry bodies can be carved by hand or machine, but they are very weak so you can't get too crazy with it.  Moist (but not soft) mix can be pressed by hand, or dry mix in a press proper.  Liquid suspension (slip) can be molded in a porous (usually plaster or concrete) mold, then the excess poured out, making hollow shapes.

Precision, adequate for making insulators, would be pretty easy with molding and carving.  Precision say for flat heatsink insulator plates, don't count on it -- you'll need a grinder for that, most likely.  Fired items can definitely be shaped, but carbide or preferably diamond tooling is required, with very slow feedrates and water cooling.

Tim

[coppercone2]

So I see you did not mention presses anywhere in your post.

Where does the press come in? All the manufacturing videos for engineering crap are made with presses. Same question as with ferrite too, how much does density of this stuff change with pressing? It sounds like you need to make a precise mix then make test cones to figure to get an idea of the heating cycle.

I don't know what you can do that much with high temperature stuff, the most appealing for me is just a multizone tube furnace and a vacuum/inert gas kiln, which can be used for high temperature synthesis and also for vacuum brazing silver, which is a very nice process, the main reason why I designed a kiln.

The maximum temperature in air is something like 1400C, anything more requires obscenely expensive heating elements of silicon carbide or mosi2

That rules out alumina and zr, thats a step for a more advanced furnace. And anything heatsink is going to need to be ground and probobly lapped, no idea how to lap ceramics, ceramic heatsinks are interesting though

[T3sl4co1l]

So I see you did not mention presses anywhere in your post.

I'm not surprised...

Dry bodies can be carved by hand or machine, but they are very weak so you can't get too crazy with it.  Moist (but not soft) mix can be pressed by hand, or dry mix in a press proper.  Liquid suspension (slip) can be molded in a porous (usually plaster or concrete) mold, then the excess poured out, making hollow shapes.

An awful lot of pottery is made without presses at all, but you can if you want to, and you'll save on drying shrinkage and warpage in the process.

Where does the press come in? All the manufacturing videos for engineering crap are made with presses. Same question as with ferrite too, how much does density of this stuff change with pressing? It sounds like you need to make a precise mix then make test cones to figure to get an idea of the heating cycle.

Maybe.  Are you making insulators, or Al2O3 substrates?  Black glaze* or low-loss ferrite?

*Iron imparts a dark color to glass, green or brown depending on reducing or oxidizing atmosphere.  Paired with a few others elements to filter out the remaining colors, you can get a quite densely black glaze.  So, ferrite with rather a lot of silica thrown in, is just black glaze.

Tek made their scopes with pressed ceramic materials over glass, for better dimensional stability; even so, they were ground to exact dimensions after firing.  Ferrite shape cores are ground on their mating faces.

The maximum temperature in air is something like 1400C, anything more requires obscenely expensive heating elements of silicon carbide or mosi2

That rules out alumina and zr, thats a step for a more advanced furnace. And anything heatsink is going to need to be ground and probobly lapped, no idea how to lap ceramics, ceramic heatsinks are interesting though

The ancients used fire clay and charcoal/coke to handle molten iron at over 1600C.  By "ancients", I mean some actually-ancient applications (bloomery, cupola) for making iron but not usually quite so hot, up to the recent past (wrought iron in a puddling (reverberatory) furnace; Bessemer converter), "ancient" then in a more technological sense.  There are two reasons modern steelmaking doesn't use clay anymore, and only one of them is strength!

Indeed, electric furnaces aren't too cheap beyond 1300C or so.  Fueled furnaces do just fine up to maybe 1800C, but you'll have a harder time doing high temperature technical ceramics in them.  But if you're doing technical ceramics anyway, I would expect you have a customer buying enough of the stuff, at a specified purity and strength and so on, to more than justify the capital cost of a furnace that handles it...

Tim

[coppercone2]

I don't know exactly what I am going to make its more like trying to figure out what I can make so I can get the most entertainment per dollar out of a furnace build to justify actually doing it

Figuring out what I can do without a press means I have a roadmap for potential workshop activities (which might include rapid prototyping of custom ferrite cores (but it really looks like you need a press here) and making ceramic structures for hot things and high voltage experiment type stuff *which will also be much easier to deep clean then fucking plastic*. I want to buy and make stuff that gives me alot of fun/scientific capability basically. I managed to acquire some serious lemons *i.e. automatic PVC pipe cutter, difficult to repair microwave equipment that I am kinda scared to use alot, specialized brazing equipment (seriously just stick with fucking 56% silver for 90% of things you want to do)* that kinda been sitting around collecting dust and this stuff requires some serious brain power to justify using in some cases..

A furnace very useful for chemistry anyway, since you can make various interesting things (white phosphorus, high temperature reductions, custom metal alloys (thought maybe induction is a better choice for some) with a furnace and make fully dehydrated molten salts and possibly make custom stuff for metal deposition etc, so its probably eventually gonna get made regardless of the electronic uses. It is kind of a beast in terms of setup and everything compared to buying some amplifiers or couplers for the same amount of money however since you need a dedicated work area for dealing with hot things safely, have dry floors, etc. And its rather big, immobile, fragile and heavy. As far as potential lemon goes, a big electric furnace that has a small interior heating space and precise control you don't necessarily need could be king lemon. The only thing that trumps it would be a car sitting on cinder blocks in front of your house or a non functional bull dozer. I have seen kilns abandoned for like 20 years in the back of garages before. They need a through road map because you can't just accept the fact you wasted money and stuff them in a tool box drawer.