Dog Bowls Show The Versatility Of Ceramic Slip Casting

Here at Hackaday, we feature projects that are built of just about every material imaginable. Silicon-spangled fiber-reinforced epoxy resin is our primary medium, but we see plastic, wood, steel, aluminum, and even textiles from time to time. It’s not often we see slip-cast ceramic molding, though, and when it pops up, it’s always good to take a look at this versatile manufacturing method.

The back-story on this one is that [thoughtfulocean], a mechanical engineer idled by COVID lockdowns, wanted custom water bowls for his dogs, one of whom is clearly a grumpy Ewok. The design started with a 3D-print of the final vessel, printed in sections and glued together. These were used to create a two-piece plaster mold into which a watery slurry of clay, or slip, was poured. The plaster mold dehydrates the slip, leaving behind a semi-solid layer of clay of the desired thickness once the excess slip is poured off. The resulting casting is then fired in a kiln and glazed.

Of course, [thoughtfulocean] ran into a few problems along the way. The first mold was warped thanks to the mold box bowing under pressure from the plaster, so the whole molding process had to be revamped. The finished bowl also shrunk less than expected after firing, which led to some more revisions. But the finished bowl look really nice, and the included pump and filter keeps the Ewok’s water free from the yuck a dog’s face can introduce. As a bonus, it sounds like [thoughtfulocean] might have created a marketable product from all this. Take that, COVID!

Slip-casting ceramic may not be all that common around here, but ceramic as a material isn’t exactly a stranger. And who says slip casting is limited to ceramic? After all, we’ve seen a similar method used with plastic resin.

[via r/engineering]

18 thoughts on “Dog Bowls Show The Versatility Of Ceramic Slip Casting

  1. Noice, always great to see a way to leverage 3D printers to make durable objects. Be great for custom insulators for HV work, stuff for hot metal, rocket nozzles, other nozzles and so on.

    1. I’ve always figured it should be pretty easy to extrude potters clay straight from a 3D printers head, I’m surprised we don’t see ceramic parts more often. Perhaps they could be dipped in resin, to add a thin layer, for strength.

        1. It’s even used to do exactly that, extrusion honing I think it’s called, used to smooth out ports in cylinder heads and cast manifolds or headers.

          However, if you could print a slipcast mould for 24 nozzles at once and by the time they’re glazed and fired, they’re actually harder than the green clay, then maybe you can bang through a print per nozzle or something.

        2. It’s only a nozzle material issue.
          There is a lot of material not seen on nozzle yet: tungsten carbide, UBE2, although we see do rubis now.
          But DIY induced cheapness is why we do not see them already.

          1. Its not only nozzle issue. Clay that could be extruded will not stick to itself enough to create solid joint, there will be pockets of air that will blow your pot into pieces and so on. With slip casting you go around it by having it harden as one piece without the need for any joint. With any coil thechnique you need some force applied to create joint (check Korean Onggi technique) then you need to smooth it out.

      1. You can 3d print clay but it ends up looking crap with very weak joints between layers. Do a bit pottery before there are techniques for joining coils of clay into vessels (like Korean Onggi pottery) but they require using force to join them, then to smooth them out. but using 3d prints as model to create casting moulds would work great.

  2. I think watery slurry is a poor description. IIRC slip is “defloculated” clay. Sodium silicate or sodium citrate (Callgon bath beads among many possible substances) is added to lower the pH and cancel the electrical attraction between clay layers. It is quite a treat to watch clay turn into a “liquid”.

  3. Slip casting ceramic is one more of the many things I’ve done. My family was one of the biggest producers of slip cast greenware in the Pacific Northwest in the 1970’s and early 1980’s. We had over 1,000 different plaster molds. Sold product to shops all over the place and taught classes. One poor gal worked on a porcelain doll for several days and after finishing it she carried it outside and immediately fumbled it, smashing it to pieces. Mom offered to let her do another at no cost but she was too upset at herself.

    To speed up production we had a special pouring table with a big stainless steel tank in the middle with a drain chute extending to both ends. The top was two long grates made of 1″ square wood. IiRC the whole table was around 20 feet long and about about 3 feet wide. Plenty of space to do large batches of castings.

    The other piece of very useful equipment was the Slip-O-Matic. A tall, cylindrical tank with a motor on top that had a drive shaft down to a special pump at the bottom. Its rotor was some weird spiral/twisted shape with a rubber surround. It’s designed to handle the abrasive slip and can pump both directions. That’s very useful for pumping most of the slip back out of the big molds like the Christmas tree.

    The trick to not getting bumps on the inside of slip castings is to first lay the mold on a side for a minute, then tip it pour hole down. That makes the liquid flow off to the side then down the side instead of drying into proto-stalactites on the bottom of your mugs and vases.

  4. Pro tip: invert the mold and raise it by a few mm then the cast item will drop clear as it shrinks, it will also dry more evenly as the set-up forms an enclosed space with more uniform humidity. Not just a theory, I have personally done it on entire production runs. Obviously your geometry and mold complexity impacts on how you do this, you may need to remove a top section before doing the above, then again some items are just not suited to the method so you have to dry them while covered in plastic, which takes a lot longer.

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