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Blunging, mixing

In ceramics, the mechanical mixing of a slurry is done with a blunger (usually a propeller mixer). Blungers of all different types are available. Some are simply a high-speed propeller on a shaft, others employ complex arrangements of paddles and container shapes. Clay slurries require the application of considerable amounts of energy to achieve a slip in which water has penetrated well between all particles. The rheology of incompletely mixed slurries will change as it ages, often quite drastically during the first few days. While industry generally has the mixers it needs to put the needed energy into the mix, potters most often do not.

Powder mixing is deceptively difficult. It might seem that shaking or tumbling some powders in a bag or container will mix them but this is not the case. The mixing and in-plant transport of powders is an entire industry (and science) unto itself. Companies constantly struggle with powder blending issues and often need to hire expensive consultants to assess the issues involving the specific type of powders they must deal with.

Simple propeller mixer with mount and switch

Simple propeller mixer with mount and switch

This is a heavy- duty unit, a 1/3 hp mixer that can handle up to 10 gallons.

The powder blender for making porcelain bodies at Plainsman Clays

The powder blender for making porcelain bodies at Plainsman Clays

All of the equipment has been washed in preparation for a porcelain run. Original container bags are broken in the dust-hood unit on the right and augered and elevated into the rotating blender/mixer. It feeds a vibrating screen (not visible) that removes paper and other contaminants. For wet clay bodies the screen feeds hoppers on the other side of the wall, they in turn feed the pugmill. For dry bodies and glazes the powder goes to one of the hoppers and that feeds a bagging unit. This type of equipment can handle 1200 lb batches (doing one every five minutes for some products, longer for others).

A small laboratory variable speed propeller mixer

A small laboratory variable speed propeller mixer

If you are at all serious about testing glazes and clay bodies, you need one of these. There are other methods, but nothing else comes close to this. These are expensive new, this one was more than $1000. But you can get them used on ebay.com. I adapted a mount (to give it vertical adjustment) from a hardware store. Propellers are also expensive, but you can design and 3D print them yourself or have them printed at a place like shapeways.com.

By Tony Hansen

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