To determine what type of equipment is best for your business, you first have to know how to differentiate between the different types that are available. Pugmills, clay mixers and pugger-mixers are the most common pieces of clay processing equipment used today. Pugmills homogenize moist clay as the internal auger compresses and drives the clay body out a reducing nozzle in a continuous log. Many pugmills offer a deairing option to further reduce wedging. Clay mixers combine and blend clay bodies and serve as a reclaimer of scraps, while pugger-mixers have the unique capability to mix and pug in a single machine, and some machines also deair.
To help compare capabilities, manufacturers rate their machines’ output. Clay mixers are rated by batch capacity, which is based on the dimensions of the mixing bucket or tub. After mixing, you must empty the clay mixer and then begin a new batch. Pugmills are rated in pounds per hour, which is based on the output. What is missing from this rating is the feed rate—that is, how fast you or your assistant can hand feed the clay into the pugmill. Pugger-mixers are rated by both batch capacity and pounds per hour. The important distinction is that the pugger-mixer as a mixer unloads itself, and as a pugmill feeds itself. This means time and effort saved for productive work.
Because of its beneficial features, many potters have selected the pugger-mixer as their clay processing equipment of choice. But once you have decided to make a pugger-mixer part of your studio, how do you determine what features you need? First, evaluate your studio’s needs. Second, talk to other potters who use a pugger-mixer and try to see a machine in use. And finally, evaluate the individual components used to build the pugger-mixer and the accompanying warranty.
Do you want to recycle scrap with minimal effort? Many times slaking buckets and storing large quantities of scrap can be eliminated by conveniently storing scrap directly in the pugger-mixer. A pugger-mixer uses powerful mixing action to completely homogenize powder, scrap, wet and greenware clay bodies, and then unloads itself through the nozzle. Clay handling is greatly reduced without the heavy labor of transferring wet clay from separate mixer to independent pugmill and back again if the consistency is incorrect.
Do you want to mix clay from powder, blend clay bodies, make test batches or add material to a body such as grog or color? Knowing the true composition of the working clay gives the pugger-mixer owner product control. Another benefit expressed by pugger-mixer owners is the space savings of a single machine for two processes.
The motor and drive gear are the power behind any pugger-mixer. The larger the rated horsepower (1 hp = 747 watts; watts = volts x amps), the greater the mixing and pugging power. Make sure the electricity available in your studio or manufacturing facility can supply the necessary power required by the pugger-mixer you choose. The vacuum pump on a deairing pugger-mixer typically is 120 volts, even if the drive motor is 220 volts. Make sure you have all the necessary power at the location you have chosen for the pugger-mixer. Just like a leaky garden hose will not provide the output expected, electrical service with old circuit breakers, corroded connections or under-sized wire will keep the pugger-mixer from performing as expected. Additionally, every pugger-mixer should have some overload protection, such as easily accessible fuses or thermal overload integral to the motor starter. Are the operator controls easily accessible when loading and unloading? This is important for convenience and operator safety. Other safety features to look for could include an automatic auger shut off when the hopper door is opened, an enclosure or shroud for any exposed drive components, or “lock out” keys.
Bearings help support the mixing/auger shaft and ensure smooth, true rotation. Clay can slowly work its way down the shaft and come in contact with the bearings, and the bearings can fail prematurely if this condition continues. To avoid this situation, pugger-mixers should include protection such as extra seals, “vent paths” for particles that make it to the bearing and “zerk” fittings to occasionally grease the bearings.
In general, well-built pugger-mixers under high to moderate use should have a product life expectancy of 15-20 years, depending on care and maintenance. During this time, certain components could need replacement—most likely electrical components, a bearing or possibly a part of the drive system. To this end, it is easier and less expensive to source “off-the-shelf” or standard components than it is to be required to purchase custom components from the manufacturer. Investigate the manufacturer’s warranty and ask about acquiring replacement parts.