POTTERY PRODUCTION PRACTICES: Understanding Batch Mixing Pugmills

September 1, 2007
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BMPs eliminate the need to slake, wedge or constantly force-feed clay through the pugmill.

Batch mixing pugmills (BMPs) combine the advantages of clay mixers and pugmills into one easy-to-use machine. A BMP has the ability to reclaim any combination of wet, dry, greenware, slip, slop and scrap. In addition, mixing from powder and water, or "warming" up commercially purchased clay, are simple tasks with a BMP.

Popular with long-time potters, BMPs eliminate the need to slake, wedge or constantly force-feed clay through the pugmill. Commonly referred to as a mixer that unloads itself and a pugmill that feeds itself, a BMP eliminates the laborious task of transferring clay from a mixer to a pugmill.

BMP Selection

A number of BMP variations are available on the market today. When choosing a BMP, it's important to consider if the unit reduces time, space, energy and complexity-all of which are beneficial. In addition, the unit's design, vacuum deairing capabilities, and advanced features should all be kept in mind.

Considerations regarding the ergonomics of the pugmill should not be overlooked. For example, where are the controls mounted? Are they easily accessible? Additional factors to keep in mind are the mobility and weight of the pugmill, maintenance requirements and complexity (i.e., how many bolts/parts need to be removed in order to clean the unit), and if and how the BMP deairs the clay (see also the Vacuum Deairing section in this article).

The unit's electrical requirements are important to consider. With rising electrical costs, the initial savings on a BMP could be quickly lost if the BMP is not designed for maximum efficiency. For example, the additional power consumption (amps) required to run a 2-hp vs. a 1-hp motor will cost several hundred dollars per year to operate. The design of the vacuum pump and the required duration to operate the vacuum pump during clay processing also adds cost to the process.

Component preservation and longevity are also important factors. It's important to keep in mind the expected quality and lifespan of the components that make up the BMP's drive system and controls. What components can be expected to fail, and how quickly, and how accessible are the replacement/spare parts?

Vacuum Deairing
BMPs have raised the bar on the quality of deaired clay available to the consumer. If properly designed, a BMP can provide warm deaired clay with superior plasticity. Again, simplicity is key to the design and functionality of the deairing system. Just ask someone who owns a standard deairing pugmill: a lot of time and energy can be spent fighting a deairing system that does not properly deair the clay or that jams while loading and pugging. For potters that depend on product for an income, problems with deairing ultimately mean lost profits.

A deairing system should effectively remove the air from the sealed pugmill, and compact and pug the clay as required. The BMP vacuum design ranges from systems that require vacuum screens and large vacuum pumps to machines that completely deair the whole batch while it is mixing through the use of a small, efficient vacuum pump.

Deairing BMPs come equipped with seals between mating surfaces to allow for proper vacuum deairing. As opposed to flat gaskets, o-ring seals are very effective, durable, and readily available since they are standard worldwide and inexpensive to replace. In turn, BMPs that are designed to completely seal can also serve as storage containers where moist clay can be kept indefinitely, which eliminates the need for slop buckets or the generation of unwanted mounds of scrap.

Some BMP designs allow the potter to mount extrusion dies directly to the end of the BMP. Tile attachments are also available on selected BMP models.

New Technology
With the success of BMPs, manufacturers continue to push the envelope with their capabilities. Some BMPs now have extrusion dies that can be mounted directly to the end of the BMP, which allows users to pull the deaired handles or coils at the push of a button.

Variable speed control is another useful option when extruding clay through small shapes. Variable speed allows the operator to control the auger speed, and thus the speed of the extrusion. This allows the operator to slow the machine down to allow smooth deaired shapes to extrude directly from the pugmill.

Tile model BMPs are also now available, along with auxiliary equipment. Updated equipment and processes designed specifically for tile making have been proven to save time, money and energy when used to replace antiquated equipment or outmoded processes. Some BMP manufacturers also have tile consultants available to support consumers' needs, specifications, installation and process refinements.

Finally, some BMPs now feature intellectual mixing technology (IMT), which allows the pugmill to speed up twice as fast as standard pugmills while maintaining proper torque in the mixing chamber. Cycle times can be dramatically reduced using IMT.

Do Your Research

When shopping for a BMP, be sure to look for equipment from a manufacturer with a good reputation and a long track record of excellent performance and customer service. This will ensure a solid return on your investment, while your new BMP works tirelessly for many years to come.

For more information about mixing and pugging equipment, contact Peter Pugger at 3661 Christy Lane, Ukiah, CA 95482; (707) 463-1333; fax (707) 462-5578; e-mail info@peterpugger.com; or visit www.peterpugger.com.


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