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Reasonably homogeneous concrete does not always meet contractors' workability needs. Even when it does, the producer faces disposal and maintenance problems involving leftover concrete-making materials and the mixer of choice, respectively.

To address these problems, inventors at Kniele Baumaschinen GmbH (Kniele Construction Machines) in Germany have just patented probably the most significant advances in concrete mixer technology in a long time. Harald Kniele and Alexander Kniele recently received a number of patents, including German Patent Office Patents DE19755239A1 and DE4100928A1 and World Intellectual Property Organization (WIPO) Patent WO01/28672. Their mixer, dubbed the "KKM-Mixer" or "Kniele Cone Mixer" (Kniele Konusmischer), was displayed at the Bauma Exhibition in Munich last spring.

The second advancement, automatic internal cleaning, also is designed to reduce production and labor costs. Once a batch has been dropped, the mixer power-washes the inside of the drum. A discharge water collector swings into place under the discharge chute to capture the cleaning water. This discharge water is then pumped into a reconditioning facility that is part of the machine, and the water returns to the mixer after reconditioning. This feature not only reduces maintenance but it also can keep local law enforcement agencies satisfied.

But the real heart and soul of the KKM is a newly developed mixing mechanism inside the drum. First, an auger runs down the center axis of the machine on the end of a drive. This screw-type mixer pulls material from the bottom of the cone to the top, constantly turning over the mixture. A second mixer inside consists of a set of paddles that rotate in the opposite direction of the auger. These paddles not only mix the contents but they also continually scrape the material away from the interior of the drum and thus return it to the mixing cycle. These paddles also scrape the sides of the drum during self-cleaning of the mixer.