Mixers are used to mix solids – from kneadable to pasty products – and/or liquids, and to homogenize multi-composite blends in the chemical, pharmaceutical and paint industries (agitator mills). They are also employed as agitator-equipped storage containers, kneaders, granulating machines, reaction vessels, dryers and heating and/or cooling units. In view of the host of requirements there is a great variety of mixer types and versions as vertical and horizontal as well as open and closed designs. The majority of mixing machines are employed in periodic operation as batch mixers. Continuous-type mixers are designed for a specific dwell time, which is conditional primarily on the type of mixing tool. One of the most versatile and effective types is the closed, horizontal large-capacity mixer with an intensive mixer in combination with one or several integral mixing accelerators, i.e. blade mills or pinned discs. Multi-stage work processes using vacuum, pressure, thermal energy and auxiliary crushers can be combined in such a machine, which depending on the version finds application as a high-speed mixer, mixing reactor or high-speed dryer. The mixing tool wipes the walls of the mixing vessel up as far as the brim, premixing the material throughout the vessel and allowing any number of material infeeds through the dispersion and crushing zone on the mixing accelerators. One-knife mills crush coarse agglomerates, multiple-knife mills break up fibres, and pinned disks are used in the powder range for fine dispersion.

Depending on the mixer type and the operating conditions, slow rotating main shafts are sealed by either stuffing box packings, shaft lips or mechanical seals, mainly as double mechanical seals with rotating counter ring. Highspeed mixing accelerator shafts are nearly always sealed by double-acting mechanical seals with counter-rotating pumping screw. The most striking design feature of these seals is their rotating counter ring on the product side, which propels the product away from the sealing gap. If necessary, a scraper or support ring made of PTFE and positioned above the stationary seal face protects the latter's O-ring against wear. The buffer fluid up against the inside of sealing gap intensifies the lubrication and cooling of the sliding faces through its centrifugal force. The housing is shaped like a flow guide for favourable guidance of the buffer fluid and hence optimum heat removal. In view of the requirements, the face materials mostly chosen for mixer, reactor and dryer seals on the product side are ceramic or silicon carbide against tungsten carbide with nickel binder, or silicon carbide against silicon carbide.