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a cone-shaped instrument for grinding and pulverizing pigments by hand on a slab, used in the process of preparing paints for painting and printing. Large mullers are made of hard stone (for example, labradorite and porphyry); small ones are made from porcelain, glass, or agate. The slab is usually made from the same material as the muller.
a machine for the mechanical preparation of molding sands and core sands; it mixes silica sands and admixtures, such as molding clay, ground coal, water, and binders. Various types of mixers are used as mullers in the preparation of moldings and core-sand mixtures: standard batch-type mixers, double mixers, oscillating mixers, paddle mixers, and rollerless (vortex) mixers.
Standard batch mixers have a fixed hopper, into which the material to be mixed is fed. Two smooth, vertical rollers move over the layer of material with a circular motion as plows guide the mixed material under the rollers. As the rollers move, the components of the mixture are mixed and become evenly distributed. After 3–12 min of mixing, the prepared mixture is removed through a discharge opening in the bottom of the hopper.
Double mixers have two pairs of vertical rollers and two hoppers interconnected in such a way that their sides form a figure eight. The molding materials are fed continuously into the first hopper, are mixed by the rollers and internal plows, and are then transferred by an external plow to the second hopper, where more mixing takes place. The prepared mixture is then removed from the second hopper by an external plow. Double mixers can produce up to 400 tons/hr, and the mixture can be removed either continuously or in batches.
An oscillating mixer has two or three horizontal rollers suspended on oscillators connected to a vertical shaft. As the shaft revolves, the rollers come close to the rubber-faced wall of the mixer’s hopper. The material to be mixed is fed by scrapers into the gap between the rotating rollers and the wall of the hopper. A batch is mixed in 1.5–3 min. The prepared mixture is removed through a small door in the wall of the hopper.
A paddle mixer may have one or two (parallel) shafts equipped with paddles mounted in a helical line and turning inside a trough. When the shaft turns, the mixture is mixed and simultaneously transported along the trough toward the outlet. Such machines can produce mixtures continuously or in batches.
A rollerless, or vortex, mixer has a vertical rotating shaft and a fixed hopper. The working elements are bent springs with heads at the end that press against the side of the hopper and mix the sand.
In the USSR the most commonly used equipment for preparing molding-sand and core-sand mixes are the standard batch-type models 1A11 and 1A12, which have a productivity of 6 and 15 tons/hr, respectively. For molding sands, the model 115 and 116 oscillating mixers, which produce 34 and 47.5 tons/hr, respectively, are most common. The model 4727 paddle mixers, which produce 3.2 tons/hr, are used to prepare granular, self-hardening mixtures.
REFERENCESAksenov, P. N. Oborudovanie liteinykh tsekhov. Moscow, 1968.
Okromeshko, N. V. Mekhanizatsiia i avtomatizatsiia liteinykh tsekhov. Moscow, 1960.
G. V. PROSIANIK