A three roll mill or triple roll mill is a machine that uses shear force created by three horizontally positioned rolls rotating in opposite directions and different speeds relative to each other, in order to mix, refine, disperse, or

homogenize Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...

viscous The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

materials fed into it. The three-roll mill has proven to be the most successful of the range of roll mills which saw extensive development in the 19th century. These included the single-roll mill and the five-roll mill. The single-roll mill works by material passing between the roll and a fixed bar pressing against the roll. The five-roll mill incorporates four successively smaller in-running nips and hence, compared to the three-roll mill, allows the use of larger agglomerates as part of the input material- but is correspondingly more complicated and expensive.

Operation of a three roll mill

The three adjacent rolls of a three roll mill (called the feed roll, centre roll and apron roll) rotate at progressively higher speeds. Material, usually in the form of paste, is fed between the feed roll and the center roll. Due to the narrowing space between the rolls, most of the paste initially remains in the feed region. The part that makes it through the first in-running nip experiences very high shear force due to the different rotation speeds of the two rolls. Upon exiting, the material that remains on the center roll moves through the second nip between the center roll and apron roll. This subjects it to an even higher shear force, due to the higher speed of the apron roll and typically, a smaller gap than between the feed and centre rolls. A knife blade then scrapes the processed material off the apron roll and the paste rolls down the apron. This milling cycle can be repeated several times to maximize

dispersion Dispersion may refer to: Economics and finance * Dispersion (finance), a measure for the statistical distribution of portfolio returns * Price dispersion, a variation in prices across sellers of the same item *Wage dispersion, the amount of variat ...

. The gaps between the rolls can be mechanically or

hydraulically Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counter ...

adjusted and maintained. Typically, the gap distance is far greater than the particle size. In some operations, the gap distance is gradually decreased to achieve the desired level of dispersion. The rollers are normally internally water-cooled. {{Citation , editor-last=Prudenziati , editor-first=M. , title=Thick Film Sensors (Handbook of Sensors and Actuators) , location=Amsterdam , publisher=Elsevier Science B.V. , year=1994 , pages=121–123 , isbn=0-444-89723-2

Application

Three roll mills are widely used to mix printing

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, electronic thick film inks, high performance

ceramics A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...

cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protect ...

plastisol A plastisol is a colloidal dispension of small polymer particles, usually polyvinyl chloride (PVC), in a liquid plasticizer. When heated to around , the plastic particles absorb the plasticizer, causing them to swell and fuse together forming a ...

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...

paints Paint is any pigmented liquid, liquefiable, or solid mastic composition that, after application to a substrate in a thin layer, converts to a solid film. It is most commonly used to protect, color, or provide texture. Paint can be made in many ...

, pharmaceuticals, chemicals, glass coatings, dental composites,

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...

, coatings,

adhesives Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

sealants Sealant is a substance used to block the passage of fluids through openings in materials, a type of mechanical seal. In building construction ''sealant'' is sometimes synonymous with ''caulking'' and also serve the purposes of blocking dust, sou ...

, and foods. With the recent development in technology, they are also utilized in the production of cable cover, electronics,

soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...

, and artificial plastics. Small bench models are used for bench-top development work, laboratory work, and low volume production. Larger bench and floor models are built to meet different production needs from pilot plants to large volume productions. Particular advantages of this process are that it allows high-viscosity pastes to be milled, and that the high surface contact with the cooled rollers allow the temperature to remain low despite the high amount of dispersion work being put in. A notable disadvantage is that the large open area of paste on the rollers causes loss of volatiles.

References

Industrial machinery