Three roll mill
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A three roll mill is a machine tool that uses the shear force created by three horizontally positioned rolls rotating at opposite directions and different speeds relative to each other to mix, refine, disperse, or homogenize viscous materials fed into it.
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[edit] Operation of a Three Roll Mill
The three adjacent rolls of a three roll mill rotate at progressively higher speeds. Material, usually in the form of paste, is placed between the feed roll and the center roll. Due to the narrowing space between the rolls, most of the paste is rejected to the feed region. The part that makes it through the first in-running nip experiences very high shear force. Upon exiting, the material that remains on the center roll moves through the second nip between the center roll and apron roll, which subjects it to even higher shear force due to the higher speed of the apron roll. A knife blade then scrapes the processed material off the apron roll and transfers it to the apron. This milling cycle can be repeated several times to maximize dispersion.
The gaps between the rolls can be mechanically or hydraulically adjusted and maintained. Typically, the gap distance is far greater than the particle size. In some operations, they are gradually decreased to achieve the desired level of dispersion.
[edit] Application
Three roll mills are widely used to mix electronic thick film inks, high performance ceramics, cosmetics, plastisols, carbon/graphite, paints, printing inks, pharmaceuticals, chemicals, glass coatings, dental composites, pigment, coatings, adhesives, sealants, and foods. With the recent development in technology, they are also utilized in the production of cable cover, electronics, soap, and artificial plastics.
Small bench models are ideal 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.
[edit] Manufacturers
Lehmann Mills Inc. http://www.lehmannmills.com/ - The Lehmann roller mill is precision designed, and manufactured, to use shear force to breakdown agglomerates and large particle sizes. Particles of .5 microns, or better, can be achieved due to the high shearing action imparted by this milling technique. Production on a Lehmann roller mill is crucial to produce the finest particle size, and the most effective blending, resulting in a constant grade of excellence. See webpage for more information.
[edit] References
Harper, Charles A. Electronic Materials and Interconnection Handbook (New York: The McGraw-Hill Companies, Inc., 2004), pp. 570-571.
Prudenziati, M. (editor). Thick Film Sensors (Handbook of Sensors and Actuators) (Amsterdam: Elsevier Science B.V., 1994), pp. 121-123.
