"M"

Magnesia - (a) Heavy calcined: Magnesium oxide by calcination of magnesite (natural magnesium carbonate), and then ground for use as a compounding ingredient for molded goods and hard rubber. (b)Light calcined: Magnesium oxide by calcination of purified magnesium carbonate and/or magnesium hydroxide. It has a fine particle size and a bulk factor of 10 to 30 pds. per cubic ft. Used chiefly in neoprene stocks. (c)Extra light calcined: Prepared similarly by calcination of magnesium carbonate, but with a bulk factor of 4 to 6 pds. per cubic ft. Used chiefly in neoprene stocks.

Maintainability - The probability that a failed system can be made operable in a specified interval or downtime.

Mandrel - A bar, serving as a core, around which rubber is extruded, forming a center hole.

Masterbatch - A preliminary mixture of rubber and one or more compound ingredients for such purposes as more thorough dispersion or better processing, and which will later become part of the final compound in a subsequent mixing operation.

Master Batch - A mixture of rubber with one (1) or more ingredients in definite but higher concentrations than those in which they normally occur in a complete rubber mix. Used for efficiency in compounding, and also to avoid the handling of small quantities of accelerators, antioxidants, color, etc...

Masticate - To work rubber on a mixing mill or in an internal mixer till it becomes soft and plastic. To break down. MASTICATOR - A machine for plasticizing rubber by mechanical work.

Metal O-rings - An o-ring usually made from hollow stainless steel tubing, with a small vent hole.

Mill - A machine with two horizontal rolls revolving in opposite directions used for the mastication or mixing of rubber.

Mill - A machine consisting of two (2) adjacent, heavy, chilled iron rolls set horizontally, and which revolve in opposite directions (i.e., upper surfaces rotate), used for the mechanical working of rubber Mills are of different types. For masticating, and mixing compounds the rolls are smooth and revolve with differential speed. For crepeing and washing rubber, mills have scored or fluted rolls and differential speeds and may be equipped to spray the rubber with water. Mills with even-speed rolls are occasionally used for different purposes. Mills are corridor hollow and equipped for internal heating with steam or cooling with water.

Mixing - The process of incorporating the ingredients or a rubber compound into the rubber, usually done on a mixing mill or in an internal mixer. The mixing process consists in (1) breaking down the rubber, (2) gradual incorporation or compounding ingredients, (3) final working of the rubber after all ingredients are in, and (4) removing the mixed compound from the mill in sheets.

Modulus - The ratio of stress to strain. In the physical testing of rubber, the load necessary to produce stated percentage of elongation, compression or shear.

Modulus - (See Elastic Modulus) In the physical testing of rubber, the ratio of stress to strain, i.e., the load in pounds per square inch or kilos. per square cm. of initial cross-sectional area necessary to produce a stated percentage-elongation. It is a measure of toughness, is influenced by pigmentation, state of cure, quality or rubber and other factors.

Mold Register - Means used to align the parts of a mold.

Mooney scorch - A measure of the incipient curing characteristics of a rubber compound using the Mooney viscometer.

Mooney Viscometer - A laboratory testing machine for measuring the plasticity of raw rubber or unvulcanized rubber compounds. A knurled steel rotor disc winch is centrally embedded iii the heated rubber specimen firmly held in a cavity under pressure is caused to rotate at a low speed (2 rpm). The resistance offered by the plastic rubber mass to the rotation of the rotor disc is the measure of the plasticity of the rubber. The machine is also used to determine the scorch characteristics of rubber mixes.

Mooney viscosity - A measure of the viscosity of a rubber or rubber com- pound determined in a Mooney shearing disc viscometer.

Mounts - A rubber molded part used as a motor mount or to mount device against a frame without allowing vibration to pass through the mounting.