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Fillers are various inert materials that are added to resins for the purposes of cost reduction, modifying mechanical properties or enhancing thermal transfer. They may be organic or metallic in nature. Their relative hardness (or abrasivity) is considered in the design and configuration of all Sheepscot meter/mix and dispense systems as it pertains to the long term durability and reliability of wetted components. A range of materials are available to optimize each system for the application.

Mohs Hardness Scale. Named after Fredrich Mohs, a German mineralogist who introduced the scale in 1812. Hardness, in general, is determined by what is known as the Mohs Scale, a standard which is mainly applied to non-metallic elements and minerals. In this scale, there are ten degrees or steps, each designated by a mineral, the difference in hardness of the different steps being determined by the fact that any member in the series will scratch any of the preceding members. The scale is as follows:

4Fluor spar



Following are commonly used fillers and their Mohs numbers:


Filler Moh’s

Calcium Carbonate (aka Limestone)3
Aluminum Tri-Hydrate. (aka Hydrated Alumina)4
Zinc Borate4
Silica (aka Silicone Dioxide, Crystalline quartz)7
Aluminum Oxide9


Talc and Calcium Carbonate are commonly used as extenders in resins and are considered to be non-abrasive.

Zinc Borate is used as a flame retardant to qualify for UL 94V-O rating. It is considered to be slightly abrasive.

Silica and Aluminum Oxide are often used to provide enhanced mechanical and/or thermal properties. They are considered to be highly abrasive.