molding powder[′mōl·diŋ ‚pau̇d·ər]
a powder or granulated material intended for processing into products by molding.
Molding powders are thermosets, which are a partially hardened mixture of 30–60 percent thermosetting resin (most often a phenol-aldehyde resin) and 40–70 percent finely divided filler (for example, sawdust, silica flour, ground mica, or short-fiber asbestos). They may also contain (by weight) 1.5–3 percent lubricants, such as stearates of calcium or zinc or a mixture of stearic and palmitic acids, and 2–4 percent coloring agent, usually ni-grosine, which imparts a black color to the powders.
The production of molding powders includes the sequential operations of preparation and mixing of the components, preliminary hardening, and particle size reduction or granulation. To achieve improved wetting and better impregnation of the filler by the thermosetting resin, the resin is frequently used in the form of a solution or emulsion. The basic characteristics of molding powders are the specific volume, granulometric composition, pouring properties, fluidity, useful life (the length of time over which processing properties are preserved after the addition of the hardener), rate of hardening, and shrinkage.
A. R. BEL’NIK