Gaskets are materials used to seal one compartment of a device ...

according to ASTM D 299, the standard for such materials. These grades are
listed in Table 1 (ASTM 1982). The dimensions of the packing are controlled
by the size and number of yarns selected (Kirk-Othmer 1981).
Another type of braided packing, braid-over-braid packing, consists of
individually braided jackets layered over a core. These packings use
wire-inserted yarns that offer greater strength to the packing material.
Rolled compression packings are constructed of woven cloth that is coated with
a rubber binder and then cut in strips along the bias to
impart maximum cloth
stretch during forming. The rubber-saturated strips are wound around a soft
rubber core and then formed into the desired final shape. The final cutting,
forming, and compression operations for all packing types are usually
performed by secondary processors (FSA l983).1
All of the packing formation processes have some characteristics in
common. First, impregnation of dry asbestos yarn with a lubricant. After
lubricant impregnation, the yarns are braided into a continuous length of
packing which in turn is calendered to a specific size and cross-sectional
shape. The formed product may then be coated with more lubricant or another
material. At this stage packings can be packaged and sold for maintenance
operations or they can be further processed by pressing into the required
shape (GCA 1980).
Finally, packings can be die-formed directly into solid rings to
facilitate handling and installation.
The packings that have been formed into
a designated shape are referred to as plastic packings (Kirk-Othmer 1981).
The uses and applications of asbestos packings are quite varied, but some
of the major areas
in which asbestos-containing packing materials have been
1 Secondary processing usually occurs at the facility where the gaskets
will be used and consists of cutting and compressing the packings as they are
needed to replace worn packings already in service in various pumps, valves,
etc.
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