Page 366 - Introduction to Marine Engineering

Engineering materials 337
materials have very good sound and heat insulating properties. Many
plastics can be foamed to give low density materials with a variety of
properties, for example, fire extinguishing. Some well known non-
metallic materials are:

Asbestos

A mineral which will withstand very high temperatures and is
unaffected by steam, petrol, paraffin, fuel oils and lubricants. It is used
in many forms of jointing or gasket material and in various types of
gland packing. It does however present a health hazard in some forms.

Cotton
A fibrous material of natural origin which is used as a backing material
for rubber in rubber insertion jointing. It is also used in some types of
gland packing material.

Glass reinforced plastics (GRP)

A combination of thin fibres of glass in various forms which, when
mixed with a resin, will cure (set) to produce a hard material which is
strong and chemically inert. It has a variety of uses for general repairs.

Lignum vitae
A hardwood which is used for stern bearing lining. It can be lubricated
by sea water but is subject to some swelling.

Nylon

A synthetic polymer which is chemically inert and resistant to erosion
and impingement attack. It is used for orifice plates, valve seats and as a
coating for salt water pipes.

Polytetrafluorethylene (PTFE)
A fluoropolymer which is chemically inert and resistant to heat. It has a
low coefficient of friction and is widely used as a bearing material. It can
be used dry and is employed in sealed bearings. Impregnated with
graphite, it is used as a filling material for glands and guide rings.