Page 346 - Plastics Engineering

Processing of Plastics 329

AWarp ends

-Fill ends

Plain Weave-In this construction.
one warp end is repetitively woven
over one till yam and under the
next. It is the firmest. mort stabte
construction, which provides for
porosity and minimum slippage.
Strength is uniform in both
directions.

Fig. 4.65 Plain weave fibre fabric

the length of the fabric. Fabrics are usually designated in terms of the number
of yams of filament per unit length of warp and fill direction.

Chopped Fibres These may be subdivided as follows
Milled Fibres: These are finely ground or milled fibres. Lengths range from 30
to 3000 microns and the fibre (WD) ratio is typically about 30. Fibres in this
form are popular for closed mould manufacturing methods such as injection
moulding.
Short Chopped Fibres: These are fibres with lengths up to about 6 mm. The
fibre (WD) ratio is typically about 800. They are more expensive than milled
fibres but provide better strength and stiffness enhancement.
Long Chopped Fibres: These are chopped fibres with lengths up to 50 mm. They
are used mainly in the manufacture of SMC and DMC (see Section 4.10.2).

Chopped Strand Mat This consists of strands of long chopped fibres deposited
randomly in the form of a mat. The strands are held together by a resinous
binder.

Manufacturing Methods
The methods used for manufacturing articles using fibre reinforced thermosets
are almost as varied as the number of material variations that exist. They
can, however, be divided into three main categories. These are manual, semi-
automatic and automatic.
The Manual processes cover methods such as hand lay-up, spray-up, pressure
bag and autoclave moulding.