Page 206 - The Tribology Handbook

B8 Brakes

FRICTION MATERIALS
on thermosetting polymers reinforced by inorganic (e.g.
A very wide range of friction materials is available, and in glass) or organic fibres, 10-15%, or 50% by weight ofsteel
many cases materials have been developed for specific fibre; and suitable fillers are added to give the pads the
applications. The friction material manufacturer should required tribological properties. The organic non-asbestos
therefore be consulted at an early stage in the design of the pads are suitable for lighter duties, and the greater the
brake and should also be consulted concerning stock amount of steel fibre the higher the temperature the pads
sizes- standard sizes are much cheaper than non- can withstand. The non-metallics tend to give less squeal
standard and are likely to be immediately available. The and groan and cold judder, and less lining and rotor wear
non-asbestos lining materials are normally made in fle- at low temperatures; steel fibres give a more stable p and
xible rolls in standard lengths, (e.g. 4 m) and widths better high temperature lining life, but they can cause
(330 mm) and various thicknesses. Linings of the required corrosion problems and they allow more heat to pass into
sizes are slit from the standard sheets. These linings are the brake assembly instead of into the disc.
bonded to the shoes and, by increasing the temperature Data for typical materials are shown in Tables 8.9, 8.10
and time of bonding, the linings can be made more rigid, and 8.11. These figures are meant as a guide only;
and able to withstand higher and higher duties. materials vary from manufacturer to manufacturer, and
Industrial disc pads are generally based on automobile any one manufacturer may make up a number of different
and CV pad types. They may be classified as organic-non- materials of the one type which may vary somewhat in
asbestos, low steel, or semi-metallic pads. They are based properties.

Table 8.9 Material types and applications
m e Manu facture Typical dimensions Uses

LININGS*
Woven cotton Closely woven belt of fabric is As rolls; thickness 3.2-25.4 mm Industrial drum brakes,
impregnated with resins which width up to 304.8 mm and minewinding equipment,
are then polymerised lengths up to 15.2 m cranes, lifts
Woven asbestos Open woven belt of fabric is As radiused linings thickness Industrial band and drum brakes,
impregnated with resins which 3.2-12.7 mm width up to cranes, lifts, excavators,
are then polymerised. May 203 mm, minimum radius winches, concrete mixers. Mine
contain wire to scour the 76 mm, maximum arc 160" equipment
surface

Non-asbestos Steel, glass or inorganic fibre and Linings: thicknesses up to 35 mm Industrial drum brakes
flexible friction modifiers mixed with Maximum radius about 15-30 Heavy-duty drum brakes-
semi-flexi ble thermosetting polymer and times thickness depending upon excavators, tractors, presses
rigid mixture heated under pressure flexibility
PADS
Resin-based Similar to linings but choice of In pads up to 25.4 mm in Heavy-duty brakes and clutches,
resin not as restricted as thickness or on backplate to fit press brakes, earth-moving
flexibility not required proprietary calipers equipment
Sintered metal Iron and/or copper powders Heavy-duty brakes and clutches,
mixed with friction modifiers press brakes, earth-moving
and the whole sintered equipment

Cermets Similar to sintered metal pad, but Supplied in buttons, cups As above
large proportion of ceramic
material present
* Many lining materials supplied as large pads can be bolted, or riveted, using brass rivets, to the band or shoe; the pads can be
moved along the band or shoe as wear occurs and so maximum life obtained from the friction material despite uneven wear along its
length. Alternatively, and particularly with weaker materials, the friction material can be bonded to the metal carrier using
proprietary adhesives and techniques (contact the manufacturer). On safety-critical applications the friction material should be
attached by both bonding and riveting.