Page 146 - The Tribology Handbook

A25 Flexures and knife edges

The main properties of interest for selection of materials Table25.3 Some materials usedto meet special
for flexures and torsion suspensions are given in Table 25.2 requirements in accurate instruments or control
and Table 25.3. Values given are intended to provide a com- systems
parison ofdifferent materials, but they are only typical and -
should not be used to specify minimum properties. Requirement Material (s)
~
Minimum hysteresisand elastic 91.5% platinum, 8.5% nickel
after-effect alloy. Platinum/silver alloy,
85/15 to 80/20. Quartz
Zero thermoelectric e.m.f. Copper
against copper

Maximum corrosion resistance Gold or platinum alloys,
(instrument torsion sus- quartz
pensions)
Maximum electrical con- Silver
ductivity

Torsionless suspensions (e.g. Stranded silk and other textile
for magnetometers) fibres)

MATERIALS FOR KNIFE EDGES AND PIVOTS

n c’7

&&

(b)
(0)
EXAMPLES OF KNIFE EDGES g (a) EXAMPLES OF PIVOTS (b)

Knife edges and pivots are bearings in which two mem- The main requirement of the materials for this type of
bers are loaded together in nominal line or point contact bearing is high hardness, so that high load capacity can be
respectively, and can tilt relative to one another through a provided, while keeping the width of the contact area small
limited angle by rotation about the contact; a pivot can also for low friction torque and high positional accuracy of the
rotate freely about the load axis. load axis.

A25.3