GEARENCH LA120 PETOL Bull Tong - Manual (Page 9)

7
Environmental Conditions
Wrench chains operate in widely varying environments, from wet outdoor conditions to
mildly or highly corrosive industrial atmospheres. They can also be exposed to abrasives
such as sand or grit.
The possible effects include:
Moisture - Corrosion and rust reduce chain strength by causing pitting and cracking.
Temperature - Very cold temperatures reduce chain strength by embrittlement.
Chemical Solutions or Vapors - Corrosive attack of the chain components’ grain structure
and/or the mechanical connections between the chain components (crevice corrosion)
may occur. Cracking often is microscopic. Propagation to complete failure can be
eventual or sudden.
Abrasives - Accelerated wearing and scoring of the articulating chain members (pins and
plates) may occur, with a corresponding reduction in chain strength. Due to
inaccessibility of the bearing surfaces (pin surfaces and plate apertures), wear and scoring
are not readily noticeable.
These conditions, when coupled with normal chain wear and inherent residual stress
(normally in the chain as constructed), can result in environmentally assisted failure. It is
impossible to predict chain life under complex conditions, as the degree of hostility and its
effects are dependent on many variables such as temperature, time of exposure, concentration
of corrosive atmosphere or medium, degree of abrasive wear, etc. Establishing the degree
and frequency of unpredictable dynamic loading is also difficult.
Normal Life Expectancy
A leaf chain’s normal life expectancy can be expressed as a maximum percent of elongation.
This is generally between 2% and 3% of pitch. As the chain flexes back and forth, the
bearing joints (pins and inside link plates) gradually wear from articulation. As with all steel
bearing surfaces, the precision hardened steel joints of leaf chain require a constant film of
oil between mating parts to prevent wear and to resist corrosion.