Nominal or Catalog Strength
of a wire rope applies only to a new, unused rope.
nominal strength of a wire rope should be considered the straight
line pull which will actually break a new, unused rope. The nominal
strength of a wire rope should never be used as its working load.
determine the working load of a wire rope, the nominal strength
must be reduced by a design factor
(formerly called a safety factor). The design factor will vary
depending upon the type of machine and installation, and the work
performed. (See chart on Generally
Accepted Design Factors.) For example, a design factor
of "5" means that the nominal strength of the wire rope
must be divided by five to determine the maximum load that can
be applied to the rope system.
and industrial organizations such as OSHA, ANSI and ASME have
established recommended design factors for various types of operations.
Wire rope should never be placed into service without an understanding
of the appropriate design factor.
rope will fail
if worn out, overloaded, misused, damaged or improperly maintained.
service, wire rope loses strength
and work capability. Abuse and misuse increase the rate of loss.
ropes wear out.
Nominal strength begins to decline the first day of service due
to natural causes such as surface wear and metal loss and continues
to decrease with each use.
overload a wire rope. Do not exceed the Working Load
Limit (WLL) of the rope. WLL equals nominal strength divided by
the appropriate design factor.
"shock load" a wire rope. A sudden application
of force or load can cause both visible external damage and internal
damage. There is no practical way to estimate the force applied
by shock loading a rope. The sudden release of a load can also
damage a wire rope.
is applied to the wires and strands of a wire rope when
it is manufactured. If the rope is operated outdoors or in a corrosive
environment, the lubricant is depleted and should be replaced
fitting attached to a wire rope may reduce its working load limit
depending on the "efficiency rating"
of the specific fitting and/or method of assembly. Efficiency
ratings must be identified and understood to ensure safe wire
rope will be damaged by extreme temperatures.
Fiber core wire rope should never be exposed to temperatures exceeding
200 degrees F and IWRC wire rope should never be used at temperatures
above 400 degrees F or below -60 degrees F.