Wire rope are a tool used for lifting and pulling heavy load, and you must select wire rope based on specific strength and construction requirements. You must use a strength chart to determine how much weight a specific diameter of wire rope can hold before the wire rope break. A strength chart remove guesswork because a strength chart provide exact weight capacities for different diameter of wire rope.
Many individual steel wires is twisted into strand, and these strands are twisted around a central core to create the wire rope. The construction type of a wire rope determine how the wire rope performs in different task. A 6×19 construction consist of six outer strands and 19 wires per strand, and a 6×19 wire rope often use an independent wire rope core.
Choosing and Caring for Wire Rope
An independent wire rope core are stronger than a fiber core, and an independent wire rope core increase the strength of the wire rope by 7 percent. A 6×19 wire rope is flexibly, so a 6×19 wire rope is suitable for use in crane sheaves. A 6×7 construction is stiffer than a 6×19 construction, so a 6×7 wire rope is better for straight line haulage where abrasion is a factor.
A 6×37 construction contain more wires, but because the wires in a 6×37 construction are smaller, the 6×37 wire rope may wear more fast against rough edges. You must choose a wire rope construction based off the specific demand of the job. The diameter of a wire rope affect the breaking strength of the wire rope.
As the diameter of a wire rope increase, the breaking strength of the wire rope increase because a larger diameter create a larger cross-sectional area of steel. For example, a half-inch wire rope has much more breaking force than a quarter-inch wire rope. Many industrial user use EIPS grade wire rope, and EIPS stand for extra improved plow steel.
You must not use the breaking strength of a wire rope as the maximum weight for a lift, because the breaking strength is the point at which the wire rope fail. Instead, you must use the Safe Working Load, or SWL. To find the Safe Working Load, you divide the breaking strength of the wire rope by a safety factor of five.
A safety factor of five is use because a safety factor of five account for rust, wear, and shock loads. A shock load occur when a load drop suddenly, and a shock load increase the force on the wire rope significently. You must always calculate the Safe Working Load to ensure that the wire rope remain safe during use.
The application of the wire rope determine which type of wire rope is most appropriate. Cranes use 6×19 wire rope because 6×19 wire rope has high fatigue resistance. Elevators require a higher safety factor than cranes, and elevators require frequent inspections to ensure the safety of the elevator.
When you use wire rope for rigging slings, you must consider the angle of the lift. If the angle of the lift is thirty degrees from the horizontal, the load on each leg of the sling increase, so you must keep the angle at sixty degrees or greater to maintain capacity. You must perform regular maintenance on wire rope to ensure the wire rope remain safe.
You must inspect the wire rope for kink, because a kink in the wire rope create a permanent stress point that can cause the wire rope to snap. You must also inspect the wire rope for rust, because rust can cause the individual wires to crumble inside the wire rope. If you see six broken wires in one lay, or if you see ten total broken wires, you must retire the wire rope.
You should of lubricate the wire rope every quarter to reduce friction and to protect the wire rope from moisture. You must use the correct hardware with your wire rope. You must place wire rope clips so that the saddle is on the live end of the wire rope.
You must use thimble to protect the eyes of the wire rope from being crushed. You must use turnbuckle to adjust the tension of the wire rope, and you must lock the turnbuckles so that vibrations does not loosen the tension. Proper hardware and proper maintenance ensure that the wire rope function as intended.
