Synthetic Hoist Rope Is 80% Lighter Than Steel
Because wire rope can be heavy and bulky and often spins under load, Mike Herbert, Manitowoc Inc.'s global product director for rough-terrain cranes, has long sought an alternative. Even with rotation-resistant designs, conventional wire rope produces some torque. Now, Wisconsin-based Manitowoc has teamed with Samson Rope, Ferndale, Wash., to create the first-ever synthetic hoist rope for mobile cranes.
The resulting KZ100 rope is torque-neutral and 80% lighter than conventional wire rope, improving speed and safety in reeving and installation and reducing damage from spooling. Michael Quinn, director of new market development at Samson, tells ENR the weight savings means crane operators have less weight below the boom tip and reduced overall weight, effectively increasing lifting capacity.
Torque is eliminated due to the rope's construction: 12 strands—six set in one direction, six in the other—of mostly Dyneema fiber rope, a high-modulus polyethylene. "It eliminates load spin and cabling," Quinn says. "With its malleable nature, if it bends, it doesn't stay bent."
Samson, the world's largest consumer of Dyneema fiber, says the development of the new hoist rope took two years and combined technology from three rope industries—commercial fishing, tug and towing, and recreational marine—to create a damage-resistant rope with ideal spooling capability. Quinn says finding the right twist level and braid angle was key, and a polyester "control core" in the center of the rope—along with other proprietary features—has given Samson a finished product full of strength.
Patrick Smith, Dyneema spokesman, says the Greenville, N.C.-based company's synthetic fiber, which is the same material found in ballistic armor, works in the KZ100 rope due to its strength, durability and abrasion-resistance coupled with less weight and fatigue—"all advantageous properties compared to the steel wire replaced in this application."
In a 22-millimeter-dia rope, the KZ100 effectively replaces a 19-mm-dia rope of the same length. "In this case, we slightly increase diameter over the wire to the same max line pull, but it still fits in the existing sheave and is the same length of rope," Quinn says. "And it is still 80% lighter."
Herbert says the rope improves performance, even on the ground. Its lightweight construction makes reeving easier and safer. Plus, without the need for lubrication, as with steel rope, the process is cleaner and requires less maintenance. But rigging experts say synthetics do not eliminate inspections, as the material can be prone to ultraviolet and chemical damage. The rope costs about twice as much as conventional wire rope, but prices would improve with higher production volumes, the manufacturers note.
Users also see a benefit in the KZ100 when they have multiple parts of line or in situations in which reeving gets changed throughout the day. "They might be lifting some light loads in the morning and need a single part of line but multiple parts for heavy loads," says Herbert. "The nature of the rope's flexibility and lightness [help] when customers need to reconfigure frequently."
Manitowoc and Samson tested 24,500 ft of rope over 14,000 testing cycles, and then Manitowoc did field trials with two partners, which the company wants to keep anonymous. "It met all our expectations, and every customer that used it in normal crane operation was excited about it," Herbert says.
The KZ100 debuted on the 70-ton-capacity RT770E Grove rough-terrain crane, introduced earlier this year. Manitowoc says the KZ100 allowed it to create a new crane with a 138-ft boom, the longest in its class, without adding more size and weight to the chassis.
While KZ100 is a Samson-owned product, Manitowoc has exclusive commercial-sale rights until September 2015. By then, lifting applications for the KZ100 may have multiplied, as the companies are looking at broader use of synthetic hoisting rope in crawler cranes. Herbert says his company plans to make the KZ100 available in all its larger- capacity products over the next year.
