SELECTING THE RIGHT WIRE ROPE
by Dave Sleightholm
Thousands of wire ropes of all different types, sizes, and construction are manufactured throughout the world, and the differences in these ropes have a dramatic effect on strength and operating characteristics. Because of their differences, wire rope selection can be a very difficult task for someone without basic wire rope knowledge.
Although it would be impossible to list the correct rope to use on each crane for every application, the following information will teach you the basics to selecting the right rope. Keep in mind, if there is ever a question about which rope to use, it is always best to consult a wire rope expert.
ASSESS THE EQUIPMENT
Whether it is a crawler crane, rough-terrain crane, truck crane, tower crane, pedestal crane, or boom truck, the first task is to make sure the selected rope meets the OEM's requirements for diameter and strength. Next, find out the specific make and model of crane, as well as what type of application the crane and rope will be used in.
It's also important to note whether the rope will be used as the main hoist, auxiliary hoist, trolley rope, boom hoist, or luffing jib boom hoist, which makes a major difference in the type and construction of rope you will use. To further complicate wire rope selection, if the machine is older, the rope used may depend on its mode of failure on the machine and application. I'll touch on that again a little later.
Once the make, model, application, diameter, and required rope strength is known, then the process to select the rope can be started.
MAIN AND AUXILIARY HOIST ROPES
Main and auxiliary hoist ropes can be either conventional six- or eight-strand or rotation-resistant ropes. If the application does not require a rotation-resistant rope, then a conventional rope should be used.
The category of rotation-resistant rope to be used in any application depends primarily on length of fall. If the maximum boom length and length of fall is within the scope of a six- or eight-strand conventional rope, then a rotation-resistant rope in not required. However, if a rotation-resistant rope is required, there are three different categories of rotation-resistant rope to choose from.
These three categories have significant differences in strength, rotation resistance, and operating characteristics. It is extremely important to match the requirements of the crane with the specific characteristics of the rope selected. The following is some basic information on the three categories of rotation-resistant rope.
 CATEGORY 1
At least 15 outer strands.
Highest strength and most rotation resistant.
Can be used with a swivel.
Category 1: Endurance Dyform 34LR
  CATEGORY 2
At least 10 outer strands.
Medium strength and rotation resistant.
Should not be used with a swivel.
Category 2: Endurance Dyform 18 (left) and Endurance 19x7
CATEGORY 3
No more than outer strands.
lowest strength and rotation resistant.
Should not be used with a swivel.
Category 3: Endurance 8
BOOM HOIST ROPES
Boom hoist ropes have some very unique and specific requirements. The ASME B30.5 standard allows boom hoist ropes to be used at a design factor of 3.5:1 with a minimum bending ratio of 15:1. Primarily because of these factors, rotation-resistant ropes are not allowed to be used as boom hoist ropes. The only exception is that a luffing jib boom hoist rope may be a rotation-resistant rope if used at a design factor of 5:1 and bending ratio of 18:1.
Boom hoist ropes typically must be resistant to crushing on the drum, and this requirement makes compacted strand or compacted ropes a good choice on some cranes. However, compacted ropes may not be appropriate for all boom hoist rope applications because they have improved resistance to crushing, but they do not have the same fatigue resistance as compacted strand or conventional ropes.
 
Compacted strand wire rope: Endurance Dyform 6 (left) and Endurance Dyform 8
MODE OF FAILURE
Operating conditions will often require the use of a different rope than what is specified as original equipment. In this case, it is appropriate to have the rope analyzed for mode of failure after it has been removed from the crane. A wire rope expert can then recommend a rope that is designed for improved operating characteristics to combat the mode of failure.
Using Bridon American's ropes as an example, an Endurance Dyform 18 main hoist rope on a mobile crane is cabling or twisting the multiple parts in service. A wire rope expert may suggest using a more rotation-resistant rope, such as an Endurance Dyform 34LR. Another example may be that a 6x26 RAL boom hoist rope on a mobile crane was crushed on the drum. The expert may suggest using a more crush resistant rope, like the Constructex.
Compacted ropes: Constructex
ENVIRONMENTAL CONDITIONS
For most applications, environmental conditions will not require special rope or lubrication. Most mill-applied lubricants also will operate at a fairly wide temperature range of -40° F to 120° F and will provide sufficient anti-corrosion properties to operate in most environments.
Almost all ropes will be required to be lubricated in service. A light penetrating lubricant is recommended, as opposed to grease or an otherwise heavier lubricant. A field-applied lubricant should penetrate into the interior of the rope but also not be too thick or dark, so it will not inhibit visual rope inspection.
SELECTING THE RIGHT WIRE ROPE, by DAVE SLEIGHTHOLM of BRIDON AMERICAN, WILKES-BARRE PA., USED BY THE CONSENT OF DAVE SLEIGHTHOLM.
|
