A wire rope consists of hundreds of components that must move and interact in unison to bend and support massive weights. Wire rope is often likened to a “machine,” and like any other machine, a good maintenance program will yield significantly longer life. Although the subject is much broader and longer than a short magazine article will allow, touching on some of the key points of wire rope maintenance is at least a good start.
Check the sheaves
A significant part of good wire rope maintenance is ensuring that the equipment it works with is also in good order. For the wire rope, that mainly means checking the sheaves. Sheaves must move freely to avoid undue abrasion and run true without wobbles to avoid vibrations that can fatigue the rope. Next, the groove must be suitable for the rope being used. It is recommended that the groove be 1 percent larger than the maximum rope diameter including its allowable tolerance. That means for a typical wire rope with 0 to +5 percent tolerance, the groove should be nominal rope diameter +6 percent.
Worn and undersized sheaves lead to deformations from forced twist while larger tolerances can lead to damage caused by a lack of support. Corrugation in the groove will both twist and wear the rope. Finally, inspection of rollers must be regarded to be as important as inspection of the sheaves. They also need to be free of corrugation, wear and stuck or worn bearings.
Wire rope inspection guidelines: OSHA and ASME standards
By: Mike Close
As a manufacturer and distributor of wire rope, wire rope slings, chain slings, synthetic slings and rigging hardware, we often see customers confused about what is involved in the inspection of their rigging equipment.Our goal is to help you understand what is required for your wire rope slings to meet ASME standards, which will help to ensure the safety of the users, help extend the service life of the slings and help reduce unnecessary equipment repair costs and loss of production due to equipment downtime.
As a starting point, the same work practices which apply to all “working” wire rope apply to wire rope which has been fabricated into a sling. A good working knowledge of wire rope design and construction is essential in conducting a wire rope sling inspection.There are two industry standards that exist to provide the end-user with guidelines for inspection and criteria that warrants removal from service: OSHA 1910.184 and ASME B30.9.
What are the basic inspection criteria for wire rope slings? The goal of a sling inspection is to evaluate remaining strength in a sling which has been used previously to determine if it is suitable for continued use. When inspecting wire rope slings, daily visual inspections are intended to detect serious damage or deterioration which would weaken the sling.
This inspection is usually performed by the person using the sling in a day-to-day job. The user should look for obvious things, such as broken wires, kinks, crushing, broken attachments, severe corrosion, etc. Any deterioration of the sling which could result in appreciable loss of original strength should be carefully noted and determination made on whether further use would constitute a safety hazard. ASME B30.9 standards specify that a wire rope sling shall be removed from service if any of the following conditions are present:
Missing or illegible sling identification: If the tag is missing or illegible, the inspector should remove the sling from service and send it to the manufacturer for current or updated certification, tagging and testing.
Broken Wires: For strand-laid grommets and single-part slings, ten randomly distributed broken wires in one rope lay, or five broken wires in one strand in one rope lay. For cable laid, cable laid grommets and multi-part slings, use the following:
Distortion: Kinking, crushing, birdcaging or other damage which distorts the rope structure. The main thing to look for is wires or strands that are pushed out of their original positions in the rope.
Heat Damage: Any metallic discoloration, fusing of wires or loss of internal lubricant caused by exposure to heat.
Damaged End Attachments: Cracked, bent or broken end fittings caused by abuse, wear or damage.
Bent Hooks: No more than 5 percent over the normal throat openings, measured at the narrowest point from the plane of the unbent hook (see ASME B30.10 Hooks).
Corrosion: Severe corrosion of the rope or end attachments which has caused pitting or binding of wires should be cause for replacing the sling. Light surface rust does not substantially affect strength of a sling.
Pulled Eye Splices: Any evidence that eye splices have slipped, tucked strands have moved or pressed sleeves show serious damage may be sufficient cause to reject a sling.
Unbalance: A very common cause of damage is the kink which results from pulling through a loop while using a sling, thus causing wires and strands to be deformed and pushed out of their original position. This unbalances the sling, reducing its strength.
Kinks: Are tightened loops with permanent strand distortion that result from improper handling when a rope is being installed or while in service. A kink happens when a loop is permitted to form and then is pulled down tight, causing permanent distortion of the strands. The damage is irreparable, and the sling must be taken out of service.
Doglegs: Are permanent bends caused by improper use or handling. If the dogleg is severe, the sling must be removed from service. If the dogleg is minor, (exhibiting no strand distortion) and cannot be observed when the sling is under tension, the area of the minor dogleg should be marked for observation and the sling can remain in service.
Wire rope lubrication
Among the most misunderstood aspects of crane rope maintenance is lubrication. When a wire rope is bent the individual wires and strands have to slide relative to each other and the rope itself glides within the sheave. Without proper lubrication, friction increases and the rope life is drastically reduced. Checking the lubrication and periodically applying a thin coating of maintenance lubricant is key to any maintenance program. As a rule of thumb, ropes require maintenancelubrication every six to 12 months.
When it comes to maintenance lubrication there are a few lesser-known things to keep in mind. First, the lubricant must be compatible with the original lubricant. Otherwise, through intermixing, the two products can form a totally different lubricant with different technical properties. Second, a lubricant designed only for wire rope is a must. Wire rope lubrication performs a very specific function with very specific properties which generally cannot be met by multi-use products such as a typical gear, chain and rope lubricant. Third, the lubricant must be able to penetrate inside of the strands to cover each component uniformly. A product that just sits on the outside does not help the wire rope life, plus it can inhibit inspection.
A common wear area of running ropes on construction cranes is at the drum. Since the rope is wound in multiple layers it is subjected to abrasion and crushing at crossover points between rope wraps and change in layers. To get optimal life from the rope it must be sufficiently tensioned on the drum to 5 to 10 percent of working load limit during installation. When a wire rope is sufficiently tensioned it tightens and gains lateral stability wires pushed out of position due to non-tensioned drum wraps, enabling it to resist crushing from the incoming loaded rope. When it is not tensioned it will crush much more easily. It is important to note that tensioning is not a one-time event. Over time, unused lower wraps and layers slowly lose this tension and therefore ropes need to be routinely tensioned as part of the crane maintenance program.
But even with perfect tension, wireropes will eventually wear at the crossover points.
RopeBlock’s Super Reeve Connector
The new Super Reeve Connector Swivel Socket (SCS-SW) from RopeBlock is the result of further development of the company’s patented Super Reeve Connector Socket (SCS). The new design adds an integral swivel. The Super Reeve Connector Swivel Socket utilizes a poured button that achieves an efficiency of 100 percent of the wire rope breaking strength, RopeBlock said.
The shorter length optimizes the hoisting height. Integrating a swivel increases safety as the torsional forces are reduced in comparison to situations where only a socket is used, the company said. RopeBlock engineers have designed the SCS-SW as a universal product that can be relatively easily adapted to all types of cranes. The SCS-SW is available for wire rope sizes from 7/16 inches to 2 1/8 inches (11mm - 54mm).
Extending the life of wire rope
Another method to extend the lifetime of wire rope is by cutting a length equal to 1-1/4 drum wraps from the drum end to move the wear points. For this method to be effective it must be done at intervals that occur prior to these sections showing more wear than the rest of the rope. Three or more times over the rope’s lifetime is recommended.
For tower cranes the problem is usually compounded. The crane starts at a base height and climbs during the job leaving lots of unused rope in the lower layers on the drum, not to be used until the crane is climbed to its final working height.
These lower layers at the start of the job cannot be practically re-tensioned or shortened until the rope climbs high enough to fully spool the rope off. Unfortunately, by the time the rope at these lower layers is needed it may already be damaged. The solution is to plan to use a different length of rope for each stage of the job. This ensures that there aren’t any unused, low tension layers becoming damaged before seeing any useful life and in most cases the ropes can be used again at the next job.
WireCo develops Betalift SP
WireCo WorldGroup has introduced a new product that will replace Apex for extend and retract assemblies on cranes. Following an analysis conducted by its technical and engineering specialists, Wireco WorldGroup is now offering Betalift SP.
“Betalift SP can be directly substituted into the application the Apex product is currently used, with equal breaking strength and even more benefits to our customers,” said WireCo WorldGroup. “Manufactured to the industry’s highest standards, Betalift SP is constructed with drawn galvanized wires that provide excellent corrosion resistance. In addition, extensive testing has shown Betalift SP provides 25 to 50 percent improvement in fatigue life.”
The company said Betalift SP is the strongest rope available for crane assemblies and is not to be used with a swivel.