Increased mechanisation is reducing wire rope life
THE INCREASING MECHANISATION IN THE FORESTRY INDUSTRY is turning wire ropes into consumable items, with ropes working far harder now than previously and subsequently rope life is on a downward spiral.
Technology in forestry equipment is advancing at a rapid rate whereas the ropes being used in forestry have pretty much remained the same for the last 30 years.
A recent trip to Queensland to visit a Harvestline crew having rope life issues is a prime example of this, says Andy Palmer, Business Manager with leading wire rope supplier Cookes.
“After trying two different makes of rope and coming up with the same results I was invited to have a look at the operation and offer some advice,” he says.
“An inspection of a previously discarded rope showed its failure was a result of bend fatigue breaks on the crown of the strands. The fast cycle rates and vastly increased productivity as a result of using a grapple was resulting in far shorter rope life than on their previous pole yarder.
“On the Harvestline the damaged was occurring in the last 100 metres of the working end of the main rope. End-for-ending the rope meant that when the rope was finally removed from service the customer had two badly fatigued 100m lengths on the ends of the rope and a 280m section in the middle which was still in good condition.
“A suggestion was made to run a sacrificial length on the working end of the rope and splice a new section each time this section was damaged.”
An offer was then extended to refresh the crews splicing techniques at the Cookes rigging facility in Auckland. The offer was accepted and five weeks later the team from GMT Logging were under the tuition of Cookes Senior Field Technician Jan Jacobs.
The training was broken down into a classroom session to understand the theory of the splice followed by hands on instruction with a smaller diameter flexible rope before finally progressing to the 19mm swage currently used on the machine. Once all participants had successfully completed a splice, the spliced rope was then placed into the 200tonne test rig to be pulled up first to the working load and then pulled to destruction to make sure that the splice would work out in the field.
Mr Palmer says this is an acceptable option for extending the life of the rope, adding: “When a rope fails from bend fatigue breaks on the crown of the strands the working rope has done its job and reached the end of its life.
“If you want to continue at the same high cycle rates, your options to improve the life of your rope primarily rests with increasing the D-to-d ratio of your sheaves, using a rope with a more flexible construction or preferably both.”
With this in mind, Cookes is reintroducing the 6x31WS swaged rope in an effort to help loggers achieve the maximum return on their ropes, whether a tail rope on a swing yarder or a live sky line running a grapple carriage.
“When I first started with Cookes 31 years ago, before the introduction of swaged ropes, you had 6x19 for skylines and 6x31 for running ropes,” says Mr Palmer.
“The introduction of swaged rope in the mid-to-late 80’s saw 6x26WS construction introduced as a happy medium between the two constructions. This is the same construction as used today, and while it worked perfectly well on a yarder running butt rigging, the rope design is not coping with the high cycle rates being achieved by today’s crews running grapples.
“The 6x31 is a Warrington Seale construction, the same strand design as used in high fatigue areas such as hoist ropes on ship-toshore cranes. The old guys knew best!
“While wire rope manufacturing has seen advances in Crane, Mining and Oil & Gas rope technology, Forestry seems to have been forgotten. Cookes – part of the BBRG Ropes Group – as a leading global manufacturer, sees this as an opportunity to work with the industry to find a solution for diminishing rope life.”
NZL