There are few mechanical components in a ski area that do more work, have more responsibility, and get less attention than the wire ropes that are involved in ski lift and aerial tramway operation. True, they are usually inspected superficially once a year and lubricated at least that often, but compared to gear boxes, motors, engines, or control equipment, they receive very little care and/or attention.
Fortunately, these wire ropes do their job very well in most cases even with the slight amount of service attention they receive. There are and have been instances, however, where wire rope performance or their service life expectancies have not been satisfactory. Many factors can enter into these situations and no attempt will be made here to describe them all. However, there are some very basic precautions to be taken that will prevent the majority of wire rope damages and shorter than normal service lifetimes.
All prominent wire rope manufacturers take great care in the manufacture and handling of wire rope within their own plant. Once the wire rope is shipped, the responsibility shifts, and not everyone else has as much concern or knowledge about the wire rope.
When damage is done, it usually occurs from the time of unloading from the transporting vehicle to the final installation. Accidents can happen, but many installation damages cannot be considered as accidents.
Unreeling the rope
Ski lifts and aerial tramways usually require a considerable length of wire rope in one piece and on one reel. The reel is normally quite heavy and difficult to handle. No attempt should be made to prepare this reel for unreeling until a person qualified in wire rope installation is present and has properly prepared the reel support, the axle it is to rotate on, the direction the wire rope is to be pulled, and the reel brake. No pull should be applied to the loose end of the rope until such a time that a suitable end fitting or connection has been properly attached so that the pull will be equal on all the rope strands. Unbalanced pull on the strands will invariably result in a “rippled,” unbalanced rope.
A swivel should never be used between the pulling apparatus and the wire rope being pulled into position on a ski lift. In fact, it is very desirable to have some sort of a pendulum attachment on the leading end of the new wire rope to insure that the new rope does not rotate while being pulled into place.
The wire rope manufacturer has taken great care to insure that the rope has the proper diameter, the proper strand clearance, and the proper rope lay length. The strands were pre-formed and the finished rope may have been post-formed at the time of manufacture to provide a tight and compact rope.
All of the manufacturer’s efforts can be defeated or destroyed if torsions (either positive or negative) are induced into the new rope while being pulled. For instance, if a rope is allowed to “unwind” during installation, the end result will be a rope with a longer rope lay, a smaller diameter, and more than likely, a shorter service life.
It seems almost unnecessary to mention that a wire rope should not be drawn over rocks, ledges, or sharp structural steel. However, this has happened many times in the past, resulting in damage to the rope. Much care should be taken to insure that the rope will not be exposed to this abrasion and abuse.
Tying off for splicing
Once a new rope is pulled into place it is important not to damage it while tying it off for splicing. The tying off ropes or tag ends should be compatible in size and hand of lay with the new rope. In other words, if the main haul rope is a left hand lay, then the tying off rope should also be of left hand lay; and if the main haul rope is a right hand lay, then the tying off rope should have the same direction of lay. The number and size of rope clips must be correct. Also, the direction of lay of the main haul rope being tied off will determine the type of rope clips used. If it is a left hand rope, then clips that are totally suitable for left hand rope lay should be used. And likewise for a right hand rope. The rope clips should be tightened to the correct torque rating as specified by the clip manufacturer. Tension on the connections should be applied slowly and evenly. Care must be taken to insure that the new wire rope is not bearing against rocks, steel structures, or mechanical equipment in the tied off position.
Constructional stretch will occur in a new wire rope. An accepted industry standard is between one-quarter and three-quarters of one percent of the length of the rope. Not all of the constructional stretch will be removed from the rope by “hanging” in a static position. However, a minimum of ten days should be allowed for “hanging” at the design tension. This is not always possible, but it must be remembered that there is contructional stretch in a new rope and the more that comes out before splicing assures less that will come out after splicing.
There are many different opinions in the ski industry today as to whether main haul ropes should be lang lay or regular lay and whether they should have synthetic fiber cores or natural fiber cores. There is also different thinking among the lift manufacturers as to whether right or left hand rope lays should be used on lifts with right and left hand loading.
Wire rope manufacturers will furnish whatever rope is specified on the order to them, and in most cases do not know what lift a particular rope is being installed on in a particular ski area.
Ordering the right rope
It is up to the customer to order the correct rope for each specific installation. A potentially serious problem could develop from mis-information for any particular rope installation. The fixed clamping devices that grip over the wire rope and are attached to the passenger carrying devices develop a “wear-pattern” after a period of service. This “wear-pattern” can be a result of abrasion from the wire rope moving within the gripping device, or it can be a “cold flow” process of the metal of the gripping device forming around the moving wire rope. In either instance the “wear-pattern” is the same as the shape of the wire rope both in strand lay direction and outer wire lay direction. The “wear-pattern” on most gripping devices is perfectly normal and will continue to develop into the gripping device until such a time that it gets too deep and the gripping device must be replaced by a new one.
When a main haul rope is replaced with a new rope of the same diameter, hand of lay, and lay type, the “wear-pattern” of the grip probably will be quite compatible with the outside shape and configuration of the new rope. If, however, the new rope is of a different hand, or type lay, the “wear-pattern” of the grip will not match the rope configuration and, consequently, there will not be a full area of contact between the grip and the rope, but rather a few very high pressure areas of contact resulting in stress concentrations to the wires in the rope. This should not be allowed to happen!!
If the size, type, or hand of rope is different for a replacement rope than the one it is replacing, make sure that all other components that function on or against this rope are compatible with the change. Each lift will be different when a replacement of the rope is made, obviously. Some gripping devices will be worn more and some less than others. The change in the rope may only be from one type of lay to another type of lay, of the same “hand”—right lay or left lay. Consequently, there is no set pattern or rule for the necessary precautions to be taken regarding this matter other than the fact that if the replacement rope is not exactly the same as the rope that it replaces, then every precaution should be taken to make sure that there will be no mis-match of components that will cause stress concentrations on the new rope and perhaps premature damage. It may require the refurbishing of the gripping devices themselves. In some cases it may require the replacement of particularly worn gripping devices. The object is to protect the new rope from any partially worn components that may not coincide with its shape and/or size.
Not all wire rope problems and damages occur to main haul ropes. When wedge sockets are used on counterweight ropes, they can be a source of considerable trouble if the installer does not understand what to do and what not to do. There is not only a problem of slippage within the socket, but also rope damage such as “nicking” and “high stranding” may occur. Remember, these counterweight ropes are just as important as the main haul ropes.
Wire ropes can be easily damaged when mishandled, or they can be strong, tough and long lasting when properly used. Don’t leave the installation, maintenace and inspection of your wire ropes to the discretion of an inexperienced individual. It will be less expensive for you to hire a person qualified in wire rope installation and inspection, or to have your own personnel properly trained than it will to risk expensive rope damage.
