Thern “Rises and Lowers” to the Occasion
All About Drums (continued)
It is very important to stay out of the paths of the load and the wire rope!
First and foremost, keep all unnecessary personnel away from the winch while it is in operation. And, never lift people (unless the equipment is designed and certified for such a purpose) or things over people. Never walk or work under a load or in line of force of any load.
The load generally is a large or heavy object that may have a high level of inertia energy. Any time a load is in motion (since a load-in-motion tends to stay-in-motion) being in the path of that load could cause an injury.
As hard as it is to imagine, wire rope generally will stretch a certain amount while under load. This in a sense will act like a very stiff rubber band. If the rope were to break or become disconnected from its attachment, there is a possibility that it will spring back in either direction. If the wire rope were to snap back, it could potentially, severely injure someone. This is also a very important reason why the wire rope should be inspected frequently for signs of wear.
Winches most often have the operator controls located directly on the winch itself and in many of those cases, the controls are in the path of the wire rope. However, there are some options available that will aid the operator in staying out of the path of the wire rope. A pendant or remote control can potentially allow the operator to stand in a safe location out of the path of the wire rope. Either of these controls might also allow the operator, or a spotter for the operator, to maintain a view of the load during the entire operation. If the load is not visible by the operator at all times, a limit switch can also be used to prevent over traveling of the load. Travel limit switches can normally be adjusted to make sure the load will only move a pre-set, safe distance during each operation. There are many other types of limit switches available that will stop the winch when the switch is triggered. The experts at Thern can help you determine the best solution for your type of winch and your application.
PROJECT FILE: Mission Possible
New Year’s Ball Winch Times Square, NY
Once per year, Thern shines on the world’s largest stage on New Year’s Eve at One Times Square, New York, New York. Thern was selected to design and manufacture a winch capable of lifting and lowering the New York Times Square Ball. This was the second winch Thern has provided for the task of lowering the ball. As improvements were made to the ball, it got much larger and much heavier – So a more powerful winch was needed.
The ball itself is twelve feet in diameter and weighs in at 11,875 pounds. A combination of 32,256 LED lights and covered with 2,688 Waterford Crystal panels, gives the New Years Ball its spectacular effects. Over one million people attend the event each New Year’s eve eagerly waiting for the highlight of the evening – the lowering of the Times Square Ball. Over ONE BILLION people watch the event on televisions all over the world as Thern’s custom winch lowers the ball with perfection.
The winch had to be powerful enough to handle the load and geared precisely in combination with the drum’s diameter to lower the ball at the speed required to make the 141-foot decent in exactly 60 seconds.
The winch is also installed via a unique under-mount system. The Times Square Ball winch is a perfect example of the need for a grooved drum which is discussed in the article below.
That Drum is Groovy Man
A “Grooved Drum” assures that the first layer of rope wraps properly and evenly within the groove pattern. When the first layer wrap is properly established, additional layers are more likely to also cooperate with the desired, even-layer wrapping. However, the actual wrap result is always dependent upon the rope fleet angle, which we will cover in our next issue.
Though always beneficial, grooved drums are generally not utilized for winch applications requiring multi-layer wrapping. Most are used when the application calls for a single-layer wrap and accurate, repeatable pay-out/pay-in distances are needed. The grooved drum will assure that the single layer rope wraps the same way each time. A winch of such design is typically equipped with a Rotary Limit Switch (RLS). With repeatable wrapping due to the grooved drum, the added control feature will provide repeatable travel stop limits for both pay-out and pay-in points. If the winch utilizes multiple-layer wrapping, a grooved drum plus an RLS can provide a repeatable travel stop point, but only for pay-out travel direction.
Another point to consider is that a grooved drum feature can add as little as $200 to the cost of a small utility winch, to several thousand dollars to the cost of a large drum industrial winch.
“Closed-Loop” rope rigging applications are another common utilization of winches with grooved drums. For these applications, the grooved drum will feature a cable anchor at both drum flanges. Two ropes will attach and exit the grooved drum in such a manner that upon rotation, one rope always pays out and the other pays in. Via use of a sheave(s) and a rope tensioner, the motion of the attached load is securely controlled in both directions. See: Typical Rigging Layouts for pulling applications.
In forming and planning any single layer grooved drum winch application the required travel distance is of utmost importance and must be determined. The grooved drum’s diameter and length must be sized accordingly to assure the application’s required travel distance.
With or without a grooved drum, a “Cable Pressure Bar” is sometimes a desirable winch feature. This option is helpful to applications where the rope sometimes becomes limp and therefore might expand or “bird nest” about the drum. If this happens the rope likely will not return to proper lay position when tension is re-applied. A cable pressure bar helps by maintaining roller contact across the full width of the drum and onto the wrapped rope. While beneficial to many applications, a cable pressure bar can be expected to provide only so much protection. If the rope becomes excessively loose and/or the winch operator commits excessive back/forth jogging of the drum when rope is not taut, the wire rope is still likely to bird nest about the drum.
Next issue we’ll cover Fleet angle, and “Level Wind” option.
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