Intro to HD: Snatchblocks Continued
We remember that wire rope is a living and working machine. It’s individual wires and strands in the independent wire rope center. They all must be free to move, so when using snatch blocks it’s important to remember how that wire rope is working. It’s twisting as it rolls across a sheave. When it rolls from one sheave to another the wire rope tends to turn counterclockwise from the other direction.
When winching with a multi-part light up in multiple blocks included in the layup, an operator should stop winching when 1 block is 36” from the other. That will prevent the wire rope from over twisting and causing internal damage to itself.
Another factor to consider is fleet angle. Fleet angle is the angle at which the wire rope departs from a sheave. We want to keep the fleet angle down to about 2 degrees or less. If the wire rope leaves the sheave at a fleet angle greater than 2 degrees, we risk damaging the snatch block sheave itself, or the wire rope.
Continued use of a wire rope on a sheave that has a fleet angle has been exceeded, will cause extreme wear to the edges of the sheave. This could result in damage or premature wear of the snatch block or the sheave that’s located at the end of the boom. It’s important to remember that a snatch block could be rated in metric tons or imperial tons. A snatch block that has a 12 metric ton rating will be 2,204 pounds per ton.
Remember: that 1,000 kg is 2,204 lbs. A snatch block that’s rated in metric tons may have a higher rating than its Imperial ton counterpart.