I would like to take this opportunity to make some comments on your article “The upper limits” (May 2005, pp17-19).
At R. Stahl SH wire rope hoists we have been using gear-based limit switches for years now.
Depending on the application we extend this limit switch by additional switching elements to get an operational limit switch. This solution increases the headroom by less than 2 in. and the price also not considerably more. Alternatively a weight-operated second limit switch is available with greater changes in headroom and price.
Limit switches of our hoists, gear-based or of other design, are electromechanical and have positive opening.
The article is very informative describing the current situation in the US.
Describing the pros and cons of the rope guide ring (RGR), your article made it clear, without saying it directly, that only a reliable RGR is a real help and safety feature, i.e., it must be able to avoid overwrapping and loose rope on the drum.
The RGR is a wearing part and must be checked, as must the rope, regularly.
Unfortunately the R. Stahl RGR was not shown in your article.
It features a rope tensioner going round the whole last rope loop (360°) preventing loose rope on drum. Grip the rope 5 in. before the rope guide ring and try to push the rope into the RGR. Compare the force necessary with other designs.
Its solid GGG 40 (spheroidal cast iron) material makes for robust construction. GGG 40 is a wear-resistant material with no temperature restrictions. This construction principle is now used on the fourth hoist generation (C, N, AS, SH types).
-Norbert Horndacher, wire rope hoist product manager,
R. Stahl Fördertechnik
