SST Wire rope for driver/driven system 1

[linares]

Hello experts,

Is there someone out there that has used SST wire rope in an application where you would normally use a belt? i. e. Where you have a driver motor and a driven load.

Could you in theory replace the belt for a SST wire rope loop/sling?

I have seen similar things in conveyor systems in the food processing industry and I wander if the equations that rule belt friction drives apply to this? I don't see why not, but perhaps someone out there has some experience in this matter.

Thanks!

 

[chicopee]

Get a book on Machine Design which will show you equations of wire ropes riding in sheave grooves.
As far as stainless wire ropes, I have not seen them use since the machinery which I was involved only required iron wire ropes.
I would that if the SS wire rope is to be used in the food industry, sanitation and sterilization may be problematic.

 

[linares]

Chicopee,

Thank you for your comments. Is there one that you would recommend that covers the topic? I have a very old Shigley (3rd edition) and there nothing on this topic (closest thing it has is belt drives).

From the research I have done it seems that in most of the application it is the designer's goal to reduce friction between the sheave and the wire rope to avoid fretting. And I guess that's OK if your sheaves are only meant for guiding the rope, but in the case that you actually want to have a driver or driven sheave high friction coefficient is desired in order to avoid high initial tension requirements (or preload). V-groove type sheaves have an uneven load distribution on the wire rope reducing life, but increasing contact pressure. Maybe it is a necessary compromise.

 

[MikeHalloran]

I don't recall ever seeing wire rope used as a single-pass, two-pulley, belt. I think it's because it's impossible to make a splice that's not fatter than the rope.

( I met a guy at the Watervliet Arsenal who spliced wire rope for a living. He could come close, but he'd been doing it for decades. That was decades ago; he's surely dead by now. )

Even if you could squeeze a splice down to the rope's diameter, you couldn't also match the stiffness of the native rope, because the splice has so many cut or crossed wires.

I have seen substantial torque converted to tension in a wire rope, always with paired parallel very large diameter multigroove pulleys, as in the headworks of mine hoists and funicular railways. Which is to say, you can't get much tension increase in a single half-wrap of wire rope over a pulley; you need dozens of half-wraps.

I don't see stainless as having a particular advantage in wire rope power transmission. You need to lubricate the rope to keep it from chafing itself to death anyway, and stainless would probably need even more lubrication than regular wire rope because of galling.



Mike Halloran
Pembroke Pines, FL, USA

 

[linares]

Mike,

Yes, The splicing has always been my concern, and I had assumed that I would just consider that the week spot and reduce the life of the rope by 20% (this is what I have heard). One the sheaves would have to be mounted on a flexible mount to not have sudden tension increases when the spliced section goes over the sheave. The material selection is because of the environment (under seawater, which also make grease lubrication impossible). What do you mean by dozens of half wraps? Parallel slings? Or one sling that loops several times?

We can't have the same rope loop back a forth several times (like in a crane or pulley system) but we can have many parallel slings.

To those out there looking for a good text book on this: Wire Ropes by K. Feyrer has a very thorough explanation of the physical models that rule these systems.

 

[chicopee]

Wire rope is used in overhead hoists, cranes, ski lifts and elevators. I have seen wire ropes used between a steam engine and line shaft in an abandoned mill along the third canal in Holyoke,MA. In that installation,each sheave had about a dozen grooves for each wire rope loop.

Get a Kent ME hdbk, Mark hdbk, books on hoists and crane such as Shapiro, or elevator code for equations that may be of interest. Traction between wire rope and sheave is the key word beside working strength, mechanical advantages, minimum bend radii, etc...
To make an endless loop is hard work. You must have these picks to separate the strands in order to intertwine them. You must also allow enough material so the intertwined ends do not slip. If you are a skier, you can tell,barely, where the ends of these cables are intertwined and you'll notice at least 10' of material intertwined.