Wire Rope Clamps - Which is better? 2

[knooper]

Can anyone provide some insight as to which wire rope clamp is better - saddle or fist? We had a major safety incident with the wire rope hoists we use to move around 3-ton rolls of paper. The dead-end of the wire rope pulled out and dropped the roll to the floor, almost landing on the operator. The saddle clamps we were using were properly oriented (never saddle a dead horse) and properly torqued. The hoist manufacturer suggested fist clamps as an alternative since they do not deform the dead-end of the cable as much, which sparked the debate as to which clamp is better. I've checked the Crosby website, but I can't find any data that tells me if one is better than the other. Can anyone provide me additional resources or insights? Thanks!

 

[aviat]

Machinery's Handbook has some info on U clips and gives a table for number of clips needed for cable size. It gives a rating of less than 80% of cable strength. It also calls for a thimble.

It does not mention fist clamps. Swaging will give 100% of cable strength if you can use that.

 

[IRstuff]

Has this been done reliably at your facility in the past? Did something change? What design margin is there for the clamp?

Presumably, the objective is to keep the free end from slipping. Counting on a single point of constraint sounds difficult to me as a starting point.

Are there alternate configurations that can be used? What if you made it a slip knot with the clamp?

TTFN

 

[knooper]

Thanks for the responses. We have used what I think you're referring to as a thimble (something that you loop the dead-end around), and there was one installed at the time of the incident. Swaging is not an option in the given application, and I'm not quite sure I understand how to create a slip knot with the clamp. The configuration was following the instructions provided by Crosby (the manufacturer of the clamps we are using) as closely as we were able to follow them. There were 2 saddle clamps holding the wire rope, but the fiber core of the rope was melted back about 6" when the ends were welded (we have since gone to steel cores). Since the saddle clamps tend to distort the dead-end of the rope, the portion of the rope without the core splayed out and over time worked it's way free, leaving only one clamp to hold the rope, which as you pointed out is not enough to hold the given load.

What I'm looking for is more in terms of general design practices. I know saddle clamps are very widely used, but they deform the dead-end of the rope. Fist clamps may be more expensive and take up a little more space, but are they better, worse, or the same as saddle clamps in general?

Thanks again for your responses!

 

[automatic2]

It is unlikely that the rope worked it's way free over time, unless the clamp was not properly torqued, or the clamp experienced trauma. As well, welding the end of the rope is fine, but don't include any of the temp affected rope into any part of the equation. I would be strongly suspicious of the installation, checking all dimensions, ie; thimble to clip distance, clip to clip distance. Because it was a safety mishap, I trust you (or the investigating team) had the installing/pm mechanic demonstrate his knowledge with a practical demonstration.

 

[ruble3]

The only other thing I could think of was the lay of the cable changed? there was some debate some time ago about using clips on 'left lay rope'-Crosby specs are for RLL (right lang lang)or RRL( right regular lay) - the clips have ridges on the contact part that are supposed to bite into the rope- on left lay ropes they are oriented the same way so won't 'bite' the same - we had some left lay ropes and the debate was do we add more clips or, as someone suggested, file the ridges off - we ended up using same # of clips and absolutely did not do any filing

 

[boo1]

NOMINAL SPLICE EFFICIENCIES are measured in terms
of efficiency (where efficiency = actual breaking strength
spliced termination divided by actual breaking strength of
the rope). The efficiency will change from splice to splice
because of the many variable factors involved in producing
the splice.

See termination efficiencies at:

http://www.safetysling.com/wrs1.htm

 

[knooper]

We have looked in to whether or not the individual who installed the clips did it right, and went so far as to check the other hoists he had worked on - all were torqued properly. I mentioned that there were a lot of issues stacked on top of each other that led to the safety incident, and inadequate distance from thimble to clip and between clips was definitely a factor. We were unaware that any of the core had melted, so we were clamping on top of an empty portion of the rope (that issue has since been remedied by switching suppliers).

ruble3, we looked into the lay of the cable, and according to Crosby, the one we're using is the appropriate one for the clip. I'm glad to hear that you decided not to file any ridges off!

boo1, that website you gave is a huge help. It looks like from a strength standpoint, there's really no difference between the two clamps.

Thanks a bunch for all your information!!
knooper

 

[chicopee]

There is nothing wrong with the clips that you used as long as you had a minimum of 3 clips for a loop efficiency of 75% to 80%. As the wire size increases Crosby recommends more than the minimum of 3 clips. So my first question to you is did you have a least 3 clips? Secondly, was the lifting capacity of the wire rope with its loop efficiency of 75% greater than the hoisted load? Was the spacing between the clips in accordance with Crosby recommendation? Lastly was the size of the wire rope fitted w/ end clips within Crosby minimum recommended rope size?

 

[ruble3]

Sounds like you've got things in order now-I had assumed from your first post all Crosby recommendations were followed ( as Chicopee pointed out, # of clips, spacing etc)- this is why I am not a big fan of making my own slings and prefer nylon or pre-made slings especially for heavy lifts

 

[boo1]

Agree with chicopee, additionally was the clip size, number of clips, turnback length (in), installation technique, and torque FT-lbs correct.

U-Bolt clips must have the U-Bolt section on the dead or short end of the rope and the saddle on the live or long end of the rope. The wrong application, U-Bolt on live instead of dead end, of even one clip can reduce the efficiency of the connection to 40%.

Never use fewer than the number of clips recommended by the manufacture. Turn back the correct amount of rope for dead ending to permit proper spacing of the clips. Always use new clips; re-used clips will not develop the proper efficiency. It is equally important to always use a thimble to prevent the rope from wearing in the eye and to provide a safer connection.

Apply the first clip one base width from the dead end of the wire rope. Tighten the nuts. Apply the second clip adjacent to the thimble, but don't tighten the nuts. Apply all the other clips, leaving equal space between each. For maximum holding power they should be installed 6-7 diameters apart. Take up the rope slack by applying tension to the eye and cable and tighten all the nuts evenly on all the clips to the recommended torque.

After the rope has been in operation for an hour or so, all nuts on the clip bolts will have to be retightened and they should be checked for tightness at frequent intervals thereafter. This is necessary because the rope will stretch slightly causing a reduction in diameter which will slacken the clips.
see:

http://www.jameswalker.com/restsite/crosbyhardware/1.htm

note
Oshaa requires inspection of the rope and related equipment at the beginning of every work period at least daily in most instances and particularly following any incident which could have damaged the rope or installation.

 

[boo1]

The allowable capacities of prefabricated components, e.g. hooks, shackles, and wire rope, are established as required by OSHA in 29 CFR part 1926.251

(a)(6) Inspections. Each day before being used, the sling and all fastenings and attachments shall be inspected for damage or defects by a competent person designated by the employer. Additional inspections shall be performed during sling use, where service conditions warrant. Damaged or defective slings shall be immediately removed from service.

(c)(1) Tables H-3 through H-14 shall be used to determine the safe working loads of various sizes and classifications of improved plow steel wire rope and wire rope slings with various types of terminals. For sizes, classifications, and grades not included in these tables, the safe working load recommended by the manufacturer for specific, identifiable products shall be followed, provided that a safety factor of not less than 5 is maintained.

c)(5) When U-bolt wire rope clips are used to form eyes, Table H-20 shall be used to determine the number and spacing of clips.

BE SAFE review your plant safety plans, sling proof testing proceedures (yearly), rigging training, and record keeping proceedures. Lawer's love this kind of stuff........

 

[sacem1]

Have you ever tried untwisting the strands at the end of the rope in two bundles lets say 3 and 4 strands on a seven strand wire rope and forming with one the loop you requiere with about 12 rope diameters left after the loop is formed and then retwist the other bundle around the formed loop keeping the formed wires aligned and following the twisting in the loop wires, after you finish the loop twist again the straight part and you will end with a rope to fix by any suitable clamp to the supporting wire rope.

The result will be more safe and secure than any rope fixing device that you will be able to put in use.

This more an art than a science, so first try it with several scrap pieces of wire rope, and you will master it in very short time.

SACEM1

 

[boo1]

When you try to weave an eyes in wire rope, wear gloves you will need them....

 

[IFRs]

I always thought that fist grip type were better and our company requires them.

In

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=FEDERAL_REGISTER&p_id=13573

search for "fist" and find an interesting discussion.

Check out

http://www.osha.gov/doc/outreachtraining/htmlfiles/slings.html

for some general sling info.

More detailed info is at

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9834