Aramid fiber ropes in dynamic applications?
Aramid fiber ropes in dynamic applications?
(OP)
In one of the projects I am working on, we need to have a very high strength, high flexibility connection between a rotating pulley and a linearly moving slide mechanisim. We are currently exploring the use of aramid fiber ropes for this connection.
My question is: Has anyone used aramid fibers in dynamic applications? Are there any big drawbacks vs. steel cabling? Any tips on terminating the ends?
My question is: Has anyone used aramid fibers in dynamic applications? Are there any big drawbacks vs. steel cabling? Any tips on terminating the ends?





RE: Aramid fiber ropes in dynamic applications?
Most people settle for 60% termination efficiency, but we consistently exceeded 95% on our production line. If your application is a one off or not weight critical then settle for 60%, the extra 35% cost a lot of time and research.
Fatigue can be an issue - what diameter is your pulley? what diameter is your rope? How good is your alignment? There's no published data on this that we could use - we ended up building a simulator that torture tested our product.
Cheers
Greg Locock
RE: Aramid fiber ropes in dynamic applications?
A pulley that has been designed for steel cable is not suitable for kevlar because the v-shaped groove crushes and damages the fibres, a rounder groove is better. I think the diameter of the pulley has to be a certain multiple of the rope diameter.
Watch out for chafe and sharp bends, there are some new ones like vectran that can be bent around tight turns. the cover of the exotic ropes are there solely for anti-chafe reasons and contribute nothing to strength. Many racing crews remove the cover entirely to save weight aloft.
regards
Paul
RE: Aramid fiber ropes in dynamic applications?
Any tips on this? I would love to be getting ~ 60% of ultimate strength from the terminations (so far I'm only to about 700 LB on a 2400 LB test line). I've been trying to do this by potting the line inside a cone shaped steel piece with epoxy, but have not been having too much luck since the epoxy tends to crush and pull through the fitting (probably because the epoxy does not fully impregentate down into the fibers). Crimping and other mechanical connection strategies are giving me even worse results.
Any input on termination strategies is appreciated.
RE: Aramid fiber ropes in dynamic applications?
The larger barrel opening has a "forked" end, which is actually a clevis, for pin and clevis connection. I've heard claims that this type of termination has near 100% rope strength capacity, for non-cyclic loading, if the geometry, etc., in the barrel and spike design is optimal (though I don't know the optimal geometric parameters nor optimal material properties). For cyclic loading, the capacity will be less than 100%, though I don't know how much less, and it might(?) still be high enough for your application or worth investigating.
RE: Aramid fiber ropes in dynamic applications?
RE: Aramid fiber ropes in dynamic applications?
Kevlar is not used much on boats anymore because it has been surpassed by the new lines like Vectran and t-900.These are far superior to kevlar for low stretch, virtually no creep, ultimate tensile strength, and durability.
T-900 will only give you 0.8% stretch at 15% of breaking strain which is 4400 pounds for a 6mm diameter line. This line splices easily. You should get close to 90% breaking strain with a proper splice.
Check with the New England Rope company.
Hope this helps.
RE: Aramid fiber ropes in dynamic applications?
RE: Aramid fiber ropes in dynamic applications?
One of the termination ideas we have come up with is to splay the fibers into a cone shaped pocket in the steel end and impregnate the fibers with epoxy. We're having trouble finding any glues or epoxies that will wick into the cone, but hold up to the stresses generated when the fibers are placed under tension. Any ideas?
RE: Aramid fiber ropes in dynamic applications?
If I understand you correctly you are using a type of 'Norseman' or 'Stalock' terminal that is generally used with wire rope. This uses the tension in the line to pull a cone, (that the core of the line is wrapped around)into a tapered body, (slightly smaller than the cone), that the terminal end is part of. If this is so then the compression between the cone or spike and the tapered body is what keeps the line in place. This crushes the fibres and is generally not used in the dynamic applications that I am familiar with.
Much better is the eye-splice. This consists of removing a portion of the line, from the core and unlaying the core into 3 or 4 or 5 strands, (it depends in the make up and material of the line). The line is then wrapped 180 degrees around a thimble, (egg shaped plastic or metal object about 5 or 6" in length) and the strands are interwoven back into the line. The cover is slid back on and sometimes sown into place.
This process is very difficult to describe without pictures, but is fairly easy and only requires a few special tools such as a fid.
The thimble then takes the strain usually from a d-shaped shackle. This removes any direct surface contact between the line and the load so all chafe is taken by metal parts.
Hope this explains it better.
RE: Aramid fiber ropes in dynamic applications?
RE: Aramid fiber ropes in dynamic applications?
The proper stuff is ridiculously expensive and is available from Jaques De Regt cables in Rotterdam in Holland. You use so little of it that there doesn't seem much point in searching for a cheaper alternative.
A conventional spike and cone joint with fluffed out fibres should give you 60% although I have no experience with such tiny joints - our spike was about 20 mm across at the small end. When analysing the joint for radial stiffness you might like to consider how the spike contracts and the cone expands under tension - and try and make sure that the fibre isn't getting cut in the process, as the spike moves into the cone. (That was a big hint).
There is an interaction between the spike's taper and the cone's taper and the relative radial stiffness of the components and the friction of them. Once we found a system that worked we stuck with it.
Cheers
Greg Locock
RE: Aramid fiber ropes in dynamic applications?
"Rigged For Success", pp.36-38 of December 2002 issue of Composites Technology.
You can find more information about the magazine, and maybe get a free copy, using the following link to their website:
http://www.compositestech.com
RE: Aramid fiber ropes in dynamic applications?
I saw this article as well. This is the same basic strategy we are working on for this. Keep the ideas coming. We're still learning about these materials as we go and any experience or ideas are appreciated
RE: Aramid fiber ropes in dynamic applications?
I have some good results terminating Kevlar in braided and parallel-lay. I use a machine part with an internal cone at an angle of 14 degrees which faces away from the load and extra counterbore well. I then spread the kevlar out using equal amounts in 3 directions approximately 120 degrees and pot the material using a 2 part epoxy by Emerson and Cuming (Part Number 2850FT and 24LV catalyst)The epoxy can be purchased in different quantities. These assemblies that I have used have given me better than 80% breaking strenght. I will add that I have also used a carrot (bend limiter) outside so the kevlar does not break from exiting the machine part.
Tofflemire
RE: Aramid fiber ropes in dynamic applications?
Excellent post. I appreciate your input.
- Rich
RE: Aramid fiber ropes in dynamic applications?
I was just wondering if you had any luck terminating/solving your kevlar?
Thanks
Tofflemire
RE: Aramid fiber ropes in dynamic applications?
We got about 95% strength at the fitting. Results were about 3x better on durability than the steel parts of the same size that we had been using, but still didn't meet our specs. We ended up redesigning the system to allow us to increase the size and number of wraps that the cable takes and we ended up going back to steel as our cable material. Seems to work well with this new design.
In short, we found that LCP rope was the best bet for our dynamic application, and we came up with a pretty nice design that ended up getting shelved for now. We'll probably get back into it at some point, but for now, we're sticking with steel.
RE: Aramid fiber ropes in dynamic applications?
Thanks for the feedback, hope my info helped pointing in the right direction.
Tofflemire
RE: Aramid fiber ropes in dynamic applications?
I'm looking for a rope terminal, similar to Norseman but not for steel wires. I don't have particular strength requirements, but I need it small and very quick to mount.
I'll be using it with simple polyesther ropes.
Anyone has a product to point to?
Thank you all.
Beppe