What type of plastic line for this application?

[blueandwhiteg3]

I'm trying to work out the best type of plastic line for an application requiring good sustained load properties, minimal plastic or elastic deformation under operating conditions, good UV tolerance. If possible, it would be transparent, translucent, or at the very least white in color.

For operating conditions, it will be underwater, exposed to direct sunlight, and under a sustained load of around 60 kg. Elasticity and stretch must be minimal. Operating temperature range would be about -12° C to 45° C.

My needs sound a lot like a high-strength fishing line. But most of those lines don't really provide good data on elasticity, UV tolerance, effect of temperature on strength, etc.

A lot of high tension polymer fiber based ropes are out there, but they tend to be drastically overkill for my application - the load values and diameters are grossly larger than I need, and consequently quite expensive.

Any suggestions on what / where to look for the kind of material I need?

 

[patprimmer]

Nylon monofilament yarn, also known as suture sewing thread or fishing line depending on diameter and grade of resin.

This is the only material that will be translucent, reasonably UV resistant and very strong.

Unfortunately as your question is quite subjective it is impossible to provide objective data.

Nylon tyre cord might be a good source of data as tyres operate at the temperature ranges you quote, although the properties will be reduced due to water absorption if the line is constantly submerged. Nylon is quite good to UV and can easily be improved with stabilisers.

Do you need to tie knots.

Could you use a thin multifilament yarn that is coaed to protect it from UV. You would loose transparency but you would open up the potential polyme choice to include aramid.




Regards
Pat
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[blueandwhiteg3]

Clarity is not crucial. A white material would be acceptable, should transparent/translucent materials not be viable, particularly if it is small.

I need the line to stretch by no more than maybe 1% under full load. If possible, we'd be more like 0.1%.

Knots wouldn't necessarily be required. I guess some of this comes back to the mounting system.

Can you point me in the direction of some specs for some of these materials? I have a hard time finding things that are "more than fishing line" and "less than high tensile engineering rope" in terms of size/spec/pricing.

Because I can't figure out exactly what I'm seeking in terms of how it would be named on the market, it's hard to find suppliers, manufacturers, specifications, etc.

 

[patprimmer]

Aramid fibre will be the best re tensile strength and elongation.

Trade names are Kevlar and Twaron.

You will need to sheath it to protect from UV light.

Generally propeties are:-

Very poor to UV.
Very poor in compression hence very poor knot strength.
Very low elongation at break.
Tensile strength stronger than steel size for size and seven times stronger than steel weight for weight.

Uses.

Bullet proof vests.
Hard armour.
Reinforcement of very high performance tyres.
Reinforcement of light weight high pressure hoses.
Guy wires for suspension bridges.
FRP as a substitute for glass where high modulus and impact are required such as top end sporting goods, high tech military and aerospace.
Optical fibre cable central strength members.

Typical idividual fibre properties:-
Denity 1.45
Decomposition temperature >500C
Tensile strength 1950 mN/tex
22.1 g/denier
2800 MPa
Initial Modulus 55 to 85 N/tex
80 to 125 GPa
Elongation at break 2.0 to 3.3%
Moisture regain 2.5 to 4.5%
Heat resistance (retained strength 48h 200C) 90%


Does this help

More information available from DuPont or Akzo Nobel.






Regards
Pat
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[SincoTC]

Try searching for monofilament wire and aramid or kevlar fiber cable. We've used tendon wire from here:

http://www.applied-fiber.com/fiber-options.html

Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK

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[Pud]

Try this:

http://www.berkley-fishing.com/prod.php?k=134073&sk=134070&u=FL10CY

"Dyneema", which is UHMWPE (I think).

Just filled two bass spinning reels with it and it's much, much better than nylon monofilament, although knots are tricky!

Cheers

Harry

 

[patprimmer]

Dynema is gel spun PE and is made by DSM. I would guess it is HDPE and the draw down a lot under heat so that the linear molecules become very well aligned.

As far as I know, it is not as strong as Aramid, but stronger than nylon. Also it does not plasticise in water. Vs Aramid:-
It is good in fatigue and compression.
It is better than Aramid to UV but still not good. It should be translucent.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[blueandwhiteg3]

Thanks for all the comments here. To clarify, this is for permanent/semi-permanent use. This material will be threaded back and fourth through "eyes" a ways, so I won't really have to tie knots anywhere, and I'll have a somewhat more limited number of endpoints that need to be tethered down.


Kevlar
--------------------
I looked at it and was concerned about water absorption and loss of strength over time. I don't care if my line absorbs a bit of water, but if it absorbs water and increases in length by 5%, we could have a problem. I was also a bit off-put hearing some reports that Kevlar lost strength as it was used; references to firefighter escape ropes that could only be used once, etc.

(After living through several gnarly, catastrophic aluminum failures - thankfully not my design or my fault - I have become wary of any materials that include disclaimers about fatigue.)

I also didn't see any immediate sources of UV-protected, small lines. Everything I found was rope-like, rated for a thousand or more kg and just ridiculous from a size/cost perspective.

I am going to look into the Applied Fiber products, but I suspect they're overkill for my needs. In the meantime, I would welcome other supplier suggestions and clarifications to my concerns around load cycling and water absorption.


Fishing Line
--------------------
I can never get good data on performance over time (UV, embrittlement, elongation), or elasticity. Will this stuff break down in a few hours? Days? Weeks? Months? Or maybe it will just slowly elongate, resulting in eventual failure of my installation? (That's what would happen, should the line elongate too much. I'd be able to see this happening before I experience catastrophe, but it would be a huge hassle to deal with replacing this.)

It's possible that by knowing the material, I can nail these properties. The problem is that I'm not far enough into polymer production to know, with certainty, that anything that's nylon or UHMWPE is going to have a certain set of properties, and there's nothing (practically) in production that will cause said properties to be lost.

If somebody could educate me on these points, I'd appreciate it.


Other Materials
--------------------
Nylon: My primary concern is stretch/elasticity. I don't really need to tie a knot as long as tethering it to the endpoints isn't a big issue. The nylon lines I've seen in the past are amazingly close to invisible in water. Some grades of fishing line do claim to limit stretch:

http://www.fishplatypus.com/products_lostretch.html

UHMWPE: I like the properties of this material, including incredible resistance to UV, chemicals, water, etc. though I'd expect it to be less transparent than nylon. I'm concerned about creep. I'm also concerned the incredibly low coefficient of friction could complicate tethering the endpoints.

Flourocarbon: I'm not exactly sure what material this is, but I'm guessing PTFE. I have similar concerns about creep and friction coefficient as UHMWPE. Several different fluorocarbon lines are listed here:

http://www.hiliner.com/newimages/momoi.pdf

Conclusion
--------------------
So far, I have learned a bit more about materials, but I haven't tracked down any concrete data on the elasticity or creep of any of the materials in question.

I would appreciate any more concrete data anybody could point me to on these points...

 

[Demon3]

Dyneema and Spectra are two tradenames for UHMWPE fiber. You can read quite a lot about the material here...

http://en.wikipedia.org/wiki/Ultra_high_molecular_weight_polyethylene

I think that's worth considering for your application. It's used in rigging for yachts and high performance sails. It won't take up water and become softer, in contrast to nylon. You'll need to make sure you get a grade specifically made for outdoor use (they probably put in additives to protect against the UV light).

Its density is less than 1.00 g/cm3 so it will float on water. Not sure if that is desirable for you.


Chris DeArmitt

 

[Demon3]

Googe book search came up with this table of properties, including mechanicals for UHMWPE fiber.

http://books.google.com/books?id=bz...hl=en&sa=X&oi=book_result&resnum=10&ct=result

Chris DeArmitt

 

[blueandwhiteg3]

HPPE shows a creep of 1 x 10-2 per day at 20% load and 22° C. 0.01% per day. That means we'll see over 1% creep over 100 days. This is going to be an issue.

Unless we can show lower creep at lower loads, I don't think it would really be suitable.

Reading up on that book suggests aramid fiber might be better and makes me feel better about the load aspect of things. However, that still leaves me trying to find a source of unusually small, UV-protected armid line.

It would be nice to find some data on nylon and perhaps even PP.

FYI: density of the material doesn't matter for this use. Size doesn't matter either, within reason.

 

[Demon3]

Hello, what do you mean by HPPE? The material we suggested was UHMWPE (very different to PE and PP).

Aramid fibers are good for stiffness but I understand that they break without warning after multiple use. That's why they are not used for parachutes. You would need to be careful in the design and how they are used.


Chris DeArmitt

 

[btrueblood]

Hmm. Our needs for aramid fibers are as reinforcement fabric in diaphragms, in hot and cold water service.

As such, we avoid kevlar aramid, due to its strength degradation over time in water (hydrolysis). We typically always specify nomex aramid fabric, as it has much better wet strength retention, even though its breaking strength is typically much lower than kevlar. I've struggled to find a "generic" description for the difference between the two aramids, but believe the following excerpt from a report I wrote awhile back is correct:

"The Nomex fabric has been previously confirmed by test and research at XXX to outperform other polymers (e.g. polyester and Kevlar) in hot water. The proposed knit fabric does not change the base polymer of the fabric reinforcement, only the method of construction (to knitted fibers instead of woven fibers). Nomex is a trade name for meta-aramid polymer fibers, Kevlar is a trade name for para-aramid polymer. It is recommended that the XXX spec. sheets for the fabrics used in our diaphragms should call out either para-aramid or Nomex fibers."

...but as always will bow to the smart folks here regarding the meta- vs. para-aramid distinction.

Far as I know, both kevlar and nomex fabrics are pale white to off-white (beige) in color, but can be dyed/colored darker. Both will suffer strength loss with UV exposure, depending on the strength of the light source and duration of exposure. A Dupont bulletin I received from them shows a 55% strength retention after 80 hrs. exposure to "accelerated UV degradation test (Xenon arc light) per AATCC Standard Test Method 16E".

 

[CoryPad]

You are correct regarding meta- and para- designation of these tradenamed aramids. Meta-, ortho-, and para- refer to branching from benzene rings. If the branches are 180 degrees away, then the structure is para-. If the branches are 120 degrees away, then the structure is meta-. And, if the branches are 60 degrees away, then the structure is ortho-.

Regards,

Cory

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[patprimmer]

Aramid is no suitable for running around pulleys, which is a point you only just mentioned.

I stated earlier it is poor in compression. The inside surface when negotiating a pulley is in compression.

Aramid is used with success in very high performance sails. They will have aramid elements where the tension is greatest and where elongation reduces performance the most. The elements that require better fatigue and abrasion resistance but still high tensile and creep resistance are gel spun PE (Spectra or Dynema). The third element which makes up the lower laded areas is polyester.

Aramid is best in straight tension and will hydrolyse very slowly at the temperatures you quote. It is used extensively as the reinforcement in the hulls of high performance boats and in aerospace where it is only in tension and never in compression, BUT as you run through pulleys it is disqualified.

From the currently listed requirements, gel spun UHMWPE seems the go. They claim excellent UV stability which surprises me as PE is inherently quite poor to UV, so I expect they are adding a lot of UV stabiliser to it. If they simply mean it is good compared to aramid, that's not saying much. If it's good compared to nylon, then you will get a very long life outdoors. Stabilised nylon fittings last many years on the decks of boats and roofs of cars.

http://www.dsm.com/en_US/html/hpf/home_dyneema.htm

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[blueandwhiteg3]

Chris, regarding HPPE, that's what they're listing Dyneema under at the Google Books link. I'm assuming it's another term that encompasses UHMWPE.

As for UV and UHMWPE, I believe UHMWPE is fairly UV resistant. I'd guess they probably still would add something to improve this, but I don't think it's terribly sensitive as a raw material.

I'm concerned about the creep issues with UHMWPE. I'm not able to find much good data on creep. The question is how load and creep behave. I just can't have this line creeping a ton on me. I have no problem overdesigning, perhaps by a lot, so long as the raw material isn't exorbitant.

One bit of data I found here:

http://www.rigging.com.au/dynex1.htm

The chart for 40 mm rope shows essentially zero creep at 22 tf on a 40 mm SK75 fiber. The table they provide shows a minimum breaking strength of 119.8 tons on the same size rope. Thus that material de-rated by a bit over 80% has very little creep. Of course, I don't know whether this creep value would scale down to the sizes I would need.

Dyneema appears to have a SK78 grade just for dealing with creep, at least halving SK75's creep:

http://www.textileworld.com/Article...y_Fabric_Of_The_Monthx_Cutting_The_Creep.html

Unfortunately, finding smaller grade lines of dyneema is proving problematic. I am guessing ~3 mm is the largest I'd need.

Here's a 1.75 mm unspecified grade but only 400 lbs load:

http://www.leisurepro.com/prod/OSBDL17.html?ci_src=14110944&ci_sku=OSBDL17

A 3 mm grade, once again not well spec'd out:

http://cgi.ebay.com/1050lb-3mm-UHMW...0ft-units_W0QQitemZ250297067065QQcmdZViewItem

Reality is, if we're talking about 25¢ a foot for this kind of material, I don't know that it's really viable for this application. We're now looking at the line being massively more costly than any other materials. Even 15¢ or 10¢ a ft is probably not acceptable. I'd really like a number more like 2-3¢ per foot for a minimally-creeping line that bears ~60 kg sustained load - maybe that's crazy impossible, though.

I think one major issue is that I have to design to such a low load value when working with a dyneema-type material to keep creep under control. If I didn't have to over-design by a factor of 5+, the cost would be a lot lower.

I'm starting to wonder if plastic lines are really what I should be considering here. I can deal with a little stretch in the line, if it's predictable based on load, but I can't deal with much creep.

It would be nice if I could get to the bottom of the question around creep and stretch on nylon, but I have yet to find solid numbers,

Nomex sounds like it could be viable if care was applied, as I'd be able to design a lot closer to spec without creep issues. However, I can't find anything near small enough.

Vectran is another interesting possibility. I've not heard anybody mention it, but it has unusually low creep it appears. The cost for larger ropes don't seem terrible, but I can't seem to easily find smaller lines.

Given that size is not an object, but cost is, I wonder if some other lower cost materials should be considered? Polypropylene? Even abandon polymers and jump to some kind of a metal cable?

As this particular application involves a lot of back and fourth of the line to secure the load, it would be possible to substantially reduce the length of line run, but proportionally increase the load, by using a material such as fiberglass to distribute the load. Of course, this would only be sensible if a low-load line was too costly.

 

[SincoTC]

Like you, I'm beginning to wonder if plastics are the right way to go to meet your for your requirements (apart from translusceny/transparency).

In the UK we've used miniature stainless wire ropes like these:

http://www.tecni-cable.co.uk/Stainless-Steel-Wire-Rope-Cable-Fittings/Miniature-Stainless-Wire-Rope

Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK

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[blueandwhiteg3]

Translucency/transparency is not an utterly absolute parameter, so metal is a possibility... if the cost can make sense.

 

[Demon3]

Finding creep data can be very hard, the measurements take too long and no-one wants to do them even though creep is an important cause of failure.

I have done some checking on creep stress versus yield stress. As a rule of thumb, if the stress you are applying to the polymer is less than 20-25% of the yield stress then there will be very little creep. Luckily data for yield stress is very common so that may be of some help to you in the absence of solid creep data.

It is estimates that 10% of all polymer part failures are due to creep. Source:

Polypropylene Definitive User´s Guide & Databook, Plastics
Design Library, New York, USA, 1998

Here is some data taken from a course I teach on polymers and composites.

Creep Stress Yield Stress
LDPE 2.1 MPa 8 MPa
HDPE 5.0 MPa 27 MPa
PP 5.0 MPa 25-34 MPa
ABS 6.3 MPa 48 MPa
uPVC 10-12 MPa 50 MPa


Chris DeArmitt

 

[patprimmer]

The Gel spinning process greatly reduces the creep, so you cannot compare normal extruded rod to gel spun HDPE or UHMWPE. I believe the difference in the Dynema/Spectra yarns vs normal PE yarns is the spinning process rather than the base polymer grade. The gel spinning process results in VERY highly oriented VERY crystalline micro structures. A very long linear base polymer molecule obviously also helps. Terms for PE like UHMW or HD re arbitrary and relative.

I have a lot of data on creep of aramid fibre and I know it is very low as it has to be for use as the central strength member in aerial optical fibre cables. A gel spun PE competes with araid in support cable and reinforcement applications,I would be astounded if they did not have similar data.

CONTACT DSM direct. Contact the head office of the Dynema division in the Netherlands. They will have the data. Call them.They will speak excellent english.


Regards
Pat
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