[TowerTalk] Phillystran and Pulleys

[John Kemker]

I have used plenty of aramid fiber (Kevlar) cordage for shock line 
protectors and shock lines for large rockets, but never as a constant 
use item.  They are inspected before use and if they fail the inspection 
for shock line, they get reused as shock line protectors to protect 
non-aramid  lines from hot ejection gases.  (Tubular webbing/cordage is 
a wonderful tool in designing recovery systems for large rockets.)

Aramid fibers can self-abrade.  They are really strong longitudinally, 
and even shear strength is high.  However, they are most susceptible to 
abrasion, which is my concern when used on a pulley.  Even the sheath 
won't protect it from abrasion, as your abrasion will occur within the 
sheath between the individual fibers in the bundle.  As they rub against 
each other, they will abrade, eventually dying from the death of a 
thousand cuts, self-induced.  The question becomes, how long does the 
self-abrasion in this situation take to cause failure?  Don't know.  
It'd be an interesting test.


donovanf at starpower.net wrote:
> Jim,
>
> Phillystran isn't intended for that application, so I doubt it would be a good choice.   Perhaps someone has specific experience in this application.
>
> Perhaps your best choice would be something like 5/16" dacron, but not the braided variety.   I'm sure you will goet some good feedback from others on good long lived ropes where motion over pulleys is an issue.  Small diameter pulleys are serious detriment to rope life, I use 3 and 4 inch shieve diameters only.
>
> 73
> Frank
> W3LPL
>
> ---- Original message ----
>   
>> Date: Mon, 22 Jun 2009 09:57:42 -0700
>> From: "Jim Brown" <jim at audiosystemsgroup.com>  
>> Subject: [TowerTalk] Phillystran and Pulleys  
>> To: "Tower Talk List" <towertalk at contesting.com>
>>
>> Crew,
>>
>> I've got some of the smaller 1,200 lb test Phillystran that I bought 
>> years ago for a wire antenna project that didn't happen. It's too 
>> small for the 120 ft Rohn 25 that I'm preparing to install, but I'm 
>> wondering if it would work on my high dipoles that are up 110 ft in 
>> redwoods? 
>>
>> The existing antennas, 80/40 fans fed with 150 ft of RG11, are held 
>> up by ropes (the "good" stuff that DX Eng and some other ham vendors 
>> sell) through good pulleys, but the black UV sheath of these ropes 
>> gradually abraid from friction as the trees sway, and eventually they 
>> fail. A 5/16-inch rope holding up my 160M Tee vertical failed after 
>> two years -- the sheath wore through completely, exposing the inner 
>> white material. Luckily I discovered it before it rotted in the sun 
>> and dropped, and was able splice in a new rope and pull it through. 
>>
>> I'm not worried about the pulling strength, which is certainly 
>> adequate, but I am concerned as to whether the Phillystran would 
>> stand up to continuous flexing at the pulleys as the trees sway in a 
>> storm. Each antenna is counterweighted (about 100#) at one end, 
>> pulleys at both ends. 
>>
>> Thoughts? Experience?  
>>
>> 73,
>>
>> Jim K9YC
>>
>>
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-- 
--JohnK
73 de W5NNH
10X 75371/M&M 117/SMIRK 6185/Six Club 285/TRA 2499/Norcross 228 F&AM




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