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[Towertalk] Kevlar Guys

To: <>
Subject: [Towertalk] Kevlar Guys
From: Tõnno Vähk" < (Tõnno Vähk)
Date: Wed, 31 Jul 2002 11:16:23 +0300
Barry, I have chosen an interesting material for my nonconductive guy wires
for my planned 140 feet rotating tower.

It's Dynamix. Used in yachting. It's a combination of Dyneema SK75 and
Aramid fibres (Kevlar). The high strength of both fibres is blended with the
low creep under constant load of Aramid, and the high resistance to flex
fatique of Dyneema. There is polyester outer cover on it to protect the
Aramid content from UV.

I will use 10mm Dynamix that has breaking load of 4000 kg! And it costs here
about $6 per meter. I will have about 25m of upper and 15m of lower guy
wires from the top of Dynamix, steel wires with a few isolators after that
to the ground.

Dyneema (called Spectra in US) is in many ways superior to Kevlar:

Dyneema is stronger (higher breaking load)
Dyneema lasts longer
Dyneema weights less
Dyneema resists much better to UV light
Dyneema has lower dielectric constant (about 2.2 vs 3.8 for Kevlar)
Dyneema has excellent abrasion resistance, low moisture absorption, very low
elongation, excellent flex fatigue resistance

Two negative aspects are:

Dyneema has lower melting point (c.a. 150 degrees C vs 400 for Kevlar)
Dyneema exhibits something called CREEP -non-recoverable elongation when
constant load is applied for long time...but for late models and thicker
ropes this is almost nonexistent

Dyneema is UHMWPE that stands for Ultra High Molecular Weight Polyethylene.
Fibers are made from this material by AlliedSignal (SpectraR), DSM
(DyneemaR), Tenfor (SniaR), and Mitsui (TekmilonR). The molecular formula
for this polymer is the same as common polyethylene, but is significantly
different because of the very high molecular weight, from 10 to 100 times
higher than commercial polyethylene molding resin.


----- Original Message -----
From: "Barry Kirkwood" <>
To: "Tower Talk" <>
Sent: Wednesday, July 31, 2002 10:46 AM
Subject: [Towertalk] Kevlar Guys

> Just like to say thanks for all the very informative and helpful replies
> my post on this topic.
> The amateur spirit is alive and well on this reflector.
> 73 es tnx
> end
> Barry Kirkwood PhD ZL1DD
> Signal Hill Homestay
> 66 Cory Road
> Palm Beach
> Waiheke Island 1240
> phone/fax 64-9-372-5161
> _______________________________________________
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