[TowerTalk] polyrod

Mon May 2 21:17:39 EDT 2005

> We got NO official analysis back from the factory.  They simply replaced 
> the coils we claimed as defective and we promised to uncoil them all as 
> soon as received to avoid a repeat..  It took a several months to receive 
> our entire order from start to finish the first time and it took a lot 
> longer time and a lot of phone calls,etc., to get it replaced.  I got the 
> impression they were having production problems with our order at the 
> time.  Our rod was black 3/8", mostly coiled in 8' diameters and covered 
> in a split

Any dark color should be avoided with fiberglass and resin (epoxy, or vinyl 
Ester)
Vinly Ester resin has a bit higher critical temperature after cure and it 
has a much lower viscosity than epoxy which allows a much more dense weave 
in the fiberglass slocth, or more linear fibers in a bundle (rod) which 
gives higher strength per weight and size.

black corrigated drain tube and cardboard.  There was no sign of shipping 
damage on any of it.  I believe our total order ended up being over 15,000 
feet or so.
>
> I've already explained what I observed from our coiled rod...with the rod 
> fibers buckling on the inner >radius from the tension imposed by the ones 
> on the outer radius exceeding the ability of the "glue" to

I didn't see your earlier explanation, but this is the expected failure 
process when the minimum bend radius is exceeded.

>hold the fibers together.  It was a gradual process, which allowed me to 
>observe it happen in various >stages at different points in the coil.  As 
>the failure progressed, the radius got tighter at the failure point,

Again, this is normal for epoxy and Ester Resin/fiberglass in a bend or even 
long span.
You should have seen fibers breaking and coming loose on the outside of the 
bend.   It's much like bending a piece of tubing, it will reach a point 
where it just gives way and Kinks although the fiberglass will not usually 
go that far unless under load.

>which accelerated the failure until the entire rod had snapped, usually 
>looking rather frayed at least >part-way through.
>

> Whether the "glue" from our batch was improper for one reason or another I 
> have no idea.
>
> It's quite possible they have changed the resin used or had a bad mix in 
> our batch which made it softer or more susceptable high temperatures.

Although the failure mode you describe is exactly what would be expected, 
there are many variables that determine *when* the failure will ocurr.  An 
improper ration of resin to catalyst, or even acellerator when used.  Too 
fast a cure at elevated temperatures can induce stress.   Mishandled fibers 
(handled with bare hands during construction) can inhibit the glass to resin 
bond.  Fiberglass strands that have been contaminated by moisture, dirt, or 
even fingerprints can weaken the end product.

*Normally* the ratio of resin, or epoxy to catalyst is not critical and can 
vary a few percent either way with no harm done. With resin, too little 
catalyst and/or acellerator will end up with a slow curing batch that may 
stay sticky for a while.  Raising the temperature will speed the cure and 
*normally* the amount of acellerator is temperature dependent. Resin is also 
"promoted" prior to use and again this is temperature dependent.

My shop is temperature controlled, but when doing multi-layer lay-ups I 
usually keep it around 75 which gets it to the "green state" where it can be 
trimmed faster.  This has the drawback or requiring me to work faster or the 
resin will gell in the pot. It only has about a 20 minute working life and 
once it starts to gell you only have about 2 or 3 minutes to save the brush 
and container before the gell sets.
When doing large lay-ups I drop the temperature to the 65 to 68 F degree 
range to slow the cure and give me more working time..

There are epoxies that use a high temperature cure that have a much higher 
critical temperature.
and I would assume that high temperature cure is used in the manufacturing 
process of the polyrod.  You'd need to know the resin and cure temperature 
to find the critical temperature of the finished product.  Still, 
eposy/resin and fiberglass pretty much follow the same properties in the way 
they fail.  The strength may vary widely as will the resistance to failure 
in the bending mode depending on the what is used and the manufacturing 
process itself.

I've been searching on fiberglass, resin, epoxy, cure temps, working temps, 
and manufacturing.  There is so much information out there I'd be reading 
for a month and I don't know which ones specifically apply to this case.

Speaking of fiberglass and resin...time to go out and put in some elevator 
rib reinforcements so they'll have enough time to reach the green state so I 
can trim them tonight and add the second lay-up which is also the final 
layer.

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com

>
> Tyler K3MM
>
>
>
>
> -------------- Original message -------------- 
>
>> >
>> > My point exactly. It certainly DOES matter why it failed,
>> > and it isn't up to customers to guess why.
>>
>> Agreed
>> >
>> > It could have been heat (they did warn me about heat, but
>> > said it had to be a lot hotter than I ever would worry
>> > about), it could have been over-bent (also cautioned me
>>
>> The summer sun on an unventelated, metal shed may create temperatures 
>> beyong
>> the those necessary for softening the resin (Vinyl Ester, or epoxy). A
>> fiberglass airplane with a colored paint job, left outdoors in the summer
>> sun even in Michigan will get far hotter than necessary to soften the 
>> resin.
>> When this happens to Vinyl Ester Resin it gets really strong and hard 
>> after
>> cooling and it raises the critical temperature by quite a bit.
>>
>> > about that), but they keep saying storage while coiled isn't
>> > an issue.
>>
>> I'd like to see someone run some tests on the stuff. Acellerated againg,
>> using heat and UV as well as the appearance of some that has been exposed 
>> to
>> the elements for a few years.
>>
>> Do they have a site where you can look at the figures for the stuff?
>> I have not been able to find anything on the web pertaining to polyrod, 
>> or
>> Polygon as far as a guy line.
>>
>> >
>> > I can't do a thing more than ask because the stuff laying
>> > around here has been in coils laying outside for years and
>> > is still in perfect shape. It would be a shame to have the
>> > problem caused by something other than being in a coil and
>> > not know what the real problem was.
>> >
>> If the stuff is light colored and laying outdoors *probably* the only 
>> things
>> to worry about are UV and moisture. If the outside is still smooth it
>> sounds like it's doing well.
>>
>> > But then I've run into this in other areas (bad electrical
>> > components like vacuum tubes and capacitors) and seen the
>> > backlash so maybe I'm more sensitive to requiring accurate
>> > answers....
>>
>> Having been a project manager for a large corporation when I retired, I'm
>> also very sensitive about why something may have failed and the 
>> engineering
>> specs for a product.
>>
>> It may be the best thing since sliced bread, but I still want to see the
>> specs and any information on aging and failures.
>> >
>>
>> 73
>>
>> Roger Halstead (K8RI and ARRL 40 year Life Member)
>> N833R - World's oldest Debonair CD-2
>> www.rogerhalstead.com
>> > 73 Tom
>> >
>> > _______________________________________________
>> >
>> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>> > Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>> > any questions and ask for Sherman, W2FLA.
>> >
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>> >
>>
>>
>> _______________________________________________
>>
>> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless 
>> Weather
>> Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any 
>> questions
>> and ask for Sherman, W2FLA.
>>
>> _______________________________________________
>> TowerTalk mailing list
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> _______________________________________________
>
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
> any questions and ask for Sherman, W2FLA.
>
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