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  #16 (permalink)  
Old 11-20-2004, 07:29 PM
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I got on line tonight and searched some fiberglass body makers.
I emailed 5 or 6 and asked what they used.
may just think I'm some wacko and not answer, but I did give full name and address so they wouldn't think I was there competition.

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  #17 (permalink)  
Old 11-20-2004, 09:23 PM
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most car parts manufacturers probably use polyester resin..
a. because its cheap
b. there isn't a regulatory body (FAA, transport Canada) standing over top of them saying "you have to use epoxy resin" These parts aren't critiqued to the same extent as an aircraft part, or used in the same extent as a race car, and so they don't have to pass the same tests that are required for safety on a race car/airplane.
c. they probably use a chopper gun so they don't really care about the strength to weight ratio... they just spray it on with the chopped fibers, roll out the air bubbles, and ship it out the door.
d. polyester resin usually sets faster so they can make more cheap parts and thus make more of a profit.

The high quality parts may be made out of epoxy resin because they know that they will have less customer complaints years down the road, and parts that do break will be easier for them to repair, the part will be lighter than the same part made out of polyester resin (if the polyester resin one was made to the same strength as the epoxy one) These manufacturers will probably also hand lay all there parts, vacuum bag, and hopefully use woven mat verses chopped strand mat, just because they want a quality part. These parts will also be more expensive and the average person won't buy them, because as our society is "well i can get that exact same part down the street for $20 instead of $100.. but you don't know the quality of item your getting (your "uninformed")


Now race cars and airplanes, why do they use epoxy resin. Its simple:
the strength to weight ratio . you use an epoxy resin with say carbon fiber (that is vacuum bagged/autoclaved so you get a 60/40 or preferably 50/50 resin to cloth ratio) and compare it to an aluminum panel that is the same size, i believe the aluminum panel would have to be 5 times as heavy in order to have the same tensile strength as the carbon layup (its been about 3 yrs since i took schooling on this so don't quote me on the numbers)
They are flexible in terms of there application.. they can be formulated to be rigid, or flexible, perform at high or low temps, or provide a combination of these characteristics
They exhibit an extraordinary ability to completely wet a wide variety of materials and to adhesively cure together a variety of dissimilar materials.
They are resistant to light, water, acids, many solvents ( they are so durable they present a problem from a disposal perspective, because they are almost indestructible
They are very dimensionally stable.
They exhibit the strongest adhesive characteristics of any known polymeric material.

Now what do you use to make a one off part for yourself... is really up to you...
I myself would probably use the polyester resin to make the mould, and then use an epoxy resin to make the part... but if i was to make the part i'd also go to the extent of vacuum bagging my part in order to get the strength to weight ratio that i was looking for, and i would probably also have molds made in order to make some sort of sandwich panel in key locations on the part. in order to make the part strong in all directions, (this would be expensive to do and you better be making more than 1 part in order to make this much work worthwhile)

Now if you aren't willing to go to the extent of vacuum bagging, using woven fabric, figuring out where to sandwich panel your parts, and investing the money in setting up your shop to vacuum bag. I would say just use the polyester resin. that way you get a part that is cheaper to make (it may break sooner, and may be harder to repair, but if you get a couple 10 - 15 yrs out of it, maybe the cost savings where worth it. (plus you can sell the parts for cheaper to the "uninformed" also to make back the cost of the mold)
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Old 11-20-2004, 10:51 PM
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I've been doing the polyester thing for several decades and as I say for non-critical parts, which grocery getters are, I have been more than pleased. All my parts have performed w/o a single problem. If I ever build a part on which my life depends, believe me, it will be properly engineered and made of epoxy and carbon fiber!!
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  #19 (permalink)  
Old 11-21-2004, 10:01 AM
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mmartin1872,
I guess I am one of the "uninformed" . Epoxy never even would have been entered into the conversation by me, I knew it existed but I never would have thought it was even an option under most circumstances.

1. The first thing I have to ask is am I looking at epoxy resin "fiberglass" or carbon fiber and not even knowing it? I picture the epoxy being this opaque resin that could would not be able to see thru, is it like that? Or are the epoxy resins used for making these high quality body parts transparent like polyester resin?

I have been seeing these ricy cars with the "carbon fiber" hoods where it has no paint on it and you can see the weaves of the cloth. You literally can see THRU the hood it is so transparent. Are these really an epoxy carbon fiber or a fake made with polyester and fiberglass?

2. With the epoxy resins, do you use a standard polyester "gel coat" or is it too,epoxy?

3. Now, I have to say, I have hung a lot of "fiberglass" hoods, bumpers,fenders and the like over the years, they all seemed to be chopper gunned fiberglass. That being said, it sure looks like regular old polyester fiberglass is the "norm" for your run of the mill street car.
Are you being anal in your obvious preference to the epoxy? Weight has little to do with the REAL reason most people would make and or install a fiberglass componant on their car. It is strictly aesthetics in 99% of these applications. So, leaving the weight to strength ratio out of the equation, is the epoxy an overkill?

4. Is it any easier to use? What are the cost differences?
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Old 11-21-2004, 10:14 AM
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Martin,
He's not being anal.

Polyester is fine to use in automotive, as its a whole lot easier to work with.

You cannot look at the resin and say this is the P word or the E word.
I really wanted to write back when you and Willy said I know these two big boat places use the P resin and ask How?
Unless your doing the repairs or saw what it said on drum you assumed, I just didn't want to piss anyone off! That why I said call and ask.
It looks the same and smells the same.

There is a lot of liability repairing a sea going boat or airplane.

Were just trying to point out there are two options and both will work in most applications its just like some people buy Nason some people by Spies, they both will work.
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Old 11-21-2004, 10:37 AM
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I know these damn forums are so one dementional, I really was serious when I said "am I looking at the epoxy and not knowing it". You are certainly not going to tick anyone off answering a question asked.


I am amazed, really, I didn't know a darn thing about the uses of epoxy. I have a lot to learn, and will keep my eyes and ears open to the use of epoxy's.

The first thing I am going to do is stop by the local "TAP PLASTICS" the retail fiberglass/plexiglass store and see if there is any info there.
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Old 11-21-2004, 10:41 AM
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Don't feel bad! Hell, I'm asking about waxes!
Duh!
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  #23 (permalink)  
Old 11-21-2004, 10:51 AM
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wow!! havent been on the site for a couple days and i am a little late on this one. i used to run the service dept. for viking yacht co. one of the largest production yacht manufactures in the world and being from new jersey where the boad building industry is very large i am familiar with the products we used and most of the other companies too, now part of my business is making custom fiberglass parts. we put out around 160 boats a year, at anywhere from 45 to 109ft and priced somewhere from 2 - 8 million a pop. first the mold, whatever the surface of your mold looks like is what your part is going to look like. if the mold is dull then your part will be dull, if its shiny then the part will be shiny so basically you want to get the mold looking perfect. a perfect mold means a perfect part. out of the probably the two dozen or so boat companies i know of, none use epoxy. the mold is gelcoated then the outer skin is a chopped stranded mat. as said before this keeps the glass print from comming through. called "read through". at viking, the outer skin is not either polyester or epoxy, its vinyl ester. then the balsa core goes in and from there its all polyester. we had a tank about 20ft diameter and about 3 stories tall full of polyester resin. it actually would come in tanker trucks. dont know how much that is but its alot of resin. the main advantage of the epoxy is the strength to weight ratio and flexibility. you wont get the part to shatter like with a ployester. you can make the same part, twice as thin and have the same strength, this is why its used in aircraft and race applications. even our fuel and water tanks were made of fiberglass and used flame proof polyester called hetron, so the polyesters are definately fuel proof or atleast diesel proof. alot of this stuff was covered before, i thought i would just stick in my two pennies
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  #24 (permalink)  
Old 11-21-2004, 01:06 PM
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Quote:
Originally posted by MARTINSR
mmartin1872,

Are you being anal in your obvious preference to the epoxy? Weight has little to do with the REAL reason most people would make and or install a fiberglass componant on their car. It is strictly aesthetics in 99% of these applications. So, leaving the weight to strength ratio out of the equation, is the epoxy an overkill?

4. Is it any easier to use? What are the cost differences?
The only reason i went into the speal was to give you a choice basically. I was just basically pointing out that if you want to make a "show" piece not a "race" piece, polyester resin is fine. but if you want to make a truly lightweight and strong piece you would probably want to go to the trouble of using epoxy resins, and taking on the added cost to do so... The difference in price is astounding... I think polyester resin is like $15 canadian a litre, while epoxy resins are like $40-$50 a litre.. The catalyst for the polyester is like $5 and the catalyst for the epoxy resins is ussually about $15... so there is a big price difference.
I guess i was kind of being anal last night about my preference to epoxy resins... Truthfully for a car, I probably never would use epoxy unless i was building a race car, or a carbon fiber panel... And at this point in my life, i don't see that being anytime soon.


Is it easier to use? I think yes, some think no. epoxy resin, you have to mix it right... if it says 1:2, you can't do 1.25:2 mix ratio, because you will have soft spots in your layup because the catalyst is actually measured exact to bond together with the resin leaving no unbonded molecules. Where as polyester resin doesn't need to be measured to such exacting standards,,, 2 drops 5 drops 10 drops of catalyst... just decides how hot and fast the resin cures.
The hard part about epoxy resin is choosing the right one for your application and choosing the right catalyst for it.
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Old 11-21-2004, 01:33 PM
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mmartin1872,
Thanks for the concise answer. I have a couple more. Barry, chime in as well if you see fit. You mentioned the epoxy needing to be accurately mixed, this is something that I have had drilled in me as a paint rep. Not just with epoxy but all 2k products.

As you mentioned the epoxy needs to have a matching amount molecules in both the hardener and resin. One with more than the other you have an incomplete cure. I have used the analogy (I wonder why "anal" is the root of that word?) of the common tubes of epoxy adhesive. I like to say, "If these tubes are useless apart from one and other and a strong adhesive together, that would mean you want to mix as accurately to perfect, equal parts as possible. If you have one more than the other you are making the mixture closer to one of those useless parts"

So, this all makes sense, be it a urethane or an epoxy. Now is when the subject gets gray to me. With a polyester resin, filler, primer,what ever, this ratio doesn't need to be as accurate. Why? What is the technology difference in that cure compared to the epoxy cure?
Thanks for putting up with me guys.
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Old 11-21-2004, 02:28 PM
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Last edited by BarryK; 11-21-2004 at 03:08 PM.
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  #27 (permalink)  
Old 11-21-2004, 02:52 PM
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Quote:
Originally posted by MARTINSR
mmartin1872,

So, this all makes sense, be it a urethane or an epoxy. Now is when the subject gets gray to me. With a polyester resin, filler, primer,what ever, this ratio doesn't need to be as accurate. Why? What is the technology difference in that cure compared to the epoxy cure?

Thanks for putting up with me guys.
Thats a good question... I'm going to pull out a couple of my old composite text books that i have and see if the answer is there... i used to know the answer.
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Old 11-21-2004, 04:15 PM
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more semi-useless trivia

Polyester and vinylester are less expensive than epoxy

Polyester can develop problems after years submerged, which is why most marine applications use vinylester now

Epoxy has much better adhesive properties and is much stronger when you are using it in a reinforcement, gusset, etc.

If I was manufacturing fiberglass on a regular basis, polyester or vinylester would be the logical choice.

But if you use a gallon or two a year, in a whole bunch of different applications, the epoxy is logical and convenient to have around and will do about anything....

It just depends what you are doing............
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  #29 (permalink)  
Old 11-21-2004, 07:03 PM
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Quote:
Originally posted by mmartin1872
Thats a good question... I'm going to pull out a couple of my old composite text books that i have and see if the answer is there... i used to know the answer.
Well this is taken straight from my Advanced Composites By Cindy Foreman book. To understand how an epoxy resin cures, imagine a two dimensional molecule interacting with similar molecules to form a 3 dimensional grid. This is, in fact, exactly what happens when the resin is cured. This three dimensional linking between molecules is referred to as crosslinking. This cross linking effectively forms a single giant molecule that is shaped like and is as large as the finished part. More specifically the finished part becomes a mollecularly interlinked plastic. The reason the epoxy resin does not crosslink immediately when it is prodcued, thus making it worthless as a matrix, is due to the inability of the epoxy molecule, by itself, to unlink the chemical bonds between the carbon and oxygen atoms. The crosslinking is made possible when a curing agent is mixed with the epoxy resin. For example, the curing agent can provide nitrogen, which then enables the carbon molecules to interact with large molecules such as the epoxy resins, thus forming a three dimensional matrix. The nitrogen atom can be made available from a variety of different curing agents. Each agent has its own particular characteristics that it contributes to the final cured material.

Now what is this saying in english. basically epoxy resins in the "resin" have carbon and Oxygen atoms.. which just hang out together doing nothing... but when you add the "catalyst" which has nitrogen atoms and other additives. it causes the carbon and oxygen plus whatever additives are in the catalyst to link together.. so the reason you have to be exact with epoxy is because there is a set # of atoms that are required in order to crosslink a set amount of carbon and oxygen atoms.

polyester resins on the other hand are polyester alkyd with vinyl acetate or styrene and cured with a peroxide catalayst (MEKP).. I can't find any more information in my text books on polyester resins though...
I believe that the mekp, just causes enough heat in the mix to start the reaction between the polyester alkyd with the vinyl acetate, and the heat actually cures the product.. i'm not too sure on this though.. easy way to find out though would probably be to take some polyester resin and heat it up, and see what happens.
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Old 11-21-2004, 07:16 PM
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Quote:
Originally posted by MARTINSR
So, this all makes sense, be it a urethane or an epoxy. Now is when the subject gets gray to me. With a polyester resin, filler, primer,what ever, this ratio doesn't need to be as accurate. Why? What is the technology difference in that cure compared to the epoxy cure?
Thanks for putting up with me guys.
Though they seem similar, polyester resin and epoxy are totally different chemistrys. Polyester resin cures with heat and time and UV light helps too. Addition of methylethylketone peroxide has a catalytic effect that generates the heat necessary to accelerate the curing process. The more MEKP you add the more heat is generated and the faster the resin sets. You can add so much catalyst that the mixture will flame! There ar other catalysts that do the job but MEKP is the most effective.

On the other hand, epoxy is a true two part resin system. Each molecule of the resin must meet a corresponding molecule of the hardener or it will not cure. Miss the mix by only a small fraction and there will be 'unhardened' molecules forever.
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