Resins

[mechart87]

Hey everyone,

I'm Art Navarro, a member of the developing San Jose State FSAE team. I'm doing some research on resins, and would greatly appreciate any feedback on the topic. I am planning to go with S-Glass (structural glass, although this is tentative to the results of sponsorship) for the body work, as it strong and light. We will also likely use S-Glass for the plenum, and a few various other parts.

So far, I have seen that tehre are three main types of resins: Polyester, Epoxy, any vinyl ester.

Polyester seems good because it sounds the easiest to work with, and the most forgiving as far as mixing ratios and curing. However, its probably the weakest.

Epoxy seems to be the optimal resin, but the most difficult to work with, and a little more expensive.

There is also vinyl ester, which seems to be a good blend of both. It is also supposed to perform well at high temperatures, making it a good candidate for use for the plenum and other engine related components.

I hope to get some samples of these resins and start working and testing them asap, but as mentioned earlier, we are a startup team, and any additional info will be much appreciated.

Thanks,
-Art

[mechart87]

Hey everyone,

I'm Art Navarro, a member of the developing San Jose State FSAE team. I'm doing some research on resins, and would greatly appreciate any feedback on the topic. I am planning to go with S-Glass (structural glass, although this is tentative to the results of sponsorship) for the body work, as it strong and light. We will also likely use S-Glass for the plenum, and a few various other parts.

So far, I have seen that tehre are three main types of resins: Polyester, Epoxy, any vinyl ester.

Polyester seems good because it sounds the easiest to work with, and the most forgiving as far as mixing ratios and curing. However, its probably the weakest.

Epoxy seems to be the optimal resin, but the most difficult to work with, and a little more expensive.

There is also vinyl ester, which seems to be a good blend of both. It is also supposed to perform well at high temperatures, making it a good candidate for use for the plenum and other engine related components.

I hope to get some samples of these resins and start working and testing them asap, but as mentioned earlier, we are a startup team, and any additional info will be much appreciated.

Thanks,
-Art

[Mully]

This is probably more of an issue when using it for tooling, but vinyl-ester can have a tendency to shrink a bit under elevated temperatures.
My personal preference is to use epoxy and the mixing ratios are pretty easy to get right if you have a set of kitchen scales to weigh out your resin and hardner and can divide by numbers like 4.
But of course, as with any FSAE project, it all comes down to the teams available resources and budget as to what we all get to play with.

Just my 2 cents

[mechart87]

Thanks Mully,

When you used epoxy, did you guys cure with an autoclave or just a natural open air rest?

-Art

[Mully]

We use a range of different epoxies for different things.
It all is dependant on the specific epoxy that we are using for the job, with some of them not needing any elevation in temperature to fully cure, while others an autoclave was absolutely necessary.
For the most part, we have done partial post cures in a hot box at our workshop before taking it to our sponsor with an autoclave to finish them off. It allows them to take the parts straight up to the temperature our hot box gets up to without having to worry about the moulds or parts exotherming greatly speeding up the process.
Again, it all depends on the resources at hand as to what you use, but not all epoxies require high temperature post cures to fully cure.

[Brian S]

I haven't looked into resins so I can't speak about which ones are better etc, but we use the West Systems 105 Epoxy resin with their slow hardener. We cure our parts overnight at room temperature. It's easy to work with as long as you have a small electronic "crack" scale to measure it out on.

[Brian Evans]

I use polyester resin for anything that is non-structural, like body parts that bear no loads and just cover up the oily bits. I use the West system for anything that has to be structural or has to have an excellent mechanical bond to existing structure, like repair work. I use the West system with anything other than glass, as well - kevlar, carbon fiber, etc. I just use the West pump system to meter out the quantities, and I use their various fillers for fairing or bonding situations where I want some volume.

Since I rarely vacuum bag stuff, I saturate the resin in the cloth, roll it and press it out, then simply use paper towel to absorb excess resin, rolling and dabbing to get it off. Very simple trick that I learned from a guy who does high level motorsport composite work. Simple sometimes works!

Brian

[RiNaZ]

Art, i think it's best that you consult with the safety ppl at your school first. Different schools have different rules on what you can keep in the school's shop. Most resins that you'll find will have styrene in it, and some schools wont allow that. And then, there's the hardener (MEKP). Some might not allow that too. So check first with your school.

I would suggest that you use polyester for all your bodywork. And hi-temp epoxy for your plenum. West Systems is good, but probably too expensive to make a big part. So save the epoxy for something important and small.

When you do wet lay-ups, just wet out the surface with resin, and then lay the glass. After that, you pour more resin, and finally, you roll out the bubbles. Try not to dip your glass into your resin cup. There will be more bubbles trap in between this way. Always, wet out the surface, lay down the glass, and wet it out some more, and then roll out the bubbles.

[mechart87]

Great Information,

I think I will probably try to go with polyester for the bodywork because its ease of use and lower cost, and possibly use a more durable resin for the plenum (As mentioned by RiNaZ). The feedback on wet laying vs. using an autoclave was also helpful.

Thanks again to all who replied,
-Art

[Composites Guy]

Here at Lehigh we use 8084 Dow Vinylester (now Ashland Company I believe) for vacuum infusion (VARTM). This is used for most of the structures that we make, and we can control the handling time from 30 minutes to several days by minor additive chemicals. It works like a dream (with glass) and is dirt cheap. We use West System for hand layup, and MGS for vacuum infusion with carbon (both are available at Wicks, Aircraft Spruce, etc.)

[Moke]

If you are going to use ether of the "esters" then make sure you use proper PPE: good gloves, respirator, glasses, tyvex suit. And do it outside or somewhere there is good air flow.

West systems is just a internationally available brand. Have a look in the phone book for local resin manufacturers. We found a good one in Auckland who make their own resins, so if you need any questions about which one to use they can really help.

[MikeDutsa]

while on the topic.... If you use male and female mold with a void between them for your part, and bolt them together squezing out the left over resen, will it still cure at room temp, or does it need to be in open air? (assumeing that you have a proper mixture) we are currently investigating doing a carbon steering wheel for the first time and are tring to work out the details.

[Brian S]

If the resin is made to cure at room temp I don't see how it would be a problem. All of our stuff is cured at room temp in vacuum bags.

Speaking of vacuum bags, we had a sponsor show us a dirt cheap way to bag things. Instead of using the actual vacuum bag material and special tape, just use painters drop cloth and duct tape. It works just as well and is a hell of a lot cheaper. The only thing you have to watch out for is corners on 3D parts, but a piece of duct tape over the bag to reinforce it works fine.

[Mully]

On the subject of cheap vacuum bags, rubbish bags are a good little alternative for small, non structural parts. The plastic ones we used had a nice stretch to them and are easy to form into a sandwhich bag.

[RiNaZ]

Mike, why do you wanna use m/f mold together for your carbon steering? No one would see the inside of the steering wheel, so im not sure why you wanna clamp both m & f together. You can pull the part out of your female for front and back of the steering wheel, and glue them together.

For something small like steering wheel, you might get away with it. But if you were doing a carbon tub or something big, you dont wanna clamp both your male and female together. I dont have a solid explanation for it, but you'll risk of having 'wet-spots' around your part. I think the resin needs to have space where air can circulate and evaporate to cure the resin. My opinion is based on the parts that i made that required me to clamp both of them together becoz of deadline issues.

On cheap alternatives for vacuum bagging, usually, these type of tricks are done by individuals experimenting with DIY projects at home or in personal garages. For FSAE teams, time is very limited, so you dont wanna spend the time experimenting with things that probably wont go together. In composite, you almost always wanna do it right the first time. Stick with the right tools. All these tricks you see or heard are usually done by highly skill technicians, who knows what to do, in case the 'trick' doesnt work out as plan.

[TG]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by RiNaZ:
Mike, why do you wanna use m/f mold together for your carbon steering? No one would see the inside of the steering wheel, so im not sure why you wanna clamp both m & f together. You can pull the part out of your female for front and back of the steering wheel, and glue them together.

For something small like steering wheel, you might get away with it. But if you were doing a carbon tub or something big, you dont wanna clamp both your male and female together. I dont have a solid explanation for it, but you'll risk of having 'wet-spots' around your part. I think the resin needs to have space where air can circulate and evaporate to cure the resin. My opinion is based on the parts that i made that required me to clamp both of them together becoz of deadline issues.

On cheap alternatives for vacuum bagging, usually, these type of tricks are done by individuals experimenting with DIY projects at home or in personal garages. For FSAE teams, time is very limited, so you dont wanna spend the time experimenting with things that probably wont go together. In composite, you almost always wanna do it right the first time. Stick with the right tools. All these tricks you see or heard are usually done by highly skill technicians, who knows what to do, in case the 'trick' doesnt work out as plan. </div></BLOCKQUOTE>

This is called a "matched die." While yes there are good surface finishes on both sides of the part, there are additional benefits that can be achieved.

To achieve the highest strength-to-weight ratio in a composite part, you are looking for the highest fiber volume ratio. You want the least resin in the part without exposing the fibers. You can achieve a higher consolidation of composite parts using a matched die by essentially clamping the sides together and running excess resin out the sides of the dies. You can maybe jump from a 60% to a 70% fiber volume ratio depending on your processes.

It can also make the lay-up process easier, too, so that can also be considered.