What would the cost difference be between epoxy and vinyl ester? Significant when doing an entire boat?
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Trying resin infusion
- Thread starter Alan Gage
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The resin technology is constantly improving, and the case for epoxy resins in VARTM (vacuum assisted resin transfer molding) is now more compelling than ever.
Historically, there have been many reasons for choosing vinyl ester and its derivatives over epoxy for VARTM. These include lower price, lower viscosity, higher UV resistance, more dynamic pot-life control, no need for post-cure (many --perhaps most-- epoxy infusion resins require post-cure in an autoclave), perceived incompatibility of epoxy resin with polyester gel coat systems, and versatility: within temperature limitations of cure, the pot life of vinyl ester resin may be modified by a single activator (MEK-P)-- whereas epoxy systems require separate and specific hardeners to yield different working times. There are others.
Temperature greatly affects viscosity, and epoxy resins may be made thinner by heating the resin, warming the room, and warming the mood itself; this is time-consuming, and one needs to be cautious: this warming reduces the working time of the resin; manufacturers have charts and graphs to show these parameters. One example I read shows an increase of 18 degrees F cuts the working time of the epoxy in half (from 30 minutes to 15).
Profit margins are slim in the recreational watercraft business, and the cost of production is critical. The price of materials like resins and brand name cloths like Kevlar weigh heavily in the corporate decision-making.
Historically, there have been many reasons for choosing vinyl ester and its derivatives over epoxy for VARTM. These include lower price, lower viscosity, higher UV resistance, more dynamic pot-life control, no need for post-cure (many --perhaps most-- epoxy infusion resins require post-cure in an autoclave), perceived incompatibility of epoxy resin with polyester gel coat systems, and versatility: within temperature limitations of cure, the pot life of vinyl ester resin may be modified by a single activator (MEK-P)-- whereas epoxy systems require separate and specific hardeners to yield different working times. There are others.
Temperature greatly affects viscosity, and epoxy resins may be made thinner by heating the resin, warming the room, and warming the mood itself; this is time-consuming, and one needs to be cautious: this warming reduces the working time of the resin; manufacturers have charts and graphs to show these parameters. One example I read shows an increase of 18 degrees F cuts the working time of the epoxy in half (from 30 minutes to 15).
Profit margins are slim in the recreational watercraft business, and the cost of production is critical. The price of materials like resins and brand name cloths like Kevlar weigh heavily in the corporate decision-making.
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Thanks for doing an edit and adding the above info. I was having a hard time imagining how a shut-off valve could control the amount of vacuum applied. That makes sense.
The seat came out good. Nice to finally have some success. It was a lot nicer working with a mold than loose parts. I think I'll scuff sand the surface and give it a light coat of epoxy. While it appears to be fully saturated the carbon on the finished side has that look like it's been sanded into. A little extra resin thickness there will make me happier.
20160222_002 by Alan, on FlickrI gave up on remaking the front and rear supports from foam so used cedar instead with a strip of alder on top for better screw purchase. They weigh about 1/4 pound heavier than the foam/carbon version. I remade the braces from 3/4" XPS foam cut down to 1/4" thick and then laid them up by hand instead of infusing. The 1/4" XPS was much stiffer than the other foam I'd been using. They still need a coat or two to fill the weave from the peel ply.
Thanks for the help!
Alan
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The seat is exquisite; nice work.
In my working days I did some epoxy infusion. We always outgassed the epoxy before drawing it into the product. I do not see any mention of degassing the above comments. Do you out gas the epoxy in a separate step or is that not necessary?
I'm pretty clueless about this so I don't know. I've heard it mentioned before but don't know exactly why it's done or the repricussions of not doing it. I took it that outgassing the resin involved simply letting it sit for a while before drawing it into the laminate. Is this correct? How long is long enough?
I did let mine sit for a few minutes before drawing it in and also heated it slightly with a heat gun to help remove bubbles.
Alan
Most of the time we used a bell jar but some time used other vacuum vessels. The last project I did I used a Aluminum pipe that was about 12 inches long and 8 inch diameter and a hose barb in the side for connecting the vacuum. It sat on a ½” steel plate with a ¼” rubber sheet for a seal. You need a hole in the rubber to keep air from getting trapped under it. The top was 1” Lexan or Plexiglas with donut cut from a rubber sheet so I could watch the epoxy. You need to be able to see the epoxy and container. Use a larger container than just to hold the epoxy maybe 5 times the size required to hold the epoxy. When you pull a vacuum on it will boil/foam up. Control the vacuum with a valve between the pump and the vessel watching to see that your epoxy container does not boil over. As the bubbles bust some will throw a small amount of epoxy so clean the cover with alcohol as soon as done. This cuts into your work time. It is faster to have a shallow container large enough to put full vacuum on it without boiling over. Don’t stir the epoxy after outgassing.
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VARTM explored from an amateur perspective necessarily includes the cost of the entire setup. De-gassing the resin after mixing is necessary to some extent for sure, and in an earlier post I mentioned letting it stand for a period of time before infusing. The amount of time you can let the mixed resin stand depends upon the size (time required) for your infusion, temperature, and the formulation 'time' spec of the resin you order-- you can buy a 30-minute resin or a 45-minute resin etc.
A proper de-gassing pressure pot with Lexan window is available from Airtech and other suppliers, and it's a step that will yield a more bubble-free product-- not all professional infusers use one for all infusion tasks.
I would recommend those interested in getting into VARTM take a proper course from an establishment like Abaris. There are other schools that teach the technology, but I went to this one and I liked it. After doing the course, there is much experimentation to be done in your own shop to iron out the details for your specific infusion projects. There are many "proprietary" processes and techniques out there, and not many canoe companies will let you see their infusion processes.
If you've tried infusion, you know what a compelling technology this is; it's just plain fun!
https://www.abaris.com/training-prog...-technologies/
A proper de-gassing pressure pot with Lexan window is available from Airtech and other suppliers, and it's a step that will yield a more bubble-free product-- not all professional infusers use one for all infusion tasks.
I would recommend those interested in getting into VARTM take a proper course from an establishment like Abaris. There are other schools that teach the technology, but I went to this one and I liked it. After doing the course, there is much experimentation to be done in your own shop to iron out the details for your specific infusion projects. There are many "proprietary" processes and techniques out there, and not many canoe companies will let you see their infusion processes.
If you've tried infusion, you know what a compelling technology this is; it's just plain fun!
https://www.abaris.com/training-prog...-technologies/
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A word of caution. Back in the day when we were invincible we used 24” X 36” glass bell jar with no cages. We also used glass bulbs with a tube coming out each side for the epoxy that passed through the product keeping it from getting to the vacuum pump. Don’t do that. If you vacuum vessel ruptures there will be a lot of energy released. I can embed glass in hard wood.
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