Anyone ever make a composite part used in a spring application?
I’ve made a few parts to be used as a spring, but all the epoxy systems I have don’t return to the same shape after unloading, after just a few days uf being deformed. The resins I used were regular infusion and layup lamination resins. I believe I should be looking for a toughened resin, but not sure.
Anyone do something similar to this and have a recomendation for a resin?
you might want to give those springs a low post cure(150f) for a few hours. most epoxies take a week or two at ambient temp to fully cure sometimes even longer depending on the system. If you put your spring under load before that it will be prone to distort. You might want to call a few different resin companies and explain what you are doing, I am sure they can help you and give you a sample to try. But I think the biggest thing to help is a post cure if you havent already tried that.
I did post cure, at about 150 for over two hours. It must be something common, I imagine it’s used in just about every fishing rod and bow.
perhaps your laminate needs more fibers in the length of the spring, try some uni-carbon. If im not mistaken, I am sure that good fishing rods and bows will use a high modulus carbon, you are probably just using standard modulus.
How much are you deflecting the part? Is it being cycled, or held in a compressed position?
One of my products is a glass leaf spring to maintain electrical contacts on a rotating component. It flexes about 20% max, and retains its strength pretty much forever.
I don’t know how springs are specified I don’t know what goes into calculating that percentage. It’s a curved flat spring, with a flexing length 1.2 cm long. If rays were drawn out from the ends, at most there would be 12 degrees of flex between these rays. It’s not cycled, always stressed to at least 5 degrees, and will spend days at 10 degrees of flex.
With the epoxies I’ve used, I’ll stress the part and after a couple days removing the stress and the spring doesn’t return to the original form.
I am using a general purpose carbon, but I think it has more to do with the resin.
I know (and have use it in our Nascar Pinto race car fiberglass panels) there’s a flex additive for PER but any for Epoxy resins?
The best I found is a toughened resin from adtech, I’ll probably talk with them and test that. Also there are toughening agents from dow. But finding someone to distribute a manageable amount from the mammoth companies is a nightmare.
What additive was that? Maybe it will give me a lead.
I say it’s a resin issue. Dpending on your layup, you obviously want more % of 0’s than 90’s. Of course, it depends on your use as well. If it seems any tourquing, than you want some 90’s and 45’s in there as well.
Also, is the resin fully cured correctly? Is the carbon sized for the resin?
I would suggest using a toughed epoxy (Cytec Engineered Materials makes some), not something like PER or VER. Of course, there are always thermoplastics!!
Yeah i need something toughened. The epoxy resins I’ve used are much too stiff and brittle. There is no torque put on the spring.
Does cytec deal with small quantities? Adtech has a toughened epoxy and I might go with them.
You’ll need a laminate with mostly unidirectional material, and I’m pretty sure most resins will work. A poly or vinylester should do just fine.
If you keep the flexing at less than 30% of the parts breaking point, it will last as long as you need it to. Make a couple, bend them until they break, and don’t flex the production parts more than 30% of that.
I got a toughened epoxy from adtech with 10% elongation where most epoxies i’ve seen are 2-3%. It was designed for snowboards skis etc. Tests with this and uni should work out.
I don’t know, but if you do it right, maybe they can send a sample for test/research/development purposes, and possibility of buying more later.
that sometimes works for me.