TheoA

I have a piece of kevlar/carbon fabric, wetted out with 205 resin, in a vac bag. Last night (around this time) I put everything in the bag. My excess epoxy (in the mixing cup) kicked off within 30mins and was hard as a rock 2-3 hours later. My piece that was in the vac bag was pulled this am, much to my suprise it was still flexable. The surrounding air temp is 50deg F, perhaps today it got up to 65. Is the temp keeping this from curing, or did I not mix it correctly somehow?

Mike James

Judging by your own words, that the resin in the cup got hard, it sounds like temperature is the culprit. (West Systems recommends that #205 resin be used at higher temperatures than you mentioned.)

Resin in a cup will always cure faster than on a thin surface. Also, you didn't mention the thickness of the part you made, but if it's a very thin part, the flexibility would obviously be more noticeable.

And West Systems epoxy does take several days at room temperature to achieve max hardness. I've attached a chart from the West Systems catalog for reference.

MikeyD

Most of the time you will find the optimum strength from epoxy comes from a heat curing process Ie....Autoclave, hotbox, or oven. Almost all manufactures will recommend the ideal cure tempature for there brand of epoxy. Most of us are here because of a hobby, and because of that we do not have access to the expensive autoclave ovens used in hospitals and the fabricating industry. The good news is that it is relatively easy to make a hotbox from your local hardware store. It is essentially a heated and insulated box. The heat source can be a lamp ( I wouldn't recommend that) or a heater or flow of hot air. The reason why I wouldn't recommend the lamp is because the heat source is extremely concentrated, and will tend to give you hotspots on your mold.

One other thing, you did not mention if you had a core material that this kevlar was wetted out on. Thin Carbon, Kevlar, will be flexible by itself, It's true strength is realized when applied to a core material to add stiffness.

TheoA

It's a chain guard for my kart. I also want to make a floor pan, but after this experiance, I'm not sure. I don't think it's nearly as hard as it's supposed to be, it seems "green" still. my layup is 2 layers of 8.0 ounce carbon/kevlar weave. Right now, I could take it off the simple mold I hav emade, and roll it into a ball.

Here is a pic of what I'm trying to do, although this one is made from carbon, which (I think) would shatter if some debris got flug around by the chain.

TheoA

Again, made from carbon, which was determined to be dangerous as it would shatter under impact. Mine will be from kevlar.

TheoA

Well, afte an entire day of being in a oven (around 100deg) I still have a sticky piece of carbon/kevlar..

I suppose this one is junk, and I'll try again. However, I don't want to make a habit of ruining stuff.

What did I do wrong, and how do I do this right?

MikeyD

TheoA
Sorry to here the demise of your project. Did you mention if you were using pumps that are sold separately from WEST? These pumps meter the exact ratio of A and B resin. If you are using the pumps than I guess you can eliminate that.

I use a product call Shell DPL, It's a great product, but is very sensitive to humidity. I have had problems in the past similar to what you describe. My particuler problem was humidity. On the other hand, I have also used WEST and have never had humidity to be the cause of a failed part.

If you are convinced that your ratio is right, what you might want to do is do a test layup of some scrap kevlar. If this happens again, I would recomend trying to vacum bag the parts and heat curing at the same time. The vacum will eliminate any humidity. If you still do not have any success, you need to re-evaluate how your mixing your epoxy, or try another batch.

TC

Mikey D

TheoA

Tonight I just made a small batch of resin with a medical measureing cup, so I know for sure the ratio is correct. I didn't go through the hassle of vac bagging it, as I don't have any mylar avalable right now. Its function over fashion for me, so as long as it hardens properly, thats what I'm after.

I'll let everyone know the results tonight or tomorrow, since it's inside (77deg), according to the epoxy chart, it should be completely dry in 4 hours.

Bruce Thompson

Theo, I would venture to say that NO epoxy resin will be completely "dry" in 4 hrs at room temp. Some will not cure properly at 55 F, others just take longer at lower temps. It may have cured in the cup because of the heat a contained mass generates. In thin film applications, ie. lay-ups, many epoxies will have a gel time of 3-4 times the published pot life. Most structural epoxies aren't finished cross linking (drying) for 5 -7 days at room temp.

Bruce Thompson

Theo, I forgot to add above, If you value your lower extremities, PLEASE DON'T make a carbon floor pan. I've made quite a few kevlar pans and if you want details e-mail me or look around here for a post i added on this topic.

CentryEagle

One thing about WEST is that if you do not have an accurate mixture. The epoxy will remain rubbery. Even slightly too much of one is already too much and its not forgiving.

And mix it in a wider cup. I used to use it on mixing cups only to see it melt away after about 10 mins but where I am, the temperature is perfect for epoxy.

Mike James

TheoA,

I think you can depend on West Systems. If the above descriptions of possible errors don't fit with your circumstance, the only other thing I could guess is that you got a batch of resin and/or hardener that is somehow "FUBAR".

(I don't work for West Systems, by the way, or sell their products, or whatever.) West Systems is a well-respected manufacturer, with a proven track record. I've used it myself exclusively for the last 8 years, and never had even a single batch cure improperly. (I'm using it today.) I use it as recommended, and I use the same pump systems.