Its absolutely fine cutting the vacuum and resin lines off when finished infusing the part as long as you have done the proper leak check pre-infusion and know its all tight. I never get any resin down the vac line outside the mould now and perfeect parts everytime.
As far as reinforcement type goes I was having major problems with unidirectional then switched to twill type and that got rid of the bubbles!
All three of you make intersting points 
Seems like this would be the key though?
Also thinking some more on it, perhaps each of those answers is correct, but dependent on the materials at hand (bagging, sealing etc) and the skill of the operator?
I can say with certainty that there are never any leaks, and I’m actually inpressed how long they will hold their vacuum when I test it, so that is not the problem, there are no other sources of air getting in, that I’m sure of, it would be very obvious if htat was happeneing.
could it be tht my mold was still too fresh? what happens with new molds? anything of this nature?
Have a look here for useful info regarding using new moulds
Some very helpful info on that site, from a company that actually makes parts, as well as selling supplies.
it is not absolutely fine to cut vacuum when infusing intill resin has cured, it would be stupid to do other wise, you may get away with it using a vinyl ester since it will cure fast, but if using epoxy this will cause many problems, and why even take the risk? even the cheapest of vacuum pumps can run for 16 hours everyday for years. a good sealed bag should hold vacuum for 15 minutes once disconnected from the vacuum soure, this is how you test to find out if you have a hole-free bag.
The first step in any infusion is to make sure you have a perfect vacuum tight seal, its not a good idea relying on the vacuum pump to make up for any leaks. Keeping the vacuum pump running just purges the resin through the job into your pressure pot and wastes expensive resin until the part gels.
if you clamp the resin line off and leave the pump running it sucks the resin out the back end of the part leaving dry areas (not recommended) so really having the pump running overtime creates more problems than anything else!
With vinylester you can apply a local heat once infusion is done on the vacuum outlet to gel stuff a bit quicker.
We infuse epoxies & vinylesters on production quantities and never run the pump after infusion is complete
I have never heard of anyone ever stoping infusing after a part has been infused. even a 100% fully sealed bag will loose its pressure over 15-20 minutes. you want to keep the vacuum running to keep your laminate compacted, and resin lean, turning the pump off is just leaving a alot of extra resin in the part and high potential of air entering back in to the part. I agree that a vinyl can be done because of its short cure time, and maybe the epoxy you use has a short cure time too, and more power to you. all the infusion epoxies I use, I leave under vacuum for atleast 12 hours
20_RC51, i think if you leave the vacuum running until just after the resin has gone past B-stage it will come out better. Just make sure you mix enough resin so when it does get into the vacuum line if the part is still infusing at that point.
My gel time really varies. sometimes it’s 4 hours until after the gel starts to solidify more. sometimes longer. Just depends on the heat outside where i work. yeah… i’d pull the heat lamp off… wait an hour or so after the part has infused then turn the lamp on. or just use the heat lamp to heat your mold, turn it off, infuse, then later turn it back on. degass your resin too
Dougie, you may be right on a medium or large size part about wasting resin… but with infusion i think most of us mix more resin than what is needed to do the part. I mix enough to fill all the lines and the part. I’m not gonna complain about $1 or less worth of waisted resin. The only waste i see is having to throw away the vacuum line after each infusion… that’s a couple dollars. Just my opinion.
all he needs to do is make a resin catch pot from a glass jar and have it below the mold, it will catch any excess resin(which should be none) and he can run the vacuum as long as he wants
Firstly in the case of cosmetic parts is there any real need to use epoxy resin systems with long cure times, when many problems could probably be avoided by using less costly polyester?
Secondly as a perfect vacuum is impossible to achieve, it seems that pumps must either run contiously, or ideally have some sort of simple switching mechanism to turn pump on when vacuum drops below a certain level?
Treat the mould with no less than 12 waxes, with 1 hour separating each application, TR-102 . It is advisable that the tool is broken in first before making any parts, to do this; 1. Coat the mould with PVA release agent, lightly by hand with a sponge is usually sufficient, 2. When dry apply a layer of gel coat, add 3% catalyst as it’s important that this gels quickly. 3. Once the gelcoat has cured apply one layer of 450csm with resin, it’s best to make sure this cures quickly also so add 2 – 3 % catalyst.
- As soon as this layer cures after 3 – 4 hours peel it off the mould. If the mould is not broken in this way the styrene from the fibreglass laminate can attack the waxed surface of the mould and cause the gelcoat to shear off or worse the part sticking to the mould. Wash the PVA release agent off with warm soapy water then apply a further 5 waxes, again leaving at least 1 hour between each application, after this treatment the mould is ready to use.
Is this the recommended way? Should a mold be broken in this way?
I did an infusion yesterday, being very careful with the whole bubbles issue and avoiding heating the mold/resin too much. I let the resin infuse through the line slowly at first to let the bubbles catsh up to the resin front and then I let it infuse faster. I on’y applied the heat a little bit at a time and near the end of the infusion, also I kept the vacuum on longer. I will see today how it turned out.
you are completely right, you can not achieve a perfect vacuum, the best test is the 15 min no drop test. any bag and molds are going to have microscopic holes that no matter what your skill level and experience they will always be present. the best you can do is get a high end bag that is duarble. I dont think it worth talking about the difference in cost of material between epoxy and vinyl/poly, I pay only a difference of $2 a pound, not worth mentionng, however with cosmetic parts it is more wise to you use a vinyl/poly because of faster cyle times and less of a chance of pulling a leak in the sealant or other place long term. bottom line infusion requires no air to be pulled in through the part, if using a epoxy you will need to leave the pump going till the resin has been set
Update
The part that I infused yesterday is top notch! I guess modulating the resin flow on first entry and making sure that it is degassed very well seems to be critical. Also I left the vac on until it was well into gelling.
I guess only repetition will tell if all this has culminated into reliable procedure for me. I will periodiacally report back. Thanks everyone. Keep the debate/ tips going it’s very benefical.
the pics are one with flash and the other without flash
thats great, good job
Here is my 2cents or pence worth.
hojo says run the vac pump throughout because you never achieve a perfect vacuum and dougie says thats wrong and you can.
Right i infused a few parts yesterday as i do everyday and i use the dougie method, perfect vacuum to start with if i cant achieve this i wont start the infusion. I cut the resin at about 75% of the part infused let the vac pump pull the rest of the way then shut the vac line on my manifold for that part and move on to the next part to be infused. I have just been to the workshop to demould the parts and as always the vacuum is as i left it yesterday with no resin in the vac line outside the mould and minimal if any inside. I reuse all my vac lines and have maybe resin in one very rarely. In the early days i would have streams of resin entering the catch pot but not anymore. If you can turn the resin flow off so that it doesnt reach the vac line then yes turn the vac pump off if you cant then leave it running.
So both hojo and dougie are right. If you have big flanges then you are more likely able to turn the pump off so the line vac maintains vaccum. Small flanges you are most likely going to have to run the pump continuously. Of course you must have no leaks which means using good materials.
Baz
Baz, you are also degassing your resin?
dougie is right as long as your are using a fast curing resin system. a “perfectly” sealed bag will hold its pressure for about 10-15 minutes and will steadly drop, so aslong as your resin will cure before bag pressure drops to low then you are good. but with long curing resin systems, such as many epoxies you will need to leave your pump running
Anyone like to comment on that? (post #32)