vacuum bag

just starting to learn vacuum bagging...ordered all parts from joe woodworker and built pump......did a test part 1'x1', 3 layers of glass, with a piece of core material. The epoxy started to pull through the fitting and into the hose going to the pump....It appeared that the fitting needed to be raised off of the part.

Question: At the ratio of 18oz epoxy per lb. of glass and pulling 18in of Hg, should the epoxy be coming thru the hose? or how do I correct this?

 

Hi,i'm in the same boat and have the same system as you.on my tests that i've done so far i've either had the through bag connector off to the side,then use 3-4 layers of extra breather-release material and bridge it to the port.i think its the release film undernieth with the small holes that keeps the resin from sucking through all the layers.

 

thanks for the info.....we are in the same boat!!.....going to try another test piece tomorrow,,,,,working up to trying to vacuum bag a large boat part next....small steps first..

 

Hi - Don't put the frog on the job. Put it to the side of the job connected with some breather material. Always have a resin trap between the job and your pump! Cheers Peter S Oh plus when you hand wet out the fibre don't add as much resin!!

 

thank you sir!!!

 

The "problem" with wet bagging is that you need areasonable amount of resin to properly saturate the fabrics in their "relaxed" state. After applying vacuum the laminate stack is compressed, and the excess resin will need to be contained somewhere else. (in the bleeder). So you need enough bleeder to contain the excess resin. It takes a bit of experience to get a feel for it.

2 more things:
-I tend to laminate the first layer a bit resin rich (even for hand laminate purposes). After the rest of the stack and a vacuum is applied, you get a bit of resin movement from the bottom / mould side upwards, taking some of the airbubbles with it.
-If you ruin your vacuum connector, just take the hose, wrap some sealant tape around it (some 4"/10cm from the end) and stick that through the bag, with the end ending on a thick patch of bleeder. You can even stick something into the hose to prevent it from closing up, if you have a soft hose. (2 or 3 ty-raps work, or a piece of rope).

In the early days we did not use catchpots, but I would higly recommend them. make one from a piece of PVC pipe and some barbed fittings. Even a pressure cooker works. Or a pan with a lid on top. I have even seen glass jars being used.

 

The catch pot I have seen used the most is a beer bottle with butyl tape around the hoses.

 

its interesting !!

Bagging is the first step , learning all about what vac actuall does . sucking a laminate down and squeezing it using atmospheric pressure . its amazing that even guys i worked with that have done bagging for a while never really understand how it actully works !! one older guy been in glass lot longer than me could never get it right no matter how many times he tried just never clicked . Bagging glass i feel is ok but you need to know how much suck and how much resin you really want to remove .
Some where there is a fine line and no one really knows where that line is between how much resin should be left there ?? and how much suck pressure is enough ???
All our suction lines always ran up hill all the way from the bag to the colletor and from there on to the pump !! also if resin has to climb its easy to see it in the pipes as they are not laying on the floor or amongst the stuff on the bench .

A good hand laid job with peel ply i think is very close to the minimum amount of resin that should be left in the glass , the percentage of resin to glass is very close . We used to lay 4 layers of glass and peel ply all at once and roll out and it was amazing how much resin would be bought out through the peelply and to the edges !! doing wet on wet was the secret and our QA guy always kept an eye on everything and was always smiling when we finished . It was his figureing we always worked to for everything and always spot on the amount everytime ,We had very accurate scales (0.000)for resin and even the catalyst and everything was sprayed ,we were using vinylester resins all the time
Because our workmanship was always 100% everytime the DNV survey inspector said there was no need to bag any of our work because the percentage of resin to glass was consistantly close enought to the same as the bagging should have been .

 

"Bagging glass i feel is ok but you need to know how much suck and how much resin you really want to remove" .

That is the big question!...We are going to install the catch pot and give it a shot this week....We are doing the cap to our micro skiff....Keep fingers crossed....

Thank you all again who replied!!! You have helped out alot.......

 

"correct" amount of resin - Hand laminating its difficult to get say less then 800g of resin to 1000g of multiaxial.This is 45% resin by weight. Prepreg is typically 35% by weight resin and bled to 30%. Infusion is 30% resin typical, can get 25% if you use very high vacuum and debulking procedures. Boeing has a program in which it infuses laminates at 30% by weight resin then puts the laminate into an autoclave and squeezes resin out until its 15% resin by weight. So I think you are along way from having too less resin. Peter S

 

how much resin is enough ?? sucking every last possible drip is not a good idea ! some where there has to be enought to hold all the glass fibres together and have enought to cure and bond properly !!
if you trying to save weight then redesign your glass schedual and use a better material stack .
I been building boats and plane bits for long time and i dont bag anything now simply using peel ply gets me what is needed an compresses the fibres enough for the max strength i need and never get failures !!

 

Hello Tunnels,
I have clients over many years who I do structural calculations for their survey vessels. They have gone from hand to wet vac to infusion. As the vessels are in survey we have to regularly test the laminate properties. By going to infusion we have leapt from 200MPa strength to 900MPa flexural strength and 12GPa stiffness to 30GPa stiffness so we can use much thinner laminates to do the same job (E glass multiaxial laminates). The big difference has also been in compression. With hand built laminates the compressive properties can be half the tensile properties but using infusion we regularly test at higher stiffness and strength then in tension. I have no doubt you don't get failures, just means the designs are correct for your laminate mechanical properties. Using more sophisticated production techniques builds better laminates otherwise we would not bother. Peter S

 

Indeed tunnels, i have heard your argument for hand layup with peel ply and have also heard you say youve never really done any infusion....

I still do wet layups and vac bagging, but these days i try to infuse everything unless its too impracitcal otherwise. The laminate quality with infusion hands down beats any wet layup, no matter how good you think you are... it has to be seen to be believed.... for example, have you ever seen a e-glass laminate +1/2 inch thick solid glass (~15,000gsm), that is so perfectly transparent it looks like a pane of window glass? Well thats what infusion does... and no hand layup will ever get near its mechanical properties... Why? The TRANSLUCENT appearance of handlayups (not transparent) is from all the microscopic air trapped within the laminate - which weakens it. The laminate is also thicker for the same weight of glass fibres because it hasnt been compressed like a bagged or infused laminate - this extra thickness is resin only, not fibre, which further increases weight for the same strength.

Opinions contrary to the facts, serve only to degrade ones credibility...