vacuum infusion problem

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#1

Hi to all,

Last month i start to infuse panels for my boats.

I use polyester resin (not vinylester or epoxy) with mekp catalyst.

During the infusion everything is good (vacuum level 85%, 1,5% catalyst, 20oC) but when the laminate start to cure everything goes white. The upper surface of this is perfect like peel ply but inside this seems like the fiberglass hasn’t the amount of resin which need.

Someone told me that i must try to infuse with less level like 70%, someother else i try with not mekp catalyst.

I will appriciate your opinion please.

Regards

George Syrigos

#2

Why do you have 85% vacuum level? Maybe you havw lwaks and suck air in the laminate.

#3

Quite common practice to infuse at ~80% vacuum with vinyl esters and polyesters due to the volatiles boiling off at full vacuum. Only happens with some brands it seems, have had it happen with an imported brand I’ve tried but then didn’t have any issues with Scott Bader Crystic.

That said, I believe the proper technique is to pull full vacuum and make sure it maintains with no leaks. Then reduce the vacuum level just before infusing. Not sure if the OP did this or not?

Can you post pictures Sygeor?

#4

There is no need for reducing the vacuum! Even if you pull full vacuum the resin is pushed in by ambient pressure, so if there is boiling then only direct at the flow front. And even then the styrene will be evacuated and it does not make a difference.

#5

The issues I faced occurred after the infusions finished. Infusions themselves went well, no air bubbles in the resin. 100% vacuum but ended up with voids. Could see it appear in the flow media, just bubbles appearing like there was a leak, but very uniform all over the part at once, very much like boiling water. Very strange.

#6

I haven’t infused with polyester for around 14 years, but I build boats with vinylester and epoxy.
Why only 85% vacuum? Did you have a leak?
Why only 20 degrees Celsius? What temp was the resin and mould ?
I always shoot vinylester at 23 deg C air temp, mould temp and resin temp. Below that the viscosity of the resin is too high. Especially on large mouldings.
Try shooting the resin at high vac and reduce vac AFTER the part has filled to avoid boiling the volatiles. Find out the appropriate vac level by degassing some catalysed resin in a vac chamber with a viewing port and then reduce the vac until the resin stops bubbling. There is a pressure gradient across the job from the resin front to the resin supply, so the volatiles will only boil on the resin front. After the part has filled and the resin lines are closed the pressure gradient across the job will even out and eventually reach the vac level. If the vac level is too high the you will get boiling in random places a cross the job. Hope this helps

#7

You have the same effect with epoxy, but not that hard. Thats what the MTI hose is made for, prevent this.

#8

Thanks to all for the interest.

I haven’t air leaks in my laminate, i do test before infusion.

Told me that the polyester resin and vinyl needs 60-70% vacuum because haven’t good behavior in high vacuum.

The problem start when the laminate start to cure, during the infusion everything is ok.

I post some pictures of the problem.

In the first picture everything well, during the infusion.
The second picture seems when it cures.
The third picture is the final result.

Also i send the resin specification.

I try to understand if i’m wrong or the resin is not proper for this issue.

Thanks again for your help

#9

Send pictures of the problems in my last post

Thanks

#10

could be the exotherm is raising the temperature so the volatiles boil off at a lower vacuum

#11

Can i solve the problem you think ?

Thanks

#12

Defenetly a vacuum problem. Your system seems to be tight but on the first picture you can see enclosed air in the little dry spots. The capillary forces saturate the fibres but the air starts to travel. Also there is a dry brake zone where the resin can travel so the air starts to expand in the laminate. That ends up in the milly laminate.
Infuse with full vacuum and try the MTI hose.
Problem should be fixed then.

#13

Thanks DDCompound for helping.

I try your way to see.

Thanks again

#14

hi Sygeor. I just saw your pictures. I didn’t realise you were using chopped strand matt. CSM generally doesn’t infuse well. Back in the day I used to use CSM as the resin break, but I wouldn’t use it in the laminate. That may be contributing to your problem, but I think the bigger issue is you are not pulling enough vac on the dry stack.

#15

I’ve infused CSM up to 5mm thick without any issues. I’ve never seen why people have problems with it.

#16

I have the same problem with triaxial fiberglass.
Maybe tissue is better for vacuum ?
A lot of people told that polyester resin don’t need up to 70% vacuum.

Regards

#17

The problem happend after curing, i don’t think that the vacuum level is the issue.

#18

Wrong resin? Is it an infusion resin?

#19

It‘s Scott bader … Vacuum injection, light RTM polyester resin.

Your opinion ?

#20

Should work if it is for Vacuum applications.
But when you get a white laminate with CSM it is most what the boat builders call spring back. And that is always a vacuum problem.