Problems Vacuum Bagging Vinyl Ester

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#1

Im somewhat new to composites other than taking a course about them at my college. Im currently working on a project at work which entails bonding a piece of fiberglass backed PFA LT plastic to a 2.5" by 13" prepared mild steel substrate. I am working with many resins but the first im trying is a Vinyl Ester. The specific vinyl Ester is a Hydrex 100 along with a Superox 46747 MEKP catalyst. The ratio calls for 10 drops of catalyst per ounce resin. After mixing my resin and hardener I wet out the fiberglass, apply the metal sheet and proceed to vacuum bag it. The problem is not a mixing mistake as my leftover resin did cure. The problem I am encountering is that after the 24 cure period the part is still wet with resin and not cured. I have heard of people vacuum bagging Vinyl Esters so I am wondering why I may be encountering this problem. I had an idea it may because of the absence of oxygen but I am unsure, any help is appreciated.

Work Environment: 80-90 degrees Fahrenheit, Medium Humidity

Equipment: 3 cfm 1/3 horse power vacuum pump

Resin: Hydrex 100 Vinyl Ester Resin

Hardener/Catalyst: Superox 46747

Ratio: 10 drops hardener per ounce

#2

It could be from the layer being so thin it can’t “heat” up enough from an exothermic reaction to cure itself, but your cup contains so much more resin that it has enough mass to do so. Their are warnings on some resins to not mix more then X amount in one container because of the exothermic reaction. I’m sure lots of users have experienced leaving a cup of resin that they didn’t use all of to see it start smoking from the reaction but their layup didn’t do the same because of the smaller mass.

Try heating it up with heat lamps. Or maybe other uses with experience in VE can suggest something since I only use epoxies.

#3

Be accurate on catalyst. On thin layers (how thin was your layer?) go slightly higher on catalst, and perhaps you should add some more cobalt or other promotor.

Also temperature plays a role.

#4

How long did you mix for? I’ve had this issue prior when i was resin infusing, and I didnt mix long enough. some parts got hard while some were still “wet”

also 10 drops to oz is for small batches…
10 ml MEKP to quart or resin is approx 1%
5 ml MEXP to 2 cups or resin is approx 1%

get a measuring cup vs the “drops” a lot easier and more accurate.

#5

I had mixed the resin/ catalyst for atleast 5 minutes making sure to scrape the sides of the cup as well as the bottom edge. Due to the vacuum pressure the layer thinned out to about 1/16th of an inch… I know that this is very thin but am unsure how to keep it thicker. After removing the structure from the bag and letting it sit the resin cures. Is it due to the styrene being starved of oxygen while in the bag?

#6

No, the stuff should cure under the bag as well. Did you take the part out of the mould? The metal mould can act as a heat sink. In combination with sloppy measuring this might have caused the slow cure.

#7

Usually the most Vinyl resins need over 10% hardener, I am using many time vinyl. Now if you want it more “TURBO” then add to resin 1-2% of cobalt.

#8

Just read the data sheets. The resin will cure in 16 hours using a normal MEKP without foaming up. The catalyst you are using is a VE MEKP. Normally, these are formulated to not make VE fizz, and they give you longer pot life and cure time. I’ve used normal MEKP on an AOC VE and it fizzes, pot life is like 10 mins. I should use a VE cat like the one you used, however your resin doesnt need it. Coupled with mixing it at 1% might be the reason.

#9

Hermans suggestion is a far better way to go. The problem with buying off the shelf promoted VE’s is that the supplier will not know what sort of layup you are going to use. So you may have a VE that will suit a much thicker or heavier layup. Never, never go above 2.5 % catalyst. Once you hit approx 3-4 % or more of catalyst the reaction can actually reverse. If you need to use that high a level of catalyst then you would be served speaking to the supplier tell them your layup and ask them for a recommended promotor level for their resin to suit your layup. If you are going to regularly use VE and have varying thicknesses of layups then buy it un-promoted and promote yourself. It also prolongs the shelf life of the resin and gives you the flexibility to tailor your lay ups and not run the risk of under curing your products. As mentioned, buy yourself a decent set of scales, one drop to a bit of this and that is not the way to go!

#10

I will be making a resin block around the substrate to not allow resin to flow away from the part and also use a non perforated peel ply to keep resin in. I am also beginning to experiment with using lower vacuum pressures to keep the resin at a higher thickness. Hoping that this higher thickness of resin will allow it to heat up and cure better. Thank you all for the help.

#11

It think that the steel substrate is going to leech the heat out regardless of the laminate thickness. Setting the steel on top of a heating pad would warm the steel and accelerate the cure.

#12

10 drops per oz.? sounds way to much. google “mek dispenser” $5-$10 dollars. buy . 10 to 25 cc per quart. no more problems . you guys are making this wayyy more complacated than it is.:push:

#13

Cubic centimetres per quart? You weird yanks are at it again! :rolleyes:

#14

you guys have “mph” on your roads! how can you measure a mile with the metric system? silly limeys…:stuck_out_tongue:

#15

Not to mention to measure the weight of fiberglass in oz per sq yard, but when it is mat (CSM), in oz per sq ft.

#16

Well, a US tape measure is easier to read. A metric one has all the lines the same length except every 5 millimeters. I have to count those dumb little lines with the tip of my pencil all the time. :smiley:

#17

You mean an imperial tape measure :slight_smile: A mil line is always within 3 lines of a bigger line.
Sixteenths, thirty seconds and sixty fourths are far more illocigal. I have to get a calculator out to find out if 9/16 is larger or smaller than 17/32.

#18

This thread has turned to comedy! Absolutely hilarious!

There should be a new thread started for this, I think it would be a great read…

#19

I prefer meters because when I ran the Paris half-marathon a few years ago, it seemed like it was going by quicker since it was marked every kilometer instead of every mile…though it did seem like it lasted longer once I passed the 13th kilometer…:smiley:

Otherwise, I have nothing useful to add about vacuum bagging vinyl ester…