Infusion layup schedule to avoid print thru

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#1

I am about to begin a fiberglass hood project, and would like to infuse the parts.

The hood will be made of an outer skin, and an inner skin bonded together.

These will be painted parts most of the time, but I would like to avoid any print through of the materials, at least on the outside surface so that I could do a carbon version as well.

If I use VE resin, then could I use either chopped strand mat, or continuous strand mat Could also use something like Rovicore, or make a cored layup with lantor soric XC or TF.

I guess I’m looking for a recommendation of ply schedule. There are so many different ways… In the past I used CSM and polyester wet layup to make similar parts. I believe it was 3 or 4 layers of 1.5 oz CSM on the outer and 3 layers on the inner with some woven roving reinforcements. Very heavy :frowning: but it worked…

Thanks for the advice

#2

Print through issues are predominately controlled by curing practices and resin choices.

Resins that have low shrinkage have fewer print-thru issues. Also, curing the more slowly can reduce the shrinkage. Resins will shrink more when rapidly cured especially if heat is applied early in the curing cycle. This is one of the reasons that many manufactures recommend letting the resin cure at room temp. for 15 to 24 hours before applying heat.

Fully curing the parts in the mold will play a large roll in reducing print-thru. This usually requires that the parts undergo a heat treatment to fully cure the resin before demolding. A heat treatment is almost mandatory for epoxies since they will not reach a full cure at room temp. Anytime in the sun will further progress the cure (and shrinkage) of a part that never underwent a heat treatment. VE resin can nearly reach a full cure at room temp but you need to leave the part in the mold for several days. VE will still benefit from a heat treatment. Do a heat treatment out of the mold with any resin and you will have more print-thru.

Simply flexing some laminates can cause print-thru.

Lastly, if the Tg of your resin gets exceeded then print-thru will happen.

In my experience the fabric type doesn’t effect whether print-thru will happen or not. If you use a fine weave the print-thru will be fine. If your fabric is coarse weave (low thread count) then the print-thru will be more noticeable. Both still can print-thru. Sometimes putting a fine weave on the outside can reduce some of the print-thru of coarser weave.

I just recently experience print-thru on a part that was made 10 years ago by another manufacturer. It was made from West System epoxy. I painted it as a plug and heated the part to 120*F to force cure the paint. The whole surface printed through. I didn’t exceed the Tg but I defiantly progressed the cure and enabled enough molecular mobility to mess the whole thing up.

I would recommend that you experiment with test layups on glass with your resin and fabrics. Try different curing rates and times in the mold to see what happens. You often won’t see print-thru show up for a couple of days (progressed cure and molecular repositioning). Put them out in the sun on a hot day and watch what happens.

#3

If you are painting the part I would start with a hand laminated 1.5 oz/sq ft chop stand mat skin coat using a DCPD/VE blend resin and allow it to cure fully overnight and then infuse your bulk laminate on top of the skin coat using a DCPD/VE infusion resin. You can also use a product like Soric between the mold surface/skin coat and the bulk laminate which improves resin flow and reduces print thru. Also, some fabrics print more than others, in general double bias fabrics (+/-45) print less than 0/90 just like lighter areal weight fabrics print less than heavier areal weight fabrics so use fabrics less likely to cause print-thru close to the mold surface.