Composite resin richness in areas with sharp contours

[rmurazzi]

Hi all,

We are experiencing an issue with one of our composite molded products. We are use a bag mold process to form a composite helmet. The layup process is wet on a headform/bladder that is then transferred to a hot mold and cured. In areas where the contour bends sharply we are experiencing resin richness. The Kevlar material is not conforming to the contour in these areas. We have tried numerous combinations of hard pushers, initial curing at low temperatures, etc. with no positive result. We are using a single layer of peel ply on the outside of the layup that appears to act a sieve and does help considerably to remove the resin - the lack of definition of the Kevlar is the biggest current issue. We do not currently have any bleedout/vents anywhere on this particular tool and we are considering their addition as we generally do have them in other tools.

This tool is not dedicated to one particular use - it is a base/insert combination and makes several sizes of product. Bleedout install can be a bit tricky and production volume is low for this item.

Any suggestions?

 

[JeniaL]

do you remove mandrel/ insert while vacuuming? we keep mandrels under vacuum bag plus we use a clamp. well in our case we don't transfer lay-up to another tool.

 

[Compositepro]

Without any bleed-outs/vents how can you call this a vacuum bagging process? Excess resin will flow to the lowest pressure areas in your part. This is always in concave areas.

 

[rmurazzi]

Hello,

This is a bag molding process not an Autoclave process. We do a wet layup on a rubber bladder (we call it a saddle) and then transfer the saddle and layup into a two piece mold. The mold opens and closes horizontally with hydraulics. Once the layup/saddle is in position we close the mold halves around it. Then the top plate on which we have a water bag (or bladder) is lowered into the layup saddle that is open on the bottom end. We then then fill and pressurize the bag with water. The bag applies pressure to the saddle and the actual composite material is between the saddle and the steel mold. Cure take place under heat and pressure.

Sorry for the confusion - we refer to this process as bag molding, there is no vacuum involved, just heat and pressure.

 

[Compositepro]

Okay, for that to work you have to have "pressure intensifiers" (a misnomer, really). Your rubber saddle has to have hard parts (solid rubber) that fit the contour of your concave mold surfaces. You cannot just use a inflatable rubber bladder that has uniform wall thickness. Trying to stretch the rubber into a concave mold takes away from the inflation pressure so the actual pressure the rubber applies to this area is less than the inflation pressure. Resin, being a liquid, flows from high to low pressure until the pressure equalizes or the resin gels.

Airtech has a product called Airpad which is an uncured rubber sheet used to fill these low pressure areas.

 

[rmurazzi]

Hello pro,
Yes, we have tried hard plastic pushers integrated into the saddle. We've also tried a harder rubber inside the saddle in the trouble area. We have seen slight improvement but not quite what we need. We also saw a greater incidence of blisters in the finished product that may be related to the harder materials.

I have been trying to get samples of product from Airtech for about a month and half. I may just have to buy some of the Airpad product.