Vacuum resin infusion

After the experience with the first side of the mold, we decided to test vacuum infusion on the other half. I’ve always wanted to infuse—as very high fiber to resin ratios can be achieved—so we checked it out in a less critical part.

The laminate layout of the mold is:

  • six quasi-isotropic glass fabric layers with a total weight desity of 1660 g/m²
  • PET foam core of 5mm thickness (3D|CORE™)
  • six quasi-isotropic glass cloth layers with a total weight desity of 1660 g/m²

The area of one half is about 4 m² (43 sq. ft), which means that roughly 48 m² (517 sq. ft.) of glass fabric had to be laminated. That’s more surface than many flats in New York or London have…

Laminating all this layers by hand is quite time and strength consuming. It gets easily stressfull, in particular when resin is hardening and vacuum is needed as soon as possible to press the core. Depending on the vacuum pump, even a small leakage can be enough to spoil build-up.

When you infuse, you have plenty of time for making the dry lay-out and vacuum bagging. Not before everything is ready and fine, you start mixing the resin. Though less stressfull, it is still elaborate to make the full lay-out, and mix and degas all the resin in one shot.

We started by applying tooling gelcoat (Formenharz P). This time we did not use a thick coupling layer, but continued to laminate two layers of 160g/m² glass directly after the gelcoat geled (about 2 hours after application). A thin coupling layer smooths the surface and prevents air bubles between the glass cloth and gelcoat. This approach guarantees that the interface with the pattern is sealed, a must for vacuum infusion. Filleting and reinforcing the corners was conducted with carbon rovings this time, which adds some extra stiffness.

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After having created a tub for the vacuum,  the dry lay-out was made using Infutac (Diatex) to fixate the layers. When everything was ready, we started to mix and degas the resin (HP-E300RI from HP-Textiles):

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It is somewhat strange to have 12 kg (26 lb) of epoxi resin at once in a pot:

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The big show started at about midnight right after having all the epoxi together. It was the first time we saw infusion live and it was really impressive. The effort was worth it, even just for seeing the resin flowing into the lay-out, wetting the glass fibres making them transparent, and exposing hidden structures:

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We shot also a video of the full process, and hope you enjoy it as much as we do:

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Making the mold

What a week! We started to make the mold and had a couple of very long and late ending sessions. In the fist session we spread a thin coat of tooling gel coat (Formenharz P, R&G Faserverbundwerkstoffe GmbH) and strew a mixture of glas shred and cotton fluffs (coupling layer) on top of the fresh gel coat:

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Properly spreading the gel coat is the most important step to obtain a high gloss surface (along with the pattern’s finish). The coupling layer is needed to have a surface on which glas fabrics can be laminated in a later step. Without a coupling layer one has to keep on laminating before the tooling gel coat has completely cured, i.e. after it started to gel. Going on wouldn’t be problem for a small mold. However, when you have several m², such as here, mixing and spreading the gel coat is already enough hard work for one session:

 

One day later, after the gel coat cured, we went on laminating several layers of glas fabrics to stiffen the mold. We started with filleting the corners and filling the surface with thickened epoxy resin (glass shred and cotton fluffs). This reinforces the corners substantially and prevents air bubbles. Then we laminated four layers of glas fabric (two 160 g/m² and two 280 g/m²). Each layer of a given weight was laminated with two different orientations (0°/90° and ±45°) to obtain a quasi-isotropic laminate. We would have wanted to keep on with the next two layers of 390 g/m², but it was late enough (about 3 o’clock in the morning!), and we, thus, decided to stop and close the session with a layer of peel ply:

 

Two days later, we laminated the two remaining layers of 390 g/m² (quasi-isotropic), glued the core material and cured everything in vacuum. This time we wanted to get sooner to bed, but to be honest, we had a terrible time to build enough vacuum. Somehow it was again 3 o’clock in the morning and we were still looking for a large leakage. As in the last session, we had to get up at 7 o’clock the next morning and get to work… A consequence of this, was that I decided to buy a stronger vacuum pump with much more volume flow!

Anyway, we started to get everything ready for the next and final layers of the sandwich. I separated the external ribs and trimmed the surpluous border. We hope to end this side of the mold this week.