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Old 11-09-2010, 09:12 AM   #281 (permalink)
Varn
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Hi Donee
The biggest parts that I have made with vacuum bagging is probably on the order of 20-30 square feet with 20 oz of material. The fun begins when you can't get a vacuum because of leak. For the larger parts such as this, I would use a slow or ultra slow set epoxy. The trick I have found is to spray glue the reinforcement cloth to the mold. I have only had one time where I couldn't get vacuum and my part, a recumbent bicycle seat came out with too much epoxy.

If I were doing some production work vacuum infusion might be an advantage but thought it to be unnecessary for the size of and thickness of parts that were being made. Perhaps you might share some of your projects.


From an ecological point of view, composites are bad. Lots of hydrocarbons are used to make the epoxy Lots of industrial operations into make the cloths Lots of waste between the layup and final product.

In addition it is hard maintain a healthy work environment. The work should be done outside. 3wheeler knows.


Quote:
Originally Posted by donee View Post
Hi Varn,

The issue (for the benefit of others) is how fast you can mix, and apply it. Its open time is short, and defenitaly variable based on the shape of the mixed container, and the final shape of the part. The practicality of this, is that really good parts can only be made so big by a single person. If the epoxy is not at the same state of cure in layers, its not going to make a good part. That is, if you have one end of an object half cured, and then apply freshly mixed epoxy on the other end there is going to be a
"knit" line that is prone to failure.

Allot of the problem can be eliminated with the vacuum bagging technique called "vacuum infusion" The epoxy is pulled into the matrix uniformly and quickly by this method. Two people can impregnate structures up to 50 foot long in a matter of hours, with a superior build quality. There was a video on the internet of this done by a Dutch boat builder. It was quite remarkable how straightforward and undramatic the impregnation was, in comparison to traditional techniques such as hand-lay-up.

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