An alternative method of making fiberglass multilayer hand layups
Note: This article was drafted by Sven Ericksson, an Express builder in Sweden, and published in their EEA chapter publication. I had sent him several letters that gave him the basic information from which to draw the following instructions titled "Method".
Sven Ericksson
Abstract: A method to make multilayer fiberglass hand layups in a convenient way is described. The method has several advantages compared to traditional hand layup.
Background: Traditional fiberglass hand layup method consists of making one dry layer at a time and soak this layer with resin before proceeding with the next layer.Drawbacks using this method are:Time consuming, easy to use too much resin, hard to keep track of exact positioning of the different layers in a multilayer layup, hard to get all airbubbles out from the matrix (resin/fiberglass composite) especially the very small airbubbles. Due to this drawbacks a new method was developed to avoid theese problems.
New method description: The layup procedure starts with drawing an exact template for the final laminate on a transparent nylon film. This nylon film is the same used in factory vacuum bagging of prepreg composite materials. The nylon film is cut oversize compared to the final laminate. All fiberglass layers needed are then cut slightly oversize or to exact size depending on if the edges are accessible for trimming or if they are buried inside other layers. Weigh all fiberglass and eventually peelply layers. Place all neccessary layers on the template in their final position outmost layer first. Catalyze an amount of resin that by weight is 10% more than the fiberglass/peelply layers and spread it in batches on top of the fiberglass layers. Let the layers soak what amount of resin they will take. Calculate about 90 seconds/layer to soak through. When the surface tends to become dry pour on more resin. At the stage when all layers have been wetted out it is possible to see through the whole laminate down to the drawn template underneath. To proceed put on another nylon film on top of the last layer and work any trapped air and excess resin out to the edges. The top nylon film makes the laminate almost as clear as a window and makes it possible to see through at least 20 layers of 9 oz/sq yd fiberglass. Trim the laminate to exact size using a large scissor to cut at the edges of the drawn template. Remove the upper(last) layer of nylon film and transfer the laminate pack to its final place and put it on. Do not prewet the surface where to put the laminate pack as this will make the surface "sticky". As before but now using the bottom nylon film as your "window", work any trapped air out. Eventually trapped air is trapped between the bonded surface and the laminate as there are no air inside the laminate at this step. When pleased with the result, remove the nylon film with the drawn template on it, clean up the surface with a brush and apply eventually needed layers of peelply. The peelply must be wetted out from the outside or else it will soak resin from the layer beneath eventually ruining the result by getting to lean on resin.
Comments:
Your resin pot life and your skill will determine how many layers you will be able to wet out at a time.
When leaving the fiberglass to soak resin by itself you get almost no entrapped air inside the laminate and what is left is easily removed
by working on the nylon film with your fingers, a stiff brush, an acetone soaked rag or a squegee.Compared to layer by layer layup, the amount of resin used will be about 10% lower.
As you wet all layers out at one time the time saving will be tremendous when laying up three or more layers.
Using an inhibitor for your resin to slow down the curing process
will be a great help when laying up many layers at a time.Contact the manufacturer of your resin to get information in this matter. If you have resin that is slow from the beginning this paragraph will not be applicable.
This method is only compatible with resins capable of soaking through multiple layers of fiberglass. Use of high viscosity resins is generally not possible.
The described method is not usable on kevlar or graphite as these materials do not become transparent when wetted out.
When getting familiar with this method you will be able to adopt this basic nylon film "window" technique on slightly different laminates where it is not possible to use the technique exactly as described.
The essence of this method is:
1.The laminate will take whatever amount of resin it needs thereby reducing the amount of resin nedeed.
2.The ability to see through all layers at once is the reason of getting a high quality layup free from entrapped air.
3. The time saving makes it possible to make bigger jobs in far less time and without someone else helping you.
4. Using the template to cut the fiberglass after being soaked with resin increases the precision of the lamination made.
Editor: Contact: Sven Ericksson at "research@researchelectronics.se"