Wind turbine blade construction.
I have a wind turbine blade designed but now I need some help with designing blade construction. I mean how the blade should be made (fiberglass, carbon fibre, how many layers etc). How should I start solving this problem?
Ok that is good !
First of all you must make sure the mold you use is very clean and very smooth as well.
The first step would be to cover your mold with a genuine unmolding agent such as :http://www.smooth-on.com/Release-Agents-and/c9_1123_1169/index.html this will make sure that your casting wont bond with your mold. (make sure to follow specific instructions)
Choosing you resin to do fiberglass you have mainly 2 choices of resin, epoxy or polyester resin. I personally prefer epoxy resin because it is stronger when cured, it is stable (polyester dissolve foam and other kind of plastic material) and finally the odor is way more tolerable (polyester have a very strong chemical odor that travel a lot (doing this in your garage would perfume all the house). I had personally very good experience with west system epoxy (westsystem.com). Also necessary to use gloves, mask and protective glasses to work with fiberglass (also put ol cloth on because resin is hard to clean).
When the unmolding agent is cured the first layer to go on in the mold would be a gelcoat layer. The gelcoat is a more viscous resin that is going to create the external layer of the blade it is also the layer that is going to create a smooth fish surface on the blade. Gelcoat could be bought as his but personally I use my epoxy resin with a bit more of harder I wait a bit for the resin to begin to be more viscous and then I brush the resin on to the mold with a paint brush. (If you want to use more the one time your brush you must clean it with acetone (watch out very volatile stuff) but cheap brush that you throw away work well). If you when to have a colored finish on you blade you could ad pigment in your gelcoat.(this also help to make sure your gelcoat is uniformly applied)
Before doing anything else you have to wait that your gelcoat is partially cured this mean that the gelcoat is not liquid anymore but still tacky (it stick to your glove but does not stay on it). Along the curing process it is good to make sure that that the gel coat will not all run in the bottom of your mold. (If so brush it gently back up.)
The second layer to put in the mold would be a 6 oz fiberglass cloth, make sure that the cloth is well wet with the resin.(you can use brush, roll or hand to make sure the cloth is fallowing the form of the mold.) Also make sure your cloth oversize you mold by at least 1 cm (this will help to join the two half of the blade).
The third layer can be applied right away or when the other layer become tacky (if you wait until it is completely dry to apply another layer, you have greater chances to face delimitation (layer separate)). For the third layer apply a 6 oz fiberglass cloth with a 45 degrees rotation (first fiberglass layer had fiber in a 0 an 90 degree orientation, this one should be 45 and 135). This is to obtain a stronger finish product that would be stronger and more stable regarding temperature variation.
For the fourth and fifth layer use the 8 oz fiberglass cloth with the same fiber alignment pattern.
Finally I would add 2 layers of a multi direction fiberglass cloth (look like an assembly of many short fibers in a chaotic way.)
Then you should let all this cured for a couple of days.
To obtain the perfect resin/fiber ration the weight of the resin used should be equal to the fiberglass cloth weight. But to be able to use this ration you have to mold with a vacuum baging setting. But since this could be a bit complex I recommend using the resin you need without fallowing a given ratio. (this should be all right for what you do).
Finally free the two parts from there molds and glue them together with an epoxy compatible glue, let them dry and cut the excess remaining.
You should also think about the way the blade should attach to the hub because you could maybe find a way to include connection piece in the molding process.
Finally the connection method you are going to use may require some additional fiberglass or carbon fiber near the hub connection to reinforce weak points.
Hope this help… I you have any additional questions feel free to ask.
Ok so if it is for you backyard it going to be easier (you can afford to do thing approximatly and not spend time doing the time consuming calculs for composite materials).
The best composite material is without any doubt the carbone fiber cause it's light and strong so it fit perfectly you need for a wind turbine blade. However it is ... expensive so maby not the most cost effective for a backyard projet. So I would probably go for fiberglass maby a mix of 6 an 8 ox cloth.
The used technique to produc the blade will also have an influence on the number of layers you need to laminate... Do you intend to use a 2 parts mold to produce de blade or you going to laminate the composite on a styrofoam core ? Every technic have some + and some -. Do you intend to produce a one piece blade assembly or seperate blade that connect to a hub ?
Should be able to give more info when I got answer to those questions.