Carbon fiber hoods?
10-28-2010, 06:03 PM
#1
Registered User
Thread Starter
Carbon fiber hoods?
im about to get a carbon fiber hood for my rx8. ive been wondering what the difference is between a regular carbon fiber hood and a dry carbon fiber hood?
10-28-2010, 07:03 PM
#10
here you go....
wet/dry doesnt refer to how the final product looks. it refers to the state of the material as it is applied to the form.
there are two basic ways of laying up composite (carbon fiber, fiberglass, kevlar and other aramids, etc.) forms.
wet layup:
you can get the raw woven cloth (which comes in many varieties of weights, weaves, densities, etc), mix up a big batch of resin (of which there are many different types...thermoplastic, epoxy, etc....all of which have their own specific formulations, etc. etc. etc.), wet out the fabric with the resin right on the form. it is literally fabric...you cut it out with shears and it lays over a form like a sheet of cotton cloth. put a big plastic bag around the whole form and pull it under vacuum, then wait for the whole mix to cure (set) before popping it off the form.
'dry layup' (in quotes because i've never heard it called dry layup--but, then i live in a hole, too). let's also call it prepreg:
prepreg is a method whereby the fabric is pre-impregnated with a very specific amount of resin at the factory with an very expensive and specialized impregnation machine. prepreg, because it is already dosed with resin, is much stiffer than raw cloth. typically you cut off strips and lay up the pieces on a mold, then bag, vacuum, and cook/autoclave the whole thing until the resin reactivates and cures. the autoclave exerts pressure externally to the composite onto the mold forcing the form. when it cools off it is done.
the drawbacks to wet layup are:
• messy
• time consuming
• there is a lot of post production (after the initial layup) work sanding out the imperfections due to the uneven application of resins. if you want that glassy, perfect, mirror finish you have to create it.
• typically heavier final pieces. because the resin is literally slopped onto the composite right on the form there are thick and thin spots. the surface thick spots can be sanded down. but, any thick spots on the inside of the mold are an unfortunate byproduct of the technique.
advantages of wet layup:
• much cheaper (that's about it)
disadvantages of prepreg:
• very very very expensive
• autoclaves can cost a $1/4 million easy
• the resins in prepreg begin to cure at the factory immediately upon production. so, they materials must be frozen immediately, transported frozen (very expensive), stored frozen (run your freezers 24/7), and only have a shelf life of 30-90 days depending upon the resin used (freezing only delays the inevitable)
• because it is so expensive to make/transport it doesnt really make sense to order small amounts....typically a roll will cost upwards of $8000, with transportation costs easily reaching $10,000-$15,000. and, you still have the short shelf life. so, you really need to be a big production user...not something for the hobbiest, or low production volumes.
the advantages of prepreg:
• very little post work. because the resin is premeasured, the results are almost perfect right out of the autoclave.
• typically lighter production pieces. because the resin is premeasured into the composite there are not thick and thin spots.
• low production time (compared to wet layup)
• no VOCs floating around the work area
wet/dry doesnt refer to how the final product looks. it refers to the state of the material as it is applied to the form.
there are two basic ways of laying up composite (carbon fiber, fiberglass, kevlar and other aramids, etc.) forms.
wet layup:
you can get the raw woven cloth (which comes in many varieties of weights, weaves, densities, etc), mix up a big batch of resin (of which there are many different types...thermoplastic, epoxy, etc....all of which have their own specific formulations, etc. etc. etc.), wet out the fabric with the resin right on the form. it is literally fabric...you cut it out with shears and it lays over a form like a sheet of cotton cloth. put a big plastic bag around the whole form and pull it under vacuum, then wait for the whole mix to cure (set) before popping it off the form.
'dry layup' (in quotes because i've never heard it called dry layup--but, then i live in a hole, too). let's also call it prepreg:
prepreg is a method whereby the fabric is pre-impregnated with a very specific amount of resin at the factory with an very expensive and specialized impregnation machine. prepreg, because it is already dosed with resin, is much stiffer than raw cloth. typically you cut off strips and lay up the pieces on a mold, then bag, vacuum, and cook/autoclave the whole thing until the resin reactivates and cures. the autoclave exerts pressure externally to the composite onto the mold forcing the form. when it cools off it is done.
the drawbacks to wet layup are:
• messy
• time consuming
• there is a lot of post production (after the initial layup) work sanding out the imperfections due to the uneven application of resins. if you want that glassy, perfect, mirror finish you have to create it.
• typically heavier final pieces. because the resin is literally slopped onto the composite right on the form there are thick and thin spots. the surface thick spots can be sanded down. but, any thick spots on the inside of the mold are an unfortunate byproduct of the technique.
advantages of wet layup:
• much cheaper (that's about it)
disadvantages of prepreg:
• very very very expensive
• autoclaves can cost a $1/4 million easy
• the resins in prepreg begin to cure at the factory immediately upon production. so, they materials must be frozen immediately, transported frozen (very expensive), stored frozen (run your freezers 24/7), and only have a shelf life of 30-90 days depending upon the resin used (freezing only delays the inevitable)
• because it is so expensive to make/transport it doesnt really make sense to order small amounts....typically a roll will cost upwards of $8000, with transportation costs easily reaching $10,000-$15,000. and, you still have the short shelf life. so, you really need to be a big production user...not something for the hobbiest, or low production volumes.
the advantages of prepreg:
• very little post work. because the resin is premeasured, the results are almost perfect right out of the autoclave.
• typically lighter production pieces. because the resin is premeasured into the composite there are not thick and thin spots.
• low production time (compared to wet layup)
• no VOCs floating around the work area
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