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| | Also, if I was going to make several of these parts, I could sand and polish the surface, wax it, and use it to create a mold with which I could duplicate it many times over... | | Also, if I was going to make several of these parts, I could sand and polish the surface, wax it, and use it to create a mold with which I could duplicate it many times over... |
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| − | --[[User:Willys36|Willys36]] 10:47, 5 September 2009 (MDT)
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| − | == '''General Comments on Fiberglassing''' ==
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| − | You may wonder how many layers of mat to use; what kind of mat or cloth to use, etc. There isn't a single answer for all parts. The shroud shown in this excellent how-to is mainly for form and has little strength requiremants so can be laid up with just the chopped strand mat. However if it were a body part or some other part that would see some stress, the design should include one or more layers of woven cloth which is many times stronger than the mat.
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| − | '''Chopped strand mat''' as shown above is rated in ounces/ sq ft. It commonly comes in 3/4, 1.5 & 2 oz/sqft thicknesses. The 2oz is probably most polular because it builds thicnkness quickly. The lighter thicknesses are obviously for smaller, more delicate applications. For most car parts, use the 2oz. This material should always be used as a first layer in a finely finished mold such as a boat hull where there is a gel coat layer (final finish colored resin layer) then the 'glas. If you lay a layer of woven cloth directly under the gel coat it will 'print' through the gel coat and you will always see the pattern of the cloth no matter how much you sand and polish. The random pattern of the chopped mat strands isolates the cloth pattern from the final surface. Again, in the 'male' mold shown above this isn't a consideration.
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| − | '''Surface Veil''' - There is a special type of chopped strand mat called veil. This stuff is very thin and light weight and is used as the first layer under gel coat,even before the 2oz mat and does even a better job of providing a finer final finish in the gel coat. It give no strength or bulk, just a finer finish. I recommend using it where gel coats and polished female molds are used.
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| − | The woven materials come in a confusing array of weights and weave patterns, all with a special purpose.
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| − | '''Woven Roving''' looks like your great Aunt's front door mat. It is woven with very coarse strands in a 90deg pattern and it's purpose is to build bulk fast while providing superior strength compared to chopped strand mat. It is quite thick and due to its weave and big strands doesn't lay around corners and doesn't bond well to other layers. It also loves to print through its weave pattern to ruin gel coats. It should be used in boat hulls, not car parts. If you insist on using it for building thikc parts, always lay it w/ alternate layers of 2oz mat to improve bonding.
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| − | '''Woven cloth''' is the star of strong FRP construction. It strangely is sized in ounces per square yard instead of square foot and comes in weights from 1/4oz/sqyd to 10oz/sqyd. It comes in '''plain weave, satin weave, 8-hs weave''', other?, patterns. Get the plain, it's plenty strong and cheaper. I usually use 1.5oz. This is what you want for 99.99% of your high strength layups.
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| − | Other cloths available for special purposes are several,
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| − | '''DBM''' - dual bias mat roving which is two roving mats stitched together with the weaves @ 45deg for morhe strength. For the boat guys, not us.
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| − | '''Graphite''' , also called carbon fiber- really exotic looks purty and necessary for the 350mph crowd, not so much for us shade tree guys. To be purty, must be laid up in vinyl ester or epoxy resin in shiny female molds. Is fairly brittle so commonly has a layer of aramid cloth or fiberglass for toughness. Ths stuff is sized in thousands of filaments, i.e. 1K, 5K, 12K, etc.
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| − | '''S-glass''' or '''E - glass''' - these are high quality woven glass that is measurably stronger than regular woven fiberglass. More expensive and not necessary in most of what we do.
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| − | '''Aramid''' - also called '''Kevlar''', this stuff is amazingly strong and tough. It is so tough, it is almost impossible to cut! It is used as strength enhancer in very light weight applicatiosn that need extraordinary strenght. Again, it is overkill for just about anything we do.
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| − | '''Unidirectional''' - like it sounds this is a specialty cloth that has most of its strands in one direction. It is sewen together and for special applications. Can be made of any of the above threads. We don't need it.
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| − | Resins available are,
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| − | good old '''polyester resin''' - use for 99.99% of what we do. It come in several types -
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| − | '''Ortho''' (made with orthopthalic acid) is what you get if you don't specify anything else. Fine for most everything we do.
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| − | '''Iso''' (made with isopthalic acid) bonds a little better than ortho but costs more and again ortho is fine for our tasks. An added benefit to using "iso" resin is that it is more heat resistant than ortho resin, it will withstand 210* F as opposed to 170* f for most ortho resins. Iso resin is also called "tooling" resin, because it is designed for moldmaking, and can withstand many heat/cool cycles and remain dimensionally stable.
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| − | '''Waxed resin''' - be sure you check whether you have 'laminating' or 'finsinh coat' resin. The former is just plain resin and is used for laying up several layers. Every layer will stick to the previous one very well. The latter contains a wax that floats to the surface of the finisned part and, if used in laminating layers, will prevent the layers from bonding causing part failure. These two resin mixtures are necessary. Polyester resin will harden all the way through except for the very outer surface which is exposed to oxygen. This exposure prevents the resin from hardening and results in an irritating sticky feel to the surface. Using the waxed resin in the final layer allows the wax to float to the surface, insulate the surface from oxygen, allowing it to fully harden. I only use laminating resin and and sand off the outer surface or prime it which seals and hardens it. No biggie, don't worry about it, just be careful to not laminate with finishing resin! Another common name for this resin is "sanding resin".
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| − | '''Gel coat''' - this is resin filled with a high solids usually colored pigment. It can either serve as a primered surface to be sanded and painted or as in the case of boats, can be the final colored finish. It is sprayed in a polished female mold without reinforcement, then 'glas is laminated on it. It is much softer than plain resin and works like a sanding primer. Good stuff.
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| − | '''Epoxy''' - much stronger than polyester but more persnikety (I think that's a word!) and expensive. Also check with the supplier for compatibility 'cause some cloths won't work with some resins. I would only use this for looks if making a carbon fiber part. Epoxy resin is also tough on skin and your respiratory tract, and is much harder to work with, vacuum bagging the parts when laminating is commonly used with epoxy, because it is so much harder to remove air pockets with rollers or squeegees.
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| − | '''Vinyl Ester''' - this is a stronger version of polyester resin and somewhere between polyester and epoxy in strength. It has the ease of workability of polyester and compliments the strength of fiberglass much better than polyester. Not usually needed in what we do. Vinyl ester is much more heat resistant than either of the polyester resins, and also chemical resistant. It also shrinks alot less, so print-through is less of a problem. If you want to easily make some very strong, rigid and lightweight parts, use vinyl ester resin, along with either fiberglass mat or cloth, and add a layer of 6 oz carbon fiber in the middle of the laminate.
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| − | As far as how much to use depends on the part you are making. If I were making that fan shroud I would lay up two layers of mat over most of it and reinforce all the edges with a third layer. All 2 oz mat. This would give a very light weight body, a little less than 1/8" thick and stronger edges a little more than 1/8" thick.
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| − | There are also many cores available for use in FRP laminates, use of a core can increase the rigidity of a part without increasing the weight or tendancy of thick parts to get mottled after time and exposure to heat. Some of the cores you can use are:
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| − | '''Balsa wood''', this is used in large flat areas and needs to be bedded in...not really a good choice but it is one of the oldest cores. Boatbuilders used it extensively for reinforcing large flat areas such as decks, hull bottoms and cabin roofs.
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| − | '''Coremat''' is a material that looks similar to the absorbent paper shop rags that come in a roll, it's made with fiberglass and microballoons, along with a binder. It's mich more flexible than balsa, and it comes in several thicknesses, 3mm, 5mm, and 8mm..This you lay up into your part, just like another layer of matt or cloth, then put another layer of mat over the top.
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| − | '''Urethane foam'''..this comes in varying thicknesses, and is used much like balsawood.
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| − | Use a core anywhere you have a large flat or gently curved area, roofs, hood tops, floorpans, bellypans. The underside of fenders above the tires is a good place to use coremat, as it will provide a cushion against stars from rocks being thrown up by the tires.
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| − | A body part would need a couple layers of 2oz mat, a layer of 1.5oz plain weave cloth and possibly a third layer of mat, depending on size. Again reinforce edges as required with a strip of mat. You can also reinforce edges with woven tape, this puts many continuous unbroken filaments parallel with the edge of a part, and will make it much more resistant to cracking from the edge in.
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| − | I made a shell for the headliner of my '53 Chevy pickup and used only 2 layers of mat (about 3/32" thick) for light weight and flexibility. It is more than strong enough. See it here [http://www.hotrodders.com/forum/journal.php?action=view&journalid=2439&page=25&perpage=5&reverse=]. This is also an example of a part made from a finished mold (the painted roof of the truck), but without the gel coat since it is coverd with upholstry and doesn't need a paitable finish.
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| − | A comment on using polyester resin - you can adjust it's hardening time somewhat with the amount of MEKP hardener you add. The more hardener, the faster it sets. You can add too little hardener and it will never set. It isn't that scary, there is a pretty wide range of hardener concentration that works fine. If you have a piece that isn't setting due to cold weather or short hardener you can set the piece in direct sunlight. UV radiation will set off this resin seems like no matter how much hardener is used. Be careful with this though, the resin setting chemistry gives off a lot of heat and too thick a part, too much hardener and/or solar acceleration can get the thing smoking and even start a fire! Closest I came to that was mixing several batches of resin in a row in a tin can and just starting the next batch on top of a gelling existing one. Got to about half a inch thick and it started bubbling, smoking and WAY too hot to touch the can.
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