Make a fiberglass fan shroud
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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) | ||
| + | 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 psrt 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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| + | 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 laternate 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. | ||
| + | Graphite - 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 epoxy resin in shiny female molds. Is fairly brittle so commonly has a layer of aramid cloth 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 waht you get if you dont specify anything else. Fine for 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. | ||
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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 winch 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! | ||
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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. | ||
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| + | '''Vinyl Ester''' - this is a stronger version of polyester resin and somewhere between polyester and epoxy in strength. Not needed in what we do. | ||
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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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| + | 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. | ||
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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=] | ||
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