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morepower
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Either way, infusion or pre-preg needs some form of clear coat to protect from UV. The time it would take to make one of my monocoque seat and fuel tank units with infusion would make the thing a lot more effort and being a 5 piece mould sealing all the joints and getting resin feeds into the almost blind seat hump would be too awkward. Infusion has its place in really large and less complex parts but it is not half the cost of pre preg.
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wozza
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I regularly have customers asking for parts in pre-preg (which I also do) but when you actually ask them why they want it in pre-preg they don't actually know. They have read on some "go faster forum" that is what they need. Also you failed to add into your costings clear coating your parts against pin holes / UV. If you clear coat after the part is cured then you are only getting a mechanical bond and is more likely to chip and peel off. If you apply something like GC50 into the mould before Infusion then you get a chemical bond and the clear coat becomes integral to the part. I also doubt very much that the average home builder using pre-preg is producing parts 20% lighter and stronger than those using infusion. The real cost saving for manufacturers producing parts from pre-preg is labour cost's, they can use semi-skilled people to "assemble" pre-preg parts using pre cut layers of reinforcement etc as apposed to employing skilled laminators.
Carbon Copies Ltd
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morepower
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Warren (Staff) (22/08/2013)
Its horses for courses at the end of the day.
Sure no ones doubting that pre-preg parts are the pinnacle of the industry at the moment.
But twice the material cost for something thats maybe 20% stronger and lighter.
Clearly not worth it for most people for larger panels. But it does have its place for smaller, complicated parts where material cost isnt such an issue.Twice the cost?? Dry cloth is about £20 per sq/m and resin works out about another £5 per sq/m Plus you need pipes and other consumables spiral tube and infusion mesh which is just under £6 per meter and there will be some extra resin wastage in the pipes through to the catch tank. So that is up to about £31 per sq/m plus VAT. Pre-preg can be had for between £36 and £48 per sq/m depending on which material you have and the PRF material is good enough for most people at less than £40 per sq/m.  This is using a pre-preg that cost less than £40.00 per Sq/m and a motorcycle body kit is anything but small... But I have a week to lay up the parts and can take my time getting it all done.  The equipment when laying up is no different to wet lay vac bagging so you can do both for no extra cost... My "oven" cost me £27 for the PID, Solid state relay and sealed electrical box, thermocouple and a £40 3kw fan heater... I can either use simple card board boxes for small parts or a clean garden wheelie bin for larger parts then if you have space you can use Kingspan insulation to make a large oven and only need to get a better fan and some ducting. That would cost about £400 to build and you can still use the heater and controller ect with any oven you build of varying size if you want as it will work with any box. One other thing I would use, but many dont, a remote wireless display meat thermometer to just check the temp of the actual part too... So the set up is a little more than setting up for infusion but there are less ongoing consumables needed and you have parts that are 20% lighter and stronger. The cost of materials is possibly 25% more expensive but when you look at the value of those parts if you are going to sell them many would rather have simple wet lay for cheapness or if they want the real deal only pre-preg is going to get the highest prices.
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Warren (Staff)
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Its horses for courses at the end of the day.
Sure no ones doubting that pre-preg parts are the pinnacle of the industry at the moment.
But twice the material cost for something thats maybe 20% stronger and lighter.
Clearly not worth it for most people for larger panels. But it does have its place for smaller, complicated parts where material cost isnt such an issue.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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wozza
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morepower (20/08/2013)
carboncactus (20/08/2013)
Breather tows are not necessary with VTF, and probably not with the easypreg surface layer, as this surfacing system actually has black glass threaded into it. Any other material, and I always use them:  Me and Wozza will agree to disagree on this one though: I do believe prepreg is more advanced than resin infusion. Mainly because the resins in prepreg are more advanced in their nature. The fact that they cure at a higher Tg and are therefore more viscous, means the curing cycle is that much further ahead and mechanical properties are better. Going further in terms of resin performance, there's a high temp structural epoxy prepreg that Im gonna sample soon which has a Tg of 320C (  ) For it to have those characteristics means the resin in the prepreg is so viscous, its actually in a B stage form. It cant even be handled by hand, it has to be pressed. On the other end of the scale, resin infusion in its nature uses watery, much weaker resins. To get equally performing parts, you have to use more material with infusion, making it heavier. That along with the fact that you can choose any carbon cloth to make your part. With prepreg, the standard modulus for fabrics used are much higher. I do agree that you can probably control the resin ratio used (apart from what lands in the catch pot and what is left in the feed pot, but with prepreg if you want to lower your resin content, you can use a peel ply. You wouldn't want to lower it anymore than that though. An interesting trial was made by Gurit. They made some blades by infusion and prepreg. Conclusion: prepreg blades outperformed infused blades in mechanical properties and production value (20% more blades produced in the same amount of time). Infused blades cost less in materials, although prepreg cost less in labour. Not to diss infusion though. I think its got its place (bonnets, boat hulls etc). Just because I don't do it day to day doesn't mean I wouldn't chose it for a particular job if it called for it. . What he said...
Lets face it F1 chassis are not infused and Pr-preg is the material of choice for the highest spec parts.. I wouldn't think I could get my seat/fuel tank down to less than 3Kg and be structural any other way.... |
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compositepro
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320c TG are you sure its not from Tencate your description of no tack sounds very familiar and we use it at the AMRC If it is you they do BMI's that can go as high as 400c TG
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morepower
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carboncactus (20/08/2013)
Breather tows are not necessary with VTF, and probably not with the easypreg surface layer, as this surfacing system actually has black glass threaded into it. Any other material, and I always use them: Me and Wozza will agree to disagree on this one though: I do believe prepreg is more advanced than resin infusion. Mainly because the resins in prepreg are more advanced in their nature. The fact that they cure at a higher Tg and are therefore more viscous, means the curing cycle is that much further ahead and mechanical properties are better. Going further in terms of resin performance, there's a high temp structural epoxy prepreg that Im gonna sample soon which has a Tg of 320C ( ) For it to have those characteristics means the resin in the prepreg is so viscous, its actually in a B stage form. It cant even be handled by hand, it has to be pressed. On the other end of the scale, resin infusion in its nature uses watery, much weaker resins. To get equally performing parts, you have to use more material with infusion, making it heavier. That along with the fact that you can choose any carbon cloth to make your part. With prepreg, the standard modulus for fabrics used are much higher. I do agree that you can probably control the resin ratio used (apart from what lands in the catch pot and what is left in the feed pot, but with prepreg if you want to lower your resin content, you can use a peel ply. You wouldn't want to lower it anymore than that though. An interesting trial was made by Gurit. They made some blades by infusion and prepreg. Conclusion: prepreg blades outperformed infused blades in mechanical properties and production value (20% more blades produced in the same amount of time). Infused blades cost less in materials, although prepreg cost less in labour. Not to diss infusion though. I think its got its place (bonnets, boat hulls etc). Just because I don't do it day to day doesn't mean I wouldn't chose it for a particular job if it called for it. . What he said...
Lets face it F1 chassis are not infused and Pr-preg is the material of choice for the highest spec parts.. I wouldn't think I could get my seat/fuel tank down to less than 3Kg and be structural any other way....
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carboncactus
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Breather tows are not necessary with VTF, and probably not with the easypreg surface layer, as this surfacing system actually has black glass threaded into it. Any other material, and I always use them: Me and Wozza will agree to disagree on this one though: I do believe prepreg is more advanced than resin infusion. Mainly because the resins in prepreg are more advanced in their nature. The fact that they cure at a higher Tg and are therefore more viscous, means the curing cycle is that much further ahead and mechanical properties are better. Going further in terms of resin performance, there's a high temp structural epoxy prepreg that Im gonna sample soon which has a Tg of 320C ( ) For it to have those characteristics means the resin in the prepreg is so viscous, its actually in a B stage form. It cant even be handled by hand, it has to be pressed. On the other end of the scale, resin infusion in its nature uses watery, much weaker resins. To get equally performing parts, you have to use more material with infusion, making it heavier. That along with the fact that you can choose any carbon cloth to make your part. With prepreg, the standard modulus for fabrics used are much higher. I do agree that you can probably control the resin ratio used (apart from what lands in the catch pot and what is left in the feed pot, but with prepreg if you want to lower your resin content, you can use a peel ply. You wouldn't want to lower it anymore than that though. An interesting trial was made by Gurit. They made some blades by infusion and prepreg. Conclusion: prepreg blades outperformed infused blades in mechanical properties and production value (20% more blades produced in the same amount of time). Infused blades cost less in materials, although prepreg cost less in labour. Not to diss infusion though. I think its got its place (bonnets, boat hulls etc). Just because I don't do it day to day doesn't mean I wouldn't chose it for a particular job if it called for it.
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morepower
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I agree with much of what Warren has said... I have never put glass tows on the flange area under the pre-preg... I understand that moulds heat up slower than the oven too so the ramp could be lower or at the right rate as the material needs... But if the mould is not thick enough it can heat up too quickly. So I always try and make the oven (cardboard box, wheelie bin or actual oven) heat up slowly to give the material the best chance. Although I do think de-bulking after the first couple of layers are put down does give a better part and having a perfect bag and not rushing to lay it then cook it. Take your time with the whole process. Lay down the first couple of layers, de-bulk, next couple of layers or final layers and de-bulk overnight before cooking it... If you have more layers bag it and de-bulk for every 2 to 3 layers if you have a thicker part.. But always make sure the bag is good and leave the pump running... If you are getting "smoke" or vapour from the pump you have a leak and really need to find it... The better the bag the better the part.. When you cook the part dont let it heat up too fast too.... I would say dwell it at 65 degrees for an hour too... before heating it up any higher... Also always work to the temperature of the part NOT the oven... One of these works fine but if you get one test it with boiling water and ice to check it is accurate. If it is accurate tape it to the part and work from this... It will give you better parts even working from home.... But it is mostly down to technique and taking your time... This part is not going to be seen so the mould was dull and is made using an out of autoclave carbon that is not supposed to give a good cosmetic finish.. But it worked perfectly with no pinholes at all...  Here is a cosmetic Out of Autoclave parts finish in a polished mould and it works perfectly fine if you take your time and do try and control how it cooks and do not rush... (No it has not been lacquered either this is out of the mould) I do work from home too even though I do have access to a larger oven for my bodywork.. but the smaller first part was made at home and cooked in a cardboard box oven..... 
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Warren (Staff)
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nothing wrong with the OP's tips and they sure do have thier places in the higher levels of advanced composites.
Use of carbon and woven materials the process' used with them are by industry standards "advanced".
most the composites industry is still using pikey spec chopped strand mat wet laid with polyester..............
Spike rollers and breather tows are something we have never had the need to use at this level. Im not sure there would be significant benefit in advising people to do it either.
Same with "issues" around ramp rates and dwell times.
Sure on large production scales and in critical industries where you need the ultimate reliability, consistancy during manufacture etc it may well be a necessary process to ensure minor faults dont screw up a large expensive layup. However that is not the case for most of our customers.
The pre-pregs we use and sell, we generally have never had issues with ramp rates needing to be too critical or dwell periods. Perfectly good parts are being achieved daily both by us, and more importantly our customers with the techniques we advise currently.
Not saying we don't welcome further advice and ways to improve, we do and update things as and when. But we also don't want to make things complicated when in practice its not necessary for most of the people using our products.
As said before, many techniques and processes have thier place, albeit with overlap.
As an example, in our workshop once we had got some experience of the pre-pregs we use, we can just put them straight into our oven (which is on all the time) with no ramp up rates or similar. The reason we "get away with it" is because a room temperature mould of any reasonable size will naturally have a reasonable temperature ramp up rate as it absorbs heat from the oven anyway.
Im sure some people will find your guide useful so we welcome extra information and advise, however what may work for you and seem the only "professional way" to do something isnt necessarily the case for others so would prefer people to be more open minded rather than saying "x is wrong, y is right, z is un-professional etc". We try to keep it friendly here so more discussion the merrier!! We don't want to end up like some other composites forums where people get dissed and slated for not doing things one way or another.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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