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Hanaldo
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MEKP also happens to have a specific gravity close to 1, so it is accurate enough to measure by weight or volume.
This may be the case with some epoxy resins, the specific gravities of one or both of their components may happen to be close to 1 as well, which is why you might get away with measuring by volume for some products. I can assure you this isn't the case for all epoxies, and in fact the way epoxies work mean that going off ratio doesn't necessarily mean the product won't cure hard to the touch, but rather it won't achieve its quoted mechanical properties. All well and good for cosmetic parts that just need to be hard and shiny, but for parts that need to perform mechanically - be accurate with the mix.
I met a man once, a chemist who was far cleverer than me. He knew how to manipulate epoxies to give it properties that he wanted, not just make it achieve what it was designed to do. He used to use an entry level epoxy, very similar to West System, and by going off ratio and using hardeners from different resin systems, he was able to make products like bullet proof sheeting from just a solid block of resin, no reinforcement. There's a company here that bought his recipe and is now using it to produce bullet proof windows and intrusion panels for the military. He even claimed to have come up with a mix that was 100% UV stable and would never yellow, though I never personally saw that product and remain a bit skeptical despite knowing how clever he was. Unfortunately he passed away last year and took all that knowledge with him.
Anyway, unless you are an experimental chemist who knows how to combine bisphenols and amines to get a material that does what you want - read the instructions and stick to them!
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Warren (Staff)
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+xOn the subject of weight versus volume, what are the densities of IN2 and hardener. I have been using accurate paint shop measuring beakers and they seem just fine. MEKP a catalyst and just activates resin as opposed to IN2 and hardener where both constituents react together to create a solid resin. The densities for each hardener and the resin are on the TDS. However they are not fixed figures but a "range" which means one batch could vary slightly from the next. Also density varies at temperature . This means mixing by volume has more potential for error than mixing by weight on accurate scales.. That is why the vast majority of our resins are measured by weight. Easy Composites / Carbon Mods - Technical Support Assistant
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Warren (Staff)
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+xJust a minor quibble. It’s great that you stick to parts by weight. But then you provide syringes for things like the MEKP hardener, which of course dispense by volume.I know...could always use the syringe to withdraw a volume then weigh it...but that kind of defeats the object of having the syring in the first place in that we need a very accurate balance for such small quantities. Also, your syringes are really, really poor (sorry but they are) in that the action is not at all smooth so you end up with a kind of “all or nothing” dispenser.I don’t believe in having a whinge without suggesting a solution...so have you thought about pipettes instead? You can get one piece plastic ones with bulbs these days, or go down the glass and separately bulb route if the materials might dissolve plastic. They won’t be graduated of course, but as mentioned above, if you always specify addition by weight that doesn’t matter - unless you can furnish us with a list of product specific gravities? The reason for using the syringe with MEKP is that its density is almost exactly 1g/cm3 which means 1g is same as 1cm3 and thus it matters not how the MEKP is measured. Due to the tiny percentage used of MEKP it can be hard to measure accurately on measuring scales where as a syringe can be more accurate for such small measurements. The syringes are medical grade syringes so should be reasonably usable although I tend to find using both hands is the smooth way of doing it. Easy Composites / Carbon Mods - Technical Support Assistant
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David Vale
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I have constructed a 'warming cabinet' out of Celotex (could use Kingspan or anything similar. The smallest oil filled radiator from Machine Mart with a thermostatic control works just fine in my unheated workshop. At UK current ambient temperatures nothing is going to cure. For smaller parts a cheap Dunelm electric blanket and an airing cupboard raided duvet works really well too. It is not difficult to keep the temperature in the mid 20's, don't go too high though as the PVC vac tube just collapses.
On the subject of weight versus volume, what are the densities of IN2 and hardener. I have been using accurate paint shop measuring beakers and they seem just fine. MEKP a catalyst and just activates resin as opposed to IN2 and hardener where both constituents react together to create a solid resin.
Retired - Thank heavens, and still don't have enough time during the day
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oekmont
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+x[quote]Just a minor quibble. It’s great that you stick to parts by weight. But then you provide syringes for things like the MEKP hardener, which of course dispense by volume.
Ec
Exactly. The important point here is "for mekp". Unlike epoxy "hardener" mekp is actually a hardener. The final structure of solid polyester is solely build of the resin component, mekp just starts the reaction. Therefore you can slightly change the mekp ratio, wich will affect the curing time. Anything between 1,5 and 2,5 % should be fine.
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martynball
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+x+xThanks for that information this has helped! My eproxy mixture has been at room temperature, however, heating has been off, so that can go down to 2 degrees! So I doubt the mixture is correct. It has been about 48 hours at least now. I will try another mixture and start again  They where only small 1CM by 0.5CM stickers anyway. OK but what resin and what hardener speed were you using? - Also, an ambient temperature that could have gone down to 2'C would certainly stall the reaction - at this temperature the resin would stay uncured for months. If you're using the IN2 resin (for example) with a slow hardener then that would take more than 48hrs to cure at 15'C so it still might be OK, just in desperate need of some warm curing conditions. Using your EL2 Laminating EProxy. The ambient temperature may not get that low to be honest, however today it was -2'C outside and the heating hasn't been on most of the day whilst we where all at work, so it would have been pretty cold. I will make another mixture and make some more but leave the ones I have made to one side see if they cure, I keep on touching one of them and it's still pretty tacky.
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GreyArea
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Just a minor quibble. It’s great that you stick to parts by weight. But then you provide syringes for things like the MEKP hardener, which of course dispense by volume.
I know...could always use the syringe to withdraw a volume then weigh it...but that kind of defeats the object of having the syring in the first place in that we need a very accurate balance for such small quantities. Also, your syringes are really, really poor (sorry but they are) in that the action is not at all smooth so you end up with a kind of “all or nothing” dispenser.
I don’t believe in having a whinge without suggesting a solution...so have you thought about pipettes instead? You can get one piece plastic ones with bulbs these days, or go down the glass and separately bulb route if the materials might dissolve plastic. They won’t be graduated of course, but as mentioned above, if you always specify addition by weight that doesn’t matter - unless you can furnish us with a list of product specific gravities?
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Matt (Staff)
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+xThanks for that information this has helped! My eproxy mixture has been at room temperature, however, heating has been off, so that can go down to 2 degrees! So I doubt the mixture is correct. It has been about 48 hours at least now. I will try another mixture and start again They where only small 1CM by 0.5CM stickers anyway. OK but what resin and what hardener speed were you using? - Also, an ambient temperature that could have gone down to 2'C would certainly stall the reaction - at this temperature the resin would stay uncured for months. If you're using the IN2 resin (for example) with a slow hardener then that would take more than 48hrs to cure at 15'C so it still might be OK, just in desperate need of some warm curing conditions.
Matt StathamEasy Composites / Carbon Mods - Technical Sales
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martynball
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Thanks for that information this has helped! My eproxy mixture has been at room temperature, however, heating has been off, so that can go down to 2 degrees! So I doubt the mixture is correct. It has been about 48 hours at least now. I will try another mixture and start again They where only small 1CM by 0.5CM stickers anyway.
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Matt (Staff)
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+xI have made a mixture and it's been drying for 24 hours, however its still tacky, im assuming I have not used enough hardner? Sorry Martin, I forgot to add an answer on this last question; if you have resin that's still not cured after 24hrs and you would like to know if there's a problem then we'll need a little more information on what resin you're using and what your cure environment is like. You mention a 100:30 mix ratio so you're most likely to be using our EL2 laminating epoxy or IN2 infusion epoxy but we also have a choice of hardener speeds on those systems too. Please confirm what resin and hardener you're using and also what the ambient cure temperature is (for the whole cure time) and I'll let you know if you have a problem.
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