It seems there are so many advantages to use heat while curing, I definatley want to setup a couple of heatboxes, that will be safe to run in my basement, can have heat controlled, safety shut off, could be set up against the wall and otu of the way. What I came up with thus far is using foil backed insulation, heat lamps, and a heat controller (ones used for automated greenhouses??) that could turn the lamps on/off… If anyone has any suggestions feel free, If I work out a system I’ll post it here later on… Thx in advance
Once you’ve worked out your insulated box, it doesn’t take a lot of heat to warm up, so a small fan for circulation would be worth considering.
I will watch this thread with interest …
Honestly, WHO amongst us does not suffer from a cold shed / garage on winter days and at other times , too ? [eg: nightime glassing sessions]
You won’t need a heatlamp. 3 or 4 100-watt bulbs will bring your over up to the 100* or so you want…
I made a duct system out of cardboard that goes on top of my 2.5’x2.5’x11’ box - The lid lifts, and one side is “free” so I can move it out of the way if needed. I fit the duct to a small space heater w/fan - blows some warm air in/around, and I’ve left a gap at one end as an exhaust port - works great. As the others have pointed out, it doesn’t take much to warm up a small contained air space. Good luck.
we used to have one that looked like a giant coffin , with a blowy heater mounted in one end …
after a surf on a cold winters day we would be fighting one another for first shot in the oven , you could lay in it and be totally thawed out in 10 minutes …
it was the funniest thing , the first time one of the boys used it to warm up after a surf , he just went missing and no one could find him anywhere in the factory , when it was cold everyone would mill in the oven room just for warmth anyway , some one says hey why dont we get in the oven and warm up , then we all hear this voice from inside the oven , "im already in here , wait your turn " . it was one of those you had to be there things …
box with a fan heater is perfect …had a huge one once , could fit up to 12 boards under vac simultaneously , big industrial blowy heater , that filled a bottom compartment , then the heat rose through each succesive compartment …vac turn around was 2 hours …insane strength …
regards
BERT
turbo- im not sure of your budget or needs, but here is what ive done (im only on board 6):
go to home depot and get the pink xps FANFOLD insulation. i dont remember the price, but im cheap so i know it wasnt expensive. one piece is something like 30’x4’ and it folds into 2x4 sections. i split it in to two pieces- one gets wrapped around the glassing stands & board, the other rests on top. like a house of cards. with my glass stands, the 4ft width is high enough to go from the floor up to about 6 inches above the board. i use a salvaged electric space heater to warm it-
have a nice day,
john
To what extent is air circulation necessary for the curing of epoxy?
Any box reasonably sealed tight with a mini-space heater (with thermostat) will be fine for a hot box. But if it needs air refreshing it gets a little more interesting.
Quote:
You won’t need a heatlamp. 3 or 4 100-watt bulbs will bring your over up to the 100* or so you want…
If that - lets do the numbers on this:
Use 1" foil backed foam, R value of around 7
which translates to 1/7 BTU per square foot per degree F difference inside-out
Call this thing 2’x2’x10’ to make the numbers easy, 84 square feet total, or (84 x 1/7 ) 12 BTU per degree difference inside to out. Figure 50 degrees F to 100 F, 600 BTUs
to convert BTUs to watts, multiply by 0.29287 - call it 0.3
Pretty much smack on 200 watts. Go with 2" insulation and you are down to 100 watts, etc. This is under ideal conditions, perfect seals on doors and all that. I might go a bit higher to account for all that, or use a cheapo hair dryer and a thermostatic switch. That’d give you heat, air circulation and all in one small-ish package.
hope that’s of use
doc…
do you really need an oven?
During the summer it gets hot enough here in Ewa to make you go batty.
couldn’t you just leave your bag out in the hawaiian midday sun and get the same 2 hour turn around time?
I guess you could buy some of those aluminum tanning screen relectors or line a cardboard box with aluminum foil and just set it around the perimeter of your racks/rocker table with no top and leave it in the hot hawaiian sun to get the same effect… or am I off base ?? Need more heat? or heat and pressure to get the desired effect?
What would be the problems of leaving your bag out in the sun like that?
would you lose more vacuum as the plastic vinyl became more pliable under the sun’s heat?
I don’t like unattended artificially heated boxes made out of wood or paper that is precurser to a fire in your basement or garage in my opinion as it happens with unattended space heaters all the time. Combine that with resin and foam dust that would release poisonous gases upon combustion and I can see a fire code problem brewing big time for us home builders…
Also do you really get the same result in 2 hours that you would if you leave your work bagged under vacuum over night (24 hours) ?
Just need some clarification here…
thanks and sorry if this is a hijack but…as a side note
Bert…
Can I build my glass+balsa shells prior to adhesion to the foam? or do I need an autoclave to do this?
I was thinking of just vacuuming the glass+balsa shells to the boards I’m replicating first and then adhering the shells to the foam+wood perimeter shape after the shells have been formed… Seems like you didn’t want your shells to adhere directly to the foam core anyway and just wanted to attached them to the wood perimeter stinger/rails.
seems like you would build the shells and then vacuum glue/glass the top and bottom shells togethor at the same time so they would be fastened or as you say “pinched” togethor at the rail joint which is solid wood. Which why you also seal your EPS to prevent direct bonding/penetration of the resin to the foam. Can this really be done without a cast-iron or steel pressure autoclave like what surftech/gary young is using?
Again sorry to mess things up here…
Quote:
do you really need an oven?
Not everyone lives in Hawaii…an oven is quite useful here. I often do fin layups at 10 PM at night, air temp 50-55F…I pre-heat the epoxy, and it still doesn’t harden enough to sand in less than 24 hours. Plus, on rainy days you can’t use sun or outside, it is nicer to have a facility independent of the weather conditions.
However, if it works where you are, mo betta.
Another benifit is a controlled amount of time. I am constantly being pulled in one direction or another. Its difficult to get uninterupted blocks of time that fit into epoxies desire to be recoated before it cures (glass, wait not less that 12 hrs but not more than 24 hours, glass other side). With an oven I could glass, go to my son’s football game, then come home and glass the other side.
Can anybody recommend a good thermostatic switch? I looked online and couldn’t find what I wanted.
Bless you doc - I love the simple math to understand too. Thanks for always sharing.
turbojets
I have been involved on a number of large racing yacht projects, (hulls of nomex core with pre preg carbon skins over 100ft loa)These were cured at 100 oC for up to 12 hours in temporary ovens built around scaffolding using 2" kingspan(foil backed foam insulation) joints taped with aluminium tape and gaps filled with expanding foam, nothing grander than that! Don’t forget the floor too. Air circulation is essential to not get any hot or cool spots however it is heated. We use hot boxes big enough for 2 boards heated with a 2kw fan heater, reaches 40 oC+ easily on one bar, heat and circulation in one go, just don’t point the heater at your board! I do worry about distortion when board not under vacuum though.
Cheers
Mark
I have a cardboard box/aluminum foil setup…it works well. However I don’t like leaving the hair-drier or heat gun on alone while I’m not around. It would also be alot more efficient if I could do a lam and then come back 2 hrs later and its done. While the 2 hrs i have I can be foiling fins or working on another board. I wanted soemthing where I could be doing two boards at the same time, and where I didn’t have something going at all times. A small heat lamp and a thermostat, some which can controll fans/vents and heaters, as well as a cutoff switch could be a viable option. The bulb probably wont be on that much just heating it up and maintaining a temperature. Greg what temperature can the RR epoxy be heated to? what would be an ideal temperature for a cure? I was thinking about 110 degrees for around 2 hours. I also wanted something more durable then a cardboard box, somethign I could just set up once and not have to worried about for awhile.
PS. The water is about 40 degrees where I am, nights are about 50 now…during the winter, my basement is probably 40-50 degrees, it takes about 12-15 hours to full cure then…
Just also wanted to mention, that I would prob try other things as well such as using heat and pressure for different skins, or fins, ect. I was also planning on leaving it under vaccum for the time it was curing, possibly increasing pressure as it cures…especially doing final layers, where you already have you skin/epoxy monocoque, I would think it would take more to crush foam and distort the board.
how about just wraping your vac job in an electric blanket? my buddie who lives in nor. cal. wraps his boards up after the hot coat has kicked… he says it works great… be careful though.
i started a similar thread a few months ago, search it out. there were some good suggestions.
it is tough to find a thermostat that goes to 140F… there are plenty of “cheap” ones that go 1-10 but your looking at over $200 for one that you can actually set the temp… i’ll dig up the link…
my plan is to build on on wheels and use it as a wet out/balsa skin work up table…looks like i am never putting a car back in the garage…
De nada, man. I’m a simple man, so simple math comes easy to me.
Now… being a simple as in ‘dumb as a rock’ man, I work construction some winters. And there is an accessory ( around $40, see your local used tool store for cheaper ) that works with kerosene fired heaters as an inline thermostat which is something that keeps our butts from completely freezing: the fan-driven and electric sparked kerosene heater gets power or not, depending on the temperature. Put it inside the aforementioned box and I think it’s prolly control a set of light bulbs or a hair dryer or what have you. Hit Amazon and do a search for Reddy Heater Thermostat and you’ll see the animal.
hope that’s of use
doc…
Here’s the link to the thermostat Doc was mentioning http://www.amazon.com/exec/obidos/tg/detail/-/B0000224F8/qid=1114033578/sr=8-3/ref=sr_8_xs_ap_i3_xgl60/104-4714572-4299167?v=glance&s=home-garden&n=507846
and here’s a link to one that I found. I don’t know if its any good but… http://www.herbach.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HAR&Product_Code=TM92HVC2293&Category_Code=HVC
Actually, I think that one would work fine, Dan.
Quote:
Range 110° to 260° F ±5° Rated 8 Amps 115 VAC, 4 Amps 230 VAC or pilot duty 125 VA, 115/230 VAC. Normally closed, opens on temperature rise. Contacts remain open until temperature has dropped approx. 25. Ideal overheat control thermostat or as a control thermostat where preset temperature is desired. Plastic case 1 H x 1 W x 3-1/8". New
As it’s rated at up to 8 amps ~800 watts at 110 volts, it’s got enough zip to do the job with a fair sized and adequately insulated box. While the wording has me a little uncertain, if I am reading it right it stays closed ( puts power through the circuit ) until a preset temperature is reached, then the contacts open until it cools again. then the whole cycle starts over. Be very simple to wire this into a circuit, and relatively simple to , oh, put a heat lamp on it with a voltmeter or ammeter connected to double check. Could also put a timer in the circuit upstream ( closer to the electric outlet ) so it’d shut off after a given time.
And for $2.50 you can’t go far wrong…
Temp range up to 260°F? Interesting. Could be that some of the epoxy pre-preg stuff will cook off in that range - there are many who will be able to tell us about that, cos I know little about it, but such a gizmo might open up a whole new range of materials. Between this, a low-end vaccum bag setup and such, you could have a poor man’s autoclave.
Good find, man.
doc…