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Heat elements and temperature for heated rocker table box?

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ScottM
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Heat elements and temperature for heated rocker table box?

Postby ScottM » Wed Jul 18, 2007 5:57 pm

Okay so I've had time now to get back to my board making project and now am at the stage where I need to consider how to heat up my rocker box. I have built an adjustable rocker setup and have it designed to be enclosed in an insulated box, with the idea to heat the vacuumed board to a correct temperature during the curing process.

I have read somewhere that 40 C is about right for good strength. I am thinking using a few rows of light bulbs could do the trick, but if there are better ways I am open to suggestions! :D

XSwind
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Postby XSwind » Wed Jul 18, 2007 9:17 pm

Well unless it is really cold outside you dont need a heated box.

I live in the UK and I do use a homemade heated box during the really cold periods.

Here is a photo of my heating setup on my old rocker table.
Note the fan and thermostatic power switch which is inside the box when it is on.

I also have a double glassed window in the fron of the box which is not shown. this is usefull to see what is happening inside the box.


Image

crabman
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Postby crabman » Thu Jul 19, 2007 8:24 am

Your heat will be governed by the epoxy cure spec on the litreture and what you can take the core up to which is never reached .I dont use a box .Plastic tent with two fan heaters .You will be amazed at the heat generated . Circulation of heat is what you want or you will end up with hot and cold spots in the lamination. Keep it simple ,if it goes wrong its easy to fix.:thumb:

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ScottM
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Postby ScottM » Thu Jul 19, 2007 12:33 pm

So circulation of heat sounds to be the key then! I am using a thin sheet of aluminium to spread the heat evenly along the bottom surface of the rocker template. The idea was that the heat generated will remain trapped withing the insulated box.

I'm using an epoxy made by Epiglass which is quite nice as it's very low in viscosity. As far as the attached diagram, is the idea that you pick a particular temprature and the time till fully cured is shown? Is there any particular reason to want to cure at a higher or lower temperature? I'm guessing 40 c is my easiest choice even if it's the longest!
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crabman
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Postby crabman » Thu Jul 19, 2007 12:49 pm

Scott that diagram is called a ramp up ,the flat at the top is a dwell time and the one going down is when everthing is switched of .The reason for holding at a higher tempreture is called post cure .This allows a composite to dance round and find its partner then join .

DO NOT USE ALUMINIUM IN THE TABLE,IT WILL TAKE AWAY ALL THE HEAT FROM THE COMPOSITE AND WILL NOT CURE. Use like for like or wood with a face for the rocker table . :thumb:

XSwind
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Postby XSwind » Thu Jul 19, 2007 12:55 pm

I used to use Crabman's tent method when I made surfboards and it was very effective too in the cold sub 0c

The insulated box and thermostat does save you money especially here in the UK where electric is really expensive and has worked really well for me.

I use electric greenhouse tube heaters, 60W each if memory serves right.
Thease were just laying around unused, I have also added a fan to ensure heat circulation and distrubution.
I used a simple 12v computer case fan which works really well.

My setup is often left over night as this is the only sspare time I usually have so I went overboard to ensure fire safety.

crabman
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Postby crabman » Thu Jul 19, 2007 2:13 pm

If you really want to push the boat out get some silicon and make a heated re usable vacuum bag .I will be trying this through the winter .Add a digital heat read out and timer ,sorted . :thumb: I still like the plastic tent if you cant do this . If you want to use a box the best is a coffin .I used one about 5 years ago .

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ScottM
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Postby ScottM » Thu Jul 19, 2007 3:28 pm

Hey Crabman,

well my idea with the aluminium sheet was to have it disipate the heat evenly into the plexiglass rocker sheet, rather than have the heat end up in just one area because of the elements. I can remove it in any case if it will be a problem. But surely once the heating element is on it'll gradually heat up? I'll try experiments and see what happens?

I like the dancing explanation for the curing epoxy, so I guess it shows even when the epoxy is hard to the touch, reactions still take place for a while?

Well I've built the "coffin" and it's fully lined with foam insulation... weights a ton though!! But it can double as a work surface I guess!! I'm pretty excited about putting together the first board. I'll do the laminations all in one go once all the inserts and rails are done.

crabman
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Postby crabman » Thu Jul 19, 2007 3:34 pm

Scott a few years ago we built a board using alu as the rocker base with a release film on top .It was a disaster .Use Melamine £10.00 a sheet .Epoxy takes about a week to fully cure unles you go over 120c Then it becomes exspensive defeating the object of self build . Keep us posted . :thumb:

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ScottM
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Postby ScottM » Thu Jul 19, 2007 3:45 pm

I'm glad I didn't buy the aluminium then... does look so nice and shiney! I'll have to look up this Melamine stuff!

So that's interesting the 120 degrees thing as that's really cooking!! :o


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