What is the highest temps you’ve achieved in your hot box with standard light bulbs or maybe a baseboard heater?
Jon
20x20x32 2 inch thick with one 75 watt bulb, 170 degrees farenheit.
I used oven heating coils, 1 inch plywood, 2 inch kingspan insulation and expanding foam to get an 8ft x 4ft x 4ft to 160 about 5 years ago. didnt want to push it any higher!
I used a shop/garage heater. Pretty small into from Walmart. With just a cardboard box as tent I was able to get 150f. Used 3/4in insulation built box of 4’x3’x2.5’. Got temps max 190f
I use 240 volt heating elements shaped to suit the job or box with a thermostat control either suspended on insulated supports with clearance from both the mould and foam box or in most cases inserted in a routered groove in aluminium moulds, I can achieve temps in excess of 120C-240F without any problems, see att pic. of foam hot box 2.4mtr x 1.2mtr over aluminium moulds.
Heating elements from say a conventional baking oven? Also, are you using any kind of circulation fan inside the box? Your 240F is about all I will ever need.
The existing oven elements are usually made to surround the box shape of the oven, I am not sure of the size or shape of your laminated product?, you have to be carefull of radiated heat and hot spots if you are going to try and use existing elements, they can be made easy and cheap as the element material comes in straight lengths, they then bend it to suit the application so you could get one made to suit your box then shield it and have a fan at one end to circulate the heated air?.
PM me if you wish and I can send you more detailed info re. elect. controls etc.
What plastic could be used for a heating tent that withstands acceptable temperatures?
How big is the tent you wish to build?
Plastic is just a membrane, so heat loss is a big factor, regardless of the type of plastic.
If you wish to go big - build a double skinned plastic tent, with a 50mm air gap between the membranes… Heat loss is greatly reduced.
For arguments sake, you could build a plastic tent from Capran (vac bag) and it would be good for 180C… If you have a big enough heat source & pocket.
Often, it’s cheaper and more effective to use insulation board like Celotex.
The tents are very large so i need them to be storable. 6 x1.5 x 0.4m just one of them. Capran is a great idea. To fill the 50mm gap it would be great to find a product that is flxible and i could store in a bag so that they dont eat up all the space in the workshop. One problem with capran is that it will be imposible to bond together to form a large tent.
The dimensions are not outrageously big, but you will struggle to make a flexible option.
The system is usually plastic is pulled tight over a frame constructed from softwood 50mm x 50mm and held in place with double sided tape and staples.
Only the inner skin needs to be high temp, as the air gap is a good insulator.
What is your target temperature?
My preference is to use Celotex as you achieve an even temperature much, much easier and efficiently - especially on a long thin oven.
For example:
The biggest one I built lately was 14m x 0.5m x 0.4m used 5 heat guns and a blower for air circulation.
I was able to have a ramp rate of 1 Deg C/min and cured prepreg at 100 C. Max variation down the length of the oven was 2C. The oven is then disassembled back into smaller parts for use on other projects. I have since made 3 other smaller hot boxes from the used panels.
The biggest oven I have seen using this method has been 35m x 10m x 8m for curing a superyacht hull in.
I am aiming at 100ºC. Have to test if vaccum bag can be glued with silicone. Is celotex extruded poliestyrene? Not sure if it will withstand 100ºC. Wanted to buy yesterday 2 dayton high temp blowers from usa and they wanted to charge me 300$ for the shipping. Need to find an alternative here in europe.
Celotex will be happy with 100C all day long.
No need to buy high temp fans/blowers…
I used a 1 KW chip extractor. ( For extracting sawdust)
It’s a small unit that has a metallic centrifugal fan and housing. I bought a B grade one and it was £80.
Worked perfectly, and the motor didn’t even get warm after a 14h cure cycle.
I just bought to high temp blowers for 100e each. One on every side. How big would you size the resistance in watts at the outlet of the blowers?
Ultimately the wattage will depend on your oven volume and construction material… 3kw per m3 is usually plenty if you want a good ramp rate. It will take some experimenting to perfect the heat source.