Curing oven heating

[Mead Camans]

Hi all,

I'm looking at ways of heating a curing oven I've recently built that will be used to fast-set laminated work glued with UF adhesive. Ideally I'd like the temperature to get up to around 60 degrees. The oven is an 18mm plywood box, approximately 1700 x 500 x 400 internal, covered in 40mm celotex insulation board.

I'm wondering if anyone has any advice/ideas about how to bring such a space up to temperature in a safe and effective way. My initial thought was to use a small 2kw fan heater that I have, although this seems impractical as the temperature safety switch trips at about 30 degrees, and I'm wary of bypassing it.

I had thought about a tubular heater such as this, however, I'm not sure if it would be powerful enough to get to the temperature I want.

I guess the ideal thing would be to use independent heating elements that could be fixed inside the box, but I'm not sure where to begin with something like that.

Any thoughts appreciated!

George

 

[baldkev]

I know very little about the effects of 60° vs 30° on glue, but I'm guessing it just cuts down the curing time?
I'd probably get the cheap tube heater ( they are safe ) and give it a whirl, i bought one for about 20 quid..... so it's not a big outlay. It won't get to 60, maybe 35 to 40? They are thermostatically controlled, or at least mine is.....

 

[sploo]

That's not a huge internal volume, and 40mm celotex should give reasonable insulation (so slow losses). I heat an admittedly much smaller resin 3D printer chamber with just a 100W PTC heater, so a bigger version of that might do the job.

There is a 200W version of the tube heater at 1500mm length, so that might work.

 

[sploo]

A quick read of the Dimplex info suggests they'll hit 85C, but I don't know if the thermostat will let you dial in a high ambient cut off temperature (such as 60C).

 

[Mead Camans]

I know very little about the effects of 60° vs 30° on glue, but I'm guessing it just cuts down the curing time?
I'd probably get the cheap tube heater ( they are safe ) and give it a whirl, i bought one for about 20 quid..... so it's not a big outlay. It won't get to 60, maybe 35 to 40? They are thermostatically controlled, or at least mine is.....

Yep it cuts down the curing time drastically. This UF glue I'm using usually takes 6 hours + to cure. Rasing the temperature to 50/60 degrees can cut that down to 2 hours, so well worth doing!

Might try the tube heater like you say then.

 

[Jacob]

There is the expensive "Wood Welder" alternative if you are going industrial.
It's quite old technology and there are lots of suppliers and varieties of kit.
Tregarn Woodwelder Curing speed 3-10 seconds!

 

[Sideways]

Depending on your electrical skills I would also consider starting with some sort of garage grade electric fan heater.
Then you have to hack it.
You need to keep the fan running at all times whether the heating element is on or off, so separate the power supply to this and wire it permanently on as long as the heater is connected to the mains.
Then look for a cheap digital PID temperature controller bundle on ebay. These are a module with a digital temp display and some push buttons to set the target temperature. You connect a thermocouple to this as a temperature sensor (put that somewhere inside your hot box in the airflow). The module will have a fairly small relay inside to turn a heating circuit on and off. This may not be adequate or durable enough so it is common to use the small internal relay to control a higher powered one - ideally a solid state electronic relay because they are very durable - and wire the supply to the heating element through this controller.

Once done, and configured, you will have a device that controls the temp to within maybe 5 degrees. I knocked up something similar to make a temperature controlled hotplate for pre heating ball bearings before assembly. Here it is below put in a mini systainer with some plugs and sockets to connect power in out and a thermocouple. Everything right of centre is an unrelated power supply sharing the box.

Recently I've seen these temperature control modules sold as a bundle with the solid state relay and thermocouple for under £20. Bargain !
Search for "digital PID temperature controller set" and similar on ebay.
It's not quite as simple as I skipped over above so if you are not experienced with mains electrical work keep looking for something ready made.

 

[Mead Camans]

Depending on your electrical skills I would also consider starting with some sort of garage grade electric fan heater.
Then you have to hack it.
You need to keep the fan running at all times whether the heating element is on or off, so separate the power supply to this and wire it permanently on as long as the heater is connected to the mains.
Then look for a cheap digital PID temperature controller bundle on ebay. These are a module with a digital temp display and some push buttons to set the target temperature. You connect a thermocouple to this as a temperature sensor (put that somewhere inside your hot box in the airflow). The module will have a fairly small relay inside to turn a heating circuit on and off. This may not be adequate or durable enough so it is common to use the small internal relay to control a higher powered one - ideally a solid state electronic relay because they are very durable - and wire the supply to the heating element through this controller.

Once done, and configured, you will have a device that controls the temp to within maybe 5 degrees. I knocked up something similar to make a temperature controlled hotplate for pre heating ball bearings before assembly.

Recently I've seen these temperature control modules sold as a bundle with the solid state relay and thermocouple for under £20.
Search for "digital PID temperature controller set" and similar on ebay.
It's not quite as simple as I skipped over above so if you are not experienced with mains electrical work keep looking for something ready made.

Great stuff thanks. I'll look into it, but it might be a bit beyond me!

 

[eribaMotters]

What about an electric towel radiator. They are generally fitted with a thermostatic heating element to cuts out at 60c.

Colin

 

[sploo]

This (link below) is a video on the heater I put together for my resin printer. At only 100W it may be a bit too low power for your application, but the basics on a heater module + fan + controller are well explained.

 

[Limey Lurker]

Take a look at a catalytic fan heater. I used them in reptile tanks because they were safe, because if it fell on its face or back, the flow of air, and thus the oxygen required for the catalysis, was shut off, and the temperature dropped to ambient. The temperature was controlled by the speed at which the fan was set, and the fan would ensure that there is an even temperature throughout the box.

 

[gmgmgm]

How fast do you want it to heat up?

If it needs to heat up quickly, then a fan-type heater is probably best (but be careful about it overheating). If you are running it all day, and it doesn't matter if it takes an hour to heat up, then a towel rail element plus some suitable liquid would give a more stable heat.

You could also rip apart an old oven, and use the dial, thermostat and heating element (and fan?) from that? Or new ones from a parts catalogue.

 

[Mead Camans]

UPDATE:

The little 2kw fan heater I mentioned seems to work after all. The little termal micro switch is still clicking off and cutting power to the heating element, but because the fan continues to run, it's still circulating the warmed air around the box. The mirco switch will then click back on (I suppose once the element has cooled enough) and re-engage the element, creating more heated air. In this way, it's getting up to around 60 degree which is perfect for what I want, and the heater seems happy with this.

I may look in to ways to increase the temperature further, but for now, this is a good solution.

Thanks to all those who have suggested ideas!

 

[Sideways]

It's always great when folk come back and tell us what worked, or didn't.
Cheers !