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I saw (around the web) that many peoples are using their hot air gun to blow hot air into a carton-box (300°C position) and turns the carton-box to a kind of oven, in order to cured painted object etc. (See attached photos from youtube) The temperature target inside the carton box is about 160°C-220°C, so the heat gun is turning-on until the box reaches to 220°C, turns-off until it go-down to 160°C and turn-on again... (in total 30 minutes).The hot air gun stays the same position all this time.I understand that this process may damage the heat-gun.My question is what parts in the heat gun may be damaged/degraded?Since that during the turn-on moments,the blow air can go-out through the bottom of the box(the box is not sealed at the bottom),i assume that the damage may happen during the turn-off moments,while the hot air from the box(220°C)will go up through the heat-gun tunnel and damage/degrade something on its way up,but what?Does the plastic fan can melt/deform on 220°C?Can the fan motor may degrade?etc...

I would like to emphasize that my question is solely aimed at the damage that may occur to the heat-gun parts and not to the improvised oven's risks.Thanks enter image description here

Marcus Müller
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Dan
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    Yes it can. Case closed. – winny Mar 08 '22 at 16:20
  • I just can't imagine this is worth it compared to the expense of a small second hand lab grade oven – crasic Mar 08 '22 at 17:29
  • I have done this many times HOWEVER, the heat gun I use has a regulated temperature output, and I was using much lower temperatures (less than 100 C). Also, there should be exhaust holes in the box to make sure the back-pressure is not too high. If the pressure in the box increases by a small amount, the airflow from the heat gun will be greatly reduced. Also, this is obviously a serious fire hazard. So keep an eye on it and make sure you know exactly what you will do if it catches on fire. – user57037 Mar 08 '22 at 18:01
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    Every part of this is terrifying to me. Risk of fire from overheating the heat gun. Risk of fire from localised overheating of the cardboard. Risk of electrocution from the foil poking into the coils. Toaster ovens and heat lamps cost so little - why would you risk loss of life and loss of property over such small savings, especially when you have to spend the time constructing this mess? – Polynomial Mar 08 '22 at 18:03
  • @Polynomial I agree. I would not do it for such high temperatures, nor with an unregulated heat gun or hair dryer or whatever. I have done it to cure epoxy at temperatures up to around 160 F. Like I said, my heatgun hsa a regulated temperature output. So I can set it to around 200 F and monitor the temperature inside the box with a probe. That will typically give me around 160 F inside. – user57037 Mar 08 '22 at 18:07
  • Your setup sounds fractionally safer, but I'm still not sure why you'd jerry-rig a contraption when a toaster oven costs next to nothing (or possibly even free - they show up on freecycle-style boards all the time!) and is easily modifiable if you need less hysteresis on the temperature control. Hobbyists have been building reflow ovens out of them for years. – Polynomial Mar 08 '22 at 18:26
  • @winny,yes,but what part in the heat gun will be damaged and why?@crasic,and if you don't have a place to keep garbage?!this is super easy to make and easy to throw away.Anyway,guys,you all missed all the point of my question,i know what are the risks,but my question was referred only to the heat gun.What parts in the heat gun may be damaged or degraded and why?leave aside the improvised oven risks. – Dan Mar 09 '22 at 12:07
  • Please edit your question to ask that instead. Also, I would recommend taking the tour and reading the FAQ on how to ask questions on EE.SE here: https://electronics.stackexchange.com/help/dont-ask – winny Mar 09 '22 at 12:29
  • Okay winny,thanks. – Dan Mar 09 '22 at 12:31
  • @Erick - Hi, You have already got answers based on your original question (e.g. where you included the cardboard box) which mean that you cannot make big changes to the question that would invalidate existing answers (by removing details which were relied upon when people wrote their answers). Otherwise, such big changes would mean that people who wrote the answers to your earlier version of the question wasted their time. So I have reverted (rolled-back) to the version of the question before that. – SamGibson Mar 09 '22 at 16:52
  • (continued) However I don't see how that is a valid question here, as answers to the current version will depend on the exact plastics etc. in that heat gun, when it being used in a way that is not intended by its manufacturer. Only a manufacturer will know about the exact plastics they use, and the maximum temperature of the fan bearings and the plastic used for the case & fan blades etc. You already have useful answers explaining the general risks. – SamGibson Mar 09 '22 at 16:52
  • (continued) More than that becomes a question about the use of products (i.e. the heat gun), and those are off-topic here as no-one except the specific manufacturer will know the exact specifications of their design. (And they likely have not tested your unintended use of their product.) Sorry. – SamGibson Mar 09 '22 at 16:52

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Typical users are careless and/or stupid often enough, and typically those hair dryers have protection (in the form of a safety self-resetting bimetal thermal switch) against overheating due to the airflow being obstructed (at least safety agency listed ones do), but that is to prevent a catastrophic fire starting inside the device, not to prevent damage or degradation to the appliance. Image from here

enter image description here

Using high temperature air to heat a flammable cardboard box (with whatever adhesives and whatever other materials may deliberately or accidentally be present) has obvious hazards and cannot be recommended.

Spehro Pefhany
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  • Yes,the heat gun has a bimetal thermal switch,but as you mentioned it is not prevent damage or degradation to the appliance and that is the essence of my question!what part can be damage and why?On the turn-on moments there will be no issue,since the air can go-out from the bottom of the box(it is not sealed).The damage may happens in the turn-off moments while the hot air will go-up through the heat gun tunnel and might damage something,melt something,but what?can 220°C melt the plastic fan?damage the fan-motor?220°C i assume,won't damage or degrade the heat coil,which works also on 600°c. – Dan Mar 09 '22 at 12:19
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I would cut some slits in the carton to make sure the fan on the heat gun can blow. I would blow into the side of the carton instead of the top (heat rises and will bit hurt the best gun on the side of the box).

I'd also do this outdoors so I don't burn my house/garage down in case my thermostat is not accurate or if the curing paint combusts/flashes. Finally, cardboard and wood will combust at 232°C (451°F). Be careful.

GT Electronics
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  • On the turn-on moments there will be no issue,since the air can go-out from the bottom of the box(it is not sealed).I concern about the turn-off moments while the hot air will go- up through the heat gun tunnel and might damage something,melt something,but what?can 220°C melt the plastic fan?damage the fan-motor?220°C i assume,won't damage or degrade the heat coil,which works also on 600°c. – Dan Mar 09 '22 at 12:23
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Imagine the lack of air flow effects over the > 1500'C heater on plastic and cardboard with chimney effects. Each cycle would increase the local ambient temp. Obvious fault without continuous airflow. Heat rises, why inject on top unless there is a plenum to distribute the air evenly and continuously?

I've designed better cheap ovens for DVT performance tests.

For 85'C in a picnic box, use a 25W soldering iron suspended in middle with fan. Dry ice for -40'C. For higher temp, air flow and gradients and insulation are more critical. 20 minute settling time.

Tony Stewart EE75
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