What may damage in the heat-gun and how?

Thread Starter

xchcui

Joined May 12, 2014
214
Hi.
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...
Thanks.hot air gun oven.jpg
 

DickCappels

Joined Aug 21, 2008
8,704
You might stress the fuse that is in series with the motor. Then there are the moving parts of the blower and the constant temperature cycling may affect the life of the heating wire.
 

MrChips

Joined Oct 2, 2009
26,077
There is thermal fuse in the heat gun. When a given temperature threshold is exceeded this fuse will blow and your heat gun will stop working.
 

Tonyr1084

Joined Sep 24, 2015
6,884
The biggest wear and tare on the heat gun will be the cycling of the heating element. I've operated a hot air soldering pencil that would work for about 6 months before going out. Maintenance would replace the heating element and the pencil would be good for another 6 months. On average. The output temperature is controlled by cycling the heating element on and off.

Many years back I built a small oven for curing epoxy samples with PCB samples inside the epoxy used for evaluating the internal structure of the boards the coupons represent. Cure time at room temperature was a little longer than preferred so I got a hold of an aluminum projects box and mounted a light bulb inside. Shielded the bulb from direct exposure to the sample cups and hinged the lid. The increased temperature (never measured) sped the cure time a lot. Don't recall ever taking cure time measurements either. Just know that it worked. Incandescent lamps can be used as heating elements for small enclosures. Just be sure of two things: One is that you don't burn something and the second is that you make sure to isolate all electrical wiring so you don't create a short or a shock hazard.
 

Thread Starter

xchcui

Joined May 12, 2014
214
Hi guys.
Thanks for your replies.
I am talking a bout temperature about 220°C,while
the heat-gun has also 600°C position.Why that the thermal fuse will blow at 220°C,while it has also a 600°C position?(that won't be used for this task).Or you meant to say,that since the fan will be off during the turn-off moments,the hot air from the box will go-up and blow the thermal fuse,since the thermal fuse has a lower value than 220°C.Is that what you meant?
Regard to the moving parts,did you refer to the blower?Can the plastic blower melt or deform?isn't it made to resist temperature as 220°C?
 

Tonyr1084

Joined Sep 24, 2015
6,884
The thermal fuse (known as a fusible link) is designed to burn out before the gun overheats. If the gun is capable of 600˚C then the link must be rated higher than that. OR it may be further back in the air stream before the heating element. If the element is on and the airflow blocked or stopped the gun will overheat and the link will blow. Since turning the gun off means turning both the element and the fan, the gun is not likely to overheat.
 

Thread Starter

xchcui

Joined May 12, 2014
214
The thermal fuse (known as a fusible link) is designed to burn out before the gun overheats. If the gun is capable of 600˚C then the link must be rated higher than that. OR it may be further back in the air stream before the heating element. If the element is on and the airflow blocked or stopped the gun will overheat and the link will blow. Since turning the gun off means turning both the element and the fan, the gun is not likely to overheat.
Okay,so the hot air(220°C)from the box that will keep flowing up through the tunnel of the heat-gun(until it get-out from the back of the tool)when the heat-gun turns-off won't blow the fuse,but will it damage/degrade the plastic blower?the blower-motor?
Btw,in regard to your project with the bulbs,can i get 200°C in the box at size like on my attached photo,from Incandescent bulbs?
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
6,884
will it damage/degrade the plastic blower? the blower-motor?
Shouldn't. At least not in the next 10 years. The heating element will have long burned out before then.

in regard to your project with the bulbs,can i get 200°C in the box at size like on my attached photo,from Incandescent bulbs?
Probably not. there's just not enough insulation, or too much heat loss.

Why do you need 200˚C? For us Yanks - that's almost 400˚F And paper spontaneously erupts (from what I believe I've heard) 452˚F. (233 1/3˚C) Can your paint withstand that kind of heat without blistering? If speeding up drying time is the desired outcome, more heat means faster cure times. The inverse is also true, less heat means longer cure times. How long can you tolerate? You probably don't need or want 200˚C in the box. At least I'd be concerned about the potential for fire. Plus the given outgassing of the paint - that too may be volatile. But I'm assuming you've done some testing without blowing up the house. A bit overkill - I know, but that might be a worst case scenario. Burning down the house can ruin your day; all for the sake of saving some time drying paint.
 

Thread Starter

xchcui

Joined May 12, 2014
214
I am using high temperature paint which resist 800°C and according to the item's instruction,it must baked at ~200°C for 30 minutes in order to be full cured.Without this process it won't resist high temperature.(it is not standard paint).
In regard to the plastic blower and the motor:
In normal use,the heat gun element will fail before them,as you mentioned,but i am talking about abnormal situation.
During the turn-off moments,the hot air from the box(220°C)will go up into the heat gun tunnel,the element coil won't be damaged,since it can handle even 600°C,but since the blower is turn-off,the hot air(220°c)will keep rising from element coil to the plastic blower and the motor(thing that isn't occurred at normal use)until it gets out from the back of the tool.This will continue for some time until the temperature in the box decrease and the heat gun will turn-on again by the user.So during the turn-off moments,the plastic blower,the motor wire's lacquer,the lubrication in the fan's bearing will be exposed to 220°C,while in normal use,when you turn-off the heat gun,the parts behind the element coil don't experience that high temperature and if it does,it is just for very short time.
So,after my detailed description,i would like to verify and understand that those parts won't be influenced/damaged in that situation?

The thermal link mentioned by @MrChips can blow if the air outlet or inlet of the heat gun in restricted so that the air gets above a set temperature.
What is usually the value(more or less)of the thermal fuse in 600°C heat guns?
 

Tonyr1084

Joined Sep 24, 2015
6,884
Well, yeah, the gun will see a back flow of heat from the oven unless you mount the gun elsewhere to prevent the rising heat from reaching the cooler parts of the gun. Perhaps a different baking arrangement would be in order. Rather than a cardboard box, get some sheet metal from an old washing machine and fashion it into an oven. Or from an old electric dryer. Now you not only have a hot box you also have a heating element. No moving parts, just the heat going into the box. Double insulate it to prevent excess heat loss. Then find a thermal switch that cuts off at 200˚C. No need for the blower or worrying about failure. No excessive noise when the gun is running. Just use an indicator light to show when the heating element is active.
 

shortbus

Joined Sep 30, 2009
9,372
Why not use a "toaster oven"? they even have a thermostat that will hold the set temperature. And many times you can find them used for little money.
 

Thread Starter

xchcui

Joined May 12, 2014
214
Why not use a "toaster oven"? they even have a thermostat that will hold the set temperature. And many times you can find them used for little money.
This was my first thought,but i don't have place to keep garbage,especially not for rare tasks.
The same idea for making a better quality box,as Tonyr1084 suggested.It is a better baking arrangement
indeed,but this one is super fast to make and super easy to throw away.Don't need to store it or spend to much time to make it.Of course you must take a safety precautions and do it ouside.
Anyway,my question is related only,but only to the heat gun and i have not gotten an answer to it yet.
Tonyr1084,you start your answer:
Well, yeah, the gun will see a back flow of heat from the oven...
So...can this 220°C hot air deform/melt the plastic fan?damage the motor?evaporate the bearing lubrication?
And what is usually the value(more or less)of the thermal fuse in 600°C heat guns?
 

Tonyr1084

Joined Sep 24, 2015
6,884
Anyway,my question is related only,but only to the heat gun and i have not gotten an answer to it yet.
Tonyr1084,you start your answer:
Well, yeah, the gun will see a back flow of heat from the oven unless you mount the gun elsewhere to prevent the rising heat from reaching the cooler parts of the gun.
So...can this 220°C hot air deform/melt the plastic fan?damage the motor?evaporate the bearing lubrication?
And what is usually the value(more or less)of the thermal fuse in 600°C heat guns?
• • • unless you mount the gun elsewhere to prevent the rising heat from reaching the cooler parts of the gun.
I think you should infer from this statement that I believe if the gun is mounted at the top of the box and the gun shuts down there is a chance - "a chance" rising heat could cause issues. Usually heat guns have their heating element well insulated from the plastic housing. But that's on the premises that air is moving in one direction - OUT the nozzle. If you were to store your heat gun in your kitchen oven and someone turns it on it is likely the plastic will melt. Even at low temperatures.

Since I don't know the exact chemistry of the plastic I can't tell you what temperature it will take to soften the plastic and at what temperature the plastic will become molten and start to sag. The motor? Likely it can withstand more heat than the plastic. However, we don't know the design specs on the fusible link that protects the motor from overheating.

As I said, if you move the gun to the side of the box instead of the top, say close to the bottom of the side, there's a better chance the gun will not see any undue heat rising out of the box. Since heat rises, chances are better that cool air will be pulled in through the gun when it is turned off due to the hot air rising and escaping via openings in the box and/or heat migration through whatever insulation you have inside.

Now that I mention insulation, I hope whatever you've chosen for insulation, assuming you've done so, you've considered the "Withstanding Temperature rating" of the insulation. Foam insulation is NOT rated for high heats such as 200˚C. It will melt and give off noxious and potentially deadly gasses. So be safe. Please. We hate losing members because of carelessness or accidental exposure to dangerous elements such as high voltages or outgassing from materials not intended for uses that some people come here thinking will work safely. Again, I don't know what or how you've approached this problem. All I can do is imagine different scenario's where something could go wrong and cause harm. Fire is one concern. Now I'm also concerned about noxious chemicals.

Did I answer your question about the plastic melting?
 

Thread Starter

xchcui

Joined May 12, 2014
214
I think you should infer from this statement that I believe if the gun is mounted at the top of the box and the gun shuts down there is a chance - "a chance" rising heat could cause issues. Usually heat guns have their heating element well insulated from the plastic housing. But that's on the premises that air is moving in one direction - OUT the nozzle. If you were to store your heat gun in your kitchen oven and someone turns it on it is likely the plastic will melt. Even at low temperatures.

Since I don't know the exact chemistry of the plastic I can't tell you what temperature it will take to soften the plastic and at what temperature the plastic will become molten and start to sag. The motor? Likely it can withstand more heat than the plastic. However, we don't know the design specs on the fusible link that protects the motor from overheating.

As I said, if you move the gun to the side of the box instead of the top, say close to the bottom of the side, there's a better chance the gun will not see any undue heat rising out of the box. Since heat rises, chances are better that cool air will be pulled in through the gun when it is turned off due to the hot air rising and escaping via openings in the box and/or heat migration through whatever insulation you have inside.

Now that I mention insulation, I hope whatever you've chosen for insulation, assuming you've done so, you've considered the "Withstanding Temperature rating" of the insulation. Foam insulation is NOT rated for high heats such as 200˚C. It will melt and give off noxious and potentially deadly gasses. So be safe. Please. We hate losing members because of carelessness or accidental exposure to dangerous elements such as high voltages or outgassing from materials not intended for uses that some people come here thinking will work safely. Again, I don't know what or how you've approached this problem. All I can do is imagine different scenario's where something could go wrong and cause harm. Fire is one concern. Now I'm also concerned about noxious chemicals.

Did I answer your question about the plastic melting?
I would like to mention(as i has already mentioned on my first post)that i took this idea from youtube.
(it is not my idea).
The box doesn't have any insulation(besides the fact that a cardboard itself is a kind of insulator)and it wrapped inside with aluminum foil(that's all).
If it had also insulation(suitable for high heat),then i guess that there wasn't a problem,since the heat was kept for enough time,but it is not the issue here.
Moving the heat gun to the side of the box will be better in the aspect of reduce the chance for heat gun's damage,but the guy from youtube,who share this idea,chose to put it's hot air gun on top of the box and i assume that he had a reason.
Maybe after few experiments he came to conclusion that it is better to put the heat gun on the top rather than on the side,but since he stopped replying to questions 2 years ago,we,unfortunately,can't ask him why he decided to do that?
Did I answer your question about the plastic melting?
Yes and No.I understand that you can't tell what will damage since you don't have the chemistry of plastic,so in practice there is no answer.
Anyway,what about the rest of my question about the bearing lubrication evaporation ?
I know that there are all sorts of heat-guns and each heat-gun may have different properties(resistance of the heat gun material,quality of the materials,thermal fuse value,etc)so i don't expect for an exact answer,but can't you give estimate answer(more or less)according to the average standard heat guns in the market that works on 300/600 °C /2000W.
Thanks.
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
6,884
what about the rest of my question about the bearing lubrication evaporation ?
Again, I don't know for sure, but I would think that bearings or bushings (more likely bushings) will be OK. Perhaps - and this is a guess - under normal use the gun would last 10 years (as far as bushings go) whereas you may see a reduced lifespan for lubrication. But again this depends on where you mount the gun.

Something about YouTuber's - they sometimes do stupid things but you never see the end results because they don't happen during the time of recording the videos. Sometimes they outright lie and resort to trickery to seemingly make their point. YT is RIFE with free energy devices. Some videos are well done, others smack you in the face as fake. So take what you see on YT with a grain of salt. I doubt the guy had any specific reason for putting the heat gun over the project. The only thing I would be concerned doing what you propose is putting the part in the direct hot air path. You could get a hot spot on the part you're curing. Even from the side, you'd want to fill the box with hot air being distributed as evenly as possible. If you're not following what I'm saying, imagine you're painting your car and you want to use heat to cure it. You put the heat gun blowing on the engine hood and hold it there until the trunk is cured. The hood is going to be way over temperature. OK, that's a stupidly extreme example, but I hope it gets the point across. That is IF I didn't fully make my point clear the first time.
 

Thread Starter

xchcui

Joined May 12, 2014
214
Again, I don't know for sure, but I would think that bearings or bushings (more likely bushings) will be OK. Perhaps - and this is a guess - under normal use the gun would last 10 years (as far as bushings go) whereas you may see a reduced lifespan for lubrication. But again this depends on where you mount the gun.

Something about YouTuber's - they sometimes do stupid things but you never see the end results because they don't happen during the time of recording the videos. Sometimes they outright lie and resort to trickery to seemingly make their point. YT is RIFE with free energy devices. Some videos are well done, others smack you in the face as fake. So take what you see on YT with a grain of salt. I doubt the guy had any specific reason for putting the heat gun over the project. The only thing I would be concerned doing what you propose is putting the part in the direct hot air path. You could get a hot spot on the part you're curing. Even from the side, you'd want to fill the box with hot air being distributed as evenly as possible. If you're not following what I'm saying, imagine you're painting your car and you want to use heat to cure it. You put the heat gun blowing on the engine hood and hold it there until the trunk is cured. The hood is going to be way over temperature. OK, that's a stupidly extreme example, but I hope it gets the point across. That is IF I didn't fully make my point clear the first time.
You make your point very clear and i understand very good what you are talking about.
You are also right at any word that you said about the YouTuber's.
This is a reason that you must have,in our case for example,some base knowledge about thermodynamics,electronic,chemistry etc.in order to make several logical calculation before you comes to conclusion whether the video that you see can be done and done safely.
This is the reason that i asked my question here,to get advice at unsolved issues from an experts,before i make any further action.
Thank,Tonyr1084,for your help and to all the other members that participated.:)
 
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