Are non-contact temperatore guns any good for getting brazing temps right?

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Hey,I need to braze some Aluminum (not with bronze but you get the idea - harris 1070 or whatever al 750 degree or so rods) and rather than use temp crayons (which I also have not tried)  I was wondering if a temp gun would work.  Any experience with this?  I'd like to get the stuff up to about 750 and THEN add flux and rod, etc.  Thanksm
Reply:Long time ago I had to fix an aluminum handle on a paint gun and was heating it up and poof..turned into a puddle...problem of fixing was solved by buying a new handle...lol...I have used some of those brazing rods..easiest was to keep one of the rods in contact with the base metal till you can see it start to melt and go from there...I guess anything to monitor temp would help, but the temp changes fast when you move the heat around...Of all the things I lost I miss my mind the most...I know just enough about everything to be dangerous......You cant cure stupid..only kill it...
Reply:you'd have to check the specs on the gun and see how large of an area they measure at a given distance. IIRC mine measures a 2" spot if held at 1 foot, the temp reported is kind of an average of the area measured.
Reply:IR temperature guns are generally calibrated at an emissivity of 0.95.Aluminum's emissivity will depend on how polished it is (so even if you have a gun with adjustable emissivity, it is not possible to get an accurate reading off of your aluminum without complex calibration), but in any case it is much lower than that.As an experiment, I tried heating empty two frying pans on medium on the stove top.  One was polished stainless (this has an emissivity similar to, but probably still a little higher than aluminum), and the other was non-stick.  Both were heated to the point that a drop of water would hit the surface and rapidly sizzle off (around 400-425F, by 450, it starts to skate around).  My Raytek showed 120F on the shiny stainless pan, and 410F on the non-stick pan.  With a stainless pot on the stove filled with boiling water, the Raytek will show around 190F on the surface of the water, but under 100F on the outside of the pot.Even if you know the emissivity, you may still be fooled by IR thermography.  I use a FLIR thermal camera at work.  It is nothing more than a miniaturized array of these IR temperature sensors behind a higher quality lens.  When looking at aluminum electrical terminal blocks, I will often see hot spots that make no sense (like on a grounding block that I know is not carrying current or near any heat source).  When I move my hand or body and see the hot spot change, it becomes obvious that I am actually seeing a reflection of my own body heat.  But I could just as well be reading the temperature of a reflection of the wall behind me too.As mentioned above, the temperature displayed is also an average of the imaging "spot".  This too can lead to misunderstandings, as the spot will be MUCH larger than the dot projected by the laser.TL;DR  No, an IR thermometer is not suitable for this application.Last edited by rlitman; 01-06-2016 at 01:34 PM.
Reply:Hey - Thanks very much for all this info.  I saw it the day I put up the question and it saved me from shelling out the boss's money on something that obviously (based on your very interesting experiments) won't work at all.  I had even already jacked up the price figuring I'd need the low emissivity knob and had a Homer moment when you mentionedthe reflection from nearby hot things result.  Thanks again for going to the effort in such a timely fashion.Regards,m Originally Posted by rlitmanIR temperature guns are generally calibrated at an emissivity of 0.95.Aluminum's emissivity will depend on how polished it is (so even if you have a gun with adjustable emissivity, it is not possible to get an accurate reading off of your aluminum without complex calibration), but in any case it is much lower than that.TL;DR  No, an IR thermometer is not suitable for this application.
Reply:Originally Posted by roadkillbobbLong time ago I had to fix an aluminum handle on a paint gun and was heating it up and poof..turned into a puddle...problem of fixing was solved by buying a new handle...lol...I have used some of those brazing rods..easiest was to keep one of the rods in contact with the base metal till you can see it start to melt and go from there...I guess anything to monitor temp would help, but the temp changes fast when you move the heat around...