IR thermometer

[Nicad]

Thinking of getting an Infra red thermometer. What temp range would be most applicable to Tig welding aluminum and general use? Is there an optimal temperature for pre heating Al? I have been having trouble getting things melting when trying to join 1/4 plate using a PT225.
Any brand that offers good quality for the money?
Thanks, Bob.

[castweld]

Bob
I weld mostly engine castings, al and iron. The ir thermometer I use goes to 1100 w/laser aim. I pre/post heat most al head castings to 350 . I needed to weld inside a cylinder head port with a 100 amp max micro torch, I could not get a puddle (100 amp 350 heat).
Heated to 500 and got it done. You need to know the anneal temp of alloy you are working with. 356 t6 al castings anneal within a couple mins at 600 degrees, at 500 you will anneal in about 2 hours. A 350 degree chunk of al will weld at approx 1/2 the amps the same part will weld at room temp.
The gun I use is Raytec.
Check the model that you like and make sure it can be calibrated for al, a lot of them can not be calibrated. A ir thermometer not calibrated for al will give incorrect temp.
Peter

[flatbustedbroke]

Thanks for the last bit castweld, that will be needed info to remember

[65535]

What you want is adjustable emissivity, it has to do with the way the IR beam is effected by the heat of the surface to pick up the temperature with the sensor.

Different materials have different emissivities. So make sure it's adjustable.

[A_DAB_will_do]

Tempil makes an electronic thermometer that is accurate and can be calibrated. It doesn't have quite the 'reach' of an IR thermometer, because you have to touch the surface with the end of the 'stick', but it will be much more accurate than most IR thermometers. We use them at work and have been very satisfied with their performance to date. Price is similar to a good IR thermometer.

http://www.tempil.com/closeup.asp?pid=23&cid=24&theme=0

[LarryO]

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[pulser]

Originally Posted by 65535

What you want is adjustable emissivity, it has to do with the way the IR beam is effected by the heat of the surface to pick up the temperature with the sensor.

Different materials have different emissivities. So make sure it's adjustable.

This is correct, and a very important point. The surface finish and color of the part being measured has a huge effect on the temperature reading. A perfect "black body" heat source,something that is a rough surface and flat black, will have an emissivity value of 1.0, versus a smooth shiny chrome surface which may have an emissivity of 0.2 (just a guess). What this means is that the IR thermometer has to adjusted properly to read the type of surface.

Generally you calibrate the IR thermometer by measuring a "typical" type of object using both the IR thermometer and a "calibrated" contact type thermometer, and you adjust the emissivity setting to make the IR meter match the contact thermometer. Then you are good to measure objects similar to the typical one used for calibration.

The other thing about an IR thermometer is the focal length and spot size. The IR sensor focuses to a given spot size at a given distance, for example it may read a area of 1" diameter at a distance of 12" from the object. If you are closer or further, the spot size is larger, and you may be measuring an area other than what you intended.