As some be aware, thermography can be carried out in the passive or active mode of operation.
In the passive mode the user is imaging an areas passive radiation signature and this is excellent for imaging sources of thermal energy against a lower or high temperature background. Passive thermography is by far the most common mode of operation for many users of thermal imaging equipment.
Thermography comes in many forms however. Thermal cameras can be used to look for defects in surfaces or to detect hidden voids or materials invisible to the naked eye. Examples of hidden structures are the metal or timber frames in a plaster wall and it’s associated nails/screws. It can sometimes be beneficial to operate the thermal camera in the active mode with the user introducing thermal energy into an area of interest and viewing the area as it heats up and cools. Different materials within a structure, or those of differing thickness will exhibit different heat uptake and cooling times. This can be images by the thermal camera as thermal contrast is evident from the thermal differential that occurs. Items like nail heads in the plaster become very defined indeed thanks to their fast heat uptake and re-radiation as they cool.
In laminated surfaces the heat is applied to the surface and any air pockets or de-laminations create insulation behind the front surface. The partially insulated are glows hotter than its surroundings as it has lower thermal density and conduction to the area behind and around it. Such techniques are used for NDT on high tech laminates as found in the air industry. De-lamination within materials is a very serious defect in some structural applications.
Without writing a long piece on NDT techniques, I will jump straight to the topic of this post. One way to introduce thermal energy into a target surface is to use what is basically a very powerful hair dryer ! There are other heating techniques but your average paint stripping heat gun is capable of introducing plenty of thermal energy into a surface without causing damage (if used sensibly). The user waves the heat gun over the surface in a similar manner to spraying with a can of spray paint. The pattern of movement is left to right then right to left as you snake down the surface. The pattern is then pleated in the other plane at 90 degrees, so up and down whilst moving across. Diagonal movements are also used where needed. The idea is to evenly heat the whole surface in such a way that the normal thermal conduction of the surface or material fills any small gaps and gives a relatively even ‘heat soak’ that will highlight thermal differentials caused by material differences, densities ir defects.
Now to the ALDI heat gun....... I saw this the other day and was surprised at its capabilities. Most DIY heat guns are just an hair dryer on steroids ! You get ON/OFF/COOL and some blower speed settings with some better units offering heater settings as well. The ALDI offering is excellent. It provides both fan speed and heater temperature settings and provides a rough temperature readout on an LCD display. Now this is no precision hot air generator but it does offer temperatures ranging from 50C to 650C
. This hot air gun would be perfect for active thermography thanks to its versatility.
The wide ranging temperature output all the way up to 650C gave me another idea. Used with a suitable insulated metal plate that is coated with high temperature, high emission paint and equipped with a PT100 sensor, the heat gun could heat the plate from the rear and effectively form a high temperature thermal check reference. My FLIR SC4000 needs a high temperature reference to calibrate its higher temperature ranges. The good thing is that in the case of the SC4000, you aim it at a surface of roughly the required temperature and just key in the measured temperature of the target as shown on the PT100 contact thermal sensor. Emissivity also needs to be set but this is easily established by other tests on the heated plate.
The ALDI heat gun was too good an opportunity to miss so I bought one. They were even on discount from £24.99 down to £17.99 I. The stores (but not online). I bought a couple for experimentation
Details copied from the ALDI Web site are here:
Product Information
Brand:
Workzone
Colour:
Blue
Dimensions:
28 x 10 x 27cm approx.
Power:
2300W
Product Type:
Tools & Equipment
Our digital heat gun is the ideal for removing paint, bending plastic pipes , removing rusted bolts and moulding plastic. This tool comes with 4 different nozzles and boasts a 6 position airflow with temperatures reaching 600°C. Buy yours today!
Contents
1 x Heat gun
1 x Reflector nozzle
1 x Scraper
1 x Cone nozzle
1 x Glass protector nozzle
1 x Fishtail nozzle
1 x Scraper hook
1 x Putty knife
1 x Instruciton manual
1 x Warranty
1 x Carry case
Features
Soft grip handle
Rubber over mould grip
D-handle
6 position airflow
Safety auto cooling function (30 second auto cooling before switch off machine)
Temperature/flow rate: 50-660°C (300-500 L/min)
LCD display
Guarantee/Warranty
3 Years
Web page:
https://www.aldi.co.uk/workzone-digital-heat-gun/p/012586266868200I will add my own pictures of the unit shortly
Fraser
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