Quartz short wave infra red heating elements

[asimpson]

I am considering a non conventional use of short wave infra red heating heating mass of steel (15-35 kg) by direct contact or near proximity. Target temperature near 1000C has proved problematic for cartridge heaters. Induction heating not feasible and I need to keep power source AC electrical.

Any body know infra red heater specialist who would be able to advise me on use of their product in this application?

Most I have found so far have not been willing of able to discuss heating in this non conventional way despite it looking feasible.

Any help welcome.

 

[IRstuff]

" Target temperature near 1000C has proved problematic for cartridge heater"

Perhaps you need to explore that some more. Standard diffusion furnaces run up to 1200ºC using electrical heaters. From your drawing, it appears that you've not devoted much volume for the heating elements. Have you determine what your heat loss is?

If you are having trouble with cartridge heaters, how are infrared heaters going to help? They're essentially long cartridge heaters, are they not?

Why is induction being precluded?

TTFN
faq731-376

 

[Compositepro]

Google "industrial quartz heater".

http://www.noblelight.net/

http://www.quartztubing.com/

 

[asimpson]

Cartridge heaters work by thermal conduction through MgO which acts as an electrical insulator within the body of the heater. Above 700C MgO looses its electrical insulation properties and begins to conduct electricity. Also heater wire like nichrome dosn't last long at elevated temperatures.

To get effective radient heating source should be several hundreds of deg. C above heated body . Short wave i.r. heaters like quartz tubes seem ideal since they burn at over 1900C and quartz can take temperatures much higher. Problems are they are fragile and ends need to be kept below 300C for electrical connections.

There may be many other issues I have overlooked.

 

[ScottyUK]

What is the surface finish of the steel? Heating a reflective surface using IR is likely to prove inefficient.

 

[Compositepro]

In a closed cavity the IR will be absorbed, although it may reflect a number of times before absorption.

 

[IRstuff]

"Heating a reflective surface using IR is likely to prove inefficient."

Actually, given that it's a closed volume, reflectivity should be irrelevant; that's the cavity blackbody effect. Given a high temperature source in the center of the well, the walls must rise in temperature, per laws of thermodynamics.

I assume you expect to be able to access the parts after heating, so part of the electrical heating question is tied to using wells for the heating. As I stated earlier, there are commercial furnaces that exceed 1200°C using electrical heating, but from the outside in:

http://www.thermcraftinc.com/diffusion/fibercraft.html

You'd place your samples inside the coils. I would assume that you could get a custom design that was more rectangular in shape.

TTFN
faq731-376

 

[IRstuff]

For that matter, why not just a conventional box furnace:

http://www.thermcraftinc.com/box-furnaces.html

http://www.thermcraftinc.com/umages/pdf/GeneralPurposeBoxFurnaces.pdf

Seems to me that you're essentially building your own furnace. Note the smallest furnace at 12"x15"x30" consumes 18 kW. If your losses are comparable to that, the heater design is non-trivial.

TTFN
faq731-376

 

[asimpson]

I tried using 1 kW quartz halogen i.r. tube and it worked quite well in the short term. So far so good.

What would be the effect on the life of heater tube to have its temperature maintained above 1000C even when not heating? Would this adversely effect the halogen cycle? Or would it extend heater life by preventing tungsten depositing on quartz tube inner surface?

 

[asimpson]

I understand zone of quartz halogen tube near electrical feet-through must be kept below 300 C . This can be done by keeping tube connector in ambient air and feeding through thermal insulation to how zone.

 

[IRstuff]

Quartz has a finite life at 1000°C, but that's longer than if it were at 1100°C. One option is to drop the temperature to, say 900°C, when not in use. This would substantially increase the life.

TTFN
faq731-376