Sintering Atmosphere

[youtectic]

Can anyone advise on a problem observed looking inside a continuous mesh belt sintering furnace whilst at temperature, there appears to be a 'will o the wisp' haze at the front section just on and above the belt in the preheat zone just behind the flame curtain, this doesn't seem to moving around much considering the amount of gas flow which should be moving towards and passing over and through this area of the furnace, what exactly is this?

 

[EdStainless]

Out/off gassing, either from your parts of from the belt. I have seen cases where the belt was picking up debris on its return and this has to burn off someplace. Or it could be one of the components of you lube.
What is it hurting? Are you making density and properties?

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P.E. Metallurgy, Plymouth Tube

 

[youtectic]

Hi
Thanks for the reply, the observed situation was made when the furnace was empty and yet to be loaded. My concern is would this be detrimental to any components to be loaded into the furnace particularly because Of the unsure nature of what this "wispy haze' was. I am surprised that the gas flowing through the furnace and towards the front was not causing more turbulence of the haze? I just wondered what the haze could be and what may be causing this.

 

[EdStainless]

First, do you know how much gas you have flowing out the front of the furnace?
And second what oxygen and dew point are you running (and what gases)?
It could be some condensation from the flame curtain or debris on the belt.

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P.E. Metallurgy, Plymouth Tube

 

[youtectic]

Sorry for the delay in replying to this post, the gas levels and flow settings have not changed, Nitrogen/Hydrogen are the main gases.
The haze area is behind the flame curtain and constantly comes from a point which is on top of the belt surface in a central position only and never moves from that area even though the belt is moving through the furnace , the flame curtain is free of any moisture/condensation.

 

[EdStainless]

The flame curtain contains products of combustion, a portion of which is water. If it does not vent well some of this moisture can be carried into the furnace, especially if the belt is cold and moisture can condense on it.

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P.E. Metallurgy, Plymouth Tube

 

[Compositepro]

If the belt is cold entering the flame curtain water will condense on it before it heat-up. As the belt heats the water will turn to steam. Your purge flow would push this steam back toward the cold part of the belt where it would recondense on the belt. That is one possible explanation.

 

[metman]

From your description, the haze appears to be very localized and minimal in volume(mass). This does not seem like it would be detrimental - maybe some surface discoloration on the parts or slight decarburization if they are steel parts. If you have a flame curtain burning, it is evidence of a positive outflow of Hydrogen which should reduce any oxides that might be present in the haze gas. You could run some samples, not necessarily actual parts, if they are expensive.

Design for RELIABILITY, manufacturability, and maintainability

 

[youtectic]

Thankyou for your replies, you are correct metman the haze is very localised and never really moves about much (strange considering the gas flows), I have never seen this before and just wondered if anyone had witnessed this type of event.

 

[metman]

First, do you know how much gas you have flowing out the front of the furnace?
And second what oxygen and dew point are you running (and what gases)?
It could be some condensation from the flame curtain or debris on the belt.

The op is running N2 apparently for purging or neutral atmosphere and H2.
Good point "what dew point?" Yes what dewpoint is the H2?

]The flame curtain contains products of combustion, a portion of which is water. If it does not vent well some of this moisture can be carried into the furnace, especially if the belt is cold and moisture can condense on it.

Could be H2O vaporizing - dew point?


Design for RELIABILITY, manufacturability, and maintainability