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preheated air


Seerp Visser
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Hello this is the first topic i try to write for the forum. I am reading the topics regularly and feel that i should do something in return for all the usefull info i get from you all.

I am a blacksmith in Belgium and we sre starting to try to make Wootz.

We started with following a workshop with Andreas Schweickert and now we are in the process of building a furnace.

 

Our first test results of the furnace with burner were supprising us.

 

We used a gastank as done by many and a burner following a design obtained from Andreas Schweickert.

As extra we installed a preheating system for our air.

As fuel we used NLG, what is in our country a mixture between Propane and Butane. In the summer there is less Propane in the mixture and in the winter more. During our tests the max gaspressure we used for combustion was 0.7 Bar.

 

We had already made some tests with our burner and it flamed well.

Now with the preheating system installed and in a period of 45 minutes we melted some pieces of steel. The last piece was ARMCO,a steel with 0,01% Carbon only. It melted as was our furnace an induction coil.

 

Furthermore our pyrometer (range up to 1600 oC) showed an overload sign.

After the test we found that the lining of our furnace was partly melted (concrete 1500 oC) and a hole in the bottom lining had appeared where the pieces of iron rested.

 

The preheating system heated the inlet air from 21 oC up to 42 oC.

 

So i think we may conclude that preheating air is very attractive way to obtain a higher temperature with lower fuel comsumption.

 

Seerp Visser, Klaas Remmen and Dimitry Gyselinck

Wootzoven trace 100504 spiraal voorverwarming klein.jpg

Wootzoven trace 100504 brander klein.jpg

Wootzoven trace 100504 002 (1).JPG

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Looks nice. But i think your preheater will not last long.

Wouldn't a heat gun a better choice?

 

Ciao Sven

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Hi.

 

Desing looks nice, but I do have doubts about how long it work.

There is not enough space for insulation + hi temp cast...also..

I think it will go way too hi temp and gas air mix can self ignite..and thats not good at all.

But if you have measured it the way you said ok..not too hi.

 

You mentioned using all most pure iron as test...but did you use crucible?

I think there is slight differens if iron melts at dirrect flame...or in crucibe.

In dirrect flame there can be a lot of oxygen and it will make iron burn...and yep melt at some point.

 

Im not saying that you cant melt iron...guite easy in fact if you get temps like that +1600 and over.

But could be safer to run that coil tube around the furnace body out side and channel it there to burner..it gets hot anyways.

Also if preheating is the way you wanto fabricate furnace, might wanto think thermocouple in airtube to look air temp...just in case.

 

Anyways, looking interesting and I hope you guys run safe melts soon.

 

BR

Niko

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Hello this is the first topic i try to write for the forum. I am reading the topics regularly and feel that i should do something in return for all the usefull info i get from you all.

I am a blacksmith in Belgium and we sre starting to try to make Wootz.

We started with following a workshop with Andreas Schweickert and now we are in the process of building a furnace.

 

Our first test results of the furnace with burner were supprising us.

 

We used a gastank as done by many and a burner following a design obtained from Andreas Schweickert.

As extra we installed a preheating system for our air.

As fuel we used NLG, what is in our country a mixture between Propane and Butane. In the summer there is less Propane in the mixture and in the winter more. During our tests the max gaspressure we used for combustion was 0.7 Bar.

 

We had already made some tests with our burner and it flamed well.

Now with the preheating system installed and in a period of 45 minutes we melted some pieces of steel. The last piece was ARMCO,a steel with 0,01% Carbon only. It melted as was our furnace an induction coil.

 

Furthermore our pyrometer (range up to 1600 oC) showed an overload sign.

After the test we found that the lining of our furnace was partly melted (concrete 1500 oC) and a hole in the bottom lining had appeared where the pieces of iron rested.

 

The preheating system heated the inlet air from 21 oC up to 42 oC.

 

So i think we may conclude that preheating air is very attractive way to obtain a higher temperature with lower fuel comsumption.

 

Seerp Visser, Klaas Remmen and Dimitry Gyselinck

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Seerp,

 

There is is mixed blessing here..efficiency is good as kilograms of fuel consumed per kilogram if steel melted should get lower, Being able to attain very high temperatures making wootz may not be an advantage. There are other ways to increase efficiency..it is kind of like tuning up a hot rod car.

 

Your design is a good one that SS tube should last a while....but your cooling gasses ( the fuel and air) are hugging the outside and the heat is mostly near the center....you may want to allow some of the heat to escape near the outside wall ( where your tube is touching that wall).

 

It will be nice to hear people express the total weight of fuel consumed and the weight of their ingots.

 

Thanks for sharing your ideas...they will probably evolve into a preheat temperature of about 150 DegC.

 

Jan

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It will be nice to hear people express the total weight of fuel consumed and the weight of their ingots.

 

Jan.

 

Last continuous run whit 33kg gas tank produced 8 kg of crucible steel

The first one takes 90 min and next after this 30min...but notised that there was no differens to 4 kg ingot.

4 kg ingot did melt same time ( 30 min ) whit same gas / air pressure.

So if first melt is 2 kg / 90min and next 3 x 4 kg, 30 min per run..total could be as hi as 14kg whit 33kg of gas..

But is there any point melting 4 kg ingots...just maby not...other issues will rise up.

 

But I do think that 8 kg crucible steel whit 33kg gas is not that bad...even its whole day job...Charge,melt,cooling down,new charge,melt,cooling down.....

 

Niko

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Jan.

 

Last continuous run whit 33kg gas tank produced 8 kg of crucible steel

The first one takes 90 min and next after this 30min...but notised that there was no differens to 4 kg ingot.

4 kg ingot did melt same time ( 30 min ) whit same gas / air pressure.

So if first melt is 2 kg / 90min and next 3 x 4 kg, 30 min per run..total could be as hi as 14kg whit 33kg of gas..

But is there any point melting 4 kg ingots...just maby not...other issues will rise up.

 

But I do think that 8 kg crucible steel whit 33kg gas is not that bad...even its whole day job...Charge,melt,cooling down,new charge,melt,cooling down.....

 

Niko

 

Thanks Niko,

I will post my next run as well.

Jan

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Hi.

 

Desing looks nice, but I do have doubts about how long it work.

There is not enough space for insulation + hi temp cast...also..

I think it will go way too hi temp and gas air mix can self ignite..and thats not good at all.

But if you have measured it the way you said ok..not too hi.

 

You mentioned using all most pure iron as test...but did you use crucible?

I think there is slight differens if iron melts at dirrect flame...or in crucibe.

In dirrect flame there can be a lot of oxygen and it will make iron burn...and yep melt at some point.

 

Im not saying that you cant melt iron...guite easy in fact if you get temps like that +1600 and over.

But could be safer to run that coil tube around the furnace body out side and channel it there to burner..it gets hot anyways.

Also if preheating is the way you wanto fabricate furnace, might wanto think thermocouple in airtube to look air temp...just in case.

 

Anyways, looking interesting and I hope you guys run safe melts soon.

 

BR

Niko

 

thank you for your advise and commments. next run we will check the temperature of the inside of the insulation at the place of the coil. I think we still have more than 2 inch insulation on either side of tube coil. For your interest i will measure the insulation thickness. The inox tube is cooled by the inlet air and is placed at the top of the furnace (not the hottest place) and the heat we are taking away from the furnace has passed already the crucible. Perhaps we loose a slight amount of radiation heat by a cooler upper part of the furnace.

I found in books that in the past preheating of air was used for steel melting furnaces. They mention 10% gain.

What lgnition danger concerns. It was remarkabel that the temperature of the air raised to dubbel (42 oC only). The mixing with the gas is done in the burner that comes after the coil in the tank.

 

I think with a lower gas pressure (down to 0.5 bar??) we can control to a lower temperature. I hope that we can arrange to a better controlled process.

 

We shall keep you informed of our next tries if there is anything special occurring. As well with the use of crucibles.

We did ot use a crucible but put a bar of steel straight in the furnace.

To install a coil at the outsie of the furnace is more difficult to bring enough heat to the outside trhu the wall of the tank.

Now the temp of the outside of the tank raised to 70 oC only.

Seerp Visser

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Seerp,

Good idea to preheat the air.

If you inject the gas at the last point with a mixing of the hot air/fuel then you get little chance of a dangerous burn.

 

 

http://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html

ignition tempos of fuel gasses vary with the chart used and your mix is not what I use, but NG is about 1076F and propane is 842F

 

I had heard propane was 1100F, but...

 

I believe SANDIA national labs in the US did a study where they found a 30% fuel savings with preheated air at 1,000F...or so I recall.

However,

I am not sure that fuel savings equals more heat. The total heat potential for a fuel is a matter of air and fuel and how that heat is contained..if you get improper ratios of fuel/air or poor insulation or the max burn is just prior to exiting the furnace then you will loose heat that could go to the metal.

Also there is the issue of what the crucible can take for heat and how the steel reacts to that temperature.

 

I am all for fuel savings, but what is the payback for that design..how much fuel is saved vs the cost of the materials in the design of the furnace.

 

Ric

Richard Furrer

Door County Forgeworks

Sturgeon Bay, WI

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I am not sure that fuel savings equals more heat.

 

 

The Sandia Lab Forge was designed with preheated air because they needed a forge that would get up to welding heat at high elevations. So preheating the air did get them more heat. If things get to hot that way just turn things down a bit. You should save fuel that way.

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I am not sure that fuel savings equals more heat.

 

 

The Sandia Lab Forge was designed with preheated air because they needed a forge that would get up to welding heat at high elevations. So preheating the air did get them more heat. If things get to hot that way just turn things down a bit. You should save fuel that way.

I am not sure the dynamics are the same with venturi vs forced air, but I recall the SANDI plans has a short chamber for the flame to burn after mixing...perhaps a larger chamber would make a difference or a "pre burner" flare on the forge chamber so the combusting fuel/air has room to expand and completely burn before exiting the furnace.

Max heat is max heat..its all in how you get it to burn and how that heat is channeled and contained. Fuel savings is one thing, but max heat is another...the BTU should be the same.

 

I am not convinced, but such is the way of theorizing.

 

Ric

Richard Furrer

Door County Forgeworks

Sturgeon Bay, WI

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  • 1 year later...

Ric,

The forge works well. We have made a number of Wootz cakes and they come out fine. We start the forge slowly and after heating up we fire with propane on a pressure of 0.6 bar or 8.6 psi. that is the maximum. After the mixture is fluid we slowly drop the pressure till we are sure the cake has a temperature of approx 700 degrees s C or 1300 degrees F.The whole process takes between two and a half or three hours.

We tested with a welding rod what melts fast in the forge.

Ihe inlet air is heated from 20 degr. C up to 60 degrees C (140F).

 

So we thought we found the ideal forge with top class burner and preheating. Now things changed a little bit. Not with melting the Wootz, but we are now building an oven to make damascus steel and with testing we could not reach a good welding temperature. The oven has no preheating but the same type of burner as our Wootz forge, only one size smaller. Since it did not work we developed about 9 other type of burners but without success. since we could only measure temperatures up to 1200 degrees C (2200 F) we ordered a thermocouple for higher temperatures. this has not yet arrived.

The first forge is quite small with an internal diameter of about 4 inch and 2 inch insulation. The outside became very hot and probably we are wasting a lot of heat through the larger openings at the front and rear of the oven. the outside of the oven became quite hot. We used an heat resistant glass panel, but this is not a great success.

 

So now we have build a second oven with a much larger diameter outside, inside 5 inch diameter and 4 inch at front and rear, with 3 inch insulation and doors we can close. As well we added a preheating system.

just as with our Wootz forge we take the heat from places iln the oven, where we don't need the heat for our Damast package.In this case from the front and rear.

As you can see we did not add the opening for the burner yet since we are developing the burner system. One of our new burners gives a much higher temperature than the burner form the Wootz forge. the pipe you see at the side is the outlet of the preheated air what will be connected to the inlet of the burner.

 

 

We will inform you as soon we have completed and tested our new oven and know about which temperatures we are talking.

 

We will do tests with and without preheating to find out the difference.

To my opinion at present, it makes an important difference, especially since we work at the maximum possibilities of propane.

 

Seerp

Oven Seerp 1112 1a klein.jpg

Damastoven II Luchtvoorverwarming klein.jpg

Oven Seerp 1201 detail luchtvoorverwarming klein.jpg

Oven Seerp 1201 klein.jpg

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I cannot say that I like the way you are heating up the forge with all the fibres inside without any coating. It could well be that you always have an amount of extra small fibres in the air due to the strong gasflow and the heat. A good coating could be of help!

The small bed, probably made from a firebrick or crock? will not withstand Borax very long, so it would be much better to use a cutopen crucible (A6 is a good size)for a bottom inside the forge.

The use of a good shaped flare will help rise the temps a lot -with the right ratio of gas-tip and pipe diameter, depending on the use of a venturi or airpressure system.

In both of your forge/smelter the fire seems to go in straight (which should be a nono when you read the instructions of how to use a crucible (tangential flame only!) so why not in a more kind of a flow like a circle? Most of the heat for forging comes from ultrared heat inside the gasforge and not directly from the flare (which might be the coldest point in the system, as Niko once pointed out)

 

by the way: what kind of foil did you use around the pipe? It is not aluminum is it?! even behind 5cm of insulation it might start to melt and ruin the coating...

just my 5 cent

 

Hi Sven, nice to see you here!

Edited by Jokke

Jokke

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Ric,

The forge works well. We have made a number of Wootz cakes and they come out fine. We start the forge slowly and after heating up we fire with propane on a pressure of 0.6 bar or 8.6 psi. that is the maximum. After the mixture is fluid we slowly drop the pressure till we are sure the cake has a temperature of approx 700 degrees s C or 1300 degrees F.The whole process takes between two and a half or three hours.

We tested with a welding rod what melts fast in the forge.

Ihe inlet air is heated from 20 degr. C up to 60 degrees C (140F).

 

So we thought we found the ideal forge with top class burner and preheating. Now things changed a little bit. Not with melting the Wootz, but we are now building an oven to make damascus steel and with testing we could not reach a good welding temperature. The oven has no preheating but the same type of burner as our Wootz forge, only one size smaller. Since it did not work we developed about 9 other type of burners but without success. since we could only measure temperatures up to 1200 degrees C (2200 F) we ordered a thermocouple for higher temperatures. this has not yet arrived.

The first forge is quite small with an internal diameter of about 4 inch and 2 inch insulation. The outside became very hot and probably we are wasting a lot of heat through the larger openings at the front and rear of the oven. the outside of the oven became quite hot. We used an heat resistant glass panel, but this is not a great success.

 

So now we have build a second oven with a much larger diameter outside, inside 5 inch diameter and 4 inch at front and rear, with 3 inch insulation and doors we can close. As well we added a preheating system.

just as with our Wootz forge we take the heat from places iln the oven, where we don't need the heat for our Damast package.In this case from the front and rear.

As you can see we did not add the opening for the burner yet since we are developing the burner system. One of our new burners gives a much higher temperature than the burner form the Wootz forge. the pipe you see at the side is the outlet of the preheated air what will be connected to the inlet of the burner.

 

 

We will inform you as soon we have completed and tested our new oven and know about which temperatures we are talking.

 

We will do tests with and without preheating to find out the difference.

To my opinion at present, it makes an important difference, especially since we work at the maximum possibilities of propane.

 

Seerp

 

 

Seerp,

I have never used a burner which was not connected to a blower..but I have gone really hot and I do not like it, as everything goes to hell at 2800 deg F. Though I do not do a lot of laminated steel welding, normal welding temps of 2000 to 2400 degF seem fine...and the corners of the steel are not dripping . Things just do not seem to hold up at those high temperatures.

 

Jan

Edited by Jan Ysselstein
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Jokke,

The coating still has to be added.

The burner opening is not yet made (with the tapered entrance of the gas) and the coating becomes very hard. So i add the coating when finishing the oven.

 

Jan,

Indeed this is alu foil. I expect the air inside the tubing will cool the pipe. I expect a temperature rise of maximum 100 degrees C before entering in the burner. The air in my Wootz oven rises 40 degrees, from 20 to 60 degrees.

In case the airflow stops or when i don't use the preheating system i can expect problems with the aluminum. The foil is made for exhaust systems and can stand some heat. However even if the aluminum should melt the pipes are well covered in the insulation so i don't expect a loss of air in my oven, but ... we will see. The pipes are made from woven flexible stainless steel.

 

When i can reach a temperature of 2400 (1300 oC plus) i shall be content. The 2000 (less than 1100 oC is too low. The first small oven on the photograph above reached over 1200 oC (2200 degr. F) that is also just too low.

What the preheating systm concerns, even when i can reach the required temperature by using an atmospheric burner or a burner with forced air, i still like to test the difference in fuel consumption.

 

Seerp

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