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Need help/advice on Sword heat-treating forge (and confessing my ignorance)


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Hey everyone!

I'm in need of some substancial help on my heat treating forge, and in order to recieve help I am going to have to gladly confess my ignorance in this area...

 

So I love making swords, and feel stable in my abaility to make them well and stand by my work and its quality.

However...

When it comes to tool-making, I'm not a fan... at all.

I'm usually lazy, impatient, and downright ignorant when it comes to making or fixing tools.
At the end of the day I just want to make swords, not damn grinders and forges!

(This is why Andy and I got so much done together. Building amazing tools is a major talent of his) ;)

 

So with that said; I need to get my heat treating forge working better, and I dont know where to begin, because if I'm honest:

despite the fact that I've been bladesmithing for over 10 years now, I for some reason still feel like I know next to nothing about proper gas forge construction or usage.... :/

(Pathetic I know, but the truth)

 

 

So, here's the lowdown on my heat treating forge.

Its strange, finicky, and troublesome upon ever single use.

 

Because its been so unreliable over the years I dont even use it for every sword, though I would like to. Almost every sword that I've made is heat treated in a new and creative problem-solving way, or in one of my other forges or at a friends shop.

But I would like to get this particular forge working consitnantly.

 

The two main issues:

- It sputters

- it seems to get uneavenly heated

 

Here is a video:

 

http://www.youtube.com/watch?v=REzj9vSdQDI

 

And some photos:

 

10553260135_e2c6833461_z.jpg

 

10553515133_ffcdc8d093_z.jpg

 

10553324914_afc2cb36d3_z.jpg

 

The sputtering: I dont know what this means? Or if its somehow even dangerous given the burners I'm using?

Given that I'm using what I assume to be called "atmospheric burners" in a space this large: do I need more air going into the burners or less?

Could the sputtering have to do with the way I've built my burners, or my forge??

 

I really dont understand the benifit of forced air burners in this regard. Every time I've tried to build one the air seems too powerful and just blows out the flame? Does this forge NEED to be forced air, or are atmospheric burners fine??

 

Also as you can see in the photo above; I'm getting hot spots where the burners hit the walls. Thus I'm not sure if I'm really getting heat to swirl or not, and seems like one side of the forge is clearly hotter than the other.

 

How much does the size of the forge change the way the burners work?

 

I'm not even sure what else to ask, other than asking that you guys simply share any advice or ideas that come to mind?

 

 

I reall really really appreciate it guys... ;)

Thanks so much!

 

- David

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In my limited experience, hotspots mean you don't have enough insulation in place--easy fix--another layer of icf and satanite. I've had issues with sputtering in the past in my main forge and it seemed to be a combination of poor draft control (it would stop once it was at temp and pulling in air it wanted, the way it wanted), and too little gas for the amount of air passing through, but your fire looks quite reducing, so I don't know.

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I had some issues with my gas line sputtering as SOON as I built my forge. One of the smiths here messaged me and said it might be that the opening to the actual forge was letting in too much air. Crossdraft, I think he called it. I have since managed to close off a lot of that opening, but haven't had the time to test it yet.

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I don't know too much about fixing the burners (if that is part of the problem) but one way to help equalize the heat would be to put a physical damper/barrier between the flame atmosphere and the sword (i.e. a pipe). The convective heat transfer will likely be, in this configuration, more inconsistent than radiation. By having a pipe of a little larger diameter than the width of the sword, the thermal conductivity of that pipe will normalize the temperature and radiate it to the sword at much more even levels than simply holding it in the forge. The only downside would be that it takes a little longer to come up to temp on the inside of the pipe. Also, I should mention that I have only done this on smaller/thinner things where the edge overheats too quickly with direct exposure to the burner flame.

 

John

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I agree with John, the hot spot issue *might* be solvable with some form of piping inside the forge. That would help even out the heat, though not eliminate hot spots. It sounds like the forced air burners you tried had too much air coming from the blowers, from my (admittedly limited) research and knowledge, the blower should only be in the 50 cfm range.

 

I'll be watching this post with interest, and I can't wait to hear the other more experianced guys chime in.

 

Good luck!

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Looks like you might have more forge than you got burner. I've seen forges half that size with three burners on them. But I have never dealt with anything that big, so I'm only guessing,

 

Search back a month or more and read the advice Geoff Keyes has given us on blown burners. If you're trying to figure it out on your own, this might be the way to go. Some folks put a gate valve between the forge and the blower to regulate air volume. I think Geoff said he just uses one of those flat magnets (like come stuck to the new phone books) over the fan intake and varies the opening to control the air.

 

Good luck.

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One other thing I might try (purely conjecture) would be to angle the burners very slightly so they point a hair upwards. That would help with the swirling motion in 3 dimensions, making everything blend together more smoothly. And adding a 3rd burner in the middle would be a help, even if it meant running them all at a lower PSI to compensate for the additional output.

 

John

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im planing on using the pipe idea on the sword forge im making and using a single forced air burner like mister fogg

 

when i was making my first forced air burner the first thing i figured out was if you have to much air you can valve it down but not enough air and your making a flame thrower and going to lose some eyebrows im running one just under 100 cfm for my geniral forge and for the sword forge i got a 150-160cmf fan to work with

 

sputtering usally means needs more gas might be your regulator building up a pulse

 

also i dont want to see any blue flame out my door if i have that i need to alow more air in the mix

 

if your getting to much propaine you can get a cool spot were the gas is hitting the forge wall back of on the gas or add air

 

with thoes burners you might be able to play with the distance of the gas orifice to the gas/air pipe neck down and get a better burn but u might try a difrent regulator or difrent tank to be able to rule them out as the sorse (man i miss spell check)

 

just looked it your set up get your selfe some gate or needle valves at both burners so you can adjust them for flow i would run up to 10 psi or more on my ventury burner to get it hot enough for some work and had a regulator on the forge to adjust my forced air has the reg and gates valves for air and gas so i can dile it in like an oxy torch full control it was a bit of fun to get it in to the sweet spot but now that it is i only adjust it when chainging from forging to welding

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David I've been fighting this as well and to be honest.. it takes all the fun out of swords. I've tried a vertical gas like yours and I could never get an even heat.. although I never tried two burners. With venturis like yours.. I've never been able to get them to run well at low pressures for heat treating. My blown burner can easily run at even below austenitizing heats.. but you can't fight physics in a vertical set up. With a horizontal set up I fight the blades warping under their own weight.

 

I tried electric and that was a disaster.

 

I believe the only good solution for double edge swords (maybe not Japanese) is do salt pots.

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When you choke both burners all the way back the problem goes away, and the flame coming out the top indicates a reducing atmosphere. Blue flame out the top is an indication of excess fuel to oxygen and thus, a reducing atmosphere. I would be inclined to run the forge for about 20 minutes, with the burners choked almost all the way back, and then peek inside and see how it looks. My horizontal setup with one Micro burner from Hybrid Burners takes about 15-20 minutes to reach temperature. Until it has heated up enough, the heat inside is inconsistant but, as it heats up (to my eye) things seem to even out.

 

It is my belief that the sputtering you are experiencing is because your venturi burners are not able to pull enough oxygen through the burner to keep up with the volume of fuel. It starts off drawing oxygen then, some force, friction or backpressure, slows down the flow of oxygen and it sputters. You could try making the orifice smaller, by the way, what orifice size are you running at now? A venturi burner requires a high pressure of fuel gas, through a small orifice, to develop the capillary draw that pulls oxygen through the burner for combustion. Another issue, that could be contributing, is that your burners do not appear to have a flair but, instead, just a straight pipe directly into the forge. A venturi burner requires something at the end of the burner tube to slow the gases down and allow combustion. I have had good luck with a reducing coupler, that it is going from small to large into the forge. Others will tell you that you must have a flair of "X" degrees.

 

Switching to a forced air system would likely solve many of the issues you are having and also provide you with more heat to get the furnace up to temperature faster.

 

I am somewhat confused by the burner placement of your forge. Heat rises. I would think, for a vertical forge, you would want the heat coming in about 1/3 of the way up. My thought process is that you want a slightly cooler zone, at the bottom, for the tip because, it heats up so much sooner than the rest of a sword.

 

~Bruce~

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He Guys!

 

Thank you all sooo stinkin much for your awesome advice and wisdom. All of it is really helpful and has made me think of things that have not crossed my mind, so thank you!!

 

 

By having a pipe of a little larger diameter than the width of the sword, the thermal conductivity of that pipe will normalize the temperature and radiate it to the sword at much more even levels than simply holding it in the forge.

 

This is a clever ida, and its actually one that Andy and I tried ages back with this forge, with not much success however.. :/

Though maybe I need to give it another try?

It did indeed take a crazy long time to heat up, and even then I think the blade was not getting hot enough.

 

 

David I've been fighting this as well and to be honest.. it takes all the fun out of swords. I've tried a vertical gas like yours and I could never get an even heat.. although I never tried two burners. With venturis like yours.. I've never been able to get them to run well at low pressures for heat treating. My blown burner can easily run at even below austenitizing heats.. but you can't fight physics in a vertical set up. With a horizontal set up I fight the blades warping under their own weight.

 

I tried electric and that was a disaster.

 

I believe the only good solution for double edge swords (maybe not Japanese) is do salt pots.

 

I totally feel you hear Scott. Though I dont think salt pots are ever a forseeable option for me. Out of do-ability, cost, and personal choice. I find them too dangerous and troublesome.

 

I didnt know you've tried electric before?

That has been another one of my thoughts honestly... Because I've talked to a few other swordmakers who swear by them!?

this interesting build thread comes to mind:

 

http://sbgswordforum.proboards.com/thread/5863

 

Simply taking two electric kilns and stacking them on top of eachother???

It almost seems too easy?... :/

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sputtering usally means needs more gas might be your regulator building up a pulse

 

also i dont want to see any blue flame out my door if i have that i need to alow more air in the mix

 

if your getting to much propaine you can get a cool spot were the gas is hitting the forge wall back of on the gas or add air

 

with thoes burners you might be able to play with the distance of the gas orifice to the gas/air pipe neck down and get a better burn but u might try a difrent regulator or difrent tank to be able to rule them out as the sorse

 

That is really great advice!

Thank you!

I definitely do need to play around with the distance of the orifice and the air mixture.

I may re-hookup the blowers just to see what they do?

 

When you choke both burners all the way back the problem goes away, and the flame coming out the top indicates a reducing atmosphere. Blue flame out the top is an indication of excess fuel to oxygen and thus, a reducing atmosphere. I would be inclined to run the forge for about 20 minutes, with the burners choked almost all the way back, and then peek inside and see how it looks. My horizontal setup with one Micro burner from Hybrid Burners takes about 15-20 minutes to reach temperature. Until it has heated up enough, the heat inside is inconsistant but, as it heats up (to my eye) things seem to even out.

 

It is my belief that the sputtering you are experiencing is because your venturi burners are not able to pull enough oxygen through the burner to keep up with the volume of fuel. It starts off drawing oxygen then, some force, friction or backpressure, slows down the flow of oxygen and it sputters. You could try making the orifice smaller, by the way, what orifice size are you running at now? A venturi burner requires a high pressure of fuel gas, through a small orifice, to develop the capillary draw that pulls oxygen through the burner for combustion. Another issue, that could be contributing, is that your burners do not appear to have a flair but, instead, just a straight pipe directly into the forge. A venturi burner requires something at the end of the burner tube to slow the gases down and allow combustion. I have had good luck with a reducing coupler, that it is going from small to large into the forge. Others will tell you that you must have a flair of "X" degrees.

 

Switching to a forced air system would likely solve many of the issues you are having and also provide you with more heat to get the furnace up to temperature faster.

 

I am somewhat confused by the burner placement of your forge. Heat rises. I would think, for a vertical forge, you would want the heat coming in about 1/3 of the way up. My thought process is that you want a slightly cooler zone, at the bottom, for the tip because, it heats up so much sooner than the rest of a sword.

 

~Bruce~

 

Thank you Bruce!

This is great knowledge and makes a lot of sense.

 

I agree that my burner placement is weird.. :/

Its due to the fact that Andy and I made it years ago when we didnt know what we were doing.

But it seems to work fine? (when the forge is running fine)

And its a much taller forge then it appears in the photo, so most sword tips are not near the floor.

 

 

I am going to apply all of these points and thoughts on the forge tomorrow when I work on it.

 

Thanks so much again gentlemen!

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And another thought....

 

If anyone has any thoughts on the do-ablity of this weird home-made electric kiln sword-heat treating method:

http://sbgswordforum.proboards.com/thread/5863

then please chime in!

I'm really intrigued by it, and want to know more, because kilns are dirt cheap on craigslist and its tempting...

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And another thought....

 

If anyone has any thoughts on the do-ablity of this weird home-made electric kiln sword-heat treating method:

http://sbgswordforum.proboards.com/thread/5863

then please chime in!

I'm really intrigued by it, and want to know more, because kilns are dirt cheap on craigslist and its tempting...

Yeah David.. I tried building a kiln in a way similar to the link you posted... .combining two kilns. Although I took one small pottery kiln and built a fire brick extension. The problem I see with the set up in that link is that it is vertical. You will get much higher temps towards the top of that thing. Heat rises and there is nothing you can do about it. If I had a system like that I would use it for heating a salt pot. Horizontal will provide a much more even heat.. but I didn't like my horizontal sword kiln because it was so difficult getting the blade in and out without bending the crap out of it. Single edge swords are fine.. but double edge was difficult. I also fought with a poor knowledge of electrical systems and I got sick of tinkering. If you are going to go electric I would message Michael Lenaghan and look into the company that built his kiln. I think it would save you a lot of heartache going that route.

 

How much research have you done on salts David? The more I look into it... it doesn't really seem all that complicated or difficult. They get a bad rap for safety.. but the issues are pretty simple regarding that. If you can build a sword length vertical gas forge then you are already part way there! The expensive part is getting the tube itself.... but really.. it's only $500 or so. I sent you a FB message... let me know if you want to talk more about this stuff. It's all a pain.

 

edit: If you want to go with a blown system.. just build the Don Fogg style... 1.5" pipe with 1/4" nipple to accept gas line welded into the side.. and then at least a 65 cfm blower attached.. and then a tapered 1.5" burner tube (black pipe). You can get it all at the hardware store (except blower) and have it built in less than an hour. It's hot and efficient and idles like a dream.

Edited by Scott A. Roush
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I don't know if I can explain this well. When I've tried face to face, folk either get it straight away or their eyes glaze over.

 

It is important to understand the difference between heat and temperature.

 

We can adjust the temperature at which gas burns by adjusting the air-to-fuel ratio. Maximum temperature is achieved when all of the fuel gas burns with all of the oxygen in the air, leaving no unburnt gas and no unburnt oxygen. This is a neutral flame.

 

If we add more air, it can't contribute to the burn, because all the gas has already been used up. All that happens is that the extra air absorbs some of the heat energy and reduces the temperature of the flame. Because there is unburned oxygen remaining, this gives an oxidizing flame.

 

If we go the other way and increase the amount of gas, it can't contribute to the burn, because all the oxygen has already been used up. All that happens is the extra gas absorbs some of the heat energy and reduces the temperature of the flame. Because there is unburnt gas remaining, this gives a reducing flame. Once the hot unburnt gas leaves the forge, it mixes with air, gets the oxygen it needs and continues to burn as the dragons breath.

 

What I think you need to do is adjust your burner to give a flame of the correct temperature. I think you'll be choked down quite hard on the air port. You should then be able to increase your gas pressure to make the flame bigger (but not hotter). The area by the burner will always be hotter than the last few inches of the forge, but increasing the size of the flame should reduce the differential. At some point, you'll get an even enough temperature to be usable.

 

Running with the flame much hotter than the temperature you want will just cause uneven heating.

 

If at all possible, get hold of a thermocouple and readout and measure the flame temperature whilst adjusting the air.

 

Sputtering is often a result of too low a gas pressure. When the flame travels through the mixture faster than the mixture is moving in the opposite direction, it will run down the burner tube until it runs out of mixture to burn. The flame will then go out. The gas continues to be fed, draws air, mixes with it and, shortly after, reaches the forge, where it ignites and the process repeats. Often, increasing gas pressure wil cure the sputtering because it increases the mixture speed until it is faster than the flame speed.

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Hi David, I fought with a 2 burner gas forge like yours for a while and after having a couple swords go bad after HT and putting 60-80 hours into them I went electric!

 

http://www.bladesmithsforum.com/index.php?showtopic=23692&hl

 

I can send you the details if you like, it was alot cheaper then you'd think and they made it to the size I wanted. all I have to do now set the temp i want and walk away :lol:

 

For double edge blades I made a little holder to keep them on the edge and you just need to be careful picking them up, but never had any real problems with warppage

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David,

I spent more hours than I care to recall researching propane burn characteristics and burner designs before building my forge. And yet more time troubleshooting after building my forge.

(edit: http://www.bladesmithsforum.com/index.php?showtopic=26862 )

So I want to jump in and give a few quick options that I hope will help you get that forge singing.

 

First thing, extend the gas injector so it reaches past the air intake and slightly down the throat of the burner tube. That greatly reduces the turbulence in the fuel/air stream and makes the burner much easier to tune. That change in itself may actually be all you need to stabilize those burners.

 

(edit to clarify: Based on your video, I am) Assuming you are getting adequate flow from your regulator, you are getting a sputter because the velocity of the fuel/air stream exceeds the velocity of the burn, or the turbulence in the fuel/air stream is disrupting the dynamics of the burn, either will push the flame away from the tube. That blow out reduces the combustion rate, slowing the air flow through the venturi and the flame moves back towards the tube increasing the rate of burn and thus air flow and you start the cycle over. Closing the damper reduces available air flow and therefore both velocity and turbulence resulting in a more stable but oxygen deprived (reducing) flame.

 

If extending the injector doesn't resolve the problem, the next thing to try is closing or restricting the openings to the forge to help control the air velocity on the other end. First openings I would close are the burner ports themselves as that will improve burner life as well as helping with the stability of the burn. Frankly I would suggest closing those while the forge is in operation simply to protect the burner tubes from exhaust gasses even if moving the injectors solves the sputtering issue.

 

Another approach is reducing the gas pressure which will reduce injector velocity and thus lower the air flow, etc. If you need the current gas pressure to reach temp, it may still be useful to back it off as the forge is heating up initially.

 

As the forge gets up to temp, two things will happen, 1 the heat will begin distributing itself a little better as the hot surfaces aren't absorbing heat from the swirling flame as quickly as they were when cold, though you will still likely have hot spots in the wall right in front of the burners. Second, a research paper I read, on the efficiency of propane fired industrial furnaces following different preheating processes, concluded that the burning characteristics of propane improve notably once the combustion atmosphere gets above ~900 F, that increases the velocity of the burn and can therefore make it more stable on the burner.

 

Hope you get your HT forge up and running more consistently!

James

Edited by James Spurgeon
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Guys, this is absolutely incredible information shared. Thank you SO much!
I really appreciate it

Yeah David.. I tried building a kiln in a way similar to the link you posted... .combining two kilns. Although I took one small pottery kiln and built a fire brick extension. The problem I see with the set up in that link is that it is vertical. You will get much higher temps towards the top of that thing. Heat rises and there is nothing you can do about it. If I had a system like that I would use it for heating a salt pot. Horizontal will provide a much more even heat.. but I didn't like my horizontal sword kiln because it was so difficult getting the blade in and out without bending the crap out of it. Single edge swords are fine.. but double edge was difficult. I also fought with a poor knowledge of electrical systems and I got sick of tinkering. If you are going to go electric I would message Michael Lenaghan and look into the company that built his kiln. I think it would save you a lot of heartache going that route.

 

I agree Scott. I think your right that messing with two kilns would be more work then its worth. And I see your point about saltpots. I'm begining to realize they are simpler and more do-able than I thought. But now with all of the info shared below I may be able to get this forge working reasonably well but I definitely am totally intrigued about simply commisioning one of those beautiful electric kilns to be made for me!

Looks like an investment well worth it possibly?

 

And Tim, that makes complete sense!
I think you are indeed right, and I'm going to apply all of this to the forge here in a little bit when I head out to the shop to work on it.

 

 

Hi David, I fought with a 2 burner gas forge like yours for a while and after having a couple swords go bad after HT and putting 60-80 hours into them I went electric!

 

http://www.bladesmithsforum.com/index.php?showtopic=23692&hl

 

I can send you the details if you like, it was alot cheaper then you'd think and they made it to the size I wanted. all I have to do now set the temp i want and walk away :lol:

 

For double edge blades I made a little holder to keep them on the edge and you just need to be careful picking them up, but never had any real problems with warppage


Now THIS is incredible!
:)
Thank you so much for sharing man!
Definitly an investment to consider in my shop...

 

David,

I spent more hours than I care to recall researching propane burn characteristics and burner designs before building my forge. And yet more time troubleshooting after building my forge.

(edit: http://www.bladesmithsforum.com/index.php?showtopic=26862 )

So I want to jump in and give a few quick options that I hope will help you get that forge singing.


James that is a wealth of knowledge that I am so thankful for you sharing!
Seriously, thank you so much. Will go through your list of things to try today while I work on it.

 

 

Thanks so much again everyone!

I think I definitely have enough info to work with in order to get this thing figured out now. So hopefully next update I'll have a smoothly-working HT forge. ;)

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Hi David.

 

I'm sorry if I missed that someone has given you this link before, but I thought this might help? http://www.britishblades.com/forums/showthread.php?99898-Vertical-heat-treat-oven it looks quite easy to build and inexpensive. A few months ago I cost it up and if I remember rightly it came under £200

 

Hope thus helps,

 

James

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David,

 

I feel a little like the student telling the teacher how to do things here.... and many have already given you great input. I have a very similar set up, and faught with the same issues when getting in running. I assume you are not running at pressures over 10 PSI to your burners. ( I am using a 0.030" welding tip in mine). I tried a 1inch tube and had the sputtering issues at lower pressure. I had to play with lenght, diameter, and orifice size for a while and ended up using a 3/4 " main tube and a longer flare that tapered up to 1.25" over maybe 2.5".The issue was I simply didn't have enough velocity to offset the burn rate and the flame wanted to burn back into the main tube, especially at lower pressues. also with the opening being so small (as mine is) you are creating some internal pressure that is also wanting to push back up your burners. does it run better with the top open?

 

I hope this is of some use to you.

 

Ian Fuller

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You could have some back pressure in the furnace, with a greater exhaust helping.

 

But mostly I want to say that you've pretty much already got a perfect set up for salts. With a simple thermocouple reader you could run it manually and it would almost entirely reduce hot spots and oxidation. All you need is the stainless pipe, welded on the bottom. High temp salts are cheap as free in places where it snows- I run mine on 50/50 calcium chloride and sodium chloride, i.e. road salts I buy at the local farm store.

 

I'd be happy to chat with you about it more if you like- see my website for pics and info on my salt set ups.

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