Willem

Forge finished but not hot

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I recently completed a ribbon burner propane forge loosely following waynecoe’s design but I’m having some issues with getting it hot enough. A piece of 1/4 in round stock will barely get red hot even if left in for 5 minutes or so. The forge is lined with kaowool and castolite so it should be insulated well enough. In addition I’ve casted Some firebrick from said castolite to act as heat barriers on the end. 

Im scared to death that I’m going to have to sink more money into this but I assume I will need a oxygen source that I can adjust. The gas supply is a 0-30 adjustable regulator then a ball valve which finally goes into a needle valve. 

I was getting rebar to start sparkling but XXXXXXXXXXXhad all the gates open all the way. The tank would also freeze up in about 20 minutes. Since then I’ve substantially toned down the propane I’m feeding it.

If ya’ll have any ideas it would be tremendously appreciated.

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Good Morning,

North West Blacksmith Association is just down the street at Longview Fairgrounds. They have a monthly get together on the last Sunday of the month. Get in touch, there a bunch of very good Propane Blacksmiths. www.blacksmith.org

Neil

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If you are running it without doors it will not get hot; you have way more opening than needed for good burn, plus it will oxidize your stock.

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I casted firebrick from castolite and use that at either end, hence the stoppers to keep them from blowing over. I also don’t have a way to regulate air it’s just a shopvac.

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You will need to be able to regulate both the air flow and the fuel flow in order to get the heat and the type of forge atmosphere you desire (oxidizing, neutral, or reducing).  If you built the burner and forge to the specs given by Wayne Coe, then you should have no trouble getting the heat you want once you can alter the fuel and air input independently.

Several people on here have come up with some ingenious ways to regulate air input.  I only ran a blown burner for a short time, but I found it useful to have a fairly precise way (such as a gate valve) to control the air input.  Once you know what you are looking for in the flames it becomes pretty easy to adjust the air or fuel as needed, but there is a little bit of a learning curve.

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Put a blast gate just after the fan. About $12 on Amazon. That will adjust the air flow.  the flame is hottest at neutral.  

What is the interior dimensions of the forge?

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2 hours ago, D.Rotblatt said:

Put a blast gate just after the fan. About $12 on Amazon. That will adjust the air flow.  the flame is hottest at neutral.  

What is the interior dimensions of the forge?

6” by the length of the 20# bottle

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22 hours ago, Willem said:

propane forge loosely following waynecoe’s design

It's been my experience not following a design to the letter will cause problems. What did you change in that design?

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Can you fire it up in low light and see whether you have a significant amount of Dragons Breath?

This will tell you whether you are running rich (fuel-rich: lots of DB) or lean (fuel-lean: little or no DB).

There is a considerable amount of misinformation about burners. Many folk will tell you that you need high CFM from a forge burner because they have successfully used a burner that claims to have a capacity of 200 CFM (for example). Usually, the fans in question are rated for an open inlet and outlet and can only produce a small pressure rise when throttled. If the fan can flow 200 CFM with a fully-open 3" discharge and the discharge is reduced to 1", that's 1/3 of the diameter and 1/9 of the area. That 200 CFM fan is now closer to a 25 CFM "system".

Using a vacuum cleaner, which is designed to produce a large pressure rise and to move air against the restriction imposed by the hose, you are likely to be getting a large proportion of the vacuum cleaners rated airflow to your burner. I am pretty certain this WILL be waaay too much air, but checking for DB in low-light is the best way to be sure. 

We usually want to run with a fuel-rich (reducing) forge atmosphere to minimize Oxidation of the workpiece. 

I calculated that each CFM of airflow will burn with 0.308lb/hr of Propane to produce a Stoichiometric forge atmosphere (Stoichiometric is a precise technical term which probably corresponds quite closely to "neutral" in smithing parlance). A rich mixture will require even more gas per CFM of air. 

Googling "shopvac specifications" gets a first hit for a spec that shows 5.1 cubic metres/minute, or 180 CFM, and 1525mm of water column, 60" WC. Peak rated power is 1400W. Even if you were only getting half of that shopvacs rated flow to your burner, you'd still need 0.308 lb/hr/CFM x 90 CFM =  27.72 lb/hr of Propane per hour. I've just used the first spec I found. Your vacuum may have a completely different spec, of course.

In your position, I would fit a tee and two valves to the air line: one valve to throttle the air going to the burner and the other to regulate the amount of air being bled off from the tee. The air would come out of the vac into the tee unrestricted and both the exits from the tee would be restricted by the valves. To help understand what is going on, I would fit a U-tube manometer to the existing steel air pipe so that you can measure the pressure.

Once you have things set up to your satisfaction, it is worth piping the bleed-off air to an air curtain in front of the forge to keep tongs/handles cool. It's worth keeping this in mind when you put things together.

 

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On 7/5/2019 at 5:25 PM, Irondragon Forge & Clay said:

It's been my experience not following a design to the letter will cause problems. What did you change in that design?

It being my first forge I followed the instructions a little too religiously in some ways. I cut it unnecessarily  in half because it was originally designed for Venturi burners. That’s welded back up now and sealed. The biggest thing besides the airflow supply would be my ribbon burner holes aren’t super specific I just kinda threw crayons in there and hoped for the best.

On 7/5/2019 at 6:38 PM, timgunn1962 said:

Can you fire it up in low light and see whether you have a significant amount of Dragons Breath?  This will tell you whether you are running rich (fuel-rich: lots of DB) or lean (fuel-lean: little or no DB).

Tomorrow night I’ll check out what one blast valve does to the oxygen mixture in the forge. Once my plumbing supply store opens back up Monday I’ll use that T design. I believe your assumptions about the environment being oxygen rich to be accurate. That blower shoots out a heck of a lot of air, it easily blows out any dust and can knock over my firebricks at the end of the forge. Would you mind elaborating the dragons breath aspect of the fire? Google isn’t much help and a search of the forum produces similar results.

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2 hours ago, Willem said:

That blower shoots out a heck of a lot of air, it easily blows out any dust and can knock over my firebricks at the end of the forge.

My forced air is more of a breeze out the ends, for regular forging I have the blast gate closed about 3/4 or more...and I don't have a large fan on it.  It'll still weld, but I put a larger fan on it for bigger stuff.  The more I read, the more I think you just have too much air, thus a very very lean mix.  I'll lay money on a blast gate (or similar) getting it under control.

Dan R

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Alright so after going all over I wasn’t able to find a blast gate and being impatient I decided to build one myself. By all means the blast gate has greatly improved the efficiency of the force but I’m still stuck getting red hot temperatures albeit closer to yellow. I can get a good rich blue flame but again it doesn’t get the metal particularly hot. I’ve searched around both on the forum and google for a detailed explanation of how to tune one of the suckers as well as trouble shooting but to no avail. Maybe you folks can The only other thing I can think of is that I melted some of the Lao wool out when I welded the two halve together and that’s causing an insulation issue. Any ideas? 

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Obviously the picture must make it appear that your forge is hotter than it really is.  If it looks like that to your eyes then it should be plenty hot. 

One thing I noticed is that you have some flames coming up out of the forge where your burner is mounted.  Normally I would expect some secondary air to be drawn in through those types of openings rather than flames coming out unless the forge is so closed off that the exhaust can't escape through the front opening fast enough.  If your burner is mounted in such a way that the flames are impinging on insulation/refractory before making it to the forge chamber that could be part of the issue as well.

On 7/6/2019 at 2:17 AM, Willem said:

my ribbon burner holes aren’t super specific I just kinda threw crayons in there and hoped for the best.

What did you mean by this?  Did you use a different number of crayons?  Were they placed haphazardly in the mold form rather than in ordered rows?  Blown ribbon burners shouldn't be as sensitive to getting the perfect number/diameter of holes as naturally aspirated ribbon burners, but you still must have enough well-mixed fuel/air throughput to get the heat you want.

Have you played around with the fuel/air mixture settings a bit to see the effects of increasing/decreasing the air and fuel?  For a single port blown burner the hottest flame is normally the loudest flame.  I don't know if that holds true for the ribbon burner or not.  Someone with experience in that area may chime in.

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All other things being equal, more holes in a multiport burner for a forced air system allows more fuel/air mixture to be available for combustion and more heat output.  Can cause problems with turndown to low heating operation though.

I don't like using shop vacs for an air supply.  They are loud, unreliable and aren't rated for hours of continuous use.  If you can hit up an HVAC repair place, or junkyard, for a "combustion inducer" from a junked model one of the newer high efficiency furnaces or boilers you will likely get a fan with variable speed control that will be quiet and efficient.  Anything in the 150-350 MBH range should suit.

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One thought.  How long are you letting the forge heat up?  If you have a thick layer of cast refractory on the kaowool (even 1/2" or more) it will take time for your forge to heat up.  It has to run long enough to heat up the refractory.  I lined one that way with about 3/8-1/2" and it took almost 30 minutes before it got to temperature (i.e. stopped increasing temperature on the pyrometer). 

That's why I use an eggshell technique to cover the kaowool.  The advantage of the thicker refractory coat is that it is stronger and more forgiving then the eggshell, and retains more heat so keeps a more stable temperature.

YMMV

DanR

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