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New to smithing and worried my forge isn't hot enough


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Hi!

 

I've very new to smithing, I've wanted to do it for years and finally got my act together and started doing some in the last couple of months. I bought a propane forge on eBay, and I think it's struggling to get to a decent heat. It's taking about 45 minutes to get the steel to reach a bright/orange red colour to start with. 

 

The forge itself is a metal box with 3 burners, white fibre insulation (which I've coated in foundry clay). I've put a hinged door on one end but the other end is completely open. 

 

Does anyone have any tips/modification suggestions I could make to get it hotter?

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Is it possible to supply us with pictures?  

 

5 minutes ago, Richard Medlock said:

It's taking about 45 minutes to get the steel to reach a bright/orange red colour to start with

Were you judging this color in the daylight or in the dark?  If this was daytime and bright sunlight, what looked bright orange/red at the time was probably closer to bright yellow.  

Where are you located?  It's possible there are smiths in your area that would be able to provide some live assist.  (If you were in SE  Portland OR, I'd offer to stop by and see if I could help.)

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I've attached a couple of photos from a couple of weeks ago. 

 

It was during the day with the roller door half closed (extractor fan on), it was mostly overcast with some sunshine. 

 

That's very kind of you, I'm based in the UK (Somerset/south west) so I think that may be a bit far. 

 

IMG_20200814_123212.jpg

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Those look like venturi burners, which I've never used, but I would wager that your fuel/air mixture is way off.  That looks like a very lazy flame that needs more air to burn properly.  

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Sir. First. I am not an expert in propane forges. From the flames I see, it would appear the burners aren't properly tuned. Or a lack of propane pressure. Your flame should be more inline with the flame produced by a propane torch. Also consider closing off the opposite end with fire brick.  You are loosing a lot of energy out that open end.. If you need it open  for longer material like the sword then leave a small opening for the sword tip. 

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The guys are correct, there's something way off about the flame.  You need more gas pressure and a lot more air getting in.  

I hate to be the bearer of bad news, but I've never seen a decent forge on ebay.  They all seem to be along the lines of this one, a tube without enough insulation and open ends, with some split firebrick on the bottom, and more burners than strictly required.  That said, you can fix a lot of this, I'm just sad these things are not plug-and-play, it discourages people. :(

You first order of business is to crank the gas pressure up to around 7 psi (0.5 bar, 48 kPa, a good strong hissing noise, whatever pressure reading you prefer) and open the chokes (if present) all the way.  If your flame doesn't look like the one in that video, it's time to look at the gas jet.  If that's too big you'll never get the velocity you need to entrain air, leading to a fluffy cool flame.  If it's too small it'll always run oxidizing.  

I don't have time to write out the full prescription as I'm at work, but check the pinned threads about forges and burners in this section.  And if Tim Gunn from Lancashire stops by, listen to him!  I'm sure there are smiths in Somerset, and if all else fails maybe you can visit the school in Plymouth to get a look.  Ideally, go take a class from Owen at www.bushfireforge.co.uk.  

Welcome to the madness!

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I'd say that looks just enough like a forge to fool the beginner into hitting the buy button: Prepare for a precipitously steep learning curve.

 

First off, can you get some photos of the whole lot? Something is obviously wrong. We can see that from the photos of the flame, but we have no information with which to diagnose the cause.

 

The flame looks horribly rich and therefore cool. There's either too much gas for the amount of air, or not enough air for the amount of gas. Same thing, but not everyone sees this.

 

My first impression is that the mixture is pants and that there's also not enough of it.

 

There could be a number of reasons. We need to start somewhere, so we'll start with the stuff that's easy to check

 

The first thing to check is your cylinder. Propane or Butane? Propane is good. Butane is not. Screw-in regulator, or clip-on? Screw-in is good. Clip-on is not.

 

If it's a screw-in regulator, what is its outlet pressure range? 0- 2 bar (0-30 PSI) is good. 0-4 (0-60 PSI) bar is perhaps better, though not by much. Some regs are 0.5-4 bar (8-60 PSI) and, whilst they do work, I really loathe them for the lack of control at the bottom end. They also make lighting the forge unnecessarily exciting.

 

The clip-on regs are fixed low pressure over here, 35 mbar for Propane and 28 mbar for Butane. No good for Naturally Aspirated burners. 

 

If you are on Propane, it is regulated to a sensible pressure, and are still getting that sort of flame, are there chokes on the burners? If so, are they open? If they are closed, open them fully and try again.

 

No chokes, or chokes fully open already, we'll need to see some detail of the air intake end of a burner. We also need to know what the gas jets are and what size they are. Mig welder tips are often used. otherwise it's usually drilled holes. The flame photos suggest the gas jet holes need to be smaller: easy if you can swap out mig tips for smaller ones (they are sized for the welding wire diameter. We'll need to know what size is marked on them and also the thread diameter and pitch). Considerably less easy if they are drillings.

 

Check the above and get some photos. We can probably make it workable.

 

Where in Somerset are you? What do you want to make initially?

 

 

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9 hours ago, timgunn said:

I'd say that looks just enough like a forge to fool the beginner into hitting the buy button: Prepare for a precipitously steep learning curve.

I was starting to fear this, thank you for confirming it. Encouraged that I might be able to do something about it though. 

 

I'm working today, I'll be in the workshop tomorrow and will take a bunch of photos and post them.

 

The cylinder is an LPG one (propane). My dad is gas safe registered and is really hot on gas safety and recommended a Gaslow cylinder above anything. (i'll include photos tomorrow). The regulator is a screw on one. Looking up the one I've got, it's 37mbar, which from what you've said isn't good enough.

 

I'll take photos of the rest tomorrow.

 

I'm based in Taunton. Initially I would like to be able to make small kitchen knives and small ornaments. 

 

Thank you all for the help! 

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And reading Alan's post, I forgot to welcome you to the addiction!  

Hopefully the purse strings aren't stretched too tight...that can make things frustrating. 

I'll also suggest joining your local Blacksmithing group in the UK.  You'll meet nearby folks and with a little effort, should be able to make friends that will invite you to their shop to use tools that you don't have yet, and also be a local resource to answer a lot of questions you come up with in person.

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Three burners that thing could get screaming hot! I would take that brick out of the bottom unless your forge welding.

 

Naturally Aspirated burners, are a pain.  They need a high pressure regulator to pull air into the system to work right.  Although its simple to put one together, there is a lot that goes into building them that makes them work.  Correct burner tube length, correct orifice opening, correct air inlet opening.

 

With more photos of your burners, I'm sure someone here can help get your going.  As long as you have ceramic blanket under that coating, it will eventually work. It may not weld, but for just starting, don't worry about that.

 

We all start somewhere, there is lots of learning, mistakes, and shortcuts that you later think, I shouldn't have done that that way. That is all part of the experience and fun.

 

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The 37 mbar delivery pressure may well be sufficient on its own to explain the poor performance. Things could be looking up.

 

There may be some deviation from normal Gas-Safe practice needed: I don't think LPG necessarily falls within the same regs as mains gas (for anyone reading this outside the UK, "Gas-Safe" is the registration body with which anyone working with mains gas in the UK must be registered).

 

Naturally Aspirated burners use the momentum of gas emerging from a jet to entrain air and mix it with the gas. This means we need a high speed through the gas jet. The gas speed through a jet varies as the square root of the pressure loss across it. Downstream of the jet will be at, or pretty close to, atmospheric pressure. Upstream of the jet will be whatever pressure your regulator supplies. 

 

37 mbar is about 0.53 PSI. At 2 bar, or 30 PSI, the amount of gas being burned (or at least fed to the forge) will be between 7 and 8 times as great as at 37 mbar.

 

Varying the pressure controls how much gas is being fed to the forge: effectively how big your flame is.

 

Varying the ratio of air to fuel controls the temperature of the flame: how hot it is.

 

Many (most?) Naturally Aspirated burners operate at a single Air:Fuel ratio. Some have an adjustable choke, allowing the ratio to be varied. The most Fuel-Lean mixture is obtained with the choke fully open. Closing down the choke then allows the mixture to be made richer and, in the case of gas forges, the flame to be made cooler.

 

Probably the biggest change from normal gas-safe practice is that we generally run fuel-rich. This is pretty much unheard-of in the world of heating. The reason for it is that it helps to prevent Oxidation of the workpiece by maintaining a reducing forge atmosphere. Your father may need coffee and aspirin.

 

Tuning a NA burner is mainly a case of finding a gas jet size that gives the richest mixture ratio consistent with achieving the flame temperature required for the highest-temperature job it needs to do. 

 

If you are buying a regulator, I recommend a plugged welding regulator for Propane. These are around 25 quid if you shop around, against around 15 quid for the cheapest thing that'll do the job. The welding regs are designed for use by hairy-ar5ed guys wearing welding gloves and are pretty rugged. They have large, grippy adjusting knobs and have the setting scale marked on the body. The scale isn't particularly accurate, but it's probably not much less accurate than the gauges that you'll find on cheap regulators and is plenty good enough for "us". We just need adequate repeatability: I'm forging today, so need X PSI. Welding needs Y PSI, etc. You'll find the values for X and Y for your setup by using it. Gauges have a tendency to get damaged. I use them when they are useful, but feel things are usually safer without them.

 

 

 

 

 

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So if I'm understanding you correctly Tim, it may be a simpler fix than anticipated by buying the correct regulator? 

 

When you're talking about a gas jet, do you mean something like an injector or simply the point where the propane enters the burner?

 

I read on another forum a post a guy made when building his own forge and he used injectors in his burners, is that something I should consider? 

 

I've got a couple more pictures I'll post from this morning 

IMG_20200912_134507.jpg

IMG_20200912_134416.jpg

IMG_20200912_134426.jpg

IMG_20200912_134444.jpg

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Ooh, those burners are even worse than I thought...

That design has been outdated for nearly 20 years.  The big questions are: inside that bell reducer, is the gas entering the burner tube via a small hole drilled in the small crosswise pipe, or is there a brass tip threaded into it?  

If it's just a drilled hole, how big and has it been deburred?

I am getting ahead of myself, though, it may be that a proper regulator will fix things enough to work.  With the one you pictured you can't get enough pressure to run a single burner, much less three.

Note that burner design can work, it's just hard to tune with all the parts.  It is vital that the gas shoots straight down the center of the burner tube, and if you can't see the hole it's hard to tell if it's lined up properly. 

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Hmm, well those do look pretty good.  Your regulator I can't answer for, but I think Tim is guiding you in the right direction.

 

Firstly, spin those chokes all the way open.  I don't like this first phase of the Ron Reil burner (there is a whole web site dedicated to making this exact burner) https://ronreil.abana.org/design1.shtml . So much info on there that the site can be hard to get a grip on.  In this configuration it is already very air restrictive, and is very temperamental. Looks much better than my first burner though.  Also with the way this is built, your gas jet, (a very small whole on the inside of that internal pipe) probably can't be changed.  Ask the guy you bough it from if he can tell you the size of your gas jet.  I don not remember the exact bit size recommenced off the top of my head but the seller could give you an idea of it. 

 

90% of the time, these burners don't want to work because there is not enough air getting into the system. If the chokes are full open and it coughs burps or blows itself out, your burner tubes may be too short.  You will have to play around and eliminate some variables.  

 

If it were me, I would take each burner out and see if I could get them to run individually first before putting them in the forge.

 

And Alan just beat me to everything I was typing.

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A new regulator seems to have done the trick! Dad needed several aspirin and a beer though (wise suggestion Tim). 

 

It's now so hot that it's eating through the fibre insulation, any suggestions on what to use as a replacement? Would bricks be better?

Photo added of the insulation fibres

16005208188231132798477263257446.jpg

Thank you all for your kind and generous guidance! 

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You need some ceramic fibre blanket with a higher temperature rating.  I bet they used the 1800 degree F stuff because it's cheapest.  You will want the 2600 degree F kind, and a refractory topcoat rated at least that high, if not more.  If Tim (or any other of our UK smiths, for that matter) drops by again he can help you source it in the UK.

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2 hours ago, Alan Longmire said:

You need some ceramic fibre blanket with a higher temperature rating. 

I'll chime in here (and warn that this post will probably prompt some opposing viewpoints), and suggest that when re-doing your insulation, spend the time and money to coat the entire surface with some sort of refractory cement, or even better, some ITC.  There are 2 (one for those who disagree with me) reasons for this.  First, it will allow the forge to last longer.  Alot of times you take out and put in a piece of steel, you will bang/rub/hit the walls of the forge and will tear up the fibers, and most smiths would agree.  The second reason (the one that some folks will disagree with me on)  is that I'm of the opinion that Kaowool is not safe when you approach the higher temp range of the material.  A friend of mine (MS if that matters to folks) said that he looked at the fibers when rebuilding his forge wleding forge (consistently running at the higher end of the material ratings) and found that the fibers had changed to become more crystaline and looked very much like asbestos fibers. 

I know the MSDS sheets say it's safe, but let's not forget that the motivation behind these spec sheets is not because industry is concerned about the overall health of the general population or planet, but rather how to liimit their liability from lawsuits over the harm that their products cause. 

Edited by billyO
speling
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2 hours ago, Alan Longmire said:

I did mention a refractory topcoat... ;)

I know.  I wasn't referring to you, Alan.B) 

And I wanted to emphasize that point beyond just one person mentioning it.

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@Richard Medlock

 

Hi and welcome to the madness. I get my refractories from Vitcas. They are based in Bristol which is hopefully not too far depending on where in Somerset you are. I bought a large box of blanket last time and still have several meters left for future use. You can have a piece but I’m based in Essex so not sure what would work best for you. Give them a call or let me know how large a piece you need and when you can collect. I also have some refractory left but that is much more difficult to figure out how much you will need.

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