is my forge hot enough to weld?

[MotoMike]

based on color I'd have guessed it was.  after it is up to temp, the whole interior is a light yellow.  several attempts to forge weld have not been successful.  cleaning, fluxing, giving it plenty of soak time, and lightly attempting to set the weld before hitting it hard.  most recently thought I had a half inch ring welded, felt nice and solid.  when trying to blend the seams, it popped loose.  I thought that perhaps I do understand the technique but I'm just not hot enough.  

I obtained a thermocouple rated for 2375°f.  It has an 8 inch probe.  I set it at the door with the probe reaching into the interior about 4 inches where it rests on the forge floor.  it reads a little over 2100.  would the be the temperature of the whole interior, or would it get hotter in the center?  it is not an Omega, but Omega's literature shows all its competitors are reading about 30 degrees low at this temp.   

your thoughts are appreciated.  

Mike

[Mikey98118]

Hotter further into the forge; yes. I think you have some other problem; not temperature.

[timgunn1962]

Unless you have some good reason to believe the thermocouple reading is incorrect, it would seem sensible to assume it is giving a true reading.

Without details of your reference, my guess would be that you are referring to something from Omega that refers to Mineral Insulated thermocouples (probably touting their Omegaclad XL sheath material) AFTER some extended period of time at high temperature. Type K is very prone to "drift" when used for long periods over about 1000 degC (1832 degF).

Has the thermocouple spent a long enough time at a high enough temperature for drift to be an issue?

What is the colour showing? Back before IR pyrometers became common, there was a pyrometer system that used an electrically-heated wire. This was viewed with the object being measured in the background. The heating current in the wire was adjusted until the wire became invisible against the background. The temperature of the wire was then read from the display. 

If the inside of the forge, or at least the workpiece, is uniformly the same colour as the tip of the thermocouple, you can reasonably take it that the thermocouple is reading the temperature of the forge/workpiece. If you cannot locate the tip of the thermocouple anywhere hot enough to match the forge/workpiece, you probably have the wrong thermocouple and/or thermocouple location. With only 4" insertion through the mouth of the forge, this seems quite likely.

What are you trying to weld?

I have seen all sorts of numbers thrown about with regards to welding temperatures and it seems that more experienced welders tend to be able to weld at lower temperatures. A few years ago, I went to a bladesmithing hammerin where lots of Pattern Welding was being done, by a cross-section of people, using a vertical Propane forge and a small Anyang power hammer. The forge was set up by an experienced smith and successful welds were produced by almost everyone from the complete beginner to the really-rather-good. At the end of the day, I stuck in a Type S thermocouple and measured the forge temperature at 1280-1330 degC throughout the working zone. As a result, I tend to regard 1300 degC, 2372 degF, as a "very good" welding temperature for steels with a Carbon content of about 0.8%. There were a number of failed welds, of course, but all of them clearly a result of some cause other than forge temperature. I can't speak for Iron or steels with lower Carbon contents, which I would "expect" to need higher temperatures than the 0.8%C steels used at the Hammerin.

Do you have pictures of your setup, or a link to a thread showing it?

One of the things I have seen on a number of occasions is NA burners built with gas jets that are too big to achieve the flame temperature needed for welding. It seems all wrong to anybody who does not understand the chemistry involved, but going to a smaller gas jet quite often raises the forge temperature by increasing the ratio of air to fuel. It usually works if there is significant (excessive?) Dragons Breath, indicating a very fuel-rich mixture.

[MotoMike]

Thanks Mikey98118 and timgunn1962 

I am trying to forge weld mild steel for decorative items.  door knockers in the present example.  it is a cheap Chinese pyrometer, K type rated at 1350C 2375F.  the tip is exposed and has ceramic beads along the two thick wire leads up to a ceramic disc with wire lugs to make the connections.  .  not much of a setup as the probe is laying on the porch with about 4 inches of it reaching into the forge at the side of the opening and the tip is resting on the floor.  we have discussed my forge before and it was noted that my dragons breath was reducing to a great degree.  pictures of the interior of the forge and the probe always seem blown out and white so I did not think they would be useful.  that is to say the pictures seem to make it look hotter than looking at it does.  It was earlier noted that I put a smaller reducer on my burner than Reil called for.  since it did seem to do the job, I did not change it, though did go to a size 59 from a size 57 jet.  It is getting warmer and I guess I will plan on a maintenance day.  I wanted to enlarge the front opening a bit anyway and check the interior for some of the dings it has suffered at my hand.  I will get there.  

[Mikey98118]

I don't bother with pyrometers. Light yellow incandescence in the forge should be plenty of heat. If I were you, I'd look into all the other factors, such as what you are using for flux. Remember that Gas Forges is only one forum on IFI. Hunt as hard for welding advice as you did for advice on forge construction.

[Hans Richter]

Hi MotoMike, checked the (mine 8in K-type probe) thermocouple in the foundry, Bonze has to melt at 1927°F and its melt at that temperature (at the pyrometer). Also many of pottery’s relay on them with good results.

So you can trust the pyrometer with a deviation of maximum <5%.

They teach me and I practice (at the solid fuel forge) that you need at least 2192°F to apply forge welding temperature (white heat) to forge weld with success. Only light orange heat is great for soft forging but unfortunately not enough especially for mild steel and his carbon contain. This (2192°F) is the temperature just before sparkling. So you have to pimp your burner (there a lot of experts to help you with that) or choose for a solid forge.

Another option is the choice for real wrought iron which is more easily to forge weld to book some success (which I do).

Be careful with the flux powder in your gas forge this will be work aggressive to your insulation. So use an extra refractory layer to rest on.

As always at your service, Der Hans

[Frosty]

Mike: If your forge is coming up to light yellow it's your technique not heat that's the problem. How many times did you do set welds before trying to "blend" things? 

Clean (shine up), stack, flux, heat, soak, weld. Repeat two more times BEFORE striking the billet on an edge and that's just to test to see if the welds are properly set. 

If it's good, go to town on it.

I use Patterson's blue welding, brazing, etc. flux from the welding supply and it seems to work as well as "real" blacksmith supply fluxes except those containing "Sal Amoniac." I like to avoid the really dangerous stuff when possible though.

Frosty The Lucky.

[Buzzkill]

4 hours ago, Frosty said:

Mike: If your forge is coming up to light yellow it's your technique not heat that's the problem. How many times did you do set welds before trying to "blend" things? 

Clean (shine up), stack, flux, heat, soak, weld.

 

12 hours ago, MotoMike said:

I am trying to forge weld mild steel for decorative items.  door knockers in the present example. 

 

[MotoMike]

Thanks Frosty.  I guess I tried light setting twice and thought I had it.  I'll try a couple more times before getting serious.  

Thanks   Buzz , not sure what you are telling me. 

[Buzzkill]

10 hours ago, MotoMike said:

Thanks   Buzz , not sure what you are telling me. 

It looked like Frosty was giving you good advice for welding damascus billets which are often high carbon steel.   You specified that you are trying to weld mild steel for decorative items, so the temperature may need to be a bit higher, and I wasn't sure if you were making billets for a pattern effect or welding rather than using fasteners on your items.

I haven't tried to weld mild steel in my propane forge so I can't speak from experience in that, but it sounds like you are using the same temperature, or very close to it, where I weld high carbon steel with good results.  If I get the time this weekend I'll try to remember to attempt a mild steel forge weld and see how it goes.

[MotoMike]

thanks Buzz

 

[Latticino]

On 3/28/2018 at 9:04 AM, MotoMike said:

it is a cheap Chinese pyrometer, K type rated at 1350C 2375F.  the tip is exposed

In my experience type K thermocouples will degrade over time when exposed to temperatures in excess of 2,200 deg. F.  I'm not sure whether their accuracy suffers, or they just crystallize and break down. You may want to consider getting a high alumina ceramic thermocouple well (sheath) that the thermocouple sits in and/or only keeping it in your forge for limited time during welding.  At minimum go for a thicker thermocouple wire (12 Ga minimum, or thicker if you can get it).  Even better would be type R or Type S thermocouple, but they are prohibitively expensive.  Remember that you need to use actual thermocouple wire for the specific type material between your thermocouple and readout device, or accuracy will suffer as well.

As noted by others, mild steel typically forge welds at higher temperatures than high carbon, and wrought iron even higher temperatures.  In any event it is important to keep the weld surfaces as clean as possible before your weld.  To achieve higher forge temperatures in a propane forge it may be necessary to change the forge atmosphere from reducing to neutral or even oxidizing.  Needless to say this can lead to trouble with scale which makes welding difficult and reinforces the need for some kind of barrier to keep the weld surfaces clean.  Personally I've had a lot more success forge welding mils and wrought in coal forges.

[MotoMike]

2 hours ago, Latticino said:

In my experience ... success forge welding mils and wrought in coal forges.

Thank you Latticino.  All very good information.  I had the notion of putting the probe though a port so that it enters the forge at the top and between the opening and the burner port about 3 inches from each.  Wondered if it is solely the temperature or the atmosphere that attacks the thermocouple.  have considered the wells you mention.  would having the thermocouple about a quarter inch into the forge then sealed from atmosphere with a couple coats of Satinite, protect it?  

[Latticino]

Not sure if it is the atmosphere or temperature.  Possibly the former, as my experience is mostly with using them at this temperature in glass furnaces, which have a very caustic atmosphere.  Still know, as indicated by timgunn above, that they are not that accurate at these temperatures.  I don't like the idea of sealing the thermocouple in place with satinite, as pulling it when not needed or replacing it may be required.  May be best to just "calibrate" your eye to be able to judge general temp for welding the type stock you want to use and going from there.  I know my type K, even in a ceramic well, pins my uncalibrated mechanical pyrometer at 2,500 deg. F in a forge that hardly seems to be up over a high yellow.  Have to try it with a more accurate electric controller, but the ribbon burner broke down and I haven't  recast same yet.  Please keep us informed of the results of your experiments.

[MotoMike]

Thanks Latticino.  It is getting warmer so my forge maintenance is just around the corner.  going to make the opening bigger and repair any cracks or dings in the refractory.  I have bumped it with work quit a lot and see some cracks.  I want the hole just a bit bigger so that I can reach the back of the forge with a gloved hand to apply refractory.  It was a pain on the initial build.  

interesting that your set up reads high.  In researching I cam across literature on the Omega Site that showed only their stainless shielded probe to be accurate at these temps and I think there were 4 brand x's there with it and they all read around 30 degrees low at the high temps we're talking about. 

 

 

[SoCal Dave]

Off the subject a little but to welding in a gas forge.  I've watched Craig Trnka, a top farrier, video and he has one with him welding some steel stock with out much trouble.  He used Iron Mountain Flux and didn't smother it in flux.  I notice he didn't use a heavy hammer either.  Most likely a 2 lb er.  He did scarf the two ends.  Watching many of his video's he does a lot of horseshoe forge welding in a coal forge.  I am not sure of the carbon content of horseshoes.  Good luck

[Frosty]

Mike: You're overthinking this significantly if you think a precision instrument telling you a temperature is going to help you weld in a gas forge. Forge welding isn't a precision practice, it's a matter of doing it right it's not the tools just follow the steps.

Prep the join by: Matching the surfaces reasonably closely.

Scarfing if necessary or advantageous.

Clean as thoroughly as practical. If the surfaces are flat enough even a file or belt grinding isn't out of the question. The cleaner the better shiny is GOOD.

Close the weld: bend, wiring or tack welding for billets to bring the joint surfaces in contact in prep for welding.

Flux and bring to temperature. My preferred method is to flux as soon after cleaning as possible, I flux the join surfaces directly before I put it in the forge. That's before tack welding even. Flux melts LONG before orange heat, approx 230 f. the water boil off paints it on everything. Oxidization is accelerated at anything above ambient temperature so bringing it to orange heat means it's forming scale by the second. This is why I flux as soon as possible even if I have to oil the steal after sanding and sticking a light dusting of flux to it. The oil prevents oxy from contacting the steel and if  if the steel is, matched well and clean enough provides enough flux to make welds. Anhydrous borax melts at around 400 f. IIRC and provides a more  durable prophylactic barrier to oxygen.

Bring it to heat, allowing enough time for the center of the joint to come to welding temperature.

Firm dead blows to set the weld in a pattern starting in the center of the join to drive any impurities towards the edges and out. If the joint is cleaned and fluxed properly a good pattern is less important but if you're relying on flux to carry scale and dirt out of an imperfectly prepared joint then the pattern becomes important.

Once set, reflux, reheat and repeat setting weld. I believe common consensus is do 3 set welds before testing on edge and general forging.

You don't need sophisticated precision instruments, your eyeballs and practice are more practical an instrument.

Welding heat is visible as a flickery or watery pattern to the steel in the fire. When you remove it from the fire the steel will be shedding vapor which is easily visible raising from it. This isn't smoke from the flux or oil, it's vaporizing steel. Get familiar with the effect by just heating steel coupons and looking at them at welding temp. You can learn to recognize watery temp and the vapor. No need to practice on billets you want to use. 

Remember do NOT stare into the fire! Check frequently but do NOT stare into a gas forge, this can cause cataracts!

Soak time depends on the thickness of the joint and NO you don't have to soak in a welding temp fire, a bit lower works just fine and sparking HOT is too hot unless you're welding wrought iron or Pure Iron.

Pyrometers only really become practical when you're heat treating. Watery or flickering temp. happens at or near welding temp almost regardless of the carbon  content but the actual temperature will vary, the higher the carbon content the lower the melting temperature and forge welding is best done at NEARLY liquidus not at because forge welding is best done as a solid phase process, commonly called "Diffusion" welding rather than above liquidus, "Fusion" welding.

This is how I get reliable welds in a gas forge. My welding flux is Paterson Blue, available in welding suppliers found in the gas welding, brazing hard soldering shelves and it's approx $26. per 1 lb. can shipping included on the shelf in Wasilla Ak. I can't afford "real?" forge welding flux whoever makes it and Paterson blue works a treat every time I've used it UNLESS I screwed up the prep. One of our guys Teenylittlemetal guy on Iforge has been including powdered charcoal with good, BETTER results at medium yellow temps. that's well lower than "watery yellow," I've had success at high orange though not as reliably as I'd like. I need practice welding at lower temps

Frosty The Lucky.

[MotoMike]

On ‎4‎/‎17‎/‎2018 at 12:41 PM, Frosty said:

Mike: You're overthinking this significantly if you think a precision instrument telling you a temperature is going to help you weld in a gas forge. Forge welding isn't a precision practice, it's a matter of doing it right it's not the tools just follow the steps....//...

 

Frosty The Lucky.

Thanks Frosty.  I did not realize you had provided such a thorough response till just now.  

 

Thanks Dave

 

[Frosty]

You're welcome Dave, it's my pleasure.

Gotta go, a friend and I are holding a, "Crazed, mad scientist, home brew zirconium silicate, bentonite experiment day" in Anchorage and I'm off in 30 mins or so after I feed the dogs, load the drill mud, kitty litter and blender."

Frosty The Lucky.