Iron-Rated Pyrometers

I have been looking for a reasonably priced iron-rated pyrometer for a long time now.

The only inexpensive iron-rated pyrometer I have found is the optical PYRO pyrometer, but I have had little luck with using it with iron, and have not been able to get a good temperature reading off the iron.
(photo below).

I am wondering if I could put a sheet of stainless steel in the exhaust stream of the furnace and get a reading off of that, but I am not sure that could be correlated to the actual temperature of the iron in the crucible.


I have always heard of the K thermocouple, and they are readily available, but I never had a good understanding of all the types available.

I have seen iron-rated immersion pyrometers used at some of the art cupola/cupolet iron pours, and they look almost exactly like the ones rated for lower temperatures, so I know such things exist, but have not had any luck with any supply house even being willing to give a quote for one.

It must be a matter of "if you have to ask the price, you can't afford it", but I have heard anywhere from $1,500 to $5,000 plus.

So I thought why not just make my own iron rated immersion pyrometer?
I looked up thermocouples, and found this link:
http://www.thermocoupleinfo.com/thermocouple-temperature-limits.htm

I found some R, S and B rated thermocouples priced here, and apparently the high-temperature units have some exotic metals in them such as platinum, and thus they are quite pricey.
http://www.omega.com/pptst/RAT-TJ.html

Here are some ratings from this page:
http://www.thermocoupleinfo.com/thermocouple-types.htm


Type B Thermocouple (Platinum Rhodium – 30% / Platinum Rhodium – 6%): The Type B thermocouple is used in extremely high temperature applications. It has the highest temperature limit of all of the thermocouples listed above. It maintains a high level of accuracy and stability at very high temperatures. The type B has a lower output than the other noble metals (type R & type S) at temperatures below 1,112F (600C).

Type B Temperature Range:
Thermocouple grade wire, 32 to 3100F (0 to 1700C)


Type R Thermocouple (Platinum Rhodium -13% / Platinum): The Type R is used in very high temperature applications. It has a higher percentage of Rhodium than the Type S, which makes it more expensive. The Type R is very similar to the Type S in terms of performance. It is sometimes used in lower temperature applications because of its high accuracy and stability. Type R has a slightly higher output and improved stability over the type S.

Type R Temperature Range:
Thermocouple grade wire, -58 to 2700F (-50 to 1480C)


Type S Thermocouple (Platinum Rhodium - 10% / Platinum): The Type S is used in very high temperature applications. It is commonly found in the BioTech and Pharmaceutical industries. It is sometimes used in lower temperature applications because of its high accuracy and stability. The type S is often used with a ceramic protection tube.

Type S Temperature Range:
Maximum continuous operating temperature: up to 2,912F (1600C)
Short term use: up to 3,092F (1,700C)

 

The price range on Type B thermocouples appears to range from about $500 to $1200 per unit.

Not very cost effective, and imagine one of these going out after a few months.

So idea #2 I had was to imbed a standard type K pyrometer behind the hot face of my new low-mass furnace, or perhaps several in various locations to compare temperature.

Even if the K-type did not read the temperature of the iron in the crucible, at least you would be able to get a relative reading of whether the furnace temperature was going up or down as the melt progressed, and more importantly get a reading of whether the furnace temperature was going up or down according to various fuel flow rates and furnace atmospheres (reducing, neutral, oxidizing).

An indirect reading seems like the only cost-effective solution.
As long as you knew the indirect reading that produced a good hot iron pouring temperature, it really would not matter what that exact iron temperature was.

As it is now, I use the 1/2" steel bar method mentioned in the Navy Foundry Manual, which is to stir the molten mix with the 1/2" rod, and if the end of the rod melts off within 15-30 seconds, then the iron is at pour temperature (I will dig up the temperature that this is suppose to represent).

As a side note, if you don't know where to find the pdf files of the scanned version of the Navy Foundry Manual, pm me and I can show you the link to those.
The files are scanned per chapter. Those files should really be stored here somewhere since they are a good source of foundry information, with a lot of photos of common casting defects, and a world of other casting information.

I am not sure what the temperature of the back side of a 1" hotface is, but I will find out when I get my new furnace rammed.

 

an optical pyrometer will not work well in daylight and prefers a DARK environment save for the metal being tested, you also have to have the metal skimmed back,, no flux slag or topping over the metal

 

You may have found these, this is what industry uses.




The T/C is protected inside a quartz tube (bottom left). They are designed to be single use, BUT if you are super careful and set them down in a holder carefully you can get mutliple uses out of them

https://www.heraeus.com

Iron is a solvent for steels, so any T/C is going to dissolve, the thinner, the faster

I would try a Marshall probe, it is thick and if you coat it with graphite, preheat it so it reads fast, and minimize dip time it may last a good long time

http://www.lhmarshall.com/



They sell just the probes online, we can build the rest of the unit in house, they want a fortune for it



Some more ideas anyways

FoundryJoe

 

Thanks Joe, that is some good information.

Sounds like iron is not too kind with the probes.

I guess will try the indirect measurement method first since I have that equipment and it was cheap.
I will put a couple of thermocouples behind the hot face of my new furnace and see how that works.
If that gets too hot, I will space them off the hot face a bit.

But the main thing is not so much the temperature of the iron, but rather the temperature of the furnace at any give fuel and combustion air setting.
I have been guessing at what burner settings produce the hottest heat, but visually it is very difficult to tell which setting is hottest.

So if I can get the furnace/burner operating at its maximum temperature, then I think the iron will get hot enough for pour temperature, regardless of exactly what that temperature is.
The navy foundry manual says that if a 1/2" dia soft iron rod is immersed in the molten iron and the tip sparkles, then the metal is at 2,700 F, and if the tip of the rod melts off, the metal is at 2,800 F or higher and is ready for pouring.

Thanks again; good info.

 

Well maybe I should read your posts, now I see what you need!

A type K will work fine for quick exposure in the flame, it will heat fast and if you pull it out right after the reading stabilizes will last a long time.
Quick in and out of a flame is no problem, it is prolonged exposure at high temp that kills them why exotic alloys are used for long term high temp monitoring

Get a stainless steel sheath, 1/4 or thicker, and long enough to keep the plastic connector out of the heat. It takes searching but Omega has them, $50 approx.

http://www.omega.ca/pptst_eng/JQIN.html

We used to use rebar scrap to remove the slag, it will melt for sure at pouring temps

In general wouldn't you just run the melter with as much fuel as your blower can burn?

My propane melter screams like a jet, I just increase the gas once the walls are hot enough to sustain the flame and add more air until it blows out, then back off a touch to get the fastest melt rate. Not sure how an oil melter would work.

 

I have tried various fuel flows and air combinations, and have not yet been able to get a consistent correlation between fuel flow, combustion air and furnace temperature.

Sometimes it all works great and I get good hot iron, and sometimes I can't seem to find a combination that will melt iron.

I have tried up to 10 gal/hr, but it does not seem to work any better than the lower fuel flows.
I think too much fuel and too much combustion air actually cools the furnace.

I will try measuring the back of the hot face and see if that works.
At least I would know if the adjustments are making the furnace hotter or cooler.

 

If Pat's messing with iron wouldn't he be better off with a INCONEL 600 Sheath?
If just wanting to get a refractory reading then the SS would be fine more than likely but if your going to purchase one, might as well get the toughest probe they offer.

http://www.specialmetals.com/assets/smc/documents/alloys/inconel/inconel-alloy-600.pdf

I use the Omega High Temperature Thermocouple Probes with Quick Disconnect NHX Ceramic Connector CAXL-18U-12-NHX but can't remember what material the sheathing is.
They also sell ceramic probe sheathings but have read bad reviews about packaging and product shows up broken.

I got a small hole drilled in to the side of the furnace and have the tip of the probe probably 1/16"-1/8" buried below the hot face surface.
Works great, have had the furnace up to 2000* to date.
I did push the probe into the chamber once and within a very short period of time it was glowing.

Thought it was going to melt and probably would have if left in there any longer than I did.

 

I would again note that my concern is not with the actual temperature in the furnace, but rather the difference in temperatures (either direct or indirect) of the furnace or exterior hotface wall, and the intent is to find out if a given change in fuel flow or combustion air flow produces more or less heat.

Right now I am just guessing at what the best fuel flow and combustion air amount produces the hottest furnace, and not having much luck with that.

All I need is to measure a relative change in some temperature related to the furnace interior, such at the exterior of the hot face, so I know whether to increase or decrease the fuel and air flows.

 

So if I'm understanding you correctly, Your wanting to;

1) Get your furnace fired up under the normal operation you set your burner at
2) Get a reading of the interior side of the furnaces refractory wall hot face at the normal settings
3) Get a reading of the exterior outside of the furnaces refractory wall at the normal settings but yet "within" the furnaces metal shell
4) Adjust the fuel/air mixtures entering the burner and see what gives your the highest temperature readings at the same point which were previously checked, if any?

Is this a correct understanding/comprehension of what your looking to do?

If so, get one of or a similar thermocouple probe as mentioned above, drill the appropriate size probe hole in the side
(my probe hole is drilled in the middle to give me an average reading overall) fire that puppy up and start taking some readings by inserting the probe and adjusting probe depths as mentioned above.

Don't know of any other way to do it other than that.

I've shot the exterior keg walls before with a digital thermocoupler and swear the walls are actually hotter than the reading I'm getting but I don't think that's part of this equation which your looking to achieve.
I only mention the digital TC because I don't have a lot of faith in them, at least the cheapo one I have.

 

Looking at this furnace section, there is a 1" hot face which will be cast from Mizzou dense refractory.

Outside of that hot face will be two 1" layers of ceramic blanket (I show one layer of ceramic blanket in the section, but have changed that to two layers), and then there will be the keg shell.

So I know that the inside face of the hot face will melt cast iron when the burner is adjusted correctly, so I don't want a thermocouple there since it would melt, being non-iron temperature rated.

I could measure the outside of the beer keg shell, but generally I can put my hand on a shell that has two layers of 1" ceramic blanket under it, so that would not tell me anything.

Dense refractory is not suppose to be insulating, but I think even dense refractory is insulating to some extent, and the exterior of the hot face will probably be significantly cooler than the interior surface.
So my idea is to place a thermocouple between the inner ceramic blanket and the hot face, ie: the thermocouple is against the outside of the hot face, or at least near it.

I would not want to drill into the hot face since it is only 1" thick, and I don't see an advantage to doing that.

With one or more thermocouples in place (I bought a cheap thermometer readout that has 4 probes with it, so I would probably put one probe at the bottom of the furnace shell, one at the top of the shell, and two evenly spaced between those two), I would fire up the furnace and pick a mid-range fuel flow of perhaps 3 gal/hr (ironsides has quoted this fuel flow before, so I figured this would be a good place to start), adjust the combustion air to neutral, and then record the temperature readings from a cold start up to perhaps 30 minutes, or basically up until the temperature stops changing.

Once the temperature readings stabilize, I would adjust the combustion air for a lean, and then a rich setting, recording the temperature change (if any) for each adjustment.

I would then try the same thing at perhaps 2 gal/hr, and 4 gal/hr, to get a constrast of the heat produced vs gal/hr.

At that point I should be able to find which fuel flow and combustion air setting produces the hottest furnace temperature, as measured on the outside of the hot face.

Ironsides has mentioned measuring the exhaust stream, and I considered doing that, but that could give a false reading, such as when you are running the furnace rich, and so the fuel is not fully combusting until it is outside the furnace.
Measuring the back of the hotface should give a good idea of what is going on inside the furnace, ie: a hotter outer hotface wall means a hotter inner hotface wall; the difference being you can use a cheap thermocouple to measure the outer hotface wall, but the end result is that you should be able to tell exactly which burner setting produces the maximum heat in the furnace.

Also, by measuring four places vertically up the interior hot face wall, I will be able to tell if it would be advantageous to elevate the crucible in the furnace, such as if the readings indicated that the upper part of the furnace was hotter than the lower part.
I highly suspect the upper part of the furnace is hotter just because the combustion air entering at the tuyere level is at ambient outside air temperature, and so it would have to swirl around for a while in order to combust and reach maximum temperature.
I know of two individuals who have done a lot of iron work who elevate their crucibles in the furnace, but it would be nice to be able to measure and verify that what they are doing is the correct thing to do.

 

I guess I could do a mock-up using a 1" thick dense fire brick with a burner trained directly upon it, and a thermocouple behind it.
That should allow me to determine if this idea will work.

 

And he actually does speak English apparently.

Now I understand where your thoughts are coming from.
Detailed info always helps.

Your staging & placement of thermocouple leads is a sound plan.

Might want to consider placing the TC leads 180* opposite of where the flame hits the interior wall.

The only way to place a probe within the furnace chamber (and it not melt) is to put a ceramic condom on it, unless somebody else knows something we're not aware of or thinking of.
Not sure if the INCONEL 600 could be placed within the furnace chamber during operation for any extended lengths of time & survive.

Would definitely like to know what the results are after testing.

 

His readings shouldn't take that long as his hot face is only going to be 1" thick.

But, there will be a variance of temps on the outside and inner chamber regardless.
How much is TBD by real world testing.

 

How do a do a quote on a reply? I don't see the button for that.

Lag time may be an issue, and I guess drilling to the hot face about 1/2" is not out of the question, but I would rather not do that.

I think an infrared thermometer would work well in this application, but I don't have one.
This is similar to what I bought, although I thought I had a 4 channel; perhaps it is only a 2 channel.

I think putting the thermocouple opposite the burner impingement wall is a good idea, since that wall seems to run hot.

Worst case I will drill into the hot face about 1/2" if the reading is too slow.

 

But the reading difference between the outside and inside of the hot face is not relevant, but rather what needs to be determined is if the readings go up or down with burner adjustments.
Knowing the interior furnace temperature would be nice, but not necessary for what I am after.

 

Ok, I see it now.

Here is the link to the temperature device I bought, or one similar:
http://www.ebay.com/itm/Digital-The...452135?hash=item2a7cbdfc67:g:wjUAAOSwuxFYv6MU

I forgot to post this link above.

I will look up that guy on yt, but from what I have heard from numerous folks (don't ask me who, I don't recall now) and also some online info, the infrared ones don't work because of the reflected IR or something like that.
I have not tried one, so who knows, perhaps they do work.

I do think an IR would read on the outside of a hotface since there are no reflections there.