How many Coats of Satanite to High Temperature Wool

Discussion in 'Furnaces and their construction' started by Melterskelter, Jan 8, 2019.

  1. Melterskelter

    Melterskelter Gold Banner Member

    I have learned from hard experience (so to speak) that hardness is easy to induce in cast iron. There is hardness and then there is extreme hardness. For parts I am making for sale (not this pulley) it is crucial that the iron be very uniformly soft. I found that at the edges of some castings a little more than 1/2" thick that the iron was measuring Rc 10-15 and this was unacceptable. Most folks would not even notice Rc 10-15 in machining a normal part. Rc 40 they would surely notice. Rc 60 would be very hard on tooling and be very difficult to machine.

    I also found that excessive FeSi leads to significant shrinkage. So, for the last 20 or so pours I have been tweaking my FeSi to find the lower limit of needed FeSi that results in normal shrinkage and yet have consistent softness.

    What I am still in the process of learning is that timing of addition of FeSi is a powerful determinant of its effectiveness. mixed into the melt more than ten minutes prior to pouring results in little effect of Fe Si at all. Mixed in less than 5 minutes prior to pouring allows very low additions of FeSi and this is consistent with reported lab experiments done in universities and industrial labs.

    So, of late I have been using 6 ounces to 50 pounds of iron roughly or .75% has worked well and I think I can go even lower based on those reports.

    Just for interest I did Rockwell test the runner I used on the pulley yesterday since it is relatively thin
    in cross section. It is 3/8" thick and 3/4 wide. I checked it at its midpoint which should be the area most prone to chilling as it is most removed from massive areas of iron. It measures Rc 0. Since adding FeSi in this proportion this has been the same reading within a few points I am finding in the previously troublesome castings.

    IMG_5111.JPG IMG_5110.JPG
     
  2. Melterskelter

    Melterskelter Gold Banner Member

    Just a short note on running my new very low mass furnace:
    Today was a splendid day weatherwise. 50, clear and light wind.
    So, I packed up a couple molds in the early morning. After a short break I fired her up and melted 40 pounds of iron and poured it in an hour and 20 minutes. that was a much shorter time by better than half compared to my old conventional cast hot-face furnace using the same burner. What a treat.

    The first time I ran the new furnace a couple days ago, because it sounds and behaves differently from the other furnace, I took quite a while to figure out that I was attempting to use too much atomizing air. Today I started out with only 20 pounds atomizing air in my Hago .75 gal/hr siphon burner and just balanced it with combustion air at that pressure without trying to make it sound and look like the old furnace. Even though I had to fight the impulse to increase atomization, as soon as the furnace warmed up I could see that this was the right combo. Within 20 minutes my initial charge of iron was already getting mushy and at 45 minutes I was adding cold iron to the melt. I poured at 2550 and had very nice results. Sweet!

    Lesson learned (I think) is that too much compressed atomizing air may cause too much cooling because of the cooling caused by expansion of the air in the furnace. So, don't run over 20 to 22 pounds of atomizing air.

    What may be going on: I have used the appearance of the flame coming out of the chimney as an indication of proper balance of fuel and air in the furnace. So, you can get 4-6 inches of orangish yellow flame out the chimney with a modest amount of atomizing air and a large amount of combustion air and the same appearance can be achieved with a large amount of atomizing air and modest combustion air. BUT, the atomizing air introduces more cooling since it enters compressed and so the furnace runs cooler with large amounts of atomizing air. So, for my furnace and burner combo, 20 pounds of atomizing air is optimal. I suspect that similar results should obtain for others using the same or similar siphon burners and diesel fuel. Incidentally my fuel is run into the burner at 9PSI and I burn 2.5 gallons per hour.

    On the subject of FeSi, I used just 3 ounces of FeSi in 40 pounds of iron and added it within a couple of minutes of the pour. Testing shows Rc 0-2 of a thin runner just like previously tested.

    Denis
     
  3. Petee716

    Petee716 Gold Banner Member

    It sounds like you've hit your stride. Great work on the new furnace. I really appreciate you taking the time to share your observations.
    It's below freezing here in Buffalo and will likely remain so over the next few months. I have about 30 gallons of oil in my tank. It's a bastard mix of everything from kerosene to heavier oils and is unheated. I did a flow test (no atomizing air) using a 1 gal/hr Delevan siphon nozzle with the oil around 35F (ambient). I'm able to back feed air through my dip tube so I bubble air through the mixture for 15 minutes or so to get the oil reasonably homogenous. I got just over 2 gal/hr at 20PSI and just over 3 gal at 30PSI.
    I know this question has probably been answered in the past, but in your experience would the addition of 20PSI atomization air have much real effect on the flow rate?

    Pete
     
  4. PatJ

    PatJ Silver

    I did a lot of experimentation with a siphon nozzle burner when I built the multi-flow valve tree, and I tried a variety of atomization air pressures, fuel flow rates, combustion air flows, etc.

    The way I finally got it figured out was to run the tests at night with a furnace that had the interior coated in ITC100.

    Adjusting an oil burner can be very deceiving since a big orange flame either inside the furnace or outside the furnace produces more radiant heat, which you can feel on your face/body, and so it is very easy to assume that big hot-feeling flames are producing more heat inside the furnace than small or no flames that have little radiant heat.

    Noise also plays a factor, and a loud roar sounds a lot hotter than a quite roar, I guess for the same reason we use to take the mufflers off of our cars as teenagers to make them sound really fast, like a race car.

    It order to tune an oil burner correctly, one generally has to ignore some of the visual/audible signals, and instead look at what is happening to the ITC coating on the inside of the furnace, and also on the inside of the short chimney section on the top of my lid, and do this at night with no lights on anywhere, and watch which settings cause the ITC coating to glow the brighest.

    You can see it in my videos. The inside of the furnace goes from dark, to dull red, to red, to bright red, with the bright/brilliant red being when you find the optimum and hotest settings for compressed air, combustion air and fuel flow.

    To get optimum heat, you have to find very close to the perfect settings for these three values.
    It is very easy to start changing too many variables too fast, and for a long time (years) I could never figure out exactly what combination worked well.

    I figured it out after I tried adjusting one setting at a time, ie: adjust the compressed air value (30 psi compressed air turned out to be hottest for my 1 gal/hr nozzle), adjust the fuel flow rate (somewhere between 2.5 and 2.75 gal/hr diesel turned out to be hottest for my 13"x14" interior furnace), and then adjust the combustion air flow using 30 psi compressed air and 2.75 gal/hr.
    The combustion air flow once again was adjusted in pitch darkness such that the most brilliant radiance was achieved not just in the furnace but all the way up the interior of the chimney to the very top.
    Slight changes would cause the brilliant radiance to either recede into the furnace, or be covered by very large yellow/orange flames which were cool in temperature.

    Fuel tank or fuel pump pressure is irrelevent. It is the fuel flow rate that determines things, and so you adjust the needle valve to get the desired fuel flow rate regardless of fuel tank pressure.
    I use about 10-15 psi pressure on the fuel tank for a consistent flow rate regardless of fuel tank level (pressurizing the fuel tank removes the variations in gravity/head pressure out of the equation).
    Edit: Some people regulate fuel flow by changing compressed air values. I can't comment on this since I always use a needle valve with a pressurized fuel tank, and hold the compressed air to a constant 30 psi.

    I am extremely pleased with my melt times so far, and I have been able to achieve very hot melt temperatures in under an hour, which is something I was never able to do before.
    I will be recording fuel usage per lb of iron in the future and will post the results here, but I am confident that my fuel flow and air settings are close to optimal.
    And the noise and flame are less than many of the other settings I tried, so flame, flame color and noise should not necessarily be used to judge furnace interior temperature.
    It also seems like the cleanest and clearest burn is also generally the hottest, and so basically there are no visible flames inside the furnace (I need to watch my videos again to verify this, but this is what I recall).
     
    Last edited: Jan 14, 2019
  5. Melterskelter

    Melterskelter Gold Banner Member

    I don't know exactly to what value you are suggesting adding 20 PSI. Do you mean adding 20 to 30 to get 50PSI and would that increase flow rate?

    I have not done that but would not expect to see much increased fuel flow rate. I think the fuel flow rate flattens out up around 30 or 30 pounds of atomization pressure. Most likely this is because atmospheric driving pressure is the limiting factor and the atomizing flow at 20 PSI must more or less provide the maximum or near maximum differential pressure between the atomizing air "vacuum" and the atmospheric pressure. To overcome this limitation I use a small 12v automotive fuel pump to provide 9 pounds of fuel pressure to the siphon and that increased my flow rate from 1.75 gal/hr to about 2.5 gal per hour for a nominal 2.75 gallon per hour flow. For my furnace that amount of flow I suspect is about all the burned fuel rate it can benefit from. I do get a faster melt at 2.5 to 2.75 gal per hour (wide open needle valve for me) than at 1.75.

    I am not trying to enter some sort of race with bragging rights for my furnace, just trying to get the time spent waiting for pourable iron down to an hour to an hour and a half. That save valuable time and allows smaller time/weather windows for melting opportunities plus it saves fuel consumption. Whether the higher temps for shorter times is harder or easier on the crucible than longer lower temp melts is an unknown for me but is also a factor as crucible life for iron melting is obviously a factor.

    I agree with PatJ's comments above that detecting optimal settings is not an exact science. I am soon going to see what can be learned by taking stack temperatures on my muffler chimney using an IR non-contact thermometer. I am interested to see how long it takes for temperature to equilibrate on the insulated chimney after setting changes and how well measure surface temp of the chimney exterior correlates with melt times. I figure there is about a 50/50 chance that this measurement will be useful. But, it would be nice to have something measurable to help guide settings on the burner. My situation is complicated by needing to burn with a stack on the chimney opening so as to reduce noise from the furnace in order to get along with the neighbors.

    Denis
     
  6. PatJ

    PatJ Silver

    I am not of that game either, but I can't tell you how exciting it is to be able to walk out to the furnace and know which settings will work well to melt iron in a reasonable and predictable amount of time.

    I was really about to give up on the iron thing before I finally got it worked out, but luckily I had a lot of prodding and help from ironsides and others that kept me going.
    I post this info here so that others will see that it can be done, see that iron is not that difficult to melt an pour if you know what to do, and perhaps save a few folks that ultra-long learning curve that I went through.

    Melting and pouring iron is very cool (slang so to speak, actually extremely hot), and produces some really nice engine parts that wear "like iron", because...........well, they are iron.

    .
     
    _Jason likes this.
  7. Petee716

    Petee716 Gold Banner Member

    Sorry I may not have framed my question clearly. My thinking has been that the pressure in my tank (20-30PSI) is the primary force that should move the oil to the nozzle, and that the atomizing air serves only to perform the task of atomizing with nominal effect on flow volume. It appears that your method relies on the atomizing air to serve both functions with the addition of the automotive pump to simply augment the flow.
    Since I assumed that tank pressure should be the primary force, I did my flow tests using tank pressure only. The gist of the question was whether you thought the addition of the atomizing air to the test would significantly affect the flow.
    It's hard for me to imagine that my cold goo could be pulled through my fuel lines under these conditions without a hard push from behind.
    I'll be back out in the shed tonight to try it.

    Pete
     
  8. Melterskelter

    Melterskelter Gold Banner Member

    I think the atomizing air does give a push (or a pull if you will) to the fuel flow. With no pressurization of the fuel line, the atomizing air will draw 70% of what it does with both atomizing air and 9PSI in the fuel line. So, I would expect to see about a 20 to 30% increase in fuel flow rate when you add in atomizing air. BUT, the ultimate heat that you get in the furnace is not solely dependent on fuel flow. I noted that too much atomizing air (over about 20 to 22 pounds in my case) tends to cool the furnace as expansion of compressed atomizing air sucks up heat more than introduction of a similar volume of uncompressed combustion air. At least that is how I try to explain the observation that turning down atomizing air resulted in a hotter burn. All this makes me think that relying more on pressurized fuel to deliver fuel through the burner to the furnace may be preferable. I am sure there is a break point there too as inadequately atomizing the fuel is known to result in poor combustion. We are all looking for that sweet spot...

    Have you tried an immersion heater in your fuel tank?

    Denis
     
    Last edited: Jan 15, 2019
  9. PatJ

    PatJ Silver

    I recall scavenger mentioning that he uses 100 psi for compressed air, and he stated that the high pressure air sort of turbo-charged the flame and made it hotter.
    I have found the opposite to be true, ie: compressed air pressure over 30 psi appears to cool the furnace, which correlates with what melterskelter is saying.

    My guess as to why a higher compressed air pressure appears to burn cooler is that it increases the velocity of the air/fuel stream too much, which causes it to climb up the back of the furnace instead of swirl around the crucible.
    It seems like slower compressed air and combustion air velocities give the air and fuel time to mix while they are low in the furnace, and then give up maximum heat as the combustion process rises.
    The high pressure/high velocity compressed air seems to make a jet stream, which does not seem to mix as well or burn as evenly as lower pressure/lower velocity compressed air and combustion air.

    I have tried higher rates of fuel with associated higher rates of combustion air, and anything higher than 3 gal/hr for my furnace size seems to burn cooler.

    It looks like scavenger uses 125 psi compressed air pressure with 20 psi pressure on the fuel tank.
    It should be noted that scavenger did over 200 iron melts, and some large ones too with a #70 crucible, so he must be doing something right, but I will stick with using 30 psi compressed air.
    A lower compressed air pressure is also a lot easier on the air compressor, and if for no other reason, it is a good idea to run the compressed air pressure as low as possible while still getting good atomization.

    I still say that when you are using a needle valve to control fuel flow, the pressure on the fuel tank and the atomizing air pressure are somewhat irrelevant since the flow is going to be determined by the needle valve only. If you are not using a needle valve, then that is a different story.

     
    Last edited: Jan 15, 2019
  10. Fasted58

    Fasted58 Silver

    Could you guys tune the oil burner for max flue gas temp w/ a Combustion Flue Gas Analyzer? O2, CO and CO2 shouldn't matter if you're tuning for faster melt times. Build a 'stack' over furnace flue outlet.

    Kind of pricey around $1K USD +/- ... but if you know a HVAC guy maybe you could beg, borrow or steal.

    I haven't tried it but I was planning on using a Skutt kiln pyrometer (2350° max) for burner tuning on my propane furnace build.
     
    Last edited: Jan 15, 2019
  11. PatJ

    PatJ Silver

    There has been discussion of measuring flue temperatures by more than one person, and I think ironsides has done that.
    Also discussions of analyzing the flue gases.

    I am not necessarily convinced that what is happening in the flue is what is happening in the furnace, and the furnace is where the heat has to be concentrated.
    If full combustion is delayed in the furnace for whatever reason, then the furnace will be cold and the flue will show a very high temperature, and thus you will get a false result.

    .
     
  12. Fasted58

    Fasted58 Silver

    Then install the probe in the wall of the furnace? Similar to a kiln pyrometer probe.
     
  13. PatJ

    PatJ Silver

    I installed three thermocouples on the outside of my hard face refractory shell, and they all melted after perhaps 15 minutes.
    Inside the furnace they may not last more than a minute or so.

    They do make high temperature probes that go on the end of iron-rated pyrometers, but even those are not rated for continuous contact, and they contact the iron, which is at perhaps 2,800 F.
    The inside of the furnace using light oil and forced combustion air can be up to 3,820 F, as I understand flame temperature.


    Radiant glow of a hot surface is a pretty good indicator of temperature though.
    I know the inside of the furnace is sensitive to the exact amount of combustion air (I leave my fuel flow at a fixed 2.75 gal/hr), because I can watch the intense glow extend upward (at night in total darkness) when the fuel/air mixtured approaches optimum, and I can even control whether the inside of the chimney on the lid glows bright red or not.

    Here is a color temperature chart.

    IMG_0041.jpg
     
  14. Petee716

    Petee716 Gold Banner Member

    Well, sort of. My tank is a 50 gal gas hot water tank. I've left the tank as undisturbed as possible ie all I did was plumb the air into the "out" fitting so the oil would come out of the dip tube. I have a strong aversion to poking any new holes into it and all of the existing ones are being used. So I have been tinkering with heater schemes that I can simply lower down into the flue, but haven't hit on anything yet that I would leave unattended.
    Sorry about the thread drift.

    Pete
     
    Last edited: Jan 16, 2019
  15. Melterskelter

    Melterskelter Gold Banner Member

    A little follow up on my lightweight furnace. Made my third iron melt in it today. 45 pounds in 1 hour and 15 minutes poured at 2550F. Love the speed which I know sets no records but is a huge improvement over my prior conventional castable hot face/ ceramic wool furnace.

    But, the Satanite has nearly fully fallen off the lid exposing the underlying 2600 degree wool. It is pretty evident that the exposed wool is not going to survive if left exposed. The question is whether my failure to first put rigidizer on the wool prior to applying the Satanite in two coats to 1;8 thickness is the cause for failure. It was the wool that failed as examination of the Satanite flakes shows that wool fibers pulled away with the Satanite. So, I am wondering if I put in a new layer of wool and then spray it with rigidizer, if that will give enough substance to the wool to support the Satanite.

    Alternative strategies are to use rigid boar covered by Satanite or, of course, to make an IFB-lined lid like OldIronFarmer's.

    Denis
     
  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I bought some rigidizer and have been fiddling around with it. I actually have a design for a wool lid I think is the way to go but for you at your temps, I wonder if the materials are up to the task. The rigidizer (I have HWI Ins-Tuff but they're all colloidal silica) I have says service temp of 2300F. Sodium Silicate might have modestly higher refractory but the wool still needs to be able to stay in the game. Other than where the burner impinges on the hot face, the vent area and lid in general is probably the toughest duty in foundry furnaces.

    I ordered some Satanite to experiment with too.

    Best,
    Kelly
     
  17. Zapins

    Zapins Gold

    Hmm that's too bad. Makes me concerned about my plans for the kiln roof with pressed fiber board and satanite. Hopefully it doesn't melt.

    Do you think it's because of the oil temperature? Or maybe two coats before firing?
     
  18. Melterskelter

    Melterskelter Gold Banner Member

    Yup, the lid has to defy gravity and put up with rapid flow of swirling hot gases. It's being punished pretty intensely. The vertical Satanite faces of the chamber have held up fine even where the flame hits the hot face.

    I am thinking there is a lot of expansion and contraction occurring in the Satanite over a very brief period of time going from stone cold to white hot in only a very few minutes. The Satanite crazes some, but that has caused few problems on the vertical faces. There is no evidence of layer 1 of Satanite delaminating from layer number 2.

    The floor of the furnace is another matter. There, drops of iron dribbled when skimming off slag have hit the Satanite overlying wool and have DISSOLVED the Satanite where it is in contact with iron. Those iron drops then continued to bore into the underlying wool. In some places marble-sized iron drip caused quarter-sized holes. That I solved quite easily and I think for the long haul by simply covering the floor with 1/2" of dense castable. I used the dense castable in a freehand method on the old furnace and noted that it seemed to be amazingly tolerant of local application and was very durable. After this morning's plus a prior session, the castable floor appears to be good to go.

    I just got a an idea (brainstorm?) I will explore some tomorrow: I think that using an Oxyacetylene rosebud to glassify the just surface of the wool prior to putting on a couple thin coats of Satanite might just toughen/harden the wool surface and first maybe 1/4 to 3/8" of the wool in such a way that will help it support the Satanite. I want to avoid in any way I can adding mass to the furnace as its low mass seems to be the key to its rapid melting. For that reason, there is no way I would go back to the heavy furnace. The new furnace is even quieter than the prior one and 2 to 3 times faster.

    I grabbed this video for another reason today. But, I'll post it for the heck of it.



    I'll update this as I go.

    Denis
     
    joe yard likes this.
  19. PatJ

    PatJ Silver

    Looks like it is running pretty well.
    I guess you can always touch it up a bit if it gets bad spots.
    If it all goes at once, then that will not be good.
    So far, so good.

    .
     
  20. FishbonzWV

    FishbonzWV Silver Banner Member

    Don't give up on lid, my first lid did the same. I just pulled it all off and re-applied thinner and wetter.
    When I apply the first layer, I mix it very thin, like paint. I think the extra water helps pull the Satanite deeper into the wool.
    You can stop with just one layer too.
     

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