Matrikote before and after- actual temps

[the2ndcashboy]

So we had some discussion in the NARB thread about whether a kiln wash like Plistix or Matrikote would actually increase the max temp of a forge, or just make it heat stock quicker. I just built my first gas forge using a NARB, so it seemed like a good time to get some solid numbers, instead of subjective color heat reading.

I'll start with the forge specs: I built it in a 20# propane sized bottle. Two 1" layers of wool, ridgidized and then coated with ~3/8" of refractory (Plibrico Hyrezist 2700, best I can tell its somewhere between Mizzou and Kastolite 27). I haven't made a slider for the brick doors yet, so for now I've been blocking about 3/5ths of the opening (4" high by 7" wide) with a fire brick. Burner is a 3/4" inducer NARB. I'd run the forge a couple times, and even semi-successfully forge welded, so I knew it was getting good and hot. I purchased a PID and type K thermocouple so I could get actual temperature readings throughout the test. Matrikote was painted onto the lining, ribbon burner flame face, and the flame side of the brick I used to partially block the opening. TC was inserted through the front, and extended about halfway to the back, directly under the burner (not ideal placement, but its a ribbon, most of the forge is directly under the burner).

 

1st test (no Matrikote):

Cold (80*F) start @ 5psi

2 minutes @ 5psi and it was @ 1500F. Forge was just starting to glow. TC was probably mostly heated by direct flame. At that point, I turned it up to 10psi and let it run.

5 minutes @ 1750F

8 minutes @ 1900F (forge is a nice high orange/ low yellow

9 minutes @ 2000F

10 minutes @ 2040

The temperature basically plateaued at 9 minutes, and had pretty much stopped climbing completely by 10 minutes. I thought about cranking it up to max (20psi) but I didn't want to damage the TC before I had a chance to try the Matrikote. K-type TCs are rated up to 2300f, but I don't think it would live long in a flame at that temp.

I waited til about 15 minutes and put in a block of cold-rolled steel measuring 2"x1.5"x1.5". Colors are somewhat subjective, but it was fully up to temp at around the 3:30 mark (bright yellow heat).

 

2nd test (after Matrikote):

Cold (82*F) start @ 5psi

1 minute @ 1500F

2 minutes @ 1680F. Increased burner to 10psi and let it run.

3 minutes @ 1750F. Spots are starting to glow in forge lining, but majority of lining is not glowing even dull red.

5 minutes @ 1900F. Entire lining is starting to glow. Some spots are bright, others still dull.

8 minutes @ 2000F (temperature stopped climbing between 5-6 minutes, then slowly started climbing again)

9 minutes @ 2035F

10 minutes @ 2060F. At this point the temp was still slowly climbing, and the forge interior still wasn't glowing uniformly yellow, so I let it continue running.

14 minutes @ 2190F. Somewhere around the 13:30 mark it stopped climbing. Forge interior is almost uniformly glowing.

I then put in the block of steel and timed how long it took to reach temp. It reached a uniform yellow around the 5:30 mark.

 

Conclusions: The Matrikote seemed to reflect the flame heat very well. Temps came up much quicker, until about the 1800F mark, after which it slowed down considerably, to the point where at 10 minutes, the before/after temps were roughly equal. The forge lining heated up much slower with the matrikote. I ran it for about 20 minutes total, and the lining wasn't totally uniform until the last several minutes. Max temperature increased by 150F, but took an extra 4 minutes or so to reach. The real surprise was the stock heating test. I've always heard plistix/Matrikote will heat stock much quicker, but instead it took considerably longer. I actually took it out of the forge briefly around the 4:30 mark, because I was sure I just wasn't seeing the color properly. It was only yellow on the corners and edges, the center was still orange. It took another minute to heat fully. I'm really not sure what to make of that. In hindsight, it would have been useful to leave the TC in the forge while heating the stock. The lining may not have had as much stored heat due to the better insulation of the Matrikote, and therefore the forge temp dropped more after the stock was put in, so if I ran the same test after, say, 30 minutes, the stock might heat quicker (although I couldn't really see a "cold" spot around the stock, so I dunno). Alternatively, the Matrikote may be insulating both ways, and blocking some radiant heat from the lining. At a lower temp, the flame would heat the stock quicker than the forge lining would, so you might get a different result. I also suspect a forge without a refractory layer over the wool would gain much more from the application of Matrikote than mine did, since they have very little thermal mass to begin with. Overall, the Matrikote was probably a good addition, but I would have liked to see a better result on the stock heating test. I'm pretty happy about the increased max temp though. I should be able to forge weld at 10psi easily. Especially once I finish the brick doors on the front and get the burner properly mounted and insulated. Once again, I'd like to thank Frosty for the NARB development and plans. The thing runs great

 

[Buzzkill]

Thanks for the info on this.  The one thing that has me baffled is the stock heating time.  That runs counter to my personal experience with Matrikote lining, unless it's just my perception that's off.  I've never timed stock heating or reheating, but my impression is that the wait time to bring stock back up to forging temperature after working at the anvil is significantly less than it was before the coating.

Was this the first firing since you applied Matrikote, or had you already fired the  forge up to max temperature at least once before?

Without a 14 minute run on the pre-coated forge I'm not sure we can draw much of a conclusion about max temperature before the coating.  You had a 40 degree increase between minutes 9 and 10 without the coating, but only a 25 degree increase between minutes 9 and 10 after the coating, yet you concluded that you hit max temperature at 10 minutes pre-coat.  I guess if the temperature had completely stopped increasing at that point that could make sense.  I do think it would be better if  you could keep the TC out of direct flame impingement, but as you said that's kind of difficult with your setup. 

Regardless, thanks for taking the time to run the comparisons and to post it for us.  I'm hoping I don't have to reline or rebuild my forge any time soon, but if/when I do I'll try to gather some info as well.  My latest build is an updraft configuration and that might affect the outcomes somewhat.

[the2ndcashboy]

This was the first firing with the Matrikote. From my understanding, there's not really a burn in process like refractory. I can stick the TC in next time I fire it up and see if anything changes. I'm definitely going to try the stock heating test again, probably after the forge has had more time to heat soak.

 

It probably would have been better to run the uncoated test a bit longer, but I was fairly confident it had stopped climbing. Uncoated, the temperature rise was fairly consistent, it didn't really "pause", just climbed steadily until it stopped around the 9:30 mark. Coated, there were several points where it stopped climbing. Especially once it hit about 1900 the rate slowed way down. It hit 1900 @ 5, and then actually dropped a couple degrees before it started climbing again @ 6 minutes. I let it run past 10 minutes because of that, and because the forge still hadn't reached that bright yellow that it had uncoated.

[the2ndcashboy]

I ran the test again today, just to see if the coating reacted any differently on the 2nd firing. The warm up curve was much more uniform this time. No weird pauses or anything. Actually tracked pretty closely to the uncoated test, with the exception that it was still climbing at the 10 minute mark, and the liner itself was obviously not heating up as quickly. It was still about 2175f @ 14 minutes though. I took the TC out at that point and let it run to 20 minutes, then put it back in and let the temp stabilize. It was at 2280f when I took the TC back out @ 22 minutes and put the stock in for the timed heat. The liner looked like it was pretty close to uniformly high yellow heat, so I hoped the stock would heat much quicker this time. It took right at 4 minutes this time, which is much better than the first coated test, but still not as good as the uncoated. I'm thinking I'll have to run the forge for a good 30 minutes to get the liner to full heat soak, and that would probably get it to heat the stock the same as the uncoated. That's kind of disappointing. I've always heard that the kiln wash will drastically cut stock heating times, but I didn't get that result at all. My guess is that the people that had the large heating improvement either didn't have a layer of castable over the wool, or were heating to a lower temperature. Or both. The stuff really does provide an insulating effect, but that may actually be somewhat counterproductive in a forge with a decent heat mass like mine, at least in short forging sessions.

 

After I finished the stock heating test, I turned the burner down to 6-7psi to see how long it would run without backfiring. After about 10 minutes it was still running fine, so I stuck the TC in to see what the temp was. It very quickly ran up over 2300f , so I snatched that thing right back out of there. Good to know it will run that hot even lower than 10psi. I'm excited to see what it does once I get the doors done and the burner mounted properly. 

 

Overall, I'd say the Matrikote was probably a good addition. It definitely increased the overall temp. It also should make the lining more durable, and with its increased insulating effect, I should be able to run the burner lower without backfiring. I do wish I'd done some more testing with the uncoated forge first though. If I had it to do over, I'd have tested the uncoated forge at more of a variety of burner psi levels, so I'd have more points of comparison with it now that its coated. I wasn't expecting the poor stock heating results after coating. I was aiming more to check the max temps and warmup rate. The stock heating test threw me for a loop.

[Frosty]

Oooh, you document good Texican guy!  Nice job and it gives me some departure points to work with, we have a club gas forge build coming up and we're going to so some Metrikote testing in a pair of forges. Good job, thanks.

Frosty The Lucky.

[the2ndcashboy]

I just hope the data I got is helpful to people, even though I should have done quite a bit more "before" testing I think. I may make a smaller knifemaking specific forge sometime this year using the same materials and a 1/2" NARB. I'll do more "before" testing if so. 

[puijkh]

Hi Frosty, 

is it possible to share plans for your club gasforge build you are talking about. Would be nice to play along.

Hans

[Frosty]

Welcome aboard Puijkh, glad to have you. I'm not the guy planning nor building this forge and I don't know if there are drawn plans. I'll post what I can when we get something finalized. Might have to post pics of the kit, maybe assembled, maybe . . . I don't know. Heck, I'mm not sure what all the guy who's doing the design is including or leaving out. 

Hold onto your hat, you won't believe this but . . . we have DIFFERENT ideas of how they should be made or what all should go into them! 

Seriously, I'm mostly doing ideas and critiquing it as it goes. Tristan has a sound design. I'll post as much of a how to as possible when we get something going.

Frosty The Lucky.

[Mikey98118]

On ‎7‎/‎21‎/‎2018 at 8:41 PM, the2ndcashboy said:

Overall, I'd say the Matrikote was probably a good addition. It definitely increased the overall temp. It also should make the lining more durable, and with its increased insulating effect, I should be able to run the burner lower without backfiring. I do wish I'd done some more testing with the uncoated forge first though. If I had it to do over, I'd have tested the uncoated forge at more of a variety of burner psi levels, so I'd have more points of comparison with it now that its coated. I wasn't expecting the poor stock heating results after coating. I was aiming more to check the max temps and warmup rate. The stock heating test threw me for a loop.

I think your tests were valuable. There has been a lot of people using Matrikote as a finish coating over high alumina refractories lately, which I consider as quilding the lilly. Can it help? Most of the time, I'd say sure, but not enough to be practical.

Plistex and Matrikote were designed as finish coats for ceramic fiber products, were among other advantages, they do provide heat reflection. How? by providing a solid surface for radiant energy to bounce off of, instead of penetrating deeply into to it.

[the2ndcashboy]

I don't think I'd want to use Matrikote as a finish coat over fiber in a forge. At least not anywhere that might get bumped or poked. I suppose you could do a hard floor of some sort and then coat the rest with matrikote. 

[Mikey98118]

You have a good point; it is a trade off. One way isn't superior to the other; its a personal decision. I've built forges and casting furnaces both ways, and like both ways. In the end, which way depends on circumstances. How heavily the forge is used, and whether or not others are allowed to use your forge are considerations.

[Mikey98118]

I would also consider Plistex as a coating over the floor area of a forge with a hard refractory hot face, if it was used for welding.