Bill Kielb
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Posts posted by Bill Kielb
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1 hour ago, davidh4976 said:
We have a few different kinds. One is a 55 gallon drum lined with ceramic fiber; about 4 cu Ft.
Do you know for sure how many btu your present burners are rated? If not you can sneak up on it with how many firings in a 20# new cylinder. Conservatively you will likely get down to 1/3 - 1/4 of full charge before it becomes difficult to use, especially at 40 degrees. There are about 4.6 gallons (440 kbtu) in a 20# tank so basically 5 times more in your 100# tank.
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32 minutes ago, nuna said:
will it actually shrink again when re-bisqued? I
Yes it will
28 minutes ago, nuna said:Do you still think glazed both sides would be safer?
Yes I do, but it is complex so testing may have helped here. My guess is it would help. Total guess though.
28 minutes ago, nuna said:I've never used sand/grog in a glaze firing (if I'm understand your suggestion correctly); I've heard it can blow around in the kiln during firing and I wouldn't want to get stuck in the glaze - thoughts?
Pres used grog, I think I said silica, alumina is great too. Pres had the super excellent idea of applying thin and evenly with a salt shaker though. All can work, all require care not to spread around the kiln. Grog is probably neatest, then silica, then alumina.
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18 minutes ago, davidh4976 said:
'm seeing 1st stage regulators that handle from 1,500,000 to 2,250,000 BTU/hour depending on the model all at 10psi. They are all in the same price range, so I assume that the higher the BTU/hour, the better. So, my conceptual configuration is shaping up as: I'd use a 100 pound tank with a 1st stage regulator reducing the pressure to 10psi, then a manifold with individual valves for each kiln, with hoses leading to adjustable regulators (0-to-30psi) near each kiln, followed by the MR750 burners. I have to figure out my hose lengths and therefore sizes.
Interesting, so the MR70’s you are using will have medium pressure orifices. A larger 1st stage regulator will not respond as well as a smaller so probably not necessary to go to the 2.25 mil. Ten psi hose from the tank easily supplies 300 k - 500k btu and a single second stage from 10 psi down to your working pressure also easy at 300-500k btu. (Larger here is definitely not as accurate as one that matches the load best). So if the kilns are on a common manifold near each other it sounds like one low pressure regulator can feed all three and just use a hand valve and pressure gauge to fire each.
Frost is complicated so as your tank empties it also has less thermal mass and tends to frost quicker. Trial and error here is almost a must. As to the primary regulator freezing, likely not much of a concern.
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One thing that comes to my mind for large pieces, is it will shrink and grab on the shelf. The rim and likely the grid if flush at the bottom will tend to drag on the kiln shelf. The grid itself if not reasonably even could also cause this to warp and bend depending on variance in thickness and construction. A waster slab and thin even silica beneath and between comes to mind to keep it smoothly moving and from grabbing. Same for glaze firing, although predicting distortion I think is tough without having tested a few shapes and if glazing only one side could deform the shape. Sounds like you can glaze both to a large extent. Quartz inversion (IMO) is almost not a thing as every piece in every firing goes through it twice each firing the world around (probably millions of pieces). Having said that a reasonable slow speed helps with the rate it shrinks and there is no reason to go to cone 04 so neither of those suggestions sounds silly. We do multiple bisques with layer applications of underglaze but always bisque to lesser temps just to set each layer of underglaze. There is no reason to waster the energy or stress the piece.
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Most burners are rated in Btuh @ a specific pressure. If you are buying them from Ward then INCHES of pressure is what you need, not PSI. 1 PSI = 27.72 inches, ward burners are typically rated to 11” wc (propane) to get to peak output. Easier way to do this is figure how many btu you will use, know this number. Once known - convert to gallons for an idea of how long the tank lasts.
Normal propane design, 1st stage regulator reduces tank pressure down to 10 psi. Second stage regulation goes from 10 psi down to 11” water column. At 90 degrees tank temp you are approaching 200 psi. Running 200 psi line not the safest idea so reducing it to 10 psi improves safety and still allows a whole bunch of btu for a small diameter hose.
Best idea I have, sketch what you want to do and include realistic distances and btu required for all the legs. From there it’s pretty easy to pick stuff from a table if all that is known. Look at the ward burner spec below and decide if you are trying to follow that or run your burners at medium pressure.
The first stage tank regulator will need to be sized by the load on it (total btuh) Proper sizing is important.
A 100 pound propane tank contains about 23 gallons. One gallon of propane contains about 91,400 btu. The MR750 will consume approximately 77,400 bru per hour full blast at 11” of water column.
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Have done this with automotive metal flake back in the day and used a gun with a stirring blade inside. That was a reliable way to distribute and spray with the viscosity needed for an automotive finish. A zebra striped metal flake auto not so desireable. Your finishes can be more random so it might be possible to suspend and spray acceptably. I have not tried anything other than spraying glaze very evenly but think it’s worth a try.
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6 hours ago, Piedmont Pottery said:
It sure looks like iron oxide to me.
Might be! Magic kitty litter bucket replaces iron filters. Might be on to something. High iron city water or just high iron clay?
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2 hours ago, Dick White said:
With a Skutt Touchscreen controller, one now must build a custom ramp-hold program that mimics whatever cone-fire program on the way up and then add one or two more steps at the end of the program for a controlled cool.
Yuck, what a pain! Good to know. @Potpotpotter pretty easy to build a schedule, the last 200-250 f is most important to get the right speed to bend cones predictably. If you are unsure tell us, this is easily solved.
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@Aurea The good news is we likely don’t need to do massive calcs and I can make some assumptions from your ambient air temps. The also good news is your 40 amp SSR likely easily operates at 60 c or more which is usually minimum design terminal temps. The somewhat hard part probably is pick a right sized computer fan that is 240v and maybe for simplicity it operates whenever plugged in. That kiln has no low voltage or neutral so 240v computer fan is likely easiest. Will chug some number later and add here to confirm reasonable size fan in CFM. Not likely to be gigantic. (Break time at work - pretty busy morning) meanwhile if you can measure center to center distance between the existing fan screws that would help. It likely was designed for an off the shelf fan.
@Aurea ok approximate (brute force) design on a napkin, here we go: The junction voltage drop will be about 1.2 volts, we don’t know the junction thermal resistance so we will use 1.4 volt drop to be conservative. Further, let’s assume 15 amps max load and the fan contributes 10 watts (fan needs to cool itself controller produces heat this is a very conservative high guess) and performance is derated by 60% of free air blowing into a case. So lots of very conservative assumptions for our napkin calc.
Total wattage = (1.4 x 15 A)+ 10w = 31 watts, convert to btuh => 31 x 3.41 = 105 btuh. So if we assume an expected 20 degree temperature difference, derate that by 5 degrees for fan heat (super conservative here and double dipping) we get:
cfm = 105 btuh/ (1.08x15) ~ 7 cfm. Very small! So the picture looks like a 60 mm fan comparing it to the size of the SSR, the fan below seems to be more than enough, is ball bearing and 240v. Install inside blowing in, wire to the terminals where power comes in so whenever plugged in the fan turns on.
The important part will be the SSR to metal connection. A bit of thermal grease and a snug fit to the metal case will remove heat from the solid state junction best.
Ok I think we were super conservative with our loads and assumptions maybe someone here can check my math but this ought to be double the air necessary.
If I guessed wrong at the spacing of those existing fan screws, you will need to order the right size. At this airflow requirement most should work. Double ball bearings a nice feature for longevity and most important operates on 240volts ac
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Yep! If you have an infrared handy takes some readings and figure where it stabilizes above ambient temp with the fan. Just to mention - the SSR should be bolted to the metal with thermal paste between it and the metal. The fan will cool the SSR and the metal. That’s a nice fan and nice test to verify it works. My hope was the graphs will give you a better perspective of the actual heat sensitivity leading to a decent solution.
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38 minutes ago, Potpotpotter said:
. So the last segment will be for drop right?
Yes, I believe so. So for me, I would program cone fire to cone 5, a fifteen minute hold at cone five and a drop and hold or cooling segment. You may have to enable the cooling segment in advance
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2 hours ago, Potpotpotter said:
Does anybody have a program that worked from them that they can share please?
As min mentioned above, but since you have a touch screen you could program a cone 5 auto fire, add a 15 min hold at the end to get to cone 6 heat work, then add your 100 degree drop (from cone 5 peak) and hold as something to start, tweak from there depending on results. This way the autofire can do most of the schedule firing for you.
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Thanks for the pictures! Best guess here is this is overheating. Solid state relays (SSR) depend on cooling. So the thing I notice most is a fan guard but no fan. If installing an SSR without a heat sink then the device must be derated significantly. I have added some design curves below to show that once these things exceed 40c (104f - pretty much body temperature) they need to be significantly derated. Most of them heat about 1 degree C per amp which almost always means for this size device which depends on the backplate for all cooling they can only tolerate 7-8 amps without being mounted to a real heat sink. Cooling them always depends on the temperature of the ambient air as well so using cool air will help this significantly.
The 40 amp SSR appears to have lasted longer than the 25 amp SSR but still heated beyond its derated value. The extra rating is great but since the backplate is a certain size it only failed at a higher temperature. It looks like this is designed to be fan cooled so I think I would install a new 40 amp and set up a fan temporarily to cool the SSR and retest while measuring the temperature of the SSR with a non contact infrared thermometer to confirm.
My best guess for now, but minimal cooling appears designed into this to save money. The time limits in the literature are probably closer to being correct - just thermal restrictions on the SSR.
Some charts below and a quick blurb of how this can be designed just as an FYI of how severely these derate without real cooling. A guess would be you are currently operating around the yellow line on the graph. Set up a temp fan, confirm with infrared and once confirmed get a decent fan installed behind the guard. Blow air into the cabinet rather than suck it out. More air molecules, more cooling. All an educated guess though from the pictures.
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@PeterH The English translation throughout the manual has a familiarity to it
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Yes, you likely match the 240v split phase grid standard in North America and 3000 watts ought to be just short of 13 amps so most relays ought to perform just fine. Please post pictures of the relay (s) making sure the part number and ratings printed on the relay are visible in the picture. Post any picture of a failed relay you may have as well. Post a picture of the relay mounted in place as well. Relays fail from contact overload, and also often because of overheating. So one thing folks will look at is where are these mounted in the cabinet and how are they kept cool. Blocked air inlet / discharge louvers sometimes contribute to the overheating. So context and clarity of the photos you post will be important.
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7 minutes ago, Piedmont Pottery said:
That's a possibility, but I would expect polyphenols in water to have a net negative charge, and therefore unlikely to bind to polypropylene.
Tannins in well water stick to most everything. Generally cause users to complain about the yellow or rust stains on fixtures (plastic and ceramic) buckets, vinyl siding or most things irrigated. Not sure what your bucket is truly made of or it’s matrix but easy to test for tannins ….. or iron for that matter if curious.
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Did you check back at your original thread? I think @Hulk found a very close manual and cone 8 seemed the limit for that kiln. Also in that thread I think there are some diagnostic suggestions that can help with this a bit as well.
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You absolutely need the insulator to keep the live electric from touching anything metal. The only way I have been able to fix something like that (temporary fix) is to torch the end of the element and unwind it while red hot to restore enough of a pigtail. Careful unwinding and torch work keeping the areas being worked red hot can get you a single or double strand pigtail without shattering your element to pieces. This is usually a temporary fix, not forever, as the resistance of this element will be slightly lower. I always tell folks to plan on new elements in the near future - most have not and just fired until next replacement.
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39 minutes ago, Fred Y said:
ps: I've attached 2 photos of the insides of the kiln...
Just my opinion, I would do it in a heartbeat. The Genesis controller by Bartlett controls is also a possibility. Bartlett has made these digital controls for most manufactures here in the states for many years and might actually make the controller for Skutt to their programming requirements. I am super comfortable with the components, wiring, electrical and thermal design though. Not insurmountable, but with thought and careful construction very doable IMO.
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It’s really hard to speculate what you might have including clearance and elevation issues. I can offer, there may be an opportunity to collect the water, let it settle daily and drain off the top layer for non potable use at the beginning of the day. Sort of a larger more convenient bucket idea. The obvious concern is use. If you rinse glazes off which may contain metals etc…. Then catching all and making sure it does not get into the garden or runoff streams becomes a concern and more of a how it’s used and then disposed of thing. Bucket or multiple settling buckets might be the most prudent for responsible use.
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7 hours ago, Mudfish1 said:
I do a real firing I will know how much reduction I got
Another technique some use for later is to mix up a copper red glaze for reduction and place samples throughout the kiln to see just how well you reduce and maintain it. This oxblood color goes ugly green / grey pretty quickly with any sneaky oxygen infiltration. It teaches the importance of keeping the kiln in full reduction top to bottom while providing a way to map the reduction performance within the kiln. Only a handful of metals are significantly affected by reduction btw.
Cracks when double-bisquing large work ?
in Studio Operations and Making Work
Posted · Edited by Bill Kielb
Just perhaps an easy thing to remember - Flat plates with a hole in them start off with a pretty distinctive stress concentration. Have seen many a clock face crack just like in the pictures above. Reinforcing around a hole can help with clay, just like many other materials, this pattern and fix are similar to help many materials survive this typical stress concentration around a hole - pictured below. We reinforce all holes in flat plates with some added uniform thickness or washer if you will. Since, along with good practices no longitudinal cracks in these clock face figures.