Bill Kielb
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Posts posted by Bill Kielb
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Sounds like worn 9.25 ohm. Use the series drawing above, I removed the parallel.
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@sal.349 I think @neilestrick is correct in that this kiln runs two 120v circuits, so individual element resistance is going to be important whether this is series or parallel. Power wise it ought to be 9.25 ohms equivalent at 240 volts. Measure and tell us the resistance of a single element before doing anything. This may need to be series wired pairs instead of parallel. So if they are 9.25 ohms each and that makes sense, you will need to make them series pairs to work.
Series hookup
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2 hours ago, kristinanoel said:
let me make sure i understand - do you recommend alumina WAX, painted on both sides of a waster slab, and not alumina sprinkled on the kiln shelf and the waster slab? is this for ease of application or...?
I sprinkle alumina whenever in question. Alumina wax only for lids to keep the alumina in place etc… for me. Yes, anything that sticks can cause issues so common sense try not to let anything stick when in question. Waster slabs can be a nice flat place to fire, maybe flatter than most shelves. There is nothing magical about them when they stick, or your ware sticks to them. In theory they will shrink at the same rate as your ware.
Millions of pieces go through quartz inversion up and down every single day. I mention because it’s really hard to control real cooling rates in an electric kiln and they may be less than you are thinking naturally. With electronic controls, more of a drop and hold function with most kilns, but if you can do it - great! If you can’t, avoiding sudden cooling is a given, don’t open the lid.
I did add a graph of a cooldown rate for a gas kiln below because most folks don’t map it. This is for a very leaky gas kiln that cools fairly quickly. After 1300 degrees its natural rate is well below 100 degrees per hour ( see the actual column). If you can control cool, have at it, but natural rates may be much lower than you are aware of.
- kristinanoel and Rae Reich
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The infinite switch is fine, unless damaged from your previous configuration. Each group of elements draws just over 12 amps. Your switch is rated for 15 amps. You need one switch per two elements. Usually elements will be jumped together at their barrel or element connector and run as just a single wire from there. See picture below of elements wired in parallel at the element connector. Ignore the yellow thermocouple and focus on the red wires leaving the elements.
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Here is the idea per element set. Each set of elements are placed in parallel and the group is wired to the infinite switch on h1 & h2. See drawing below. Proper electrical wiring, new crimps, no splices, no tape that will melt, high temperature wire made for kilns, other wire is not rated for the heat. Use the MG wire that came with the kiln, no butt splices, crimp new ends on the existing wire. You will NOT use the neutral when configured this way. Your kiln must be grounded for safety though, just no use for the neutral.
Your kiln draws 25.9 amps so code requires for a continuous load, a breaker not less than 125% of the load but not exceeding 150% of the load. So 1.25 X 25.9 amps = 32.375 amps MINIMUM size and 1.5 X 25.9 amps = 38.85 amps MAXIMUM breaker size. Best pick for breaker (and wiring) would be a 35 amp double pole breaker. So your 30 amp two pole breaker seems undersized per code. Kilns are considered continuous loads but even so normally sizing for breakers is not to exceed 80% of its rated load. A 30 amp breaker can only be continuous loaded to 24 amps. I don’t think he sized this correctly.Somebody here can check my elements though, I think they are about 37 ohms each and all four in parallel (full power) approximately 9.25 ohms.
Edit: see below for series pair wiring
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I only use alumina, because I have a ton of it and it will not stick to anything. Folks have done well with Silica though and it has better shape. All said, nobody makes silica wax.
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2 hours ago, neilestrick said:
If the waster sticks to the shelf it will crack
When it cracked it stuck which means when it cracked it moved independent of its normal rate. It’s often still much smoother than a shelf so most often fine and the only way but if the ware sticks to the waster and the waster cracks, same issue. A bit more rare, but same result. Alumina both sides works wonders for things that just can’t break. And yes I have seen it happen, especially clock faces.
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My direct experience making these - Dragging on shelves — major issue with large discs. It’s not just shrinkage either, everything move a little bit even after fired by the amount of their COE. Something to prevent it, alumina, or silica, not a bed, just enough to smoothly slide on. (Evenly spread Salt shaker if you will). Waster slabs in theory expand and contract same as parent clay, except …… if they stick on the shelf, same issue. Cooling - lots of speculation on this, just never found a lot of validity or physics here. Kilns cool by losses through shell then radiation and conduction. Don’t open the lid, let it cool fully.
So very flat shelf, something to slide on (alumina, silica), load towards the middle of the kiln if you are worried about cooling too quickly. Flat is less likely to drag or catch than sharp narrow foot. Eased edges - always.
If these discs have a hole in their center such as a clock face, then all bets are off as the drilled hole sets up a very common stress in these pieces and generally requires reinforcement around the hole no matter the material drilled. Google: stress concentrations around holes for a bit ot technical reasoning.
- Rae Reich and kristinanoel
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Yeah, not good - we can’t guess at this. It is easy, but just connecting wires is likely gonna end in disaster. The infinite switches will not use the neutral present in the kiln in a material fashion. Each pair of elements will need to be series wired and 240v will be applied across the series pair from h1 & h2 of the new infinite switch. Taping splices, not a great idea either. Not sure how the tape is being used. Best idea I have is to be able to work off a suggested sketch here but to be safe best if you have someone familiar with wiring safety, connection, reading a schematic etc…. To help.
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@sal.349 Do you have two rotary switches? A better picture would help also, I see five element connections in this pic. There should be an even number. Can you confirm the drawing below?
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This may help, an article on the forum from 2020 and a schematic.
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2 hours ago, Kelly in AK said:
how much could be gained by wrapping an existing kiln in fiber blanket, or a second layer of soft brick?
It’s really no different than adding insulation to your house. Adding double reduces losses to ~ half. R value of materials are basically additive for homes, kilns are similar. How it’s done is key so if just building a kiln no worries. If retrofitting then removing the steel shell easiest way. The lid is also an issue as over heating the already banded bricks can cause larger deflections and lid failure. Easiest improvement for the effort I have seen is Add 2” rigid to the interior of top and bottom where maximum heat loss exists anyway. But to answer your question, more insulation, less power to make cone, but also slower to cool down.
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Since this does not appear to have a sitter or shutoff device it’s quite old and likely needs to be fully supervised while firing. I would not operate this until it’s been inspected and confirmed safe, confirmed it will meet your needs for the cone you fire to, and the cost to improve it makes sense for those needs.
- neilestrick and Hulk
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31 minutes ago, Pres said:
Anyone try it?
I have tried several, some with an air brush. Kinda ok, not sharp like I wanted, really hard to keep it from creeping under the surface for me. Sticky, stretchy from Crickut machine seemed best.
Best stencil idea not entirely related was real pin stripe tape, exacto knife, make your own stencil, then cover adjacent and chemically etch the existing clear glaze for custom personalized mugs including personalized painted scenes. Those were pretty pricey or very custom appreciation gifts that needed to leave with zero flaws. Could not find any stencil combination that did not have too many minor flaws. They were meant to be premium quality, porcelain, sign artwork on mug ……… never want to make those ever again!
The automotive pin stripe tape held very sharp lines throughout the entire process though, best I have tried, but lots of work put into those mugs.
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I have had my best luck with stamp pads and a well cut stamp. If it can be symbolic such as three dots …. Etc it’s far easier than a scripted name. Picture below is one of our test bowls, stamp is a bit inconsistent. It takes significant effort to get it perfect and has to be rolled evenly to match the shape when stamping. So smaller and maybe symbolic is far easier.
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6 hours ago, yinjuehua said:
So I can safely try to fire cone 6? I'
Since you may wind your own elements, you may want to calculate first and see what you have watts/ sq in. Presently. Being able to go 100 degrees per hour in the last 200 degrees of the firing is sort of a sweet spot for cone predictability and can usually wear down to 60 degrees per hour in final 200 degrees, but usually not a whole bunch lower. Gives you an idea of a target final speed I think in your test fire. It not only has to make it but make it with reasonable ending speed.
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The maximum temperature a.kiln can reach predominately depends upon the power supplied to it and the shell losses. L&L has some great measurements. Looks like to be safe ~3-1/2watts per internal square inch surface gets you to cone 10 rating. Firing elements hotter makes them wear out much sooner.
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6 minutes ago, Hulk said:
It spots on the Stull graph just under cone 4.
Stulls graph does not show melting point in cones
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I am thinking the confusion arises from the lack of explanation of cones. While their chemistry is established they indicate by bending so not really fully melted. A cone 4 cone ground up and fired to cone 8-10 turns out to be a fully melted glaze. At present there is not a straightforward exact predictor of when a composition will fully melt. Stull did his work at cone 10 I believe (likely closer to cone 11 today). His map was for a very specific flux ratio and his glazes. Katz showed a reasonable correlation at cone 6 and lower further incorporated boron as a means to lowering the melting temperature. Sue McCleod presented a cone six version of this at a2018 NCECA (Google Sue McCleod and Stull. Stulls map does not predict the temperature something melts at. Higher melting temperatures would progress from left to right and upward in relative ranges. Limits are these tested ranges, but are approximate guidance Testing is generally the only way to know with reasonable certainty when something will fully melt.
Advanced knowledge of durability is a Katz thing where certain flux ratios may be an indication of durability.
I think the simple answer is cones fully melt 4-5 cones higher than their rating. I don’t think the author clearly represented this in the cited link.
I would also suggest that much of pottery is understanding the variability and by experience important trends. It is somewhat very exact and scientific but verified through testing.
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Looks like a small well powered kiln. Depending on reduction schedule and firing speed restrictions of the wares you will fire likely 8 - 10 hours. If your wares are not particularly thick and you can go 400 - 600 degrees per hour with let’s say a 45 minute early reduction maybe gets you a bit faster down to 6 hours. This kiln looks like it can go to cone 10. One thing about small updraft kilns folks are prone to stalling them in very heavy reduction. The supervision of damper and gas is often something to get used to and too heavy a reduction will drop your speed a bunch. In my experience most folks tend to stall these kilns on their way to cone 10 so cone 6 reduction should be easier to hit.
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1 minute ago, elenab said:
I have to process it now, then I come back.
It’s pretty easy to do by hand and if you are proficient with excel, there are some spreadsheets that relate it well. Regardless, knowing the concept then comparing glazes under UMF evens the playing field so to speak so one does not have to learn it to use it productively. The comparisons have more meaning and trends are more easily recognized under UMF.
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6 hours ago, Elmoclayman said:
Do I need to do a "Strike" at the end?
Sounds like you figured out gas / damper and reduction indicators for you so your heating rates are acceptable. I have never had to strike or go into heavy reduction at the end but if you get the result you are looking for, then it is a technique successful for you. There are many schedules and techniques, I have never had to strike nor clean up the kiln at the end. My goal is always to get the uniform reduction I am seeking without a smokey mess and waste of fuel. Some test tile pics and midfire / later fire flames below. I use an O2 probe and built monitoring equipment, so a bit unfair, but a way to learn / teach basic reduction.
What works best for you and your glazes you will figure out - have fun firing!
4 way switches to Infinite switch
in Equipment Use and Repair
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For 120v pilot light - one side of the light to the P terminal and the other side of the pilot to your neutral wire. This is the only thing you will need the neutral for now. I would leave the top receptacle disconnected for now, it will just likely be confusing.