JD18-JH Update: Kanthal A-1 Elements

admin | Kilns | Tuesday, April 29th, 2008

With the new JD18-JH, I was supposed to get 2.2 mm Kanthal APM elements. At the point where the kiln was ready for shipment, there was a 4 week wait on the APM wire of that gauge, so I opted for the 12 gauge (≈ 2.0 mm) Kanthal A-1.
One of my plans was to compare the lifespan of APM to A-1, using digital images, ohm measurements, and kiln interface software (K.I.S.S.) to record what was happening as each set started to go.
An educated guess was that it would take longer for the APM’s to fail, so I thought that it made sense to get the A-1’s first after all.

I’ve fired several kilns in the past using both “standard” (15 gauge) and “heavy duty” (14 gauge) elements. With either, once the coils start leaning in on each other and bunching up in the corners, their performance declined quickly.
Most of those past firings were in the ^9-10 range, occasionally pushing for a “soft ^11″. After about 15-20 firings, the elements would show the leaning and bunching described above. Past that, I’d average 25-35 firings total before the rate of rise to peak was noticeably slowed, and my firings suffered.

Currently, I’ve performed almost forty ^11-12 (true 90° bend on a self-supporting cone) firings* with the JD18-JH.
When graphed, my rate of rise is still tight with the programmed set point line, and ohm readings taken after each firing remain the same… but hey, pictures are worth a thousand words:

Unfired 12 gauge Kanthal A-1 Elements:

Kanthal A-1 Elements 2.0mm New

…the same elements, after the 37th ^11-12 firing:

Kanthal A-1 12 gauge Elements, Firing 37

The elements settled nicely into the element holders after the first firing… aside from that, and the oxidation coating on the metal, the elements appear to be in perfect condition.

My Current View on Kanthal A-1 vs. APM Wire:

With A-1’s being less than half (almost 1/3) the price of APM’s, the latter would need to possess at least 3-4 times the life span of the former to qualify the difference in price. One could argue that the downtime associated with replacing the elements factors into the equation; however, if I can get 100+ firings in between element changes, I’ll really have to consider whether I want to replace them with APM’s. My reasoning here, is that accidents can happen with either… For instance, if a bit of glaze, ceramic, or even so much as a few grains of sand fall onto your APM element, I don’t imagine that it would have a better survival rate over any other wire. At that point, replacement costs can really hit home.

*Note: For the record, there are also nine ^04 bisque (I usually use my other kiln for this), and sixteen low temp luster/ glass enamel firings on this element set.

Large Electric Studio Kiln Power Consumption

admin | Kilns | Sunday, April 13th, 2008

In the spring of 2006, I had an electrical meter connected by a certified technician from the local power company. This meter was set inline between my kiln and the breaker box and was separate from the main meter, so it recorded only the power used by the kiln. During that time I performed firings in the high, middle, and low temperature range to calculate what different firings were costing me.

These firings were performed in a 7 cu.ft. L&L JD230HD with:

  • Single phase/240v
  • Computer-controller w/ “type S” thermocouples,
  • 3″ K23 softbrick (walls, floor, and lid).
  • Standard (small) gauge elements… which were not new, but not worn out either. They had eleven firings (four ^04 bisques, and seven peaking at 2345-2355F) total on them when the meter was hooked up.

The meter was zero’d out prior to installation, and I kept track of the energy consumption by photographing the dials as reference.

Firing 1: Peak at 2345 F Hold for 2 minutes + 5 hours of holds b/t 2000 and 1900 F.
Reading: 87 Kw.

Firing 1: 2345 Peak

The national average for a kilowatt hour was 9 cents,
87kw/h x $0.09 =
Cost: $7.83

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Firing 2: “Fast Glaze” program to ^018 (1384F).

2nd Firing: ^018

Reading: 104 kw/h - 87 = 17 kw/h used.
Cost: $1.53
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Firing 3: 270F/hr to 2000F.

3rd Firing

Reading: 139 kw/h - 104 = 35 kw/h used.
Cost: $3.15
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There were seven firings total, all yielding the same costs (give or take a few cents) per firing.

It would have been nice to see what the difference was in terms of new elements vs. the ones at this stage –and even vs. aged elements (although I rarely let mine get that far gone). But since this meter was on temporary loan from the power company, I was still interested in seeing these readings, and I think they may represent the longest stage in terms of the elements lifespan.

I currently have a meter hooked up to my JD18-JH …you can see those readings as they progress HERE.

Main Kiln Energy Consumption Page.

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