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