Some more Heat Treatment Oven time.

The little Heat Treatment Oven has been in use for a while and I have been thinking about the process cycle time for a while so yesterday we wound a new element with a calculated 2.5kWatts which should speed things up a bit.
First job was crunch some numbers and I use a spreadsheet for this, in fact I use spreadsheets for everything, even our RFD register! The advantage of the sheet is I can see what changes to the element length (Resistance) make to things like the current draw and power. I can also experiment with different gauges of the Kanthal A-1 wire I use which was handy as when I went to order the gauge used before, nobody stocked it in the length I needed.
A couple of entries on the sheet and I could instantly see if the alternative works and how much was needed. In the end I opted for 19AWG and ordered the wire.
The thing about the wire is it is just that, wire and not a heating coil so first job is clean it with acetone and wind it onto a mandrel on the small lathe. This is a bit of a two person job as having someone to hold and feed the wire to me saves potential kinks in the wire. Luckily the Viking was to hand as she usually is.
With the coil wound it was a simple matter of trimming it to final length and putting it in place, connecting in the terminal box and starting to test.
My target temperature for this test was 925-950 degrees centigrade (1700/1750F) This sort of temperature allows me to heat treat spring steels which I work with, a lot. Hence the target and I wanted to get to it in under half an hour so testing is important if only to prove my maths are about right.

Starting at 25C the oven hit 100C in 42 seconds, 500C/932F in just under 4 minutes and I stopped the test at 925C/1697F at a bit under half an hour which was perfect.

.The oven should be good for another 100-150C so I can have a play at knife making one day.

Right now I am watching the cool down temperature time.

The outside of the oven was cold to the touch at the 30 minute point however it is quite warm to the touch now at 90 minutes, however it is not hot which is excellent.
On the subject of spreadsheets, I created a plot of time vs temperature which I can use as a reference. The highlighted areas are the spring hardening and tempering temperatures I tend to work with, however these are material dependant.
Finally, I know, I really should get around to putting some decent labels on the control cabinet. Maybe next year
As a final note, if you fancy having a bash at making your on HT oven, I am happy to share whatever information may be of use to you.
Take care all.

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