Here you can find: Heat Treating Part II
Finally after a long delay I have gotten back to actually using the heat treating oven. I have actually used the controller described in Part II for a couple of other applications but now it is time to use it for the heat treating oven.
I connected the thermocouple from the oven to the controller box and plugged in the power cord to get the oven ready for a test run. Not knowing how hot the exterior of the oven was going to get, I placed it on the metal top of the washing machine rather than on my wooden work bench.
A trial run showed that the oven could easily reach 900 F and the outside did not get too hot. It was hot enough to not touch but not hot enough to start a fire. The temperature went up to 900 F and overshot to 925 F, finally settling down to 900 F. The heat treating specifications say 900 =/- 10 F. Now I could put the springs in after the oven warmed up and avoid the overshoot but I also wanted to see how well the PID function in the temperature controller worked so I let the oven cool down and activated the autotune function on the controller. After running the autotune cycle the oven would heat up to the 900 F set point without overshoot.
Part of the reason for all this is that it would be difficult to cut the spring material to size after it had been heat treated. To get ready for heat treating the springs I cut the stock material to size, sanded the edges and degreased them. Often when heat treating carbon steel items the items to be heat treated are wrapped in stainless steel foil to keep them from oxidizing. At 900 F this is not likely to happen but for grins I wrapped the springs in aluminum foil which will not melt at 900 F.
After spending a hour at 900 F the springs came out a nice golden color.
I did not measure the stiffness of the springs before heat treating but they don’t feel any different.
Next I will be casting the bases for the seismometers out of aluminum.