RC20 said:
Templiaq sent me two more when I had issues with the 750 melting before the 800.
I am not wanting to be argumentative, either, I am just trying to understand the problem and the difference between crayons and liquid form behavior. You say the 750 liquid melted first, but isn't that what you expect? As you heat something up to 800 you will pass through 750 first. Or are you saying the 800 melted first?
Also, as the temperature increases, heat is being lost to air faster, slowing the rate of temperature increase, so you'd expect the 800 to melt second and to take longer to melt. But if it didn't go that way, you have an interesting puzzle on your hands.
One factor with all PCM's (phase change materials; including waxes) that go from solid to liquid (melting or thawing) or from liquid to gas (boiling or evaporating) or from solid to gas (sublimation) is that they have not only to hit certain temperatures to change phase, but to will tend to stall the rise in temperature while they absorb enough heat to complete the change of phase (in this case from solid to liquid). The amount of heat such a material has to absorb to make the change is called its enthalpy of fusion. A pound of ice, for example increased in temperature about 2°F for each Btu of heat absorbed, then at 32°F it has to absorb about 143.5 Btu's to convert to liquid phase, and then, in liquid form, it heats 1°F/Btu absorbed. If you measure the temperature of the center of an ice cube in a glass sitting in room temperature air, it first rises to 32°F, stays there until it melts, then the newly melted water temperature starts to rise again, but only half as fast just above the melting point as the ice was doing just before reaching the melting point.
Waxes are PCM's, too, but often not highly pure. Alkenes (paraffins) will need anywhere from about 40 to 100 Btu/lb to melt, depending on the purity of the carbon chain lengths in the material. And, in impure form, instead of holding at exactly one temperature as they melt, they melt over a range of temperatures called the slush zone. So it wouldn't surprise me if a crayon labeled 750 actually started melting at 730 and didn't finish until 750, or some such range. It wouldn't surprise me if, due to differences in purity or in impurities, such as the coloring material, one had a lower enthalpy of fusion than another, affecting how long they needed to be exposed to a given temperature to melt. If you let two waxes come into contact, you will get a mix at the interface that has an even wider slush zone and may confuse the exact melting point.
Lots of trouble to get into, and because of the timing issues for different enthalpies or for the exact compositions having different thermal effusivities (a measure of ease of heat transfer to the wax from the metal surface it is on) or different thermal diffusivities (a measure of the ease of heat spreads within a material), it is possible to have the two appear to work perfectly if you heat the work very gradually, but appear to be off or even reversed if you heat the work quickly.
If the problem is with the latter, then the indicators may simply be unsuitable for any but slow methods of case neck heating. It might then be better to calibrate by coating each neck with candle soot to maximize IR emissivity (a lot of 'x'-sivities in this topic) and use an IR thermometer.
On top of all that, since the metal has to change its grain structure and some of those changes are time-dependent at any given temperature, I'm not convinced we don't need to hit a higher temperature when heating at very high power for 0.25 seconds than we do when heating for 2.5 seconds with less power, and I don't know what those temperature differences might be. And they may change with the alloy being used. I think that's what the AMP annealing people are getting at. Their finding they need different times for different amounts of brass mass and different alloys and find measuring the hardness they get the only way to be consistent with the results.
As a friend of mine like's to say, "Oy vey Maria!"
