Mold preheating and casting temperatures

What temp range do you casters use for mold preheating and for monitoring mold temps with thermistor-adapted molds during casting?

I preheat my brass molds on the hot plate with the temp setting just below medium.......so I do not really know what the actual temp is. I suppose I could measure it but no need to, since by the time the alloy is ready in the pot, the mold is at a perfect temp, just about right to drop 4 perfect boolits every cycle.

I also do not know the temp because I use an old table side coffee pot warmer. I just put the molds I will be using that day on the warmer and they are the perfect temp by time the metal is ready. I have to say we got the warmer as part of two pot coffee set as a wedding gift 32 years ago and I always complain that the wife never throws anything away. Sure was glad when she pulled it out of a box when I mentioned I was looking for a way to warm and keep warm molds for casting.

I crank the lead pot up to its highest and set the molds (I usually cast 2 different ones at a time) on top of the pot until the lead is liquid. Usually have to throw away the first cast or two but then all goes well. I don't mind a frosty bullet so I always cast as hot as the pot will go.

I have a number of instrumented molds. Temp varies with mold size and type (Al or Brass).
I have a NOE 4 hole that runs best at 212, a NOE 5 holer that likes 196.
My Mihec brass 2 cavities like ~ 285, the 4 cavity like ~260.

The actual temp varies with melt temp - but not as much as you might think.

I have never used a lead thermometer so I do not know actual temperatures but I have developed my own system and know what is "hot" and what is not.

I cast using a cast iron pot on a propane stove because I ladle cast. I heat the lead until I get a slightly golden dross skin on top ~ that is a little hooter than I want fir casting.

I pre-heat the mould on a piece of 3/16" plate over another open flame until the oil on it starts to smoke ~ that is below the melting point of lead but hot. Then I start casting and as the mould comes up to temperature I start to turn down the pot flame until I get a nice balance of casting speed and sprue puddle freezing time.

It is simple and has worked for me for over 40 years. And yes, I oil all my moulds for storage and just wipe off before use. With new un-oiled moulds, I lube with a bit of sprue plate lube and heat until that smokes.

That doesn't really answer your question but you might check the temperature for oil to smoke and use that as a basis for pre-heating the mould.

I find that iron moulds overheat fairly quickly so require more flame turn down to maintain a good casting speed and brass moulds require steady fast casting with less flame turn down to keep up to temperature. NOE aluminum moulds require similar treatment to brass moulds.

Longbow

I only use Mihec brass these days but I preheat in a mold oven that holds two molds to right at 250ºf They work first time every time. I turn on the pot and the oven at the same time. The mold oven is stable at 250 well before the lead is molten. That way I'm sure the molds are evenly heated. I experimented up and down the scale and this works the best for me.

I use a coffee warmer for my molds.