Hot Plate Temperature

[GregLaROCHE]

Now that things are cooling down, I have decided to use a hot plate to keep my moulds at a good and consistent temperature. I figure I can check the temperature with a infrarouge thermometer. What temperature should I be shooting for? How critical is it. Does the alloy temp make much of a difference?

[Gtrubicon]

Great question, I’ve often wondered what it should be at. I always start on high while I’m setting up, I turn it down after 5 minutes or so. I do this even in warm weather. I can usually get acceptable boolits after the first pour. I’ll be interested to see what the mentors have to say.

[Hossfly]

I’ve put a thermocouple in the mold cavity and gotten to around 400’, started casting and was surprised first dump of boolits, no wrinkles.

Set some ingots on plate of aluminum to warm up and they melted, what a mess, that hot plate will get too hot so watch it and check for temp with your ray gun. It does help with not cooling pot down when adding more alloy to pot.

[kevin c]

I asked here what temp the mold should be preheated to, and the replies were mostly around 400°F, so whatever would get you there? Someone else recently commented that he set his hot plate to maximum to get to the right mold temperature, and I find that I need to do much the same, though I've been warned not to set the mold directly on the coil for fear of warping the blocks. I have some aluminum stock in rectangular cross section that I'll be experimenting with on the coil.

Just like my pot, in cold weather the actual desired temp takes longer to reach, and maybe a higher setting to boot.

[Old School Big Bore]

My hot plate is the ten dollar GTC model, and it seems that a point just above 'medium' works pretty well for the first throw. I keep my stirring screwdriver and skimming ladle on the hot plate, to keep the tinsel fairies away, and the 'low' setting works fine to keep them dry. I also set the mold I'm working with on the plate with the tools when I move the gang sprues from four- and six-cavity molds back into the pot (I move them about every ten sprues, that lets me keep tabs on production), or add ingots and re-flux. If I'm casting a large quantity, I use a small cast-iron pot on another hot plate to preheat ingots. Since it's a pot, if they go ahead and melt, no loss. I used to pre-melt ingots in a ten-lb pot suspended to pour straight into the twenty, but running that much wattage along with the hot plate, fans, lights etc got to be problematic popping breakers.
Ed <><

[bangerjim]

My hotplate is a professional laboratory style flat surface one with electronic temp control and I set it at 475F. I also use it to pre-heat all my feed ingots to about 10-15F below liquidous temp (depending on the alloy mix) so the feed ingots melt almost instantly when they hit the pot, allowing much faster recovery time while casting.

But 400-450°F should be good to start playing around to find what works best for your casting sessions.

Remember a IR gun will NOT read correctly off of shiny surfaces! You need to use some Birchwood-Casey Aluminum Black solution to turn the end of your Al molds black so the gun will read properly.

banger

[Conditor22]

I heat mine to 400°

[Mike W1]

Did some testing earlier this year. Hotplate is PID controlled and the particular mould casts best around 320°. Shop was 62° and I found it worked best for me to have the hotplate set for 440° which insured if I sat the mould on the hotplate to take a break that it'd be about 320° when I got back to things. The normal warmup of the pot time is around 20 minutes from cold start and the hotplate will have the desired temp when I cast the first bullets. The first ones will be good.

Even a 15° lower temperature on the hotplate and I didn't get that desired 320° I wanted to maintain things.

[midnight]

I keep a 1/2 inch thick 8 inch diameter aluminum disc on the hotplate. Many of my molds are drilled for a temp probe. I find pre-heating the mold between 375 & 400 degrees usually drops good bullets on the first pour.

Bob

[jsizemore]

I set the thermocouple alarm for 400degF. Above 375 works but may not be filled out completely. At 400 they're good from the start.

[Conditor22]

Mike W1 brings up a good point; hotplate (and countertop oven) temperatures are affected by surrounding temperatures.

many people put a metal coffee can with a side cut out for the mold handles to help contain the heat

[Walks]

I have a cast iron diffuser plate on top of my hot plate.
I turn on the hot plate to max it will go to 600+ degrees.
After 5min I back it down to 400degrees. When I'm ready to cast, I remove molds and replace them with ingots to warm up to refill the pot with. I hang the ingots over the edge of the diffuser plate, makes it easier to grab with channel locks.

[GregLaROCHE]

Mike W1 brings up a good point; hotplate (and countertop oven) temperatures are affected by surrounding temperatures.

many people put a metal coffee can with a side cut out for the mold handles to help contain the heat

That is a good point. Especially if the wind is blowing.

[Silvercreek Farmer]

I cast outside, usually in the winter, and the tin can method really helped out. Otherwise the mold was hot on the bottom and cold on top. I worried about warping the blocks trying to get the sprue plate warm enough. I also set ingots on top of the can to prewarm them. Holds the can steady and helps drive off moisture. Depending on how long they sit there, they probably get up to 120-130F.

[porthos]

did i read somewhere that you should not put a aluminum mold directly on a hotplate??

[bangerjim]

That only applies to the cheap bare coil type hot plates. The tend to get VERY hot on the coils and can warp a mold. Mine is totally flat top lab style, so heat is distributed evenly. If you use a bare coil one put an old saw blade or a 1/4" thick plate of Al on it.

[Hossfly]

I have piece of 1/2” thick covering entirely both coils.( Aluminum) works and heats very well. Will melt ingots also.
Use it to warm ingots, keep on cooler side.

[bangerjim]

I have piece of 1/2” thick covering entirely both coils.( Aluminum) works and heats very well. Will melt ingots also.
Use it to warm ingots, keep on cooler side.

That's the way......uh huh, uh huh.........I like it!

Gotta cover those bare coils to get even distribution of heat or you could be in for a spot of trouble with your mold(s).

I bring my feed ingots to 10-15F below liquidous temp of the alloy I am using. They melt almost instantly in the casting pot!

And you don't want to just WARM your molds....bring them to FULL CASTING TEMP B4 ever starting!

[Mike W1]

Mine's also 1/4" aluminum with a small piece drilled and tapped for a TC on it. I set it so it keeps my mould at the temperature it prefers and also to prewarm ingots but don't get them as hot as bangerjim does as I use 2 10# pots and the feeder pot takes care of the additional warming.

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