Heat cycling new molds

[Wolfdog91]

So I've never done this because to day all my molds where used ,but I'm gearing back up slowly to start casting again ( still got a few months to go). Well this is gonna involve new molds and I'm just curious what exactly does heat cycling actually do ?like I see some people say do it some people say don't but noone really saying exactly what the heck the point is

[Sam Sackett]

Here is my opinion, and it’s just that. My opinion.

First step when getting a new mold is to scrub out and residual oils from production. Some use Dawn push detergent and a toothbrush. Some boil the mold in water. Some spray the mold with BrakeKleen or scrub with acetone. Any of these methods will work.
Second step is to heat cycle the mold several cycles. I take mine to about 400*F, then let them fully cool. Do this at least three times. My belief is that it does a couple of things. First thing it does is that when the mold gets hot, residual oils that may have penetrated the surface of the mold will thin and hopefully work it’s way out of the metal. The second thing it seems to do is the surface of the mold develops a “patina”. This may or may not be seen, but I consider it similar to seasoning a cast iron pan. The patina forms a very thin layer on the surface of the mold, helping to keep the lead from sticking to the mold. This is quite apparent on brass molds, not so visible on aluminum and steel.

Again, this is my opinion based on my experience and others may disagree. Hope it helps.

Sam Sackett

[M-Tecs]

Heat cycling to my understanding is mostly for brass molds. It builds up surface oxidization on the mold so tinning becomes less of an issue. I have never heat cycled an aluminum or an iron mold. I have never NOT heat cycled a brass mold.

[Beagle333]

I have seen no difference in cycled versus non-cycled molds. I scrub them with a toothbrush and Dawn and then heat them in the mold oven (hot plate and coffee can) and start casting. I have heat cycled a few and it made no difference. They all cast better after the third casting session, with or without any special treatment before. And I have well over a hundred brass molds, so it isn't just a fluke. But it definitely doesn't hurt to heat cycle it before, if you just want to. Have fun and enjoy casting, no matter how you do it. :grin:

[Winger Ed.]

I just clean a new Lee mold and start making boolits.
I've never had a brass mold.

Heating and cooling an Iron mold- or just using it, seems to somehow help season it like Grandma's old cast Iron frying pan.
Mine release easier and easier over time.

[dkf]

I mainly do it with brass molds to build a little "patina" on them before making bullets. Aluminum I usually just do the dawn dish soap, hot water and toothbrush or just hose them down with brake cleaner, lube and cast.

[megasupermagnum]

NOE states in their instructions "This will help seat the alignment pins and start the oxidization build up on the cavities
This oxidization will help in the bullets releasing from the cavities"

I have not in a long time, and will not again bother with heat cycling new molds. Not even brass. I have never found a mold get easier with use, other than you figure out what works best. If they don't work new, they aren't going to work with a dozen heat and cooling cycles. You always hear this nonsense about porous metals soaking up oils. It's metal, it isn't a sponge. Liquids can not go into solids. There can be residual oil on the mold, since even polished metals are rough on a microscopic level, but this doesn't effect casting. Anything on your mold burns off real quick when you are casting. You could spend an hour heat cycling, or you could just cast some bullets and have to reject the first few shots.

[Dusty Bannister]

I have only had the pins move on one Lee 6 cav mold. It was new and I loaned it to an experienced casting friend. I had heat cycled other Lee molds so did not expect a problem. The mold had never been heat cycled and the pins moved. My experience may be different from others.

[GregLaROCHE]

I’ve always only cleaned with brake cleaner and then scrubbed with dish detergent to get all oils off with new steel and aluminum molds. After that I just start casting. I have a new brass mold and have been wondering if I shouldn’t use a different method with it. Don’t expect your boolits to cast perfect the first time. Molds tend to cast better after a few sessions.

[Outer Rondacker]

I just clean a new Lee mold and start making boolits.
I've never had a brass mold.

What he said. Same for me. It was only this year I think I got my first new mold. (lee)

[charlie b]

I don't....but....it also takes a couple of casting sessions to get really good bullets. Part of this is developing the cadence for that mold. How fast can I cast with it. Does it need more cooling between pours, etc. I have had two molds that cast well right away. They were both 6cavity Lee molds (.45 and .357). The .30 cal 210gn mold I have from Accurate took a long time for me to figure out (long skinny bullets), but, now it casts great.

Do clean the molds before use. I use acetone.

[Bigslug]

I think NOE's instructions are probably closest to the mark. Most of us are using either aluminum or brass molds with steel alignment pins. Those different materials are going to expand and contract at different rates, so the object, supposedly, is to get the parts to settle into their final positions. How this will happen differently from just using the mold is a mystery to me.

Heat will burn off the residual protective oils you'll put on your iron molds for storage, or that come on new aluminum and brass - probably cutting fluid - but then, so will brake cleaner.

Oxides (brass) will happen whether you cook your mold in the oven or just let it return to room temperature after a casting session.

I think about the only thing we'll agree on is that it won't have any negative effect other than to cycle your oven to 400F a few times.

[mdi]

I have heat cycled new molds a few times, the last one being a 2 cavity Lee 158 gr. SWC ,357. I put an old circular saw blade on my hot plate, set on high, and set the mold on the blade. Haven't tried to measure temp., but it gets really hot (hotter than casting temp) then turn off hot plate and let it cool. I did this 3-4 times. I got good boolits from the first cast from the mold warmed on the got plate. I didn't have an identical mold to check the cycled mold against so how much difference did cycling it make? I couldn't tell you.

[Mal Paso]

If you heat cycle, do it with the mold open, cavities exposed so the mold develops oxides on the surfaces that contact lead. This helps prevent lead from sticking, more so on brass molds.

I don't clean molds any more, just heat cycle to 400F which evaporates any oil left from machining.

[Mk42gunner]

My opinion is that heat cycling is only really needed on brass molds, to help build up the patina of oxide to keep lead from sticking. Any plumber will tell you that solder (a lead alloy) will not stick to brass or copper unless it is clean. You could do the same by leaving it set with no protection for a few years, but who wants to take that much time?

I don't believe it is necessary on iron or aluminum molds, aluminum oxidizes almost instantly upon contact with air. Although I did have one Lee 312-185 that didn't start freely releasing boolits until about the fourth time I used it. I then proceeded to cast a coffee can full of them, still shooting them years later.

I have had only one alignment pin move on a six cavity Lee, unfortunately it was the very first six cavity I had ever seen and a custom one at that. Took me a while to figure it out.

Robert

[Rcmaveric]

I will be that odd ball who has never heard of heat cycling.

I just buy the mold then boil it in dish soap. Preheat the mold on a hot plate then lube the mold. Then cast fast and hot to burn off residual oils. I do the same on second hand molds to clean off preservatives or oils.

If the mold dropped bullets that wants to stick to cavities. I cool the mold. Check all edges with q-tip. Remove any burs or sharp edges with an exacto knife. Heat the mold back up and cast away. If thw mold is still stubborn then i will cool the mold and break all edges of the cavity.

I guess that kind of heat cycles it.

Then i cast 20lb to 60 lbs of bullets. Afterwards, the molds get placed in an ammo can with vaper paper and dessicant. Vaper paper is awesome. When it comes in contact with moisture it releases anti corrosive vapor. Molds look great even if I don't use them for a year.

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[Multra]

I just hose them off with brake cleaner, hit the cavities with a match to get some carbon build up, and start casting.

[Rich/WIS]

I have heat treated my NOE 5 cavity molds because it was recommended in the instructions. Have not done that with my LEE 6 cavity molds. If it made a difference with the NOE molds don't know as I never tried one without the heat treating. FWIW figured if the mold maker recommended it then there must be a reason and I followed his recommendation.

[Larry Gibson]

If the mould is cleaned properly, I've never found "heat cycling" to be necessary. Heat cycling is just a crutch to remove the moisture (oil or whatever) that is not removed properly when cleaning.

[243winxb]

For iron molds, skip the lube .https://www.thehighroad.org/index.php?media/casting-with-lee-molds.4127/full

[waksupi]

If you heat cycle, do it with the mold open, cavities exposed so the mold develops oxides on the surfaces that contact lead. This helps prevent lead from sticking, more so on brass molds.

I don't clean molds any more, just heat cycle to 400F which evaporates any oil left from machining.

I've used cold blue on brass molds to do the oxidizing step.

[Mal Paso]

I've used cold blue on brass molds to do the oxidizing step.

Interesting! Which one or do you make your own?

[gwpercle]

Let me put my 2 cents in WolfDog ,
Moulds cavities get "seasoned" through use , like a cast iron frying pan ... you know how an old seasoned pan cooks better and without sticking ... Like that ...heat cycling just is a short cut to getting the seasoning patina built up . I do it by warming a mould and casting boolits untill I'm getting frosty ones , cast 50 or so , wrinkles don't mater , you just heating the mould up hot ... and stop . Cut off pot , mould on top of pot to slowly cool down .
Put all the cast boolits back in pot and remelt . Repeat three times and clean cavities with acetone between each session . These new CNC cutting machines drive cutting oils deep into the pores of the aluminum or brass ... heating the moulds drives out more and more oil until by the 4th session it has all been driven out ...the oil keeps coming out and giving wrinkled boolits ... the seasoned patina build up makes the non-stick surface so the boolits drop free .
It does help new Alum. and Brass moulds , the cycling with an oven is just a short cut ... me I like pouring hot lead into cavities to get them broken in ... but me is old school and I don't have a toaster oven and my wife wont let me put it in the microwave oven or her stove oven .
Gary

[Hanzy4200]

I have probably 25 molds. All steel or aluminum. I have never heat cycled. A first cleaning is critical. The next important thing, prepare for the slew of angry casters, NEVER SMOKE YOUR MOLD! One of the casting legends (FortuneCookie45LC) advised me years ago on a problem mold. He said to stop smoking my molds. If they don't drop, it's due to burrs. He was exactly right. My molds now freely drop, zero smoking. If you have old or particularly problem mold, a little mold release spray will fix it.

[jsizemore]

Doesn't heat cycling normalize the metal's grain structure from the stress of being machined and make it more ductile?

[Ia.redneck]

I agree with post #8. The only Lee mold I didn't heat cycle 3 times had the alignment pins move.

[Wolfdog91]

Interesting,that k you eveyone

[Rapier]

Good luck with replacing your molds, I sure would hate to even contemplate replacing my molds.

[waksupi]

Interesting! Which one or do you make your own?

Plain old Birchwood Casey Super Blue, just because that's what is usually in the shop.

[blackthorn]

Let me put my 2 cents in WolfDog ,
Moulds cavities get "seasoned" through use , like a cast iron frying pan ... you know how an old seasoned pan cooks better and without sticking ... Like that ...heat cycling just is a short cut to getting the seasoning patina built up . I do it by warming a mould and casting boolits untill I'm getting frosty ones , cast 50 or so , wrinkles don't mater , you just heating the mould up hot ... and stop . Cut off pot , mould on top of pot to slowly cool down .
Put all the cast boolits back in pot and remelt . Repeat three times and clean cavities with acetone between each session . These new CNC cutting machines drive cutting oils deep into the pores of the aluminum or brass ... heating the moulds drives out more and more oil until by the 4th session it has all been driven out ...the oil keeps coming out and giving wrinkled boolits ... the seasoned patina build up makes the non-stick surface so the boolits drop free .
It does help new Alum. and Brass moulds , the cycling with an oven is just a short cut ... me I like pouring hot lead into cavities to get them broken in ... but me is old school and I don't have a toaster oven and my wife wont let me put it in the microwave oven or her stove oven .
Gary

I thought that metal in a microwave was really bad Ju-JU. Is lead different from, say aluminum foil???

[gwpercle]

Interesting,that k you eveyone

Back in the days BC (Before Computers) you just cast with a new mould untill it started dropping good boolits . Grease it for storage and next time you kept casting untill the grease was all burned off ... We wasted a lot of time casting bad boolits . With a steel mould , a clean mould will break in fairly quickly . Aluminum moulds were a Bear ... hence the "Smoke " the cavities or use spray on "mould release" ... which just mucked them up something awful . The heat cycling just saves you some time and eliminates the need for standing there and casting a bunch of bad boolits .
I think the heat cycling and break in is more important with aluminum moulds ...and it does something with setting the alignment pins ...all though I don't quite understand how the pin setting works ... I do the heat cycling - break in .
Gary

[gwpercle]

I thought that metal in a microwave was really bad Ju-JU. Is lead different from, say aluminum foil???

My wife is smarter than me ... don't put aluminun . lead or steel in a microwave oven ...it will do nasty things in there .

That was a Joke Boy ...a Joke ...You missed it Boy ... it went right by you ..Boy ...you got to keep your ears open ... Son...Keep on your Toes ...Boy ...don't let them Jokes get by you ...Boy !
Foghorn Leghorn
Watch out for them there fast ones .. I say Boy !

[Mal Paso]

Plain old Birchwood Casey Super Blue, just because that's what is usually in the shop.

Thank You!

I've tried their Brass Black which was so so. Can't help thinking there has to be a better tarnish out there. LOL

[DocSavage]

Ran my NOE blocks thru heat cycles in my oven heat,cool repeat 4 times.

[Shuz]

Ran my NOE blocks thru heat cycles in my oven heat,cool repeat 4 times.

That's what Swede Nelson of NOE recommends for his aluminum moulds. He says heat to 300 to 400 degrees and let it cool each time to room temperature. He said that it helps set the alignment pins. Since I just received a new mould from him yesterday, I m gonna try that method.