Heat cycling molds

[Firesubie]

I'm sure this has been covered before, but I'll ask anyway.

Why do new molds need to be heat cycled? What does it do to the mold and what are the negatives to not heat cycling before the first use. I do it, but only because that's what I was told to do.

[kungfustyle]

It helps with consistency. You don't have to heat cycle, however the mold may take a few casting sessions before you get real consistency. Metal will expand and contract with heating, so people have discovered that if you heat cycle you get to a more consistent mold faster.

[HWooldridge]

I don’t know why, but I know it works, especially with aluminum blocks. I’ll usually start seeing real consistency after about three sessions and at least 50 casts. After that break-in period, they will be consistent immediately after the mold is preheated.

[THE_ANTIDOTE]

Makes no difference at all. I am fairly new to casting and was repeatedly told the same thing...you have to heat cycle every new mold. I bought a bunch of brand new MP molds in brass, a lot of Lyman molds...some new, some used and began heat cycling on a few of the MP molds and one or two of the Lyman molds because I was convinced it had to be done...hog wash! I got tired of hearing it and thought...well what could happen if I don't? Nothing! Didn't change a thing, all my molds work great, obviously the more cavities, the longer it will take to get going...this was the only difference I ever noticed. I believe it just comes down to technique and practice. Best advice I can offer as a newbie caster myself is...trust your abilities and believe in yourself.

[Bigslug]

I've done it. . .and not done it. Doesn't seem to make any difference - a new mold usually needs a couple dozen pours to start behaving regardless. Of late, it's just been set them on the hot plate while the lead melts, then roll with it.

The supposed advantage is that it helps the alignment pins settle into their nooks, though I can't see how.

[Firesubie]

I'm pretty new to casting too, and trying to figure all the ins and outs of it. I have several molds now, some new, some used, and I couldn't figure how heat cycling did anything different than filling the mold with hot lead. I have heat cycled all the new molds I bought (except for 2) and pre-heat them on a hot plate prior to casting. I did buy a couple of lee molds that I took out of the box, cleaned them, pre-heated, and straight to casting and they had no wrinkles by the third pour, whereas the MP brass molds take 10-15 pours to get good bullets from. But I'm still learning how to do this casting stuff and loving it.

[georgerkahn]

Makes no difference at all. I am fairly new to casting and was repeatedly told the same thing...you have to heat cycle every new mold. I bought a bunch of brand new MP molds in brass, a lot of Lyman molds...some new, some used and began heat cycling on a few of the MP molds and one or two of the Lyman molds because I was convinced it had to be done...hog wash! I got tired of hearing it and thought...well what could happen if I don't? Nothing! Didn't change a thing, all my molds work great, obviously the more cavities, the longer it will take to get going...this was the only difference I ever noticed. I believe it just comes down to technique and practice. Best advice I can offer as a newbie caster myself is...trust your abilities and believe in yourself.

I cannot speak re aluminum moulds, as I do not use these. With ferrous (iron) moulds, my thoughts include there being even microscopic materials in the pores of the iron. The heat cycle cooks these. Most of the moulds I use now are brass, and I do not recall ever having one that dropped (almost-)perfect bullets at the git-go. From a few heat cycles a patina coating seems to appear. From dire experience I have had moulds which I "smoked"; those I diligently used Q-tips to find the culprit which made the bullets impossible to drop out; and, I even resorted to commercial spray mould-release agents.
There is a saying, "the older the violin the sweeter the music" and I honestly believe use of moulds is similar. I recall one MP mould that -- even after three heat cycles -- would really frustrate me. But, I stuck it out for seven or eight sessions -- and now it is one of my most favourite moulds.
Perhaps a better way of looking at the situation is to take your brand new mould and... cast with it. If it meets or exceeds your expectations then go with it! BUT, if you have bullets that won't readily drop and/or other challenges -- a few heat cycles can't but help. As stated, my brass moulds have developed a tad darker than new patina on them, and I have thought this patina greatly adds to dropability of the bullets.

[Firesubie]

Well, I couldn't help myself. Just heat cycled my newest molds. I guess I'm just a rule follower.

[justindad]

It’s for brass molds, mostly. Brass needs a patina to keep from tinning. The patina is an oxide layer that keeps lead-tin alloy from getting stuck on the surface of the mold. Patina builds faster while the brass is hot.

[JonB_in_Glencoe]

It’s for brass molds, mostly. Brass needs a patina to keep from tinning. The patina is an oxide layer that keeps lead-tin alloy from getting stuck on the surface of the mold. Patina builds faster while the brass is hot.

Yes but...
sometimes a new alum mold benefits from a few heat cycles. A brand new alum mold doesn't always release the boolits easily and sometimes the light oxide layer that builds up after 3 or 4 heat cycles helps that.

But to others, this is not a rule or even necessary, I've had brand new Lee molds that functioned great right out of the box. I've had troublesome molds (any brand), that needed "more" than just a few heat cycles...sometimes they need to be deburred, sometimes they need the venting improved, sometimes the cavities need to be polished.

[JonB_in_Glencoe]

I've done it. . .and not done it. Doesn't seem to make any difference - a new mold usually needs a couple dozen pours to start behaving regardless. Of late, it's just been set them on the hot plate while the lead melts, then roll with it.

The supposed advantage is that it helps the alignment pins settle into their nooks, though I can't see how.

You triggered a memory, I believe Al (at NOE molds) told me in a phone call about 10 years ago, that the Heat cycling (expansion-contraction) settles the block metal molecules and the pin metal molecules. I suspect if there were to be a pin movement problem, it would be in the first couple casting sessions...maybe the heat cycling avoids that? Seems like a good guess anyway, LOL.

[Bigslug]

You triggered a memory, I believe Al (at NOE molds) told me in a phone call about 10 years ago, that the Heat cycling (expansion-contraction) settles the block metal molecules and the pin metal molecules. I suspect if there were to be a pin movement problem, it would be in the first couple casting sessions...maybe the heat cycling avoids that? Seems like a good guess anyway, LOL.

I've got to wonder about that too. Melting point of brass - about 1700F. Melting point of pure aluminum - about 1200F. Melting point of our casting alloys - somewhere down around 500F, while being poured at 700-800F. Operating temp of our molds - 400F (ish).

The molds would appear to be running at a temperature far enough from their point of structural change that it would seem like expecting the molecules of an ice cube to "settle" when raising the temperature from 100 below zero to 60 below zero, when nothing at all is going to happen until you get up to +33.

I'm not saying it's voodoo and hokum, but the logical sidewalks in my brain lead me away from the notion. Oxide and patina maybe, but that should be happening during use and regular cool down.

[gwpercle]

It "Seasons" the metal surface like you season a cast iron frying pan .

Back in the stone age , you picked up a new mould and just started casting boolits ... you didn't expect good boolits to begin falling untill 500 - 600 "throwbacks" had been made ... the first 25 were simply to heat the mould .
You had to break-in a new mould and you did that buy casting boolits , putting them back in the pot and casting more boolits .

Heat cycling shortens the break-in and "seasoning" time ... it's a short cut and does work ... I do it with all new alumn. NOE moulds .

Also there is a lot of Voodoo and Hokum to boolit casting ... at least here in Louisiana .
I've paid an old lady , who lives in the swamps , more than one bottle of Rum to remove the curse from a boolit mould .
Gary

[Firesubie]

The analogy of seasoning like a cast iron skillet makes sense to me. I certainly don't mind to do the heat cycling if it serves a reasonable purpose. I just couldn't see how just heating it up on a hot plate or in an oven would do anything to the mold other than just getting it hot, since heat cycling doesn't involve putting any substance inside the mold. The iron molds I have are well used and came that way to me. The brass MP molds I bought have all been heat cycled but still require several pours to get good bullets. I hope they get better with use. I'm very new to this casting stuff and just trying to learn all I can. Thank you to everyone who has responded. I really appreciate the help.

[trapper9260]

I use all 3 types of mold made from and for me I clean a new mold with alcohol and let it dry then , I smoke it then put it on the hot plate while I melt my alloy then I cast a few yes at times not good ones , but after the mold it up to temp .I am good to go. I do not use anything for the bullets to drop out. They do it on their own. I know smoke the mold helps alot. Yes the more it is use the better it get but also make sure the mold it up to temp and each mold have its own way it works. Not all will work the same no matter if it is iron or brass or alum . You can have alum molds and thinking it will work the way it looks to work and then you have one that it change things on you . Same as the others types .

[JSnover]

We're not affecting the microstructure at all, at the temperatures we work with. "Heat cycling" or just doing several casting sessions is a mechanical break-in process. The pins, the holes, the surfaces, even the handles need to be worked a bit.
If you want to alter the grain structure or the carbon matrix, that would take a LOT of heat. My advice would be to buy a new one. You'll need it after you 'heat-cycle' your first one.
The break-in is a Real Thing, it just doesn't work the way some people think it does.

[justindad]

Mal Paso did some work creating artificial patinas on brass molds to prevent running. If you look into that, you’ll understand more about why they recommend heat cycling.
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https://castboolits.gunloads.com/sho...ghlight=Patina
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https://castboolits.gunloads.com/sho...ghlight=Patina

[farmbif]

I probably have about 50 molds ive accumulated over the decades and the only way I have ever heat cycled a mold is by pouring molten lead into the cavities until the mold heats up and starts dropping good formed bullets the misformed ones go back in the pot.
some folks as written above heat and cool a mold before getting into a casting session. everyone is after the same thing to get well formed consistent bullets.
. maybe I'm lazy or maybe I,m ignorant but what I have always done works for me.

[Firesubie]

After reading the Mal Paso thread, it seems like there have been differing opinions of heat cycling for quite a while.

[Tripplebeards]

I use warmed up vinegar and salt mixture and elevate my molds above the mixture. I make sure to cover it inside Tupperware. It oxidizes them better than heat cycling process. Works really good for me. Doesn’t really make any difference because I always get my lead and molds too hot and tin them no matter what I do.Lol but to me that’s the key of making a really good hollow point!

Here’s what mine looks like I couldn’t find my old post when I did it in the process but it’s number 11 on this post. You can see what it looks like after the patina sets in from sitting. Normally takes a half an hour to two hours to make make it look really nice. It builds up some really nice patina, a.k.a. oxidation to keep from tinning.

https://castboolits.gunloads.com/sho...low-Point-Mold