mold temp control question

[Jeremy Horn]

I hear a lot of people talking about using a hot plate to bring them up to temp. I'll probably get one sooner or later. What I'm wondering is, is there a point where the mold gets too hot? If so, how do you cool it down? Just set it aside for a bit? Put it back on the hot plate to cool it down but keep it hot enough to use? What is the danger of it getting too hot? Bad bullets? Damage to the mold?

Thanks again for the advice, guys.

[MikeS]

Depending on just how hot you get the mould it's possible for the mould blocks to warp. I don't know just how hot they have to get before they warp, and it would depend on what the moulds are made from. An easy way to avoid overheating the moulds is to use a thermometer to keep track of the temp. Some folks make mould ovens that cover the hotplate, and have a thermometer in them. I have some thermometers I got that are similar to the ones used to keep track of the alloy temp, except that they're only 2" long, and the shaft diameter is .125", and I insert one into one of the pour holes in the sprue plate. Using a thermometer in this fashion I find that when it reads between 250 and 275F that the mould is ready to cast. The actual mould temp will be higher than shown because of the fact that only about half of the temp sensor area is actually in the mould, so it shows somewhat cooler than the actual temp of the blocks, but I don't really need to know the exact temp of the mould, only that when my thermometer says 275F the mould is ready to cast. I find if the thermometer says 300 than the first few pours will be frosted, but simply holding the mould in front of a small fan for a few moments is enough to cool off the blocks to the proper casting temp.

[JonB_in_Glencoe]

I've warped a sprue plate from a Lee 6-cav. mold on a hotplate that was set too high.
Jon

[theperfessor]

The fastest way to cool a mold in air is just open it up. And to retain heat close it as soon as you drop out the bullets. It's all a matter of mass and surface area. Some people cool a mold or the sprue plate on a damp rag. I feel that is more likely to cause warpage, and I prefer not to overheat a mold enough to need to cool it faster than air cooling can provide. Just my two cents.

I use a screw-in thermocouple attached to a PID controller to monitor mold temperature and control a hot plate during the pre-heat phase.

[Jeremy Horn]

I guess I should have been more specific. What I meant was, can I overheat a mold by casting? I would assume that if I leave it on the hot plate it would get too hot. But what about just casting? I notice that as I'm casting it gets easier and easier to cut the sprue off. That's a sign that it's getting hotter, right? Can that become a problem? My casting "coach" uses two molds at once and alternates to keep them from getting too hot. I'm not sure what "too hot" is, really. The mold is made of aluminum, if that matters.

[JonB_in_Glencoe]

I judge mold temp (while casting) by the number of seconds that it takes for the sprue puddle to freeze, Ideally I like 4 to 6 seconds. when just starting a casting session, this tells more what the sprue plate temp is, then the mold temp. But if you preheat the mold and start the your casting cadence, after 10 or 20 pours, it's also a good judge of mold temp.

So to re-word that, I start casting with a preheated mold. I watch how long it takes for the sprue puddle to freeze, if it's less then 4 seconds, I cast faster. If it's longer then 6 seconds, I open the mold to cool it down a bit and also cast slower.

[Dannix]

I set this on my sprue plate on my mould on the hot plate, with a cover to help the sprue plate stay close to the same temp as the rest of the mould. (The cover was salvaged from an old computer AT PSU.)
Coverite Pocket Thermometer (http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXB352&P=7)
Avoid going over, oh, what, 450F or so? I forget precisely. I just look for my mould to be about 430F or so.


I use a screw-in thermocouple attached to a PID controller to monitor mold temperature and control a hot plate during the pre-heat phase.
My problem is I'm using my PID to control my pot. Perhaps I'll end up giving Frozone more money to get me squared away with another PID.

[theperfessor]

Yeah, I built a dual controller to do that, there's a sticky in the Casting section about that. Really handy to have.

[Le Loup Solitaire]

Starting with a cold mold and casting to bring it up to correct temperature can take a while, but some people do it that way. Usually the first 10 or so casts are not good. Another approach is to pre-heat the mold with a hot plate. This works as it brings the mold up to near the temperature needed to make good bullets. If the heat source is too hot it will overheat the mold or can even warp it so the heat has to be watched, or a thermometer used. The use of a torch to pre-heat a mold is risky (imo) as is dipping a corner of iron molds in the melt. You can also overheat a mold (with larger & heavier bullets) by casting too fast, but you won't warp it that way. The first sign of overheating is the sprue puddle taking longer to freeze and then longer and longer. If one doesn't wait for the freeze and attempts to cut the sprue then smearing of lead across the tops of the blocks and as well on the underside of the sprue cutter. Big PITA! A mold or alloy that is too hot can also produce frosted bullets; not a big deal, but many people object to them. The use of a small electric fan helps to keep things under control and the whole scene cooler. It is not necessary to pre-heat the mold from cold right up into the proper casting range. Half way to 75% is sufficient and the first few casts will then bring the mold to where it has to be in order to continue successfully. If the alloy temp and cadence are right then things will progress ok. But the time for the sprue to harden needs to be watched....as well as the quality of the bullets coming from the mold.... so like with everything else, stay alert and keep mind on what you're doing. LLS

[.22-10-45]

Hello, Jeremy Horn. I've never warped mould from casting..but have had them get too hot where sprue solidification takes longer. My answer to this is a heat sink..a big block of copper or alum. Usually have some cooling & alternate.
holding mould upside down with plate in contact for few seconds does the trick. No danger of warping or water splash.

[Dale53]

I pre-heat the mould with a hot plate. I consider the ideal to have the mould just under proper casting temperature that requires one or two moulds full to be up to speed. You can easily find that temperature by trial and error.

It IS possible to overheat a mould. Once, I had a large single cavity mould that I held in contact with the melt too long. The bullet actually soldered itself to the inside of the cavity (actually, just kind of "leaded up"). I had to get the mould hotter and wipe the cavity out. Taught me a lesson, tho'.

I also have a small (6"or7") manicurist's fan mounted to maintain mould temperature. I cast rather fast so the fan keeps the sprue hardening in 2-3 seconds. It also maintains the whole mould temperature. Further, it cools the pile of "just cast" bullets so when my pot is empty I can immediately load the bullets in a box to take to my basement shop (I cast in my utility barn) for lubing and sizing.

I find the hot plate and fan to reduce the aggravation factor big time and recommend to any who will listen. Neither need be expensive and definitely make the casting experience more pleasant.

FWIW
Dale53

[HARRYMPOPE]

I cool the sprue with a wet rag.Just oil it up so it doesn't rust before you put it away.

[ipijohn]

I warm up and maintain mold temperature using a mold "oven" on a hot plate. My oven is a 2# coffee can with a window cut in the front for the mold. I have a 2" stem BBQ thermometer through a hole in the top of it. Have found that 400* is a good place for my molds to be warmed or maintained at. I had some difficulty casting HP's until I started using the oven to keep the HP pins hot.

[zomby woof]

I got the NOE BBQ mold thermometer. It's been very helpful. I heat up a mold on a hot plate. I try to keep a LEE 6 cavity around 340 degrees, it makes real nice boolits at that temp. I keep it a that temperature with a fan and or damp rag. Your casting speed also makes a difference. Having an eye on alloy and mold temperature sure makes for nice consistent boolits. No more frosted boolits for me.

[leadman]

I cast with alot of 6 and 4 cavity molds and they can get too hot. I use several methods to cool them. The first is opening the blocks and holding them in front of my fan that is sucking air away from me. Usually do this with the 2 cavity. I also have a small piece of flat steel I set the mold on. If I'm in a hurry I follow the instructions from Richard Lee and set it on a wet sponge in a shallow dish of water. Great if you are in a hurry but it can cool too much in a hurry so one has to really pay attention when doing this.

[Andrew Mason]

i did some casting with my lee 6 cavity today.
45acp. 230 grain.

i definatly overheated it today.
i got going really fast with it, and forgot
about the importiance of mold temp.

a little later when i am less pissed
ill go out and see what i ended up doing
as far as damage goes.

so, just a reminder of how importiant mold temp is

[wv109323]

I just read George Nonte's book on Reloading. This is not the most Hygiene way to tell the correct mold temperature but he said he knew several casters that used "fried spit" as a guide. When the mold would boil water it was correct to mold bullets with. I suppose you could have a small amount of water and drip a very small amount on the mold to see if the mold would evaporate the water. All caution of water and molten lead would need to be exercised.
A hot plate just speeds up the process to heating or pre-heating the mold to temp. As others have said when the sprue takes a long time to solidify the mold is getting to hot. Frosted Bullets can indicate that the mold or meltrd lead is too hot.To cool it down I open the mold up and fan it in the air. I then cast a little slower. It don't think iron or brass molds can be warped by the average caster.

[MtGun44]

Touch a too-hot mold to a damp rag put on the bench for that purpose. I adjust casting rate and/or metal temp
to keep mold temp correct.

Bill

[kbstenberg]

I second what woofer said. I use NOE's mold temp. monitor both to keep the mold from over heating and to keep consistent bullet weight.
I have 1 Lee mold that the casting temp is so narrow between under heated blocks and the same blocks being overheated I couldn't cast without the monitor.

[fcvan]

I cast with Lee, Lyman, and Saeco molds. My lead pot is a Lee 110 v 10 pounder. Years ago I cut out a tin can lid to cover the top of the pot. I usually set two molds on top of the lid so that when the pot is up to temp so are the molds.

While casting, I judge temp by the amount of time it takes for the sprue to cool. I also pre-heat ingot by setting one on the top rim of the pot. I generally cast with two molds at a time and get into a rhythm.

Sometimes I have my alloy get a little warm and so I will drop in an ingot that isn't pre heated or I will wait a short while before putting one on the rim to pre-heat. I generally don't have to fool with the temp dial unless I'm casting on a really cool day or I'm casting large boolits and going through alloy faster. The only molds I have that are really temp sensitive are my Lee hollow point molds. Based on tips I have learned here I started casting those hotter which for me means one mold at a time while watching the sprue closely and inspecting the base before even opening the mold.

I read an article 25 years ago about a guy who ladle cast from a 40 lb pot heated by natural gas or propane. The guy wrote a really detailed article about shooting one hole groups with a 30-06 using cast boolits. The large volume pot kept a very even temp and ladle casting helped with fill-out. The interesting part of the article was how he had taken the barrel of the 30-06 and put it through holes in the side of a trash can and then filled the can with cement so that the rifle was dead solid. I cut out the article and put it with my gun magazines which are in a box. I hope I still have that article so I can scan and put it up for others. If anyone else remembers this article or knows who the gentleman was that would be great. Frank

[dromia]

I would like to read that article.

[I'll Make Mine]

The interesting part of the article was how he had taken the barrel of the 30-06 and put it through holes in the side of a trash can and then filled the can with cement so that the rifle was dead solid. I cut out the article and put it with my gun magazines which are in a box.

Hard to aim, but very, very steady -- makes a benchrest "iron monster" look light and portable.

[Pooch]

Every mold is different. Just a matter of knowing what each individual mold wants. There's no crystal ball. I use a PID controller on my pot & different molds like different temperatures. With my alumnum molds I find my self leavng the mold open for 10-15 seconds after I drop the bullets and my PID is set at 630F. Sometimes I pre-heat my mold gently with a propane torch. It's not rocket science. Just trial & error.