Mould release

[jethunter]

I'm going to dispute Jethunter's numbers a little bit. Mind you I have only recently started closely paying attention to temperatures: until six months ago I cast using the pot factory thermostat and preheated the mould with a few dummy casts and didn't measure any of it. But now I'm having a lot of fun putting my data logging laptop to a new chore.

Anyway, I was casting yesterday and confirmed numbers I had seen previously, namely that the mould (a Lee 6-cavity .38) had a very tight preferred operating range, and it was significantly hotter than 300-350F. Cutting sprues was acceptable at 220°C but the effort required rose rapidly if temperature dropped below that number. On the other hand, if I opened the mould while it was hotter than 240°C I would start getting hot tearing at sharp shoulders. After a little while I fell into a groove where I would try to fill the mould when it was between 225-235°, watch the temp jump several degrees with the addition of hot lead, wait a few seconds, cut the sprues, then if necessary wait until the temp fell to 235° before opening the mould. Repeat. The melting pot was not on a PID during yesterday's session and the temperature swung pretty widely. It didn't seem to matter, as Jethunter said the mould temp is really the important one.

I have only worked out technique like this with this one mould. It could be that different mould materials, or a different bullet, or a different alloy would change this working temp range considerably. So the number of 300-350°F may well be correct in some situations, but it would not have worked very well with the arrangement I cast most often.

Yeah, I agree I don't agree with so much of that at all. but maybe we're talking about 2 different things. I described peak temperature, maybe you're describing cooled temp.

Where and how do you measure the mold temp? Internally with a probe, or on the outside surface? Different probe position will see different temperatures, closer to the cavity will be hotter than farther away. The temperature is not uniform through the mold, it's hotter in the center than it is on the surface. Depth and position of the sensor will affect the measured temperature.

The temperature swing in the mold varies depending on how much molten alloy you put in it. More volume equals more heat. With a 700 gr bullet 3 cavity mold I wait at least 40 seconds with a cooling fan to cut the sprue or the base is still molten and it smears. But on a 90 gr bullet 4 cav. mold i pour, cut and dump almost without pause just to keep the mold warm enough to get good fill.

The 700 gr 3cav mold heats up to over 400F right after the pour. The 90 gr 4 cavity might not hit 300. The peak mold temperature corresponds directly to the volume of lead you pour into it .

I cast at fairly high temperature to get good fill and better consistency on the bullets.

I cast somewhere around 100,000 bullets a year by hand, with about 60-70 molds. The better quality molds like Accurate and NOE last 4 to 5 times longer than the Lee. I've never had much problem with burrs or roughness that cause sticky bullets in Accurate, MP, or NOE molds. I have had that issue a few times with Lee molds.

I don't use mold release and never had to, but I do scrub mold cavities with hot soapy water and a toothbrush every couple thousand bullets, or if the mold hasn't been used for a while.

 

[DANS40X]

Any brass or aluminum mold will have a feathered burr induced during the machining process.
Sand the cavity edges w/ 600 grit emery cloth backed by a file to keep edges square.
Draw a pencil eraser around the edges of each cavity to remove any feathered burr.

Use the file to bevel the sprue plate edges & blended w/ the emery cloth.
Use the file & emery cloth to smooth the sprue plate pour holes.
Apply a drop of 2 stroke pre mix oil into the sprue plate pivot bolt hole prior to re-assembly.

A paper shop/hand towel folded into 1/4 size
Apply 2 stroke premix oil
Wipe mold halve face & mold cavity top surface & both surfaces of the sprue plate w/ shop towel
Dip a q tip into the 2 stroke premix oil
dab each cavity w/ the q tip & 2 stroke oil
preheat the mold to 150 degrees & swab each cavity w/ a clean q tip

Verify pot alloy is 750 degrees w/ thermometer
pre heat the mold to 475 degrees verified w/ a Fluke hand held infer red scanning thermometer for a perfect first pour.
Sprue should take a count of 8 to set
weather it be a 2 cav,3cav,4cav,5cav,6cav ALL sprue should set at the same time or your mold/sprue plate temps are low & will produce different size bullets per cavity.
Cut sprue
dump bullets

when finished casting
apply the 2 stroke premix oil to all mold surfaces & apply into the cavities w/ a qtip.

Next casting session,preheat mold faces & wipe w/ paper shop towel/2 stroke oil
A clean q tip to wipe out cavities

No washing
No smoking
No hassles
No corrosion

It's been my technique for 30+ years
It simply works

 

[DANS40X]

If one does not have a lead thermometer-

Pure lead at 750 deg F scale will appear as shiney as chrome.
Too hot it will have a purpleish hue to the top surface.

Alloy will have a slight grey-ish straw hue to the top surface at 750 degrees F.

Any sprue or material added back to the pot has to be fluxed to remove the oxidation to float it to the top as dross.

The 2 stroke premix oil w/ 1 part of paraffin & 1 part beeswax is a perfect flux that does NOT flare/flame up & does NOT draw moisture when cooled & is NOT corrosive.

Place the oiled paper shop towel over the melt after if has cooled to room temperature to keep debris out of the dross.

Remove the paper towel prior to heating the pot.

 

[kjohn]

Boy! Lots of "how to do it" advice here. I just cracked out a new LEE 6 bullet mold for 155 grain .309. Late model with the gas escape channels. I gave it a quick clean with a toothbrush and mineral spirits, wiped it as clean as I could with a blue shop towel, smoked it with wood matches and started pouring. I set the 10 lb. bottom pour LEE to a temp that works nice and go to it. I use WW with a bit of lino and flux the mix with a bit of Marvelux. I usually have one other mold to use so as to keep the mold temps reasonable.

Mind, I am not selling commercial bullets, and the shooting I do doesn't require absolutely perfect bullets. This plan has served me well for years now. I make ingots with straight WW's, flux with Marvelux, and use smaller sized muffin tins for the ingots. I just refill the pot with maybe four or five ingots, put in some lino, stir it up, skim the crap off the top, and pour bullets.

I was fortunate to score maybe 80+ lbs of little lino type-setting dealies, and have other big bars of it too, plus a boatload of WW material. The pot I use for pouring bullets is often the same pot I use for making ingots. I set the temp a bit higher for ingots.

 

[DANS40X]

Boy! Lots of "how to do it" advice here. I just cracked out a new LEE 6 bullet mold for 155 grain .309. Late model with the gas escape channels. I gave it a quick clean with a toothbrush and mineral spirits, wiped it as clean as I could with a blue shop towel, smoked it with wood matches and started pouring. I set the 10 lb. bottom pour LEE to a temp that works nice and go to it. I use WW with a bit of lino and flux the mix with a bit of Marvelux. I usually have one other mold to use so as to keep the mold temps reasonable.

Mind, I am not selling commercial bullets, and the shooting I do doesn't require absolutely perfect bullets. This plan has served me well for years now. I make ingots with straight WW's, flux with Marvelux, and use smaller sized muffin tins for the ingots. I just refill the pot with maybe four or five ingots, put in some lino, stir it up, skim the crap off the top, and pour bullets.

I was fortunate to score maybe 80+ lbs of little lino type-setting dealies, and have other big bars of it too, plus a boatload of WW material. The pot I use for pouring bullets is often the same pot I use for making ingots. I set the temp a bit higher for ingots.

You still need a couple percent of antimony in your mix &/or all the flux in the world will not blend your w/weights & linotype.
(hardened/magnum shot of #4 & larger is an excellent source of antimony)

When pre-heating an aluminum mold.
Holding direct heat on one surface will push heat out the opposite side.
Rotate the mold radially while pre-heating it for best results.

 

[HIGHRPM]

I have only smoked one mold to try and see any difference. From that moment I do not smoke any mold as I saw no improvement with the bullets releasing. It might be different for all of us. I just make sure the mold has been washed out real well with brake cleaner, which leaves zero residue and then keep the mold temp up and the pot temp up.

 

[Opcx6]

Kroil!

 

[kjohn]

You still need a couple percent of antimony in your mix &/or all the flux in the world will not blend your w/weights & linotype.
(hardened/magnum shot of #4 & larger is an excellent source of antimony)

When pre-heating an aluminum mold.
Holding direct heat on one surface will push heat out the opposite side.
Rotate the mold radially while pre-heating it for best results.

It is my understanding that WW do have antimony. I have done some heavy reading on the subject, but there is an outside chance that I may be wrong. Can't speak for others, though.

I seldom preheat any of my LEE molds. I do a couple of sets of bullets and they are usually good to go. I have on pot set to the seemingly ideal temperature for casting, so it stays that way. Another one is cranked up a bit higher for melting WW. I just found a third one a couple of days ago. That's what happens when you move 4 or 5 times. I am pretty sure I have a 20 lb. LEE pot, but it seems to be in a safe place!

LEE says to smoke their molds, but what do they know! I smoke mine once in a while, after I give them a cleaning, which doesn't happen too often.

 

[yomomma]

It is my understanding that WW do have antimony. I have done some heavy reading on the subject, but there is an outside chance that I may be wrong. Can't speak for others, though.

I seldom preheat any of my LEE molds. I do a couple of sets of bullets and they are usually good to go. I have on pot set to the seemingly ideal temperature for casting, so it stays that way. Another one is cranked up a bit higher for melting WW. I just found a third one a couple of days ago. That's what happens when you move 4 or 5 times. I am pretty sure I have a 20 lb. LEE pot, but it seems to be in a safe place!

LEE says to smoke their molds, but what do they know! I smoke mine once in a while, after I give them a cleaning, which doesn't happen too often.

Correct. WW have about 3% Antimony.

Most people do not realize that molds have to be broken in just like cast iron fry pans.

 

[OttawaHunts]

DO you smoke the molds after cleaning to build up a soot/carbon layer. This is all I have ever done, assuming you have given a good soap and water cleaning and deburred. I either use a bamboo shiskabob long stick or a beewax candle.

 

[Dogleg]

I clean molds with electrical contact cleaner and smoke them with a bic lighter. I never use a candle because I found that I got gas wrinkles when I tried that. Besides that I preheat molds by floating them on the molten lead until the lead drops away cleanly. Once that state is reached I float a second mold and do a couple casts with the first and discard without even looking at them. If they look filled out I'll start in on the second mold, alternately filling and setting down, picking up the next and dumping it then filling and setting down. It can be quite mesmerizing once the rhythm is set. Sometimes the molds get a bit hot and the sprues aren't solid when I pick it up. I'll graze that mold on a damp cloth I have close by to restore the rhythm.

 

[big boar]

Dogleg, is there a chance, when you tried smoking your mold with a candle, that you also got some "soot" on the vent lines of the mold? I've used candles for smoking before and never had an issue as long as I only got soot on the actual bullet, not touching the vent lines. If you get ANY smoke or soot on the vent lines you may get wrinkled bullets because that prevents air from exiting the cavity when you cast. Sometimes, if I cast fast with a large cavity mold and I pour too fast I can occasionally get an imperfect bullet.

 

[Goodwin81]

I smoke all my molds with a butane lighter. Nothing drastic, just enough to turn the cavities a nice golden color. It definitely helps, but keep in mind as others have said, some bullets are "prone" to sticking dependant on their design, contours and edges.