Tweaking alloy properties

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  • Last Post 27 August 2024
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Wm Cook posted this 23 August 2024

If I start with a full 20lb pot of alloy, cast say around 200pcs or about 1/3 of the pot. Then I find that the mold has some flashing on the face and they are all rejects and put them back into the pot or maybe I just refilled with previous castings that were no longer needed/used.

When I repurpose them back into the pot the appearance/aesthetics comes out not as good as the pure #2 alloy I started with. It seems to me that pure clean #2 alloy looks a whole lot closer to Linotype than casting from alloy that has been through the casting process a time or two.

Does the alloy change after refills using discards and culls? And what would I do to correct it? Thanks for the help. Bill C.

ps: Dropping spruce’s back in as I’m casting seems to have no effect. Alloy temp while cast is always ~700 & mold temperature is ~390.

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Wm Cook posted this 23 August 2024

It’ happens with both the old and new Lyman cast pots I have, both controlled and or monitored with a PID. Alloy temp of ~700 & mold temp +/- 5 degrees somewhere in the 380 to 400 degree range seems best for the single, double cavity molds (brass, iron) I use. I went overboard these past two years understanding mold and alloy temperature and ladle vs bottom pour. My current method is to stay with bottom pour because I can drop a couple hundred one cavity bullets in two hours and after that I get sloppy.

If I stick to straight Linotype with only the sprue cuts being added as I cast I can get them to drop +/- .15g for about >95+% of the drops. Understanding that it’s PID controlled, and the mold is holding +/- 5 degrees. With pure #2 alloy with only the sprue cuts being added as I cast I can get them to drop +/- .3g for ~80+% of the drops and I get much better looking bullets. Using repurposed #2 the discard rate (rejected because of appearance) jumps to 40%. Similar rejection rate with repurposed Linotype. They show “rust” unfilled spots, slight frost but not clean.

I probably have 50lbs of good #2 that were cast but never resided repurposed because of this problem. Pure #2 or pure Linotype cast clean. In the back of my mind I was hoping I could add a 1/4lb of tin and the rejection rate would decline. Haven’t tried that yet but I was going to give it a try based on feedback from the forum. Or maybe I should drop the temp down to 680. Don’t know. Thanks for listening to my whining. Bill C.

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Duane Mellenbruch posted this 23 August 2024

A look at the RCBS cast bullet manual shows a suggested casting temperature of Linotype and Wheel Weights at 775 degrees F.  Lead/tin mixes at 700 F.  The presence of antimony is a factor.  Reducing the temp is going the wrong way.  Bullet weight can also be a factor as heavy bullets in a single cavity mold put a lot more heat into the mold.  Frosty appearance is from the Antimony.  I am not familiar with what "rust" might be nor what you mean by "resided".  Perhaps you refer to the dull finish when an occlusion is formed in the surface of a casting?  Are you filling the mold quickly, without pause and with a full stream from the nozzle into the center of the sprue plate hole?

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Wm Cook posted this 23 August 2024

Typo on the "resided", meant to say repurposed.  Mold fill with clean #2 or Linotype is the same as what I'm using.  Moderately quick fill, big sprue, frost, count Mississippi 1, Mississippi 2 and cut the sprue watching to stay between a tear and a smear.  I've always had luck with hot molds and the time from cutting the sprue to getting the cavity(ies) filled is brief to keep the mold temp up.  Frost it normal on both Linotype and #2 when things are running right. 

They show “rust” unfilled spots, slight frost but not clean.

Below you can see a minor example from one that was kept as a fouler.  Nothing of this caliber would effect group size but the bullets I culled were worse.  And sorry to say I haven't shot what I think is bad head to head with what I think is good.  Haven't been able to get to the range due to family health reasons. But the defects that were culled were justified.  Not a cold alloy or a cold mold looking defect, just a "rusty", micro termite looking appearance.  Looks dirty.

Regarding alloy temperature.  I though that temperatures over 730 causes one of the properties in the alloy be effected or to be lessened.  I believe tin was mentioned.  Not sure what post it was in.  

Since I've avoided using repurposed alloy the past year I hadn't had any issues.  Actually I've had pretty good success using clean #2 alloy.  Last week I left the pot unattended during warmup and my catch tray which normally collects the drip up to the nozzle didn't work as planned and I wound up with about 5 pounds of alloy had leaked out and collected around the base of the Lyman Mag furnace I was using.  The pot had reached temperature in the lower half and drained out but the top half hadn't melted.  Once I got that mess sorted out I put the 5lbs that had leaked out back into the pot, gave it a good flux and stir and when I started up I saw the quality drop off.

I guess I could just drain the pot and start with fresh alloy but I was hoping I could add tin to the alloy that was in the pot to give it a better finish.  Maybe its just one of those things.  Thanks, Bill.

 

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RicinYakima posted this 23 August 2024

Those appear to be dirt or tin oxide or antimony oxide from not fully fluxed. Just a thought. 

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Eutectic posted this 23 August 2024

The tin in the alloy forms a thin coating of tin oxide on the bullet or sprues. Remelting of small pieces like cast bullets, type or type spacers looses about 0.1 to 0.2% of the tin on every remelt. Some antimony is lost but the amount is small. Smaller pieces = larger surface area = more loss. Linotype operators added plus metal ingots when remelting to maintain alloy composition. You can do the same with about an inch of 60/40 solder for each Kg (2.2 pounds) of alloy.

Dross also builds up. The most efficient fluxing is when the alloy is just completely melted. Liquid flux should float on the surface. The flux should not ignite. Stir it in thoroughly and scrape the walls of the pot. Remove dross and any excess flux. Then increase to casting temperature. 

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Wm Cook posted this 24 August 2024

Rick’s “Those appear to be dirt or tin oxide or antimony oxide from not fully fluxed.“

Steve’s “Remelting of small pieces like cast bullets, type or type spacers looses about 0.1 to 0.2% of the tin on every remelt.”

Steve’s “Linotype operators added plus metal ingots when remelting to maintain alloy composition.”

I think 2/3’s of my problem is that I’m losing alloy composition and 1/3 is in my fluxing method. I can’t do much about the latter because I cast indoors so I have to stick to candle wax and then burning off. As I may have said I cast in increments of ~2 hours which uses up about a third of the pot.

For the past year I’ve been doing fine with fresh Linotype or #2 by scraping down sides & bottom, then wax & burn off before each casting session. So continuing this practice might not be perfect but it seemed to work for me.

Losing the original alloy composition could be the issue. That 5lbs that leaked onto the bottom the furnace stand did not come away gracefully, and I added it back into the pot in all sorts of ugly chunks. Not unlike a handful of reject cast being tossed into a pot of stable alloy.

Again, just to repeat, for the past year I haven’t had this problem since the only thing that went into the pot were the spruce’s as I was casting and ingots fresh from RotoMetal.

If adding 8” of 60/40 solder, 1/4 lb of tin (1.5% of the pot) or even a combination of the two to add properties to the alloy it would be a win. Thanks much. Bill C.

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RicinYakima posted this 24 August 2024

Another thought; have you considered emptying your pot and cleaning the crucible to bright metal. Both with boiling water and a wire brush?

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Wilderness posted this 24 August 2024

Bill - this is in line with what Rick suggests, although I don't go as far as bright metal.

I work in fairly small quantities. I have a pot that holds 10-11 lbs that I heat with a single element electric stove. I cast with a dipper, and dip from an area of the surface from which I have pushed back the rubbish.

When I'm finished my casting run I flux and pour the leftovers, usually about half a pot, into ingots. As well as the rubbish I get out with the flux, I generally find quite a bit remaining in the pot after I've poured off the metal, at least as much as I've skimmed. With the metal gone I can scrape out the pot with something like a screwdriver, or wash it if I'll be putting it away for a while.

Crud in the bullets like you illustrate comes only if I'm careless with what I pick up in the dipper, or a bit slack with fluxing, although I used to get a bit of it when I still had a bottom pour pot. I might or might not flux at the start, depending on what's in the pot, then I flux at about the 100 bullet mark, and again at the end before emptying out.

Provided the metal and mould are hot enough at the start, I get good bullets almost from GO, and throw the sprues back in as they accumulate. My alloys are nothing special. Mostly I just stiffen my scrap with linotype until I get the bullet weight/hardness I require.

Bottom line - empty and clean the pot after each casting session and I think you'll see an improvement. My casting sessions with single and double cavity moulds are usually 200 - 250 bullets, so the pot cleaning cycle is geared to that.

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Wm Cook posted this 24 August 2024

Rick: “ emptying your pot and cleaning the crucible to bright metal”

Bill: “… Bottom line - empty and clean the pot”

Great practical suggestion. Sort of like a reset. Once clean I can try adding solder/tin and start out with the repurposed alloy I had been avoiding. By my math it would take about 1/4lb of tin to add 1.3% to the alloy.

When I clean a pot I normally drain then plug the nozzle with a toothpick and soak overnight in 50/50 solution. With little scrubbing It comes away spotless. If memory serves me well (at my age that’s not always a given) I haven’t cleaned it since I started to use only ingots from RotoMetal and the sprites as I wam casting for the last two years.

So in short, seriously flux the alloy, clean the pot, refill the pot with the repurposed alloy then add tin or solder. Thanks guys, I owe both of you. Bill C.

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RicinYakima posted this 24 August 2024

What is your "50/50" solution? I use water and a few drops of Dawn dish soap. Most of the stuff is water soluable. 

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Wm Cook posted this 24 August 2024

To a degree a 50/50 mixture of hydrogen peroxide and white vinegar can dissolve/loosen lead, but it’s not strong enough to remove buildup of anything more than a light buildup. It’s mildly corrosive, but less dangerous than other options. That said, care must be taken as it can irritate skin, lungs and eyes.

I never looked into it but I would only use it on steel. Pots come out looking great. Bill C.

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Bud Hyett posted this 24 August 2024

For years I used corn meal as a flux. Seemed to work well and the aroma was good. The ash on the top captured the other crud and  was easily skimmed off with a spoon.

Now and then I got a bullet with the impurities as pictured. I took a file to one of these bullets and carefully filed away to see what the inclusion was. It was the ash with the impurities trapped somehow in the alloy. Using a bottom pour pot, this was flowing into the mold and sticking to the side of the mold. 

I surmised the crud was sticking to the side of the pot from my stirring the corn meal into the alloy while fluxing. Scraping the side of the pot while fluxing helped, but these still (more rarely) showed up. The answer has been to use paraffin as a flux. I have source of old paraffin/beeswax candles that I use. 

Scrubbing the pot as discussed is the final answer. I've come to do this on an annual basis. 

Farm boy from Illinois, living in the magical Pacific Northwest

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Wm Cook posted this 24 August 2024

Bud: “I took a file to one of these bullets and carefully filed away to see what the inclusion was. It was the ash with the impurities trapped somehow in the alloy.”

Good analysis. I would not have thought of digging into the flaw from that perspective. I’m feeling pretty optimistic.

Funny how you fall into habits like I was; using only commercial ingots, avoiding the work of understanding alloy properties, forgetting to clean your pot and how it will eventually bite your butt when least expected.

And this all started with a leaking unattended pot. From what I learned out of that fiasco, I can say that it was worth the effort that it took to clean up the mess. Thanks, Bill C.

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Shuz posted this 24 August 2024

At the risk of "flames", have you guys ever used Marvelux? I have used it for nearly 60 years  now, and am very happy with the bullets that are cast from my RCBS Pro Melt, and the various Lyman  and Saeco bottom pours before the Pro-Melt .

I also put kitty litter on top of my melt to keep it from oxidizing the melt and the heat in.

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Wm Cook posted this 24 August 2024

Marvelux & I just didn’t get along. Candles wax and a match is working pretty good for me. Bill C.

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John Alexander posted this 24 August 2024

By now you guys know the type of thing to expect from me but I will go ahead anyway.

I don't think yours is a problem of not cleaning the pot often enough. I say that because I have never cleaned my melting pots (20 &10 pound Lees) other than scraping the sides with a spoon when I flux and I don't flux often.  I also don't believe I have ever gotten the type of inclusions in the picture. However, my memory, like Bill's, is suspect so maybe in the past it has happened to me but not in the last 10 years. This has been true when using WW & scrap (most of my life) or softer alloys from rotometals the last few years. I'm not the only one.  Read Dan Hudson's article in the November Fouling shot. If anything his casting habits are worse than mine but it would be difficult to say that Dan doesn't cast good bullets.

I often cast using a pot of old bullets/sprues/ingots and have never noticed any difference in bullet quality from casting from new Rotometals ingots. Have other casters noticed the dramatic difference in bullet quality when reusing alloy? This is the first time I have heard of the problem. Have some of you, besides Bill had this problem when reusing an alloy?

I am mystified by this happening only with repurposed alloy and wish I had an answer but other than casting at higher temperatures and see what happens I can't think of anything.

However, in the absence of other solutions, I too would clean the pot and hope that it helps.

John

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RicinYakima posted this 24 August 2024

Marvelux is not a product to use in low humidity areas. One of the biproducts of its decomposition is HCl (anhydrous hydrochloric acid). I used about an eighth of a can one winter, casting season, and within a month every piece of iron in the shop had surface rust that was exposed to the air in the room. That was a month project to protect my tools and clean. 

Bill Ferguson, the antimony man, told me if the humidity was over about 50% it would just flow out with the air exchange. At 25% it would condense and leave hydrochloric acid on the surface of everything. 

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Duane Mellenbruch posted this 24 August 2024

There was a comment in and earlier post that tin is lost in remelting the linotype when used repeatedly.  Also that Linotype Plus was added to bring the alloy back to original composition. This plus metal is commonly in factory ingots of 11-18-71 .   If only adding tin to your alloy, you are still not replacing the antimony back to the melt. 

A test of composition change over an extended period of time was performed by a person that had access to the XRF scan equipment and he found that all elements oxidized from the melt and not in any great difference of proportions. 

One very common complaint with a bottom pour pot is leaking or dripping due to dirt in the melt preventing the valve from properly seating.  This was belatedly reported by the OP.  Perhaps the real issue is lack of diligent fluxing and reducing of the melt when preparing to cast, and not the "loss" of elements through oxide formation?

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Wilderness posted this 24 August 2024

I used Marvelux for a few years but gave it up on account of dippers and pot collecting so much moisture between uses. They'd be dripping wet, though not rusting.

Like Bill, I now use candle wax. I use two dippers - Lyman for making bullets and Lee for skimming etc. Both will be in the pot during the melt to make sure everything is dry. When I'm ready to flux I hold the hot Lee dipper to the candle and drip wax on to the melt and into the Lyman dipper (it needs to be part of the flux). If the metal is hot enough the wax will light of its own accord, though I can make sure by lighting the candle before I start the drip procedure, and that lights the wax in the pot. Lighting the wax eliminates the domestically disapproved smoke and smell.

As an aside I sometimes blue cleaned up screws and small parts in the lead pot - leave them in until the colour is right, then remove. Putting some wax on the surface of the melt before putting the part in makes it easy to wipe off the crud afterwards.

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pat i posted this 25 August 2024

Bill no malicious intent but you really need to stop sweating the small stuff and try to sneak a range session in once in a while. I've seen it before so you're not the first but getting all wrapped up in things that don't amount to a hill of beans and will drive a teetotaler to the bottle while not making a damn bit of difference will drive you insane. Turn the heat up, forget the idea of shiny bullets equal good bullets, and flux (or not) the way you're comfortable with remembering to scrape the sides of the pot with your spoon and things will fall in to place. As I've said a million times....this ain't rocket science and a cast bullet BR rifle will never equal a jacketed bullet BR rifle so once thats accepted its clear skies ahead. On the subject of fluxing. Dan Hudson and I discussed this issue after a match today. He said he never fluxes. Now as we know Dan is world famous for his frugality so I don't know if he doesn't do it because he doesnt find it necessary or if the idea of wasting a perfectly good candle gives him the vapors but one thing you can't argue with is his results at the bench.

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