The topic of silicon in casting alloys

[Harold_V]

Big Dave,
Assuming the day comes when I am faced with formulating my own casting alloys (I have several hundred pounds of pure copper and copper alloys in various forms), in your experience, how does one go about adding silicon? I gathered that it is key to fluidity. In iron, it is added via ferro-silicon, a commercially prepared additive. I have no clue how it might be added for copper alloys.

Harold

[steamin10]

I make the discalimer, that I am but an ameteur in the casting of non-ferrous metals in small scale. My larger experience in heavy foundry was working AROUND the casting armors for tanks, metals for mill rolls and 400 ton pours for major equipment bases and housings. You learn things by watching and asking questions, and working the heats, but does not make for an expert by any means. Owning a Piano, (or a lathe) opens the possiblity for thought and practice, but is not testament to expertise. I call myself a Hack, because I play loose with the rules, and generally get away with my practices. However when the money is on the table, knowing the diference of what works, and fails, can make all the diference in wasted effort ($) or getting paid for your performance. This you must know.

I still have some lump silicon, (it is a metal on the atomic chart) that is very roughly cubic and silvery, and has rough shear lines, as it is broken up to large gravel size, when I get it. A digital diet scale is handy for the wieghts observed. This is when a casting log comes in handy for quality control. Weights, temps , pour temperatures, can all be read back to eliminate grainy, pourous, and non-filling misruns. Other chemicals such as Phosphorous, come from innoculant shot of Phos copper, that is another key to good tight castings with fine surface detail. All the supply houses have a list of alloy additives, and can lead you to the amounts needed, (mostly small). The real trouble is in calculating the weights, for the additions, as this is Molar chemistry, and not necessarily the actual heat weight. The tables for Iron founding are adjusted, but many times an additive goes bonks because of oxides and proportions being off. A furnace 'Boil' can knock a considerable amount of nickle to be held in the slag, which must be worked to get back into the heat or be lost($). (tool steel/armor)

Given this weight problem, when creating your desired chemistry, it is far more controllable to make master metal bars from a large heat we create to be spot on for chemistry. Those bars poured from the master heat can be of most any smaller size consistant with the pouring work we do, as we can set more molds of various things needed for future work, to soak up the volume of our virgin metal. It is unwise to melt a large volume for small work, and pig a lot of it, and think it is the same as when we started. It just doesnt work that way, and is why innoculants for the last qualities we search for are added just before pouring so as not to be lost to the natural oxidations and currents of the metals involved.

I had thought you above all would have a handle on this, but I realize you were in the refining of fine gold and silver, not the alloying, which is done by the consumer in your case. That brings up a question I have about alloying small (jewelry) pieces. In my world I dunno how anyone can take a few beads of shot and accurately make a 16 ct. alloy in a torch crucible. I know they buy cheap waxes and forms, trees and all that, but the metal stock is easy to miss being right on for alloy.

In my case for aluminum, the scrap feedstock is shake and bake. No iron is allowed as it quickly contaminates the aluminum and cannot be removed. screws rivets, bolts, are big problem. So is zinc. While not wholly desirable, zinc in the melt (from diecastings)can allow higher detail, at he cost of grainy weak or pourous castings. Iron and silicon are the major controlling elements for fine pours. Silicon for fluidity, and Iron for the reverse, raising surface tension, and promoting large grain structure. Diecast can be handy for fish sinker style parts, but ages quickly, and is notorious for weak fracture, and repairs that are unnattainable.

Early on , in my cast iron cooking pot days, I played all day, without a single acceptable casting being produced. Truck frames. I finally gave up and tried to pig the remaining metal. It looked like a silvery mush bicuit, and would not flow, only to be spat on the ground and hold a blobby shape. I cut it open the next day, and it was full of gas, grains, and pretty ugly. I described it to an old hand, and he laughed. 'Pop cans inna cast iron pot? The scrappers wont even take that if they know.'

Ok, I got windy again, but know this all relates to the nuances of casting, and what the meaning of 'is', is. I bid you peace.

Edit: Open mouth insert foot. It is not Molar. Apologies.

[Harold_V]

I still have some lump silicon, (it is a metal on the atomic chart) that is very roughly cubic and silvery, and has rough shear lines, as it is broken up to large gravel size, when I get it.

The description rivals that of ferro-silicon, so that makes me wonder. By contrast, I've seen pure silicon chips (haven't we all?) which closely resembles the color---the only difference being they are surfaced, so there is no crystalline pattern discernable. I can see where one might assume that silica for use in alloying aluminum (or copper alloys ) might not have any particular appearance.
This is one of the things I'd like to explore, so I have a better understanding.

The real trouble is in calculating the weights, for the additions, as this is Molar chemistry, and not necessarily the actual heat weight.

That's a good point. Right now, I do not know if alloying for base metals is by weight, or molar. I expect it is NOT molar, however. I'll seek more information before forming an opinion.
That being said, I know that alloying for precious metals is by scale weight, not molar. While I haven't done a lot of alloying it was one of the services I offered my customers. Most preferred to have pure gold returned, as that allowed them to deal with all issues gold related. There's a huge number of gold alloys---so it makes little sense to have values of that nature tied up in stock that may or may not get sold in the immediate future. With pure gold casting grain, they could alloy that which was needed, and hold nothing else in inventory. For the most part, however, yellow gold was king, so that's the vast majority of material that was sold.

Consider that there are several colors of gold alloy----purple, green, red, yellow, blue, white, and most likely something I've left out. Couple that with the fact that it can be alloyed as 10K, 14K, or even 18K, you can see how holding alloyed gold isn't the smartest idea.

It is unwise to melt a large volume for small work, and pig a lot of it, and think it is the same as when we started. It just doesnt work that way, and is why innoculants for the last qualities we search for are added just before pouring so as not to be lost to the natural oxidations and currents of the metals involved.

Jewelers face the same problem, so you come to understand that those who use good casting practice do NOT melt excessive amounts. With luck, the only gold (or silver) that gets melted a second time is the sprue, which can't really be avoided. The oxidation you mentioned becomes a huge problem with precious metals, generally resulting in porosity of the casting, and a poor finish when it is polished. It isn't uncommon for a manufacturer to submit gold for refining, simply because it has lost its qualities.

I had thought you above all would have a handle on this, but I realize you were in the refining of fine gold and silver, not the alloying, which is done by the consumer in your case. That brings up a question I have about alloying small (jewelry) pieces. In my world I dunno how anyone can take a few beads of shot and accurately make a 16 ct. alloy in a torch crucible. I know they buy cheap waxes and forms, trees and all that, but the metal stock is easy to miss being right on for alloy.

You have to think beyond the common ways of things. You most likely understand that jewelers (at least the old school jewelers) deal in troy ounces (not grams), along with pennyweights (dwt's) and grains. A scale capable of weighing grains is employed. Because casting grain is typically quite small, and not of a standard size--it's dead easy to weigh out the precise proportions. It's also dead easy for the dishonest benchman to weigh out less than the appropriate amount of gold, which is known in the trade as under-karating. That's against the law, but so is bank robbing. Doesn't appear to be a deterrent for some folks.

As I said previously, precious metals are alloyed by weight. Give that some thought while considering the specific gravity of the metals involved. While gold is the major constituent in the alloys, it is not by volume. Amazingly, for 18K white gold, 25% nickel (or palladium) will override the gold color, yielding a white (or whitish) alloy. That most likely wouldn't be the case on a molar basis.

Thanks for the comments on aluminum. While I'm far from well versed, I, too, am aware of keeping iron out, and shake my head in wonder when I see the recommendation to use a steel vessel for melting. I don't get it. Have these people no pride in the work they do?

If I'd have kept my wits about this subject, I'd have included RONALD in the question, as he has considerable experience, and I value his comments. Perhaps he'll chime in with his thoughts.

Harold

[steamin10]

Um, now I get to stir with a diferent spoon. Metalurgy, casting, and its controls and pitfalls, are a huge block of information. Like the statement that Silicon is a metal. Well , it is, like 70% of the periodic table of elements, but it lies at the end of the metals, and is called a transitional element, because of its properties with electrical conductance. It is not sure it is a metal, along with germanium, and selenium, to name two more, are noted as semi conductors. What is important to note is that these key elements command electrons to bond a certain way, and that effects the grain structure of the physical alignment of the metal alloys, imparting certain paterns. These are more a catylist to structure and properties than they are alloy effect, as it is the molecular (electron) arrangement that is at work here, organizing the lattice patterns, that dictate grain structure and crystal growth. Chemistry, that dictates physical nature. Then any working of the metal physically, can strengthen or destroy the metal created. Copper and bronzes work harden, wrought iron can be strenthened by drawing its grain. (Wrought iron has not been commercially produced in the USA for nearly 80 yrs now) Steels can be heat treated, to many forms and uses. Bronze chisels built the pyramids, as the points got tougher from the work hardening, against the limestone.

These are some of the things that give me headaches. That started, when I found out there were many colors of gold, used by Fabriget in creating his famous eggs for Russian royalty. Gold that is not gold color? White gold? Red, Blue, Ya gotta be kidding me.

I may seem versed in this direction, but believe me, for every question researched, and every door opened, there is a labyrinth of other details and knowledge to persue.

AS far as being expert, in casting, sorry to disappoint. While I have a system that I do, an expert, has the knowledge, the experience, and finally understanding of the entire process. Most neophytes make the claim after a few successful sessions, and get lost in the woods, for some point missed. I have gone there and returned with a huge respect for those that commonly do what I seek in smaller scale. I Carpenter, weld, finish, paint, design and build a large range of items. What is it, expert of trades, and Master of none? Call me a Hack, or fixit guy, I take no insult from it. I am good at what I can do. I share that ground with many others, here on this board and elswhere.

Edit: Ya, Lead is heavy, but gold is heavier by a large margin. What is the typical shot size? I dont have a clue. I take it the size is small and a bit random so there is variation. Compared to a BB shot, same, smaller?

Now as I sit back and think, my bag is lableled Silicon. So the question becomes, is it ferro silicon, (iron is bad for aluminum) or is it another compound, if not reasonably pure? .. Hmmm! See what I mean? What the meaning of is, is.

[RONALD]

I'm a Live Steamer, and the purpose of me getting into metal casting was to make parts, not as a metal casting hobby.

I prefer to use ingots that are already alloyed because they give the best consistent results, and tho I have lots of scrap, I have rarely melted or attempted to alloy it, if I did tho it would be by percentage of weight. I have never cast anything in the copper-silicon family. For the last few years, I have mainly cast C99700 a manganese brass, followed by C83600 the common Red Brass, and C91300 Bell Bronze.

Here are five pages out of the first edition of AFS publication "Casting Copper - Base Alloys" on Cu-Si.

If you would like to purchase the second edition: http://www.afsinc.org/ProductDetail.cfm?ItemNumber=4185

Here is more to research, if you can spare the time:

http://www.copper.org/resources/supplie ... Search.jsp

http://www.afslibrary.com/

[rrnut-2]

In the foundry that I worked in, the melters (the guys that actually did the melting) had available both ferro-silicon and silicon. In the iron based alloys, ferro-silicon is ok, but you do have to account for the percentage. In the cobalt alloys, they didn't want the "extra" iron.

So silicon is available, I just don't know where. Here where I work, we have tons of silicon literally, as we build the machinery for making ingots of silicon for the solar industry.

As far as determining the weights, I will see if i can get Liz to answer your question Harold. She works in the "met" lab at the foundry analizing heats all day.

However, nether of us have experience with the brass and bronze alloys.

Jim B

[steamin10]

Thanks RONALD, Harold, and Jim B.

Making train parts was the reason got into casting too. The pages you posted are typical of the manuals that abound on metals and casting. I use general scrap for casting many things, according to what it used to be, figuring it falls in the range of what I want. Otherwise Virgin bar is called for.

I'll go lay down now, I have a headache.

[Harold_V]

These are some of the things that give me headaches. That started, when I found out there were many colors of gold, used by Fabriget in creating his famous eggs for Russian royalty. Gold that is not gold color? White gold? Red, Blue, Ya gotta be kidding me.

All the result of how mixing one element with another results in alloy created reflecting a different portion of the light spectrum.

Blue gold? Simple. Alloy gold with iron.

Purple gold? Aluminum.

In both of these instances, the resulting alloy has poor qualities in that they are rather brittle (ductility of the resulting alloys is not good).
They tend to cast such colors, using them as cast, with no further alterations aside from polishing, because the alloy cracks if there is an attempt to work the item.

Green gold? One would imagine that mixing silver with gold would yield a pale yellow alloy, but in the proper proportions, it is green. Not a bold green color, but definitely green.

Ya, Lead is heavy, but gold is heavier by a large margin.

Correct. Lead and silver have a similar weight, but gold is heavier, by far. Few elements weigh more, platinum being one of them. Specific gravity of 21.1, while gold (and tungsten) are at 19.3.
By the way, lead and gold are not compatible. Traces of lead in gold, not even enough to affect color, destroy gold's ductility. It is said that simply melting gold in an atmosphere where there is lead in the air will result in brittle gold, as gold readily absorbs lead.

What is the typical shot size? I dont have a clue. I take it the size is small and a bit random so there is variation. Compared to a BB shot, same, smaller?

Preparing shot is a bit tricky. If one pours molten metal over the lip of a melting dish (or from a crucible), in to water, the resulting form is what I call "corn flakes". Try as you might, it borders on the impossible to make round bits.
In order to make shot, or, rather, bits that are not flat, and have no sharp edges, molten metal is discharged from an orifice. Something as simple as 3 mm (1/8") holes drilled in the bottom of a crucible, or melting dish, as was my situation, yields reasonably round objects. Size varies, from miniature balls (just a small fraction of a grain) to balls about the same size as the orifice diameter. The majority of the resulting bits may be as large as the orifice. My melting procedure was to drop the molten gold about 12", to chilled water, which was circulated by a small pump. If the water gets too warm, and is not circulated, the area beneath the stream of molten metal can become superheated and allow molten gold to hit the bottom, where it has the potential to fuse to the vessel.

Here's a picture of the resulting gold. It was dispensed this way, for ease of weighing by the consumer.

Now as I sit back and think, my bag is lableled Silicon. So the question becomes, is it ferro silicon, (iron is bad for aluminum) or is it another compound, if not reasonably pure? .. Hmmm! See what I mean? What the meaning of is, is.

That's the very question I have. What do you really have? Could it be used in alloying copper?
We need more information before making that decision.

Harold