I'm taking machining/casting classes

Is anyone out there?

Week 14, 12-1-10:

I decided to bring my good camera today. The cell phone shots just don't do it justice.

Preheating the ladle.



Pouring a chemistry sample.



..in the ATAS.



Knocking off the slag. A piece went down a girl (my coworker) 's shoe and she ran off to the side and her boyfriend pulled her shoe off and just stared at her burning sock. She was ok.



Inoculating. In other words, sprinkling the magic dust.



Tapping.



..another chemistry sample.



Pouring the mold. Lost foam. Don't breath the black smoke.



My mold.



I dare you to touch it.



The casting + gating + risers.. and some flash. The saw was not cooperating today, so I'll save it for tomorrow.

Very very cool.

Yup, and loving the better quality pics ...

Sorry but my addled memory has failed me. Have you explained the whys and wherefores of what's involved in checking the chemistry at the various stages?

If you have already, just tell me where to look ...

Keep up the good work



John

Well, you're in luck since I work in the foundry, too. I was part of the charge calculations yesterday.

Basically, we're pouring to a grade. In this case, it's 60-40-18 ductile iron, which means it's got a tensile strength of >60,000psi, yield strength of >40,000 psi, and > 18% elongation. To get this, it takes a specific mixture of C, Si, Mn, P, S, Cr, Mo, Ni, Al, Cu, Ti, V, Sn, Mg, Fe, etc. That's what the arc spectrometer shows.

Anyways, we vary the grade by varying the constituents. We use a weighted spreadsheet that tells us how much (pounds/kg) of a specific metal we need to throw in. Yesterday, I weighed out Sorel (pig iron), superseed, steel punchings, graphite, left over ductile iron, and some other stuff. I was shooting for a specific amount of each without getting anal about it. The spread sheet then told me what else of each kind of scrap (or whatever) we need to throw in to achieve the right percentage of the aforementioned elements.

Then, when it's all melted down, a chemistry sample is taken with the ATAS system (tellirium in a ceramic(?) cup with a thermocouple fed to a laptop) to record the cooling data and a permanent mold. Then, innoculant is added into the stream when it is tapped from the furnace into the ladle. Everything gets all crackly and sparkly. Then, another chemistry sample is taken. Finally, it is poured.

To elaborate:
The chemistry samples involve the ATAS cooling data (from the thermocouple) and a specific permanent mold of just the metal (no thermocouple). The ATAS cooling curve has certain characteristics that indicate the presence of certain elements. (My professor, and the guy that runs the foundry can spot this and that really easily. For us mortals, taking the derivative of the cooling curve really shows the interactions via peaks in the curve.) The permanent mold part of the process is for a crystallographic/microstructure view. It is cut, magnified, and analyzed... as a sample of what our actual castings are, without damaging or modifying them.

..and this was only the 100 pound furnace. I toured Nucor-Yamato steel in Arkansas a month ago. 150 ton furnace. THAT was very, very cool.

Very interesting thread, thanks!

Thanks for the explanation.

I understood almost all of it ... except when you start referring to psi. I'm more of a N & mm² kind of guy myself ...

Nice one

John

That's awesome.

I don't even understand it.



PS: It looks like this thread will last a semester longer than I intended. My daydreams have already started to drift to the CNC classes I'm taking next semester (my last as an undergrad).

But, I've got some ideas for building my own waste oil furnace for a forge and foundry. I just need a break from school..

did you ever figure out the "coursness" on the other side of the casting? Just as a wild guess it's surface porosity from air/gas not being able to evacute the cavity. Might it be clinging to the surface due to surface adhesion?

Haven't really determined what it is/was yet.

One guy in the lab is going to be grasping at straws to not fail, so he's been following me around like a little annoying puppy dog lately. Since I've been a 1-man group and written all the reports, made both the designs, and ran the simulations, I'll have him look at that (and micro-structure).. if he feels like actually doing something. If not.. well, I have until Wednesday to figure it out. That's when I'm giving my design(s) presentation.

Drummer:

Can you elaborate on a few things? The 60-40-18 - Is that just a goal you need to hit in order for this specific batch of metal to be good for the intended purpose? Or, did you or someone just make up these ratios and then see if you can hit it? Is the 60-40-18 a standard mix for certain kinds of applications?

What would happen if this got spilled onto your foot? You mentioned the one person with a burned sock, but I kinda thought this would just burn a hole all the way through anything it touches.

Can you detail for me (unless it's too much work) what these items are:
"To get this, it takes a specific mixture of C, Si, Mn, P, S, Cr, Mo, Ni, Al, Cu, Ti, V, Sn, Mg, Fe, etc. "

I find this thread fascinating and the new pictures are terrific.

Tom

Your pour on the previous page reminded me of high school metal shop 1976. We were going to mass produce aluminum beer mugs with the school mascot on the design. First pour we didn't have enough air holes and only partially filled the mold. We fixed that and ended up with a couple of good prototypes. I guess we ended up only making about 5 mugs.

Think about what it would be like to have your classmates at a job site.

Those are abbreviations for elements.

C=Carbon
Si=Silicon
Mn=Manganese
P=Phosphorous
S=Sulfur
Cr=Chromium
Mo=Molybdenum
Ni=Nickel
Al=Aluminum
Cu=Copper
Ti=Titanium
V=Vanadium
Sn=Tin
Mg=Magnesium
Fe=Iron

All found on the periodic table.

Most metal that we use to make things from are alloy, or mixes of various elements. Different mixes give different properties like density, strength, hardness, toughness, corrosion resistance, thermal and electrical conductivity, and on and on.

For the Ferrous metals, carbon is usually considered the most important alloying element. It, more that any other element, contributes to strength and hardness when mixed with iron. Some of the alloys of iron are Cast iron, Steel, Pig Iron. The difference is defined by carbon content. Very roughly and incompletely <2% C = Steel, > 2ish % =Cast Iron, > 6ish % = Pig.

The primary purpose of refining steel or iron is the control of Carbon, but impurities (like sulfur in most cases) are removed and other things like molybdenum, nickel, and chromium are added to give the steel/iron it's desired properties. Sometimes elements are added to drive others out of the alloy.

Alloys can contain dozens or even hundreds of elements, but not all are present in quantities that have a significant outcome on the material properties, so only the ones that are considered important are referred to.

There are several standards organizations that give numbers to the various mixes that create alloys (like AISI) and numbers like 4130 or 4340 are used to represent these mixes. In this case however the number relates to the properties of the steel

60-40-18

60=min tensile strength in thousands of pounds/in squared
40=min yield strength in thousands of pounds/in squared
18=% elongation in tensile test

www.Ductile.org has a lot of reference info for the type of material he is casting.

This is a scaled down gating design project for a railcar brake piece. It's ~18(?) inches long. My first one:



I assume that's what's used in the real world for this piece: "buckeye tender truck" apparently.

It's one of many "standards."

Well, if you dipped your foot into the furnace, or they poured it in your shoe, you'd probably be missing a limb (it's 2700+ degrees F). What happened in class was the TA was slagging it off and knocked the rod on a metal stand. A spark flew off and down into the girls boot. I'd compare it to getting a welding spark down your shoe. Painful, but you'll be ok.

Even though she was wearing a metatarsal boot, sometimes you get unlucky. She should have been wearing clip-on silvers when working that close to the furnace (she was directing the charge).

Loved reading this thread, and have always wanted to play with a home brew forge. Keep us posted on your progress. Thinking of trying the hairdryer 5 gallon steel bucket version. This kind of work is really interesting.

I don't know anything about iron casting (Sadly- my grandfather was a grey-iron foundryman for 50 years. I wish I'd learned from him when I had the chance.), but that kind of porosity/roughness in a jewelery casting would indicate sprues (gates?) that are too small. The cooling, contracting liquid metal needs a reservoir to pull from, or it will pull from the piece.

But lost-wax gold may not work the same as iron...

It looked as though you leave the foam cores in the molds, and just let the iron burn them out? Weird. Jewelers burn the wax out in an oven before pouring metal.

The sprue is the part through which the metal travels from the pouring cup to the runner. The gates are where the metal travels from the runner to the casting.

The point of risers is to feed liquid metal into the casting to make up for this solidification shrinkage, based on Niyama criterion.

The gates were not too small, but the risers were (using a rule of thumb that the risers should have 120% the modulus (volume/area) of the local modulus of the casting).

Note, that was my first casting. The second one turned out much better. Once I am done with this take-home final (my last thing to do for this semester), I will update this thread more thoroughly.

How does it look like that?





Additionally, it's not that weird to actually leave the foam in. I chose not to because I wanted hot, good metal in there as fast as possible. In lecture, we discussed the metal front as it spends energy burning the foam out, and we actually saw an x-ray video of a casting doing just that.

Well, then. The semester is over.

To recap: My group was a bunch of losers who never showed up or did anything. On Sunday after my last update, I got an email from one group member asking if I had made the presentation yet. The last time I talked to (or saw) this guy was 2 months prior, so I responded telling him that we all decided I was to be in my own group, and yes.. I already made my presentation. He replied saying that he wants to have a meeting with me, the professor, and the department chair. I agreed, suspiciously. I figured it would be in my best effort to document all our interactions, so I made a 2-page spreadsheet consisting of times/dates/topics/actions/etc of everything everyone in the group had done. During the meeting, he started crying out that I never let him do any work, and that I kept him from succeeding and that he sent email after email to me and I ignored them all. I whipped out my sheet, and from that point on, it was all over for that lying scumbag.

Let's see, he showed up TWICE out of 16 weeks in the lab, and almost as many times in the lecture, and it's my fault?!

ANYWAYS...

To recap the design:

First one sucked.



Had porosity and surface roughness.



Second one did not suck, but did have a lot of flash.. and a sand problem at two of the gates (not at the parting line). The one guy who meows to himself in the corner (did I mention he does that?) came up and was standing so close to me, I could feel his long hair on my neck as I was packing the sand. JUST A BIT distracting. Everything went fine during the pour, and the casting came out great. A sledge hammer broke off everything easily enough; light swings on the risers while it was laying on the floor, then a drop of the hammer on the gates.



..and she looked damn good. No real surface roughness or porosity.







On both designs, I incorporated a simulated "washburn core" on the risers. That is, a design such that the riser doesn't have full diameter where it meets the casting. A short, small cylinder (or tapered square) is in between the riser and casting for ease of removal. That's why on the second design (without having to wait on zero input from WORTHLESS group members), I incorporated something similar in the gating. (Finishing is part of the design! It isn't supposed to take 5 hours to removed the gating and risers.) Studies show that the small volume in between the riser and casting has no detrimental effects (in terms of feeding the casting liquid metal on solidification). A real washburn core is a donut of sand placed in between the casting and riser, instead of a small piece of foam with sand packed around it.

Anyways, here's what the bottoms of the risers looked like after hammered off.



I wrote up the report (19 pages) and gave a 31-slide presentation by myself.

Then, when I turned in my take-home final for the lecture class, my teacher and I got to talking.. and I scored some scrap gray iron for my brother for a cylinder on a miniature engine he is machining.

I could go into a lot more detail, but.. I'll save it unless anyone has questions/comments.

Next semester is CNC!

Just read through the whole thread. Super cool!