Casting gear blanks from scrap aluminium

[Pipescs]

Hey Ike

The patterns are coming to an end and I hope to have the castings done by New Years.

11 inch Pattern


I will do the three small disc as flats

Too early to commit on the price of shipping but I do not think the large gear will weigh over 8 pounds ( As this is the largest Crucible I have and the hope is that I can fill this mold with it. If not I will simply weld up a steel pipe and give it a wash of clay.

[Doug_Edwards]

Once again, I never pour on concrete, it expodes with a spill.

I have heard this over and over. I have always poured bronze on concrete, as I never had a better place to pour, and have not yet had the concrete pop due to metal spills. I have never poured on green concrete, or wet concrete, btw.

Of the foundries I have visited in the last 30 years, only two did not have concrete floors that they were pouring on. Both are pre WW2, and I doubt have any floor other than dirt or sand.

Attached is an image of a leaking mold. The material is either steel or stainless (I don't remember at this point), and the floor is concrete. The floor did not pop or explode.

You might get different results, but this is my experience!

Fwiw.

Regards,

Doug

[Harold_V]

Commenting on Doug's experience----I have had a concrete explosion, and it was just from molten lead.
Concrete, even fully cured and aged, holds water within, albeit chemically bound. It's part of the hydration process of cement.
I don't profess to understand why some experience explosions, while others do not, but suffice it to say, one is wise to avoid the potential, as it can have devastating results.

Harold

[redneckalbertan]

As it was explained to me and I understand it: as concrete cures it looses moisture, this continues over the life of the concrete. All things being equal the newer the concrete the more moisture will be in it. The older the less moisture. The chance of experiencing a concrete explosion is related to the amount of moisture, the greater the moisture the greater the chance of explosion. This does not mean that old concrete wont explode and new will but the chances are greater with newer concrete.

I have had concrete explode from molton steel slag from a cutting torch. Not fun, WEAR YOUR PPE. Other times nothing. If I am doing a larger amount of cutting in one spot I now grab a piece of sheet metal (in my case the piece from the back of a dryer because that's what I had handy once and have kept it for that purpose since then) and toss it on the concrete where I am working to prevent the explosion.

[TomB]

July 4th, 1976 my neighbor had built a bonfire on a 10' x 10' concrete slab. Many neighbors has arrived with 6-pack and lawn chair and settled in for an evening of BS. I left for a minute to check an what was holding up my wife and as a was walking back the fire exploded. Flaming logs were air bound and there was enough force to roll some lawn chairs backward. No one was hurt we put the logs back on the fire and replaced any beer that had been spilled.

The next day we seep off the concrete and found a 3' diameter 3" deep in the center hole. The hole is still there to this day. The concrete was a pad about 10' square and about 6" thick that the kids had put in under the basketball hoop. At the time the kids were about 20 so the concrete was probably 10 years old. When they poured it they must have used an old swing set for reinforcing steel plus some fence and short black iron pipe. There were numerous pieces of steel visitable in the hole.

I never figured out what caused the explosion, perhaps steel expanding had buckled out the concrete, perhaps concrete expanding in the center was resisted by the steel reinforced perimeter. but whatever it was it made a big explosion and it was only firewood driven. I have to believe that a molten metal spill could put more heat into the concrete, but maybe it would take more than just the small spills that occur when pouring into a mold. A correctly engineered concrete floor would not have as much steel as that pad so that also could be a variable.

Tom

[steamin10]

It is not always about steam. They carved the Indian Monument with torches that spalled off the rock. (Granit) It can be about heat diferential.

It may be the foundry floor is so broken and cracked, it acts like gravel or sand.

The speckled grey granit we used for capstone on my pickle line, were 6 and 8 inches thick. They had a 2 inch hole drilled a bout 18 inches in from the sides, and 1/4 inch was sawed out to the hole. I asked, and was told by the Engeneering staff that it was necessary to prevent the Granits from cracking, when starting up the line. The edges would remain cool, and the center would heat to bath temps of 160* and force an edge split, that most likely would run through the granit and destroy it for our purposes. In 11 years we lost about 7 granits of various configurations to breakage due to thermal cracking. I have 4 of them.

If you dont believe concrete breaks or pops from molten metals, just try a dragon burner (propane weed burner) on a piece of sidewalk. Please wear PPE during your reality check.

I set a vessel down on concrete to change from lifting tongs, to a pouring loop. The concrte blew so hard it broke the vessel and released the contents for more fun. it was aluminum, so not as hot as it could be, about 1300* not like iron that would be about twice as hot and glowing, like the picture.

[scmods]

Ike,

The scrapyard may not be the ideal source for pistons as they are way down inside the engine and require extensive disassembly to extract. Most of the guys around here would rather just dump the engines whole into the dumpster as mixed scrap and be done with them.

The engine rebuilder, however, is a different story. The reality is that new pistons are so cheap versus their importance to the whole scheme of things, that they are replaced as a matter of course. My local rebuilder generates them by the bucketful, and, as he is in the engine building business, not the scrap salvaging business, giving him a couple of cents a pound over scrap price is a go, as he doesn't have to make a trip. Lots of times, a donation to the employees' benefit and beer fund is all that is necessary, not even a "business" deal. While you're there, grab a dead crank or two so you have some cast stock in hand. Around here, Ford 351 cranks have a $10 core and its just not worth it to send them in. The Fords are nice, as they have the thrust bearing on the center journal rather than on #5, and you get a nice slug. Thermally aged too!

The moisture issue is worthy of re-mention. Steam, unlike thermal expansion, continues to push after the confining material fractures. Also, the release of confinement permits the boiling of superheated water, maintaining the push.

I had an experience that appears to have been similar to Harold's and still have the scars. I got the message.

Good Luck

Bill Walck

[Glenn Brooks]

Make sure you allow for the shrinkage in you pattern with plenty extra to machine on the gear face.

So what amount is "plenty extra" when making a mold?

I have an opportunity to experiment making a pattern of a 4"x6" steam cylinder and valve chest on a 3d printer. However don't know how much extra to allow for shrinkage.

Thanks

[Harold_V]

There is no fixed amount for shrinkage, as each alloy shrinks at its own rate. You would be best served to search by the alloy you intend to cast. However, there is a rule of thumb for given alloys, for which there are shrink rules available. You can see examples of these by exploring the Starrett catalog. They aren't a requirement for making patterns, but they make life easier. They are not cheap.

Steel shrinks far more than cast iron. Ductile iron, depending on the exact alloy, may have no shrinkage at all. Aluminum shrinks more than grey iron.

Harold

[Mike Walsh]

Nothing like the smell of molten aluminum hitting a concrete floor....

Gets my spidey senses going when I'm at work!

[tomc]

How true, better to have sand to spill on!

Tom C.