incomplete pour problem

I memory serves me,,and sometimes it doesn't,, thought they were investment casting those doorknobs,, if that were the case they would have been removing the molds from a burn-out oven after burning off the wax. Bear

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bear
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Trevor, how high a temp will your pyrometer read to? TIA Bear

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bear

That's because they're just a bunch of slobs who do investment casting. TOH only deals with artistes, who have better marketing -- er -- aesthetic -- skills.

They used plaster of paris, prompting me to do some web research. Apparently it's a good way to do near-investment quality casting in aluminum and bronze, but can't be used with steel or iron because the melt temperature is high enough to fry the plaster before the cast solidifies. Do an Altavista search on +plaster +aluminum +casting or some such for links.

Reply to
Tim Wescott

The catalog description says 1370degC / 2434degF but it only reads in Celsius (waddya want for $15?).

The item is from Princess Auto, labeled as Power Fist brand, and is item # 0700366 and includes a small thermocouple junction with it. A real thermocouple must be got or made if you want to use it to check molten metal.

Type K is what is needed.

If you Google princess auto and the item number you should get a page on making one of these.

Cheers Trevor Jones

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Trevor Jones

Reply to
bear

A couple friends of mine, that take a far more scientific approach to casting than I do, are pretty good at keeping records of their results. Theory is along the lines of measure, pour, check results, repeat if it works, or assess what needs to be changed by the resultant failure.

I don't know what kind of accuracy level these things can acheive, but they are working quite well for the guys. Accuracy does not mean much unless you are attempting to use information from one tool to match information from another tool. If you use the same tool to measure each time, you can at least expect the measurements to match at the same reading.

Either make up a quickie conversion chart, or just get used to reading it as a number, rather than as a temperature. Probably just noting the melting temp of the metal you are working with and proceeding from there would suffice.

Cheers Trevor Jones

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Trevor Jones

my needs aren't that precise,, just want way to know what temp a small gas fired forge is running,, mainly for heat treating carbon steels

Bear

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bear

- Rod White Dies, I had the privilege of shoveling greensand into a muller as a night job while in high school oh-so-many years ago. The foundry was in back of a pattern shop, and 2-3 nights a week and Saturdays, a top skilled foundryman would work a second job there. He was a magician with sand, an expert marksman, and had the steadiest hands of any person I have known. He could draw a cylinder eight inches tall with less than a half-degree of taper on the sides up out of a mold freehand, and never disturb the sand at all. I would hold my breath while he did some of those draws...

On to some suggestions:

1 Make the sprue larger (1.5"- 2" is not out of the question) 2 Make a big reservoir in the drag (bottom) offset toward the casting 3 Cut wide, thick gates in the cope, (top) from the reservoir to multiple points in the casting. I saw one thin section cast with a gate leading more than half way around the casting. At intervals, feeder gates were cut in the sand from the surrounding gate to the casting. 4 On the farthest corner from the sprue, poke a 3/4 inch diameter riser up through the cope a short distance away from the casting and gate this to the casting. You need the air to get out of there fast! It also serves as a secondary reservoir to reduce shrinkage as the metal cools. 5 Pour as cool as possible. Having said that, the red-almost orange color mentioned in another post is my best memory of what we poured at. The molten metal in the pot will be dull on top, stir it a bit to observe the color. BE SURE THAT EVERYTHING that touches molten aluminum is DRY! 1200 degree steam has a LOT of power to throw metal in the wrong directions [first hand experience talking]. 6 Work the sand fairly dry if using water bonded greensand. Water (overly wet sand) rapidly cools the metal.

The theory is kinda like this; you want a lot of molten metal to move into that hole in the sand very quickly with minimum turbulence. The cooler it is, the smoother your casting is and the slower it flows so the metal freezes quicker, with less shrinkage. BUT,you want the metal hot enough to flow into all corners and pick up the detail, however the trade-off is... at some point the metal gets hot enough to actually shape to and bond to the grains of sand. This gives you a nasty casting covered with silica that will dull your hss tooling very quickly. At even higher temperatures, you alter the alloy and burn off some elements, causing ugly castings.

Some alloys just don't flow quickly. If you are using scrap extrusions for your pour, you may not have as good a luck as with a specific alloy made for casting (no flames on this, please! I use scrap too).

Good luck! When you are through I might be interested in the patterns...

Rex in Portland in the rain, wishing the forge/furnace was running today.

Reply to
Rexarino

Wow! Would have loved to see that guy in action. It would make a wonderful piece for the History Channel.

And a hardy thanks to all! I did a perfect casting of the base today! I experimented at night to get a feel for the temperature using a steel rod to check the metal. In one or more of the many suggestions that I read, someone said the temperature would be correct when the aluminum stopped sticking to a small steel rod. That seemed to work for me. I tried bigger vent's than just a small wire and put the sprue directly in the center of the pour so that the metal would only have to make one turn to be in the mold. Don't know if that helped but it seemed to make sense to me. Anyway, bottom line is I got the base for my lathe! And I feel like I learned a lot. Well, maybe a little...

Robert

If time is the 4th dimension, then money is the 5th dimension. We are always concerned about dollars per hour for the space we occupy. - Rod White

Reply to
Dies Deambulo

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