Casting a windmill gear in grey iron

Ok, I can do that.
A bit more trouble, but no problem.

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But look at the size of that CAT! You don't piss that thing off and not lose some blood!

 

Oddly enough, he is the nicest cat we have (out of six).
Does not bite, and just sort of hangs out and acts cool.

Tortoise shell are the worst.
They are very hot tempered, and have a "make my day" attitude.
I have lost a lot of blood on that one, as has any visitor who makes the mistake of petting the pretty little brown cat (tasmanian devil).
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You just might want to check with guiness... That thing could be a winner.

 

Pat, I made an interesting mistake today that taught me something about the iron flow capacity of a small a hole (read that as “runner”).

I was pouring my 18” straight edge patterns today in two molds one after the other. By accident and prior to the pour unknown to me, I made a 1/8” diameter vent hole in the bottom layer of the mold penetrating the sand right under the 4” high sprue. I later poured the mold and noted a 5 pound runout of metal under the mold—-a first for me. And very aggravating I might add Only later did I discover the reason was the 1/8” hole that actually ended on the bottom board of the flask adjacent to a drilled hole in that board. So there was not even a straight shot for the iron to follow. Nevertheless, 5 pounds of iron ran out that hole. I was impressed and understand more fully that one need use much smaller than one might think runners and gates. I am , of course, not suggesting 1/8” diameter runners, but ,by comparison, a 1/2 x 1/4 runner that used to look sort of small is actually a geneeous portal for 10 to 20 pounds of iron.

Attached are pics of the hole casting and the “floret” the vent generated seeking a way to the bottom exterior of the mold.

Denis

 

Amazing! Thanks for posting that. Did it freeze off, or affect the pour?

 

I think the hydraulic pressure inside a mold is higher than one would imagine.
I know this because I cement my bound sand mold halves together, which makes for a pretty strong mold, but I have had brass break the mold halves open, and that was a mold that had very little head height.

I have started cementing the mold halves together, and adding weights on top.

I don't know how to calculate the uplifting force, but it seems significant, and thus I can understand the iron following any path, even a small path.
Flash at the joint is a good example of that.

I tend to agree, the runners and associated parts can no doubt be many times smaller than the rough approximations that I have been using.
I think over time I will have a better feel for what is too small and what is just the right size.

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It evidently froze off as head pressure reduced since the pouring basin nearly, but not quite, emptied. There was about a 1/4" of metal in the basin leaving about a 1/2" of head to the top of the casting. . I nearly just knocked the mold apart moments after finishing the pour just to see what had gone wrong as I was "sure" the casting would have not filled.. But, in order to not induce needless stress on the possibly intact casting by shaking it out hot, I contained my curiosity and waited 5 hours to shake it out. I'm glad I waited as the casting was fine!

Anyway, I was positively amazed so much metal could squeak through that tiny hole, run into the bottom board, form that floret, and still make it to the outside world. Initially on seeing the "cowpie" of metal under the mold, I surmised that somehow the sand had collapsed in the drag. Nope, a teensy leak only!

That experience reinforces the fact that a while back I reduced my runner cross sections to 25% of my earlier ones and they actually worked better by eliminating contraction defects at the gates etc.

You learn nothing when all goes well.....

Denis

 

Static uplifting force is not hard to calculate. Dynamic force of slowing a fast moving stream can add a lot but I feel the static head, after all flow is stopped, is a good approximation.

You can do it by manipulating the units. Assuming your pour weighs 0.275 lbs per cubic inch, and the head is 4 inches, 4*0.275=1.1 psi. (in*lbs/in3=lbs/in2) Then you have to calculate the area of all the metal covered by sand. If you have a frying pan 9" in diameter that's 64 sq in, then a handle 4" by 3/4" adds 3 sq in. Add another 5 sq in for runners and gates and you get 72 sq in. 1.1 psi over 72 sq in is 1.1*72=79.2 lbs. If you have a little flashing it counts too bringing the load to over 80 lbs. A 12x12 cope likely won't weigh close to 80 lbs. Now, if the cope starts to lift the extra metal trying to run out will add lift for every square inch it spreads and continue to float it.

 

So you also learned how little head you need to fill, and by providing more head you saved this casting but if everything had gone right you had excess head to give you more turbulence during initial pour. I'm thinking about putting my pouring basin well down into the cope (maybe a 1" tall sprue) to establish flow and fill the runners then let filling the basin provide the additional head to get to the top of the mold.

 

Not a bad idea. Did you mean well down into the drag? For me turbulence seems to be reduced by using a small runner and that allows relatively slow filling of my ten-pound mold. Takes about 12 to 15 seconds. That is through a 3/8" wide by 1/4" deep pinky-shaped carved runner that goes from the sprue 1" to a riser and then 1" to a gate. No problems with voids/shrink defects/pouring short/ cold shuts etc.
So I am not too inclined to mess with success on this particular pattern.

Denis

 

My runners are usually at the top of the drag. I'm thinking a 1" high sprue above the drag so I can cut a basin in the cope and still have 1/2" of sand for handling. I learned (from who knows where) to put a settling basin in the drag then cut the runners from the top of the settling basin. The free fall through a sprue to the basin gave a lot of mixing. Recently I've been trying the pouring basin with a weir into the sprue. (I know this is rehash), and the foam plug to make sure the sprue stays flooded. I'd like to get under 20 in/sec on initial runner filling and am realizing I can't do that with the 0.04 or 0.05 sq in runners, compared to your runners at maybe 0.07 sq in, if I'm dropping more than 2" down the sprue. Trying to get the sprue shorter in a 3" tall cope I was considering dropping the pour an inch farther into the basin and hope I can get the dross to float before going over the weir. It is just a lot of tradeoffs. For shallow castings I realize it is important for me to make shallow flasks.

It's foolhardy to change what is working. I make some trivets with gosh awful large sprue and runner but it's on a match plate and works well. May try a smaller sprue.

 

If I don't get it cast in the next few weeks, I am going to drop back and punt.

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I use steel moulding boxes made from 3mm (1/8") sheet, with steel locating dowels on the ends. When the cope and drag are assembled, a split-pin is inserted through a hole drilled just below the lower surface of the locating plate on the drag. This prevents the cope from lifting, but a weight or two is nice to use as well but not really needed on the small castings I make,

Cheers Charlie

 

If I used standard flask sizes, I think locking the cope to the drag would be a good idea (clamps on the side at the handles works too).

But I use custom wood snap flasks, and I don't pour with the flask in place, so I use a combination of furnace cement between the bound cope and drag, and some weights to help keep it all together.

Charlie - What are you castings? You got pictures?

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I only have the facilities to cast aluminium.

I still can't work out how to post pictures on this forum!

Cheers Charlie

 

If you have a picture on your computer resize it to 640x480. Then click the "Upload a File" button. Find the folder you have the picture in, select it and click open. Easiest method on the internet.

 

Thank you chaps! Absurdly simple with a little bit of coaching

Pat J, would you like a photo of the moulding boxes and locking pins?

Cheers Charlie