Thread: Casting about for cast iron casting ideas

If anyone has a sketch of a straight edge I could probably get some made here in Sydney.I could machine a 36" on the Bridgeport and perhaps get it ground, I know MTA have the facillities to grind them. Thoughts?

Well a handy foundry item seems to be popular....

I had no idea what these sorts of things were worth.. But they seem to be worth a bit, as well the bidder location are not exactly what you would call prime foundry locations

Metal Analyser, Spectro Model Spectromaxx Type LMF04, S/No. 4R0109 with The Auction (0641-5002737) | GraysOnline Australia

Originally Posted by Swarfmaker1

If anyone has a sketch of a straight edge I could probably get some made here in Sydney.I could machine a 36" on the Bridgeport and perhaps get it ground, I know MTA have the facillities to grind them. Thoughts?

Here's a photo of something similar to what I'm planning:
You'll most likely have to make your patterns yourself as that is the most expensive part of the casting process to have made for you.



RC, I can't say for sure but I understand such things have come down a fair bit in price as modern electronics has made small compact units practical such as those metal analysers the American scrap dealers all seem to use.

Quite a neat looking bit of gear Mark. No more than it needs to be.

Carpets a nice touch.

Originally Posted by Anorak Bob

Quite a neat looking bit of gear Mark. No more than it needs to be.

Carpets a nice touch.

Sorry Bob, that's some guy's shed in the States. I did however score a load of non slip red rubber floor tiles 1200 square in size for my floor.

Originally Posted by Graziano

Here's a photo of something similar to what I'm planning:
You'll most likely have to make your patterns yourself as that is the most expensive part of the casting process to have made for you.

does anyone know the shrinkage factor for the metal you're planning to use?

Originally Posted by ian

does anyone know the shrinkage factor for the metal you're planning to use?

Nope....but I know people who do. I was just going to borrow an iron shrinkage ruler for the pattern and put fat runners on it and see how it goes. If it fails, then modify the pattern to suit and try again.

Good luck with the shrinkage ruler.
I think many were tossed into long term storage when pocket calculators arrived.
One standard ruler, a table of shrinkage factors and a calculator, and a patternmaker was right to go.

Searching for 'casting metal shrinkage" gave up this (among others)
Sand Casting: Allowance
Usually a reputable source.
Really for what you are doing though it should not matter as any straight edge you make will be complete as it is. I'd be more worried about shrinkage if you were trying to make a part that had to fit/ match something else already made.

Michael

Originally Posted by Michael G

Searching for 'casting metal shrinkage" gave up this (among others)
Sand Casting: Allowance
Usually a reputable source.
Really for what you are doing though it should not matter as any straight edge you make will be complete as it is. I'd be more worried about shrinkage if you were trying to make a part that had to fit/ match something else already made.

Michael

I agree, it's about 0.8-1% for thermal shrinkage. I was more worried about solidification shrinkage which is another thing entirely from the thermal shrinkage. Bronze and aluminium (4.9 and 6.6.%) need a runner that solidifies last to keep feeding the casting as it shrinks and solidifies. Iron can shrink and even expand depending on the type of iron: +5.5 to -4.5%.

Either way a generous runner/feeder that's not completely filled up should do the trick for the first go-around.

Originally Posted by Michael G

Searching for 'casting metal shrinkage" gave up this (among others)
Sand Casting: Allowance
Usually a reputable source.
Really for what you are doing though it should not matter as any straight edge you make will be complete as it is. I'd be more worried about shrinkage if you were trying to make a part that had to fit/ match something else already made.

Michael

Michael, where I'd be worried is making the web section of the mold too thin for the molten metal to flow into them without risking cavities and the like.

I suspect that the web section on some straight edges is around the thinest possible without experiencing casting failures.
Which suggests that making a sand mold from an existing straight edge could be problematic

Hi,
Just thought i'd thow another idea in to the mix for one offs or even the straight edge's. I have been doing a bit of research into lost foam and have read it works with iron as well as ally and copper alloys. Using foam means any number of angles, lightening holes etc can be cast in with no fear of mold damage when removing the pattern. And really, how hard would it be to bust out a series of straight items in foam?

Ewan

Sometimes I look at the product of Victorian Foundrymen and am amazed at the thinness of the sections they have achieved and the length of the runs they could get metal to flow. This all without digital thermometers and thermostatically controlled furnaces.
While geometry of sections is something to consider, I think that there is a lot in the casting process that is art rather than formal smarts - that is, there is a balance between the mechanism of making a cavity and pouring metal into it and 'knowing' the right moment to pour, what temperature the metal should be at, how much in the way of additives are needed in the melt and even preparing the mould prior to pouring.
In a way it's sad that we (as a society) are not prepared to reward excellence in trades as much as we seem to reward say marketing skills or those of a financial trader. I know which occupation I regard as more useful...

Back to the issue at hand -
Lost foam works by the metal melting/ burning the foam when it is poured, so there is no reason that it shouldn't work for almost any casting process. The smell is something awful but like the foam that's a one off too. The foam model has to be a perfect shape though as anywhere there is not foam there will be sand and so metal won't get there. This means you have to have all the chamfers, fillets and blends right on the model for example

I once took a 28" camel back I have to a foundry and asked if they could use it as a pattern to make a copy. It had 1/4" webs and all sorts on it. The answer was yes, but it would cost, mainly because of the difficulty of using it as a pattern - no draft on the working edge, no where to hang onto it to pull it out, dags on the original casting that had not been fettled of when new and the list went on.

Michael

The inlet manifold on my car looks like it's cast with styrofoam as the resulting manifold has that foam texture, it actually looks like it's styrofoam painted grey. I can see for production work of complicated shapes it would work well.

For a straight edge a normal wood pattern for the straight edge would do the job, there's nothing complicated about the shape of it that would require lost styrofoam. I suppose if I wanted to add an undercut areas to the top and bottom of the straight edge I could insert a strip of foam (to the pattern before moulding the sand).

The resin bonded sand is fairly strong mechanically, it allows patterns with fairly thin sections to be moulded easily without bits breaking off. After casting the resin bonding breaks down with the heat after the metal has solidified which makes cleaning the casting a lot easier than digging solid chunks of sand out.

You can see the resin has let go round the edges of the bronze and gone white and crumbly.



In this photo, the aluminium hasn't heated the sand enough for it to crumble and it has to be dug out mechanically.

Greetings Chaps The shrinkage for ordinary cast iron is 100 thou per foot. Allow for this plus a healthy amount for machining and you are OK. Instead of Cast Iron I w0ould think about SG Iron This is substantialy stronger than cast iron and machines more like steel. If you are using a foundry let them cut the ingates and runner bars. I read some where on this forum That you should cut ingates as big as possible. This is not right A large ingate takes longer to solidify and could suck metal from the main Casting. The comment about concern that the thickness web on the straight might not run is also inaccurate, Iron runs like water and if it is poured at the correct temperature it will fill the cavity. The only thing I would suggest is a series of risers from the bottom part of the mould to allow the iron to flow through. A split pattern would be advisable on this case. If the mould is vented properly then it should pour and run correctly. I made Parallel Strips 4 inches high and 2 inches wide without any problems. Happy days Yours 4-6-4