Author Topic: Some sand casting efforts  (Read 911 times)

Offline Dick Morris

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Some sand casting efforts
« on: June 04, 2023, 07:08:52 AM »
Various parts I made a few years ago. This was before I was doing investment casting.

The pedestals were cast in ZA-27. It casts at about 750 degrees and casts and machines very nicely. It is supposed to have a tensile strength similar to cast iron. It's also supposed to be a good material for bearings. ZA-8, ZA-12, and ZA-27 are all suitable for sand casting. I used ZA-27 because it was available as an ingot of known quality. A problem with using unknown scrap is that trace amounts of lead will result in corrosion cracking. These alloys are mostly zinc with the number indicating the amount of aluminum in them. I used a SS pan and a couple of propane torches to melt it.
 
A master pattern was made in wood, a silicone mold was made, then a casting pattern was made in two-part urethane. There are actually a couple of variations on the pattern, I added the railroad's name on one. The plaque for the RR name was made using photo etching. (The resist was printed on a laser printer on a shiny magazine page and and transferred to the brass with an iron.) Today I would have 3D printed the plaque.
The journal that fits into the pedestal was also sand cast in ZA-27 and had a core to hollow the bearing area to decrease the amount of material needed and lessen the amount of shrinkage.

I usually prefer using split patterns on pattern boards. They are more work to make, but easier and more accurate to mold and cast. There are photos of the two sides of the pattern, the silicone mold I used to make the core, and a core. I think I used plaster of Paris for the core. I was able to use PoP because of the ZA-27's low melting temperature.

The small washers were cast in aluminum.

I use Petrobond sand for all of my sand casting. 



« Last Edit: June 04, 2023, 07:12:21 AM by Dick Morris »

Offline A7er

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Re: Some sand casting efforts
« Reply #1 on: June 04, 2023, 08:51:35 AM »
That is a very similar process to one I have been thinking about, mainly, would it work? You have shown me that it would work so I feel more confident about trying it. The main difference is that instead of using the silicone to make a two piece urethane pattern, I would use a two piece silicone mould to produce a one piece wax pattern. After cleaning any flash or defects in the wax, I would then cover the wax with investment to make a mould, burn out the wax, and pour metal in. This process is mainly for small pieces, about the same size as a matchbox. But, I wonder if it could be used for say, a small ohv cylinder head 60mm dia by 35mm deep, with a water jacket?

Thanks for posting this, those parts turned out great.

Offline Dick Morris

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Re: Some sand casting efforts
« Reply #2 on: June 04, 2023, 11:21:34 AM »
A7er - I started two threads, this one for sand casting and another for investment casting. What you are interested in falls under investment casting. Although I have a wax injector and some of the proper wax, I don't think I've ever actually cast anything using wax.

Offline A7er

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Re: Some sand casting efforts
« Reply #3 on: June 04, 2023, 05:17:50 PM »
I am watching both threads!

Offline Dick Morris

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Re: Some sand casting efforts
« Reply #4 on: June 05, 2023, 06:55:45 AM »
Another project. This one was for the full-sized locomotive. It's a 3" diameter twist lock electrical plug for the 32vdc in the cab that probably hasn't been available commercially for 60+ years. There were no drawings so I only had an original plug, lower right, to replicate and had a socket to check the fit.

The original used die cast aluminum for the body and cast iron for the nut to retain the cable. I sand casted the body and machined the nut from a chunk of bronze that I casted. I initially tried to use the original body as a pattern but it had almost no draft. Plan B was to draw and 3D print the pattern. The contacts in the original were bent from 16 gauge brass. I decided it would be a lot easier to investment cast them from bronze. The grey insulator was Bakelite in the original. I 3D printed it in a resin that was stronger and would withstand a higher temperature than generic resin. The body required some lathe work to open up the interior back/inside as I had to use quite a bit of draft to get the pattern to pull cleanly. The slots on the sides were done on the mill with the casting mounted on a spin indexer. I made three of four of these.

Offline Admiral_dk

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Re: Some sand casting efforts
« Reply #5 on: June 05, 2023, 10:45:23 AM »
Nice reproduction  :ThumbsUp:

Per           :cheers:

Offline PJPickard

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Re: Some sand casting efforts
« Reply #6 on: June 05, 2023, 11:16:55 AM »
Nice work! What is your source for the ZA-27?

Offline Dick Morris

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Re: Some sand casting efforts
« Reply #7 on: June 05, 2023, 03:05:31 PM »
I got the ZA-27 many years ago at Budget Casting Supply.

Offline bent

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Re: Some sand casting efforts
« Reply #8 on: June 05, 2023, 07:14:30 PM »
Very cool.  Taking notes and  :popcorn:

Offline petertha

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Re: Some sand casting efforts
« Reply #9 on: June 05, 2023, 07:24:41 PM »
I know this might be a broad question, but when you cast ZA-27 purchased new, does it mitigate some of the other necessary additives I hear about when people are using recycled aluminum stock for impurities, degassing, flux...? (sorry I'm not up to speed on casting but getting more interested as I see these nice parts). Also, any comments if this material is within the domain of some of the smaller electric forges?

Offline A7er

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Re: Some sand casting efforts
« Reply #10 on: June 05, 2023, 07:53:46 PM »
petertha.
My home made electric foundry running on UK power, is capable of reaching 1000C. I haven't had it that high, but in theory, it should. I wound the elements myself, and it consumes about 1.5kw. The next time I make new elements I will take it up to 2kw, just to melt the metal quicker. Or I might make a new one and make it bigger. It will take a crucible 180mm high by 100mm dia. That's a bit small, but big enough for what I do.
Have a look at the electric foundry Myfordboy uses. Very neat.

 

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