Hot Rods Aluminum casting Guys

Hi Guys, I would like to try to do some casting of aluminum, can anyone tell me how much aluminum shrinks during the cooling stage, I will try to compensate during the mold building stage. or is it worth it ?....Thanks...Mike

 

I build patterns to 102% of final part size.

 

Lots of info. here.
https://www.google.com/search?q=how...e..69i57j0.10558j0j4&sourceid=chrome&ie=UTF-8

 

I agree with Alchemy 102%

 

My grandpa was a pattern maker and had special rulers and calipers scaled on the shrinkage of different metals. Took the math out of every pattern measurement, but you had better not mix them up or use them for some other purpose.

 

Rulers are called Shrink rules. I have several that I no longer use. I worked in a pattern shop for 35 years. Most of our work went by 1/8" shrink per foot.

 

Don't forget that all the surfaces need draft angle on them all to help release from the core box.

 

Make your own scales. Set a nice ruler on the copier, and bump up the percentage to 102%. Then have it laminated. Cost under a dollar. But make sure to write on it very clearly that it's 102%!

 

The “Aluminum Association” has a book named “Standards for Aluminum Sand and Permanent Mold Castings” that has a lot of information about castings including draft angles, shrinkage, alloys, standards, etc. that would be very helpful information. Not sure if it is online or only available as the paperback shown below. Might try doing a Google search or contact the Aluminum Association to see if it is still available.



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Thanks Guys

 

There was a good series of books years ago by David Gingerly. “The Charcoal Foundry” has lots of good info.

 

Make a rod for a pattern a foot (or other known length) long.
Use the rod to make the sand mold.
Make a casting using the metal that you are planning to use.
Measure the casting and figure the amount of shrink.
Takes all of the guesswork out of it.

 

First copy the ruler at 100% to make sure the copier is accurate. Years ago when I was teaching wood shop I had to teach them how to read a ruler. The copier would distort the line lengths I had drawn on the work sheets for the students to measure. I had to copy the ruler too so the worksheet lines and the copied ruler had the same distortion.

Now a couple of questions. If you cast aluminum around an iron object, does it shrink away from the object or shrink tighter against it? Would chilling the object help the casting to fit tight to the object?

 

Casting iron/steel insets into aluminum castings is quite common however rarely is a metallurgical bond achieved. Typically a mechanical bond is achieved and usually with the aid of the iron/steel being prepared with grooves, splines irregular surfaces or heavy grit blasting. When the aluminum is poured into the mold it fills the grooves, splines, etc. to lock the insert into the cast aluminum. This is a mechanical bond and if the casting is sectioned/cut up the aluminum can be separated from the iron/steel fairy easy. The shrinking of the aluminum enhances the mechanical bond.

A metallurgical bond can be achieved between aluminum and iron/steel but it is more involved. Pistons often have a cast iron ring land cast into them that is a metallurgical bond.This is achieved using the Al-Fin process in which the iron insert is dipped in pure aluminum just prior to being cast with the aluminum. There are some other processes using aluminum enhanced with other chemical elements to form a soluble alloys which will metallurgically bond to iron/steel.

Usually if iron/steel is chilled it has the opposite effect and the molten aluminum will form a solidified skin next to the iron/steel insert resulting in the aluminum not flowing around the insert and no mechanical bond will be achieved.

 

Can you share with us what you are trying to cast? It would be more helpful in understanding what the complexity/potential issues you may have with your design.

 

Man that was was quick and to the point. This place amazes me.

 

I want to build an intake to fit on top of a 671 blower with 4/6 Rochester 2bbl carbs

 

Now THAT is ambitious.

 

Years ago a HAMB'r did a very detailed writ eup on home casting some aluminum valve covers. He made a wood buck and then made the sand casting box and then cast them. He talked about shrinkage. It was a pretty amazing thread.

EDIT: holy cow I found it. if the pics don't show up, hit reply and you will be able to see them in the reply.

https://www.jalopyjournal.com/forum...lhead-valve-covers.142941/page-2#post-1593073

 

@bonehead thank you for starting this thread. I’ve had casting on my bucket list of things I want to learn and try but haven’t had the time to sit down and start the research. This has definitely inspired me. And thank you to all the brilliant member’s replying. Keep it coming.


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