TECH: Make a Bellhousing out of an old Intake Manifold!!

Three words:

Oil Bonded Sand

 

I toured the foundry that casts my parts yesterday. They make it look SO easy. But in reality, it's not much more than Loudpedal has except bigger equipment. A messy job, but looks like FUN!

 

It is easy once you learn the skill. What is not seen here is the danger... like failure to heat a skimming iron up to drive off the moisture before you put it into the crucible, like charging a piece of scrap in to the crucible without preheat.. like not weighting or clamping the molds before pouring.. and the list goes on. Spilled aluminum shows no heat color (steel is red when hot). Hand burns are common until you learn "don't pick anything up off the floor in a foundry". The "hot foot" from stepping on a spill. A ball of molten aluminum will go right through a running shoe and half way through your foot before it stops because your blood cooled it down below 1100*F, and its still hot and you are trying to pull that shoe off knowing that there are more things hot in that area. BE CAREFUL!!!!!!!!!!!!!!! This is only 30 years in the foundry talking and I say this should not be looked at as easy but as something that should be approached in a well planed manner. Be very careful or you may end up making a ash out of yourself.

Regards
Greg Hornbostel

 

Man this is a really awesome thread. Very good info but I'd be hesitant to run a bellhousing I cast myself rather than an OE or better yet a Scattershield. I'd love to give it a shot on some less critical part though for sure.

 

One of the guys I talked to yesterday told me of the time he had a splash burn through his boot. He ran so fast into the pour room he didn't realize he was just sloshing the molten alum around inside his boot. He said he ripped the boot off so fast without even untying the laces.

 

That s why you are not supposed to lace the boots

 

well i tried a small pour with sandy clay wetted with used motor oil... smoked like a sonofabitch! but i had better results than sputtering splashing aluminum and a blown up mould.. but it's no where near the quality i want .. being poor as dirt leads to some true hands on learning.. gotta make EVERYTHING.. but it's worth it and i'm having fun.. also.. you all ought get leather blacksmith's aprons and make thin sheet steel covers for your boots .. so far both have saved me a TON of pain.

 

Bumping a great thread.

Also, I read somewhere that using 2 stroke oil to bond the sand will cure the smoke problem.

 

To make cores, I've been using a mix if sand and linseed oil, baked in the oven.
It works perfectly.

 

On something like a bell housing, or an intake, How do you factor in the shrinkage and build that into your pattern?

 

Just make the pattern bigger

 

Anyone else? I read somewhere else that your part for the mold should be 102% bigger then your final part. Any truth to this? I'm not real sure how to make sure they the piece is 102% bigger.
Thought about making a pattern and having it 3D scanned and scaled up, or drawing a 3D model and scaling it up, and then having it 3D printed. But there has to be a lower tech way.

 

Well. Just think about your question ...

The shrinkage for aluminium is 1/8 for one foot.
One foot is 12 inches, so 96 x 1/8.
A 96 x 1/8 part will skrink to 95.
So the pattern size has to be (100 x 96)/95 = 101,05 % bigger than the final part.
1/8 is approximative, it depend of the alloy.

When the final part is small, nobody cares about the difference.
Or casting is a bad choice of technology, and you'd better use a CNC machined part.
When the part is more than 1 foot, if the pattern is made of wood, like most of them, all you have to do is use a ruller and check the size.
There's no rocket science involved here.

 

A common standard for aluminum is .013" per inch per shrink. Shrink rates vary by type of metal (aluminum, bronze, steel, etc.) and also can vary within those families by alloy. What that means is that is you are making a pattern for a matchplate from which plates will then be made, then that is two shrinks (first one to make the matchplate and the second to make the parts) and you need to allow 0.026 per inch. Back in the day the (traditional) patternmakers used a "shrink rule" (http://www.freemansupply.com/starrettsteelshrin.htm) that has the shrink figured in so if you compared shrink rule at 10" to a regular scale it would actually measure out at 10.13". Does that help? Have you tried Google? (how to figure shrinkage for castings)

 

This thread got me into casting. Just some shift knobs and tag toppers but its fun.

 

Great reading your post is very interesting, thanks

 

I know it's not rocket science, but I'm thinking on something like an intake manifold, it's going to shrink in every dimension. Meaning that all your runners will shrink some throughout the length, etc.
I understand measuring the length slightly longer for it on a simple part like a bracket or something, but what about for every dimension? Am I over-thinking it?

 

Bump

 

When I have done a casting night with the buddies, we normally do a few pours. I have found that the propane bottle freezes and the pressure drops to unusable pressures. Any one have suggestions other than a torch? I was thinking of using a NOS bottle warmer.

 

Oil works with no smoke when the furnace is hot.

 

.... best sh#t ever. To the top !

 

IIRC, doesn't the rate of shrinkage also vary with the thickness of cross-section? It been 35 yrs since I have done this, but I seem to recall something like that from my days in machinist school...

 

http://www.mgprecision.com/resources/design-for-manufacturability-tips-for-die-cast-parts.html

 

i always wanted to try this and make a few small things. does it make much smell? im pretty close to my neighbours and i try not to do anything for them to complain about

 

Note that this article is for die casting which is different than sand casting. YMMV

 

Good point. I just vaguely remember that being mentioned when we did sand casting in our machinist training, but it was a LONG time ago, I could be getting it wrong. We poured and scraped babbit too, good course.

 

I cannot see the pictures. Are they still available somehow?

 

I would really like to see these pictures, but cannot. Have they been removed?

 

Photobucket third party warning?
Firefox and Chrome have add-ons that will allow you to see the pictures. Just need to add the add-on and then refresh the page. Instant pics.

 

Gosh, I used to teach sand casting in the foundry in high school metal shop.
We used Petrobond sand.
Funny how what was once taught is now so unique and popular.