Foundries

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

time for a moan to take me mind off things.

Foundries are where metal castings are produced. Castings like engine blocks, heads, manifolds, pumps etc.

Foundries used to have a lot of black art methods which got results, these black art methods died out and as a result we have to rely on science to do the job.

Now this is perfectly plausable as if you can do a good casting once you can do it twice, ten times or a million times if you understand and know what the right combination was.

Sadly due to various reasons this is rarely executed.

As a fiddler of castings I see all sorts of crap castings. Headwork I need to fight with these issues.

The main problems are core shift and insufficient saturation leading to pockets (even sand pockets).

How are things cast? Well a sand and resin mix are made into moulds of a specific shape and put together like a jigsaw. If you look at the combustion chamber of a 16V head the dimple is where the hole for the sand/resin mix was poured into the mould.

Molten MAGMA

or cast iron/aluminium is then poured in.

When its poured in thats a gravity fed cast, there are methods that include pumping it in from underneath etc, pumping is better than gravity as it tends to make for a thicker, denser casting with less air pockets etc.

When the dies are not held properly you get core shift, the molten metal nudges them slightly and sends things askew.

When the metals poured and its cooled the dies are then broken, the sand then comes out. The sand can and does get stuck so it should be thoroughly flushed.

Now depending on how competant the foundry is there might be a lot of sand etc stuck or there may be none.

Really good foundries can cast with an accuracy that requires almosy no machinining, others on the other hand need millimetres machined off to get the items even close.

Renault use poor foundries.

Cosworth have their own and its excellent. They made their own due to the crapness of their outside foundry (motor and aero castings in the midlands). A coscast head is prettyy much ready to go straight from the foundry.

Anyway end result is the blocks, heads etc are of an unknown quantity. Also when the heads been ported right some ports may not look pretty, they may even look stock, this is bacause in that place the material is needed, removing it to smooth things is detrimental to efficiency. So if you see a head thats all super bling shiny chances are its a pretty job, not a proper job (especially on the inlet side).

Machining is another area which is again crap. Main issues are things not being milled accuractly.

Some places chuck the head on the floor then throw it on the bed, clamp it down then mill it.

The heads never going to be flat as they never clamp it evenly. So theres an issue, so they mill a bit more off to get it flat.

Accuracy very poor.

Also the machinery, a nice new machine is all very well, but give me an old one. A bed thats shifted about for 560 years has stopped shifting, its not 'seasoned' thus its not going to alter. A new machine has a lot of wiggling still to go.

Anyway bored now, breakfast time.

Site Subscriber Joined: 11 Feb 2005 Posts: 2929

Good stuff mate, very interesting.

Site Subscriber Joined: 28 Jan 2005 Posts: 3547

Aye, im alot more knowedgeable now from what i have read by Chris! Very Happy

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

As someone who has spent a couple of years full time as a machinist Iâ€™m going to cause a stir and disagree about the milling machine comments. Just like cars, maintenance plays a part, but wear is wear (usually uneven), backlash is backlash and newer machines are generally more accurate. In my experience, that is.

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

new tooling on an old bed is more than acceptable, a crucial point I left out.

The best tools are always converted ones anyway.

A between centres jig, for example, removes any guesswork but normally means adaptation of the other machines, machining a complex casting like a head for exampel will always benefit from this, ensures a nice even milling of the valve spring seats below the deck hieght for example.

Thats a real issue btw, a lot of engines have to say they are better these days, one end the nose pressure on the cam is totally different from 1 end to the other.

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

Also, I went to visit a foundry at Maycast Nokes a couple of months back for work, amazing stuff. Saw a HUGE cylinder head that had been broken out of the sand, was about 5 foot long for some massive truck diesel engine or something.

The investment casting process is very interesting as well, can get very fine tolerances with that. They were making, amongst other things, some nice helicopter gearbox housings by that method.

This place: www.maycast.co.uk

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

what sand do they use? Zircon sand is the sand to use btw.

Aero parts are always made in pretty much every foundry.

The old gemini choppers used abotu 5 different foundries for intakes, boxes, etc etc

Forum Moderator Joined: 18 Feb 2004 Posts: 7432

Chris H wrote:

new tooling on an old bed is more than acceptable, a crucial point I left out.

what do you mean by that?

Chris H wrote:

The best tools are always converted ones anyway.

And that?

Chris H wrote:

A between centres jig, for example, removes any guesswork but normally means adaptation of the other machines, machining a complex casting like a head for exampel will always benefit from this, ensures a nice even milling of the valve spring seats below the deck hieght for example.

How does a between centres jig relate to adapting machines, or machining a cylinder head?

Forum Moderator Joined: 02 Mar 2004 Posts: 19978

an old bed has moved about and is now settled, new beds warp as they settle.

old tooling using new bits for accuracy.

many machines are not compatable, or they never used to with one another.

So 1 machine you had 1 jig then another you used a different jig, after unclamping the first.