Why do you use cast iron vs cheap mild steel?

[EmGo]

I've been building engines for sixty years and had a stint in a steel foundry and have never seen a steel engine block.

Ha ! gotcha ! (maybe). I'm pretty sure the 300 SLR block was steel. But I agree, that's cheating because it was a built-up weldment. Also radial engine cylinders were commonly steel, but for the reason you pointed out, strength. Come to think of it, there were some steel Dytch cylinders made for drag racing, again, strength. Liberty V8's ? Maybe those Junky aircraft diesels ?

 

[john.k]

Large diesels are often cast steel parts welded together .......steel is more costly to cast ,and in thin sections ,problematic due to high shrinkage rates. ..........big steel castings like railway bogie frames are often hollow inside ,which doesnt matter ,as they are plenty strong.

 

[Jaxian]

There is more to this than just cast iron vs steel. As Boslab alluded to there are LOTS of different flavors of cast iron. My Cincinnati Milling Machine catalog for the horizontal mills brags on using 14 !!! different grades of cast iron in one of their mills. I am guessing the cast for the table is not that same as the cast for the handles and so on. If I can ever find the text in my bazillion Cincinnati catalogs I will attach the relevant information.

 

[boslab]

Technically you could cast steel into an engine block quite easily, however due to the variable thicknesses present steel would naturally adopt different phases due to the time temperature transition graph, even annealing will result in different cooling rates, upper bainite here austinite there etc.
Cast doesn't have the same unless a chill is inserted to make cementite Fe3C harder than a ginger step mum
Hence cast iron is preferred, semi steel or malleable is a favourite compromise where machining is required ( malleable iron) shove some silicon in and the viscosity of molten iron is similar if not exactly the same as water.
Fills complex moulds with relative ease, old decorative castings are invariably high silicons ( hence wetting when brazing can be challenging)
All fun and games, I know 2 people who’s doctoral thesis were iron based, some tricky stuff in there.
Also as correctly stated previously the high stiffness of iron is great to damp vibration ( I was told it was to do with the free graphite trapped in the matrix, seems plausible)
Mark

 

[PackardV8]

Ha ! gotcha ! (maybe). I'm pretty sure the 300 SLR block was steel. But I agree, that's cheating because it was a built-up weldment. Also radial engine cylinders were commonly steel, but for the reason you pointed out, strength. Come to think of it, there were some steel Dytch cylinders made for drag racing, again, strength. Liberty V8's ? Maybe those Junky aircraft diesels ?

The 300 SLR has two four-cylinder banks made of silumin with chromium-coated aluminium cylinder sleeves; the heads are cast together with the cylinder banks (i. e. block and head are a single cast piece)

The production 300 SL used the same cast iron block as the 300 sedan.

The Liberty V12 did use steel cylinders.

The Liberty V12 proved a technological dead end for aircraft use and thousands of surplus engines were sold cheaply for use in boats, wind generators, et al.

jack vines

 

[EmGo]

The 300 SLR has two four-cylinder banks made of silumin with chromium-coated aluminium cylinder sleeves;

You lost me. The 300SLR is a straight eight.

he Liberty V12 did use steel cylinders.

So did the eight

Yes, they came as an eight cylinder engine also. I think even before the 12 ?

 

[PackardV8]

So did the eight

Yes, they came as an eight cylinder engine also. I think even before the 12 ?

The eight cylinder Liberty was a failed experiment. Fewer than ten test engines were built and only a couple installed in aircraft. There was little benefit over the twelve, so the eight never went into production.

jack vines

 

[DMF_TomB]

I've been making a lot of replacement parts for machine tools and can't help but notice that cast iron is often 50% more expensive than even commodity 1018/mild steel (and Durabar...whew $$). Putting aside large machine tool bases/foundations/columns...etc, various non-critical parts are often cast (gears, control arms, small parts) on older machines anyways. Typically cast is used because it "should" be cheaper. Do you guys pay up for cast just for its anti-vibration property or am I missing something? Maybe vintage manufacturers made small parts out of left over castings bits?

I use
Cast Iron grade A or grade 35 usually thinner than 1.5" (tensile strength is 35000 psi)
Cast Iron grade B or grade 40 usually thicker than 1.5"
Ductile Iron 65-45-12 (tensile - yield - ductile % elongation limit) usually >1.5" thick
Ductile iron 80-60-3, usually <1.5" thick
.
...... ductile iron is usually more expensive than cast iron grade A or B but stronger, tougher, etc
typically machine short chips with cast iron, with ductile iron short to medium length chips but
nothing like long chips with steel
.... a casting is cheaper cause a large 2 ton casting would be easily over 20 tons if a solid
block. small parts out of durabar ductile iron 65-45-12 the main advantage is less
warpage after machining. steel can be stress relieved before machining but durabar
is already in machinable condition
.... Part warpage can be .0003 per 40" (or less) with cast iron depending on part
with steel warpage >.0300 per 40" is often seen especially if not stress relieved before
machining
.
hit cast iron <3/4" thick on dirt ground with sledge hammer it breaks
hit 65-45-12 ductile iron and sledge hammer will bounce and good chance hammer
bounces back and hits you, quite a difference, might be called "ductile cast iron"
but quite different than grade A or B cast iron

 

[mhajicek]

I've used ductile cast iron for fixture bases, with hardened steel inserts for holding the parts. Don't know if it helped vibrations or not, since I didn't do an A/B comparison.

 

[DMF_TomB]

I've used ductile cast iron for fixture bases, with hardened steel inserts for holding the parts. Don't know if it helped vibrations or not, since I didn't do an A/B comparison.

.
some steel parts cause tougher stronger are made thinner. cast iron cause it is not as
strong or tough parts are often made much much thicker than a steel part, it's the weight and
mass that helps
.
from experience when cast iron is less than .75" thick and especially <.5" thick it
will vibrate from machining. I have seen facemills leave a mirror finish doing 40" per
minute feed on 1.5" thick parts but on thinner sections can easily get vibration even at
15" per minute feed
.
ductile cast iron 65-45-12 some call semi steel. but take a bench vise. a cast iron vise
35,000 psi tensile strength can easily break hitting a part in a bench vise. a ductile cast iron
65-45-12 bench vise can easily be 200% more expensive but 10x less likely to break
so easily as cast iron vise, 35,000 psi cast iron sometimes called 35-35-0 which I believe means
it doesn't stretch elongate its ductility is 0 it snaps first usually before elongating even 1%

 

[mhajicek]

from experience when cast iron is less than .75" thick and especially <.5" thick it
will vibrate from machining. I have seen facemills leave a mirror finish doing 40" per
minute feed on 1.5" thick parts but on thinner sections can easily get vibration even at
15" per minute feed

 

[EmGo]

The eight cylinder Liberty was a failed experiment. Fewer than ten test engines were built and only a couple installed in aircraft. There was little benefit over the twelve, so the eight never went into production.

This is backwards. They built the eight first and it worked okay so they went ahead with the twelve.

Designed the engine in 5 days, built the first test engines (V8's) in two months, then the first 12 came along a month later, since the design was modular.

A V-twin would be kinda cool on the front of a tricycle-car.

 

[???]

from experience when cast iron is less than .75" thick and especially <.5" thick it
will vibrate from machining

A lot of cast iron machining is done with wiper inserts in the auto industry. Not really good on the thinner stuff.

 

[PackardV8]

This is backwards. They built the eight first and it worked okay so they went ahead with the twelve.

The Liberty's purpose was American mass production of standard units when the U.S. entered World War I. Co-designed in a week in mid-1917 by Jesse Vincent of Packard Motor Car and Elbert Hall of Hall-Scott Motor Car, with a planned series of 4-, 6-, 8-, and 12-cylinder models, Fifteen L-8 prototypes were manufactured as the first Liberty engine. However, power requirements made the L-8 obsolete before entering service and only the twelve-cylinder Liberty was then built.

jack vines