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Radials have an aluminium crankcase, steel cylinder barrels, and aluminium heads.Modern (for WWII) liquid cooled engines, like a Merlin, used aluminum crankcases and cylinder blocks (with steel sleeves). Something like an R-2800, will have steel cylinders (with aluminum bands) to better handle the increased cylinder head temperature of the air cooled engine. My understanding is that the crankcase will also be steel, but perhaps I am mistaken
Eh?Cast Iron isnt cast aluminium. Heat treated cast iron isnt cast iron it is iron normalised, stress relieved or whatever.
I responded to your post discussing cast Iron and now you are discussing cast aluminium. How can you call cementite "not metal" Steel is also an alloy of Iron and Carbon. Martensite is a super saturated solution of carbon in steel, it has very little carbon but that small amount makes it very hard.Eh?
Cast aluminium is cast aluminium. According to my metallurgy textbook, cast iron is anywhere between 2 and 6.67% carbon. 6.67% carbon makes it a mineral called cementite Fe3C, not a metal at all. Apparently, 2.5 to 4% is normal. They don't heat treat it for higher strength. They might anneal it to relieve stresses.
We were discussing cast iron versus aluminium engine blocks. For the record, my metallurgy text is Introduction to Physical Metallurgy, Second Edition, by Sydney H. Avner, professor at New York City Community College. I took this stuff in college.I responded to your post discussing cast Iron and now you are discussing cast aluminium. How can you call cementite "not metal" Steel is also an alloy of Iron and Carbon. Martensite is a super saturated solution of carbon in steel, it has very little carbon but that small amount makes it very hard.
The post I referred to you were discussing converting cast iron to aluminium based on yield strength, cast Irons dont have a yield strength. All Irons and steels have carbon in them as part of the production process and because carbon as an alloying element allows a massive range of properties. If you are arguing that cementite is not metal, you are arguing that steel is not metal either. In fact that has some scientific truth because they are all alloys. The problem comes from the names of all these things being given before the science. You need to already be very good at making things out of steel before you can make a tensile testing machine, tensile testing didnt become common until about 60 years after the first steam locomotive ran. The rest of your post is what I did in my first weeks at Longlands college Middlesbrough, training as a metallurgist. BTW arcraft are generally not made of Aluminium they are made of duralumin, an alloy of aluinium and copper (plus others). The USA and Germany used almost identical dural alloys, the British slightly different.We were discussing cast iron versus aluminium engine blocks. For the record, my metallurgy text is Introduction to Physical Metallurgy, Second Edition, by Sydney H. Avner, professor at New York City Community College. I took this stuff in college.
Martensite is defined as a supersaturated solid solution of carbon trapped in a body centred tetragonal structure. It is the product of extreme heat treating. Carbon makes it harder. Steel alloys normally are below 1% cargon. At high temperature, iron's molecular structure is body centred cubic (austenite). At room temperature, it normally is face centred cubic (ferrite). These phase changes are what makes it heat treatable.
Cementite is not metal. It is a mineral. The molecule is three iron atoms and one carbon atom. Look up the densities and do the arithmetic.
When discussing strength are you discussing yield strength or ultimate tensile strength, most cast irons dont have a yield strength unless produced to have one like ductile cast iron and malleable cast iron. The cast irons used typically dont have a yield or elongation value, table below from wiki.The R-2800, at least "The crankcase is composed of three forged aluminum alloy sections held together by through bolts. The nose section houses the reduction gears and torquemeter and has provisions for a full-feathering;, reversible propeller governor" (P&W R-2800).
(emphasis theirs)
Depending on alloy and processing, the strength of cast iron is 295 to 580 MPa. Aluminum, depending on alloy, can be up to 640 MPa. Engine blocks are probably more stiffness-dominated than strength-dominated structures, and stiffness in a complex structure is at least as much a function of geometry as elastic modulus.
Name | Nominal composition [% by weight] | Form and condition | Yield strength [ksi (0.2% offset)] | Tensile strength [ksi] | Elongation [%] | Hardness [Brinell scale] | Uses |
---|---|---|---|---|---|---|---|
Grey cast iron (ASTM A48) | C 3.4, Si 1.8, Mn 0.5 | Cast | — | 50 | 0.5 | 260 | Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases |
White cast iron | C 3.4, Si 0.7, Mn 0.6 | Cast (as cast) | — | 25 | 0 | 450 | Bearing surfaces |
Malleable iron (ASTM A47) | C 2.5, Si 1.0, Mn 0.55 | Cast (annealed) | 33 | 52 | 12 | 130 | Axle bearings, track wheels, automotive crankshafts |
Ductile or nodular iron | C 3.4, P 0.1, Mn 0.4, Ni 1.0, Mg 0.06 | Cast | 53 | 70 | 18 | 170 | Gears, camshafts, crankshafts |
Ductile or nodular iron (ASTM A339) | — | Cast (quench tempered) | 108 | 135 | 5 | 310 | — |
Ni-hard type 2 | C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0 | Sand-cast | — | 55 | — | 550 | High strength applications |
Ni-resist type 2 | C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5 | Cast | — | 27 | 2 | 140 | Resistance to heat and corrosion |
UTS. Of course, yield is going to be used for design against operational loads if the structure's design is strength limited. I suspect that crankcase design is more constrained by the need to limit deflections, for example of the main bearings, and production technology than tensile strength. Either cast iron or aluminum blocks are likely operating far below yield strength.When discussing strength are you discussing yield strength or ultimate tensile strength, most cast irons dont have a yield strength unless produced to have one like ductile cast iron and malleable cast iron. The cast irons used typically dont have a yield or elongation value, table below from wiki.
Comparative qualities of cast irons[9]
Name Nominal composition [% by weight] Form and condition Yield strength [ksi (0.2% offset)] Tensile strength [ksi] Elongation [%] Hardness [Brinell scale] Uses Grey cast iron (ASTM A48) C 3.4, Si 1.8, Mn 0.5 Cast — 50 0.5 260 Engine cylinder blocks, flywheels, gearbox cases, machine-tool bases White cast iron C 3.4, Si 0.7, Mn 0.6 Cast (as cast) — 25 0 450 Bearing surfaces Malleable iron (ASTM A47) C 2.5, Si 1.0, Mn 0.55 Cast (annealed) 33 52 12 130 Axle bearings, track wheels, automotive crankshafts Ductile or nodular iron C 3.4, P 0.1, Mn 0.4, Ni 1.0, Mg 0.06 Cast 53 70 18 170 Gears, camshafts, crankshafts Ductile or nodular iron (ASTM A339) — Cast (quench tempered) 108 135 5 310 — Ni-hard type 2 C 2.7, Si 0.6, Mn 0.5, Ni 4.5, Cr 2.0 Sand-cast — 55 — 550 High strength applications Ni-resist type 2 C 3.0, Si 2.0, Mn 1.0, Ni 20.0, Cr 2.5 Cast — 27 2 140 Resistance to heat and corrosion
Last I knew, it was pretty universal in helicopter transmissions and gearbox housings. It was also used in the compressor housing of the T-55, T-53, and ALF502 engines and the fan case for the 502, at least until the USAF got pissy about magnesium-based alloys.I understand that Magnesium alloy was investigated for crankcase components as well. Not sure if it made it into production though. I do know some modern turbo-prop engines use it in cases.
HiI understand that Magnesium alloy was investigated for crankcase components as well. Not sure if it made it into production though. I do know some modern turbo-prop engines use it in cases.
Any idea why BMW would build the case out of steel, rather than aluminum? Maybe Aluminum was considered more of a strategic resource?The R2800 is aluminium, in terms of mass produced engine only the BMW801 had ferrous crankcases, and they were
most certainly NOT cast iron, but forged steel.
Sadly I dont have enough BMW records to have the conference meeting minuites where you might actually find that out.Any idea why BMW would build the case out of steel, rather than aluminum? Maybe Aluminum was considered more of a strategic resource?
Modern (for WWII) liquid cooled engines, like a Merlin, used aluminum crankcases and cylinder blocks (with steel sleeves). Something like an R-2800, will have steel cylinders (with aluminum bands) to better handle the increased cylinder head temperature of the air cooled engine. My understanding is that the crankcase will also be steel, but perhaps I am mistaken
In the US SOME of the Wright R-1820's and R-2600's (and maybe R-3350's?? - I never worked on one of those) had FORGED steel crankcases - everything else was alloy.
DeHavilland used magnesium in the Gipsy Major series of engines, and I understand in the Gipsy Queen and six series as well. The top cover and rear case was Mg.All the Brit engines I have worked on used Al alloy for the main castings though some apparently used magnesium.