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Medium and large engine blocks and crank cases?

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enginesrus

Mechanical
Aug 30, 2003
1,013
I've wondered why there are some manufactures using cast iron for the topic of this thread. Not so for larger engines but for medium speed ones. Since cast iron is so difficult to repair I personally don't see the logic other than maybe manufacturing cost, I know if I was in a position to purchase such engines I would take fabricated over cast iron every time. Can anyone spread more light on this?
 
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Cast iron (often ductile iron) is easy to cast and machine. It has good strength (and if austempered it can have great strength), good damping properties, and reasonable toughness.
I would prefer a DI part over a fabricated unit with welds in it any day.

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P.E. Metallurgy, Plymouth Tube
 
Cast iron is less expensive, and does the job just fine.

Whether or not something can be easily fixed after a catastrophic failure is rarely part of the design criteria for anything.
 
I guess you all haven't factored in the expense to replace a 2000 or 3000 ton engine, if it was made of cast iron and could not be easily fixed in place. Even a large medium speed engine like a PC 4.2 or something like that would be very costly. Fair Banks Morse seems to not prefer cast iron. I can see cast iron on a small automotive application and to keep costs down. I agree the qualities of cast iron is desirable until it has a crack or hole or worse yet catastrophic destruction of a good portion of the casting.

<Whether or not something can be easily fixed after a catastrophic failure is rarely part of the design criteria for anything. > I think the ship building and owning world has a different mentality than automotive when it comes to fixing things.
 
The very few times such a failure occurs doesn't weigh up to the costs of a welded crankcase compared to a cast-iron one. Yes, from a perspective of having to replace a complete engine, for which often a hole has to be cut in the hull and much more, a repairable engine makes more sense. But, damage to a cast iron case is often relates to a piston rod hammering through the side of the engine. The amount of secondary damage when this occurs in a welded crack case is also likely to be huge and may not be easy to repair on board (think crankshaft alignment)
 
enginesrus said:
I think the ship building and owning world has a different mentality than automotive when it comes to fixing things.

And this is based on......
 
The huge dollars needed to remove or purchase a brand new engine for one.
 
I suppose that would sum up everything in the world and in engineering.
 
I just need to add, we have insurance for this. The cost of replacement seldom comes directly out of pocket. It's the downtime that is more costly and that is a moot point as the time of line-boring a block in-situ after welding is similar to the time cost of cutting a hole in the side of the ship and slipping a new engine in.
 
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