[Schurkey]

Originally Posted by steve25

When you read up on the arc melting process just like what’s stated in the video it produces a cleaner iron with less impurities then the old crucible method at the get go.

Agreed.

Originally Posted by steve25

So does this not make for a better cast iron?

The melting process is better. The iron and resulting castings may--or may not--be better, due to any one or a combination of the hundred things involved in producing cast-iron parts.

A few variables:
What alloy agents are intentionally mixed-in with the iron, and in what percentages? Are the alloy materials consistent?
What elements/impurities are unintentionally or negligently mixed-in with the iron, and in what amounts? Are these impurities consistent, or random?
How hot is the iron when poured into the mold?
How fast is the casting allowed to cool?

Originally Posted by steve25

My main reason for this post was to see if for instance the change over to the electro arc method may have came about at the same time in 55 with the first V8s showing up, or if it was later.

Or earlier.

Given the amount of iron that GM would melt and pour, it wouldn't surprise me to find that arc melting went WAY back. And it may be much like "powdered-metal, cracked-cap, near-net shape" connecting rods. Sounds all modern and improved...until you discover the REAL reason for powdered-metal, cracked-cap, near-net shaped rods is that they cost MUCH less to produce in quantity than old-style forged (or cast) and machined rods and caps. I bet if the volume is high enough, arc-melted iron costs less than crucible-melted iron.

[hurryinhoosier62]

Originally Posted by Schurkey

Agreed.


The melting process is better. The iron and resulting castings may--or may not--be better, due to any one or a combination of the hundred things involved in producing cast-iron parts.

A few variables:
What alloy agents are intentionally mixed-in with the iron, and in what percentages? Are the alloy materials consistent?
What elements/impurities are unintentionally or negligently mixed-in with the iron, and in what amounts? Are these impurities consistent, or random?
How hot is the iron when poured into the mold?
How fast is the casting allowed to cool?


Or earlier.

Given the amount of iron that GM would melt and pour, it wouldn't surprise me to find that arc melting went WAY back. And it may be much like "powdered-metal, cracked-cap, near-net shape" connecting rods. Sounds all modern and improved...until you discover the REAL reason for powdered-metal, cracked-cap, near-net shaped rods is that they cost MUCH less to produce in quantity than old-style forged (or cast) and machined rods and caps. I bet if the volume is high enough, arc-melted iron costs less than crucible-melted iron.

Looks like GM first started using arc melt furnaces for cast iron after WW2.

[Shiny]

Originally Posted by Schurkey

The melting process is better. The iron and resulting castings may--or may not--be better, due to any one or a combination of the hundred things involved in producing cast-iron parts.

A few variables:
What alloy agents are intentionally mixed-in with the iron, and in what percentages? Are the alloy materials consistent?
What elements/impurities are unintentionally or negligently mixed-in with the iron, and in what amounts? Are these impurities consistent, or random?
How hot is the iron when poured into the mold?
How fast is the casting allowed to cool?

This seems a good summary of the complexity. Begs the question of "what is better", which also requires defining what's important to the application to answer.

The topic of differences between arc and crucible melting, specifically for cast iron, is interesting to me, but as Shurkey alludes, it's hard to know if the finished product performance improved or if the melting process is more about manufacturing cost than product performance.

What impurities are reduced by arc melting and how do they affect the properties of the casting? How do those properties affect the performance of the cast part?

In general, I'm asking what is the definition of "better" for a finished cast iron block or head?

I'd expect the alloy content and cooling rates to play a bigger role on product performance than impurities but I'm just guessing.

Given the amount of iron that GM would melt and pour, it wouldn't surprise me to find that arc melting went WAY back. And it may be much like "powdered-metal, cracked-cap, near-net shape" connecting rods. Sounds all modern and improved...until you discover the REAL reason for powdered-metal, cracked-cap, near-net shaped rods is that they cost MUCH less to produce in quantity than old-style forged (or cast) and machined rods and caps. I bet if the volume is high enough, arc-melted iron costs less than crucible-melted iron.

I agree the change in melting process was probably driven more by cost than by cast product properties. I don't know how they heated the crucibles before the change to arc-melting but if they were heated in electric furnaces, maybe arc-melting used less power? If the crucibles were heated by gas, maybe the costs got too high? Or maybe it was more about the cost of "consumables" like the crucibles themselves? Or maybe the change was driven more by the need for flexibility in the process as the foundry started using different alloys for different parts/applications?

I've downloaded a few GM docs about materials. Based on one titled "Armasteel and Malleable Iron Castings", it appears the "Central Foundry" was marketing both to other divisions and to outside customers. The parts applications they supplied was huge. This is why I guessed the arc-melting process may have been better suited for a variety of alloys and parts than crucible melting.

Mike

[steve25]

Yes there are other factors to the game also.

For instance I have heard that Pontiac aged there cast iron pieces long before machining them, and here once again it would be nice to know if that where true.

Other things matter much also.

I have ground on many a Ford head to find such porosity that plans made to port them to a certain level of air flow had to lowered, and I have just found this condition in a AMC head I just ported.

So then to me with a condition like this, one has to wonder when, other then cylinder walls and lifter bores ware wise how much a good quality iron matters if there’s inclusions everywhere.

[MatthewKlein]

Originally Posted by steve25

Yes there are other factors to the game also.

For instance I have heard that Pontiac aged there cast iron pieces long before machining them, and here once again it would be nice to know if that where true.

Other things matter much also.

I have ground on many a Ford head to find such porosity that plans made to port them to a certain level of air flow had to lowered, and I have just found this condition in a AMC head I just ported.

So then to me with a condition like this, one has to wonder when, other then cylinder walls and lifter bores ware wise how much a good quality iron matters if there’s inclusions everywhere.

I was told around 20 years ago or so. When much of the brake rotor production moved to China. That cast iron has to be aged outside for 3 months before machining. That it stabilizes during that time. We were experiencing major rotor warping issues back then.

I was also told at that same time that iron castings for a lathe or mill have to be aged for years. Otherwise the final machining tolerance of the surfaces will move and be inconsistent.

[70GS455]

According to the guys on the Engine Power show, current OEM procedures balance engines to about 0.25 in-oz and the show strives to balance at 0.125 in-oz in house

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[Mister Pontiac]

Enjoyed watching this again. Luv the old footage!

[Half-Inch Stud]

PMD's engine lead designer's son-in-law told me the Lead designer not only designed the Stratostreak from beginning to testing, but also had some say in modifying the GM CFC (Central Foundry C) processes in the cast nodular iron process.

As if he lead the process for cast steel. We'd all figure that a team of specilized metallurgist were needed, and I assume they were a tight team.