[Pav8427]

I am more of a reader than poster. Resent thread on block metallurgy got me thinking.
I know for stock block builds it is obvious that by the time a block has a bunch of miles and heat cycles on it, that the stress from casting is no longer present.
I am curious as to what the new block manufacturers are doing. Would guess they have a process. But wondering if more stress relieving would help?
Probably wouldnt hurt considering the cost of them.
Anybody ever look into it??

[Steve C.]

Related. Cryogenic treatment has been done to engine blocks.

Quote from one source... "Cryogenically treated engines and components exhibit less wear and are less prone to cracking. Engine blocks that are treated prior to final honing benefit from reduced friction, which increases horsepower and torque. And cryogenic engine treatment makes your engine components more durable and longer lasting."


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[Half-Inch Stud]

Wonder if the modern production does bore and hone with a TQ Plate.

[Shiny]

You would have to heat gray iron well above engine operating temperatures to effectively relieve residual stress from the casting operation.

Here is a chart from a quick Bing search (Link to 1948 NRL Paper):



Is residual stress an issue in a Pontiac engine block? What problems does it cause?

Residual stress MIGHT make it more susceptible to fracture but that would depend a lot on the geometries and how the non-uniform stress was "held" within the engine structures.

Thermal stress relief will decrease tensile strength a little but I doubt it would affect wear properties significantly.

[Elarson]

Everything that Shiny said is true. But you may be wondering how an old seasoned block is stress relieved without going to the temperatures shown on the chart. The answer is an effect called creep. Over many thousands of hours at low stress, moderate temperatures and vibration, there is a very very slow movement in the metal that is undetectable short term but is a real effect long term.

An interesting example of creep....have you ever noticed that old windows look wavy? That's because gravity is creating a low but constant stress causing the glass to flow downward. Undetectable short term but wait a hundred years and you'll start to see it.

Eric

[steve25]

If your talking in terms of the iron aftermarket blocks that we have for our Pontiacs and the fact that they can handle 2000 hp, then for the average racer running them and not looking to make over 900 hp then it’s more about accurate machining then seasoning I would have to say!

That being said if I was running a aftermarket block and had the funds then I would put it they the Cryo treatment process, and with a factory block looking to make 700 hp or more with strokes over 4.00” and live a good life, I would sure do the same!

[pastry_chef]

Something like 25 years ago I read a nice article - had Paul Pfaff Racing who offered a service.
https://www.bonal.com/

[Shiny]

I think stress relief occurs by creep mechanisms in general. Higher the temperature, the faster it happens.

One thing that may contribute to "seasoning" an engine block (I'm not really sure what this term means or how to measure but I assume it means stress relief) is the temperature gradients that occur during operation.

Operating temperatures will be VERY non-uniform within an engine. Even though the material is homogeneous, temperature gradients will drive differential thermal expansion - the hotter the material the more it expands.
Example: if you take a metal strip and heat it on only one side, it will curve. The hot side expands and causes the strip to curve. If you force it to stay flat while heating, the hot side will be under compressive stress and the cold side will be under tensile stress. These "balancing" stresses will be present anytime there are thermal gradients in a component.

If the thermally-induced stresses inside an engine block happen to "add" to residual stresses from the casting process, you could greatly accelerate creep.

[Shiny]

Originally Posted by pastry_chef

Something like 25 years ago I read a nice article - had Paul Pfaff Racing who offered a service.
https://www.bonal.com/

This is cool. Thanks! I had never heard of vibrational stress relief.. interesting!

[Dragncar]

Originally Posted by Elarson

Everything that Shiny said is true. But you may be wondering how an old seasoned block is stress relieved without going to the temperatures shown on the chart. The answer is an effect called creep. Over many thousands of hours at low stress, moderate temperatures and vibration, there is a very very slow movement in the metal that is undetectable short term but is a real effect long term.

An interesting example of creep....have you ever noticed that old windows look wavy? That's because gravity is creating a low but constant stress causing the glass to flow downward. Undetectable short term but wait a hundred years and you'll start to see it.

Eric

I have always wondered why old glass looks wavy. We have a lot of old Victorians around here, some quite grand. Full of wavy glass.
Learned something today, cool.

[Murf]

https://engineering.mit.edu/engage/a...nge-over-time/

[cfmcnc]

WE have the Meta Lax system here..We do all new blocks.And some used blocks by request..

[Pav8427]

That system is what got me thinking about the subject to begin with. I too remember that article years ago. We actually have one also. We use it for LARGE weldments. (#18,000) for BNSF track equipt. Recently used it to try and solve a issue with Aluminum forgings for large cal. auto hand guns made locally. I know the weldments there are no changes to them except for what the Meta-Lax tells you. Will know more with the forgings. They are trying to chase a .030 warp after machining.
CFMCNC. Are there any measurable changes in the block when you do use the Meta-Lax system?
Ever try on anything else? Cranks. Rods.
Would guess you would want to do anything that is torqued. Or maybe even fasteners.

[mgarblik]

The IA II solid blocks we were running in the Boss Bird went through the HIP, (hot Isostatic Pressing) stress relieving process before we received them. Not sure if all the IA II aluminum blocks get that treatment. Edelbrock utilizes the HIP process on many of their aluminum castings as well. The Pro Port heads had this process performed. Not sure about the regular production castings. Joe Mondello, (RIP 2011), was a leader in stress relieving iron, steel and other engine parts. Also a leader in DLC coatings, anti-friction coatings and other cutting edge treatments in the 1990's. He had cryogenic freezers in house as well as vibratory treatment. There is some advantage to the process, heavily utilized by NASCAR and other forms of racing. It's a cost/need/benefit equation we each need to solve.

[AG]

Originally Posted by Elarson

Everything that Shiny said is true. But you may be wondering how an old seasoned block is stress relieved without going to the temperatures shown on the chart. The answer is an effect called creep. Over many thousands of hours at low stress, moderate temperatures and vibration, there is a very very slow movement in the metal that is undetectable short term but is a real effect long term.

An interesting example of creep....have you ever noticed that old windows look wavy? That's because gravity is creating a low but constant stress causing the glass to flow downward. Undetectable short term but wait a hundred years and you'll start to see it.

Eric

Glass is a super-cooled liquid (not a solid) that can actually flow and has a very different molecular viscosity than cast iron. Stress relief in a block can be a kinetic event that is governed by time and temperature, and is the reason a block can stress relieve over time even with normal engine operating temperatures.

[Shiny]

To clarify..

Glass is an amorphous solid at room temperature. A solid material is basically anything that holds its shape ( vs a liquid or gas). In an amorphous material, the atoms are arranged "randomly".

Most other solids are polycrystalline, with each grain having "ordered" atoms (crystals). A single crystal is not commonly used to make parts.

[AG]

Glass is an amorphous solid at RT, but molecularly it is a super-cooled liquid with a very high viscosity and is above it's Tg at RT.

[Pav8427]

Would be interesting to deck, bore, torque plate hone and line hone a run of the mill block. Record dimensions. Then stress relieve and re-check to see if anything actually moves.

[Shiny]

Agree with that description but it's pretty technical and could leave one thinking typical glass at room temperature can flow and/or spontaneously stress-relieve. Practically, the viscosity is simply too high for this to happen IMO.

As to the HIP stress-relieving, I'm assuming that is done for aluminum blocks, correct? Sounds like an expensive process on something so large!

And back to the topic of stress-relief of a cast-iron block, do performance shops thermally stress-relieve used iron blocks before machining?

I assume the most common issues caused by stress relief in service are main and cam bore misalignment and maybe decks moving.

While the temperatures during operation are insufficient to fully stress-relieve cast iron, whatever does happen should be done on a used block and I wouldn't expect a big need for further stress relief prior to machining a used engine block.

If you trued up a used block, then heated it above what it saw in operation, the situation would change and I would expect a lot of movement still.

[lust4speed]

Which brings up a related question. The Shake-and-Bake process of cleaning old cast iron blocks requires heating the block to around 450° and then finishing up in another machine that rotated the block in a bath of steel shot. Always was told that a line hone would be necessary because the associated stress relieving was also allowing the block to relax and shift. True?

Results always made the blocks look like new cast iron with no hint of paint or rust on the exterior or calcium residue inside the coolant passages.