Aging cast iron = Old wife's tale?
 

It is baffling to me why most people here are saying day temperature has little effect on the metal. I was once told and also read that well ground gauge blocks can unite completely if left over night. This tells me that there is motion of atoms even at day temperature state of energy. I am only a toolmaker so I can't state with authority that curing of cast is important or not however I feel dismissing it based on laboratory tests conducted on limited time is fatal.

Aging cast iron = Old wife's tale?
 

On Sun, 26 Nov 2017 13:24:43 -0800 (PST), wrote:

It is baffling to me why most people here are saying day temperature has little effect on the metal. I was once told and also read that well ground gauge blocks can unite completely if left over night. This tells me that there is motion of atoms even at day temperature state of energy. I am only a toolmaker so I can't state with authority that curing of cast is important or not however I feel dismissing it based on laboratory tests conducted on limited time is fatal.


Oh its quite true and I agree...its a bit wierd why they would think
that.

I found a gage block that had been stacked on another gauge block at
least 70 yrs ago..and then forgotten... a 1x2 and a .750 x 750 that
had fallen down a hole in a lath and plaster wall sometime around
WW2...and I had a hell of a time getting them apart without damaging
them. When I did...the surfaces between them were as shiney as the
day they were packaged. They were marked Pratt and Whitney.


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Aging cast iron = Old wife's tale?
 

On 11/26/2017 2:14 PM, Gunner Asch wrote:
On Sun, 26 Nov 2017 13:24:43 -0800 (PST), wrote:

It is baffling to me why most people here are saying day temperature has little effect on the metal. I was once told and also read that well ground gauge blocks can unite completely if left over night. This tells me that there is motion of atoms even at day temperature state of energy. I am only a toolmaker so I can't state with authority that curing of cast is important or not however I feel dismissing it based on laboratory tests conducted on limited time is fatal.


Oh its quite true and I agree

You wouldn't know, dole scrounger.

Aging cast iron = Old wife's tale?
 

On Sun, 26 Nov 2017 13:24:43 -0800 (PST), wrote:

It is baffling to me why most people here are saying day temperature has little effect on the metal. I was once told and also read that well ground gauge blocks can unite completely if left over night. This tells me that there is motion of atoms even at day temperature state of energy. I am only a toolmaker so I can't state with authority that curing of cast is important or not however I feel dismissing it based on laboratory tests conducted on limited time is fatal.

It isn't clear what you're referring to here, but gray cast iron does
stress-relieve over time. Pratt & Whitney Machine Tool used to leave
their castings out in the yard for six months before machining them.
That was common practice before people figured out the cost of "work
in process" (WIP).

You can accelerate it at elevated temperatures or you can use
vibratory stress relief. This may sound silly, but the foundries and
machine tool builders who were located next to a freight-train track
got the fastest stress relief.

As for gage blocks, the problem with them used to be delayed
martensite conversion. It they weren't properly soaked at the
tempering temperature, they culd grow over time, even for years, if
you're using them at the limits of their resolution. Today, they
usually go through two temperings and then they're giving a cryogenic
soak.

That takes care of it -- again, if done properly. Martensite is less
dense than austenite or ferrite, so conversion to martensite causes
steel and iron to grow. It's not something you'd ordinarily notice,
but with gages, where you can detect 2 microinches of growth in a gage
block, it can be troublesome.

--
Ed Huntress

Aging cast iron = Old wife's tale?
 

On 26-Nov-17 7:15 PM, Ed Huntress wrote:
....

It isn't clear what you're referring to here, but gray cast iron does
stress-relieve over time. Pratt& Whitney Machine Tool used to leave
their castings out in the yard for six months before machining them.
That was common practice before people figured out the cost of "work
in process" (WIP).
....

Back 50 year ago now, nearly, bought a Powermatic Model 66 TS and
arranged for direct pickup from factory in McMinnville, TN. Talked them
into tour while there; they had mounds of raw castings pile all over the
yard 20-ft high; they used 18-months for jointer tables and the like; a
year for the TS tables.

Now, it's an abandoned lot... :(

--

Aging cast iron = Old wife's tale?
 

On Mon, 27 Nov 2017 01:29:52 -0600, dpb wrote:

On 26-Nov-17 7:15 PM, Ed Huntress wrote:
...

It isn't clear what you're referring to here, but gray cast iron does
stress-relieve over time. Pratt& Whitney Machine Tool used to leave
their castings out in the yard for six months before machining them.
That was common practice before people figured out the cost of "work
in process" (WIP).
...

Back 50 year ago now, nearly, bought a Powermatic Model 66 TS and
arranged for direct pickup from factory in McMinnville, TN. Talked them
into tour while there; they had mounds of raw castings pile all over the
yard 20-ft high; they used 18-months for jointer tables and the like; a
year for the TS tables.

Now, it's an abandoned lot... :(

Wow, a year and a half. That's a long time to tie up your working
capital and pay or lose interest on it. But, as I said, it once was
common practice, and it worked.

Not to belabor this, but the OP actually was asking about two
different things. The stresses in castings are the result of different
rates of cooling in thin versus thick sections. Stresses build as the
metal contracts upon cooling. Over time, or with heat or vibration,
the metal grains will slip across each other to relieve the stresses.

The gage block (yes, the spelling of "gage" is intenional) issue is
different. That's about growth in the metal that results from a phase
change -- from austenite to martensite, in this case. And that's the
result of incomplete conversion to the harder martensite when you
heat-and-quench.

--
Ed Huntress

Aging cast iron = Old wife's tale?
 

"Ed Huntress" wrote in message
...

Not to belabor this, but the OP actually was asking about two
different things. The stresses in castings are the result of
different
rates of cooling in thin versus thick sections. Stresses build as
the
metal contracts upon cooling. Over time, or with heat or vibration,
the metal grains will slip across each other to relieve the
stresses.

Ed Huntress

Do steel welds slowly stress-relieve?

-jsw

Aging cast iron = Old wife's tale?
 

On Mon, 27 Nov 2017 12:45:07 -0500, "Jim Wilkins"
wrote:

"Ed Huntress" wrote in message
.. .

Not to belabor this, but the OP actually was asking about two
different things. The stresses in castings are the result of
different
rates of cooling in thin versus thick sections. Stresses build as
the
metal contracts upon cooling. Over time, or with heat or vibration,
the metal grains will slip across each other to relieve the
stresses.

Ed Huntress

Do steel welds slowly stress-relieve?

-jsw

I think so, but I'd have to check to be sure. BTW, vibratory stress
relief, as a commercial operation, was developed in Germany to
stress-relieve the welds on their big steel weldments, including those
on machine tools.

--
Ed Huntress

Aging cast iron = Old wife's tale?
 

On 27-Nov-17 10:11 AM, Ed Huntress wrote:
On Mon, 27 Nov 2017 01:29:52 -0600, wrote:
....

Back 50 year ago now, nearly, bought a Powermatic Model 66 TS and
arranged for direct pickup from factory in McMinnville, TN. Talked them
into tour while there; they had mounds of raw castings pile all over the
yard 20-ft high; they used 18-months for jointer tables and the like; a
year for the TS tables.

Now, it's an abandoned lot... :(

Wow, a year and a half. That's a long time to tie up your working
capital and pay or lose interest on it. But, as I said, it once was
common practice, and it worked.

The old mill foreman that took me around explained they had come to the
various time periods from long observation of results for various aging
periods. The jointer tables were the most problematic being so varied
in thickness from the gibs area to the long tapered bed tails. The
Model 60 8" tables were each 24" long so they had the longest cure.

Made sense but was surprising on first blush to see the piles of rusty
castings scattered all over the lot...

Not to belabor this, but the OP actually was asking about two
different things. The stresses in castings are the result of different
rates of cooling in thin versus thick sections. Stresses build as the
metal contracts upon cooling. Over time, or with heat or vibration,
the metal grains will slip across each other to relieve the stresses.

The gage block (yes, the spelling of "gage" is intenional) issue is
different. That's about growth in the metal that results from a phase
change -- from austenite to martensite, in this case. And that's the
result of incomplete conversion to the harder martensite when you
heat-and-quench.

Yes, I understood the difference...

--