Cast Iron Stress relief?

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Mike Ginn

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I am about to machine the cylinder liner for the KIWI. The bar of cast iron seems to be good quality with no hard skin. I have rough cut the liner to 0.9inch bore and 1.3 od needing to finish up at 1inch bore and 1.125 od (with a lip). The bore depth is 2 1/4inch with a 3/4 inch of solid for chucking.

My question to HMEM is:- do I need to stress relieve the material? I have researched this topic and find the results very confusing. Answers range from - don't bother, chuck it into the BBQ embers, leave outside for 1 or 2 years and quite technical discussions about temperature controlled furnaces etc.

My gut feeling is to ignore the issue but I seek greater wisdom please!

Many thanks

Mike
 
I have seen folks machine cast iron sleeves for racing motorcycles, and they don't do any aging of the bar stock prior to machining.
These engines see very extreme racing conditions, and the guy is not reporting any problems with his sleeves or engines.

Some folks purchase gray iron castings that were either cooled too quickly in places, or did not have the correct amount of ferrosilicon added (using the exact correct amount of ferrosilicon is critical for having machinable gray iron that does not have internal hot tears).
They end up heating the castings red hot, followed by a slow cool, which I understand helps clear up the hard spots.

When you heat gray iron to a red state, you are changing the properties of the metal, and as I understand it, you can shift a Class 60 to a lower class, which means you are creating a metal with lesser desirable characteristics.

Some of the more mild aging uses processes use less extreme heating, but I can't recall the temperatures.

I have also heard that some of the old engine block manufacturers use to set their blocks out in the sun for two years, to age them.
I think a block is a special situation, since the casting is so large, and any movement could cause problems along a long crankshaft distance.

I don't think aging material for a cylinder liner is necessary, but this assumes you are using some known composition of gray iron bar stock, such as purchased Class 40 gray iron.

.
 
There is a sort of running joke about castings being left under the bench to season for years and years. That, of course, is not the real reason. For quality work, such as machine tool beds, castings used to be left outside in all weathers to season naturally for a year or so, sometimes also after rough machining. The process of stess relieving cast iron can also be be done by head treatment. On the other hand, in mass production, I am pretty sure I remember from somewhere, a casting might well be machined the day it came out of the mould.

My castings have usually had protracted under bench treatment before they get to be machined. Sometimes I rough out and leave for a while before finishing, just to be on the safe side.

In practice, especially with a piece of continuous cast bar, I would say there is unlikely to be any problem. Cylinder liners I would rough out and leave for at least a couple of weeks before finishing, but it is probably quite unnecessary.
 
When you're as long in the tooth as most of us on here you don't have time to age castings.;)
 
The cylinder material is con cast bar which is very stable, I make precision gears up to 5” diameter from it without any distortion,
 
Thanks for the advice. I think I can summarize the views as "don't worry". On this basis I will carry on without consigning my liner to "mature" in the garden for 2 years. On a serious note I have found the cast iron bar (continuous casting?) to be well behaved. The skin had no hard spots and upon machining the outer and bore I found no other hard spots. I also realized that I have had this bar for about 20 years and it was originally purchased from Woking Precision Models which was purchased by Henningway Kits in 2006 - where has the time gone?

Many thanks for your collective views/help

Mike
 
I have seen folks machine cast iron sleeves for racing motorcycles, and they don't do any aging of the bar stock prior to machining.
These engines see very extreme racing conditions, and the guy is not reporting any problems with his sleeves or engines.

Some folks purchase gray iron castings that were either cooled too quickly in places, or did not have the correct amount of ferrosilicon added (using the exact correct amount of ferrosilicon is critical for having machinable gray iron that does not have internal hot tears).
They end up heating the castings red hot, followed by a slow cool, which I understand helps clear up the hard spots.

When you heat gray iron to a red state, you are changing the properties of the metal, and as I understand it, you can shift a Class 60 to a lower class, which means you are creating a metal with lesser desirable characteristics.

Some of the more mild aging uses processes use less extreme heating, but I can't recall the temperatures.

I have also heard that some of the old engine block manufacturers use to set their blocks out in the sun for two years, to age them.
I think a block is a special situation, since the casting is so large, and any movement could cause problems along a long crankshaft distance.

I don't think aging material for a cylinder liner is necessary, but this assumes you are using some known composition of gray iron bar stock, such as purchased Class 40 gray iron.

.
Piano manufacturers also used to leave the frames outside for a longish period for stress relieving.
 
I have several things aging under the bench.....:)
Doug
yeah I can relate maybe a dead rat and aged dog poop after the dog lapped up he rat blood. I can’t imagine anything laying around a couple years in my garage . I do clean house occasionally, I might pick it up and think “ what’s this” then toss in the recycle Ike . Just stick the bar in your machine and start making chips. If it’s a engine cylinder bore and leave .003 for hone finishing get going on your project so we can see progress.
 
Hi Guys,
About 1967 I had the privilege to work with a machinist who worked at Curtis Wright making B29 engines. He said it was Curtis Wright practice to rough machine the cylinder and put them outside for about a year. In NJ that means temperatures from about 0-10 degrees F to about 100 degrees F.

My Comment: Since critical details on the engines were being found and fixed - and maybe re fixed several times - for years, there was plenty of time to age a simple proven part like the cylinder sleeve.
 
Hi Guys,
About 1967 I had the privilege to work with a machinist who worked at Curtis Wright making B29 engines. He said it was Curtis Wright practice to rough machine the cylinder and put them outside for about a year. In NJ that means temperatures from about 0-10 degrees F to about 100 degrees F.

My Comment: Since critical details on the engines were being found and fixed - and maybe re fixed several times - for years, there was plenty of time to age a simple proven part like the cylinder sleeve.
im going to disagree with this as unsubstantiated hearsay Curtis eight was under the gun to get the SBD heldiver carrier qualified. They had endless troubles with it before it was accepted . At this pint the govt went after CW FOR excessive costs among other things and poor design work . Mean time Pratt & Whitney was under the gun to get the b 29 engines ready this was the R 4360 27 cylinder radial . In the B 39 proto types they had endless fires anD motor issues a little known fact is that the atom bomb attacks were already planned there were to be a number of fly overs and practice flights to make sure everything was ready . By the time time the first flights over Tokyo started P&Whitney had only delivered 7 complete and tested engines for the Enola Gay I think there were 17 flights made before the actual event so that meant that on the base the Enola Gay was stationed there were only 3 spare engines available. Now if there had been any more problems the event was to be cancelled P&W had this engine under development for only about a year and a half remember the entire country was mobilized all auto mfg GSD been converted to aircraft and war material production so there were plenty of machine shops working on everything
leaving cast iron parts out to ” age” was simply out of the equation the cylinders and cast iron parts were machined ass soon as they cooled enough to handle the P&W engine
in the hell diver was derived from the R 2800 used in corsairs, hell cats and P 47 these were needed for immediate use so again it’s just not in the time frame of the war to have cast iron laying around aging”

I worked in a big Diesel engine plant on the main assembly and machining line . This was a “ just in time” manufacturing plant cast iron engine blocks came from numerous suppliers world over. These were unloaded from shipping containers right onto the assembly line believe me none of these blocks were “aged” it was said that they were still cooling from casting when the went on machining line . The first station was a wash to get the final sand off then the first machining operation was done while the blocks were still dripping wet . Major suppliers were Mexico Brazil and Korea. The design was only a year old when I started there so again no “ aging” was possible
Hi Guys,
About 1967 I had the privilege to work with a machinist who worked at Curtis Wright making B29 engines. He said it was Curtis Wright practice to rough machine the cylinder and put them outside for about a year. In NJ that means temperatures from about 0-10 degrees F to about 100 degrees F.

My Comment: Since critical details on the engines were being found and fixed - and maybe re fixed several times - for
 
Last edited:
im going to disagree with this as unsubstantiated hearsay Curtis eight was under the gun to get the SBD heldiver carrier qualified. They had endless troubles with it before it was accepted . At this pint the govt went after CW FOR excessive costs among other things and poor design work . Mean time Pratt & Whitney was under the gun to get the b 29 engines ready this was the R 4360 27 cylinder radial . In the B 39 proto types they had endless fires anD motor issues a little known fact is that the atom bomb attacks were already planned there were to be a number of fly overs and practice flights to make sure everything was ready . By the time time the first flights over Tokyo started P&Whitney had only delivered 7 complete and tested engines for the Enola Gay I think there were 17 flights made before the actual event so that meant that on the base the Enola Gay was stationed there were only 3 spare engines available. Now if there had been any more problems the event was to be cancelled P&W had this engine under development for only about a year and a half remember the entire country was mobilized all auto mfg GSD been converted to aircraft and war material production so there were plenty of machine shops working on everything
leaving cast iron parts out to ” age” was simply out of the equation the cylinders and cast iron parts were machined ass soon as they cooled enough to handle the P&W engine
in the hell diver was derived from the R 2800 used in corsairs, hell cats and P 47 these were needed for immediate use so again it’s just not in the time frame of the war to have cast iron laying around aging”

I worked in a big Diesel engine plant on the main assembly and machining line . This was a “ just in time” manufacturing plant cast iron engine blocks came from numerous suppliers world over. These were unloaded from shipping containers right onto the assembly line believe me none of these blocks were “aged” it was said that they were still cooling from casting when the went on machining line . The first station was a wash to get the final sand off then the first machining operation was done while the blocks were still dripping wet . Major suppliers were Mexico Brazil and Korea. The design was only a year old when I started there so again no “ aging” was possible
Have heard of - - not used vibration stress relieving tools.
Different size head depending upon the mass of the object.
Especially useful for weldments.
Wonder if that is now an integral part of the procedures? (Dunno)
 
Have heard of - - not used vibration stress relieving tools.
Different size head depending upon the mass of the object.
Especially useful for weldments.
Wonder if that is now an integral part of the procedures? (Dunno)
Eh, that's easy enough to achieve with the part in place - just build the engine unbalanced (not hard to do!) and run it; it will do plenty of vibrating ...

:):):)
 
Add my opinion
Cylinder, ring or piston : buy cast iron and make
The stress relief for cast iron I think is not necessary
During the final dimensioning process, I usually wait about 5 minutes - this helps bring the material back to room temperature - to check the size or fit.
But: For the first 2 or 3 times, I didn't wait 5 minutes to measure or check fit and the engine still had good compression from the start.
My conclusion: waiting for the material to return to room temperature only gives an exact measurement or perfect fit
 
When you pour the iron in a mold it cools from the outside inward which creates stresses. How this stress is measured is to put an indicator on the metal and slowly machine away material. For a simple shape you can use standard stress theory equations to determine the stress removed by the metal removed.
The general approach is to machine the part in steps and let the metal deflect from the stress removed by machining. Before you get to the final dimensional cuts. heat the part up to a few hundred degrees above the maximum temperature for at least 4 hours but better if longer. They back to machining off another step. This is the same approach that is needed for machining plastic bar stock.
 
When you pour the iron in a mold it cools from the outside inward which creates stresses. How this stress is measured is to put an indicator on the metal and slowly machine away material. For a simple shape you can use standard stress theory equations

Today my stress is relieved easily , normally it would be something like yhis, grab a cold beer and sit back in my chair . I don’t drink or smoke so those are out . Instead. I just mix up cold glass of raspberry iced tea and a couple vanilla wafers then sit back and see what else has been going on here. I can go back k to the hobby shop and fiddle around, fully relaxed and stress relieved. LOL
We used to stress relieve the welded race car chassis but after a couple runs something was always cracked or bent and needed to be rewelded or cut out and repaired stress relieving was all done . Eventually we did not do anything to the chassis powder coating has long been against the rules as you can’t see cracks . The chassis isn’t even painted anymore. Just a light coat of coconut oil sprayed on ito prevent rusting . It’s easily removed for welding too
to determine the stress removed by the metal removed.
The general approach is to machine the part in steps and let the metal deflect from the stress removed by machining. Before you get to the final dimensional cuts. heat the part up to a few hundred degrees above the maximum temperature for at least 4 hours but better if longer. They back to machining off another step. This is the same approach that is needed for machining plastic bar stock.
Add my opinion
Cylinder, ring or piston : buy cast iron and make
The stress relief for cast iron I think is not necessary
During the final dimensioning process, I usually wait about 5 minutes - this helps bring the material back to room temperature - to check the size or fit.
But: For the first 2 or 3 times, I didn't wait 5 minutes to measure or check fit and the engine still had good compression from the start.
My conclusion: waiting for the material to return to room temperature only gives an exact measurement or perfect fit
Add my opinion
Cylinder, ring or piston : buy cast iron and make
The stress relief for cast iron I think is not necessary
During the final dimensioning process, I usually wait about 5 minutes - this helps bring the material back to room temperature - to check the size or fit.
But: For the first 2 or 3 times, I didn't wait 5 minutes to measure or check fit and the engine still had good compression from the start.
My conclusion: waiting for the material to return to room temperature only gives an exact measurement or perfect fit
When you pour the iron in a mold it cools from the outside inward which creates stresses. How this stress is measured is to put an indicator on the metal and slowly machine away material. For a simple shape you can use standard stress theory equations

to determine the stress removed by the metal removed.
The general approach is to machine the part in steps and let the metal deflect from the stress removed by machining. Before you get to the final dimensional cuts. heat the part up to a few hundred degrees above the maximum temperature for at least 4 hours but better if longer. They back to machining off another step. This is the same approach that is needed for machining plastic bar stock.
When you pour the iron in a mold it cools from the outside inward which creates stresses. How this stress is measured is to put an indicator on the metal and slowly machine away material. For a simple shape you can use standard stress theory equations
to determine the stress removed by the metal removed.
The general approach is to machine the part in steps and let the metal deflect from the stress removed by machining. Before you get to the final dimensional cuts. heat the part up to a few hundred degrees above the maximum temperature for at least 4 hours but better if longer. They back to machining off another step. This is the same approach that is needed for machining plastic bar stock.
When you pour the iron in a mold it cools from the outside inward which creates stresses. How this stress is measured is to put an indicator on the metal and slowly machine away material. For a simple shape you can use standard stress theory equations
to determine the stress removed by the metal removed.
The general approach is to machine the part in steps and let the metal deflect from the stress removed by machining. Before you get to the final dimensional cuts. heat the part up to a few hundred degrees above the maximum temperature for at least 4 hours but better if longer. They back to machining off another step. This is the same approach that is needed for machining plastic bar stock.
 

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