Stress relieving by Ringing Cast Iron

[Richard King]

Hello all I am new to this forum and need some information on Stress relief in Cast Iron Castings.

I am a machine rebuilder, teach it plus I scrape Cast Iron Master Straight-edges. They were cast in sand and then high temp stress relieved. They will be machined and hand scraped. My question is for many years I was taught to Ring It. The casting that resembles a one sided parallel or some call them camelbacks that look like an airplane wing. Holes in a camel back structure with one side that is flat to .00005"/12".


During the machining and scraping process we hang and "ring" the casting(s) which vary in size of 12" to 72" long and weigh from 12 pounds to 200 pounds depending on lengh, width and thickness.
We hang the casting on a nylon strap or rope and hit it with a rubber, leather, lead, wood hammer or chunk of wood so the casting vibrates and removes any built in stress. I have always been told and re-tell it calling it "Ringing".

I have seen the flat surface I am testing it to a granite surface plate .00005" to .0001". or the flat surface will test flat and then I hang and hit it and it changed. I tap it lightly so it vibrates like a bell or tuning fork. It has helped me for years as a way to relieve small stresses when I am scraping. My question to you is "has anyone ever done this and can you send me or show me here copies of scientific / engineering papers, articles or books demonstrating, discussing or teaching this procedure? Thank You in advance. Richard King

 

[EdStainless]

There are commercially available 'vibratory' stress relief systems, this is what you are doing.
This method does not actually relive stresses, but ti can help them even out better.
Getting the existing residual stress more uniform can help improve long term stability.

We used to cast tooling pieces and we would thermal cycle them a bunch (5-8 times) from below our operating temp (about 40F) up to 400F. We would hold at 400F for a while. We used very gentle heating and cooling in a liquid bath to avoid distortion.

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P.E. Metallurgy, Plymouth Tube

 

[Richard King]

I have the castings High Temp Stress relieved and the vendor cooks it for 20 hours at 1170 F and then cools them over 8 hours with the oven door closed and shut off. I have no issues with that as his method works better then any of the other places I have used. That is not what I need or am asking. I could link it to a You Tube show, but that could be considered advertising I figure. I am looking for documentation of this process. I am a Journeyman and my Journeyman and his Journeyman told him to use this method. It works when we are scraping and holding .00005 - 1/2 tenth. After ringing it several times it stops moving. I have been asked to show documentation. Thank You . Rich

 

[EdStainless]

The only documentation that you are likely to find is advertising for people making vibratory or acoustic stress relief equipment.
Go ahead and show people some of the adds (if you can find ones that are not too outrageous in their claims).
Yes it works.
But it does not lower the average stress, it just helps bring everywhere to average.
It sounds like your heat treater understands. Uneven cooling is the largest source of residual stresses.

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P.E. Metallurgy, Plymouth Tube

 

[DAVIDSTECKER]

I've also heard that letting the castings age will also allow the stress' to relieve them selves.
Mata-lax is one of the vibratory systems out there.
I've been trying to use one of those for years but haven't found anyone locally to send a sample to.

 

[metengr]

https://www.twi-global.com/technica...relief-as-effective-as-thermal-stress-relief/

https://www.sciencedirect.com/topics/materials-science/stress-relieving

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1559-3584.1943.tb02307.x

 

[arunmrao]

Vibratory stress relieving is popular for cast iron castings,instead of thermal treatment. BCIRA had done work on vibratory stress relief of cast iron castings.

Machine tool iron castings are normally naturally aged for a period of 1-2 years, so that dimensions do not move .They are marked and placed in open yard exposed to natural elements.

There is a discussion in eng-tips,please refer to the same.
" Stress relief of machined castings".

https://www.eng-tips.com/viewthread.cfm?qid=274803

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Richard King]

Thank You everyone, I have replied to the interested parties with the links you provided. I also emailed an old acquaintance Professor Alex Slocum of MIT and he said "vibration stress relief" IS well known—the question is for how long…

So those articles back each others conclusions. I see their is debate, but Scraping is not a science, it's an art. I stress relieve my casting first by Thermo and use the vibration technique's of ringing it by hitting it with a soft hammer only hard enough to vibrate the casting like a bell does when it is rung. I also had a students write that he had a small cast iron surface plates error of .002 change to .001" after ringing it. I'm working in tenths of an inch not inches. If anyone has an questions about machine rebuilding or way scraping please ask away as that is my specialty and have traveld the USA and world teaching it.
Rich

 

[EdStainless]

I worked in a plant that had four Blanchard vert spindle grinders.
We rebuilt one each year, rewound the motors, the chuck, and scraped the ways.
The guys that did the scraping were in their 70's.
I have great respect.
The machines were built in the 30's and when I left in the 90's they would still hold tighter tolerances than any new grinders that we could buy.

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P.E. Metallurgy, Plymouth Tube

 

[SnTMan]

Certainly not within my area of expertise (if any), but this is the kind of discussion that makes Eng-Tips such a fascinating place to hang out.

Stars for all.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Tmoose]

Hi Richard King,

I have nothing of much value to add to answer your question.

"They were cast in sand and then high temp stress relieved. They will be machined and hand scraped."

Machining operations can induce stresses into a part.
On our relatively thin high chrome abrasion resistant iron castings, grinding is a real problem in that regard.

I wonder what would happen if your castings were thermally stress relieved (again) just before the scraping operation.

I'd be interested in asking the folks that machine the csstings to comment on any dimensional change during the machining operations, or any tricks they use to make the machined castings come out nice. I'd expect only general comments, not any trade secrets.

 

[btrueblood]

"I have been asked to show documentation. "

So write a document that says (essentially) 'this is how it's done. Why? Because it works.'

"Scraping is not a science, it's an art."

Yup. Stephen Gotteswinter has a utube video on the subject, amongst many others. Like Ed said, I have much respect for people who have the patience to do it and do it right; like good wheelwrights and balancing tech's too.