Surface Crack Internal Crack in En19 Shaft (18 mm dia)

you mention -

"After analysis it is found , surface crack or internal crack is root cause."

what analysis have you carried out?

analysis of the nature of the crack? of the root cause of the crack?

is this a "one of" failure? or a "frequent occurrence"? or a "consistent repeat"?

if it a field failure? or a product under development?

the said shaft may have been made from defective material in the first place - in which case the design specification being correct and yet there is a sourcing and/or incoming quality lapse.

is the failure really in torsion? i suggest you do not rule out an additional shear component in your analysis. i have seen (not in circuit breakers though) that have failed due to combined effect of torsion and shear at points of support.

what is the magnitude of the torque? and how much is the angular movement? in how much time does the movement happen?

you have asked a very good question. addressing some raised by me will help you along in your striving for a solution.

i suggest you also take this question to the electrical engineering board of CR4 - many switchgear professionals there will share their experience . . . .

Wholesome answer, GA.

i have done some analysis and simulation of the Masterpact ACB of Schneider, which uses the "D-shaft"+Latch system. Here is an image. i expect your CB has a similar system, thought this one is a small Dshaft (8mm i think).

i am not sure of the material, it was 58-61 HRc, which made me think of using bearing steel, EN31, thru-hardened. The stroke of the latch is ≈ 2mm, so the impact is not much.

Sorry i can't help more, being an electrical engineer.

i expect case-hardening will help, since you only need a hard outer surface for wear resistance.

Good luck.

GA Milo. Suggest to scan for spell-check for happy reading.

Thanks. My typing is not a strength.

The frustrating thing that I have with spell check is that it usually doesn't know my technical terms, and so it becomes as much of a chore as just answering. But your advice is sound and I will follow it.

Milo

VGA, Milo. i, for one, was waiting for your expert view.

This is quintessential R&D. Going deeper and deeper until you find the root cause.

_{Ahem....Root cause... reminds me of a very effective story in one of my management courses...please bear with me....}

_{Joe was suffering from a severe headache 24/7. He was contemplating suicide, and went to several doctors... no use ... until he met this specialist. The doctor said, "Joe, the good news is I can cure your headaches.
The bad new is that it will require castration. You have a very rare
condition, which causes your testicles to press on your spine and the
pressure creates one hell of a headache. The only way to relieve the pressure is to remove the testicles."
Joe was shocked and depressed. He wondered if he had anything to live
for. He had no choice but to go under the knife. When he left the hospital, he was without a headache for the first time in 20 years, but he felt like he was missing an important part of
himself.
As he walked down the street, he realized that he felt like a
different person.
He could make a new beginning and live a new life.
He saw a men's clothing store and thought, That's what I need... a
new suit."
He entered the shop and told the salesman, "I'd like a new suit."
The elderly tailor eyed him briefly and said, "Let's see... size 44
long."
Joe laughed, "That's right, how did you know?" "Been in the business
60 years!" the tailor said.
Joe tried on the suit. It fit perfectly.
As Joe admired himself in the mirror, the salesman asked, "How about a
new shirt?"
Joe thought for a moment and then said, "Sure".
The salesman eyed Joe and said, "Let's see, 34 sleeves and 16 neck."
Joe was surprised, That's right, how did you know?"
"Been in the business 60 years.
Joe tried on the shirt and it fit perfectly.
Joe walked comfortably around the shop and the salesman asked, "How
about some new underwear?" Joe thought for a moment and said, "Sure."
The salesman said, "Let's see... size 36."
Joe laughed, "Ah ha! I got you, I've worn a size 34 since I was 18
years old."
The salesman shook his head, "You can't wear a size 34. A size 34
would press your testicles up against the base of your spine and give
you One hell of a headache."
New suit - $400
New shirt - $36
New underwear - $6
Second Opinion - PRICELESS}

_{Second Opinion - PRICELESS}

Today I received a mail from a friend stating that- PRICE and WORTH have similar meaning then why PRICELESS and WORTHLESS have not?

Every language has its quaint ones...

"Fat" and "Slim" mean opposite things, but "Fat chance !" means the same as a "Slim chance"