Crack detection
Crack detection
(OP)
I am looking for a coating (paint like) that can be applied to any part of a machine. When the part cracks the coating will make it blaringly obvious. The part can then be replaced before total failure.
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RE: Crack detection
Cheers
Greg Locock
RE: Crack detection
"1942
Aeronautical engineer Greer Ellis is granted a patent for Stesscoat®, a brittle coating used in quantitative stress analysis. During that same year, Continental Motors uses Stresscoat® for design/weight reduction and gets published in LIFE magazine giving widespread exposure to MAGNAFLUX."
Unfortunately, I don't think they make this coating any more. You can try http://www.magnaflux-online.com/ to get a contact. Maybe they have some Stresscoat in a warehouse gathering dust.
RE: Crack detection
You seem to be suggesting that your parts are cracking in normal service. This suggests they are overstressed of manufctured with crack-like defects which grow during service. Only something like an ultrasound scan will show these up. I know of no way of getting a quick visual indication of when a part has cracked beyond its limits.
RE: Crack detection
RE: Crack detection
Just to elaborate on the problem, we produce a high speed production machine mostly made out of steel. In order to achieve higher production rates, I am going to re-design some parts out of aluminum. Because these parts experience high cyclic loading, the aluminum will eventually fail. The plan is a two part construction, one smaller than the other. The smaller part should fail first giving indication of the failure.
What do you think?
RE: Crack detection
If you have the ability, you might be better off installing a vibration sensor connected to an alarm (audible or visual). Under normal operation you would know the standard frequency, and if the component started to fail, the frequency would change.
If that sounds too complicated, you might want to check out this coating that NASA uses, it's $20 sqft.
http://www.isa.org/journals/intech/brief/1,1161,384,00.html
"Happy the Hare at morning for she is ignorant to the Hunter's waking thoughts."
RE: Crack detection
Blacksmith
RE: Crack detection
RE: Crack detection
To me it sounds like (I have been following this thread)the choice very similar to what we have between a replaceable rubber seated butterfly valve where the rubber sleeve is replaceable and the integral rubber seated butterfly valve where the rubber seat is totally moulded with the body.
I guess whatever the methods are,It is best left to the customer to decide what kind of product suits him best.In the case of your product if it is the aluminium part which you want it to be replaceable then you have to first convince the customer of the economical benifits of the new design and also you have to be carefull not to have more than the required numbers of the replaceble parts because in the end the customer should feel confident about your new designed machine.
RE: Crack detection
I have some ejection seat background. All ejection seat systems have at least one high pressure braided hose. One the ACES II (as found in the F-16, F-15, A-10, B-1, and B-2 aircraft), on either one or both sides of the seat, these high pressure hoses can be found. The fitting on the end are screwed all threaded together. After these fittings are connected and torqued, we use to apply a thin stripe of bright yellow enamel paint across the fittings. If they were to loosen, the pint would crack and flake off. It was real easy to see if something moved.
Is it possible that this type of method could be used?
Don Shoebridge
Sr. Product Developement Engineer
www.geocities.com/donshoebridge
RE: Crack detection
Why can't you tell the customer? If this is the type of high-speed assembly machine that I am thinking, wouldn't it come with a service/owner manual? Wouldn't this manual suggest a standard maintenance schedule so the customer could keep this expensive machine working at an optimum level?
If so, you could tell the customer to check this "failure part" on a bi-annual or annual basis, looking for signs of fatigue. Sounds like you are designing it to fail anyway, so it's already a repair/replacement part to begin with.
"Happy the Hare at morning for she is ignorant to the Hunter's waking thoughts."
RE: Crack detection
RE: Crack detection
I still strongly feel that at some point you have to trust your customer.
RE: Crack detection
It sounds like you are looking for something to act as a mechanical fuse. It is allways a good idea to think about how something would fail and the results. This is often called a failure mode analysis or FMEA and there are people that make a serious science out of it.
If you use the wrong paint it will hide cracks instead of showing them.
Good luck and please tell us what your final decision is and the outcome.
RE: Crack detection
Thanks to all for your input.
RE: Crack detection
Sorry if I'm running over old ground for you, but I'm a founder member of the 'steel is often as light as aluminium, when all things are considered' club.
Or you could invoke the grand tradition of copying what everybody else does: what are automotive conrods made of?
Cheers
Greg Locock
RE: Crack detection
RE: Crack detection
Another device I've seen is a shear wire, a thin wire that will break at the first fracture or over-stress signalling an alarm.
RE: Crack detection
If you think aluminum will fail, you need to get familiar with your crack length at failure - you'll find that a lot of stiff materials are much more ugly about this than mild steel. What loads are you producing that get within a few percent of your member's strength? Your likely failure modes are around the journals, which fiber directionality and concentration would help greatly!!!
Other than that, look again at steel, or properly design an aluminum part - not just knock off a steel part.