The importance of crack testing

[Stuart Giles]

Do you find the magnetic spray better than the red dye penetrating stuff?  When we use the magnetic,  we had to pass a very low voltage and a few amps through the part to be tested. Clamped the bit to be tested between two lead jaws.
bob

Hi Bob,
Sorry for the slow reply, a bit busy.

I've used the dye pen in the past, but didn't get on with it very well. I'm sure if others use if often they would get better result.

The company that sells the cans, also sell the electric magnet machinery "thingy" to use with the tins. But these professional units can cost £2.5k. A bit pricy for home use.

You can see the results we get with a simple magnet, the cracks are quite obvious.

And yes I agree that just because something is cracked, does not mean it is scrap. BUT if it's a steering or brake part. It's your life and your risk if you use it.

For me if I know we're a part cracks, especially steering parts. I'll test them before I sell them. it's NOT a garrantee for the future use of the part. It shows customers the parts are in an acceptable condition when they buy them.    Think of it like an MOT ?

Tony.

this thread has been an interesting read. I always use a penetrating  dye on important mechanical and/or "life or death" bits. This crank looked OK when tested with an Ardrox type dye and developer, but I decided to get it Magnafluxed to be absolutely sure whilst doing a fairly routine  "freshen up" on a motor.  



The lines indicate the (otherwise invisible) cracks in No. 4 big end. Bit of a b*gger that an apparently perfect crank is now a doorstop, but have at least avoided the carnage that would have been caused if that crank had let go at high revs.

BTW, one of the Magnaflux tests involves passing a current through the part, turning it into an electromagnet; cracks  with a 90 degree orientation are detected  by magnetising the part conventionally -all to do with the  direction of the magnetic flux lines in each test. I wonder how the aerosol magnetic test results would compare? certainly looks like something worth trying, I pay about £70 to get a crank Magnaflux  tested.