Bar stock defects...

[Victor3]

 Other day at work I was looking at some parts rejected by NDT. They were 1.875" OD x 1.125" ID, machined from 2" SAE 1117 solid bar.

 These parts had a full-length longitudinal seam (crack) from OD to ID. Inspection of the remaining bars in the lot revealed one bar with a similar seam for ~2/3 of its length.

 Cannon barrels came to mind, seeing as how if one was made from this particular bar, it would most likely fail eventually (if not on the 1st shot).

 I know we've had a few threads concerning "proofing" of barrels. I didn't consider the above when I posted about it.

 Although inhomogeneous (wish I could hear James Earl Jones say that word ) steel bar stock is not common, I've encountered it several times over the years.

[seacoastartillery]

     Victor3,   That would be a bad one to make into a cannon barrel, but without special equipment and processes, the cannon tube maker has few options with which to discover such material defects.  One way you can detect inclusions or cracks is to polish your tube to a finer degree than what's really necessary for use.  I have seen cracks in only 6 of the thousands of steel and aluminum parts that I have inspected over 30 years.  The Dye-penetrant depts. picked up on quite a few more when they inspected critical function hardware in the aerospace and aircraft plants where I worked.  Only one, a 2.5 inch 1026 steel round could have been used for a cannon tube.

     Inclusions can also ruin or weaken an otherwise good piece of material.  As far as inclusions go, not too many people can top Mike's experience with a large inclusion in a 6061-T6 aluminum tooling plate which was being machined into a support fixture.  He was waiting to inspect it's thickness as a 10 inch dia., 12 carbide insert tooth face mill was singing over the surface, removing a quarter of an inch as it went.  Suddenly, a machinegun sound replaced the normal humming of the Big Mill.  Everyone nearby dove for the floor!...and the machinist finally found the emergency OFF SWITCH.   On the Millicron's table was a fine finish on the tooling plate, up to a barely visible, 1/2" circle, and a nasty finish beyond.  After prodding the circle a bit, one-half of a hardened ball bearing popped out!  Every carbide tooth on the face mill was shattered and coffee was leaking out of a styrofoam cup on a roll-away about 20 feet away! 

Mike and Tracy

[cannonmn]

I never would have thoght it possible to buy a block of aluminum with an undetected piece of steel in it.

[Victor3]

     Victor3,   That would be a bad one to make into a cannon barrel, but without special equipment and processes, the cannon tube maker has few options with which to discover such material defects.

 I agree. However, a serious seam defect (one that would make a barrel prone to catastrophic failure) might open up enough to be obvious after one substantial load was fired, no?

 IMO, it would be good practice to carefully clean and visually inspect any brand new barrel for danger signs after the 1st firing. I don't think I've seen that mentioned here as a standard safety practice.

 Maybe I've been involved in too many nit-picky EHS buy-offs of new machinery

 

As far as inclusions go, not too many people can top Mike's experience with a large inclusion in a 6061-T6 aluminum tooling plate which was being machined into a support fixture.....  After prodding the circle a bit, one-half of a hardened ball bearing popped out! 

 Hmmm... I might not be able to top Mike's inclusion. However, see my post #65 in Gary's casting thread 

  I cut into a ball bearing in one of their castings once.