Crack, or normal casting? Options

[veekry9]

Yep,that is why we had the specialized fire extinguishers and 'smothering powder' while machining the metals.
As I recall,one 'prototype aircraft titanium splice plate' was ruined because the finish chips sparked up,he didn't get it out quick enough.
Started out as a 6' x 6' x 2" thk plate,real pricey piece of scrap,the chips were recycled,of course.

Somewhere out there is a treatise on the physics of why the shrink risers appear,and the crystalline solidification of light metals.
The temperature gradient while cooling is from the outside in,as the effect is seen in micrographs of etched castings.
A close inspection of the results of modern casting techniques show a reduction of the surface upsets,by a more refined control of cooling the castings.

https://www.google.ca/search?q=cfd+metal+ca...bIfW72dKk0ZM%3A

This may be of interest,to do a minimum of chassis calculation:
https://www.youtube.com/user/expertansys/videos

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[ThePaintedMan]

Without this turning ugly, I suggest that you Google "magnesium fires". If you go back to the early days of the Beetle, VW used magnesium for its cases. The magnesium did not "spontaneously combust". Fires usually started from other faults such as fuel leaks or electrical fires. Once the engine saw fire, the magnesium would combust. I saw one burn like that when I was in college back in the 60's. And, water will not extinguish a magnesium fire. You let them burn until they run out of fuel. Or, you can foam the fire, though I never did witness that.

And, I believe that VW went to aluminum because it was less expensive than magnesium, and more stable. Not for its combustibility as you pointed out.

It is my understanding that this was part of the 1955 Le Mans disaster as well. The Mercedes that Levegh was driving was completely destroyed and scattered parts throughout the crowd, killing 80+ people, but the frame of the car, or significant portions of it were magnesium. As the (few) medics on hand tended to the crowd, the fire marshalls tended to the car which was already on fire. They sprayed water on it and it exploded into a white-hot fireball, making matters worse. All the while cars were still flying by at 150+ mph. Scary times those were.

[Beach914]

Magnesium solids will not normally combust when exposed to flame. My experience machining magnesium thorium gearcases in the 80's for GE (B1 Bomber) showed that we had to contain and control the dust and chips from the machining. We had powder extinguishers and all personnel in the CNC machining Cells were trained and certified to extinguish mag fires.

Certainly a sustained high intense heat source from the fuel in a racing wreck would probably cause any magnesium to join in the combustion process.

I purchase magnesium extrusions for concrete tools today and it is the chips, dust, and moisture that I have to control to keep my operation safe.

[mbseto]

In college chemistry, we had a stash of magnesium turnings about 1/16" thk and 1/8" wide. You couldn't light them with a match, but you could with a bunsen burner and they were very bright and could not be extinguished.

The jet engine industry knows about metal combustion, and it is most definitely a hazard and the aftermath can be pretty dramatic.

[Mikey914]

You can light them with a flare, so it takes a good amount of heat, but a torch to an assembled engine is just asking for trouble.

[veekry9]

George,you have attributed those words to me,a response to what I've said.
You should make the correction so others will not make the assumption that what you've posted is true.
(IMG:style_emoticons/default/dry.gif)

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[bretth]

I didn't think someone would take a torch to an assembled engine installed in their car. Maybe I assume too much? (IMG:style_emoticons/default/confused24.gif)