Brake Drum material for heavy duty truck? 2

[Henryzhang]

Hi,Every engineer!

Who can help me answer following questions:
1 what kind of cast iron Commonly used on heavy duty truck(eg.for 16 and 24 tons),and what's their mechanical property?
2 What kind of faliure does brake drum often undertake and what's the reason?

Thanks in advance

 

[rmw]

I will leave the actual casting metallurgy to others. Some are cast and some are centrifugally cast in steel liners. But, I can't state the specific grade until I return to my office.

But, Brake drums fail due to cracking principally, unless they just wear out first.

The severe heat loads that some brake drums see cause surface cracking or sometimes it is called checking, in the inside where the shoes rub.

If a truck or trailer is using its brakes heavily, and they are red, yes, literally red hot, and suddenly it splashes through a water hole, quenching parts of the drum unequally, whole "hunks" or segments of the drim can crack severely enough to fall off the rest of the drum.

I have seen brake drums so hot that it melted the valve stems out of the wheels.

Now, if a drum survives all that, it will just wear to a point where the ID is so great that the shoes will not 'cam' out and touch it, and the "S" cam that pushes the shoes apart turns completely over, or 'cams over'. If your brakes 'cam over' your brake drums are way past worn out.

rmw

 

[Markoos]

Brakes work by converting kinetic energy into thermal energy via friction. Therefore a material with a high thermal coonductivity is required to dissipate the heat quickly.

Good quality brake discs (and I'm sure drums would be the same) use high carbon cast iron. The cast iron should contain flake not spheroidal carbon. The intercarbon spacing determines the thermal conductivity. Download the articles at the following link for more info.

http://www.eurac-group.com/research.php