Heat usually, with glowing char and gas hits a grate from above.
Below the grate there usually is a bit cooler space and less radiation?
A grate radiates the received heat further downwards, and “tries” to “survive”.
If we have a fully exposed flat grate-bar surface upward against full glowing char, the heat “intake” is tremendous.
A poor grate-bar has difficulties to “get rid of” the overwhelming “heat-offering” from abowe by radiating it downward.
Now, if the upper and lower surfaces are about the same
the grate bar will “settle” for a mean temperature between the intensively glowing char and the ash temperature below.
Practice is teaching, that this temperature is too high for any long endurance for low grade materials.
I was saying, that adjusting the ratio between heat intake and delivery outward
from a grate bar will affect its mean temperature and lifetime!
When the upper face of of a grate-bar is mostly covered by ash, the heat-receiving ability is grately reduced.
This will “tilt” the ratio in/out favorably.
Using an angle-iron profile as grate bar will increase the outward (downward) radiating surface by 1.4 times compared to a flat surface.
The upward facing “ditch” will keep a steady layer of hardening ash for its protection against radiation.
Is it any clearear now, Bill?