Lesson 1/Learning Event 1
To provide light weight and enough strength, some drums are made of
steel with a castiron liner for the braking surface. This type is
known as a centrifuse brake drum. Cooling ribs are sometimes added
to the outside of the drum to give more strength and better heat
dissipation. Braking surfaces of drums may be ground, or they may be
machined to a smooth finish.
For good braking action, the drum should be perfectly round and have
a uniform surface. Brake drums become "out of round" from pressure
exerted by the brake shoes or bands and from the heat produced by the
application of the brakes. The brake drum surface becomes scored
when it is worn by the braking action. When the surface is badly
scored or the drum is out of round, it is necessary to replace the
drum or regrind it or turn it down in a lathe until the drum is again
smooth and true.