Angular Momentum: Why Not Conserved w/ Friction?

[phymatter]

if two circular discs of different radius and angular velocity are brought togather , they experience friction and finally there is no slipping between them , why is the total angular momentum not conserved in this case ? there is no eternal torque , friction is an internal force of the system !
please help!

 

[rcgldr]

Angular momentum will be preserved, but not angular energy, some of which is converted into heat by the friction.