Patent ID: 8857224

Claim:
A washing machine, comprising: a housing; a water reservoir; a spin tub rotatable by receiving a rotational force from a driving motor through a rotary shaft, the spin tub including a cylindrical body, a front member, a rear member and an annular recess provided along an outer circumferential edge of the front member or the rear member of the spin tub, the annular recess having an inner annular side wall and an outer annular side wall; and a balancer having an annular shaped body placed in the annular recess of the spin tub and including viscous fluid and a plurality of balls disposed and movable within an internal space of the annular shaped body of the balancer, the annular shaped body having a cross section providing an internal quadrilateral space in which the viscous fluid can flow to rounded internal corners of the internal quadrilateral space, wherein the annular recess has a depth greater than a diameter of the balls contained in the ball balancer, whereby during a rotation of the spin tub the balls contained in the ball balancer are supported in a direction of centrifugal force by an outer wall of the annular shaped body, the outer annular side wall of the annular recess and the cylindrical body, the outer wall of the annular shaped body being in contact with the outer annular side wall of the annular recess, and the outer annular side wall of the annular recess being in contact with the cylindrical body to provide a triple wall structure.