PURPOSE: To harden only the serrated edges of metallic card cloth uniformly, by advancing the metallic card cloth in water with its serrated edges directed upward, by heating the serrated edges on the way at a temp. not lower than the transformation temp. by jetting flames thereby removing the water, then by advancing the card cloth in water once again.

CONSTITUTION: Cooling water for quenching is introduced into a quenching tank 1 through a water pipe 3 attached at the lower part of the quenching tank 1. At the same time, metallic card cloth 7 is charged through an inlet 4 of the quenching tank 1 and is discharged through an outlet 5. On the way, strong flames 9 are jetted from flame nozzles 2 arranged over a plane 10, so that the water under the flames are removed and the serrated edges 8 of the card cloth are exposed on the plane 10. The edges 8 are heated by the flames 9 to a temp. not lower than the transformation temp. When the card cloth 7 advances to the left, it is not affected by the flames 9 and the edges 8 are wholly immersed in water, hereby the serrated edges 8 are quenched and hardened. Steady operations for heating and the following quenching allows to manufacture easily metallic card cloth having serrated edges of uniform hardness.