A sliding element, in particular piston ring, has on at least one running surface, from the inside outwards, a coating having a metal-containing adhesive layer and a hydrogen-free amorphous carbon layer with a thickness of at least 10 \u03bcm. In one embodiment, the method includes heating the stillage to a temperature sufficient to at least partially separate, or unbind, the oil therefrom The method further includes recovering the oil from the stillage. Thereafter, the workpiece is irradiated with light having the set light intensity distribution to raise its temperature. The parking brake is further provided with a mechanically actuating locking device for maintaining the blocking device in the non-blocking condition, and with an electromagnet that can be supplied with current and that maintains the locking device in the locking position. In one embodiment the invention provides a convenient means of upgrading an existing reactor that has previously been used for conventional liquid phase alkylations such as those catalyzed by aluminum trichloride. Wherein, a stick with a designated length is prepared firstly, where one end of the stick is a bending portion, and another end of the stick is an embodying portion; and then, at least one side of the bending portion is partially removed so as to form a smooth surface thereof; finally, the bending portion are bent so as to form a tool bit with a pivoting hole.