Screw having an underhead bearing surface including lubricant pockets

摘要

The screw comprises a head (5) having an underhead bearing surface (12), and lubricant pockets (13) that are arranged in a part of the underhead bearing surface and are designed to be circumferentially closed as seen in cross-section. The lubricant pockets are arranged to be distributed in an irregular way, and are designed not to be continuous in the radial direction and in the circumferential direction of the underhead bearing surface. The lubricant pockets have an average diameter of 100-300 mu m. The bearing surface has an average surface roughness of 15-50 mu m for forming the pockets. The screw comprises a head (5) having an underhead bearing surface (12), and lubricant pockets (13) that are arranged in a part of the underhead bearing surface and are designed to be circumferentially closed as seen in cross-section. The lubricant pockets are arranged to be distributed in an irregular way, and are designed not to be continuous in the radial direction and in the circumferential direction of the underhead bearing surface. The lubricant pockets have an average diameter of 100-300 mu m. The underhead bearing surface has an average surface roughness of 15-50 mu m for forming the lubricant pockets. The underhead bearing surface includes projecting portions and deepened portions, where the deepened portions form the lubricant pockets, and the projecting portions are designed to be rounded and to have an average diameter of 100 to 300 mu m. The lubricant pockets are only arranged in a part of the underhead bearing surface, and are designed as cold formed lubricant pockets. Independent claims are included for: (1) a washer for combination with a screw; (2) a screw joint; and (3) a method for producing a screw.