FASTENING BOLT FOR USE IN CONCRETE

摘要

A fastening bolt includes a shaft defining a central axis, a head, a drilling portion, and first threads alternating with second threads. The first threads and the second threads have different outer diameters. Each first thread has a trailing surface facing the head and inclined to a line perpendicular to the central axis by a trailing angle and a leading surface facing the drilling portion and inclined to the line by a leading angle. The trailing angle is smaller than the leading angle to build an asymmetrical form. Some threads near the drilling portion form respective cutting grooves and recesses thereon. Each cutting groove is formed by walls with different lengths and opened at an angle which does not exceed 90 degrees. The bolt breaks the workpiece quickly by the cutting grooves and recesses. The asymmetrical first threads help enter the workpiece quickly and attain a firm engagement therewith.

主权项

1. A fastening bolt for use in concrete comprising:
a shaft defining a central axis; a head disposed on a first end of said shaft; a drilling portion defined on a second end of said shaft opposite to said first end; a plurality of first threads spirally disposed on said shaft and extending from said drilling portion toward said head; and a plurality of second threads spirally disposed between said first threads, wherein an outer diameter of said second threads is smaller than an outer diameter of said first threads, some of said second threads close to said drilling portion having a plurality of recesses formed thereon; wherein each of said plurality of first threads has a trailing surface facing said head and a leading surface facing said drilling portion, said leading surface and said trailing surface converging on a thread ridge, said first thread defining a line which is perpendicular to said central axis of said shaft and passes said thread ridge, said leading surface being inclined to said line at a leading angle, said trailing surface being inclined to said line at a trailing angle, said trailing angle being smaller than said leading angle, some of said first threads close to said drilling portion having a plurality of cutting grooves formed thereon, each of said plurality of cutting grooves being formed by walls with different lengths and opened at an angle, said angle being not over 90 degrees, each of said plurality of cutting grooves being opened in a direction opposite to a screwing direction of said shaft.