What are the common defects of screw fasteners

When using screw fasteners, we will see that some screw fasteners do not look very good, and some will have cracks. What are the surface defects of screw fasteners? The following high-strength standard parts of the small program to talk about a simple, common screw fastener defects; convenient for you to buy screw fasteners in the future when there is a direction.

First, crack

Cracks are usually caused by excessive stress in a metal during forging or other forming or heat treatment.

Among them are quenching cracks, forging cracks, forging bursting, shearing bursting.

1. Quenching cracks may occur during heat treatment due to excessive thermal stress and strain. Quenching cracks usually appear on the surface of fasteners with irregular intersecting and irregular directions.

2. Forging crack forging cracks may occur in the cutting or forging process, and located on the top of the screw head, as well as the protrusion part of the cavity head.

3, forging burst may occur during forging process.

4. Shear burst.

Shear burst may occur during forging, as in the circumference of the round head or flange head screw or flange face, usually about 45 degrees from the axis of the screw.

2. The crack or strip of raw material is usually a thin straight line or smooth curve extending along the longitudinal direction of thread, bare rod and head. It is usually the inherent defect of the manufacturing material of fasteners.

Three, dent dents are shallow holes or dents on the surface of screws. There is a rush or imprint caused by chips or cutting burrs or rusty layers of raw materials that cannot be eliminated in the forging or upsetting process.

Four, wrinkles and wrinkles are metal folding on the surface of fasteners during forging. In the process of one impact forging, wrinkles occur due to the displacement of the material caused by insufficient volume and different shapes.

Five. Cut marks are shallow grooves in longitudinal or circumferential directions. It is due to the movement of the tool beyond the surface of the screw.

Six. Damage screws on any surface. Produced in the manufacture and transportation of screws by external influences.
The above six are the common defects of screw fasteners, we must pay attention to the surface of the screw when we buy screw fasteners to see if there are any of these defects.