The Types Of Screw Surface Defects

When using screws, we sometimes see the appearance of some screws are not very good, and some will have cracks. What kind of surface defects do the screws have? Screw surface defects:

1. Crack

Cracks are usually caused by excessive stress during forging or other molding processes or heat treatment.

Among them are: quenched cracks, forged cracks, forged bursts, shear bursts.

• Quenching cracks

During the heat treatment, quench cracks may occur due to excessive thermal stress and strain. Quenching cracks are usually irregularly intersecting and appear in the direction of fasteners in an irregular direction.

• Forging cracks

Forging cracks may occur during the blanking or forging process and are located on the top of the head of the screw, as well as the raised portion of the pocket head.

• Forging Burst

Forging bursts may occur during forging.

• Shear burst

Shear bursts may occur during forging. If it appears on the circumference of the round head or flange surface of the round head or flange head screw, it is usually about 45° with the axis line of the screw.

2. Cracks or streaks of raw materials

Cracks or streaks of raw materials are usually a thin straight line or a smooth curve extending longitudinally along the threads, polished rods, and head. It is usually a defect inherent in the raw materials used to make fasteners.

3. Dent

Dents are shallow pits or depressions that appear on the surface of the screw. It is caused by chipping or cutting burrs or the rust layer of the raw material caused by urgency or embossing, and can not be eliminated in the forging or upsetting process.

4. Wrinkle

Wrinkle is the folding of metal that appears on the fastener surface during the forging process. During a single stroke of forging, wrinkles are generated due to displacement of the material due to lack of volume and shape.

5. Shear mark

The cut is a shallow groove in the longitudinal or circumferential direction.

6. Damage

Screw nicks on any surface. In the manufacture and transportation of screws, it is influenced by the outside world.

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