When using screw fasteners, we will see that some screw fasteners are not very good in appearance, and some may have cracks. So what are the types of surface defects in screw fasteners? The following Shishitong will come to talk with you briefly, the common screw fastener defects; convenient for everyone to buy the screw fasteners in the future.
1.Crack
Cracks are usually caused by excessive stress during the forging or other forming process or heat treatment of the metal.
Among them are: quenching cracks, forging cracks, forging bursts, shear bursts.
1) Quenching crack
During the heat treatment, quenching cracks may occur due to excessive thermal stress and strain. Quenching cracks are usually irregularly intersected and irregularly oriented on the surface of the fastener.
2) Forging cracks
Forging cracks may be created during the cutting or forging process and are located on the top surface of the head of the screw and the raised portion of the pocket head.
3) Forging burst
Forging bursts may occur during the forging process.
4) Shearing burst
A shear burst may occur during the forging process, such as on the round head of a round head or flange head or the circumference of the flange face, usually about 45° to the axis of the screw.
2. Cracks or streaks in raw materials
The cracks or streaks of the raw material are usually a thin straight line or a smooth curve extending longitudinally along the thread, the polished rod, and the head. It is usually a defect inherent in the manufacture of fastener raw materials in China.
3. Dent
A dent is a shallow pit or depression that appears on the surface of the screw. It is very urgent or embossed by the rust layer of chips or shear burrs or raw materials, and cannot be eliminated in the forging or upsetting process.
4. Wrinkles
Wrinkles are the folding of the metal that appears on the surface of the fastener during the forging process. During the impact of forging, wrinkles are generated due to the displacement of the material due to insufficient volume and shape.
5. Cut marks
The cut is a shallow groove in the longitudinal or circumferential direction. It is caused by the delivery of the tool beyond the surface of the screw.
6. Damage
The nick of the screw on any surface. Produced by external influences during the manufacture and transportation of screws.
The above six kinds are common defects of screw fasteners. When buying screw fasteners, we must pay attention to see if the surface of the screws has these defects.
