Types And Causes Of Nut Surface Defects-Cracks

Fastener nuts are common parts of connectors. For the use of fastener nuts, the common surface defect problems are cracks (quenched cracks, forged cracks and slag cracks, cracks in the locking part of the all-metal effective torque type lock nut, cracks in the washer seat of the nut-washer assembly), shear bursts, bursts, cracks, wrinkles, dents, cut marks and damage, etc. As a professional fastener manufacturer, Xinchi Fastener Company is willing to explain some problems of fastener nut surface defects in detail.

A crack is a clear (crystalline) break along or across the boundary of a metal grain and may contain the inclusion of foreign elements. Cracks are usually caused by high stress in the process of forging or other forming processes or heat treatment, and there may also be cracks in the raw materials. When the workpiece is reheated, the crack is usually discolored by the peeling of the oxide skin.

Quenching crack

Quenching crack

Reasons for quenching cracks: During the heat treatment process, due to excessive thermal stress and strain, quenching cracks may occur. The quenched crack usually appears on the surface of the nut in an irregular direction.

Note: Quenched cracks of any depth, length, or location are not allowed.

Forging cracks and slag inclusion cracks

Forging cracks and slag inclusion cracks

Reasons for forging cracks and slag cracks: Forging cracks may occur during cutting or forging and are located on the top or bottom of the nut, or where the top (bottom) meets the opposite side plane. Slag cracks are caused by non-metallic slag inherent in raw materials.

Note: Cracks located on the nut-bearing surface or bottom and top surfaces shall meet the following requirements respectively:

1. There should be no more than two satin cracks running through the supporting surface, and the depth should not exceed 0.05D.
2. The crack extending into the screw hole shall not exceed the complete thread of the first buckle.
3. The crack depth on the first complete thread shall not exceed 0.5H1.

D-nominal diameter of thread; H1-thread actual tooth height; H1=0.541P; P-Pitch.

The crack of the lock part of an all-metal effective torque-type lock nut

Crack of lock part of all-metal effective torque type lock nut

Cause: Cracks in the locking portion of an all-metal effective torque-type lock nut may occur during beveling or forging or closing (flattening) and appear on external or internal surfaces.

Note: The cracks produced by forging and located in the locking part shall meet the mechanical and working performance requirements of the nut and shall also meet the following requirements:

1. There should be no more than two cracks running through the top circumference, and the depth should not exceed 0.05D.
2. The crack extending to the screw hole shall not exceed the complete thread of the first button.
3. The crack depth on the first complete thread should not exceed 0.5H1.

Cracks due to closing (squashing) and located in the locking section should not be allowed.

D- nominal diameter of thread; H1-thread actual tooth height; H1 = 0.541, P; P- indulge.

Crack in the washer seat of the nut-washer assembly

Crack in the washer seat of the nut-washer assembly

A crack in the washer seat is a crack in the edge or raised part of the metal during the process of securing the washer to the nut.

Cause of washer seat cracks in nut-washer assemblies: Washer seat cracks may occur when pressure is applied to edges or raised parts during washer assembly.

Note: The crack of the gasket seat should be controlled within the edge or raised part after turning the riveting, and the gasket should be able to rotate freely without falling off.

Xinchi Fastener Company is a trustworthy fastener company, especially in furniture nuts. And we are the designated fastener supplier to“STAPLE”. As a trusted fastener supplier,  Xinchi Fastener Company can offer a wide range of high-quality fasteners, including tee nuts, screws, bolts, rivets, washers, etc. If you want to know more about fasteners or want to wholesale fasteners, please feel free to contact us. And then our experienced and expert service team will reply to you as soon as possible.