Quality identification of self-locking nuts

self-locking nut is based on the core principle of mechanical locking and anti-loosening. By optimizing preload control, locking structure reliability and material strength, it achieves the synergy of threaded connection anti-loosening, corrosion resistance and reusability. It is widely used in high-vibration scenarios in aerospace, automobile manufacturing, rail transit and heavy machinery. In engine fastening, it is used for creep resistance in high-temperature working conditions; in bridge structures, it meets the stress corrosion protection in high-humidity and high-salt environments; in automated production lines, it ensures the long-term stability of robot joints. Compared with ordinary nuts, self-locking nuts have the characteristics of asymmetric thread deformation, nylon insert preloading or all-metal elastic locking, and are core components in the field of anti-loosening fastening.

Zhongke Testing is a product quality appraisal service organization registered with the court. It can provide self-locking nut quality appraisal services. It has a professional appraisal team and advanced instruments and equipment to provide fair and accurate appraisal results for self-locking nut quality appraisal.

has significantly increased the number of quality disputes associated with the upgrading of security standards. Judicial disputes focused on: HTMLGTOKEN1HTMTAGTOKEN21, performance indicators dispute: failure of anti-frosting test, failure of lock-down lock-down;

self-locking nut quality identification technical methods mainly include:

1, physical detection method

The physical detection method is one of the commonly used methods in identification. For example, by measuring the size, shape and other parameters of the equipment to determine whether the processing accuracy of the equipment meets the requirements; using a hardness tester to detect the hardness of parts and components to determine whether the quality of the material is qualified; using non-destructive testing methods, such as ultrasonic testing, magnetic particle testing, etc., to detect whether there are defects inside the parts.

2, chemical analysis method

Chemical analysis method can be used to detect the chemical composition and purity of equipment materials. For example, through spectral analysis and other methods, the content of various elements in the material can be determined to determine whether the material meets the design requirements. Chemical analysis methods can also be used to detect the composition and quality of equipment surface coatings to determine whether the coating has good protective properties.

A high-speed rail parts manufacturer of the applicant signed a "Titanium Alloy Self-locking Nut Purchase Contract" with a fastener factory of the respondent, and it was agreed that there would be no loosening after vibration for 3,000 times. After being installed and running for half a year, batch loosening occurred. The manufacturer argued that it was caused by improper installation torque.

identification analysis results:

The quality analysis expert group discussed and synthesized technical data on "self-locking nuts" related information, contract technical agreements, on-site investigation case materials and other data. After technical analysis, the following quality analysis opinions were made:

The stress concentration coefficient in the thread deformation zone of the self-locking nut involved in the case exceeded the agreed value by 2 times, and the residual pretightening force was only 60% of the agreed value; the beta phase content of the titanium alloy was >5% (agreed ≤3%), resulting in insufficient fatigue resistance.

The appraisal conclusion determined that defects in structural design and material phase change control were the main reasons for the failure.

Self-locking nut quality appraisal report should include:

1, appraisal purpose (such as safety accident attribution, technical compliance verification) and reference standards;

2, involved product batch, process parameters, testing data;

3, testing method and equipment list (such as Vibration testing machine, DSC analyzer);

4, correlation analysis between test data and failure (such as the impact of stress concentration on fatigue life);