JB/T 51126-1999

Manufacturers of internal combustion engines and quality inspection agencies use this standard to grade the quality of cylinder head bolts and flywheel bolts. By defining clear indicators for qualified, first-grade, and premium-grade products, it helps ensure that bolt mechanical properties, dimensional accuracy, and surface quality meet varying application needs. This standard is critical for ensuring the reliability and safety of key fasteners in internal combustion engines.

内燃机制造商和质检机构使用该标准来评定气缸盖螺栓和飞轮螺栓的质量等级。它通过设定合格品、一等品和优等品的明确指标，帮助确保螺栓的力学性能、尺寸精度和表面质量满足不同应用需求。该标准对于保证内燃机关键紧固件的可靠性和安全性至关重要。

This standard JB/T 51126-1999 specifies quality grading requirements for cylinder head bolts and flywheel bolts in internal combustion engines, classifying products into three grades: qualified, first-grade, and premium-grade. It covers mechanical properties (tensile strength, yield strength, hardness), metallographic structure, thread tolerances, geometric tolerances (perpendicularity, coaxiality, straightness), surface roughness, surface treatment, and visual appearance. Inspection methods include tensile testing, hardness testing, metallographic examination, magnetic particle inspection, thread precision measurement, and surface roughness measurement. Sampling inspection follows GB/T 2828, with specified AQL values and decision schemes for each grade. The standard applies to reciprocating internal combustion engines with cylinder diameters up to 200 mm, providing a unified basis for product quality assessment.

本标准JB/T 51126-1999规定了内燃机气缸盖螺栓和飞轮螺栓的质量分等要求，将产品分为合格品、一等品和优等品三个等级。标准涵盖了力学性能（抗拉强度、屈服强度、硬度）、金相组织、螺纹公差、形位公差（垂直度、同轴度、直线度）、表面粗糙度、表面处理及外观质量等指标。检验方法包括拉伸试验、硬度试验、金相检验、磁粉探伤、螺纹精度测量和表面粗糙度测定等。抽样检验按GB/T 2828执行，规定了不同等级对应的AQL值和判定方案。该标准适用于气缸直径200mm以内的往复式内燃机，为产品质量评定提供了统一依据。