无损检测专业英语教学课件ppt作者晏荣明unit4-MagicTesting课件.ppt

4.1 Introduction Magnetic testing (MT), also referred to as magnetic particle inspection (MPI), magnetic particle testing , is a relatively simple test method that can be applied to a variety of product forms such as castings, forgings, and welding. 4.1 概论 磁力检测(MT)也可以称为磁粉检测(MPI)，是一种相对简单的检测方法，适用于铸件、锻件和焊接件等各种产品的检测。 4.1 Introduction Magnetic testing consists of magnetization of the article, application of the particles, and interpretation of the patterns formed by the particles as they are attracted by magnetic leakage fields 4.1 概论 磁粉检测的过程包括工件磁化，磁粉施加，漏磁场吸附磁粉形成的磁痕的解释。 4.2 Theory and Principles4.2.2 flux leakage field The magnetic field spreads out when it encounter the small air gap created by the crack because the air cannot support as much magnetic field per unit volume as the magnet can. If iron particles are sprinkled on a cracked magnet, the particles will be attracted to and cluster at the poles at the edges of the crack. 4.2 理论和原理4.2.2 漏磁场 由于空气传导磁场的能力比磁铁差，所以，当磁场遇到裂纹内的空气层时就会溢出工件。 如果铁粉洒到有裂纹的磁体，磁粉会被吸引并聚集在裂纹形成的磁极周围， 4.3 Testing system4.3.1 stationary unit Stationary magnetic particle testing units are usually large, not easily moved, are hard wired to a commercial source of electricity and have a wet bath built into them. Most equipment has a thermal circuit breaker which interrupts the operation if an overload occurs and , after sufficient cooling time , restores it again. 4.3 检测系统4.3.1 固定式探伤机 固定式磁粉探伤机体积大，不易移动，与商用电源连接，探伤机中有储液槽。 大部分的设备都具备热断路器，当发生过载的时候可以中断操作，经过一定的冷却时间再重新启动。 4.3 Testing system4.3.2 Electromagnetic yoke Most yokes are also equipped with AC, which can be used for either demagnetization or AC inspection with dry particle techniques. Some yokes have articulated legs that can be adjusted in two places in order to change the distance between the legs and thus vary the flux density. 4.3 检测系统4.3.2 电磁轭 大部分磁轭都配备交流电源，既可用于退磁也可以交流电的干法检测。 部分磁轭的两个磁极是可调的关节，可以在两个位置上调节以改变磁极间的距离，进而调节磁通密度 4.3 Testing system4.3.3 Mediums To achieve the required test s