Magnetic powder flaw detection principle and summary

Magnetic powder flaw detection principle 

Magnetic powder flaw detection is also called MPT(Magnetic Particle Testing),suitable for steel and so on magnetic materials surface flaw detection ,take advantage of principle of iron be attracted by magnet to detect。When doing magnetic powder flaw detection ,make detected objects received  the effect of magnetism  ,make magnetic powder distributed on its surface,then the flaw section surface leak magnetism will attract magnetic powder，forming indicating diagram，indicating diagram is more ten times than real flaw ,so it is easy to find flaw 。

Magnetic powder flaw detection method

Magnetic powder flaw detection is divided into earlier stage processing、magnetization、usage of magnetic powder 、Observation and after treatment。

The follows respectively introduce summary of every step

(1)    Earlier stage processing 

If the detecting surface has  grease、painting、rust or other things, they will not only obstruct magnetic powder absorb flaw,but also happen to magnetic powder absorb out of flaw and form picture,so before magnetization,it needs to adopt physical or chemical deal to eliminate dirt。

 (2)  Magnetization 

It is important to make detecting object magnetized properly .usually adopting flaw direction and magnetic line vertical magnetization ,in addition ,for magnetizing properly,according the shape of detecting object,a lot of ways can be used,the japan industry regulation (JIS G 0565-1992) regulates as follow seven methods of magnetization。

①　Axial Current flow method....... On the axial direction of detecting object pass the current directly

②　  Vertical current flow method...... Pass the current on perpendicular to the axis  

③　Prod method..... Place two pole at the partial of detecting object

④　 Central conductor method ....on the hole of detecting object utilize the current

⑤　Coil method ....put coil into detecting object and connect current to coil

⑥　Yoke method...... Put detecting object or needed to detect into electromagnet or permanent magnet 

⑦　Magnetic line linking method..... Bring alternating magnetic line to strong magnetic objects of hole that cross the detecting object

(3)  magnetic powder usage ,the principle of magnetic powder flaw detection

 The kinds of magnetic powder

 For making magnetic powder absorb magnetic pole of flaw part to form image,the magnetic powder must be easily magnetized by weak magnetic field on the part of flaw, Absorbed on the magnetic pole ,that means it needs brilliant absorbing property ，in addition ,requiring formed magnetic powder image must has high level of  identifiability 。

Normally ,practical magnetic powder in the magnetic powder flaw detection has white 、black、red and so on magnetic powder,and fluorescent magnetic powder that take advantage of fluorescent ,In addition,according to the place of magnetic powder usage,there are powdered dry magnetic powder,and wet magnetic powder that use in the water or oil。

The using time of magnetic powder

The using time of Magnetic powder is divided into crossing magnetizing current  and use of magnetic

(4)  observation 

For being convenient to observe magnetic image that attach flaw part,must create easily observed environment,common magnetic powder should be observe under the environment that as bright as possible,fluorescent magnetic powder will be observed by using ultraviolet radiation lamp and make surrounding environment dark 

(5) after-treatment

At the end of magnetic powder flaw detection,detecting object maybe still be a product or needed to sent to next processing step to receive machining 。Then it is needed to do demagnetization eliminate magnetic powder and rust prevention .