船舶焊接生产基础 (19).pdf
Content The concept of magnetic particle testing 1 The principle of magnetic particle testing 2 Magnetic particle testing system 3 Magnetic particle testing process 4 The concept of magnetic particle testing The concept of magnetic particle testing Magnetic particle testing is a non-destructive flaw detection method that uses the magnetic field leakage at the defect to interact with the magnetic powder to produce magnetic marks,and detects the surface and near surface defects of ferromagnetic materials.The principle of magnetic particle testing.1 0 After the ferromagnetic material and the workpiece are magnetized,due to the presence of discontinuities,the magnetic field lines on the surface of the workpiece and the near surface are distorted locally and the magnetic field leakage is generated,and the magnetic powder applied to the surface of the workpiece is adsorbed to form a magnetic mark visible under the appropriate light,thus showing the position,shape and size of the discontinuity.Basic principle The principle of magnetic particle detection The principle of magnetic particle detection 1-Leakage field,2-crack,3-Near surface stomach,4-Scratch,5-Internal air hole,6-Magnetic induction line,7-Workpiece.1 Magnetic particle testing is suitable for detecting discontinuous defects with small surface and proximity surface sizes,extremely narrow gaps(e.g.,cracks 0.1 mm long and micron wide)that are difficult to see visually.Scope of application of magnetic particle detection The principle of magnetic particle detection 2 Martensitic stainless steels and precipitation hardened stainless steels are magnetic and can be MT performed.MT can find defects such as cracks,inclusions,hair lines,white spots,folding,cold insulation and looseness.Scope of application of magnetic particle detection The principle of magnetic particle detection 3 MT cannot inspect austenitic stainless steel materials and welds welded with austenitic stainless steel electrodes,nor can it inspect non-magnetic.materials such as copper,aluminum,magnesium,and titanium.Scope of application of magnetic particle detection The principle of magnetic particle detection Magnetic particle detection system Magnetic particle detection equipment Magnetic powder and magnetic suspension Standard specimens Magnetic particle detection system portable Magnetic particle flaw detector Fixed Magnetic particle flaw detector Magnetic particle flaw detector Mobile Magnetic particle flaw detector Magnetic yoke type Magnetic particle flaw detector Magnetic conical Magnetic particle flaw detector Magnetic particle detection system Application of magnetic particle detection equipment Portable magnetic particle flaw detector Mobile magnetic particle flaw detector Fixed magnetic particle flaw detector Magnetic particle detection on site Pressure vessel and boiler local flaw detection Small and medium-sized workpieces Workpieces that require a larger current Large workpieces that are not easy to move The type of magnetic powder Magnetic powders are divided into two categories:non-fluorescent magnetic powder and fluorescent magnetic powder.Non-phosphors are divided into black magnetic powder,red magnetic powder and white magnetic powder according to color.Magnetic powder and magnetic suspension Magnetic particle detection system Black magnetic powder：The composition is mainly Fe3O4,which is mainly used for the inspection of light-colored workpieces,and is more commonly used in magnetic particle flaw detection.Red magnetic powder：The main component is Fe2O3,which is often used to inspect black workpieces.White porcelain powder：It is synthesized by black magnetic powder and Al2O3 or MgO,and is mainly used for black workpieces.Magnetic powder and magnetic suspension Magnetic particle detection system 磁粉及磁悬液 Magnetic suspension：The solution that mixes the magnetic powder and liquid in a certain proportion is called the magnetic suspension.Magnetic particle detection system Magnetic powder and magnetic suspension 磁粉及磁悬液 There are three types of magnetic suspensions Oil suspension Water suspension Fluorescent magnetic suspension Magnetic particle detection system Magnetic powder and magnetic suspension Used to verify the combined performance of magnetic particle detection equipment,magnetic powder and magnetic suspension(system sensitivity).It is used to detect the magnetic field direction,effective magnetization range and approximate effective magnetic field strength on the surface of the workpiece to be inspected.Standard specimens have the following uses：Magnetic particle detection system It is used to check whether the testing process procedures and operating methods used are appropriate.When it is not possible to calculate the magnetization specification of a complex workpiece,a small,soft specimen is attached to the uneven part of the complex workpiece to roughly determine the ideal magnetization specification.Standard specimens have the following uses：Magnetic particle detection system Magnetic particle detection process The general process of magnetic particle detection pretreatment 1 Magnetization 2 Apply magnetic powder 3 Magnetic trace analysis 4 Demagnetization 5 Post-processing 6 Residual magnetism 02 Continuous method 01 Inspection process Magnetic particle detection process pretreatment-Workpiece magnetization and application of magnetic powder-Post-sequence process.The magnetization time is long,the magnetization effect is good,and this method is generally used for welds and large and medium-sized workpieces.Continuous method Magnetic particle detection process Magnetic particle detection process Magnetic particle detection process M a g n e t i c p a r t i c l e d e t e c t i o n p r o c e s s Residual magnetism pretreatment-Workpiece magnetization-Apply magnetic powder-Post-sequence process.The sensitivity of the residual magnetic method is lower than that of the continuous method,which is only suitable for checking surface defects,but the residual magnetic method is particularly suitable for small workpieces produced in series.Thanks for watching
