In general, the detection ability of some small defects on the workpiece through the fluorescent magnetic particle flaw detection machine is called the sensitivity of the magnetic particle flaw detection machine. Some factors that affect the sensitivity of magnetic particle inspection machines include:

① The selection of specific magnetization schemes and methods;

② The size and direction of magnetization;

③ Magnetism, particle size and color of magnetic powder;

④ magnetic levitation concentration;

(5) Size, shape and surface condition of the sample;

Some unique physical properties of the workpiece and the structure that may have defects;

⑦ Detection methods and processes and whether they can be sufficiently standard and accurate.

To be specific:

1, when the magnetic field strength is unevenly distributed on the surface of the workpiece, it is difficult to estimate the size of the magnetization current of the magnetization detector used for multiple random workpieces. It is only necessary to rely on the usual detection work experience of magnetic particle detectors, and it is often difficult to develop when choosing magnetization currents to achieve the desired magnetization. Therefore, when using a magnetic particle flaw detector to detect chaotic workpieces, more sensitive samples can be selected to choose a better magnetization standard.

2, the sensitivity test bar can be used to detect: liquids with magnetic induction and magnetic suspension applications (such as magnetic detectors) can detect the magnetic field distribution at each point on the surface of the workpiece.

The main applications of the test type sheet in the magnetic particle flaw detector are:

1) First, the adhesive tape of the sample using the standard slotted side is placed on the clean surface of the workpiece to be inspected.

2) Then, the workpiece and test piece can be magnetized together with the magnetic powder detector, the magnetic suspension is sprayed on the test piece, and the magnetic mark on the test piece is asked.

3） In the case of sensitive samples, if the magnetization current of the magnetic particle flaw detector is appropriate, the magnetic gap of the groove can be clearly seen on the surface of the sample before the detection function is achieved.

Expansion: Portable magnetic particle inspection machine is usually equipped with probe models generally A, D, E, O these four models:

Type A (horseshoe probe) : It can detect the internal and external angles of various fillet welds and large workpieces.

Type D (electromagnetic yoke probe) : The electromagnetic yoke probe is equipped with a movable joint, which can detect the surface and plane workpiece.

E type (rotating magnetic field probe) : can be used for a variety of welds, surfaces of various geometric shapes, planes, pipelines, boilers, spherical tanks and other pressure vessels for a one-time all-round inspection, the rotating magnetic field probe can also check the full range of defects and scars on the surface of the workpiece.

O-type (magnetic ring coil) : The magnetic ring coil of the portable flaw detector can meet the circumferential crack detection of all workpieces that can be placed in the coil, and it is very convenient to detect the fatigue marks of the workpiece, and it can also be used to demagnetization of the workpiece.

Common steps for portable magnetic particle flaw detection machine to reduce motor heat release:

1. The rotating motor is equipped with a brake device to ensure that the hook tail frame can be accurately in place when rotating.

2, when the motor is in the power input, the coil and the coil of the brake are energized at the same time, at this time the magnet disc of the brake overcomes the spring pressure and is sucked to the side of the magnetic pole group, so that the friction sheet is separated from the brake plate and the motor can be started.

3, when the power is cut off, the magnet disc is pushed out by the spring due to the disappearance of the magnetic field, so that the friction plate on the magnet disc and the brake plate friction, and the motor is quickly braking.

4. Disassembly the brake, the brake skin attached to the magnet disc falls off, resulting in a longer braking distance, up to about 10mm, the electromagnetic suction becomes weak, the magnet disc can not be separated from the system plate, and the friction generates heat.

5, grinding brake disc on the grinder, adjust the brake pad clearance to 0.5mm, test, motor rotation, braking normal.

Quick way to distinguish false magnetic marks of flaw detection machine:

1, the concentration of magnetic powder suspension is too large or may cause unnecessary false magnetic marks, easy to identify, loose powder, the outline of the magnetic track is not clear, and the elimination of magnetic marks after rinsing.

2, the presence of oil, fiber material hair and dirt will adhere to magnetic powder and form magnetic marks. As long as a careful look can be found, and then by cleaning the workpiece profile can be eliminated.

3, the rough surface of the workpiece (such as the depression on both sides of the weld, rough machining and casting surface) will retain magnetic powder to form magnetic marks. The accumulation of very loose powder, the outline of the magnetic track is not clear, the workpiece can be kerosene or wet powder magnetic marking mark can be removed by rinsing.

4, the oxidation and rust of the workpiece profile and the retention of magnetic powder on the edge of the paint spots will form magnetic marks, and the magnetic marks are clearly identifiable after careful inspection.

5, scratches and knife marks: when the magnetizing current is too large, the powder will be absorbed from scratch, but there is no strong magnetic field repeatable.

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