Magnetic particle inspection - an effective way to detect product defects

At the moment, there are many methods for checking the condition of surfaces of industrial products made of ferromagnetic materials. They help determine product quality. One of the proven and recognized methods is magnetic particle inspection. This method allows you to identify all sorts of defects - cracks, defects in welded joints and so on.

Method Description

Magnetic particle control is designed to test different products: from large to small-sized products, including all kinds of shapes. It is an effective verification method. At the same time, certain material features should create magnetization. It is necessary for the formation of a field to eliminate defects in the product. This will contribute to the attraction of particles of a special powder. For a greater chance of finding flaws, it is necessary that their plane be at right angles to the magnetic flux. This is an important condition. If this angle is reduced, the ability to detect defects is reduced.

Method Feature

Magnetic powder control method depends on certain properties of the product material. Their presence is important in this case. These include:

• Magnetic induction.
• Coercive force.
• Residual Magnetization
• The presence of roughness on the surface of the product.
• The greatest magnetic permeability.
• Illumination of the surface of the product.
• The magnetic field strength and its location relative to the plane is flawed.

Application area

The specified method is used in various industries. Mainly magnetic particle control is used in machine, ship and automotive industries. It is also used in the oil and gas industry. Magnetic particle control (GOST 21105-87) is characterized by high productivity, sensitivity, which allows to identify the presence of flaws at the time of their appearance. This is his important property.

Magnetic particle control: method steps

1. Preparing the product for inspection. The surface is cleaned of dirt, rust and various oils. If the surface of the product is dark, then the magnetic powder is not visible. In this case, a layer of white paint is applied to the part.
   
2. Magnetization of the product. This is the main stage of control. It is important to choose the correct method of magnetization. This determines the sensitivity and likelihood of finding flaws.
3. Coating the surface of the product with magnetic powder or suspension. This stage requires considerable care. When applying the suspension, the product is immersed in a container with this liquid, or, more technologically, they are doused with a hose from a hose under low pressure. The use of dry powder is characterized by applying it with an air stream.
4. Inspection of the product. Reading drawing and grading. Inspect the part visually or using optical instruments should the controller after applying and removing the magnetic substance. For sorting, comparison with existing photographs of various flaws is necessary.
5. Demagnetization and removal of the remaining specified indicator. This stage is the final one. In this case, there are two options for demagnetization:

• The most effective is to heat the product to the Curie temperature. In this case, the magnetic properties of the material disappear . However, this method is used very rarely. This is due to the fact that with the indicated heating, a change in the mechanical properties of the material of the product can occur, which in many cases is unacceptable.
• The second method is based on demagnetizing the part using an alternating magnetic field with an amplitude that should uniformly decrease from a certain maximum point to zero. This method is more popular. The frequency of the indicated magnetic field used depends on the size and shape of the part being tested.