Magnetic control - an effective way to detect product defects

At the moment, there are many methods to verify the condition of the surfaces of industrial products made of ferromagnetic materials.They help determine the quality of products.One of the proven and recognized methods is a magnetic particle inspection.This method allows you to identify the different kinds of defects - cracks, flaws in welded joints and other.

Description of the method

Magnetic particle inspection is designed to test various products: from large to small HVD products, including all kinds of shapes.It is an effective method of verification.At the same time some characteristics of the material must create magnetization.It is necessary to eliminate the defects of the field of education products.This will facilitate the attraction of particles of a special powder.For more likely to find flaws is necessary that their plane is at right angles to the flow of magnetic flux.This is an important prerequisite.In the case of reduction of this angle is reduced ability to detect defects.

special way

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

  • Magnetic induction.
  • coercive force.
  • residual magnetization.
  • presence of roughness on the surface of the product.
  • highest permeability.
  • surface lighting products.
  • strength of the magnetic field and its location relative to the plane of the defect.


this method is used in various industries.Basically, magnetic particle inspection is used in mechanical engineering, shipbuilding and automotive.Also it is used in the oil and gas industry.Magnetic particle inspection (GOST 21105-87) is characterized by high productivity, sensitivity, allowing you to identify the presence of defects at the time of their appearance.This is its important feature.

Magnetic control: the stages of the method

  1. Preparation of the product to the audit.Produced cleaning the surface of dirt, rust and various oils.If the surface of the object is dark, the magnetic powder is not visible.In this case, the item is a coat of white paint.
  2. Omagnitichivanie products.This is the main stage of control.It is important to choose the way of magnetization.This determines the sensitivity and the probability of finding flaws.
  3. for coating articles magnetic powder or a suspension.This step requires considerable care.When applying the slurry product is dipped into a container of this liquid or, more technologically, pour the product from the hose under a weak pressure.Use of the dry powder is characterized by its application airflow.
  4. Survey products.Reading drawings and grading.Visually inspect the item, or by using optical devices must controller after application and removal of the magnetic substance.For grading should be a comparison with the available photos of various defects.
  5. Degaussing and removing said remaining indicator.This is the final stage.In this case, there are two options demagnetization:
  • most effective is the implementation of heating the article to a temperature of the Curie point.Thus there is a loss of the magnetic properties of the material.However, this method is used very rarely.This is due to the fact that with this heating may occur changes in the mechanical properties of the material of the article, which in many cases is unacceptable.
  • second method is based in the conduct demagnetization parts using an alternating magnetic field with an amplitude which is equally to be reduced by a certain high point to zero.This method is more popular.The frequency of this applied magnetic field depends on the size and shape of the checked items.