The magnetic particle method in the system of non-destructive quality control of materials occupies one of the leading positions. Approximately 80% of the controlled ferromagnetic products are controlled by the magnetic particle method [1-3].
The high sensitivity of the control method, its versatility, relatively low labour intensity, and the visibility of the results ensured its widespread use in industry.
Magnetic particle inspection is based on the attraction of magnetic particles by the forces of inhomogeneous magnetic fields that arise above defects in a magnetized part, with the formation of indicator patterns in the defect zones in the form of clusters of magnetic particles.
A simple aqueous suspension of 25 ± 5 g of magnetic powder per 1 litre of water is most widely used. However, the use of too hard water can lead to coagulation of the suspension (particles sticking together) on the surface of the part, which makes it difficult to decipher the results of the inspection. To soften water, surfactants are added to reduce the surface tension of water. Besides, anti-corrosion and anti-foam additives may be included in the suspension formulation. The main disadvantage of an aqueous suspension is that it is unsuitable for operation at low temperatures, therefore, as a rule, kerosene, oil or kerosene-oil suspensions are used.
The advantage of kerosene suspensions is that kerosene has very good wettability and penetrating power. Since kerosene is a combustible material, when using it as the basis of a suspension, circular magnetization by electrical contacts is prohibited - to avoid ignition of the suspension during sparking in the electrical contact zone.
The purpose of this work is to test the performance of experimental magnetic suspensions on the MO-1 control sample and to analyze the obtained indicator patterns, which reflect the presence of artificial defects in the sample.
The experimental suspensions were based on the black magnetic powder of the Crocus type, grey powder of the Diagma type, black powder Diagma-1100, red-brown magnetic suspension concentrate Diagma-1200, black powder Fe3O4 (TU-6-14 -1009-79), and specially made concentrated magnetic suspensions of γ-Fe2O3 and Fe3O4 suspended in kerosene. "Diagma" and "Crocus" magnetic powders and concentrated magnetic suspensions of γ-Fe2O3 and Fe3O4 were manufactured in 2021. "Diagma-1100" (from two different batches) and "Diagma-1200" powders in 2010 and have expired (24 months). Fe3O4 (TU-6-14-1009-79) was manufactured in 1987 and also expired. The performance test of expired powders was carried out based on the fact that many industrial enterprises, as a rule, do not take into account the expiration date of powders and continue to use them even after their expiration, for 10-35 years or more.