No 9 (2023)

Using the example of assessing the technical condition of the trunnions of drying cylinders of cardboard-making machines (CDM), the question of the possibility of ranking cyclically loaded elements of dynamic equipment according to the degree of damage to their material by fatigue cracks using acoustic emission (AE) measurements is discussed. As a result of special laboratory studies with varying loads in the cycle of loading and lubrication of the crack banks, the features of AE from the friction of the crack banks and plastic deformation at the crack tip during its growth in a viscous material have been established. It is shown that during cyclic loading of the material, AE signals from the friction of its shores are detected more steadily than AE signals from a crack jump with an increase in its length, and that tracking the former ensures the detection of fatigue damage of the material even under loading conditions insufficient for crack growth. Based on the data obtained, three AE signs of the presence of fatigue damage of the material of the elements of dynamic equipment were developed under the condition of cyclic activation of the movement of the crack banks. As a result of industrial testing of the developed AE features, their operability was confirmed and their boundary values on the operating trunnions of CDM drying cylinders were clarified, and a method for ranking trunnions by the level of damage by fatigue cracks was proposed. By comparing the results of AE measurements with ultrasound control, the reliability of the proposed approach was evaluated, which showed the probability of detecting a fatigue crack in the trunnions of CDM drying cylinders at the level of 71 %, with the probability of their skipping and false rejection of the product 12 and 17 %, respectively. The developed technique is also transferable to other massive dynamic equipment after clarifying the boundary values of AE signs of fatigue damage of the material on this type of object.

If there is a spread of “parasitic” delays between the elements of the antenna array, more than one fourth of the carrier frequency period, the quality of the reflector image reconstructed by the digital antenna focusing (DAF) method will deteriorate due to non-optimal focusing. The paper proposes a method to take into account the influence of “parasitic” delays between antenna array elements during DFA image reconstruction. Its application allowed to increase the frontal resolving ability of the CFA-image of reflectors approximately twice when using a low-quality antenna array with a range of “parasitic” delays in one period. CFA-images reconstructed taking into account the coherent factor are presented.

A review of the methods of production of corundum ceramics with specified characteristics is carried out and possible causes of hidden defects are indicated. Ceramic samples for research were obtained by the method of slip casting and their physical properties were determined. The possibility of diagnosing the integrity of corundum ceramic plates was investigated by the method of active thermal non-destructive testing. Various testing schemes and sources of thermal stimulation of the studied samples were applied. As a reference method, X-ray inspection was used, which confirmed the characteristics of the defect detected by the thermal method in the control sample.

The possibility of detecting defects in the threads of pump rods by the multiple shadow method has been investigated. A specialized electromagnetic-acoustic transducer screwed onto the tested thread was used to implement the method. The proposed approach is based on the spectral method of signal processing and the analysis of the defect influence on the formation of the separate components in the signal spectrum caused by the presence of resonance properties of the thread.

Issues related to the design of a dynamic indentation sensor are presented in this paper. The use of a magnetic induction method for recording the motion parameters of a striker with a differential circuit of inductors is proposed. A prototype of the primary transducer and a sensor model with a new mechanism for the striker reset system are developed.