The paper presents the implementation of the method of own residual magnetic field to identify damages occurring in a steel rope. A special measuring head with 4 residual magnetic field sensors, spaced evenly every 90 degrees, was used. The measuring head was also equipped with a path or a time sensor. The measurement consists in recording normal and tangential components of the residual magnetic field and their gradients. This method has a number of advantages with regard to classic magnetic methods. It does not require special magnetisation of the rope or its special preparation for testing. Validation of the obtained test results of this rope was conducted by the classic MTR method and a very good compliance in the detection of damage was demonstrated. It was found that the strong magnetisation used in the MTR method does not affect the detection of damage to the rope using the residual magnetic field method.
The brake linkage of a hoisting machine is a very important component determining the safety of the hoisting machine’s entire braking system. It is subject to weekly inspections. However, an efficiency test of brake performance is carried out every 6 months. Once every 3 years, a test must be carried out by an appraiser who pays particular attention to the executive and control components of the brakes as well as the strain - brake system and brake release components. The legal provisions regulating the testing of braking system linkages are not precise. So far, the control has been based on random measurement of strains using electrical resistance strain gauges stuck to the surface of the linkage. A new method for measuring the strains of the linkage has been proposed in the work. It is based on fibre optic strain sensors with Fibre Bragg Gratings (FBG). They are mounted using specially designed and tested holders for mounting on the brake linkage. They provide quick assembly and the measurement of strain in the direction parallel to the axis of the linkage. The structure of the holder also allows for the measurement in 4 positions turned every 90 relative to one another. Such a measurement enables a comprehensive analysis of strains and stresses in the brake linkage. In the work, it was shown that there is a complex state of strain and stress in the brake linkage. The previous procedures for linkage testing are inadequate in relation to this condition. An experimental and numerical method was proposed to assess the state of linkage stress. It should constitute the basis for the decision of the appraiser to allow the linkage for further use. The method proposed in the work also allows for continuous measurements of linkage strains as well as dynamic braking tests.
The paper presents a new method for measuring the strain and load of wire ropes guide using fiber optic sensors with Bragg gratings. Its principle consists in simultaneous fiber optic measurement of longitudinal strain of the rope and transverse strain of the bolt fixing the rope. The tensometric force transducers which have been used so far were only able to determine the load in the head securing the rope through an indirect measurement using a special strain insert. They required calibration, compensation of temperature changes, as well as periodic checking and calibration. The head fastening the rope required significant design changes. Measurement based on fiber optic sensors does not have these drawbacks and is characterized by a much higher accuracy and safety of measurements, because the working medium is light. The fastening head does not change. The measurement of the rope load may be based on the change of strain value or indirectly by means of measuring the deflection of the bolt fixing the rope holder. The proposed solution consists in placing the optical fiber with Bragg grating inside the bolt. It enables continuous measurements with a frequency of 2 kHz. A special test bench was built at the Research and Supervisory Centre of Underground Mining. Testing on guide ropes was carried out in a mining hoist in the Piast mine.