OBRABOTKAMETALLOV technology Vol. 26 No. 3 2024 Changes in the submicrostructure characterize the adhesive polymerization process. A decreased height of the profile irregularities indicates that the polymer chain formation process is uniform and the chains further grow after ultrasonic treatment. The treatment conditions of 10 and 25 µm resulted in the greatest smoothing of the submicrostructure by 2.7 and 1.92 times, respectively. In these processing conditions, a sufficient number of cavitation bubbles are formed and stable large-scale acoustic flows arise, which are necessary for uniform processing of the entire adhesive volume. The large height of the irregularities obtained at 25 µm is associated with heating the adhesive to a temperature of 45 °C, which accelerates the polymerization process. Low-amplitude processing ξm = 4 µm occurs with a significantly smaller volume of the cavitation region localized under the radiator, and the absence of large-scale flows does not allow bubbles to spread rapidly through the treated volume. As a result, ultrasound does not process the entire volume of adhesive, which is illustrated in the image of the submicrostructure, with a clear boundary between the treated and untreated parts of the adhesive. This leads to anisotropy of the properties of the hardened polymer. Changes in microhardness and shear stress correlate with changes in the polymer structure. The maximum results were achieved when processing at an amplitude of 10 µm for 5 seconds. Microhardness increases by 30 %, while shear stress by 24 % during stretching. Effect of ultrasonic vibrations on the assembly of a threaded joint The analysis of these studies makes it possible to find the optimal mode of ultrasonic treatment during the assembly of a threaded joint. When shear vibrations are communicated, the maximum increase in the relative torque of loosening Tl is achieved in the conditions of ξm = 5–9 µm. The best results in ultrasonic treatment of epoxy adhesive were achieved at an amplitude of ξm = 10 µm. As a result, vibration amplitude of 9 µm was selected for the assembly of the adhesive-threaded joint, at which the threaded parts do not heat up above 50 °C, and which, according to the effects occurring in a liquid medium, corresponds to a transient processing mode (8–12 µm). Ta b l e 2 Properties of adhesive under various treatment modes treatment mode No treatment xm = 4 мкм, t = 20 с xm = 10 мкм, t = 5 с xm = 25 мкм, t = 5 с Surface image 308×308 nm (constant height method) Average height of profile irregularities at the submicrolevel Rac, nm 2.63 1.67 0.98 1.35 Microhardness, kg/mm3 0.77 0.75 1.01 0.92 Shear stress τ, MPa 5.5 5.1 6.8 6.2
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