When mining machinery operates under complex conditions for extended periods, the difference in thermal expansion coefficients between its wear plates and the substrate material can lead to interfacial stress concentration, cracking, and even detachment, directly impacting equipment lifespan and safety. This difference stems from variations in material composition and crystal structure; for example, high-chromium cast iron wear plates typically have significantly different thermal expansion coefficients than low-carbon steel substrates, requiring a systematic design strategy to address.
Material matching design is a fundamental approach to resolving thermal expansion differences. Priority should be given to material combinations with similar thermal expansion coefficients, such as using a nickel-based alloy wear-resistant layer combined with a substrate of the same material, or adjusting the proportions of alloying elements to reduce the difference. If perfect matching is not possible, an intermediate transition layer can be introduced, with a thermal expansion coefficient between that of the wear plates and the substrate, forming a gradient transition structure. This design disperses interfacial stress, preventing cracking caused by localized stress concentration, while maintaining the overall strength of the composite structure.
Structural optimization design can effectively mitigate thermal stress accumulation. Using flexible structures at the connection points between the wear plates and the substrate, such as corrugated, dovetail, or stepped interfaces, can absorb some of the thermal expansion differences through geometric deformation. For example, elastic buffer grooves can be incorporated into the edges of wear plates to allow for slight deformation during temperature changes without damaging the bonding surface. Furthermore, optimizing welding process parameters, such as employing segmented symmetrical welding or low-temperature annealing, can reduce the cumulative effect of residual welding stress on thermal expansion behavior.
Prestress compensation technology counteracts differences in thermal expansion by actively applying reverse stress. During assembly, prestress is applied to the wear plates, placing them in a slightly compressed state at room temperature. As the temperature rises, the expansion tendency of the wear plates is partially offset by the prestress, thus aligning with the expansion of the substrate. This technology requires precise calculation of the relationship between the magnitude of the prestress and the temperature variation range, typically necessitating optimization design combined with finite element simulation to ensure stress balance throughout the equipment's lifespan.
Dynamic temperature control is an effective measure to address extreme operating conditions. Temperature monitoring sensors are installed in key components of the mining machinery to provide real-time feedback on the temperature distribution between the wear plates and the substrate. When the temperature difference exceeds a set threshold, the cooling or heating system is automatically activated to adjust the local temperature, maintaining both surfaces at similar operating temperatures. For example, circulating cooling water channels are installed around the wear-resistant sleeve of the hydraulic support column. By controlling the water flow rate, a constant temperature is maintained, preventing interface failure caused by temperature fluctuations.
Surface treatment techniques can enhance interfacial bonding strength to resist thermal stress. Sandblasting, laser roughening, or chemical etching are applied to the interface between wear plates and the substrate to increase surface roughness and contact area. Simultaneously, coating the interface with a metal bonding layer or ceramic transition layer improves material compatibility and enhances anti-peeling ability through micro-mechanical interlocking. These treatments significantly improve interfacial bonding energy and delay the initiation and propagation of thermal fatigue cracks.
Regular inspection and maintenance are crucial for ensuring long-term stable operation. Non-destructive testing techniques such as ultrasonic flaw detection and infrared thermography are used to regularly assess the bonding status between wear plates and the substrate. Special attention is paid to monitoring stress concentration areas and locations with temperature gradient changes to promptly identify potential problems. For interfaces with microcracks, in-situ repair can be performed by localized remelting or injection of repair agents to restore load-bearing capacity and sealing performance.
The difference in thermal expansion coefficients between wear plates and the substrate material in mining machinery needs to be addressed through a comprehensive approach, including material matching, structural optimization, prestress compensation, temperature control, surface treatment, and regular maintenance. These strategies work synergistically to mitigate the damaging effects of thermal stress on the bonding surface and improve the overall performance and reliability of the composite structure, ensuring the long-term stable operation of mining machinery under harsh conditions.
