The binding agent of grinding wheels

The binding agent plays a pivotal role in securely bonding abrasive particles, thereby ensuring that the grinding stone possesses crucial mechanical properties such as strength, toughness, wear resistance, and heat resistance. It also provides the necessary holding force to the abrasive during the grinding process. There are three primary types of grinding stone bonds: ceramic-based, metal-based, and resin-based. Ceramic bonds are noted for their stable chemical properties and exceptional heat resistance. However, their brittleness and poor thermal conductivity make them unsuitable for the rigorous conditions of rail grinding, which involve high speeds, heavy loads, elevated temperatures, and intense vibrations. Currently, there are no reported instances of ceramic bond grinding stones being used in rail grinding.

Metal-bonded materials can impart high strength, high thermal conductivity, and high wear resistance to grinding stones. Jiang et al. prepared copper-based [1] and iron-based [2] metal-bonded grinding stones using powder metallurgy. The grinding experiments revealed that the grinding ratio of the iron-based grinding stone was approximately 15 times higher than that of the resin-based grinding stone, reaching as high as 686. However, the high strength of the metal bond makes it difficult for the bond to wear during the grinding process, thereby exposing the abrasive and resulting in poor self-sharpening of the grinding stone. Additionally, since rail grinding cars lack the conditions for passivation grinding stone sharpening, metal-based grinding stones do not have an advantage in line grinding operations. Furthermore, the sintering temperature of metal-bonded grinding stones is high, the process is complex, the manufacturing cost is high, and the economy of the grinding stone is poor. Currently, there are no instances of metal-bonded grinding stones being used in line grinding. In the future, research will focus on balancing the strength and self-sharpening of metal-based grinding stones, finding low-cost production raw materials, and streamlining the manufacturing process. Resin binders, which possess high strength, toughness, and low raw material prices, along with a simple molding process, are widely used in abrasive manufacturing. Currently, the grinding stones (active grinding and high-speed passive grinding) equipped on rail grinding vehicles for rail transit lines both domestically and internationally are all resin-based grinding stones [3,4]. Rail grinding conditions are harsh, and the grinding temperature is high in the dry grinding state. Therefore, the grinding stones generally utilize phenolic resins with high temperature resistance, good adhesion, and easy molding, as well as newly modified varieties such as epoxy, polyvinyl chloride, polyamide, polyvinyl ether, bismaleimide, and other modified phenolic resins [5]. Polyphenol ether resins and polyimide resins with higher heat resistance and mechanical properties are also commonly used [6]. Zhang et al. [4] studied the grinding properties of four phenolic resin grinding stones and found that ensuring the strength, toughness, and heat resistance of the resin at high temperatures were crucial factors for the preparation of high-performance grinding stones. The results of Zhang et al. [7] showed that low-strength (low binder content) grinding stones had good self-sharpening and large material removal but were prone to burning the rail and had poor wear resistance. Conversely, high-strength (high binder content) grinding stones exhibited good wear resistance and a high grinding ratio but poor self-sharpening. Zhang et al. [8] suggested that the debonding of the abrasive/binder interface was the primary reason for the premature shedding of the brown fused alumina grinding stone abrasive, leading to a low grinding amount and grinding ratio. These findings indicate that the strength, toughness, heat resistance, and wettability of the resin on the surface of heterogeneous materials (abrasives, fillers, etc.) directly affect the comprehensive properties of the grinding stone. Therefore, it is of great scientific significance to select resins with high strength, toughness, thermal decay resistance, and strong wettability, and to clarify the bonding mechanism of resin/abrasive, resin/filler, and other heterogeneous interfaces within the grinding stone system.

[1]SUN Daming, JIANG Xiaosong, SUN Hongliang, et al. Microstructure and Mechanical Properties of Cu-ZTA Cermet Prepared by Vacuum Hot Pressing Sintering[J]. Materials Research Express, 2020, 7(2): 26530.

[2]SUN Daming, JIANG Xiaosong, SUN Hongliang, et al. Microstructure and Mechanical Properties of Fe-ZTA Cermet Prepared by Vacuum Hot-pressed Sintering[J]. Materials Research Express, 2020, 7(2): 26518.

[3]China Railways Corporation. Q/CR 1-2014. China Railway Corporation Enterprise Standard: Technical Specifications for the Procurement of Grinding Wheel for the Rail Grinding Train[S]. Beijing: China Railway Publishing House Co, LTD, 2014: 1-13.

[4]JI Yuan. The Systematic Study in the Evaluation Technology of Grinding Wheel for Rail Grinding[D]. Beijing: China Academy of Railway Science, 2019.

[5]ZHANG Guowen, HE Chunjiang, PEI Dingfeng. Study on the Effect of Phenolic Resin on Grinding Performance of Rail Grinding Wheel[J]. Railway Quality Control, 2015, 43(02): 21-24.

[6]WU Leitao. Study on the Effect of Copper-Tin Alloy Powder on Mechanical Properties and Grinding Performance of the Resin Bond Superhard Products[D]. Zhengzhou: Henan University of Technology, 2011.

[7]ZHANG Wulin, FAN Xiaoqiang, ZHANG Pengfei, et al. Probing the Eeffect of Grinding Stone Strength on Rail Grinding Behavior[J]. Tribology, 40(03): 385-394

[8]ZHANG Wulin, LIU Changbao, YUAN Yongjie, et al. Probing the Effect of Abrasive Wear on the Grinding Performance of Rail Grinding Stones[J]. Journal of Manufacturing Processes, 2021, 64: 493-507.