Contact-type mechanical seals are widely utilized across various industries, including aviation, maritime, and chemical engineering, owing to their exceptional sealing capabilities. During their operational lifespan, these seals are subjected to diverse frictional states, namely dry friction, boundary lubrication, and hybrid lubrication. In the context of dry friction and boundary lubrication, the predominant mode of friction between the seal faces is attributed to direct contact between microasperities, which significantly contributes to seal wear and impairs its longevity. However, when operating under hybrid lubrication conditions, both fluid film lubrication and microasperity contact play substantial roles in the overall frictional behavior. Given the prevalence of hybrid lubrication as the dominant operating state for contact-type mechanical seals, it becomes imperative to thoroughly investigate the intricate frictional mechanisms governing such conditions. Understanding the underlying phenomena will shed light on the fundamental aspects of friction in hybrid lubrication, thereby facilitating the development of effective strategies to optimize seal performance and enhance their reliability.

In order to investigate the friction mechanism under hybrid lubrication conditions, a comprehensive study was conducted by integrating a rough surface elastoplastic model and solving the Reynolds equation considering the influence of seal face roughness. The impact of various operating conditions, such as rotational speed and fluid pressure, on the friction parameters governing the sealing performance in the hybrid lubrication state was thoroughly examined. Furthermore, an energy formula for the emitted acoustic waves during sealing was derived to quantify the energy distribution. To experimentally validate the findings, a specialized test rig for contact-type mechanical seal friction was developed. Concurrently, the collection of seal face temperature data and acoustic emission signal data was performed. By analyzing the acquired seal face temperature data, the hybrid lubrication state was categorized into distinct wear and stable periods. Subsequently, utilizing the 1.5-dimensional spectral theory, the acoustic emission signals were processed to extract the characteristic frequencies associated with the sealing behavior, thereby unraveling the frictional evolution patterns prevalent in the hybrid lubrication state. The outcomes of this investigation underscored the significant influence of friction parameters on the energy amplitude of the emitted acoustic waves, and established that the form of seal friction underwent alterations throughout the hybrid lubrication state. Specifically, during the wear period, a rapid rise in seal face temperature was observed, accompanied by a pronounced amplitude of characteristic frequencies related to microasperity contact, signifying that microasperity contact dominated the seal face friction. Conversely, during the stable period, the seal face temperature fluctuated within a stabilized range, concomitant with an increased amplitude of characteristic frequencies associated with viscous shear friction of the fluid film. This observation suggested an intensified viscous shear effect, with localized microasperity contact exclusively presented on the seal faces. The conclusions derived from this comprehensive investigation beared crucial theoretical implications for the study of friction mechanisms governing contact-type mechanical seals operating under hybrid lubrication conditions.