The operational process of a wet paper-based friction disc can be divided into three consecutive stages: squeezing, mixed surface contact, and compressed contact. During the squeezing stage, lubricating oil is forced into the pores of the friction disc and the mating steel plate; as pressure gradually increases, the oil is compressed to form a thin film, causing friction to rise while the lubrication regime remains primarily hydrodynamic.
Upon entering the mixed surface contact stage, the lubricating oil is squeezed out of the pores by the engagement pressure. When the oil film thickness falls below the height of the asperities on the paper-based material's surface, these asperities come into contact with the mating steel plate, marking the onset of the mixed lubrication stage.
As the compressed contact stage begins, the oil within the pores continues to be squeezed out, and mechanical contact between the friction disc and the mating steel plate progressively increases. The mixed lubrication stage gradually gives way to the boundary lubrication stage, during which the coefficient of friction rises further.
Wear is inevitable during the repetitive operation of wet paper-based friction discs, primarily manifesting as thermal wear, adhesive wear, abrasive wear, and fatigue wear. Thermal wear arises from heat generated by the repeated engagement and disengagement of the friction disc and steel plate, causing reactions such as high-temperature decomposition and oxidation in the paper-based material. Adhesive wear occurs when asperities on the paper-based material undergo plastic deformation under high stress and bond to the mating steel plate. Abrasive wear stems from particles formed by fillers within the paper-based material after resin curing. Finally, fatigue wear results from the long-term accumulation of stress concentration and plastic deformation in the contact zone caused by the relative sliding between the friction disc and the mating plate.
