How to determine the interference value of hot-mounted sealing rings

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Since the linear expansion coefficient of the ring seat material is greater than that of the ring, as the temperature rises, the initial interference value gradually decreases. When the temperature reaches a certain level, the interference value drops to zero, and the reliability of the sealing ring is lost. Using this as a basis, the interference value at room temperature is calculated inversely. The expansion amount of the ring at operating temperature is △d1 = d1α1(t1 – t0), while the expansion amount of the ring seat at operating temperature is △d2 = d2α2(t2 – t0). Here, d1 and d2 represent the outer diameter of the ring and the inner diameter of the ring seat, respectively ； α1, α2 —— are the linear expansion coefficients of the ring (YG6) and the ring seat, respectively ； t1, t0 —— represent the operating temperature and room temperature respectively ； d1t, d2t —— are the diameters of the ring and the ring seat at the operating temperature, respectively. As can be seen from Figure 26, the interference value e at room temperature is given by: e=△d2-△d1 =d2α2(t2-t0)-d1α1(t1-t0). Taking d2=d1 and t2=t1=t, where t is the temperature of the pumped medium. At room temperature, the interference value e for the ring and the ring seat is given by e = d1(α2 – α1)(t – t0). In actual operation, the temperatures of the ring and the ring seat are different, but the difference is not significant. Furthermore, since most pumps in the sealed box have cooling water jackets, the temperature of the medium is higher than t1 and t2; therefore, the interference value calculated using the above formula is relatively safe and reliable. For example, when the ring seat material is 3Cr13, the ring material is YG6, and the operating temperature is 30°C, the interference value e = (11.5 – 4.5) × 10^-6 × (300 – 20)d1 = 1.96 × 10^-3d1. Let’s recall again the hot oil pump at 250°C discussed in the section on “What are the reasons for the failure of heat-mounted sealing rings?”; in that case, the interference value between the ring and the ring seat should be 0.00196d1 = 0.00196 × 57.1 = 0.11 mm. The interference fit of the sealing ring purchased from the manufacturer is only 0.04 mm, and the ring seat material is 1Cr18Ni9, whose linear expansion coefficient is 1/3 higher than that of 3Cr13; thus, loosening during use is inevitable. For ease of memory, for rings of type YG6 (YG8), 3Cr13 is used for the ring seats; in cases where the operating temperature is below 300°C, the interference value can be taken as (1.8~2.0)×10-3d1