What are the reasons for the failure of hot-mounted sealing rings?
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Hot-mounted sealing rings combine the excellent properties of cemented carbide (such as YG6) with a lower cost, which is why they are widely used; they represent the most common type of structure in use both domestically and internationally today. Problems can also arise if it is not designed and used properly. If the interference amount is too large, the cemented carbide ring will deform or even break under high compressive stress ； If the interference amount is too small, loosening will occur during use. Currently, the sealing rings produced by sealing manufacturers often exhibit the latter defect. When assembling the hot-fit sealing ring set, only the ring seat is heated; once it reaches a certain temperature and expands to an appropriate extent, the cemented carbide ring is placed into it freely. After the ring seat cools down to room temperature, the assembly is completed. The sealing ring surface must be ground and polished before it can be used. Over time, under the effect of extrusion stress, the flatness of the end face of the cemented carbide ring changes. Therefore, sealing rings that have been stored for an extended period should have their flatness of the sealing end face checked before use. Through long-term observation and analysis, the main reason for the loosening of hot-mounted sealing rings is the difference in linear expansion coefficients between the ring seat and the cemented carbide ring, which results in a gap at operating temperatures. For example, there is a hot oil pump with an operating temperature of 250°C (using heavy oil as the working medium); the outer diameter of the YG6 ring is 57.10 mm, while the inner diameter of the ring seat is 57.06 mm, giving an interference amount of only 0.04 mm. The material used for the ring seat is 1Cr18Ni9. Below, their expansion is calculated separately, with the temperature at the sealed chamber taken as 200°C. At the operating temperature, the diameter of the ring is d1t = α1d1(t – t0) + d1 = 4.5×10^-6×57.10×(200 – 20) + 57.10 = 57.146 mm. The diameter of the ring seat is d2t = α2d2(t – t0) + d2 = 16.6×10^-6×57.06×(200 – 20) + 57.06 = 57.23 mm. The gap between the two is δ = d2t – d1t = 57.23 – 57.146 = 0.084 mm. In the formula, 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 ； t, t0 —— are the operating temperature and room temperature respectively ； d1t, d2t —— are the diameters of the ring and the ring seat at the operating temperature, respectively. Calculations show that at 200°C in the sealed chamber, a gap has appeared between the ring and the ring seat, preventing torque transmission. It can be seen that there are two fundamental reasons for the failure of hot-mounted sealing rings: one is a low interference value, and the other is an improper selection of the ring seat material with a too high linear expansion coefficient.
The main reasons for the failure of hot-fit sealing rings can be summarized as follows: 1. **Improper interference amount**: If the interference amount set during assembly is not appropriate, an excessive amount may cause the cemented carbide ring to deform or break under high compressive stress, while too little interference may lead to loosening during use. 2. **Difference in linear expansion coefficients of materials**: Due to the different linear expansion coefficients of the ring seat and the cemented carbide rings (such as YG6), temperature changes during operation cause variations in the clearance between them. In the example you provided, calculations of linear expansion at the operating temperature of 200°C show that a gap of 0.084 mm will occur between the cemented carbide ring and the ring seat. Such a gap will reduce the ability to transmit torque, which in turn can lead to the failure of the sealing ring. 3. **Change in the flatness of the ring’s end face**: Under prolonged exposure to compressive stress, the flatness of the end face of the cemented carbide ring may change, which affects its sealing performance. Before use, check the flatness of the sealed end face to ensure good sealing performance. 4. **Improper design and use**: Failing to take various operating conditions into proper consideration during design, or not following the correct installation and maintenance procedures during use, can both lead to premature failure of the heat-mounted sealing ring. Therefore, to ensure that the hot-mounted seal ring functions reliably, it is necessary to select appropriate materials, calculate the interference amount precisely, take into account the thermal expansion effects under operating conditions, and carry out regular inspections and maintenance to maintain the flatness of the sealing surface and the overall structural integrity. .