Failure Cause and Improvement Design of Titanium Liquid Pump Shaft Seal

Based on the analysis and experimental research into the failure causes of the original titanium seal in the titanium liquid pump, suitable friction materials were identified, and two improved structural designs were proposed. After testing under production conditions, the enhanced seal demonstrated a life increase of 4 to 6 times compared to the original shaft seal. With proper flushing, its service life can be further extended. **Reasons for Failure and Improve Design of Rotating Axial Seal in Titanium Dioxide Processing Pump** Dong Zongyu et al This paper analyzes the failure reasons of the original axial seal in a titanium dioxide processing pump. Based on experimental investigations, appropriate friction materials were selected, and two improved structural designs were tested in industrial settings. The results show that the operating life of the improved rotating axial seal is 4 to 6 times longer than the original one, with even greater improvements possible under optimal conditions. **Keywords:** titanium dioxide processing pump, seal, failure reasons, improved design **1 Introduction** The titanium dioxide production line at Panzhihua Iron and Steel Company uses concentrated sulfuric acid to decompose ilmenite powder, involving several titanium liquid pumps. Due to the highly corrosive nature of the titanium liquid and the presence of solid particles, both the pump’s flow components and sealing parts suffer from corrosion and wear, leading to frequent failures and replacements. This not only increases maintenance costs but also causes serious environmental pollution. Recently, the average service life of the shaft seals in these pumps has been around 50 hours, which is clearly an urgent issue to address in terms of cost reduction and environmental protection. **2 Existing Shaft Seal Problems** The factory's titanium pumps use FSP corrosion-resistant pumps, with the original shaft seal structure shown in Figure 1. It is a single-end external mechanical seal. A silicon nitride (Si3N4) stationary ring is mounted on the pump body flange, with a PTFE ring embedded in the bellows groove. A clamping ring is fixed on the impeller shaft through the spring seat, allowing it to rotate with the shaft and compress the spring to apply sealing force. A radial groove above the stationary gland is connected to an external water pipe for flushing and cooling the sealing surface. Although this mechanical seal has a compact structure and good corrosion resistance, the intermittent operation of the titanium liquid pump leads to temperature drops after shutdown, increasing the viscosity of the liquid and causing precipitation of fine crystals such as titanium sulfate and titanium oxide. This often results in rapid seal failure due to the following issues: (1) Severe wear and deformation of the sealing surface: During restarts, precipitated solid particles cause abrasive wear on the seal face. The original material combination of silicon nitride and filled PTFE, while resistant to corrosion, has poor friction and wear properties. Filled PTFE, though low in friction, is not wear-resistant. When hard particles are present, they can embed in the PTFE surface, causing grooves and damage during sliding. Additionally, PTFE tends to undergo “cold flow” under pressure, especially in the outflow structure, leading to excessive wear and deformation. (2) Loss of corrugated pipe compensation: The original Teflon corrugated pipe has a rectangular wave shape with small pitch. While easy to machine, it is prone to clogging by solid particles, reducing its axial compensation ability and ultimately causing seal failure. (3) Reduced auxiliary sealing function: The original design did not properly account for the need for fluid flow into the back of the sealing surface, resulting in poor sealing performance and reduced effectiveness of the auxiliary seal. (4) Poor flushing effect: The original flushing method only cleans leaked medium, failing to prevent solid particles from entering the seal face, which worsens the working environment. **3 Improved Seal Design** Through inspection and testing, the failure causes were confirmed. Without changing the main pump structure, the focus was on selecting better friction materials, improving cooling and flushing measures, and enhancing the compensation mechanism. **3.1 Friction Material Selection** Various materials, including SiC, high-silicon cast iron, WC-Co, graphite, and PTFE, were tested for corrosion resistance and friction compatibility. SiC showed the best performance, with the lowest wear rate. If the site conditions do not allow sufficient flushing, SiC/SiC is recommended. Otherwise, SiC/graphite could also provide long service life. **3.2 Static Ring Structure and Flushing System Design** For mechanical seals with solid particles, introducing external flushing coolant helps block and lubricate the seal surface. The static ring was redesigned as a combination of titanium and SiC, with flushing water directed into the ring for effective cooling and protection. **3.3 Moving Ring and Auxiliary Sealing Design** Two designs were proposed. One used a trapezoidal corrugated bellows with a small spring, while the other integrated SiC directly into the PTFE bellows. **3.4 End Pressure Calculation** Using the formula Pc = Ps + (K - λ)P, calculations showed that a large spring structure provided a more appropriate end pressure, making it more practical for field conditions. **4 Field Operation Test** Both small and large spring structures were tested. The improved seals lasted 4 to 6 times longer than the original ones. However, due to insufficient flushing pressure, their full potential was not realized. **5 Conclusion** (1) Replacing Si3N4/PTFE with SiC/SiC significantly increased the seal life. (2) Large spring structures are more practical for field applications. (3) Changing the corrugated pipe shape to trapezoidal improves its performance. (4) Proper flushing design is critical for extending the life of mechanical seals in solid particle environments.

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