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 selected, and two improved structural designs were proposed. After testing under production conditions, the improved seal showed a life increase of 4 to 6 times compared to the original one. With proper flushing, the 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 industry. The results show that the operating life of the improved rotating axial seal is 4–6 times longer than the original one, with even greater potential for improvement.
**Keywords:** titanium dioxide processing pump, seal, failure reasons, improved design
**1 Introduction**
The titanium dioxide production process at Panzhihua Iron and Steel Company involves the use of concentrated sulfuric acid to decompose ilmenite powder, which includes 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 elements are subjected to corrosion and wear, leading to frequent failures and replacements. This not only increases maintenance costs but also causes environmental pollution. In recent years, the average lifespan of the shaft seals in these pumps has been around 50 hours, highlighting the urgent need for improvements to reduce costs and environmental impact.
**2 Existing Shaft Seal Problems**
The factory uses FSP corrosion-resistant pumps, equipped with an original mechanical seal structure shown in Figure 1. It is a single-end external mechanical seal, with a silicon nitride (Si₃N₄) stationary ring mounted on the pump body flange, and a PTFE ring embedded in the bellows groove. A clamping ring, fixed on the impeller shaft, compresses the spring to load the sealing face. A radial groove above the stationary gland allows flushing and cooling of the seal surface through an external water pipe.
Although this mechanical seal has a compact structure and good corrosion resistance, intermittent operation leads to temperature drops after shutdown, increasing the viscosity of the titanium liquid and causing crystal precipitation. This often results in rapid seal failure due to:
(1) Severe wear and deformation of the sealing surface: Solid particles precipitated during shutdown cause abrasive wear on the sealing surface. The original material combination of Si₃N₄ and filled PTFE lacks sufficient wear resistance, especially when hard particles are present. PTFE is prone to cold flow and deformation, leading to excessive wear and early failure.
(2) Loss of corrugated pipe compensation performance: The rectangular wave-shaped Teflon bellows tend to trap solid particles, reducing their axial compensation ability and ultimately causing seal failure.
(3) Reduced auxiliary sealing function: The original design failed to account for proper fluid flow into the back of the sealing surface, leading to reduced effectiveness of the auxiliary seal.
(4) Poor flushing effect: The original flushing method only cleans leaked media, failing to improve the overall operating environment.
**3 Improved Seal Design**
Through inspection and testing, the failure causes were confirmed. The improved design focused on material selection, enhanced flushing, and better compensation mechanisms without altering the main pump structure.
**3.1 Friction Material Selection**
Various materials such as SiC, high-silicon cast iron, WC-Co, and graphite were tested for corrosion resistance and friction compatibility. Results showed that SiC had the best corrosion resistance and lowest wear rate. Graphite/SiC combinations were found to be optimal, while SiC/SiC was more suitable for environments with poor flushing conditions.
**3.2 Static Ring Structure and Flushing Cooling System Design**
A combined static ring made of titanium and SiC was designed to allow effective flushing. Flushing water enters the back of the ring, lubricating and cooling the sealing surface.
**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 embedded the SiC ring directly into the bellows.
**3.4 End Pressure Ratio Calculation**
Using the formula Pc = Ps + (K - λ)P, calculations showed that a large spring structure provided a more suitable end pressure.
**4 Field Operation Test**
Both small and large spring structures were tested. The improved seals lasted 4–6 times longer than the original ones, though limited flushing performance restricted further improvement.
**5 Conclusion**
(1) Replacing Si₃N₄/filled PTFE with SiC/SiC significantly improves seal life. Proper flushing can further extend it.
(2) Large spring structures are more practical in real-world conditions.
(3) Trapezoidal corrugated pipes reduce particle accumulation and improve compensation.
(4) Effective flushing design is crucial for improving seal life in solid-particle media.
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