Based on the analysis and experimental research on the failure causes of the original titanium seal of the titanium liquid pump, the suitable friction material was screened out and two improved design schemes of the structure were put forward. After the test results of the production operation proved, Improved seal than the original shaft seal life increased by 4 to 6 times, under the conditions to ensure that the flushing, the life can be further improved. Reasons for Failure and Improve Design of Rotating Axial Seal in Titanium Dioxide Processing Pump Dong Zongyu et al Reasons for failure of the original axial seal in titanium dioxide processing pump were analyzed. On the experimental investigation basis, suitable materials of a pair of friction components were selected , 两过 设计 constuctions were used for industrial test, the result indicates that operating life of improved rotating axial seal is 4 ~ 6 times longer than original one.Operating life will be much longer. Keywords: titanium dioxide processing pump, seal, reasons for failure, improve design 1 Introduction Panzhihua Titanium Dioxide Factory uses concentrated sulfuric acid decomposition of ilmenite powder production line of titanium dioxide in its production process has a series of titanium pumps, due to the titanium liquid has a strong corrosive, and contains solid particles [ 1], resulting in the pump over-current components and sealing elements by the dual role of corrosion and wear easily damaged or abnormal failure, frequent replacement of sealing elements, and serious Dyed environment. In recent years, the factory titanium liquid pump shaft seal average life expectancy is only about 50h. Obviously, this is an urgent issue to be solved in terms of reducing production costs or reducing environmental pollution. 2 the existing problems of shaft seal The factory process titanium pumps are used FSP corrosion-resistant pump, the original configuration of the shaft seal structure shown in Figure 1. The shaft seal for the single-end exterior, exterior mechanical seal. Silicon nitride (Si3N4) static ring gland fixed to the pump body flange, filled with PTFE ring in an intrusive way embedded in pure PTFE bellows annular end surface groove. The clamping ring is fixed on the impeller shaft through the inner surface of the spring seat by the clamping ring so as to rotate with the shaft and simultaneously compress the spring to load the sealing end surface. Above the back of the static gland, a radial groove is communicated with the external water pipe for flushing and cooling the outer periphery of the sealing surface. Although this mechanical seal has the advantages of compact structure and corrosion resistance, the intermittent operation of the titanium liquid pump, due to frequent parking, start, stop the titanium liquid temperature decreases, the viscosity increases, and precipitation Titanium sulfate, titanium oxide and other fine crystal particles, often the following problems will result in rapid sealing failure. (1) Severe wear and deformation of sealing surface When starting again after stopping, crystal particles and other solid impurities precipitated in the titanium liquid will cause abrasive wear on the sealing surface, while the original sealing end surface adopts silicon nitride / filled polytetrafluoroethylene Of the material group, both in the titanium liquid although have good corrosion resistance, but its poor friction and wear properties, especially filled with PTFE, the friction reduction is good, but not wear-resistant, when the seal Between hard particles, hard particles easily embedded in the surface of the material, the relative sliding in the process of cutting the surface of the material, resulting in smooth and straight sealing surface multi-groove-like wear marks. In addition, PTFE under the action of external forces easily produce "cold flow" and deformation [2], especially the outflow structure, in order to compensate for the sealing ring wear the end surface of the seal still need to maintain the sealing force, often in the beginning Mechanical seal installed, intentionally increase the spring pressure, resulting in the end pressure is too large, resulting in a serious deformation and excessive wear PTFE seal ring, which is leading to premature sealing failure important reason. (2) The compensation performance of the corrugated pipe is lost. The corrugated pipe structure of Teflon used in the original sealing has a rectangular wave shape and a large number of waves with small wave pitch. Although the machining is convenient and the axial compensation performance is good, Medium containing solid crystalline particles, once the particles sink into the bellows groove is difficult to discharge, will seriously affect the bellows axial elastic compensation performance and lead to seal failure. (3) Auxiliary sealing function to reduce the external flow spring mechanical seal structure, when the use of PTFE or rubber bellows to do moving ring auxiliary seal, usually by the application of pressure or interference with the bellows tail close to the shaft Shoulder or circumferential sleeve tighten the sleeve in order to prevent the fluid axial leakage purposes. The moving ring or ring installed ripple and the minimum inner diameter of the head and the sleeve should be a certain gap between the end face of the moving ring to ensure that the axial float after the wear, while pressure sealed fluid through this gap into Moving ring sealing surface back sealing surface can play a self-tightening effect. However, the original titanium liquid pump mechanical seal structure did not consider these issues, but also with the impeller made of plastic sleeve and cylindrical bellows inner circumference of the size and shape accuracy are poor, neither for axial compensation, but also can not The fluid into the back of the sealing surface, thus greatly reducing or even completely lost the bellows auxiliary seal function. (4) poor flushing effect Original seal design flushing method is to run through the static gland mounted on the gland cover and the back of the radial groove rushed to the stationary ring and moving ring contact surface, in order to achieve flushing and The purpose of cooling the end. However, in this structure, the sealing medium actually enters the sealing surface through the clearance between the inner periphery of the stationary ring and the sleeve. Therefore, flushing only flushes the medium that has leaked through the end surface to the ground, preventing the leakage and preventing leakage. Not conducive to the improvement of operating environment. 3 improved design of the seal Through the operation of the process of seal leakage inspection, and the failure of the detection of residual seal components confirmed the above conclusions. To this end, without changing the structure of the original main pump under the premise of this article focuses on the selection of friction materials, strengthen the cooling measures flushing, improve the function of compensation agencies and other aspects of the seal reform. 3.1 Selection of friction pair material Through the static corrosion test of titanium carbide (SiC), high silicon cast iron, tungsten carbide (WC-Co), immersion glass graphite and other materials in titanium liquid (see Figure 2) and graphite / SiC, Graphite / WC-Co, Graphite / Al2O3, Filled PTFE / SiC, Filled PTFE / WC-Co, Filled PTFE / Al2O3, WC-Co / SiC, WC-Co / WC- The tribological properties of the seal rings of multiple material pairs in an aqueous medium (see Figure 3) show that silicon carbide has the highest corrosion resistance in titanium fluids compared to several other materials; The friction coefficient in the water medium is relatively small, indicating that several materials have good frictional compatibility [3], and from several materials were compared with the graphite group wear value with PV curve ( See Figure 4) [4] point of view, SiC lowest. So from the overall characteristics of graphite / SiC group is more reasonable, if the production site operating conditions can not be fully guaranteed good washing conditions to prevent the solid particles into the sealing surface, the choice of SiC / SiC friction pair material group is more appropriate. Figure 2 several kinds of material corrosion results