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渣浆泵转速对易损件的寿命影响

渣浆泵转速对易损件的寿命影响

作者:admin    来源:未知    发布时间:2019-10-05 09:42    浏览量:
渣浆泵转速对易损件的寿命影响
    更换磨损零件有关的修理工作周期,不仅与磨损零件寿命有关,而且与由相对耐磨性决定的零件相互关系有关。
    实际上最有意义的是泵易损件(叶轮,叶轮和压水室入口侧密封件)的磨损量与比转数之间的关系,因此也就是零件寿命与比转数之间的关系。
    在其他条件相间的情况下,零件磨损量与固液混合物的流速和固体颗粒的浓度有关。但是,如果在零件孔穴内没有观察到固体颗粒有明显分离,那么就可以认为其磨损量只与液流速度有关,而固体颗粒浓度采取为定值,它等于平均值。这是针对封密件而言。
在间隙尺寸恒定时,混合物在密封处的速度与其内静压降的1/2次方成正比。而压降等于叶轮出口压力与液流扭曲在腔内产生的反应力之间的压力差。可以近似地采用压力,腔内的反压力以及两者的压力差都与液流速度的二次方成正比。这时密封处混合物速度与静压力的1/2次方成正比。因为密封件表面磨损量与混合物速度二次方和通过此处颗粒的数量成正比,所以为了定性分析采用它与压力成正比,即与扬程(因为P-H)的3/2次方成比(决定通过密封处固体颗粒数量的密封泄漏量,在其他条件相同时与速度成正比,即与H成正比)。
在流量和转速但定时,扬程与比转数的4/3次方成反比,即得到在泵压水室流道内,输送含有中细颗粒的固液混合物时,也没有观察到固体颗粒的明显分离,因此在比较压水室磨损时,如上所述,可以采用它们与液流速度之间的关系,假定固体颗粒浓度恒定。但是,在过渡到输送砾石固液混合物时,固体颗粒沿着压水室断面上强烈的重新分布,并且在外壁面上其浓度明显增大。
   图3-3-4 (b)上示出压水室计算断面上液流速度up.c与过流断面尺寸系数Kn和比转速m,之间的关系,从图上可知,n, 降低将导致压水室计算断面上流速显著增大。因为它个断面的磨损量,通常是最大的,所以它决定了整个压水室的寿命。
  定量分析指出,磨损量与液流速度平方成正比时,扬程增加(即比转数n,下降),在其他参数恒定时,将导致压水室磨损量急剧增大,即压水室寿命降低。压水室磨损量或者寿命与比转数的关系,可以根据本篇第三章第二节资料计算得到的液流速度比较结果确定。
二、固体颗粒浓度的影响
  在叶轮叶片之间流道内,随着叶片正面上颗粒浓度增大,固体颗粒将发生强烈的重新分布。因此在确定叶片磨损量作为比转速n,的函数时,必须考虑液流局部流速和固体颗粒浓度。但是应该考虑泵在抽送细颗粒泥沙时,不是所有工作面的磨损而只是出口边(决定叶轮出口直径)的磨损对泵特性变化有影响。
  比转速ns=80的泵应用最为广泛,因此在评价易损件相对寿命时,采用n,=80泵零件寿命作为标准。
  在图3-7-14上示出了泵抽送中细颗粒固液混合物时泵零件寿命近似关系T/T=80。假定n,=80泵压水室寿命作为1。绘制下列两种情况时叶轮和叶轮入口密封件寿命曲线,即n,=80泵压水室寿命超过叶轮寿命1倍(虚线)和1.5倍(点划线)。
    从图3-7-14上可知,当比转数变化时,压水室和密封件寿命变化最大,叶轮变化最小。在ns=60时,叶轮和压水室寿命近似相同,当比转速增大时,压水室寿命超过叶轮寿命。与叶轮相比,压水室具有较大的尺寸、质量和相应的成本;拆卸相当困难,因此在降低压水室寿命时,提高了泵技术服务方面的费用,即降低了使用质量。在国内外实践中,很少采用比转速nn,<80的渣浆泵。
    泵零件相对寿命的上述分分析,只有在泵抽送送中细颗粒的固液混合物时才是正确的。在抽送大颗粒的固液混合物时,叶轮寿命不是由叶片出口边的磨损量而是由叶片入口边磨损量确定,其磨损量与比转数无关。此外,与其他零件磨损量相比,叶轮入口密封件的磨损量明显降低,因为大颗粒不进入间隙中。渣浆泵

Effect of Slurry Pump Speed on the Life of Fragile Parts
The repair cycle related to replacement of worn parts is not only related to the service life of worn parts, but also to the relationship between parts determined by relative wear resistance.
In fact, the most significant part is the relationship between the wear volume and the specific speed of the pump wearing parts (impeller, impeller and inlet side of the pressure chamber), so that is the relationship between parts life and specific speed.
Under other conditions, the wear of parts is related to the flow rate of solid-liquid mixture and the concentration of solid particles. However, if no obvious separation of solid particles is observed in the hole of the part, it can be considered that the wear rate is only related to the velocity of liquid flow, and the concentration of solid particles is taken as a fixed value, which is equal to the average value. This is for sealers.
When the gap size is constant, the velocity of the mixture at the seal is proportional to the 1/2 power of the internal static pressure drop. The pressure drop is equal to the pressure difference between the outlet pressure of the impeller and the reaction force produced by the fluid flow distortion in the cavity. It can be approximated that the pressure, the back pressure in the cavity and the pressure difference between the two are proportional to the quadratic of the velocity of liquid flow. At this time, the velocity of the mixture at the seal is proportional to the 1/2 power of the static pressure. Because the wear on the surface of the seal is proportional to the quadratic velocity of the mixture and the number of particles passing through it, it is used for qualitative analysis to be proportional to the pressure, that is, to the 3/2 power of the head (because of P-H). (The leakage of the seal which determines the number of solid particles passing through the seal is proportional to the speed when other conditions are the same, that is, to H.)
When the flow rate and rotational speed are fixed, the lift is inversely proportional to the fourth third power of the specific speed. That is to say, when the solid-liquid mixture containing medium and fine particles is transported in the flow passage of the pump chamber, no obvious separation of solid particles is observed. Therefore, when comparing the wear of the water chamber, as mentioned above, the relationship between them and the velocity of liquid flow can be used, assuming that the concentration of solid particles is constant. However, during the transition to conveying gravel solid-liquid mixtures, the solid particles are strongly redistributed along the section of the water chamber, and their concentration increases significantly on the outer wall.
Figure 3-3-4 (b) shows the relationship between up.c of liquid flow velocity on the calculated section of the water chamber and the size coefficient Kn and specific speed m of the cross section. From the graph, it can be seen that n, lower will lead to a significant increase of flow velocity on the calculated section of the water chamber. Because the wear of this section is usually the largest, it determines the life of the whole water chamber.
Quantitative analysis shows that when the wear rate is proportional to the square of the liquid flow velocity, the head increases (i.e. the specific speed n, decreases), and when other parameters are constant, the wear rate of the pressurized water chamber increases sharply, that is, the life of the pressurized water chamber decreases. The relationship between the wear rate or life of the pressurized water chamber and the specific speed can be determined by comparing the fluid velocity calculated from the data in the second section of the third chapter of this chapter.
II. THE EFFECT OF SOLID PARTICLE CONCENTRATION
In the flow passage between impeller blades, with the increase of particle concentration on the blade front, the solid particles will be strongly redistributed.  Therefore, when determining blade wear as a function of specific speed n, the local velocity of liquid flow and solid particle concentration must be taken into account.  However, when pumping fine sediment, it should be considered that the wear of the outlet side (which determines the diameter of the impeller outlet) is not the wear of all working faces, but the wear of the outlet side (which determines the diameter of the impeller outlet) has an effect on the change of pump characteristics.
The pump with specific speed ns = 80 is most widely used. Therefore, in evaluating the relative life of vulnerable parts, the life of n = 80 pump parts is used as the standard.
Fig. 3-7-14 shows the approximate life relationship T/T=80 for pump parts when pumping medium-fine solid-liquid mixtures. Assume n, = 80 pump chamber life as 1.  The life curve of impeller and impeller entry seals is drawn in the following two situations, that is, N, =80 pump pressure chamber life exceeds impeller life expectancy 1 times (dotted line) and 1.5 times (dot line).
From Figure 3-7-14, it can be seen that when the specific speed changes, the life of the pressurized water chamber and seal changes the most and the impeller changes the least. When ns = 60, the life of impeller and water chamber is approximately the same. When the specific speed increases, the life of water chamber exceeds the life of impeller. Comparing with the impeller, the pressurized water chamber has larger size, quality and corresponding cost; disassembly is quite difficult, so when reducing the life of the pressurized water chamber, the cost of technical service of the pump is increased, that is to say, the quality of use is reduced. In practice at home and abroad, the slurry pump with specific speed NN and < 80 is seldom used.
The above analysis of the relative life of pump parts is correct only when the solid-liquid mixture of fine particles is pumped by the pump. When the solid liquid mixture of large particles is pumped, the life of impeller is not determined by the wear volume at the outlet edge of the blade, but by the wear amount at the inlet edge of the blade, and the wear volume is independent of the specific speed. In addition, compared with the wear rate of other parts, the wear volume of the impeller entry seal is obviously reduced, because large particles do not enter the gap. Slurry pump
 

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