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渣漿泵轉(zhuǎn)速對(duì)葉輪磨損的影響
一、 泵轉(zhuǎn)速對(duì)葉輪入口邊磨損和出口邊磨損的影響
在相似狀態(tài)時(shí)，液流速度與轉(zhuǎn)速比值成正比，而磨損量與轉(zhuǎn)速三次方比值成正比。于是泵的工作部件其中包括葉輪在輸送固液混合物時(shí)的單位體積磨損量與轉(zhuǎn)速二次方比值成正比，用FrY160/31.5型試驗(yàn)泵抽送平均粒度為10mm礫石固液混合物試驗(yàn)，在轉(zhuǎn)速?gòu)?/span>
1000r/mnin變化到1450r/min時(shí)，證實(shí)了這種關(guān)系。
在選擇重新設(shè)計(jì)泵的轉(zhuǎn)速時(shí)，在流量Q和揚(yáng)程H給定的條件下，必須評(píng)價(jià)泵零件在不同轉(zhuǎn)速時(shí)(Q和H不變時(shí)）的磨損。這時(shí)，最有意義的是承受最嚴(yán)重磨損的葉輪。
因?yàn)槿~輪葉片入口邊和出口邊水力磨蝕性磨損過(guò)程各不同，所以分別評(píng)價(jià)轉(zhuǎn)速對(duì)它們的影響。
現(xiàn)在就研究葉片入口邊磨損強(qiáng)度。根據(jù)式(3-7-2)，入口邊磨損量取決于液流相對(duì)速度的三次方和液液角和葉片安放角正弦之比值。不同轉(zhuǎn)進(jìn)時(shí)，葉輪人口直花之比等于單位直徑之比（在相同入口直徑系數(shù)ko時(shí)），值為
如果葉輪寬度變化與入口直徑成正比，那么所得到的關(guān)系式是正確的。但是，在設(shè)計(jì)輸送固液混合物泵時(shí)，除了流量和揚(yáng)程之外，過(guò)流斷面最小允許尺寸也是給定的，即在轉(zhuǎn)速變化時(shí)，斷面尺寸，其中包括葉輪寬度，都應(yīng)該保持恒定。因此，在評(píng)價(jià)轉(zhuǎn)速對(duì)磨損影響時(shí)，具有實(shí)際意義的是下列情況，即此時(shí)除Q=const和H= const外，葉輪寬度b是常數(shù)。這時(shí)，軸面速度之比與D,b積成反比cna2/c1o =(n2/m)/0.
因此，入口速度三角形不相似。因?yàn)閳A周速度與轉(zhuǎn)速的2/3次方成反比，所以相對(duì)速度之比(unin/un.n)<n/m)0.完全可以確信，在轉(zhuǎn)速降低時(shí)，液流角B.增大，即hinl./ing..>1n [根據(jù)式(3-7- 4)]，這將導(dǎo)致磨損有所增加。因而，葉片人口線性磨損量之比為轉(zhuǎn)速的函數(shù)，即有
只根據(jù)對(duì)相對(duì)速度值的分析，不能評(píng)價(jià)葉片迎面的磨損量和葉片出口邊的磨損量，因
為固體顆粒在葉片迎面上的濃度不是常數(shù)，并且不等于平均濃度，磨損不僅與速度有關(guān)，前且與顆粒濃度有關(guān)。因此，確定葉輪轉(zhuǎn)速對(duì)葉片表面磨損的影響，不僅要考慮相對(duì)速度而且也要考出固液混合物靠近磨損表面濃度變化。
為了計(jì)算承受最嚴(yán)重磨損葉片出口邊區(qū)液流相對(duì)速度，下面分析轉(zhuǎn)速下降即比轉(zhuǎn)速降低時(shí)速度三角形的變化。在這種情況下，葉輪出口處圓周速度u2和徑向分速度Cn減小(由于Q= onst時(shí)直徑D,增大)，但是c.有所增大和葉輪出口液流相對(duì)速度w;減小，這將導(dǎo)致磨損降低。
由于上述速度和磨損的計(jì)算結(jié)果可以得到，以一定近似程度可以采用
根據(jù)全加速度在圓周切線方向上投影響的分析[式(3- 7 -3)]，可以確定固體顆粒在葉片迎面上濃度與轉(zhuǎn)速之間的關(guān)系，而顆粒在葉片之間流道內(nèi)濃度重新分布強(qiáng)度與切線加速度有關(guān)。加速度ar的三個(gè)組成部分中的最大值，通常是式(3-7-3) 右邊第一項(xiàng)，一般它決定了aT值。在轉(zhuǎn)速降低時(shí)，第二項(xiàng)和第三項(xiàng)有所減小，并且第二項(xiàng)是由于葉輪流道長(zhǎng)度增加所致，第三項(xiàng)是由于葉輪尺寸其中包括葉片曲率半徑Ru增大所致，但是第三項(xiàng)的值遠(yuǎn)小于前兩項(xiàng)之值。
二、固體顆粒濃度的影響
在進(jìn)一步分析時(shí)，不考慮式(3-7-3) 的第二項(xiàng)和第三項(xiàng)，并且采取固體顆粒在葉片之間流道內(nèi)的濃度與ar成正比。于是，在不同轉(zhuǎn)速時(shí)，顆粒在葉片迎面上的濃度之比等于它們?cè)谙鄳?yīng)加速度場(chǎng)內(nèi)沉降速度之比
根據(jù)式(3-7-2) 和式(3-7-5)，考慮到相對(duì)速度和固體顆粒濃度的變化，當(dāng)轉(zhuǎn)速變化時(shí)，線性磨損量比值為
確定轉(zhuǎn)速降低時(shí)，例如，降低1/3（從n=1500r/min降到n=1000r/min)時(shí)，線性磨損量的變化)，即葉片出口處線性磨損量大致降
低1/2左右，
根據(jù)對(duì)葉片之間流道內(nèi)發(fā)生的現(xiàn)象分析和考慮一些假設(shè)，可以得到式（3-7-7）和計(jì)算結(jié)果。這些現(xiàn)象的復(fù)雜性，不允許考慮所有影響葉片在轉(zhuǎn)速空化時(shí)磨損的因素，所以，實(shí)際上轉(zhuǎn)速降低時(shí)，磨損量下降，可能有些別的原因，就是上面所得到的那些原因。例如，根據(jù)所進(jìn)行的分析，采用所有處在固液混合物中的顆粒都很小。如果混合物中含有大的固體顆粒而不影響葉片工作面(或者稱為迎面)的磨損，那么由于轉(zhuǎn)速下降而磨損減小將是相當(dāng)小的。此處，轉(zhuǎn)速下降將導(dǎo)致(根據(jù)公式d,-1.26.6N元)臨界尺寸d增大，即處在固液混合物中參與葉片工作面磨損的小顆粒部分增加:這時(shí)磨損增加，即根據(jù)式(3-7-7)得到的磨損下降將小一些。
沒(méi)有進(jìn)行過(guò)那種檢查葉輪磨損量與轉(zhuǎn)速之間關(guān)系的專門(mén)試驗(yàn)(在所有其他參數(shù)保持相等時(shí))。根據(jù)砂泵轉(zhuǎn)速降低運(yùn)行資料以及全蘇非金屬建筑材料和水力機(jī)械化科學(xué)研究所進(jìn)行的兩臺(tái)挖泥泵轉(zhuǎn)速比額定轉(zhuǎn)速值降低1/3時(shí)串聯(lián)試驗(yàn)結(jié)果，葉輪壽命T與轉(zhuǎn)速之間的關(guān)系為式中，m=1.8~2。渣漿泵廠家
Effect of Slurry Pump Speed on Impeller Wear
1. The effect of pump speed on impeller wear and outlet side wear.
In the similar state, the liquid flow velocity is proportional to the ratio of rotational speed, while the wear rate is proportional to the ratio of rotational speed cubic. Therefore, the working parts of the pump include the unit volume wear of impeller when conveying solid-liquid mixture, which is proportional to the second square ratio of rotational speed. The average particle size of gravel solid-liquid mixture is pumped by FrY160/31.5 test pump. At rotational speed, the wear rate of impeller is proportional to the second square ratio of rotational speed.
The relationship was confirmed when 1000r/mnin changed to 1450 r/min.
When choosing the speed of the redesigned pump, under the given conditions of flow Q and head H, it is necessary to evaluate the wear of pump parts at different speeds (when Q and H are unchanged). At this time, the most significant is to bear the most severe wear impeller.
Because the hydraulic abrasive wear process at the inlet and outlet sides of impeller blades is different, the effect of rotation speed on them is evaluated respectively.
Now the wear strength of the blade inlet is studied. According to the formula (3-7-2), the wear rate at the inlet depends on the ratio between the three power and the liquid liquid angle and the sine angle of the blade placement angle. The ratio of impeller to population diameter is equal to the ratio of unit diameter (when the same inlet diameter coefficient is KO), and the value is
If the width of impeller is directly proportional to the inlet diameter, the relationship is correct. However, in the design of solid-liquid mixture pump, in addition to the flow rate and head, the minimum allowable size of the cross-section is also given, that is, when the speed changes, the cross-section size, including the impeller width, should be kept constant. Therefore, when evaluating the effect of rotational speed on wear, it is of practical significance that the width of impeller B is constant except for Q = const and H = const. At this time, the ratio of axle velocity to D, B product is inversely proportional to cna2/c1o=(n2/m)/0.
Therefore, the entrance velocity triangle is not similar. Because the circumferential velocity is inversely proportional to the second-third power of the rotational speed, the ratio of relative velocity (unin/un.n) < n/m) is 0. It is absolutely certain that when the rotational speed decreases, the liquid flow angle B. increases, i.e. hinl. / ing. > 1n [according to formula (3-7-4)], which will lead to an increase in wear. Thus, the ratio of linear wear of blade population to rotational speed is a function of the rotational speed.
According to the analysis of relative velocity value, the wear on the blade face and the wear on the blade outlet can not be evaluated.
For the solid particle concentration on the blade front is not constant and not equal to the average concentration, the wear is not only related to the velocity, but also to the particle concentration. Therefore, to determine the influence of impeller speed on blade surface wear, not only the relative velocity but also the concentration change of solid-liquid mixture near the worn surface should be considered.
In order to calculate the relative velocity of liquid flow at the exit edge of blade under the most severe wear, the change of velocity triangle is analyzed when the speed decreases, that is, when the specific speed decreases. In this case, the circumferential velocity U2 and radial partial velocity Cn at the impeller outlet decrease (due to the increase of diameter D at Q= onst), but C. increases and the relative velocity W at the impeller outlet decreases, which will lead to lower wear.
Since the above calculation results of velocity and wear can be obtained, they can be used to a certain degree of approximation.
According to the analysis of the projection of the total acceleration in the tangential direction of the circumference [Formula (3-7-3)], the relationship between the concentration of solid particles on the blade face and the rotational speed can be determined, and the redistribution intensity of the concentration of particles in the flow passage between the blades is related to the tangential acceleration. The maximum of the three components of acceleration AR is usually the first item on the right side of equation (3-7-3), which generally determines the aT value. When the speed decreases, the second and third terms decrease, and the second is due to the increase of the length of the impeller passage. The third is due to the increase of the impeller size including the radius of curvature Ru of the blade, but the value of the third term is much smaller than that of the first two terms.
II. THE EFFECT OF SOLID PARTICLE CONCENTRATION
In further analysis, the second and third terms of equation (3-7-3) are not considered, and the concentration of solid particles in the flow passage between blades is proportional to ar. Therefore, at different rotational speeds, the ratio of the concentration of particles on the blade front is equal to the ratio of their settling velocity in the corresponding acceleration field.
According to formula (3-7-2) and formula (3-7-5), considering the change of relative velocity and solid particle concentration, the linear wear ratio is obtained when the rotational speed changes.
Determine the change of linear wear when the speed decreases, for example, when the speed decreases by 1/3 (from n=1500r/min to n=1000r/min), that is, the linear wear at the blade outlet decreases roughly.
It's about a second lower.
Formula 3-7-7 and calculation results can be obtained by analyzing the phenomena occurring in the flow passage between blades and considering some assumptions. The complexity of these phenomena does not allow all factors affecting blade wear during cavitation at rotating speed to be taken into account. Therefore, in fact, when rotating speed decreases, the wear rate decreases. There may be some other reasons, which are the above reasons. For example, according to the analysis carried out, all the particles in the solid-liquid mixture are small. If the mixture contains large solid particles without affecting the wear of the blade working face (or face to face), the reduction of wear due to the decrease of rotational speed will be quite small. Here, the decrease of rotational speed will lead to the increase of critical dimension D (according to formula d, -1.26.6N yuan), i.e. the increase of the small particles in the solid-liquid mixture which participate in the wear of the blade working face: at this time, the increase of wear, i.e. the decrease of wear obtained according to formula 3-7-7, will be smaller.
No special tests have been carried out to check the relationship between impeller wear and speed (when all other parameters remain equal)
