泵轴弯曲分析

轴承以同样的方法被轴的移动影响,它被泵/电机的错位影响.这里将有一个轴承负载 的增加和一个相应的润滑油温的增加
Bending of the pump shaft 泵轴的弯曲

A fourth problem with shaft movement is often overlooked. The pump has several critical tolerances and shaft movement changes them. The most obvious are wear ring clearance, impeller clearance, bearing fit, and seal face loading. These changes can cause additional heat generation, loss of capacity and loss of efficiency. 轴移动的第4个问题是经常被忽略.泵有几个临近的误差和轴的移动改变它们.最明显的是磨损环 间隙,叶轮间隙,轴承配合,和密封面负载.这些改变能够引起附加的热产生,损失容量和损失效率 In summary then, shaft deflection is certainly undesirable. If the L 3/D4 is too high you will not be able to operate in slight cavitation or very far from the Best Efficiency Point and in the real world that is not very practical. 总之，轴挠度肯定是不可取的.如果L3/D4太高,你将不能运行在轻微的气穴现象或离你的最佳效 率点很远和在现实的世界这是非常不现实的 Be careful of most small pumps, they often operate at above 3000 rpm and their L 3/D4 ratio is atrocious. 当心大多数的小泵,他们通常运行超过3000RPM和它们的L3/D4是糟糕透顶的。
Bending of the pump shaft 泵轴的弯曲
Steven_Tianjin
Bending of the pump shaft 泵轴的弯曲

When a centrifugal volute type pump is operating at its best efficiency point (B.E.P.) the bending forces are evenly distributed around the impeller. 当一个离心蜗壳类型的泵运行在它的最佳效率点上的时候,弯曲力将均匀的分布在叶轮上. If the pump discharge is throttled from this B.E.P. then the fluid velocity is changed and you will experience an increase in pressure at approximately 240 degrees from the cutwater in the direction of shaft rotation. 如果泵的排放从这个B.E.P截流,那么液体的速度被改变和你将经受一个压力的增加,在轴的旋转 方向中从分水角大约240度的地方 It also follows that if the pump capacity increases because of a lack of sufficient head then this change in flow will cause an increase in pressure in the opposite direction, or at approximately 60 degrees from the cutwater. 它也遵循如果泵的容量因为缺少充足的压头而增加,那么这个流量中的改变将引起相反方向中压 力的增加,或在大约从分水角60度的地方



Bending of the pump shaft 泵轴的弯曲

Since the F is the same in both pumps, along with 3, 1/4 and 64; and since the Modulus of Elasticity is just about the same for all shaft materials, we can cancel out those terms and we are left with Y = L3 /D4 This ratio then becomes a logical method of comparing two competing pumps that have different shaft sizes. This ratio is often called the stiffness ratio, slenderness ratio, or the flexibility factor. 因为F在两个泵中一样,连同3,1/4 和64;和因为弹性模量对于所有的轴大约相同,我们 能消除这些术语,我们保留为Y = L3 /D4 ,这个比率然后变成比较有不同轴尺寸的两个 竞争的泵的合理的方法.这个比率通常被称为硬度比,长度直径比,或挠曲系数 If we assume that the length of the shaft from the center of the inboard bearing to the center of the impeller is a fixed amount (8 inches or 200 mm.) then we can easily see the affect of varying the shaft diameter in the stuffing box area. The following table shows the relationship



Bending of the pump shaft 泵轴的弯曲

A bending shaft can be deadly to a mechanical seal because it increases the opportunity for the rotating part of the seal to contact a stationary portion of the pump, causing the lapped seal faces to open and let solids penetrate. If we can keep the lapped seal faces together the seal will not leak and solids cannot penetrate between them. The more shaft movement we have, the more likely the faces are to open. 一个弯曲的轴对于机械密封是致命,因为它增加密封的旋转零件接触泵的固定部分的 机会,引起重叠面打开和让固体穿透.如果你能保持重叠面在一起,密封将不会泄漏和 固体不能在它们之间穿透.我们有更多的轴的移动,面更可能打开 Bearings are affected by the shaft movement in the same way they are affected by pump/ motor misalignment. There will be an increase in the bearing loading and a corresponding increase in the lubricating oil temperature.



如果我们假设从内侧轴承的中心到叶轮的中心的轴的长度是一个固定的量.(8英寸或 200毫米),然后我们能容易的看到填料箱区域中不同轴径的效果.以下的表显示这个关 系
Bending of the pump shaft 泵轴的弯曲

If you keep this ratio below 60 (2 in the metric system) you will not have too much trouble with shaft bending. If, however, you do not have a low L3/D4 you will have problems with the shaft packing, mechanical seals and the pump bearings. Keep in mind that we are measuring the shaft diameter. If there is a sleeve on the shaft, do not measure the diameter of the sleeve. 如果你保持这个比率低于60(在米制系统中为2),你将对轴的弯曲没有太大的麻烦.如果,仍然你没 有一个低的L3/D4,你将对轴的填料,机械密封和泵的轴承有问题.记住我们测量轴的直径.如果在 轴上有一个衬套,不要测量衬套的外径 Pump packing has a very poor memory and is not able to follow the bending or deflection of a badly designed shaft. Some packings can be readjusted for the changing leak rate, but in almost every case additional heat will be generated requiring even more flush water to remove the extra heat. If the packing is not re adjusted with the changing of the pump discharge head then excessive leakage will follow, and along with it emdash; all of the problems associated with too much leakage. 泵的填料有一个非常不好的记忆,和不能跟随弯曲或恶劣设计的轴的偏斜.为了改变泄漏率,一些 填料能够被调整,但几乎在每种情况下附加的热将会产生,需要更多的冲洗水来移除额外的热.如 果在改变泵的排放压头时,填料没有再调整,那么过多的泄漏将跟随;所有跟太多泄漏有关的问题


Bending of the pump shaft 泵轴的弯曲
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The following illustration shows these forces.

以下的图解显示这些力
Bending of the pump shaft 泵轴的弯曲

How much the shaft bends depends upon the length of the shaft and its diameter. The strength of the shaft has nothing to do with this. The strength only determines if the shaft will break. 轴弯曲多少依靠轴的长度和它的直径.轴的强度对这个不能做任何事情.强度仅仅确定 轴是否将破裂 The following formula is a simplified version of this longer formula. It is the formula we use for a single stage centrifugal pump with a solid, round shaft and an over hung impeller. 以下公式是这个更长公式的简单版.它是为一个有实体,圆轴和整个吊起叶轮的单阶离 心泵使用 You will note that shaft strength does not enter into the formula. The important number is the Modulus Of Elasticity (E), and as you will learn just about every shaft we use in the pumping business has the same modulus 你将注意到轴的强度没有进入公式中.重要的数是弹性模量,和随着你将认识到仅仅是 我们在泵的事业中使用的轴有相同的模数