宣化北伦平衡机制造有限公司

 
  Xuanhua Beilun Balancing Machinery Co Ltd  

风机叶轮平衡机

通用平衡机

 

电脑电测箱

2014版

(自有知识产权)

HP-15 硬支承平衡机计算机电测仪

摩擦磨损试验机

重型特殊平衡机

汽车行业

专用平衡机

旋转机械振动

 

振动平衡技术

 

 

 

 

 

 

 

     

如何提出合理的平衡精度

如何检测及简单判断平衡机的工作状态及平衡精度

关于平衡机的描述

中国机械CAD论坛关于动平衡的问答

机械振动原因与振动频谱分析法

关于平衡机技术,平衡机设计的问题

特殊转子平衡工艺

新式光电头

软件资料下载


平衡机的基本知识

任何转子在围绕其轴线旋转时,由于相对于轴线的质量分布不均匀而产生离心力。这种不平衡离心力作用在转子轴承上会引起振动,产生噪声和加速轴承磨损,以致严重影响产品的性能和寿命。电机转子、机床主轴、内燃机曲轴、汽轮机转子、陀螺转子和钟表摆轮等旋转零部件在制造过程中,都需要经过平衡才能平稳正常地运转。

根据平衡机测出的数据对转子的不平衡量进行校正,可改善转子相对于轴线的质量分布,使转子旋转时产生的振动或作用于轴承上的振动力减少到允许的范围之内。

因此,平衡机是减小振动、改善性能和提高质量的必不可少的设备。

通常,转子的平衡包括不平衡量的测量和校正两个步骤,平衡机主要用于不平衡量的测量,而不平衡量的校正则往往借助于钻床、铣床和点焊机等其他辅助设备,或用手工方法完成。

有些平衡机已将校正装置做成为平衡机的一个部分。

重力式平衡机和离心力式平衡机是两类典型的平衡机。

 

重力式平衡机一般称为静平衡机。它是依赖转子自身的重力作用来测量静不平衡的。 如图,置于两根水平导轨上的转子如有不平衡量,则它对轴线的重力矩使转子在导轨上滚动,直至这个不平衡量处于最低位置时才静止。 被平衡的转子放在用静压轴承支承的支座上,在支座的下面嵌装一片反射镜。当转子不存在不平衡量时,由光源射出的光束经此反射镜反射后,投射在不平衡量指示器的极坐标原点。如果转子存在不平衡量,则转子支座在不平衡量的重力矩作用下发生倾斜,支座下的反射镜也随之倾斜并使反射出的光束偏转,这样光束投在极坐标指示器上的光点便离开原点。根据这个光点偏转的坐标位置,可以得到不平衡量的大小和位置。 重力式平衡机仅适用于某些平衡要求不高的盘状零件。

对于平衡要求高的转子,一般采用离心式单面或双面平衡机。 离心式平衡机是在转子旋转的状态下,根据转子不平衡引起的支承振动,或作用于支承的振动力来测量不平衡。其按校正平面数量的不同,可分为单面平衡机和双面平衡机。

单面平衡机只能测量一个平面上的不平衡(静不平衡),它虽然是在转子旋转时进行测量,但仍属于静平衡机。

双面平衡机能测量动不平衡,也能分别测量静不平衡和偶不平衡,一般称为动平衡机。 离心力式平衡机按支承特性不同,又可分为软支承平衡机和硬支承平衡机。

平衡转速高于转子一支承系统固有频率的称为软支承平衡机。这种平衡机的支承刚度小,传感器检测出的信号与支承的振动位移成正比。平衡转速低於转子一支承系统固有频率的称为硬支承平衡机,这种平衡机的支承刚度大,传感器检测出的信号与支承的振动力成正比。

平衡机的主要性能用最小可达剩余不平衡量,和不平衡量减少率两项综合指标表示。前者是平衡机能使转子达到的剩余不平衡量的最小值,它是衡量平衡机最高平衡能力的指标;后者是经过一次校正后所减少的不平衡量与初始不平衡量之比,它是衡量平衡效率的指标,一般用百分数表示。

在现代机械中,由于挠性转子的广泛应用,人们研制出了挠性转子平衡机。这类平衡机必须在转子工作转速范围内进行无级调速;除能测量支承的振动或振动力外,还能测量转子的挠曲变形。挠性转子平衡机有时安装在真空防护室内,以适合汽轮机之类转子的平衡,它配备有抽真空系统、润滑系统、润滑油除气系统和数据处理用计算机系统等庞大的辅助设备。

根据大批量生产的需要,对特定的转子能自动完成平衡测量和平衡校正的自动平衡机,以及平衡自动线,现代已大量的装备在汽车制造、电机制造等工业部门。  


转子的动平衡和静平衡概念介绍

转子的动平衡和静平衡

1、  定义

1)静平衡 在转子一个校正面上进行校正平衡,校正后的剩余不平衡量,以保证转子在静态时是在许用不平衡量的规定范围内,为静平衡又称单面平衡。

2)动平衡 在转子两个校正面上同时进行校正平衡,校正后的剩余不平衡量,以保证转子在动态时是在许用不平衡量的规定范围内,为动平衡又称双面平衡。

2、  转子平衡的选择与确定 如何选择转子的平衡方式,是一个关键问题。其选择有这样一个原则:只要满足于转子平衡后用途需要的前提下,能做静平衡的,则不要做动平衡,能做动平衡的,则不要做静动平衡。原因很简单,静平衡要比动平衡容易做,动平衡要比静动平衡容易做,省功、省力、省费用。那么如何进行转子平衡型式的确定呢?

需要从以下几个因素和依据来确定:

1)  转子的几何形状、结构尺寸,特别是转子的直径

        D与转子的两校正面间的距离尺寸b之比值,以及转子的支撑间距等。

2)  转子的工作转速。 有关转子平衡技术要求的技术标准,如

          GB3215API610第八版、GB9239ISO1940等。

3)  转子做静平衡的条件在GB9239-88平衡标准中,对刚性转子做静平衡的条件定义为:

"如果盘状转子的支撑间距足够大并且旋转时盘状部位的轴向跳动很小,从而可忽略偶不平衡(动平衡),这时可用一个校正面校正不平衡即单面(静)平衡,对具体转子必须验证这些条件是否满足。在对大量的某种类型的转子在一个平面上平衡后,就可求得最大的剩余偶不平衡量,并除以支撑距离。如果在最不利的情况下这个值不大于许用剩余不平衡量的一半,则采用单面(静)平衡就足够了从这个定义中不难看出转子只做单面(静)平衡的条件主要有三个方面:一个是转子几何形状为盘状;一个是转子在平衡机上做平衡时的支撑间距要大;再一个是转子旋转时其校正面的端面跳动要很小。

 对以上三个条件作如下说明:

1、  谓盘状转子主要用转子的直径D与转子的两校正面间的距离尺寸b之比值来确定。在API610第八版标准中规定D/b6时,转子只做单面平衡就可以了;D/b6时可以作为转子是否为盘状转子的条件规定,但不能绝对化,因为转子做何种平衡还要考虑转子的工作转速。

2、支撑间距要大无具体的参数规定,但与转子校正面间距b之比值≥5以上均视为支撑间距足够大。

2、  转子的轴向跳动主要指转子旋转时校正面的端面跳动,因为任何转子做平衡试都是经过精加工的,加工后已保证了转子的孔与校正面之间的行为公差,端面跳动很小。

根据上述转子做单面(静)平衡的条件,再结合有关泵方面的技术标准(如GB3215API610第八版),只做静平衡的转子条件如下:

 1=对单级泵、两级泵的转子,凡工作转速<1800/分时,不论D/b6D/b6只做静平衡即可。但是如果要求做动平衡时,必须要保证D/b6,否则只能做静平衡。

2=对单级泵、两级泵的转子,凡工作转速≥1800/分时,如果D/b6只做静平衡即可。但平衡后的剩余不平衡量要等于或小于许用不平衡量的1/2。如果要求做动平衡,要看两个校正面的平衡是否能在平衡机上分离开,如果分离不开,则只能做静平衡。

3=对一些开式叶轮等转子,如果不能实现两端支撑,只做静平衡即可。因为两端不能支撑,势必进行悬臂,这样在平衡机上做动平衡很危险,只能在平衡架上进行单面(静)平衡。

4、转子做动平衡的条件 在GB9239标准中规定:"凡刚性转子如果不能满足做静平衡的盘状转子的条件,则需要进行两个平面来平衡,即动平衡。"只做静平衡的转子条件如下(平衡静度G0.4级为最高精度,一般情况下泵叶轮的动平衡静度选择G6.3级或G2.5): 1、对单级泵、两级泵的转子,凡工作转速≥1800转/分时,只要D/b<6时,应做动平衡。 2、对多级泵和组合转子(3级或3级以上),不论工作转速多少,应做组合转子的动平衡。


 

风机平衡中工艺轴的技术要求

在平衡机的技术指标中,有一个精度的参数:

 

mar=1gmm/kg(μm)

 

    这个参数的意义意味着平衡机的测量精度在微米的数量级上,而工件的几何加工精度在1丝--10丝之间,也就是说在10微米-100微米之间。从这个数量级的具体意义来看,转子的平衡精度主要决定于工艺轴的几何加工精度。

转子的平衡精度体现在具体的参数上为:

设:转子的质量W=30公斤,

工艺轴的加工跳动为e = 5丝=50微米

转子的半径为 r =200毫米

那么,由工艺轴的跳动引起的不平衡量 m

m=W×e/r=30×50/200=7.5g(克)

U=mr=7.5×200=1500克毫米=150克厘米

由此看来,5丝的精度有如此大的影响,而5丝的保证已经有所不易,所以平衡工艺轴的加工一定要经过磨削工艺,这样才能保证平衡的最终精度目的。

平衡工艺轴的修正极限为:当跳动大于5丝时,必需修正,否则平衡效果为假平衡。

平衡工艺轴的材料以45号钢,并经过调质热处理后为最低要求。

风机的平衡精度要求 G=6.3mm/s

G=6.3mm/s=eω/1000=en/10000

U=We=10000WG/n 克毫米=mr

m=U/r 克

转子的质量 W 公斤 30公斤

工艺轴的加工跳动为e 微米

转子的半径为 r 毫米 200毫米

不平衡量 m 克

转子的工作使用转速 n 转/分 2800转/分

例如:U=10000×30×6.3/2800=675克毫米

m=U/r 克=675/200=3.375克

 


 

What is dynamic balancing

Excessive vibration in rotating machinery can cause unacceptable levels of noise and, more importantly, substantially reduce the life of shaft bearings. Hence, the ideal would be to remove all causes of vibration and run the unit totally "smooth". Unfortunately, in practice, the ideal cannot be achieved and, whatever one does, some inherent cause of vibration, or unbalance, will remain.

The best one can do is to reduce this unbalance to a level that will not adversely effect the bearing life and will reduce noise levels to an acceptable level.

The process of reducing the out-of-balance forces that cause vibration in rotating machinery is called

"Balancing". The unbalance is caused by an effective displacement of the mass centre line from the true axis caused by some mass eccentricity in the unit

 

The process of "Balancing" is the removal or addition of weight to the unit such that this effective mass centre line approaches the true axis. A multitude of books and papers has been written about this complex subject and, as such, the following is intended to be no more than a brief outline to the balancing of rotating components. Where balancing grades or levels are referred to here, and in subsequent sections, they are referenced to ISO1940.

The simplest form of, "Static", balance involves placing the unit on low friction bearings and allowing it to rotate and "settle" with the "heaviest" point falling to the bottom. Material is then removed from this point (or added at the top point) and the unit gently rotated until, when stopping, the new "heavy" point again falls to the bottom. This process is then repeated until no obvious "heavy" point seems to exist.

Advancing this one stage further, the unit can be mounted on a purpose built "Balancing Machine" which has its bearings connected to sensors (displacement or acceleration type depending on the design of the machine) which detect the "heavy" point, in relation to a datum on the unit, whilst it is being rotated. This increases the sensitivity and, hence, the accuracy of the balance. If one considers correction at a single position along the length of the unit, the balance is said to be "Single-Plane" (see

If the unit being balanced is very short in relation to it’s diameter Single-Plane Balance will, normally, be very acceptable. However, if the unit has any appreciable length, correction at a single plane, say in the centre of the unit, will probably give a dangerously false correction. If you consider a shaft with two flanged ends, it is quite likely that the major unbalance will arise in the two flanges, probably caused by the inherent concentricity machining errors. The two "heavy" points may fall in precisely the same angular position but, more likely, they will not and, thus, the displacement of the mass centre lines from the true axis will be a different orientation in both ends, as will the size of this displacement. If the unit is now being balanced by the Static or Single-Plane method, as it can easily be, the overall effect would appear to be correct on the Balancing Machine but, in operation, since no account has been taken of the vibration between the two ends, a "Force Couple" will exist which will again introduce vibration in the two machinery shafts

To overcome this problem, a "Multi- Plane" or "Dynamic Balance" must be performed. In this case the balancing machine will have both sets of bearing pedestals connected to sensors and the unbalance at the two planes can be independently identified and, thus, corrected. By the use of electronics and computer control, the actual correction planes can be at any convenient position along the length of the unit relative to the running bearings and, in the case of very long units, more than two planes can be considered, although this is rarely an advantage unless the unit is to run at speeds above its lateral critical speed.("Super-Critical").

For units which will operate well below their lateral critical or "whirl" speed and which are considered "stable" with regard to the speed of operation (a category into which all but the longest flexible couplings fall), there is no necessity for the balance operation to be performed at the actual running speed. Because Balance Grade, whether it be specified as Q0.6 or 4W/N for example, considers operational speed when the calculation of the actual permitted physical amount of out-of-balance is made, balance at a speed much below the operational speed will result in the same final level of balance.

If the unit is to run "Super-Critical" then the actual characteristics of the unit, after passing through the critical speed, may well be different to those below it, hence, such units should be balanced at running speed.

A final complication arises if a unit is to operate at speed close to its critical lateral frequency. In this case there may be some finite movement of, say, to shaft section of a coupling and, hence, it becomes important to balance such a unit at the final running speed. In addition, if this unit is to be subject to multi-speed operation, such as might occur in a two speed motor driving a fan, then balance must be performed at both speeds with a compromise between the two unbalanced forces being made.

It should be appreciated that however close to the ideal the coupling is balanced on the balancing machine, this will change when mounted between driving and driven machines - albeit only slightly. As it is impossible to achieve zero unbalance, all rotating elements will have an inherent error so that, when cojoined, each element will have an influence to increase or decrease the overall balance of the train by a small amount.

 

 

 


 

宣化北伦平衡机制造有限公司

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