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关于振动评定、轴振动的测量与评定

2024-05-07

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振动评定

1、机器分类

在10-1000Hz的频段内,振动速度均方根值相同的振动,被被为具有相同的烈度,为使各种不同的旋转机械能用同一烈度标准进行评定,本标准根据机器的尺寸和功能(振动体质量、尺寸、机器的输出功率等)、机器一支承系统的刚性等将旋转机械分为如下4类:

I--小型转机如15KW以下的电机;

II--安装在刚性基础上的中型转机,功率300KW以下;

III--大型转机,机器一支承系统为刚性状态;

IV--大型转机,机器一支承系统为挠性支承状态。

2、评定振动标准

每类旋转机械分4个区段作振动状态评定,振动烈度评定界限见表1。当振动烈度变化达到表中所列一级数值时,表示振动烈度变化了1.6倍,即相差了4dB,表明大多数机器振动状态发生了有意义的变化,应及时报告。振动烈度变化了两级,意味着振动变化了2.5倍,即振动状态变化了一个区段,应及时调查研究,分析原因。

表1 振动烈度评定等级表

①I、Ⅱ、III、Ⅳ为机器分类,见机器分类;

②A区-新交付使用的机器应达到的状态或优良状态;

B区--机器可以长期运行或合格状态;

C区一机器尚可短期运行但必须采取相应补救措施,或不合格状态;

D区一不允许状态。

关于轴振动的测量与评定

1、测量方法与要求

(1)轴相对振动测量

通常使用非接触式传感器进行测量。在轴承内安装传感器时,不能影响润滑油膜压力区。在支架上安装传感器时,支架的固有频率要高于机器转速的10倍以上。

(2)轴绝对振动测量

轴绝对振动测量有两种方法,即有接触式轴振动传感器方法和把惯性传感器与非接触式,传感器结合使用的方法。当采用惯性传感器与非接触式传感器结合使用的方法时。要求惯性传感器和非接触式传感器固接在一起,刚性地安装在机器的轴承座上,以保证两个传感器在测量方向上承受相同支承的绝对振动。两种传感器的灵敏度轴线应尽量重合,以保证它们输出信号的矢量和能成为轴绝对振动的精确测量值。

(3)两种轴振动测量方法,都需确定由于轴表面金相组织不均匀、局部剩磁及轴的机械偏差所引起的总的非振动性偏差,其值不超过振动位移允许值的1/4或6um两者中的较大值。

2、轴振动评定准则

当评定指标为轴承动载荷或径向间隙时,用轴相对振动值为评定参数。

当评定转轴的振动变化时,如果传感器支承结构的绝对振动值等于或大于转轴相对振动值的20%,要进行转轴绝对振动测量。

3、轴振动评定标准

(1)轴振动A区(优良状态)上限值,推荐按下式计算:

式中Sp-p——测量方向上振动位移的峰峰值;

Nmax——机器工作转速,r/min。

(2)轴振动B区(合格状态)的上限,建议取为A区上限的1.6-2.5倍。工作转速较高者取下限,工作转速较低者取上限。其值建议定为黄灯值(一级报警)。

(3) 轴振动C区(不合格状态)的上限,建议取为B区上限的1.5倍,其值建议定为红灯值(二级报警)。

(4) 要重视振动值的变化。在稳定运行条件下,尽管振动值仍在合格范围内,如果振动值发生明显变化,例如其变化量大于B区上限值的25%,无论振动值是变大还是变小,都要及时报告并进一步分析原因。

(来源:网络)