轴摩擦是旋转机械中常见的故障源，其引发的振动现象具有显著的特征性，且会随摩擦类型、严重程度及设备结构差异呈现不同表现。深入理解这些振动规律，是设备故障诊断、风险预警及维护决策的核心依据。

一、轴摩擦的核心分类（振动现象的根源差异）

轴摩擦的振动特征首先由摩擦类型决定，不同摩擦形式的作用机理不同，直接导致振动信号的频率、幅值及稳定性存在本质区别。

摩擦类型核心定义典型发生场景振动信号基础特征干摩擦两接触表面无润滑介质，直接发生 “金属 - 金属” 接触摩擦润滑失效（油膜破裂、缺油）、轴承卡死、轴与静止件（如密封、轴套）刚性刮擦振动幅值大、频率成分复杂（含大量谐波与冲击）、伴随强烈噪声边界摩擦接触表面存在极薄润滑膜（厚度＜1μm），部分区域仍直接接触低速重载设备（如低速齿轮箱）、润滑不足、启动 / 停机阶段振动幅值中等、频率以低频为主（接近转速频率）、信号存在小幅波动流体摩擦两表面被完整润滑膜分隔，摩擦仅发生在流体内部（黏性摩擦）正常运行的高速轴承、滑动轴承（油膜支撑）振动幅值小、频率平稳（以流体扰动频率为主）、信号无冲击成分

二、轴摩擦振动的典型现象与特征

轴摩擦引发的振动并非单一模式，而是通过频率特征、幅值变化、时域波形、伴随现象四个维度综合体现，这些特征也是故障诊断的关键依据。

1. 频率特征：从 “基础频率” 到 “复杂谐波”

振动信号的频率成分是区分摩擦故障与其他故障（如不平衡、不对中）的核心标志，主要包含三类关键频率：

• 基础频率：转速频率（1X）及其倍频（2X、3X…）轴旋转时，摩擦作用会周期性激发与转速同步的振动，因此1X（与轴转速一致的频率）是最基础的频率成分。随着摩擦加剧，接触表面的 “卡滞 - 释放” 循环会强化，进而产生 2X、3X 等倍频（谐波），且倍频幅值会随摩擦严重程度同步增大（例如：轻微摩擦时仅 1X 明显，严重干摩擦时 3X、5X 等高频谐波幅值可接近 1X）。

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• 特征频率：摩擦副的固有频率 / 冲击频率若摩擦伴随 “间歇性冲击”（如轴与静止件的局部刮擦、轴承滚道剥落），会激发摩擦副的固有频率（如轴的横向固有频率、轴承外圈固有频率），表现为振动频谱中出现尖锐的 “冲击峰值”，且峰值频率与设备结构参数（如轴径、材料刚度）相关。

• 异常频率：混沌频率 / 宽频噪声严重干摩擦时，接触表面的摩擦系数会随温度、压力剧烈波动，导致振动从 “周期性” 转为 “非周期性混沌状态”，频谱中出现宽频带噪声（无明显峰值，频率覆盖范围广），此时设备已处于高故障风险（如轴磨损、过热变形）。

2. 幅值变化：从 “平稳” 到 “突变” 的动态过程

振动幅值（通常用加速度、速度或位移衡量）的变化规律，可直接反映摩擦故障的发展阶段：

• 初期（轻微摩擦）：幅值缓慢上升，且随转速波动（如低速时幅值小，高速时因摩擦加剧幅值略增），但整体处于设备允许的振动阈值内。

• 中期（中度摩擦）：幅值进入 “波动增长期”—— 因摩擦热导致接触表面轻微变形（如轴的热弯曲），振动幅值出现周期性波动（波动周期可能与设备温升周期一致），部分时刻超出阈值。

• 后期（严重摩擦）：幅值 “突变式增大”—— 摩擦热累积引发恶性循环（变形→摩擦加剧→更严重变形），振动幅值在短时间内（如几分钟到几小时）飙升至正常水平的 3-10 倍，伴随设备剧烈抖动。

3. 时域波形：从 “正弦波” 到 “冲击波” 的形态演变

时域波形（振动位移 / 加速度随时间的变化曲线）是摩擦故障的 “直观画像”，不同阶段波形差异显著：

• 正常 / 流体摩擦阶段：波形接近正弦波，幅值平稳、无明显毛刺，仅存在小幅随机扰动（由流体黏性引起）。

• 边界摩擦阶段：波形出现轻微 “削波” 或 “凸峰”—— 因局部接触导致周期性小幅冲击，正弦波的波峰 / 波谷被轻微 “flatten”（压平），但整体仍保持周期性。

• 干摩擦 / 严重摩擦阶段：波形偏离正弦波，呈现 **“冲击脉冲波” 形态 **—— 每旋转一周，摩擦接触会产生一个尖锐的冲击峰（幅值远高于正常波动），且脉冲间隔与转速周期一致；**情况下，冲击峰叠加混沌波动，波形无规律可言。

4. 伴随现象：振动之外的 “辅助诊断信号”

轴摩擦的振动通常伴随其他物理现象，可作为故障验证的重要补充：

• 噪声：干摩擦时伴随 “刺耳的金属刮擦声”（频率高、响度大），边界摩擦时为 “低沉的摩擦异响”，流体摩擦时仅存在设备正常运行的低沉噪声。

• 温升：摩擦会产生大量热量，接触区域（如轴承座、轴套）温度显著升高 —— 轻微摩擦时温度上升 5-10℃，严重摩擦时可超过设备允许温度（如轴承温度超 80℃，甚至出现冒烟）。

• 磨损碎屑：润滑油中出现金属碎屑（通过油液分析可检测到铁、铬等元素含量激增），或设备端盖、密封处出现金属粉末（干摩擦的直接产物）。

三、轴摩擦振动的危害与诊断要点

1. 核心危害（为何需重视振动现象）

• 直接损伤：摩擦导致轴颈、轴承、密封件等关键部件快速磨损，缩短设备寿命（如轴承因干摩擦可能在几小时内报废）。

• 次生故障：振动加剧会引发 “连锁反应”—— 如轴的热弯曲导致不平衡振动，摩擦热使润滑油劣化进一步加剧摩擦，最终可能导致轴断裂、设备停机等灾难性故障。

• 能耗增加：摩擦会消耗额外的旋转能量，导致设备能耗上升（如电机电流因摩擦增大而增加 10%-30%）。

2. 关键诊断要点（如何通过振动识别摩擦）

• 频率判断：若频谱中同时出现 “1X 转速频率 + 多倍频 + 宽频噪声”，且无明显的 “不对中特征频率（如 2X 轴向振动）” 或 “不平衡特征（仅 1X 突出）”，大概率为轴摩擦。

• 幅值关联：振动幅值与温度、噪声呈 “正相关”（温度越高、噪声越大，幅值越大），可排除其他非摩擦故障（如不平衡的幅值与温度无直接关联）。

• 时域验证：观察时域波形是否存在 “周期性冲击峰”，且冲击间隔与转速周期一致（可通过转速计算冲击间隔，与波形实际间隔对比）。

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四、常见误区：轴摩擦振动与其他故障的区分

实际诊断中，易将轴摩擦与 “不平衡”“不对中” 混淆，需重点区分：

• 与 “不平衡” 区分：不平衡振动仅以 “1X 转速频率” 为主，几乎无倍频或宽频噪声；而摩擦振动的 1X 幅值会随温度升高而增大，且伴随倍频。

• 与 “不对中” 区分：不对中（尤其是平行不对中）的振动以 “2X 转速频率” 为主，且轴向振动幅值显著大于径向；摩擦振动的径向振动通常更突出，且无固定的 “2X 主导” 特征。

VALENIAN技术团队提醒，轴摩擦的振动现象是 “多维度信号的综合体现”，需结合频率、幅值、时域波形及伴随现象进行系统分析，才能实现精准诊断，避免故障扩大化。

以上翻译成英文

Shaft Friction Vibration Phenomena

Shaft friction is a common fault source in rotating machinery. The vibration phenomena caused by it are highly characteristic and vary with friction types, severity levels, and equipment structure differences. Gaining an in-depth understanding of these vibration laws is crucial for equipment fault diagnosis, risk early warning, and maintenance decision-making.

I. Core Classification of Shaft Friction (Root Differences in Vibration Phenomena)

The vibration characteristics of shaft friction are first determined by the friction type. Different friction forms have distinct action mechanisms, which directly lead to essential differences in the frequency, amplitude, and stability of vibration signals.

Friction TypeCore DefinitionTypical Occurrence ScenariosBasic Characteristics of Vibration SignalsDry FrictionNo lubricating medium exists between the two contact surfaces, resulting in direct "metal-to-metal" contact friction.Lubrication failure (oil film rupture, oil shortage), bearing seizure, rigid scraping between the shaft and stationary parts (e.g., seals, bushings).Large vibration amplitude, complex frequency components (including numerous harmonics and impacts), accompanied by intense noise.Boundary FrictionAn extremely thin lubricating film (thickness < 1μm) exists on the contact surfaces, but direct contact still occurs in some areas.Low-speed, heavy-load equipment (e.g., low-speed gearboxes), insufficient lubrication, start-up/shutdown phases.Moderate vibration amplitude, low-frequency dominance (close to the rotational frequency), slight fluctuations in signals.Fluid FrictionThe two surfaces are separated by a complete lubricating film, and friction only occurs inside the fluid (viscous friction).Normally operating high-speed bearings, sliding bearings (oil film-supported).Small vibration amplitude, stable frequency (dominated by fluid disturbance frequency), no impact components in signals.

II. Typical Phenomena and Characteristics of Shaft Friction Vibration

Vibration caused by shaft friction is not a single mode but is comprehensively reflected through four dimensions: frequency characteristics, amplitude variation, time-domain waveform, and accompanying phenomena. These characteristics are also the key basis for fault diagnosis.

1. Frequency Characteristics: From "Fundamental Frequency" to "Complex Harmonics"

The frequency components of vibration signals are the core identifier for distinguishing friction faults from other faults (e.g., unbalance, misalignment). They mainly include three types of key frequencies:

• Fundamental Frequency: Rotational Frequency (1X) and Its Harmonics (2X, 3X, ...)During shaft rotation, friction periodically excites vibrations synchronized with the rotational speed. Therefore, 1X (frequency consistent with the shaft rotational speed) is the most fundamental frequency component. As friction intensifies, the "stick-slip" cycle on the contact surface strengthens, generating harmonics such as 2X and 3X. Moreover, the amplitude of these harmonics increases synchronously with the severity of friction (e.g., only 1X is prominent in mild friction, while the amplitude of high-frequency harmonics like 3X and 5X can be close to that of 1X in severe dry friction).

• Characteristic Frequency: Natural Frequency/Impact Frequency of the Friction PairIf friction is accompanied by "intermittent impacts" (e.g., local scraping between the shaft and stationary parts, spalling of bearing raceways), the natural frequency of the friction pair (e.g., the lateral natural frequency of the shaft, the natural frequency of the bearing outer ring) will be excited. This manifests as sharp "impact peaks" in the vibration spectrum, and the peak frequency is related to equipment structural parameters (e.g., shaft diameter, material stiffness).

• Abnormal Frequency: Chaotic Frequency/Broadband NoiseIn severe dry friction, the friction coefficient on the contact surface fluctuates drastically with temperature and pressure, causing the vibration to transition from a "periodic" to an "aperiodic chaotic state." Broadband noise (no obvious peaks, wide frequency coverage) appears in the spectrum. At this point, the equipment is at extremely high fault risk (e.g., shaft wear, thermal deformation).

2. Amplitude Variation: A Dynamic Process from "Stability" to "Sudden Change"

The variation law of vibration amplitude (usually measured by acceleration, velocity, or displacement) can directly reflect the development stage of friction faults:

• Early Stage (Mild Friction): The amplitude increases slowly and fluctuates with rotational speed (e.g., small amplitude at low speed, slightly larger amplitude at high speed due to intensified friction), but overall remains within the allowable vibration threshold of the equipment.

• Middle Stage (Moderate Friction): The amplitude enters a "fluctuating growth period" — mild deformation of the contact surface (e.g., thermal bending of the shaft) caused by frictional heat leads to periodic fluctuations in vibration amplitude (the fluctuation period may be consistent with the equipment temperature rise cycle), and the amplitude exceeds the threshold at some moments.

• Late Stage (Severe Friction): The amplitude shows a "sudden surge" — accumulated frictional heat triggers a vicious cycle (deformation → intensified friction → more severe deformation), causing the vibration amplitude to soar to 3-10 times the normal level in a short time (e.g., several minutes to hours), accompanied by violent equipment jitter.

3. Time-Domain Waveform: Morphological Evolution from "Sine Wave" to "Shock Wave"

The time-domain waveform (curve of vibration displacement/acceleration changing with time) is an "intuitive portrait" of friction faults, with significant waveform differences at different stages:

• Normal/Fluid Friction Stage: The waveform is close to a sine wave, with stable amplitude and no obvious burrs, only slight random disturbances (caused by fluid viscosity).

• Boundary Friction Stage: The waveform shows slight "clipping" or "convex peaks" — periodic small impacts caused by local contact lead to slight "flattening" of the peaks/valleys of the sine wave, but the overall periodicity is still maintained.

• Dry Friction/Severe Friction Stage: The waveform deviates completely from the sine wave and presents a "shock pulse wave" shape — each rotation cycle produces a sharp shock peak (amplitude much higher than normal fluctuations) due to friction contact, and the pulse interval is consistent with the rotational speed cycle. In extreme cases, shock peaks overlap with chaotic fluctuations, resulting in irregular waveforms.

4. Accompanying Phenomena: "Auxiliary Diagnostic Signals" Beyond Vibration

Vibration caused by shaft friction is usually accompanied by other physical phenomena, which can serve as important supplements for fault verification:

• Noise: Dry friction is accompanied by "sharp metal scraping noise" (high frequency, high loudness), boundary friction produces "low-pitched friction noise," and fluid friction only generates low-pitched noise from normal equipment operation.

• Temperature Rise: Friction generates a large amount of heat, leading to a significant temperature increase in the contact area (e.g., bearing housing, bushing) — the temperature rises by 5-10°C in mild friction, and can exceed the allowable temperature of the equipment (e.g., bearing temperature exceeds 80°C, or even smoke appears) in severe friction.

• Wear Debris: Metal debris appears in the lubricating oil (the content of elements such as iron and chromium can be detected to surge through oil analysis), or metal powder is found at the equipment end cover and seal (a direct product of dry friction).

III. Hazards and Diagnostic Key Points of Shaft Friction Vibration

1. Core Hazards (Why Vibration Phenomena Need Attention)

• Direct Damage: Friction causes rapid wear of key components such as shaft journals, bearings, and seals, shortening the equipment service life (e.g., bearings may fail within hours due to dry friction).

• Secondary Faults: Intensified vibration triggers a "chain reaction" — for example, thermal bending of the shaft causes unbalance vibration, and frictional heat degrades the lubricating oil to further intensify friction, which may eventually lead to catastrophic faults such as shaft breakage and equipment shutdown.

• Increased Energy Consumption: Friction consumes additional rotational energy, resulting in higher equipment energy consumption (e.g., motor current increases by 10%-30% due to intensified friction).

2. Key Diagnostic Points (How to Identify Friction Through Vibration)

• Frequency Judgment: If the spectrum shows "1X rotational frequency + multiple harmonics + broadband noise" simultaneously, and there are no obvious "misalignment characteristic frequencies (e.g., 2X axial vibration)" or "unbalance characteristics (only 1X is prominent)," it is highly likely to be shaft friction.

• Amplitude Correlation: Vibration amplitude is "positively correlated" with temperature and noise (the higher the temperature and noise, the larger the amplitude), which can rule out other non-friction faults (e.g., the amplitude of unbalance has no direct correlation with temperature).

• Time-Domain Verification: Observe whether there are "periodic shock peaks" in the time-domain waveform, and check if the shock interval is consistent with the rotational speed cycle (the shock interval can be calculated based on rotational speed and compared with the actual interval in the waveform).

IV. Common Misunderstandings: Distinguishing Shaft Friction Vibration from Other Faults

In practical diagnosis, it is easy to confuse shaft friction with "unbalance" and "misalignment," so key distinctions are necessary:

• Distinction from "Unbalance": Unbalance vibration is dominated by "1X rotational frequency," with almost no harmonics or broadband noise. In contrast, the 1X amplitude of friction vibration increases with temperature rise and is accompanied by harmonics.

• Distinction from "Misalignment": Vibration caused by misalignment (especially parallel misalignment) is dominated by "2X rotational frequency," and the axial vibration amplitude is significantly larger than the radial one. For friction vibration, the radial vibration is usually more prominent, and there is no fixed "2X dominance" characteristic.

In summary, the vibration phenomena of shaft friction are the "comprehensive reflection of multi-dimensional signals." Systematic analysis combining frequency, amplitude, time-domain waveform, and accompanying phenomena is required to achieve accurate diagnosis and prevent fault escalation.