What are bearing defect frequencies?

Bearing defect frequencies are characteristic vibration frequencies generated when a rolling element bearing has a localized defect on one of its components (outer race, inner race, rolling elements, or cage). Each component produces a unique frequency based on bearing geometry and shaft speed.

How can an outer race fault appear in a spectrum?

An outer-race defect can produce components near BPFO and its harmonics. FTF or other sidebands can also occur because load, slip, transfer path and modulation affect the spectrum. A frequency match alone does not prove a defect; confirm with envelope analysis, trends and inspection context.

What is the difference between inner and outer race indicators?

Outer-race defects are investigated around BPFO; inner-race defects around BPFI. Shaft-speed modulation is common around BPFI, while BPFO can also show FTF or other sidebands. Interpret the pattern together with loading, measurement position and envelope spectrum.

Why do harmonics matter in bearing analysis?

Harmonics and sidebands can strengthen a bearing-fault hypothesis, but their count is not a universal severity scale or remaining-life calculation. Evaluate amplitude trends, envelope spectra, noise floor, operating condition and corroborating measurements.

Where can I find bearing geometry data?

Bearing geometry data (number of rolling elements, ball diameter, pitch diameter, contact angle) can be found in manufacturer catalogs from SKF, FAG/Schaeffler, NSK, Timken, NTN, and others. Many manufacturers also provide online tools and databases. Some vibration analysis software includes built-in bearing databases.

免費工程工具 #035

軸承故障頻率計算器

根據軸承幾何形狀與軸速計算 BPFO、BPFI、BSF 與 FTF。包含用於振動診斷的 2× 與 3× 諧波。

BPFO BPFI BSF FTF

結果

BPFO — 外圈故障頻率

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BPFI — 內圈故障頻率

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BSF — 滾珠自轉頻率

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FTF — 保持架（滾子架）頻率

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軸頻

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諧波表

頻率	1×（Hz）	1×（轉數倍率）	2×（Hz）	2×（轉數倍率）	3×（Hz）	3×（轉數倍率）

軸承故障頻率

當滾動軸承產生局部故障時，重複性衝擊會產生取決於軸承幾何形狀與軸速的特徵頻率。四大基本故障頻率如下：

基本保持架頻率（FTF）

保持架的旋轉頻率。FTF 升高表示保持架磨損或損壞。

滾動體通過外圈頻率（BPFO）

滾動元件通過外圈滾道上某點的速率。BPFO 附近的峰值可支援外圈故障診斷，但其出現與振幅取決於負荷區、傳遞路徑、滑動與測量位置。

滾動體通過內圈頻率（BPFI）

滾動體通過內圈上某一點的速率。內圈故障通常在 BPFI 周圍以軸速為間隔呈現邊帶。

滾珠自轉頻率（BSF）

滾動體繞自身軸線的旋轉頻率。滾動體故障通常出現在 2× BSF，因為故障點每轉一圈會同時接觸內外兩圈。

注意： 這些運動學公式假設為純滾動且無滑動。實際頻率會因負荷、游隙、潤滑、轉速與滑動而偏移；請將計算值作為搜尋標記，而非缺陷的確切證明。

實務範例

演算範例 — 指定幾何參數，1500 RPM

已知： Z = 9, B_d = 7.94 mm, P_d = 38.5 mm, α = 0°, RPM = 1500

軸頻 = 1500/60 = 25 Hz

B_d/P_d = 0.2062, cos(0°) = 1

FTF = 25/2 × (1 − 0.2062) = 9.92 Hz

BPFO = 9/2 × 25 × (1 − 0.2062) = 89.30 Hz

BPFI = 9/2 × 25 × (1 + 0.2062) = 135.70 Hz

BSF = (38.5/(2×7.94)) × 25 × (1 − 0.2062²) = 58.03 Hz

⚠️ 注意： 請使用軸承製造商提供的內部幾何參數與接觸角，以對應確切的軸承型號。切勿僅憑型號推斷接觸角或滾動元件尺寸。