Why do bearings need a minimum load?

Rolling bearings need a minimum load to ensure proper rolling contact between the rolling elements and raceways. Without sufficient load, the balls or rollers may slide (skid) instead of roll, causing smearing damage, increased heat, and premature failure.

What causes bearing skidding?

Skidding occurs when the friction force is insufficient to maintain rolling contact. This happens at high speeds with light loads, especially with grease lubrication. The rolling elements accelerate in the unloaded zone and decelerate in the loaded zone, causing sliding.

How is the minimum load factor kr determined?

The minimum load factor kr is a bearing-specific value listed in the manufacturer's product tables. For deep groove ball bearings it is typically about 0.025. Roller bearings require proportionally higher minimum loads (manufacturers often quote Frm of roughly 0.02 C0), so this calculator uses higher equivalent factors of about 0.25 to 0.3 for roller types.

Does lubrication type affect minimum load?

Yes. Grease-lubricated bearings generally require higher minimum loads than oil-lubricated ones because grease has higher viscous drag, especially at startup. The kinematic viscosity used in the formula should reflect the actual lubricant at operating temperature.

What if my actual load is below the minimum?

If the actual load is below the minimum, you can: apply a preload (axial spring), use a heavier bearing arrangement, increase the load path, or switch to a bearing type with lower minimum load requirements. For vertical shafts, adding a spring-loaded washer is common.

免費工程工具 #047

軸承最小負荷計算器

計算防止滾子/滾珠打滑所需的最小徑向負荷。輸入軸承尺寸、轉速和潤滑類型。

防止打滑潤滑脂 / 潤滑油滾珠與滾子

軸承內徑 d (mm)

軸承外徑 D (mm)

轉速 (RPM)

運動黏度 ν （工作溫度下的 mm²/s）

軸承類型

潤滑類型

快速預設

結果

最小徑向負荷 F_min

—

平均直徑 dm

—

係數 kr

—

ν × n 乘積

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最小負荷公式（簡化版）

防止打滑的最小徑向負荷估算如下：

k_r — 來自製造商產品目錄的最小負荷係數（深溝球軸承通常 ≈ 0.025；滾子軸承的等效值較高 — 請見下表）
ν — 工作溫度下的運動黏度 (mm²/s)
n — 轉速 (RPM)
d_m — 軸承平均直徑 = (d + D) / 2 (mm)
對於潤滑脂潤滑，此計算器會將結果額外乘以 1.5 的保守係數，因為使用潤滑脂潤滑的軸承需要更高的最小負荷

平均直徑

典型 kr 值

軸承類型	k_r
深溝球軸承	≈ 0.025
角接觸球軸承	≈ 0.03
圓柱滾子軸承	≈ 0.25
調心滾子軸承	≈ 0.25
調心滾子軸承	≈ 0.3

球軸承 k_r 值是製造商產品目錄的典型值（例如 SKF 列出每種軸承的 k_r 值，深溝球軸承約為 0.02–0.06）。對於滾子軸承，製造商使用專屬的最小負荷關係式（例如 F_rm ≈ 0.02 × C₀ 或基於轉速的公式）；上述滾子係數為近似等效值，以便此簡化公式能重現相同的數量級。請務必在軸承產品目錄中查閱精確數值。

實務範例

範例 — 6208 深溝球軸承

已知： d = 40 mm, D = 80 mm, n = 3000 RPM, ν = 20 mm²/s, k_r = 0.025, 油潤滑

d_m = (40 + 80) / 2 = 60 mm

F_min = 0.025 × (20 × 3000 / 1000)^2/3 × (60 / 100)²

= 0.025 × 15.33 × 0.36 = 0.14 kN (≈ 140 N)

使用簡易規則 F_min ≈ 0.01 × C₀進行交叉驗證：對於 6208 軸承（C₀ ≈ 17.8 kN），結果約為 ≈ 0.18 kN — 數量級相同。

⚠️ 注意： 此為簡化估算。對於關鍵應用，請諮詢軸承製造商特定的最小負荷指南。實際最小負荷取決於內部游隙、保持架類型和潤滑劑特性。