What is permissible residual unbalance?

Permissible residual unbalance is the maximum amount of unbalance allowed to remain in a rotor after balancing, defined by ISO 21940-11 (formerly ISO 1940). It depends on the rotor mass, maximum service speed, and the required balance quality grade G.

How do I choose the right balance grade G?

Use the grade specified by the rotor drawing, manufacturer, applicable product standard, or engineering agreement. Example application lists are informative and must not be used as a universal automatic grade selector.

What is the difference between ISO 1940 and ISO 21940-11?

ISO 21940-11 replaced the older ISO 1940-1 standard. The technical content is essentially the same — the formula and balance grades remain unchanged. The new number reflects the reorganization of the ISO 21940 series.

How do I split unbalance between two correction planes?

For rotors balanced in two planes, the total permissible unbalance is distributed between the planes based on their distance from the center of gravity. A common simplification is to allocate 50% to each plane when the CG is approximately centered.

What units is unbalance measured in?

Unbalance is typically measured in g·mm (gram-millimeters) or oz·in (ounce-inches). The SI unit is kg·m, but g·mm is more practical for most industrial rotors. 1 oz·in ≈ 720 g·mm.

免費工程工具

許用殘餘不平衡量計算器

使用 ISO 21940-11 計算剛性轉子的允許剩餘不平衡量。輸入轉子質量、最大服務轉速以及指定的平衡品質等級。

ISO 21940-11:2016 + Amd 1:2022 ISO 1940-1 G0.4 – G4000

轉子質量 (kg)

最大服務轉速 (RPM)

平衡等級 G

校正平面

快速預設

結果

總許用不平衡量

—

比不平衡（偏心）

—

單平面不平衡量

—

角速度 ω

—

平衡等級

—

許用比不平衡量

根據 ISO 21940-11，許用比不平衡量（偏心）為：

G — 平衡品質等級 (mm/s)
n — 最大服務轉速 (RPM)
ω — 角速度 (rad/s)

總許用殘餘不平衡量

其中 m 為轉子質量 (kg)。結果 U_每單位為 g·mm，當 e_每單位為 μm 且 m 單位為 kg 時。

平衡品質等級

等級	e·ω (mm/s)
G0.4	0.4
G1.0	1.0
G2.5	2.5
G6.3	6.3
G16	16
G40	40
G100	100
G250	250
G630	630
G1600	1600
G4000	4000

實務範例

範例計算 — 指定等級 G6.3

已知： 轉子質量 = 120 kg，轉速 = 1500 RPM，等級 = G6.3

ω = 2π × 1500 / 60 = 157.08 rad/s

e_每 = 6.3 × 1000 / 157.08 = 40.11 μm

U_每 = 40.11 × 120 = 4,813 g·mm

每平面（2 平面，50/50 分配）：4,813 / 2 = 2,407 g·mm

⚠️ 注意： 對於盤狀轉子，當重心居中時，兩平面間 50/50 分配是可接受的。對於長轉子，請根據重心相對於校正平面的實際位置使用槓桿法則。