ISO 21940-13：中型與大型轉子現場動平衡標準與防護措施
ISO 21940-13 是規範在機器實際所在位置——即轉子自身軸承與支撐結構內——進行轉子動平衡實務的專門國際標準，也就是 現場或原位動平衡不同。其完整標題為 「機械振動 — 轉子動平衡 — 第 13 部分：中型與大型轉子現場動平衡的標準與防護措施。」 當專用 動平衡機 無法使用時——因為轉子過大、移除成本過高，或僅在實際運轉條件下才會出現異常——本部分闡明了何時現場動平衡是正確選擇以及如何安全執行。它補充了以公差為重點的 ISO 21940-11 （剛性轉子）與 ISO 21940-12 （柔性轉子），通過解決在運轉、已安裝機器上工作的現實問題。
1. 範圍與適用性
該標準為中型與大型轉子的現場動平衡提供了指導方針與安全防護措施，此過程在轉子仍處於其自身軸承與支撐結構中時進行——通常位於其最終運轉位置。實務上，無論轉子表現為 剛性 或 柔性 ：決定方法的是整個 轉子-軸承系統的動態特性，而非孤立轉子。該文件是為必須決定、規劃並安全執行現場動平衡活動的技術人員、工程師和管理者編寫的。
2. 標準：何時現場動平衡是合理的
現場動平衡並非每個高 振動, and this chapter supplies a decision framework. The standard identifies several scenarios where in-situ balancing is the appropriate course:
- Removal is impractical or uneconomic: stripping out a large turbine, generator or fan rotor for a shop balance may be prohibitively expensive or simply not feasible.
- Unbalance only appears in service: some unbalance is created by conditions that exist only when the machine runs — 熱變形, 氣動力, or process build-up such as debris and product caked onto a fan blade. A shop balance cannot reproduce these.
- Final trim after reinstallation: a rotor that was shop-balanced may still need a 微調平衡 once reassembled into the machine, to absorb the small shifts that assembly introduces.
Critically, the standard insists on confirming first that the high vibration really is caused by 不平衡 — and not by 不對心, 共振，或 機械鬆動, which mimic or compound an unbalance signature. Adding weights to a misaligned or resonant machine wastes time and can make matters worse.
3. Procedures and Methodology
This section is a step-by-step guide to executing the job. It first sets the instrumentation requirements: a multi-channel 振動分析儀 能夠測量振幅與相位，一個或多個振動感測器（相對於軸的接近感測器及/或安裝於機殼的 加速規），以及一個 phase-reference sensor — typically a photo-tach or 雷射測速儀 — to put a once-per-revolution timing mark on the shaft.
值得注意的是，ISO 21940-13 規定了標準、儀器與安全防護措施，但刻意未規定從測量振動資料計算校正配重所使用的具體方法，將演算法的選擇留給實務操作者。實務上，普遍使用的技術是 影響係數 方法：分析師記錄初始振動向量（振幅與相位），安裝已知的 試重 at a known angular position, measures the new “response” vector, and then uses 向量數學 to compute the mass and angle of the required 校正配重，根據機器需求在單一平面或兩個平面中應用。這正是便攜式儀器自動化的工作流程： Balanset-1A, a two-channel field balancer and analyser, measures 1× amplitude and phase in the machine’s own bearings at operating speed, computes the influence coefficients, and reports the correction mass and angle for each plane — letting an engineer balance and verify without removing the rotor. A 試重計算器 helps size that first test weight sensibly.
4. Balance Quality Evaluation — Vibration, Not Residual Unbalance
Here the standard draws its most important distinction from shop practice. Shop balancing aims to meet a specific 剩餘不平衡 tolerance derived from a G 級. Field balancing has a more pragmatic objective: to reduce the machine’s operational vibration 至可接受的水平。因此，驗收標準並非基於 g·mm 的殘餘不平衡量，而是基於最終振動振幅。標準規定此評估應使用其所參考的配套標準中定義的運轉振動限值—— ISO 7919 用於軸振動，以及 ISO 10816 用於非旋轉部件的振動（兩者現已整合至現代 ISO 20816 系列）。實務目標是將 1× 運轉速度 component down until the machine’s overall level falls into an acceptable evaluation zone — Zone A or B — for long-term operation. You can check a reading against those bands with the ISO 20816-1 Vibration Zones calculator.
5. Safeguards and Safety Precautions
This chapter is arguably the reason the standard exists, because field balancing carries hazards absent from a controlled workshop — chiefly, deliberately running a machine with added trial weights that could be flung free. It mandates a rigorous, documented safety approach:
- Mechanical inspection first: verify before any run that all fasteners are tight and every guard is in place.
- Positive weight attachment: trial and correction weights must be securely fixed — welded, bolted, or seated in dedicated holders — so they cannot become projectiles.
- Controlled access zone: a cordoned exclusion area around the machine during every test run.
- Clear communication: unambiguous protocols between the balancing analyst and the machine operator.
- 緊急停止： a pre-defined, rehearsed shutdown procedure ready before the first start.
This emphasis on safety is paramount: at the speeds and masses of medium and large rotors, a thrown weight or an unguarded coupling can cause serious injury and catastrophic equipment damage.
6. 關鍵概念總結
- Field vs shop balancing: the standard is entirely about balancing a rotor 在機器內，在真實的運轉狀態下校正整個總成，而非在車間的平衡機上進行。
- 振動降低為目標： 成功標準是依據 ISO 7919 / ISO 10816（現已整合為 ISO 20816）達到可接受的運轉振動，而非殘餘不平衡量數值。
- 安全第一： 在運轉中的機器上刻意添加配重，使得文件化的安全防護措施成為不可妥協的要求。
- 影響係數法： 通用的現場技術——測量初始向量，添加已知試重，測量響應，並透過向量數學計算校正量。
