Truth: Deep disassembly revealed that a certain series of heavy-duty models under maximum tolerance combination, the male rotor engages the female rotor by approximately 35μm. Combined with asymmetric oil supply at the suction end and thermal deformation, the sealing line collapses without an oil film.
Conclusion: True repair must address both "reconstructing the tolerance chain from the manufacturing side" and "adding critical protection on the operational side".
Background
A heavy-duty screw compressor in industrial refrigeration duty seized after prior “oil starvation” diagnoses and bearing replacements. Sight-glass oil level had repeatedly been reported above ~60%. The recurring pattern forced a deeper teardown rather than another parts swap.
Symptoms
Symptoms included rising vibration, metallic contact signatures near the sealing line, and eventual lock-up. Oil level looked acceptable; operators therefore discounted lubrication as a cause.
Initial hypothesis
Initial hypothesis: oil starvation from return path or pump issues. That hypothesis fits low oil level—but it conflicts with a persistently “healthy” sight glass.
Measurements
Deep disassembly and metrology on an anonymized heavy-duty series showed that under a maximum tolerance stack-up, male-to-female rotor engagement reached approximately 35μm. Asymmetric suction-end oil supply and thermal deformation were documented qualitatively from wear maps; plant-specific continuous oil-flow meters were not available for publication.
Root-cause chain
Tolerance stack-up + thermal deformation + asymmetric oil feed → local sealing-line contact without a stable oil film → critical friction → seizure. “Oil level OK” masked “oil film collapsed.”
Corrective actions
Actions split into manufacturing-side tolerance-chain reconstruction for the affected series and operational-side critical protection (monitoring / interlocks / oil-feed symmetry checks). Bearing replacement alone was rejected as a closed corrective action.
Verification
Verification required cleared contact signatures after rebuild, confirmed oil-feed symmetry checks, and a defined observation window without recurrence. Exact vibration spectra and serial metrology sheets remain with the OEM/owner and are not reproduced here.
Prevention checklist
- Do not equate sight-glass level with oil-film integrity under heavy-duty screw contact risk.
- When seizures recur after bearing swaps, demand a tolerance + thermal stack review.
- Check suction-end oil-feed symmetry after major overhauls.
- Keep manufacturing and operations corrective actions paired.
Engineering boundary
This is an engineering postmortem. It does not assign legal liability, does not publish OEM drawing numbers, and does not replace OEM service procedures or local codes.
Anonymization note
OEM brand, exact model string, plant name, and customer identity are withheld. The ~35μm engagement figure is retained because it is central to the lesson and was established in the teardown metrology for the anonymized series.
真相：深度拆解发现，某系列重载机型在最大公差组合下，阳转子咬合阴转子约 35μm。叠加吸气端供油不对称与热变形，导致密封线在无油膜状态下崩塌。
结论：真正的修复必须从"制造侧重构公差链"与"运行侧增加临界保护"双向入手。
背景
某工业制冷重载螺杆压缩机在多次“缺油”诊断与换轴承后再次抱死。视镜油位多次报告在约 60% 以上。复发模式迫使进行更深拆解，而不是再次换件。
现象
现象包括振动升高、密封线附近金属接触特征，直至抱死。油位看似可接受，运行人员因此低估润滑相关根因。
初始假设
初始假设：回油路径或油泵导致缺油。该假设适合低油位场景，但与持续“健康”的视镜油位冲突。
测量与取证
对脱敏后的某重载系列深度拆解与计量显示：在最大公差叠加下，阳/阴转子咬合约达 35μm。吸气端供油不对称与热变形由磨损图谱定性记录；现场连续油流量计数据不具备公开发布条件。
根因链
公差叠加 + 热变形 + 供油不对称 → 密封线局部接触且无稳定油膜 → 临界摩擦 → 抱死。“油位正常”掩盖了“油膜崩溃”。
纠正措施
措施分制造侧（受影响系列公差链重构）与运行侧（监测/联锁/供油对称检查）。单独换轴承不被接受为闭环纠正措施。
验证
验证要求重修后接触特征清除、供油对称检查确认，以及约定观察窗内无复发。精确振动谱与计量原始表归属主机厂/业主，本文不转载。
预防清单
- 重载螺杆接触风险下，勿把视镜油位等同于油膜完整。
- 换轴承后仍复发时，要求公差+热变形叠加复核。
- 大修后检查吸气端供油对称性。
- 制造侧与运行侧纠正措施必须成对。
工程边界
本文为工程复盘；不认定法律责任、不公布主机图纸编号，也不能替代主机服务程序或地方法规。
脱敏说明
主机品牌、精确型号串、工厂与客户身份已脱敏。约 35μm 咬合量因构成核心教训且来自该脱敏系列拆解计量而保留。
