The Challenge of Low-Temperature Environments: How to Maintain Forming Precision in Welded Pipe Mills at -10°C?

In regions like Russia and Northern Europe, winter temperatures often drop below -10°C. Extreme cold can reduce the transmission efficiency of welded pipe mills and cause fluctuations in forming precision (roundness error may increase from ±0.08mm to ±0.15mm). To address this issue, technical modifications to lubricating oil selection and motor preheating systems are required, combined with materials science and thermodynamics principles to achieve stable production.​

I. Core Impacts of Low Temperatures on Mills: From Lubrication Failure to Precision Deviation​

The key challenge in low-temperature environments lies in abrupt changes in the physical properties of materials:​

• At -10°C, the viscosity of ordinary mineral lubricating oil increases 3-5 times compared to room temperature, causing a sudden rise in resistance in transmission components such as roll bearings and gearboxes, with response delays reaching 0.5 seconds, directly affecting forming synchronization;​

• The insulation resistance of motor windings decreases in low temperatures (Class F insulation materials may see insulation resistance drop from 100MΩ to 20MΩ at -10°C), increasing peak starting current by 20% and easily triggering misoperations in control systems;​

• The ductility of steel strips decreases by 5-8% in low temperatures. If forming force is unstable, pipes may wrinkle or crack, raising scrap rates to over 8%.​

II. Lubricating Oil Selection: A Viscosity Index ≥140 is the "Baseline" for Low-Temperature Lubrication​

According to ISO 3448 standards, synthetic gear oils are required for low-temperature environments, with core indicators including:​

• Viscosity Index (VI) ≥140: A higher VI means smaller viscosity changes with temperature. For example, a PAO synthetic oil has a kinematic viscosity of 150cSt at -10°C and 120cSt at room temperature (25°C), with a viscosity change rate of only 25% (compared to 60% for ordinary mineral oils);​

• Pour Point ≤-30°C: Ensures the oil does not solidify in extreme cold, achievable by adding pour point depressants (e.g., polymethacrylate);​

• Extreme Pressure and Anti-Wear Properties (Timken OK value ≥35kg): Oil films on metal surfaces are prone to rupture in low temperatures, requiring sulfur-phosphorus additives to form chemical protective films and reduce wear on roll bearings.​

III. Motor Preheating System Modification: Precise Application of Thermodynamic Principles​

When a motor starts directly at -10°C, it takes 30 minutes for the winding temperature to rise from -10°C to operating temperature (80°C), with output torque fluctuations reaching 15% during this period. The modification plan is based on gradient heating theory:​

• PTC Heater Integration: 12 pieces of 200W PTC ceramic heaters are embedded in the motor stator windings, with PLC-controlled "stepwise heating" — first heating to -2°C at 50% power (10 minutes), then to 5°C at 100% power (additional 5 minutes), ensuring insulation resistance recovers to above 50MΩ;​

• Temperature Closed-Loop Control: PT100 sensors are installed in the motor housing and windings to monitor temperature differences (≤5°C) in real-time, preventing insulation aging due to local overheating;​

• Linked Preheating of Transmission Systems: During motor preheating, hydraulic pumps drive rolls to idle at low speed (10m/min), using frictional heat to assist lubricating oil warming, shortening the "warm-up time" for formal production to 15 minutes.​

Data Verification: After modification, the peak starting current of motors at a Northern European factory dropped to 5 times the rated current (previously 7 times), forming roll torque fluctuations were controlled within ±5%, and the roundness error of φ32mm pipes stabilized at ±0.07mm.​

IV. System Integration Effects: From Laboratory to Production Line Validation​

After modification, the ZY32 mill at a Russian customer site achieved the following at -12°C:​

• Lubricating oil system: Pressure loss at -10°C decreased from 0.8MPa to 0.3MPa, with bearing temperature rise stable at 45K (international standard ≤60K);​

• Motor system: 100% success rate for first startup after preheating, with no shutdown failures caused by low temperatures;​

• Product precision: Welded pipe scrap rate dropped from 7.2% (before modification) to 2.1%, reducing monthly losses by approximately 120,000 euros.​

Precision control in low-temperature environments essentially relies on materials science and thermodynamic design to offset environmental interference. For the Russian and Northern European markets, selecting synthetic lubricating oils with VI≥140 and intelligent preheating systems is not only necessary for production but also a technical competitive edge to break through geographical limitations.​

Zhangjiagang Zhongyue Metallurgy Equipment Technology Co., Ltd,pioneers precision metallurgical equipment manufacturing. With More than one hundred and fifty annual productions, our high-frequency welded pipe mills and H-beam lines empower automotive, medical, and renewable energy industries. Committed to R&D excellence and customer-centric innovation, we drive smart manufacturing evolution globally.