The oil monitoring data can accurately determine whether the NGW122-35.5 reducer needs to be preheated from the five core dimensions of viscosity characteristics, temperature response, abrasive particle characteristics, moisture and contamination, and physical and chemical decay of the oil . Each dimension can reflect the risk of lubrication and startup at low temperatures, as follows:
1. Low temperature viscosity and viscosity change rate dimensions
This is the core indicator for judging whether preheating is needed. The viscosity of lubricating oil will rise sharply at low temperatures. For medium and heavy-duty planetary reducers such as NGW122-35.5, if the measured kinematic viscosity at 40°C deviates by more than +20% from that of new oil (for example, the viscosity of ISO VG 220 oil rises to more than 300cSt at low temperatures), or - Dynamic viscosity exceeding 10,000 mPa·s at 10°C will lead to poor oil fluidity during startup, making it difficult for gears and bearings to form an effective oil film, causing dry friction and startup shock. Through the monitoring of a viscometer or online viscosity sensor, if the viscosity far exceeds the equipment's adaptation range after stopping and standing, and the viscosity drops slowly at the beginning of startup, it means that preheating is necessary - preheating can increase the oil temperature to 15-25°C, return the viscosity to the normal range, and avoid tooth surface micropitting and bearing raceway damage. At the same time, if the viscosity change rate fluctuates greatly after multiple starts, it also indicates that local shear and oxidation are aggravated due to low temperature start without preheating, and the preheating process needs to be strengthened.
2. Oil temperature response and temperature rise rate dimensions
Oil temperature is an intuitive data reflecting the necessity of preheating. In a low-temperature environment (such as below - 20°C), if the oil temperature of the reducer is lower than 5°C after shutdown and is not preheated before starting, 'cold start temperature rise abnormality' will occur: the oil temperature rise rate at the initial stage of start-up is <0.5°C/min, and the temperature difference between the bearing end and the middle of the box exceeds 8°C, indicating that the oil circulation is not smooth and the local friction heat cannot be effectively diffused; if 30 The oil temperature is still lower than 10°C within 10 minutes, or rises to 15°C and then stagnates, indicating that the oil is not flowing sufficiently, and the oil temperature needs to be raised through electric heating or no-load preheating. On the contrary, if the oil temperature rises to 15-20°C evenly after preheating, the temperature rise rate is stable at 1-2°C/min after startup, and the temperature difference at each point is ≤5°C, there is no need to extend the preheating time. In addition, if the oil temperature peak is low and accompanied by increased vibration after multiple cold starts, it is also a typical sign of insufficient preheating.
3. Dimensions of metal abrasive particles and particle contamination
Abrasive particle data can indirectly confirm whether preheating is necessary. Starting at low temperature without preheating will lead to increased wear of gears and bearings. Monitoring through spectral analysis and particle counting: If the content of iron, chromium, nickel and other metal elements in the oil suddenly increases (such as iron content>100ppm), or the ISO 4406 cleanliness level exceeds 21/19/16 (>14μm per milliliter) The number of particles exceeds 1300), and the abrasive grains are mostly cutting-like and fatigue-like (judged by ferrogram analysis), which indicates that the low-temperature start without preheating caused abnormal wear of the meshing surface and the bearing. For NGW122-35.5, the meshing accuracy of the planetary gear train is high. The abrasive particles caused by not preheating at low temperature will accelerate the damage of the inner ring gear and the sun gear. If the abrasive particles continue to increase, the startup wear must be reduced through preheating, and the preheating time must be optimized based on the particle data (such as extending the preheating to 60 minutes at extremely low temperatures).
4. Dimensions of moisture content and oil emulsification state
Low temperature can easily cause water in the oil to condense, exacerbating lubrication failure. This dimension can help determine the need for preheating. Through Karl Fischer moisture meter or online moisture sensor monitoring, if the oil moisture content is >0.1% (mass fraction), or milky white emulsification occurs, the moisture will freeze and block the oil circuit at low temperatures, while destroying the integrity of the oil film. When starting without preheating, frozen water will scratch the metal surface as the oil flows. Preheating can increase the oil temperature, causing the water to evaporate or separate from the oil to avoid the risk of freezing. If the moisture content exceeds the standard and is accompanied by an abnormal increase in viscosity, it means that the mixing of water and oil at low temperatures leads to a decrease in fluidity. At this time, the water must be preheated and removed before starting the equipment to prevent superposition of rust and wear.
5. Dimensions of oil oxidation and acid value changes
This dimension reflects the impact of long-term low temperature without preheating on oil life, thereby reversely verifying the necessity of preheating. When starting at low temperature without preheating, poor oil circulation leads to local overheating and accelerated oxidation. Through acid value titration monitoring, if the increase in acid value compared with new oil is >0.5 mgKOH/g, or the residual carbon content in the oxidation stability test is >0.1%, it means that the oil is oxidatively degraded due to low temperature starting without preheating, and the generated acidic substances will corrode gear tooth surfaces and bearing metal surfaces. If the acid value continues to rise after multiple cold starts and the sludge content in the oil increases (blocking the filter), preheating is required to improve the fluidity of the oil and reduce local oxidation. At the same time, the acid value changes are regularly monitored. If the acid value growth rate is reduced by more than 50% after preheating, it means that the preheating has effectively protected the oil and components.
