What are the metal processing oils involved in wind power gear machining?

January 04, 2024

What are the metal processing oils involved in wind power gear machining?

As an important clean energy, wind energy will assume the major responsibility of the main force of new energy, it can be expected that in the next few decades, wind power generation will maintain a good momentum of development, the rapid development of wind power industry, inevitably put forward higher requirements for the quality and reliability of the core components of wind power system, wind power gearbox as one of the key components of wind turbines, The role of matching speed and transmitting torque in the fan is crucial to the normal operation of the wind power generation system, and the manufacturing and processing of wind power gearbox and gear is the key to quality control from the source.

The metal processing oil involved in wind power gear processing mainly has the following three categories: cutting oil used in cutting processing (including milling, grinding, etc.), heat treatment oil used in heat treatment process (mainly quenching oil), Anti-rust Oil used in packaging and transportation protection.

1. Cutting oil for wind power gear processing:
Gear processing technology includes hobbing, rolling, milling and grinding processes, supporting the use of mainly pure oil type cutting oil for lubrication and cooling, according to the supporting process can be divided into cutting oil and grinding oil. The cutting oil matching hobbing, gear shaper, gear drilling and other heavy load technology, applied to high-grade machine tools, can well meet the quality of gear processing, while effectively extending the service life of the tool; The grinding oil mainly supports the grinding process, which can ensure the surface accuracy of the workpiece and maintain the sharpness of the grinding wheel.

Wind power gear parts have large processing allowance, difficult processing and high precision requirements, especially gear grinding, which is the most critical processing process at the end of the process, and its grinding quality directly affects the overall quality of the gear box. The diameter of the gear processed by the large gear grinding machine can reach more than 2000 mm, the speed of the processing wheel is greater than 5000 r/min, and the selected grinding oil should be considered lubricity, cleaning and cooling.

The high quality grinding oil can not only effectively reduce the grinding temperature, extend the service life of the grinding tool, but also effectively wash the grinding chips and grinding wheel, and improve the surface quality of the workpiece. At the same time, high-quality cutting oil/grinding oil should also have good abrasion resistance to extreme pressure to play a role in anti-abrasion and anti-sintering, as well as better oil mist resistance to improve the working environment on site.

2. Heat treatment oil for wind power gear processing:
Gear heat treatment is one of the key processes to determine the service life of gear, at present, in the surface hardening technology of gear, carburizing hardening process is widely used in the process of surface strengthening of wind power gear due to mature technology, and is mostly used for the external gear treatment of wind power gear box, and the inner gear ring due to quenching deformation is large, mainly using nitriding hardening or high frequency induction hardening and other processes.

Carburizing is the steel in the carburizing medium heating and insulation, so that carbon atoms penetrate into the surface of the steel chemical heat treatment process, its purpose is to improve the carbon content of the surface of the steel and form a certain carbon content gradient, after quenching and low temperature tempering to improve the surface hardness and wear resistance of the steel, while maintaining good toughness inside the steel.

The effective hardening layer of wind power gear carburizing quenching is deep, and direct quenching can not meet the organizational requirements. At present, the reheating quenching process is mainly used, that is, after carburizing, cooling to room temperature, reheating to austenitizing temperature, and then cooling with quenching medium.

The gear quenching medium mainly includes oil medium and nitrate medium, and the heat treatment oil medium is the quenching oil supporting the process.

The typical heat treatment conditions of a domestic wind power gear production enterprise and the requirements for the use of quenching oil are as follows: the gear material is 18CrNiMo7-6 steel, 20CrNiMo steel and 20CrMnMo steel, etc. The effective size of the gear is φ1000 mm×L200 mm, and the basic process is gas carburizing after quenching.

Typical technical parameters of gear quenching oil are shown in Table 2.

Table 2 Typical technical parameters of gear quenching oil

From the technical parameters in Table 2, the technical parameters of gear quenching oil are roughly equivalent to the fast or ultra-fast quenching oil in the "Heat treatment oil" : SH/T 0564 industry standard, but the actual control requirements of its cooling performance and other physical and chemical indicators are much higher than the industry standard requirements; Moreover, there are deformation and hardness control requirements such as the elliptical distortion of the gear is not more than 0.2mm, and the allowable deviation of the surface hardness inhomogeneity is less than 2 HRC. It can be seen that the quenching conditions of large wind power gear are very harsh, but at the same time, it is also a technical guarantee for the quality of gear production.

The high-quality rapid quenching oil or ultra-fast quenching oil suitable for the heat treatment of wind power gear must not only ensure good organization and performance, but also maintain the dimensional accuracy of the workpiece, which is often contradictory. In order to obtain sufficient depth of quenching, the workpiece needs to be cooled vigorously, but this leads to the occurrence of quenching stress, increasing the tendency to deformation and cracking. As a large-size thick wall workpiece, the cooling speed of the quenching oil in the high temperature zone is fast enough to ensure the hardness and depth of the hardened layer after quenching, but at the same time, the cooling speed in the low temperature zone should be appropriately slow to reduce the cracking and deformation of the gear workpiece.

For some gear parts that need to use isothermal quenching or fractional quenching process, isothermal fractional quenching oil can be used (it is suitable for parts with a high degree of precision). In addition to achieving the required hardness and organization after heat treatment, it also requires smaller deformation and solves the problem of excessive size change of the workpiece. Because the use temperature of isothermal fractional quenching oil is 120 ℃~160 ℃, the cooling performance and thermal oxidation stability of heat treatment oil are put forward more stringent requirements.

In addition, with the deepening of the concept of clean heat treatment process, water-based quenching liquid has been widely promoted and used, which has partially replaced the traditional quenching oil, solved the problem of oil smoke during the quenching process, and can basically achieve clean quenching.

The induction quenching medium of the inner gear ring of the wind power gearbox is usually an aqueous solution of the polymer (water-based quenching liquid), and its cooling rate is between water and oil. The quenching medium is one of the key factors affecting the induction hardening effect of the inner gear ring and the suppression of cracks, which needs to be controlled from the aspects of content, temperature, flow rate and pressure.

3. Anti-rust oil for wind power gear processing:
The design life of the wind power gearbox is 20 years, and the anti-corrosion life is not less than 15 years, so it mainly relies on the paint painting process and Gear Oil and other equipment oil to protect the wind power operation. However, in the early parts production, assembly, storage and transportation of wind power gearbox, temporary anti-rust and anti-corrosion protection is also very important, which is the basis for ensuring the smooth installation and operation of wind power gearbox.

Anti-rust oil coating is the last process of the gear processing process, which requires that the anti-rust oil should have excellent moisture and heat resistance, certain salt spray resistance and anti-overlap performance, and provide good long-term storage and anti-rust protection for the packaged gear, and even meet the anti-rust requirements for the export of the gear after packaging.

The choice of anti-rust oil is usually lube type anti-rust oil and solvent dilution type anti-rust oil. For lubricating oil type rust prevention oil, it is required to balance the competitive adsorption between rust prevention agent and lubricant, and meet certain cleanliness requirements; At the same time, it also needs to have good compatibility with grease, gear oil, etc. For the solvent dilution type rust prevention oil, in addition to meeting the requirements of long-term storage and rust prevention of the gear, it is generally required to have both dehydration or cleaning functions to meet the requirements of thin oil film coating, easy to use, and no cleaning. At the same time, in order to protect the environment and meet the requirements of gear box exports overseas, some equipment manufacturers also require that the composition of anti-rust oil does not contain the heavy metal barium element.

In addition, because the metal surface of the closed system cavity of the wind power gearbox is hidden and not easy to find rust during storage and transportation, the use of oil-soluble gas phase rust prevention oil is one of the effective ways to solve the problem.

Ordinary anti-rust oil cannot fill the inner cavity of the closed system, and due to the periodic change of temperature difference between day and night, the water in the cavity is periodically "evaporation-condensation - dripping", and the metal is slowly corroded under the action of oxygen. Because the gas phase Corrosion Inhibitor is contained in the gas phase corrosion inhibitor, even in the parts where the rust oil is not infiltrated, it can also be protected by the volatilization of the gas phase rust prevention, which helps to the long-term storage of the large gear box and ensure the effectiveness of the wind turbine before installation and operation.

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