Wind power equipment is erected and operated at high altitudes, which is not convenient for regular maintenance. The maintenance period determined in equipment design is usually 20 years, or even 30 years. Therefore, the fatigue strength of casting materials and the reliability and durability of casting quality have very strict requirements.
The equipment operates at high outdoor locations and the temperature is very low in winter. The casting material must also ensure good toughness at low temperatures. Because of this requirement, the main castings of wind power equipment are made of Ferritic Ductile iron, and there are strict requirements in low temperature impact toughness and fatigue strength.
In conventional casting production, the required mechanical properties are based on single cast bar. The measured data may be quite different from the actual properties of the key parts of the castings. For important castings, it can be stipulated to attach casting blocks to the key parts of the castings. The mechanical properties measured by this method are close to the properties of the castings themselves. But for wind power castings, the use of attached cast blocks is still not enough to confirm the reliability of its quality.
Wind power castings manufacturers, in addition to dissecting castings and measuring the properties of castings in the trial production process, must also have an effective quality assurance system to ensure the reliability of castings quality.
In the process of process design, computer simulation must be used as a reference to avoid arbitrariness in process design.
In the production process, a perfect process control system must be established so as to minimize the process parameter variables of each process. In the aspect of cast iron melting, there should be a system to control the consistency of the quality of furnace charge and various raw materials, a means to ensure little fluctuation of chemical composition, a stable spheroidizing treatment and inoculation treatment process.
The quality inspection of castings should include:
Methods to detect various mechanical properties;
Means to detect metallographic organization;
Means of checking the surface defects of castings, such as magnetic particle testing facilities or penetration testing facilities.
Means of checking internal defects of castings, such as ultrasonic flaw detection equipment. If the buyer requests radiographic inspection, there should be a facility suitable for radiographic inspection of heavy castings (which can also be cooperated with nearby qualified units).
The abnormal metallographic structure of the castings, such as too few graphite spheres, obvious intergranular segregation, and deterioration of graphite shape, will greatly reduce the impact toughness and fatigue strength at low temperature. Shrinkage, shrinkage or slag inclusion in the castings will also lead to a significant decrease in low temperature impact toughness and fatigue strength. Therefore, the metallurgical structure of castings must be strictly controlled.
