1. Casting process
Fig. 1 is the casting process diagram of the main frame and hub of 6 MW wind turbine generator. Both of them are of multi box shape. The main frame machine adopts the inner sprue and the sprue, which are three sets of independent bottom pouring systems of ceramic pipes, while the inner sprue adopted by the wheel hub is the slit gate, and the sprue is two sets of independent bottom pouring systems of ceramic pipes. The calculated pouring time is 153 s and 139 s respectively. One heating and insulation riser with d = 300 mm and four duckbill risers with d = 230 mm are set on the top of the main frame machine casting; Three heating and thermal insulation risers with d = 300 mm shall be set at the top of the hub casting, and cold iron shall be placed on the thick section and machining surface.
2. Smelting process
Medium frequency induction furnace melting adopts the impulse method and the combination of light and heavy rare earth spheroidizing agents for spheroidizing treatment, and the compound inoculation treatment is carried out by flow inoculation and in ladle inoculation. The chemical composition and particle size of spheroidizing agent and inoculant are shown in Table 1.
| Material name | Mg(%) | Re(%) | Si(%) | Al(%) | Ca(%) | Ba(%) | Particle size mm |
| Light rare earth spheroidizing agent | 5.50~6.10 | 0.60~1.20 | 43~47 | 0.4~0.9 | — | — | 5~30 |
| Heavy rare earth spheroidizing agent | 6.90~7.40 | 1.90~2.60 | 40~44 | 0.9~1.5 | — | — | 5~30 |
| Flow inoculant | — | — | 71~77 | 0.9~1.2 | 0.5~0.9 | — | 0.2~0.8 |
| Package inoculant | — | — | 71~77 | 0.9~1.2 | 0.9~1.4 | 1.9~2.9 | 3~8 |
3. Production and quality inspection
(c)Wheel hub casting test block (d)Wheel hub casting machine
| Casting | Rm/MPa | Rp0. 2/MPa | A（%） | Impact absorption energy (- 20 ℃) / J |
| Main frame machine | 381 | 262 | 26.45 | 12 14 13 |
| Hub | 381 | 252 | 26.23 | 14 13 12 |
After measurement, the actual pouring time of main frame and hub is 143 s and 124 s respectively. After pouring, the surface quality, shape and size, physical and chemical inspection, magnetic particle flaw detection, ultrasonic flaw detection and metallographic analysis of the body shall be carried out. The inspection results meet the requirements of the technical specifications. The experimental results of mechanical properties are shown in Table 2 and the chemical composition is shown in Table 3. As shown in Figure 2, the metallographic analysis photos of the cast test block and its body of the main frame and hub are shown. It can be seen from the figure that there is no graphite distortion such as graphite flowering in the cast test block and body of the main frame and hub, and there are very few graphite floating and slag inclusion. The produced castings meet the technical specifications.
| Casting | C(%) | Si(%) | Mn(%) | P(%) | S(%) | RE(%) | Mg(%) |
| Main frame machine | 3.54 | 2.11 | 0.09 | 0.028 | 0.010 | 0.017 | 0.057 |
| Hub | 3.48 | 2.07 | 0.08 | 0,027 | 0.010 | 0.014 | 0.058 |