Pouring temperature refers to the temperature when the molten metal enters the gate. If the pouring temperature is too high, it will not only waste energy, but also lead to defects such as coarse grains in the internal structure of sand castings and poor feeding effect of risers due to too long solidification time; If the pouring temperature is too low, it will affect the fluidity of liquid metal, which will lead to difficult filling of liquid metal and casting defects such as insufficient pouring, especially for sand castings with complex structure.
| Pouring temperature (℃) | 1530 | 1560 | 1590 | 1620 | 1640 | 1650 | 1660 | 1680 |
The liquidus temperature of 20CrMoH used in sand casting is 1511 ℃, and the size of sand casting is small and the structure is relatively complex. The recommended pouring temperature is different according to different production experience, and the previously selected pouring temperature is 1650 ℃. The main influence of pouring temperature on casting defects is shrinkage defects. In order to further study the influence of pouring temperature on shrinkage defects of spiral bevel gear sand casting, the pouring scheme of central top injection mold is simulated with pouring temperature as variable. The specific design is shown in the table.
The figure shows the shrinkage and porosity distribution of the tooth surface and riser section of gear blank sand casting at different pouring temperatures. It can be seen from the observation drawing that when the pouring temperature is 1530 ℃, serious shrinkage and porosity defects appear on the top surface of the tooth shape of the gear blank sand mold casting, and the casting defects at the root of the tooth shape are also serious, which indicates that the pouring temperature is too low and the cooling and solidification speed of the sand mold casting is too fast, resulting in a large number of defects; Then, with the increase of pouring temperature, the defects of sand castings are gradually reduced; When the pouring temperature reaches 1640 ℃, the shrinkage and porosity defects of sand castings have been significantly improved, and the shrinkage and porosity defects of tooth surface and internal structure of sand castings are relatively slight; When the pouring temperature is raised again, the structural defects of sand castings have basically remained unchanged.
To sum up, in a certain temperature range (1510 ~ 1640 ℃), the higher the pouring temperature, the smaller the shrinkage defects of gear blank sand castings; When the pouring temperature reaches 1640 ℃, the casting defects of sand castings are the least. The higher the pouring temperature, the more energy will be consumed; Therefore, 1640 ℃ is the optimum pouring temperature of spiral bevel gear sand casting.