The series of experiments were carried out on the filling process of lost foam casting of gray cast iron by using the computer data acquisition system, and the following conclusions were obtained:
- The orthogonal test results show that the relative importance of the technological factors affecting the filling rate of molten metal in lost foam casting of gray iron under the test conditions is in the order of vacuum degree, pattern density, pouring temperature, hydrostatic head of molten metal, pattern thickness, coating permeability and ingate area. Among them, the vacuum degree has the greatest influence and the ingate area has the smallest influence.
- The filling time of molten metal in lost foam casting is longer than that in cavity casting. The existence of foam plastic model changes the filling state of molten metal, which is the main reason for this difference. The filling velocity of molten metal in lost foam casting of gray cast iron is generally between 10-30cm / s, which is about one fourth of that of cavity casting.
- During liquid metal filling in lost foam casting, the blocking effect of decomposition products between liquid metal front and pattern reduces the inertial effect of liquid metal filling. Regardless of side injection, bottom injection or middle injection, the molten metal is displaced with the foamed plastic model in a radial arc form from the ingate and pushed forward until the whole mold cavity is filled. The last filling position of the molten metal is the farthest from the ingate. The change of process parameters such as vacuum degree, pattern density, pouring temperature and coating permeability will affect the curvature and relative shape of the front arc of liquid metal.
- Whether there is negative pressure and the degree of negative pressure in dry sand lost foam casting are the main factors affecting the filling shape and filling speed. The filling velocity of molten metal increases linearly with the increase of negative pressure. When the negative pressure is high, the molten metal tends to fill forward along the mold wall, and the front of the molten metal is fluctuating, which is easy to involve the pattern fragments and decomposition products into the molten metal, resulting in pore defects. The basic condition for obtaining sound gray iron castings by lost foam casting is to pour under negative pressure of – 200mmgh – 400mmgh.
- The decomposition process of foamed plastic pattern is an endothermic process. The performance of pattern material, especially the density, has a considerable impact on its pyrolysis characteristics. The decomposition process of low-density pattern consumes less heat and gas decomposition products. When using low-density pattern, the metal liquid filling speed is fast.
- With the increase of pouring temperature, the filling speed of molten metal in lost foam casting tends to increase at the beginning, but after exceeding a certain value, the filling speed decreases with the further increase of pouring temperature. Under the test conditions, the filling velocity of molten metal reached the maximum at about 1370 ℃.
- The hydrostatic head of molten metal in lost foam casting has a great influence on the filling speed. With the increase of hydrostatic head, the filling speed of molten metal in lost foam casting increases significantly. Under the experimental conditions, the hydrostatic head of molten metal is doubled, and the filling speed of molten metal in lost foam casting is almost doubled.
- With the improvement of the permeability of the coating, the filling speed of the molten metal in lost foam casting tends to increase whether the vacuum is evacuated or not. When the air permeability of the coating is too poor or other factors affect the gas generated by the decomposition of the model in the pouring process, it is too late to discharge through the coating and the molding sand. Under the action of the back pressure of the pyrolysis gas, the liquid metal is blown out from the gate, and the back injection phenomenon will occur.
- When the initial static head is equal, the change of effective static head of lost foam casting metal liquid is related to the pouring mode with the progress of filling process. Under different pouring modes, lost foam casting metal liquid has different filling acceleration. The order of filling speed of molten metal is that side injection is the fastest, middle injection is the second, and bottom injection is the slowest. The filling speed of molten metal during side injection is much higher than that during bottom injection.
- The box model test shows that the filling speed of molten metal in lost foam casting is different along the length and width of the model. At the end of filling, the molten metal flows through different distances in two directions.