The combination mode of model clusters can basically reflect the characteristics of castings and the form of filling and shrinking of castings. The cross-sectional size of each part of the pouring system is related to the size of castings, the combination of model clusters and the number of pieces per box. For this reason, when designing the process of new castings, it should be calculated according to the characteristics of castings and referring to the characteristics of similar casting systems. Table 1 Casting classification model, model cluster combination method, application scope, replenishment method, a box of one large casting riser replenishment combination on the sprue (no cross-runner), small casting straight sprue (or riser) replenishment combination Small casting on the runner.

The runner (or riser) packing combination on the riser. The small casting riser packing on the riser. Because of the existence of the model, the model gasification needs to absorb heat during the pouring process. Slightly higher than sand casting. For different alloy materials, compared with sand casting, the pouring temperature of lost foam casting is generally controlled at 30-50 ℃ higher than sand casting. The heat of the metal liquid which is higher than 30-50 ° C can meet the heat required by the model gasification. If the casting temperature is too low, castings are prone to defects such as insufficient casting, cold insulation, and wrinkled skin. Castings with too high casting temperature are prone to defects such as sticky sand. The most taboo operation of casting in lost foam casting is intermittent casting, which is likely to cause cold insulation defects in the casting, that is, the temperature of the molten metal that is poured Straight reducer copper tube company first decreases, resulting in cold insulation between the molten metal that is poured later. In addition, the lost foam casting casting system mostly uses a closed casting system to maintain the stability of casting. In this regard, the form of the gate cup is closely related to whether the pouring operation is stable. When pouring, the liquid level in the gate cup should be kept stable to make the pouring dynamic head stable. Negative pressure is a necessary measure for ferrous alloy lost foam casting. The role of negative pressure is an important guarantee measure to increase the strength and rigidity of the sand mold, and it is also the main measure to exclude the model gasification products.

The size and holding time of negative pressure are related to the casting material, model cluster structure and paint. For paints with better air permeability and a coating thickness of less than 1 mm, the negative pressure for cast iron parts is generally 0.04 to 0.06 MPa, and the upper limit is taken for cast steel parts. For aluminum castings, the negative pressure is generally controlled at 0.02 ~ 0.03MPa. The holding time of negative pressure depends on the structure of the model cluster. When the number of model clusters in each box is large, the holding time of negative pressure can be extended properly. Generally, the solidified crust on the surface of the casting reaches a certain thickness, but the negative pressure is removed. For thicker coatings and poor paint permeability, the negative pressure and retention time can be increased appropriately.