(1) control the gating system to be full all the time
The pouring process of negative pressure lost foam casting is the process of hot metal filling and plastic mold vaporization disappearing. If the runner is not full, due to the limited strength of coating layer, sand collapse is very easy to occur, resulting in casting meat shortage.
(2) controlling the liquid steel to return from the bottom to the top is conducive to stable filling and is not easy to form an empty cavity.
(3) due to the suction of vacuum, under the action of gravity and suction, the filling speed of molten steel is accelerated, and the gating system is suitable to be larger.
2. Type of gating system for the guard plate of shot blasting machine
Casting method selection: vertical casting, bottom pouring, casting spacing of 70 ~ 100 mm, a total of 13 pieces (1 ton furnace, ladle capacity of 1 ton).
(1) the difference between vacuum EPC and sand casting is that the general cast iron is open type, while the negative pressure EPC adopts closed system, and the inner gate must be closed. This is mainly due to the fact that the sprue before the inner gate must be kept full.
(2) the size and location of the gate
When molten steel enters the model, the plastic mold begins to burn and vaporize, and a temporary cavity is formed at the front end of the liquid flow. In order to prevent molten steel from being melted by radiation at high temperature, forming a large cavity and collapsing sand, the design speed of hot metal filling is approximately the same as that of model disappearing, and the filling speed of molten steel is suitable to be fast. The inner gate is slightly larger than the previous design.
The location of the inner gate is 20-30mm above the lowest pouring position of the casting. According to the gating system design of ordinary sand casting, the size of inner gate is calculated. When the size is less than 1 / 3, the cross-section of inner gate is 30 × 2omm.
To prevent Shot blasting machine guard The casting is close to the runner, and the mold is deformed and melted at high temperature. The inner gate is properly extended and the design length is 5 mm.
The cross-section size of runner is 70 × 6 mm.
The section size of the sprue is 70 × 7 mm.
(5) gate cup
The pouring head is greater than 200-250mm.
Be sure to have a sprue cup. The main function of the gate cup is to accumulate molten iron, so that the sprue section is filled instantaneously and the hot metal flows orderly and stably.