Die casting mold pouring system structure
The gating system of a die-casting mold is the critical channel connecting the die-casting machine’s pressure chamber to the mold cavity. Its structural design directly impacts the molten metal’s filling speed, pressure transmission, venting, and casting quality. A well-designed gating system guides the molten metal to smoothly and evenly fill the mold cavity, minimizing eddy currents, air entrapment, and oxidation, while also reducing thermal shock to the mold and extending its service life. A typical die-casting mold gating system consists of a sprue bushing, main runner, branch runner, inner gate, and overflow trough. The structural parameters of each component must be designed in coordination with the casting’s shape and size, as well as the die-casting process parameters, to form an efficient molten metal delivery and distribution system.
The sprue sleeve is the starting point of the gating system. Its function is to guide the molten metal from the die-casting machine’s pressure chamber into the main runner, while also withstanding the high pressure of the molten metal. The sprue sleeve is typically cylindrical in shape, with one end mating with the die-casting machine’s pressure chamber and the other connected to the main runner. The inner bore is tapered (typically 2°-4°) to facilitate the flow of molten metal and the release of the solidified material during mold opening. The inlet diameter of the sprue sleeve must match the diameter of the pressure chamber, typically 0.5mm-1mm smaller, to prevent molten metal from overflowing through the gap. Furthermore, the sprue sleeve must be made of high-strength, heat-resistant material (such as H13 steel) and quenched (hardness 50-55HRC) to resist erosion and wear from the molten metal. It is typically installed using an interference fit or bolt fastening to ensure a tight fit with the die plate and prevent loosening.
The sprue is a crucial component connecting the sprue bushing and the runners. Its structural design must balance the flow resistance and pressure loss of the molten metal. The sprue typically adopts a conical structure with a taper of 1°-3°. The inner wall should be polished to a Ra of 0.8μm or less to reduce frictional resistance during molten metal flow. The sprue should be kept as short as possible, generally no longer than 150mm, to minimize heat loss and pressure decay during molten metal flow. For large molds, the sprue can be designed with reinforcing ribs to enhance rigidity and prevent deformation under high pressure. The junction between the sprue and runners should have a smooth, rounded corner (radius 5mm-10mm) to avoid eddy currents and pressure loss caused by right-angle turns, ensuring efficient energy transfer from the molten metal.
The function of a runner is to distribute the molten metal from the main runner to the individual ingates. Its structure and layout are determined by the number and distribution of cavities in the casting. Common runner cross-sectional shapes include circular, trapezoidal, and U-shaped. The circular cross-section offers the lowest flow resistance but is more challenging to machine. The trapezoidal cross-section (8mm-15mm upper base width, 6mm-12mm lower base width, 5mm-10mm height) is simple to machine and widely used. Runner lengths should be as consistent as possible to ensure uniform filling of the molten metal in each cavity and avoid partial undercasting or overpressure in the casting due to distance differences. For multi-cavity molds, the runners can be arranged symmetrically or radially. A symmetrical arrangement ensures balanced pressure and flow across the runners, while a radial arrangement is suitable for center-fed circular castings and shortens the flow path of the molten metal.
The ingate is the final passage for molten metal to enter the mold cavity, and its structural parameters have the most direct impact on casting quality. The ingate should be located within a thick wall or in an area conducive to molten metal diffusion to avoid direct impact with the cavity wall or core, thereby preventing splashing and air entrainment. The ingate’s cross-section is typically rectangular (5mm-20mm wide, 0.5mm-3mm thick). The thickness is determined based on the thickness of the casting, generally 1/3-1/2 the thickness of the thinnest part, to control the molten metal filling speed (typically 5m/s-50m/s). The ingate’s length should be as short as possible (typically 1mm-3mm) to minimize pressure loss and facilitate subsequent removal of sprue. For complex castings, multiple ingates can be used for simultaneous feeding, with each ingate responsible for filling a specific area of the cavity to ensure simultaneous filling of the entire cavity.
Overflow chutes and vent chutes are auxiliary components of the gating system, but their role cannot be ignored. Overflow chutes are typically located at the last point of molten metal arrival or at the corners of the mold cavity. They serve to store the first incoming cold metal, slag, and entrained gases, preventing these impurities from entering the mold and causing defects. The overflow chute typically accounts for 5%-15% of the casting volume and has a rectangular or circular cross-section. It connects to the ingate via a narrow slit (3mm-8mm wide), facilitating the entry of molten metal while also creating a certain level of backpressure. Vent chutes are connected to the overflow chute or directly located on the parting surface. They have a depth of 0.02mm-0.05mm and a width of 10mm-20mm, ensuring the smooth escape of gases within the mold cavity. The design of the overflow and vent chutes must be coordinated with the ingate location and the molten metal filling path to form an efficient purification system that “exhales first, then stores slag,” further improving casting quality.
