Three Constraints in the Design of Gravity Casting Mold Pouring System

Three Constraints in the Design of Gravity Casting Mold Pouring System
The pouring system of gravity casting needs to be solved under three constraints: pouring time, gate position, and hot spot distribution. Any imbalance of these factors can lead to shrinkage or cold shut.
The pouring time is determined by the wall thickness
The pouring time is often estimated based on the wall thickness, with 1-2 seconds per millimeter. For parts with a wall thickness of 8mm, the pouring time is about 8-16 seconds.
The time is too short, the flow rate of aluminum liquid is high, and the risks of gas entrainment and sand flushing increase. If the time is too long, the temperature at the front end will decrease, and cold insulation is inevitable.
Thick and large parts can be appropriately extended, while thin-walled parts should be shortened. The unified time applies to parts of the same family, and cross category calculations need to be recalculated.
The position of the gate determines the temperature field
The gate should be located at the thick wall, allowing the high-temperature aluminum liquid to pass through the thick wall first and then flow towards the thin wall. This solidification sequence is consistent with the direction of shrinkage.
The gate is located at a thin wall, where the thin wall solidifies first and the thick wall loses its contraction channel, resulting in axial shrinkage and looseness.
When using multiple gates, it is important to avoid liquid flow reversal. Hedging will generate eddy currents and involve oxide films, which can easily lead to inclusions in the inner cavity of the casting.
The distribution of hot nodes should match the riser
The hot spot is the final solidification point and requires a riser to compensate for shrinkage. The volume of the riser is usually taken as 1.5-2.5 times the volume of the heat node.
The riser position deviates from the hot spot, and the contraction channel is cut off. The supplementary distance generally does not exceed 4 times the wall thickness, and if it exceeds, additional cold iron needs to be added.
The function of cold iron is to create a temperature gradient and guide the hot spot towards the riser direction. The thickness of the cold iron is often taken as 0.8-1.2 times the wall thickness.
The ratio of sprue to runner
The ratio of the cross-sectional area of the sprue to that of the runner and sprue is commonly 1:2:4 or 1:3:6. The proportion determines the flow velocity of each section.
Proportional imbalance, low flow rate in the transverse runner, and insufficient upward movement of slag. If the flow rate is too high, it will also wash away the sand mold.
Xinfeng Mold will first conduct filling simulation in the design of the gravity mold pouring system, confirm the liquid flow path, and then determine the number and position of gates.
The relationship between exhaust and pouring
The exhaust capacity of the pouring system is often overlooked. Insufficient exhaust from the mold cavity, increased back pressure, decreased filling speed, and increased risk of cold insulation.
It is recommended to configure the exhaust plug area at 1% -2% of the projected area of the cavity. Thin walled components can take higher values, while thick walled components can take lower values.
The exhaust plug should be located at the end of the liquid flow, not the front of the liquid flow. The position was wrong, and the exhaust plug was quickly blocked by aluminum liquid.
Common Misconceptions
The first misconception is to increase the gate to improve the filling capacity. If the gate is too large, it will form a new hot spot, and the position of shrinkage will only shift.
The second misconception is to ignore the pouring temperature. For every 20 ℃ decrease in temperature, the flowability significantly decreases, and the original pouring time is no longer applicable.
Misconception three is to simply copy the parameters of similar components. The wall thickness difference is 1mm, and the pouring time and gate area need to be recalculated.
Verification method for pouring system
The first piece cutting is the most direct method. Cutting along the flow path to observe the relationship between shrinkage and gate position is more useful than looking at the appearance.
Thermocouples for temperature measurement can also be used to place points at different positions in the mold cavity. If the solidification time difference exceeds 3 seconds, it indicates that the temperature gradient design needs to be adjusted.
Frequently Asked Questions
Question: How to determine the pouring time?
Answer: Estimate based on 1-2 seconds per millimeter of wall thickness.
Q: Where should the gate be located?
Answer: For thick walled areas, ensure sequential solidification.
Question: What is the volume of the riser?
Answer: Usually take 1.5-2.5 times the volume of the heat node.
Question: What is the thickness of the cold iron?
Answer: Usually take 0.8-1.2 times the wall thickness.
Q: How to match the exhaust area?
Answer: Configure according to 1% -2% of the projected area of the cavity.
Q: Can we simply copy the parameters of similar components?
Answer: No, if the wall thickness difference is 1mm, it needs to be recalculated.
Recommended search keywords
Gravity casting mold, pouring system design, gravity casting process, riser design, cold iron layout, gravity casting mold manufacturer, aluminum alloy gravity casting, pouring time calculation, casting process design, mold manufacturer