How to design the exhaust system of low-pressure casting molds

How to design the exhaust system of low-pressure casting molds
The exhaust area of low-pressure casting should be configured at 1% -2% of the projected area of the mold cavity, and should be located at the end of the liquid flow rather than the front of the liquid flow.
The consequences of insufficient exhaust
The back pressure of the mold cavity increases, the filling speed decreases, and there is insufficient pouring or cold insulation at the distal end of the thin wall.
Gas is pressed into the aluminum liquid, forming pores. Pores are mostly distributed on the surface and corners of the inner cavity of castings.
Excessive exhaust is also a problem. The exhaust area is too large, and aluminum liquid is prone to enter the exhaust channel, causing blockage and flash.
Estimation of exhaust area
Configure according to 1% -2% of the projected area of the cavity. Thin walled components are taken as high values, while thick walled components are taken as low values.
A set of 500mm diameter wheel hub molds with a projected area of approximately 0.2 square meters and an exhaust area of approximately 2000-4000 square millimeters.
This area should be distributed and not concentrated in one place. Centralized exhaust can cause abnormal local flow velocity.
Types of exhaust plugs
There are three commonly used types: gap type, mesh type, and sintered metal. Gap style exhaust is fast, but it is easy to be blocked by aluminum liquid.
The mesh exhaust is uniform and suitable for large-scale layout. Sintered metals have good breathability and high cost.
The gap between exhaust plugs is usually 0.05-0.1mm. If the gap is too large, aluminum liquid will seep in; Too small, poor exhaust.
Principles of location selection
The exhaust plug should be placed at the end of the liquid flow and in the final filling area, not opposite the gate.
The exhaust focus of the wheel hub mold is on the far end of the wheel rim, the end of the spoke, and the bolt hole protrusion.
The exhaust plug should avoid the sand core. Facing the sand core will suck sand particles into the channel, causing blockage.
Maintenance and cleaning
The exhaust plug should be cleaned every 2000 cycles. When the aluminum liquid is not degassed, it is shortened to 1000 mold cycles.
Use compressed air to blow back during cleaning, do not use sharp tools to poke, as it will widen the gap.
Blocked exhaust plugs can cause local material shortages. Found repeated material shortage in the same position of the casting, check the exhaust first.
The method of Xinfeng Mold
Xinfeng Mold will mark the end area according to the filling simulation results on the exhaust layout of the wheel hub mold, and then arrange the exhaust plug.
The number and location of exhaust plugs are numbered on the drawing for easy cleaning and replacement on site according to the numbers.
Coordination between exhaust and coating
The cavity coating will partially block the exhaust plug. After spraying, it is necessary to check whether the exhaust plug is unobstructed. If it is blocked, it should be cleaned or replaced in a timely manner.
When the coating thickness is uneven, the exhaust plug at the thin part is easily penetrated by aluminum liquid, forming local blockage.
Verification of exhaust effect
First article inspection to ensure that the distal corner is fully formed. Shortage or blurred corners are often signals of insufficient exhaust.
Practical tips
When replacing the exhaust plug, align it according to the number. Installing it in the wrong position is equivalent to not installing it, which is a common low-level error on site.
The cleaning record of the exhaust plug is registered by number, indicating that the design needs to be adjusted if there is more blockage at that location.
The design of the exhaust system should leave room for modification, and the decision on whether to add plugs should be made after the first round of trial molding, which is more reliable than doing it all at once.
Frequently Asked Questions
Question: How is the exhaust area calculated?
Answer: According to 1% -2% of the projected area of the cavity.
Question: Where should I put the exhaust plug?
Answer: The end of the liquid flow is not opposite the gate.
Q: What is the gap between the exhaust plugs?
Answer: It is usually 0.05-0.1mm.
Q: How often is it cleaned?
Answer: Usually 2000 cycles, and 1000 cycles before degassing.
Q: How about excessive exhaust?
Answer: Aluminum liquid enters the channel, causing blockage and flying edges.
Q: What should I check for repeated material shortages first?
Answer: First check if the exhaust plug at the corresponding position is blocked.
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