Mechanism and Cleaning Cycle Setting of Exhaust Groove Blockage in Gravity Casting Molds | Optimization of Exhaust System for Motorcycle Wheel Hub Casting Molds
Slag accumulation and blockage in the exhaust groove of gravity casting molds are the direct causes of 44% of casting defects such as gas entrapment, cold insulation, and oxidation inclusions.
If the depth of the exhaust groove is greater than 0.45mm, aluminum liquid is prone to enter the groove and quickly form aluminum slag blocking the channel; Depth less than 0.12mm, high exhaust resistance.
The total cross-sectional area of the exhaust groove outlet is less than 22% of the cross-sectional area of the inner runner, resulting in insufficient gas discharge capacity and rapid increase in the holding pressure of the mold cavity.
The surface Ra of the exhaust groove is greater than 1.6, which increases the adhesion speed of oxide scale and release agent carbon slag by 36%, and shortens the blockage cycle by half.
The slag collection bag is directly connected to the exhaust groove without a buffer section, and the aluminum slag is directly flushed into the exhaust channel. Continuous production of 80-120 molds can achieve half blockage.
The distance between the exhaust groove and the filling end exceeds 16mm, and the holding area cannot effectively release pressure, resulting in continuous and repeated local air entrapment defects.
Gravity casting molds rely on the self weight filling of aluminum liquid, and the exhaust speed is much lower than that of differential pressure and low-pressure processes, resulting in a smaller fault-tolerant space in the exhaust design. Low pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), differential pressure casting molds for wheel hubs, low-pressure casting molds for wheel hubs, structural component casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, low-pressure casting tooling molds, and different process exhaust groove specifications cannot be used interchangeably. Zhejiang Xinfeng Machinery Statistics Trial Case: Many novice designers only look at the number of exhaust slots and ignore the total cross-sectional area ratio. There are many slots but the total flow area is insufficient, and they still feel suffocated. Small factories in Southeast Asia often use steel wire for simple groove cleaning, which can easily scratch the groove wall, increase roughness, and cause faster blockage in the future; Recommend using a soft copper brush for cleaning. Under continuous production conditions, it is recommended to inspect and clean the conventional exhaust groove every 120 molds; Aluminum materials with high levels of dust and impurities can be reduced to less than 70 mold cycles. At the end of the exhaust groove, an air guide plate can be added to guide the gas to be quickly discharged, but the air guide plate is a thin piece that is easily deformed, and spare parts need to be kept on hand. We cannot rely on increasing the depth of the exhaust groove to solve the problem of holding breath. If it is too deep, it is easy to flash, and the subsequent polishing cost will increase sharply. Many customers have smooth exhaust during the trial stage, but after a few hours of mass production, there is a rebound in poor performance, mostly due to gradual blockage of the exhaust groove, which is a hidden failure.
FAQ
1. Question: What is the recommended depth range for gravity mode exhaust slots?
Answer: 0.12-0.45mm, balancing exhaust and anti runaway aluminum.
2. Question: What is the minimum ratio of total exhaust cross-sectional area?
Answer: The total area of the exhaust outlet is ≥ 22% of the cross-sectional area of the sprue.
3. Question: What is the recommended surface roughness for the exhaust groove?
Answer: Control within Ra1.6 to delay slag accumulation and blockage.
4. Question: What is the regular inspection cycle for mass-produced exhaust ducts?
Answer: Normally, aluminum material should be cleaned once every 120 molds.
5. Question: What is the upper limit of the distance between the exhaust groove and the filling end?
Answer: Try to control within 16mm and exhaust nearby.
6. Question: Why not use hard steel wire to clean the exhaust duct?
Answer: It is easy to scratch the groove wall, reduce roughness, and clog faster.
