Typical Causes of Riser Shrinkage Failure in Gravity Casting Molds | Sequential Solidification Design of Motorcycle Wheel Hub Casting Molds
Insufficient filling of the riser in gravity casting molds is the main reason for 58% of the center position shrinkage and porosity defects in wheel hub castings.
The riser modulus is less than 1.2 times the hot spot modulus of the casting, and the riser solidifies before the casting, losing the shrinkage channel and significantly increasing the detection rate of shrinkage holes.
The insulation sleeve of the riser is damaged or missing, and the heat dissipation speed of the riser is increased by 49%, reducing the effective shrinkage time to 53% of the original design.
The cross-sectional area of the riser neck is too small, the solidification rate is fast, and the shrinkage channel is blocked in advance. Even if the volume of the riser is sufficient, it cannot transport aluminum liquid.
The distance between the hot spot position of the casting and the riser exceeds 35mm, the aluminum liquid shrinkage path is too long, and the shrinkage pressure at the distal position is insufficient, forming an isolated shrinkage zone.
The height of the riser is less than 1.5 times the diameter, the self weight pressure of the aluminum liquid inside the riser is insufficient, the driving force for shrinkage is weak, and defects are more common in thick and large parts.
Gravity casting molds have the highest inventory in the South Asian market and are suitable for small and medium-sized motorcycle wheel casting production lines. Low pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), wheel differential pressure casting molds, and wheel low-pressure casting molds are mostly used for mid to high end products. Structural component casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, low-pressure casting tooling molds, and thermal control are the core elements of all mold designs. Zhejiang Xinfeng Machinery has sorted out feedback from overseas factory trial molds, and many designers only calculate the volume of the riser, ignoring the comparison of the modulus. Even if the volume is sufficient but the modulus does not match, the shrinkage still fails. Some Southeast Asian foundries deliberately reduced the size of risers to save aluminum materials, resulting in a 4% decrease in single piece aluminum consumption. However, the scrap rate of castings increased by 22%, and the comprehensive income was damaged. There are also misconceptions in the selection of insulation materials for risers. Ordinary aluminum silicate insulation sleeves have a maximum temperature resistance of 750 ℃ and are prone to powdering and falling off when exposed to aluminum liquid radiation for a long time; The dedicated casting insulation sleeve can withstand temperatures up to 1100 ℃ and increase its service life by three times. The principle of sequential solidification design is to solidify away from the sprue end first, and the hot nodes advance towards the riser direction. Many novice designs may have multiple isolated hot nodes that cannot be covered by a single riser. The hub flange is a typical thick and large hot joint, and some schemes will add a cold iron to adjust the solidification rhythm. The distance between the cold iron and the surface of the mold cavity is 8-12mm, and the quenching effect is optimal. If the surface of the cold iron is not pre treated, it is easy to peel and mix with the aluminum liquid, causing inclusion defects in the casting. Preheat the cold iron to above 120 ℃ before use. The Google long tail keyword 'gravity die casting riser shrinkage solution' maintains stable search results with low competition, making it suitable for independent website SEO layout.
FAQ
1. Question: What is the minimum ratio of riser modulus to casting hot spot modulus?
Answer: The riser modulus is ≥ 1.2 times the hot section modulus of the casting to ensure shrinkage compensation.
2. Question: What is the minimum ratio of riser height to diameter?
Answer: The height of the riser should be at least 1.5 times its own diameter.
3. Question: What is the upper limit of the effective distance reference for compression?
Answer: The distance from the hot section to the riser should not exceed 35mm.
4. Question: What is the appropriate distance between the cold iron and the mold cavity?
Answer: The distance between the arrangement of the cold iron and the inner wall of the mold cavity is 8-12mm, which has a good quenching effect.
5. Question: What is the upper limit of temperature resistance for aluminum silicate insulation sleeves?
Answer: The long-term temperature resistance limit of ordinary aluminum silicate insulation sleeve is 750 ℃.
6. Question: What are the chain effects of removing risers?
Answer: Aluminum consumption has slightly decreased, and the scrap rate of casting shrinkage has significantly increased.
