Views: 29 Author: Site Editor Publish Time: 2018-10-09 Origin: www.fuchun-casting.com
The quality of molding sand has a great influence on the quality of castings and the rejection rate. In sand casting, especially in clay sand green casting, the properties of molding sand have a significant influence on the quality of castings and the rejection rate.
Good molding sand needs not only high strength, suitable compaction, suitable moisture and composition, but also suitable temperature. Therefore, it is very important to adjust the sand temperature for the sand treatment system of large-scale continuous production workshop. Excessive sand temperature will lead to the formation of casting defects.
Harmfulness of excessive molding sand temperature：
1、Molding sand requires low temperature and stability when molding. Most old sand temperatures are much higher. If the sand is not cooled, the performance of the sand will be unstable, so it is impossible to produce uniform compactness sand moulds on the moulding machine. The lower the temperature of molding sand, the higher the compactness. Because of the high sand temperature and the deterioration of compactness, a lot of problems such as sand mold rupture, viscous mold and sand mass appear in the sand, which reduces the molding speed and increases the waste mold.
2、Too high sand temperature leads to poor quality of sand mold, resulting in quality problems of castings and high reject rate. Casting defects such as pinholes, inclusions, sand washing and surface roughness often occur when the sand temperature is too high. If these defects are not found until sand drop, cleaning, shot blasting or machining, it will cause greater waste.
3、When hot sand is added to the sand mixer, water vapor condenses in the sand mixer and absorbs dust that should have entered the dust collector, as well as clay that should have been mixed into the sand mold. Dust accumulates in the mixer and reduces the efficiency of the mixer. The excessive evaporation of water during sand mixing requires higher water addition, which results in longer sand mixing period and lower productivity of sand mixer.
In order to prevent and solve the hot sand problem, the most important measure is to increase the actual capacity of sand system, reduce the number of cycles of sand use, and adopt humidifying ventilation cooling treatment in the design stage of sand treatment system, which can greatly reduce casting defects.