Sand burning is a common casting defect
In sand casting, Sand burning has always been a common casting defect that puzzles foundry workers. It not only increases the cleaning workload, affects the appearance, but also causes the casting to be scrapped in serious cases.
Sand burning in castings is the result of the interaction between the mold and the liquid metal interface including mechanical action (static pressure, dynamic pressure), thermal action and chemical action. Generally, it can be divided into hot bonded sand, chemical bonded sand and mechanical bonded sand. Metal penetration is the infiltration of molten metal into the mold, which is difficult to clean and has a serious impact.
How to solve Sand burning of castings
The measures to solve the Sand burning of castings are generally to use effective coatings and improve the properties of raw sand / mold. The common anti sticking sand special sand is chromite sand, which has a long history of use and good effect. However, it is rarely used as a single sand due to its large proportion, poor grain shape, high price, strong alkalinity and other reasons.
Since the end of the last century, people have developed a variety of special sands, which generally have the advantages of nearly round grain shape, high fire resistance, high particle strength, wide particle size distribution, etc., such as Fused ceramic sand, CB sand, spherical sand formed by flame sintering, ceramsite sand, etc., which are generally reported to have good anti sticking effect.
Comparative experiment of various foundry sands
Practice is the only criterion for testing truth. Only through experimental analysis can it be more convincing. Some foundry workers conducted sample pouring tests to compare the anti-sintering and anti-metal-penetration abilities of several common artificial sands, anti-Sand burning ability.
The disc-shaped casting was used in the test, with 6 circular holes uniformly distributed in the ring, and different raw sand was used to make sand cores. The gate is set in the center of the disc to ensure that the heating conditions of each sand core are the same. The surface of the sand core is coated with magnesia coating, and the core is poured after flame drying. The weight of loose sand after casting and shot blasting of different sand cores was weighed respectively, and the anti -sticking ability of various original sand cores was quantitatively compared.
After the test, the anti-sticking ability of various sand cores was ranked. The results showed that the anti-sticking ability of chromite sand was good, followed by fused ceramic sand, flame sintering sand, CB sand, silica sand, ceramsite sand, etc. The test also found that the Fused ceramic sand core with higher strength (24kgf/cm2) had a much stronger anti sticking ability than the Fused ceramic sand core with lower strength (14.2kgf/cm2), indicating that the sand core with higher strength was conducive to preventing metal penetration.
Through further analysis and discussion, it is found that fused ceramic sand has better performance
1. Chromite sand has good anti-sticking effect, but its anti-sticking mechanism is different from that of other spherical artificial sand. It is mainly through thermal sintering to form "glaze layer", and then spalling after cleaning to reduce Sand burning. Other spherical artificial sand will not be sintered basically.
2. Compared with other spherical sand, Fused ceramic sand has better anti-sticking performance, thanks to its higher fire resistance and smoother surface.
3. On the contrary, the finer the original sand particle size, the wider the particle size distribution, and the more conducive to reducing Sand burning.
4. The tighter the mold (sand core) and the higher the strength, the more conducive to reducing Sand burning, especially mechanical Sand burning.