Led by Mr. Eric Chen, Newton's domestic sales department and international trade department paid a study tour to AIV foundry workshop in Qingtian. The main purpose of this trip is to learn about the coated sand process and its production process.
As an expert in this field, Mr. Yu in the casting workshop guided Newton team and made the explanation and analysis. Firstly starting from the housing, the special sand from Vietnam is shot into the mold under a pressure of 8kgs. It takes about 20 to 30 seconds to complete the shot. Then it is sintered at 200 degrees Celsius for about 200 to 300 seconds. Remove the core and cavity, and use steel wire to reinforce it after assembly. Because there is moisture in the housing at this moment, the entire housing will be placed in the oven and dried at 200 degrees Celsius for about 3 hours to eliminate moisture completely. This step is very important, which is related to the quality of the casting, because if the water is not dried, it will turn into steam by the high temperature during casting, and a large number of pores will be generated in the casting. Then the housing is ready to start smelting molten iron. Taking GS-C25 as an example, melting the molten iron at 1610 degrees Celsius. Please note that the temperature of the molten iron can not be too high or too low. When the temperature is too high, the shrinkage is larger and it is easier to shrink holes and loose. When the temperature is too low, there will be cold partition or insufficient pouring. Sampling and testing is neccesary before pouring. If the chemical composition does not meet the requirements, adjust the elements until they are qualified. The pouring speed must be fast , otherwise the molten iron will be cooled, which will affect the quality and have to be returned to the furnace. After pouring the coated sand, the sand shell is automatically converted into powder, and it’s very convenient to clean the sand. You will find that the casting is just casted, our pouring riser is large and high, and the small diameter pouring riser accounts for 1:1. The purpose is to increase the pressure to achieve a better shrinkage effect and with better density. Post-furnace test will be carried on the newly-made castings. After passing the test, normal heat treatment at 890 degrees Celsius is carried out for 3 hours to achieve better grain structure, mechanical properties and cutting performance. Air cutting is used to remove the pouring riser, then the first shot blasting treatment is carried out, and the uneven places are polished and trimmed, and then the second shot blasting treatment is performed. The castings can only be delivered by passing all the test and inspections.
After learning the process of coated sand, Mr. Yu shared with us the advantages and disadvantages of coated sand compared with other casting processes:
Advantages: 1. Highly automatic of coated sand with high production efficiency, and low environmental pollution. 2. The coated sand itself has a layer of film, and the surface of the casting is smooth. 3.Little gas production of coated sand and few defects. 4. The coated sand is easily removed and cleaned, which is suitable for casting complex models. 5. Coated sand can produce multiple castings at one time.
Disadvantage: 1. The nominal size of coated sand cannot be too large.