1. Molding sand properties
In order to ensure good surface quality of castings, the performance of green molding clay sand is particularly important. The control of molding sand performance is an important link in the production process control. Use a 3T rotor sand mixer to add a certain proportion of recycled sand, fresh sand, bentonite and pulverized coal into the sand mixer in sequence. After a certain period of time, mix the sand to produce molding sand that meets the requirements. The specific sand mixing parameters are shown in Table 1.
|Raw material||Reused sand||Fresh sand||Pulverized coal||Bentonite|
|Dosage /kg||3 000||10||15||35|
Feeding sequence: (reused sand + Fresh sand) + water + (pulverized coal + bentonite) + make-up water. The first amount of water added is 80% of the historical amount of water added. The amount of water added is automatically added and adjusted according to the online test results. When the total mixing time exceeds 200 s, the molding sand is discharged and no longer used. The control range of molding sand properties is shown in Table 2.
|Project||Moisture /%||Compaction rate /%||Air permeability||Crushing index /%||Wet compressive strength /MPa||Temperature / ℃||AFS fineness||Effective bentonite content /%||Burning loss rate /%||Silt content /%|
2. Smelting and spheroidizing process
Q10 pig iron, briquette scrap and QT450-10 recycled material are used as raw materials. The proportion of furnace charge is 50% recycled material +20% pig iron +30% scrap. The feeding sequence is recycled material + scrap + carburizing agent + pig iron + recycled material. In order to ensure the absorption rate of carburizing agent, the carburizing agent is added to the electric furnace with the scrap. The standing temperature is 1535 ~ 1555 ℃, the standing time is 3 ~ 5 minutes, the furnace discharge temperature is 1495 ~ 1525 ℃, and the sampling temperature is ≥ 1490 ℃, The tapping mass is 696 ~ 704 kg.
After smelting adjustment, the chemical composition control of molten iron after melting is shown in Table 3. The residence time of molten iron with qualified composition in the furnace shall not exceed 30 minutes, otherwise the carbon content needs to be re tested and readjusted if necessary. Using wire feeding spheroidization, the amount of W (mg) of spheroidized wire is 29.5%~32.5%, the amount of W (RE) is 2.0%~2.5%, the diameter of core wire is 13.0~13.7 mm, and the particle size is 0.1~2.5 mm. In the process of tapping, attention must be paid to ensure the consistency of tapping quality, tapping temperature and molten iron turnover time of each package of molten iron. At the same time, in order to prevent shrinkage defects inside the casting caused by excessive residual magnesium and ensure the spheroidization rate of the casting, spheroidization temperature, spheroidization time, pouring temperature and other parameters must be strictly controlled. During the wire feeding spheroidization reaction, the package must be covered tightly to avoid and reduce the spillage of molten iron outside the package, which is conducive to the smoking and dust removal effect of environmental protection equipment in the workshop and avoid environmental pollution. The process parameters of wire feeding spheroidization are shown in Table 4.
|Project||Wire feeding length /m||Wire feeding speed /m · min-1||Temperature before wire feeding / ℃||Reaction time /s||Pouring temperature / ℃|
|Numerical value||14.5±0.15||18±0.2||1 430～1 450||40～60||1 400～1 360|
The inoculation treatment is divided into three times: the first inoculation is when the molten iron is discharged from the furnace, the silicon barium inoculant with particle size of 2.6~4.5 mm is added into the transfer package, and the amount is 0.2%; After the second inoculation, when the molten iron is transferred to the pouring basin after spheroidization, silicon barium inoculant with particle size of 0.6~2.5 mm is added, and the amount is 0.3%; During the third inoculation, silicon barium inoculant with particle size of 0.2~0.5 mm is added by the method of flow inoculation, and the inoculation amount is 3 g / s. In order to ensure the effect of spheroidization and inoculation, the pouring time of the whole package shall not exceed 8 min.