The direct production of gray iron lost foam castings by using water slag iron smelting can melt the water slag iron particles that are difficult to contain in the melting process (the water slag iron block is formed in the melting process of water slag iron) into molten iron, so as to directly pour the molten iron into lost foam castings. This method uses water slag iron instead of gray iron to melt and manufacture qualified molten iron casting, which meets the requirements of low-carbon and circular economy. The specific implementation of the method is carried out according to the following steps:
Step 1: water slag iron particle is to send the waste water slag iron block purchased from the steel plant to the cement plant for crushing, crush the water slag iron block into particles, and conduct magnetic separation on the crushed particles to obtain water slag iron particles (particles) that meet the production requirements.
Step 2: take a certain proportion of standard gray iron raw materials used in the production of normal gray iron lost foam castings according to the mass fraction ratio, place them at the bottom of the medium frequency furnace, preheat the medium frequency furnace (for 10 ~ 15 minutes), then increase the power of the medium frequency furnace to full load, make the temperature in the furnace reach above the liquidus temperature of gray iron, and heat it for a period of time, Make gray iron raw materials melt into molten iron.
Step 3: after the gray iron raw material in step 2 is completely melted into molten iron, add a certain amount of water slag iron particles screened in step 1 to the molten iron, continue to increase the power of the medium frequency furnace to full load, raise the temperature in the furnace above the pouring temperature, and continue heating until the water slag iron particles in the medium frequency furnace are completely melted into molten iron.
Step 4: when all the raw materials added in step 3 are melted into molten iron and the distance from the molten iron surface to the furnace mouth reaches a fixed value, the molten iron is sampled for pre furnace test and analysis, and the elements in the molten iron in the furnace are adjusted according to the analysis results to make the element content in the molten iron meet the requirements. The carbon silicon content of molten iron is determined by the carbon silicon rapid analyzer in front of the furnace (C element in HT standard lost foam casting is 3.25 ~ 3.45 and Si element is 1.10 ~ 1.40; C element in QT standard lost foam casting is 3.80 ~ 4.00 and Si is 0.2 ~ 1.40). The hot metal elements in the furnace are adjusted according to the analysis results. The C of 750KG medium frequency furnace can be reduced by about 0.1 per 15kg scrap and the Si can be reduced by 0.1 ~ 0.13 per 10kg scrap; Every 1kg of furnace mouth carburizing agent (C-1) can increase to about 0.1, and every 1kg of ferrosilicon (fesi75) or composite inoculant can increase Si to 0.1).
Step 5: when the element content in step 4 meets the required fixed temperature rise value of molten iron, add purifying agent, modifying agent and inoculant to the molten iron. When the raw molten iron meets the control conditions, when various types of lost foam castings HT150, HT200, HT250 and HT300 are to be produced, the material ratio and purification and modification method are as follows: when the molten iron is discharged from the furnace, the purification agent (sodium fluoroaluminate), modification agent (rare earth ferrosilicon alloy) and inoculant (ferrosilicon fesi75) prepared in proportion in advance are mixed and put into the molten iron ladle dried in advance, When the molten iron comes out of the furnace in place, fully stir and react for a certain time to obtain the standard cast iron molten iron. By adding different contents of purifying agent, modifying agent and inoculant, we can extract different grades of gray iron molten iron (HT150, HT200, HT250, HT300).
Step 6: when pouring lost foam castings, always fill the gate cup, and the pouring rhythm is slow fast slow. When the ladle is aligned with the gate cup, the liquid metal shall be injected slowly. When the liquid metal along the current edge rushes the gating system out of a channel, it must flow in a large flow and pour continuously. When the lost foam casting is full, the pouring speed shall be slowed down until the end of pouring. If the molten iron contains impurities, pay attention to slag filtering during pouring.
Step 7: after the lost foam casting is air cooled, turn over the box and clear the sand, test the performance of the lost foam casting, and obtain the required lost foam casting.