5.Buried box with empty shell
5.1 preparation before embedding
The inner wall of the roasted hollow shell cavity is smooth, and there is no trace of carbon black; when roasting in the kiln, the discharge port is downward, and there should be no debris falling into it; in order to be safe, it is customary to blow with compressed air before sealing; the case model is placed horizontally, and the cable hole is naturally in a horizontal state. In order to ensure that the molding sand is filled tightly, the glass sand should be filled before embedding, In addition, it is solidified with CO2; the pouring riser (big hole) is sealed with plastic film; the rubber discharging hole (small hole) of electric hand drill is sealed with fire-resistant fiber cloth; sand is prevented from entering the mold cavity when the box is buried.
5.2 sand embedding
Measure the height of the model, calculate the thickness of bottom sand, place the empty shell of the model after adding sand, vibrating and scraping, and the upper edge of the pouring riser needs to be 20 mm ~ 30 mm higher than the sand box; in this case, each box is equipped with 6 models (4 in horizontal direction and 2 in horizontal direction); sand is added twice, and the height of the first sand is leveled to level the casting body; after vibration compaction, sand is added again to level the sand box After tamping again, scrape it flat, cover with plastic film, and protect the sand layer on the film shelf to prevent the liquid steel splashing and breaking the film during pouring, resulting in pressure relief.
6 Negative pressure casting
Before pouring, the ladle must be baked to 700 ~ 800 ℃. Ladle baking is one of the important measures to ensure the purity of molten steel when pouring by hand ladle, because glaze will be hanged in cold ladle; after molten steel is discharged from the furnace, slag collecting agent shall be spread to clean the glaze slag, and the temperature of molten steel shall be measured to ensure high temperature pouring; in this case, 0.5T hand ladle is used for pouring, in order to ensure pouring temperature, molten steel is tapped in three times, and two pieces are poured each time; the negative pressure during pouring is maintained at 0.02 MPa.
7 Casting cleaning
The casting started at 12 o’clock at night, and the first box was sent out at 8:00 a.m. the coating cracked and peeled off as the casting cooled down. When the casting fell to normal temperature, the coating shell basically fell off.
After cleaning, there are no defects on the surface of castings, no defects in flaw detection and no waste products in machining; the quality is stable during mass production; the cable head is used for the traction wire rope of cable-stayed bridge, with key position, concentrated stress and heavy responsibility. The material and performance of castings are very strict, so it is wise to adopt the casting process of lost foam casting.