The lost foam casting pouring process scheme of gray iron castings mainly includes pattern making, coating, gray iron casting layout, pouring riser design, pouring parameter determination and so on.
1) foam pattern making: foam pattern including gray iron casting, runner and riser, etc. the foam pattern of the underframe is molded by the whole mold, and the shape of pouring directly to the runner and riser is relatively simple, handmade. With hot melt adhesive, gray iron casting, runner, riser and so on are bonded together to form foam pattern clusters.
2) Coating: Guilin No. 5 coating with good air permeability and high temperature resistance used in this process adopts dip coating method; Coating thickness of 1.5~2mm, two times of coating, the first dip coating to be dry after coating and then second times to ensure that the foam pattern is covered by paint.
3) lost foam casting process generally adopts bottom injection or side injection gating system to produce iron castings, because under negative pressure, the graphite in gray iron castings has self feeding function in the hard cavity of gray iron castings, and there is no need to use other external feeding measures for feeding. In the process of producing gray iron castings by lost foam casting process, the bottom injection gating system can make the liquid metal rise steadily in the mold, and the top injection gating system can feed the gray iron castings. Therefore, two trial casting schemes of bottom injection and top injection were adopted to produce the gray iron casting.
4) The feeding riser of lost foam casting is designed flexibly, which can be spherical, cylindrical and square, and the position of riser is relatively free. The purpose of placing the gray iron at the top of the riser of the casting can not only prevent the gray iron from shrinking, but also prevent the gray iron from being placed at the top of the riser of the casting.
5) Gray iron castings are produced in large quantities: according to the size of the sand box (1700mm) × 1500mm × 1100mm) and the size of gray iron castings, it is proposed to adopt the layout of six pieces in one box, and adopt vertical pouring to facilitate the sand filling and compaction inside the gray iron castings and prevent box waste during pouring.
6) Pouring parameters include the following:
Casting material: gray iron casting material: HT150; Foam choice for easy processing, cheap EPS, foam density 0.015g/cm ³； The dry sand material is Baohua pearl sand. Pouring temperature: the casting temperature of lost foam casting process is higher than that of the traditional sand mold. The temperature required for foam filling is 1380 30~50 ~1480. Because the underframe is produced in large quantities and the process requirements of using water slag iron to produce gray iron castings, 1450 ℃ is used as the pouring temperature.
Negative pressure condition: maintain a negative pressure of 0.05Mpa during the mold filling of gray iron castings. After the mold filling is completed, maintain the pressure for 10 ~ 15 minutes, and the pressure maintaining negative pressure is 0.025-0.04mpa. To ensure the stability of the mold cavity, prevent box collapse and facilitate the discharge of pattern degradation products during the mold filling process; Ensure the rigid strength of the mold during solidification, facilitate the self feeding of graphite, and reduce or avoid the occurrence of shrinkage cavity and porosity defects.