In addition to the general performance requirements, the coating requirements for motor shell lost foam casting castings also have three points that deserve special attention:
(1) The coating of lost foam casting has better crack resistance and hanging property at normal temperature. Since almost 95% of the surface of the motor shell is vertical, it is difficult to ensure the coating thickness of each pass if the coating is not good. The motor shell has many radiating ribs, thin walls, and a threading slot on the inner wall. The coating of lost foam casting is easy to be poorly coated at this place, which is very easy to cause uneven coating. Over-thick water-based coating is prone to crack during drying, and these cracks are difficult to be found. If not handled properly, it will lead to sand sticking during pouring, and often cannot be cleaned, leading to the scrapping of lost foam casting. ZHY Casting adopts the dip-coating process. Before the dip-coating operation, the coating of lost foam casting is stirred for 1 h with a stirrer to ensure uniform coating. Put the assembled white mold into the lost foam casting paint pool with uniform mixing and Baume degree conforming to the process, slowly press the white mold manually to enter 200~300 mm, with uniform force, stop for 1 min, rotate 90 degrees, stop for 1 min, and then rotate until all are hung evenly, and then lift it out, put it on the shelf, and use a brush to find the leakage. After 2 hours, transfer to the drying room.
(2) High temperature crack resistance. Due to the large number of radiating ribs, there will be many deep and narrow parts on the outer wall of the casing, and these parts will become hot spots after pouring. Therefore, these parts have very high requirements for lost foam casting coating. If the pouring process can not resist the impact of molten iron, there will be sand sticking defects, as shown in Figure 1; If the fire resistance of lost foam casting coating is not enough or the use of binder is unreasonable, the surface will be scabbed and rough after shot blasting, as shown in Figure 2.
(3) Peeling performance of lost foam casting coating. The threading slot in the inner cavity of the motor shell, during the shot blasting process, the steel shot can not enter the threading slot normally, and the coating of the lost foam casting needs high stripping performance. ZHY Casting added additives into the lost foam casting coating, and finally added 2% Fe2O (3 iron oxide red) in the aggregate through multiple adjustments, which met the use requirements.