ZHY casting adopts 20 ~ 40 mesh quartz sand and manual bag sand adding method. The size of sand box is 1450mm × 1 200 mm × 1 000mm, lost foam casting sand box structure is shown in Figure 1. The vibrating table adopts GK free floating vibrating table. The difference is that the motor is suspended on both sides of the vibrating table, with one motor on each side.
1. Sand sticking of lost foam Castings
Due to the weak lateral filling capacity of the vibrating table and the low compactness of the molding sand at the dead corner of the Yellow mold, the molten iron breaks through the coating and forms bonded sand during pouring; In addition, the consistency of lost foam casting sand boxes is poor, and the vibration acceleration at individual places is up to 3 times. lost foam casting sand boxes with low acceleration are very easy to produce sand sticking (as shown in Figure 2), which is difficult to clean, and often cause castings to be scrapped.
2. Lost foam casting deformation
In the production of thin-walled castings such as gearbox side wall and flywheel housing stop, due to the large difference in vibration acceleration at different parts, the maximum difference in acceleration at both sides can reach 2 times, resulting in sand flow in lost foam casting sand box and pressure deformation of yellow mold. Serious visual observation can observe the movement of yellow mold in lost foam casting sand box. After measurement, the amplitude of lost foam casting sand box is 0.4 ~ 0.7 mm.
The bottom of the sand box used by ZHY casting is supported by 20 support sleeves welded between two layers of 8mm steel plates. During the production process, it was found that the support sleeve began to be desoldered after a 20 support sleeves are welded between two layers of 8mm steel plates at the bottom of lost foam casting sand box used by ZHY casting. During the production process, it was found that the support sleeve began to be desoldered after a period of production, the vibration force after desoldering could not be transmitted upward through the bottom, the compactness of molding sand was low, and the size of castings in the vertical direction became larger; At the same time, the bottom plate of lost foam casting sand box is thin. Due to long-term vibration and impact, the maximum deformation of the bottom plate reaches 2.3 mm. The molding sand in the vertical direction retreats and compacts repeatedly, resulting in the further increase of the size of the casting in the vertical direction. Taking the gearbox middle shell as an example, the theoretical dimension in the height direction is 534 mm, and the actual measured dimension in the height direction is 535.2 ~ 538 mm, resulting in problems such as inconsistent machining allowance and thin hole wall, and the machining deformation scrap rate is 2.9%.