Implementation of EPC process scheme for nodular cast iron vacuum rim casting

1. EPS foaming white mold

EPS material has good cutting performance, fast NC machining speed and high precision. The mold investment is not considered in the preliminary test, and the development cycle is fast. Generally, considering the requirements of mold investment cost and development cycle, the EPS material plate can be directly carved (or supplemented by bonding) into a white mold by using the NC machine tool. Due to the structure of vacuum rim casting and the requirements for appearance quality, it is determined to develop foaming mold and adopt EPS plastic foaming white mold. In order to reduce the deformation tendency of white mold, the white mold density is increased to 26 ~ 32 g / L (as shown in Figure 1).

According to the characteristics of EPC process, the final mold of vacuum rim air hole system, valve hole and tire bolt hole system can be cast, and EPS plastic foaming white mold can make air hole system, valve hole and tire bolt hole system.

2. White mold modification, anti deformation reinforcement, bonding pouring and feeding system

If the EPS white mold made of foaming has surface defects such as pits, meat deficiency or bumps, the surface shall be modified with modification paste or modifier, and a cross shaped anti deformation reinforcement shall be made at the open rim of the rim.

Considering the influence of casting structure on sand flow filling, the top injection process of vacuum rim opening upward and multi sprue injection is designed. At the same time, 6 ~ 8 slag collecting bags are arranged at the top. After the process is determined, the bonding pouring feeding system forms a white mold sample (as shown in Figure 2)

3. Coating dipping and drying

After the completion of the white mold, dip or brush the coating, or dip and brush the coating in combination. Coating performance directly affects the surface quality of EPC Castings. Coating dipping and drying will also affect the surface quality of castings. Dip and brush the water-based quartz silica sand powder coating twice. After each coating, dry it naturally or at the temperature below 55 ℃ for 8 ~ 10h. During the drying process, the appearance shall be placed stably to prevent deformation (as shown in Figure 3).

4. Sand filling, packing, molding and negative pressure pouring

The dried pattern of the dipped paint is buried in the pearl sand, and the bottom sand is laid, vibrated and leveled; The vertical support is firm. When adding sand, pay special attention to fill the inner cavity, dead corner and shadow parts that are not easy to be compacted under negative pressure, add sand to be flush with the top of the sand box, and compact with three-dimensional vibration at the same time; Lay plastic film to cover the upper opening of the sand box, cover it with a certain thickness of dry sand, and press and protect the plastic film.

Place the sand box with sand filling molding in the pouring area, connect the vacuum pipe, open the negative pressure valve, and tighten the negative pressure; When the negative pressure and vacuum degree reach 0.04 ~ 0.06 MPa, pour the molten iron of nodular cast iron; 5 ~ 10min after pouring, close the negative pressure and remove the vacuum.

5. Cleaning

The casting shall be kept in the sand box for 2 ~ 2.5 h. After the casting is cooled to 200 ℃, the sand shall be dropped and unpacked. After the casting is cooled, the gating system and slag collecting bag shall be removed, and then the surface shall be cleaned by shot blasting or sand blasting, and then the complete casting shall be further cleaned (as shown in Fig. 4).

6. Overall inspection

In the pouring process of vacuum rim casting, due to vacuum adsorption, its pouring speed is relatively fast and its mold filling capacity is good. Under the normal pouring temperature of nodular cast iron, there is no supercooling, insufficient pouring and so on; After twice trimming and die adjustment, the size requirements are met; Due to the vacuum adsorption and the cooling effect of the pouring cavity of thin-walled parts, the internal structure of the casting is dense.

The air hole system and valve hole finally cast by the EPC process meet the quality and installation requirements. Due to the comprehensive influence of the casting size error of the graduation circle diameter of the tire bolt hole system and the tire bolt hole diameter on the position degree, the accuracy of the hole and hole system still retains the subsequent processing process. However, due to the pre hole cast by the tire bolt hole system, the subsequent processing workload is significantly reduced, The processing efficiency is improved.