Determination of casting process scheme of nodular cast iron intercooler base pipe

1. Nodular cast iron molding process

The two box core molding is adopted to enlarge the sand filling core of the side lower molding to the top surface of nodular cast iron (Fig. 1). At the same time, in order to make full use of the existing sand box and simplify the mold structure, the lower molding pattern is only made to the center of the water pipe. After all the sand cores are laid down, the middle sand box is sleeved, and the sand is filled and compacted on the back of the sand core, which not only simplifies the molding operation, but also saves the mold manufacturing cost.

2. Selection of nodular cast iron gating system

The intercooler base pipe has a large through hole. The gating system is set at the bottom of the ductile iron inner cavity in the form of bottom return gating system (Fig. 2), in which Σ f straight: ∑ f transverse: ∑ f inner = 1:1.85:1.19. The filling process is: the metal liquid enters the transverse sprue from the sprue, distributes to each inner sprue, and then enters the casting from the bottom of nodular cast iron. The bottom return gating system can keep the runner full all the time in the whole pouring process, even when the pouring is cut off, which can effectively prevent the slag from entering the mold cavity and prevent the slag inclusion casting defects; The molten metal enters the mold cavity from the bottom of nodular cast iron, and the mold filling is stable without splashing and oxidation, so as to prevent the occurrence of casting defects such as iron beans; It can effectively reduce the flow defects of the cast iron ball in the cast iron mold by setting a short distance in the cast iron mold; The pouring system does not occupy the sand mold space, which can reduce the size of the sand box, reduce the amount of molding sand and reduce the production cost.

3. Error proof design of nodular cast iron sand core

Due to the core modeling, the positioning is added between the upper and lower layers of the inner cavity sand core to ensure the accurate positioning of the sand core; The four sand filling cores on the side interfere with the water pipe cores on both sides when lowering the core, which cannot be lowered into the mold. The core base must be enlarged by 20mm to the rear and outside, and the fixed sand core shall be filled after lowering the core; The sand cores with the same side structure and similar structure are added with error proof design, that is, each sand core is designed with significantly different positioning devices, which can not be lowered into the mold in case of misoperation (Fig. 3), so as to effectively avoid the scrapping of nodular cast iron caused by the mistake of sand core.

4. Dfesign of ductile iron core support and cooling

Change the thickness of the iron sheet on the supporting surface of the core support to 2mm, and the shape is consistent with the outer circle of the sand core (Fig. 3), so as to increase the stability of the sand core and ensure that the sand core does not float up under the action of liquid iron buoyancy. In order to speed up the solidification speed of local hot spots, cold iron is set at the thick lap of nodular cast iron to balance the solidification speed of nodular cast iron and prevent shrinkage and porosity casting defects after drilling.

The quality of nodular cast iron for intercooler base pipe produced by this process is significantly improved, and the casting defects such as slag hole and cold shut are completely eliminated. After machining and hydrostatic test, the casting defect rate of shrinkage cavity, porosity and leakage is greatly reduced, and the scrap rate can be controlled below 3%; The workload of modeling and fitting is reduced and the production efficiency is improved.

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