Nodular cast iron intercooler base pipe is an innovative design for the company’s large internal combustion engine. The material is QT500-7, which integrates the functions of intake and intake of diesel engine. It is a thin-walled box casting. The overall dimension of nodular cast iron intercooler base pipe is 2154mm × 506mm × 232mm (Figure 1), weighing about 235kg, the main wall thickness is 10mm, and 50mm is evenly distributed on the back of the flange × For 50mm lap, the wall thickness difference is large, and the tolerance of wall thickness is only ± 0.405mm.
(1) After processing, the base pipe of nodular cast iron intercooler needs to be subjected to hydrostatic test. The pressure in the inner cavity of the whole box and the pipelines on both sides shall be maintained at 0.5MPa for at least 5min, and there shall be no leakage at any part. The machined surface shall be free of any casting defects such as pores, shrinkage cavities and porosity.
(2) The surface quality requirements are high, and casting defects such as sand sticking and iron infiltration are not allowed. The inner cavity of nodular cast iron is smooth transition, and the surface roughness of inner and outer walls must meet the specified requirements after shot peening.
(3) High dimensional accuracy is required. The wall thickness of nodular cast iron needs to be checked and cannot exceed the tolerance range. The weight of finished products is required to be 225kg with a tolerance of 5%
For nodular cast iron with large through holes, the bottom return pouring system is set in the through holes, which can effectively ensure the stable pouring and filling, increase the slag retaining effect, and prevent the casting defects such as slag holes and cold insulation of nodular cast iron; The joint surface of the core support is consistent with the shape of the sand core, and the thickness is appropriately increased, which improves the stability of the sand core and can significantly reduce the floating of the sand core; Setting cold iron at local hot joints can basically eliminate shrinkage cavity and porosity casting defects; The three box model is changed to two box model, which simplifies the modeling operation and improves the dimensional accuracy of nodular cast iron.