Why is the pouring criterion for cast iron ground rails an essential foundation?
If the sulfur content in the raw molten iron is too low, the magnesium in the nodularizer for cast iron ground rails cannot combine with sulfur. Excessive residual magnesium not only hinders graphitization but also causes shrinkage casting issues in cast iron ground rails. If the amount of nodularizer added is reduced, comprehensive considerations may raise concerns about affecting the nodularization rate. Therefore, when the sulfur content in the raw molten iron of cast iron ground rails is very low, measures must be taken in the selection of the nodularizer, the amount of nodularizer added, and the nodularization process to ensure the quality of the nodules.
The temperature of the mold for cast iron ground rails is one of the main parameters in the molding process. When pressing wax patterns for cast iron ground rails, if the mold temperature is too low, the fluidity and filling capacity of the wax material are reduced, making it difficult to quickly fill the mold cavity, thus causing flow marks on the wax patterns. Before pressing the wax patterns, first clean the residual and dirty substances from the surface of the cast iron ground rail mold cavity. Then, use a brush or gauze to apply an appropriate, thin layer of release agent to the cavity surface and parting surface to prevent local accumulation of the release agent on the cast iron ground rail mold cavity surface or parting surface. Choose a release agent suitable for the paraffin-stearic acid wax material of cast iron ground rails. Transformer oil is generally selected, and it must be inspected upon arrival according to relevant standards to ensure its quality. Strictly control that unqualified transformer oil cannot enter the factory, strengthen the management of stored transformer oil, and ensure that deteriorated release agents are not used in production.

When smelting non-ferrous alloys for cast iron ground rails, the charge, flux, tools, and pouring ladles must be fully preheated and dried, with rust and oil stains removed. The amount of repeatedly remelted charge for cast iron ground rails should be appropriately limited. Prevent excessive oxidation and gas absorption of the molten metal during the smelting process, and carry out deoxidation, degassing, and slag removal. Add a covering flux on the surface of the molten metal pool in the pouring ladle to prevent gas absorption and the return of harmful impurities to the molten pool of cast iron ground rails.
Before pressing wax patterns for cast iron ground rails, clean the mold cavity thoroughly, remove any dirt from the cast iron ground rail mold cavity, and wipe away any cold water in the cavity. During molding, strictly control the wax material temperature for cast iron ground rails between 48–52°C, and the mold temperature should ideally be between 18–25°C to ensure good filling of the wax material and improve the surface quality of the wax patterns for cast iron ground rails. Apply appropriate pressure, which should be maintained between 0.2–0.6 MPa, and continuously inject the wax material without interruption. If necessary, increase the diameter of the wax injection nozzle to allow the wax material to fully and smoothly fill the cavity.
In the specific operation of cast iron ground rail production, if the amount of release agent used is excessive or if it is applied unevenly, causing local accumulation, flow marks may appear on the wax patterns. If the release agent is improperly selected or has expired and deteriorated—for paraffin-stearic acid wax patterns, transformer oil or turpentine oil is generally used, with transformer oil being easier to procure—improper selection or deterioration of the release agent for cast iron ground rails can easily cause flow marks on the wax patterns. Low injection pressure and slow injection speed are also main parameters in the molding process. When pressing wax patterns, if the injection pressure is too low and the injection speed is too slow, the fluidity and filling capacity are reduced, making it difficult for the wax material to quickly fill the mold cavity, thus causing flow marks on the cast iron ground rail wax patterns.
Modify the design of the mold cavity for cast iron ground rails or trim the cavity to reduce the surface roughness of the cast iron ground rails and meet the surface quality requirements of the wax patterns. Dry the sand mold coated with the cast iron ground rail coating, touch it with a finger, scrape it, observe the coating peeling situation, break the sand mold, and observe the coating thickness. The gas evolution test for cast iron ground rail sand molds should be conducted according to GB/T2684, using the four-level evaluation method for testing鑄造用砂及混合料試驗(yàn)方法 (Test Methods for Foundry Sands and Mixtures).
Weiyue Machinery, Ms. Xie, 15350773479