The cast steel split pump casing (typically featuring single-stage double suction or multi-stage split designs) is one of the most pressure-bearing and structurally complex castings in pumps. Unlike the ordinary wooden molds mentioned earlier, these casings, made of cast steel and often operating under high-pressure conditions, demand much stricter requirements for mold precision, casting processes, and internal quality.
1. Structural and Material Characteristics
The split-type structure: The pump body is horizontally split along the axial centerline into two halves—the pump body and the pump cover. The inlet and outlet flanges are typically located on the lower pump body, which facilitates maintenance (the rotor can be removed by lifting the cover without disassembling the pipeline).
Common cast steel grades:
Carbon steel: The most commonly used is ZG230-450 (equivalent to the old designation ZG25), suitable for medium and high-pressure clean water or similar media. Its strength is higher than cast iron, with typical application pressures exceeding 1.6MPa.
Alloy/Steel: For corrosive or high-temperature media, ZG1Cr13 (martensitic stainless steel), CF8/CF8M (304/316 stainless steel), or duplex stainless steel (e.g., 1.4460) will be used.
2. Key Points of Wooden Molds and Casting
Regarding the wooden mold for the steel casting of the open-type pump body, which you previously focused on, the following points need attention:
Greater shrinkage allowance: The shrinkage rate of cast steel is approximately 1.5% to 2.0% (around 1.0% for cast iron), requiring precise dimensional enlargement during wood mold fabrication. Otherwise, insufficient shrinkage may result in undersized runners or mounting holes after the casting cools.
Molding and Core: Typically, the mold is parted along the mid-parting plane (with the mid-parting plane facing upward for casting). The internal volute flow channels are complex and require high-precision core boxes for sand core production. To ensure the accuracy of the center-to-center distance of flow channels (especially for multi-stage mid-parting pumps), integral sand cores or stringent gauge plate inspections are commonly employed.
Prevention of deformation and cracking:
Wood mold anti-deformation: For cast steel parts with significant wall thickness variations, multi-layer glued wood materials (such as red pine or ginkgo wood) with excellent drying properties should be selected for the wood mold to prevent moisture absorption, deformation, and dimensional inaccuracies in the castings.
Casting process: Risers and chill blocks must be installed in thick and large sections (such as mid-split flanges and long bridges) to achieve sequential solidification, preventing shrinkage cavities, shrinkage porosity, and hot cracks. A bottom-gating or gating system with a slag trough should be used to reduce steel liquid oxidation and slag inclusion.
3. Quality and Acceptance
Pressure resistance requirement: As a pressure-bearing component, hydrostatic testing is required (typically at 1.5 times the working pressure, e.g., 6MPa, with no leakage after maintaining pressure for 30 minutes).
Non-destructive testing: Critical areas (flanges, split surfaces, flow channels) often require PT (penetrant) or RT (radiation) inspection, with internal structures needing to be dense and free of shrinkage