The "upper and lower covers" of a split-case pump (also known as a single-stage double-suction centrifugal pump) specifically refer to the upper pump cover and the lower pump casing. These two parts are formed by the horizontal split of the pump housing along the central axis of the pump shaft, which is the origin of the term "split-case.".
Lower Pump Housing: Typically the stationary part, featuring the suction and discharge ports on this half, connected to pipelines, and housing the rotor components internally.
Upper Pump Cover: Fixed to the pump body with bolts and locating pins. During maintenance, simply remove these bolts and lift off the upper cover to directly inspect or remove internal components such as the impeller and shaft. There is no need to dismantle the bulky inlet/outlet pipelines or motor, making maintenance extremely convenient.
The upper and lower covers (pump body and pump cover) of a split-case pump are a type of shell casting characterized by complex structure, significant wall thickness variations, and extremely high requirements for sealing surfaces. The core challenge in their casting process lies in ensuring the flatness of the split-case mating surfaces, the smoothness of the flow channel surfaces, and the overall internal density.
Common materials: Standard clear water pumps typically use gray cast iron (e.g., HT200, HT250) or ductile iron (e.g., QT400-18, QT500-7). When the pressure exceeds 1.6 MPa or when used with corrosive media, cast steel (e.g., ZG230-450) or stainless steel (e.g., 304, 316, CA6NM) is employed.
Mainstream Process: Resin sand molding (manual or machine molding) is widely adopted. Since the mid-axial split pump is horizontally divided along the axis, the parting line is typically set along the mid-split plane, with upper and lower sand molds produced separately. The internal flow channels are formed using sand cores. This process offers good dimensional accuracy and strong collapsibility, facilitating the cleaning of complex internal flow channels.
Pouring and Gating: A bottom or mid-pouring system is commonly used to ensure smooth metal flow and minimize oxidation slag. For thick sections such as the volute, flange, and bearing housing in the pump body, risers and chill inserts must be properly designed to achieve sequential solidification, preventing shrinkage porosity or looseness at hot spots that could lead to pressurization leakage.
Difficulties and Quality Control: The greatest challenge lies in the dimensional accuracy control of the opening and flow channel surfaces (often requiring sample inspection for the flow channel), as well as preventing cracks, sand sticking, and internal shrinkage. Castings typically undergo annealing or normalizing heat treatment to eliminate stress. After rough machining, hydrostatic testing and non-destructive testing (PT/RT) are often conducted to ensure no leakage or defects