Cast Steel Screw Pumps: In-Depth Analysis of Material Characteristics, Application Advantages, and Development Limitations

In marine applications, from fuel transportation to seawater desalination, marine cast steel screw pumps ensure the stable operation of ship systems by virtue of the excellent properties of cast steel materials and the unique structure of screw pumps. However, they also have certain limitations. A deep understanding of the classification of marine cast steel materials and the advantages/disadvantages of cast steel screw pumps helps in the better application of this important equipment.

I. Classification of Marine Cast Steel Materials and Their Adaptability to Screw Pumps

The performance of marine cast steel screw pumps is closely related to the selected cast steel materials. The common classifications and application characteristics in screw pumps are as follows:

1. Carbon Cast Steel

Carbon cast steel takes carbon as the main alloying element, with typical grades such as ZG230-450 and ZG270-500, usually containing 0.12%-0.6% carbon. It has good comprehensive mechanical properties, with a tensile strength of 450-600MPa and a yield strength of 230-300MPa, as well as certain toughness and weldability. In marine screw pumps, carbon cast steel is commonly used to manufacture non-critical moving parts such as pump bodies and pump covers, suitable for low-pressure (≤1.6MPa) and non-corrosive medium transportation scenarios, such as ship lubricating oil circulation systems and bilge water drainage pumps. With relatively low costs and mature processing techniques, it is a commonly used material for basic marine cast steel screw pumps.

2. Alloy Cast Steel

Alloy cast steel significantly improves material performance by adding alloying elements such as chromium (Cr), molybdenum (Mo), and nickel (Ni).

Cr-Mo Series Alloy Cast Steel: For example, ZG20CrMo, containing 1-3% chromium and 0.5-1% molybdenum, has a 40% increase in high-temperature strength and outstanding hydrogen corrosion resistance. In marine screw pumps, it is often used to manufacture key components such as screws and rotors under high-temperature and high-pressure conditions, such as high-temperature fuel transportation pumps for ship main engines and circulating water pumps for exhaust gas boilers. These pumps can operate stably in the environment of 300-500℃ and withstand system pressures of 3.5-6.4MPa, meeting the strict requirements of ship power systems.

Ni-Cr Series Alloy Cast Steel: Containing 2-4% nickel and 1-2% chromium, the typical grade is ZG340-640, with excellent low-temperature toughness and an impact energy ≥27J at -40℃. It is suitable for screw pumps of polar navigation ships, transporting media such as fuel and fresh water in low-temperature environments to ensure the normal operation of ships in extreme climatic conditions.

3. Stainless Steel Cast Steel

Stainless steel cast steel occupies an important position in marine screw pumps with its excellent corrosion resistance.

Austenitic Stainless Steel Cast Steel: Represented by 304 (ZG0Cr18Ni9) and 316L (ZG00Cr17Ni14Mo2), it has a corrosion rate <0.01mm/year in media with pH 2-12. It is commonly used in marine food-grade fresh water transport pumps, drinking water circulation pumps, and liquid medicine transport pumps for pharmaceutical ships to meet hygiene standards and avoid media contamination.

Duplex Stainless Steel Cast Steel: Such as 2205 (ZG0Cr22Ni5Mo3N), with strength twice that of 316L and 3-5 times enhanced chloride ion stress corrosion resistance. It is widely used in screw pumps for marine seawater desalination systems and ballast water treatment systems, which can effectively resist seawater corrosion, extend the service life of pumps, and reduce maintenance costs.

II. Core Advantages of Marine Cast Steel Screw Pumps

1. Strong Adaptability to High-Pressure and Heavy-Duty Conditions

Marine cast steel screw pumps can withstand the high-pressure and heavy-duty conditions during ship operation. Screw pumps made of alloy cast steel can withstand system pressures of more than 10MPa at the highest, far exceeding those of ordinary material screw pumps. In the high-pressure fuel injection system of ship main engines, cast steel screw pumps can stably provide high-pressure fuel to ensure sufficient atomization and combustion of fuel, improving the efficiency of main engines; in the ballast water transportation system of large ships, they can meet the needs of rapid loading and unloading of large-flow and high-pressure ballast water, ensuring the navigation safety and stability of ships.

2. Excellent Wear Resistance and Fatigue Resistance

Cast steel materials have excellent wear resistance and fatigue resistance through reasonable alloy 配比 (alloy ratio) and heat treatment processes. Taking Cr-Mo series alloy cast steel as an example, the surface hardness of screws made of it can reach HRC 35-45, and when transporting media containing tiny particles (such as impurities in fuel and sediment in ballast water), the wear rate is 30%-50% lower than that of ordinary carbon cast steel. During the long-term operation of ships, cast steel screw pumps can maintain stable performance, reduce the failure frequency caused by component wear, extend the service life of equipment, reduce maintenance costs and downtime, and ensure continuous ship operations.

3. Good Adaptability to Complex Marine Environments

Ships are long-term in marine environments with high salt spray, high humidity, and strong corrosion. Marine cast steel screw pumps show good environmental adaptability by virtue of stainless steel cast steel or alloy cast steel materials. Stainless steel cast steel can effectively resist the corrosion of seawater and acid-base media; Ni-Cr series alloy cast steel can maintain stable performance in low-temperature environments. Whether in the high-temperature and high-humidity environment of tropical seas or the severe cold climate of polar regions, marine cast steel screw pumps can operate reliably to ensure the normal operation of various ship systems and reduce the risk of equipment damage caused by environmental factors.

4. Stable Transportation Performance and Small Pulsation

Screw pumps rely on the meshing of screws to form sealed chambers to push the media forward, with stable flow and small pressure pulsation during operation. Marine cast steel screw pumps can accurately control the flow rate when transporting media such as fuel, lubricating oil, and seawater, avoiding the impact of flow fluctuations on ship equipment. For example, in the process of ship fuel transportation, stable flow helps the main engine burn stably and reduces fuel consumption; in the seawater desalination system, stable water supply flow ensures the continuity and stability of fresh water production.

III. Application Disadvantages of Marine Cast Steel Screw Pumps

1. Cost and Price Disadvantages

The raw material cost of cast steel is high, especially for alloy cast steel and stainless steel cast steel, which is 3-5 times that of ordinary carbon steel. The manufacturing process of marine cast steel screw pumps is complex, requiring multiple processes such as precision casting, heat treatment, and high-precision machining, further increasing production costs. In addition, marine equipment needs to meet strict classification society certification standards, increasing certification costs. Therefore, the market price of marine cast steel screw pumps is usually 60%-80% higher than that of ordinary material screw pumps of the same specification, putting great cost pressure on ship operation enterprises during equipment procurement.

2. Large Weight and Difficult Installation

The density of cast steel is 7.85g/cm³, resulting in a large overall weight of marine cast steel screw pumps. A DN100 specification marine cast steel screw pump can weigh up to 80kg, while the same specification aluminum alloy screw pump is only about 25kg. The large weight increases the difficulty of installation and handling of equipment in the narrow space of ships, may require professional hoisting equipment and personnel for operation, and also increases the load of ships, affecting the fuel economy of ships. In addition, cast steel screw pumps have strict requirements for installation coaxiality (≤0.03mm); otherwise, abnormal wear of screws and increased operating noise will occur, and the installation and debugging are more difficult.

3. High Complexity in Processing and Maintenance

Cast steel materials have high hardness, great difficulty in cutting processing, serious wear on tools, processing efficiency 30%-40% lower than that of ordinary steel, and processing costs increased by 25-35%. In terms of maintenance, the precise structure and high-strength components of marine cast steel screw pumps require professional maintenance equipment and technicians. For example, the repair of worn screws requires high-precision gear grinding equipment and professional heat treatment processes, and the maintenance process needs to follow the relevant standards and specifications of classification societies. When ships are sailing at sea, once cast steel screw pumps fail, the maintenance is difficult and the cycle is long, which may affect the normal operation of ships and even bring potential safety hazards.