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

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

1. Gray Cast Iron (HT)

In gray cast iron, carbon mainly exists in the form of flake graphite. Typical grades include HT200 and HT250. It has a compressive strength of 200 - 300MPa and a tensile strength of 150 - 250MPa. It features excellent vibration damping performance, with a vibration attenuation capacity 10 times that of steel, but relatively poor toughness. In the manufacturing of screw pumps, gray cast iron is commonly used to produce non - critical load - bearing components such as pump bodies and pump covers. It is suitable for the transportation of low - pressure (≤1.6MPa), non - corrosive or weakly corrosive media. With relatively low costs and mature processing techniques, it is a commonly used material for entry - level cast iron screw pumps.

2. Ductile Cast Iron (QT)

Ductile cast iron undergoes special treatment to make graphite distribute in a spherical form, significantly improving the material's properties. Common grades are QT500 - 7 and QT600 - 3, with a tensile strength of up to 400 - 800MPa. Its fatigue resistance is 30% higher than that of gray cast iron, and its toughness is close to that of steel, while its corrosion resistance is equivalent to gray cast iron. In screw pump applications, ductile cast iron is suitable for medium - and high - pressure (≤3.5MPa) working conditions and is often used to manufacture key moving parts such as screws and rotors. When transporting media containing particles, the service life of ductile cast iron screw pumps is 2 - 3 times longer than that of gray cast iron screw pumps.

3. Malleable Cast Iron (KT)

Malleable cast iron is produced by graphitizing and annealing white cast iron. Its impact toughness is 3 - 4 times higher than that of gray cast iron, with a tensile strength of 300 - 450MPa, making it suitable for manufacturing complex - structure castings. In screw pumps, malleable cast iron is mostly used to produce non - critical pressure - bearing components such as connectors and end covers of small screw pumps. Its component accuracy can be optimized through forging, reducing operating noise by 10 - 15dB.

4. Special Cast Iron

Corrosion - resistant cast iron: Corrosion - resistant cast iron with added elements such as chromium, nickel, and silicon, like high - silicon cast iron, has 5 - 8 times higher acid and alkali resistance than ordinary cast iron. It is suitable for screw pumps transporting acidic or alkaline media in the chemical industry. However, due to its high cost, its application is relatively limited.

Wear - resistant cast iron: Wear - resistant cast iron, which undergoes surface hardening treatment, can reach a hardness of HRC55 - 60. It is commonly used for screw pumps transporting high - viscosity, abrasive - containing media, such as mud transport pumps. However, it has high processing difficulty and strict requirements for manufacturing techniques.

II. Core Advantages of Cast Iron Screw Pumps

1. Strong Capability in Transporting High - Viscosity Media

Cast iron screw pumps rely on the meshing of screws to form sealed chambers that push the media forward. They are especially suitable for transporting high - viscosity media with a viscosity range of 100 - 10000cSt, such as lubricating oil and sludge. During transportation, their volumetric efficiency can reach 80% - 90%. In contrast, the efficiency of centrifugal pumps in handling high - viscosity media is only 30% - 50%. Cast iron screw pumps can stably maintain flow and pressure, ensuring the efficient transportation of high - viscosity media. For example, when transporting thick jam in food processing plants, cast iron screw pumps can precisely control the flow rate, ensuring continuous production.

2. Excellent Self - Priming Ability

Cast iron screw pumps have a strong self - priming ability, with a self - priming height of up to 6 - 8m, far exceeding that of centrifugal pumps (usually 3 - 5m). This feature allows them to achieve self - priming without additional auxiliary devices, making them suitable for scenarios such as pumping water. In working conditions without priming conditions, cast iron screw pumps can quickly build up delivery pressure, reducing startup time and operation complexity, and improving work efficiency.

3. Stable Operation and Low Noise

The meshing motion of the screws in screw pumps is smooth without pulsation. Combined with the good vibration - damping performance of cast iron, cast iron screw pumps have small vibrations and low noise during operation. Generally, the operating noise can be controlled within 65 - 75 decibels.

4. Simple Structure and Easy Maintenance

Cast iron screw pumps have a relatively simple structure, mainly composed of components such as pump bodies, screws, bearings, and seals. During maintenance, only a few components need to be disassembled to replace worn screws and seals. Professional and complex equipment or techniques are not required, and ordinary maintenance personnel can operate after simple training. Compared with other types of pumps, cast iron screw pumps have a long maintenance cycle, low maintenance costs, and short downtime, which is conducive to ensuring continuous production.

III. Application Disadvantages of Cast Iron Screw Pumps

1. Cost and Price Disadvantages

Although the cost of gray cast iron is relatively low, the prices of materials such as ductile cast iron and special cast iron are high, especially corrosion - resistant cast iron and wear - resistant cast iron, which cost 2 - 3 times that of ordinary gray cast iron. At the same time, the manufacturing of cast iron screw pumps requires precision machining to ensure the meshing accuracy of screws, increasing manufacturing costs. As a result, the market price of cast iron screw pumps is usually 30% - 50% higher than that of centrifugal pumps of the same specification.

2. Speed and Efficiency Limitations

The rated speed of cast iron screw pumps is generally low, usually ≤1500rpm. If this speed is exceeded, the wear of the screws will intensify, and noise and vibration will increase significantly. In contrast, the rated speed of centrifugal pumps can reach 2900rpm. When transporting low - viscosity media (<20cSt), the hydraulic efficiency of cast iron screw pumps is only 60% - 70%, 15% - 20% lower than that of centrifugal pumps. Therefore, they are not suitable for high - speed and large - flow transportation of low - viscosity media such as clean water.

3. Poor Adaptability to High Temperature, High Pressure, and Strong Corrosion

Screw pumps made of gray cast iron and ductile cast iron should not operate continuously at temperatures above 120℃ for a long time, otherwise, the material strength will decrease. Under high - pressure conditions exceeding 3.5MPa, screws are prone to deformation and accelerated wear. In addition, ordinary cast iron is not resistant to strongly corrosive media. When transporting strong acids, strong alkalis, and other media, special corrosion - resistant cast iron or coating treatment is required, increasing costs and maintenance difficulties. Moreover, the service life of the coating is limited, generally only 1 - 2 years.