1. Definition and material properties
Ductile iron valves are valves made of ductile iron (QT400-15, QT450, etc.) as the main material. By adding magnesium or rare earth elements to cast iron, graphite is distributed in a spherical shape to form a metal matrix with high strength and toughness. Its tensile strength is ≥450MPa, and its yield strength is about 50% higher than that of ordinary gray cast iron (HT200), while retaining the casting convenience of cast iron.
2. Core structure and components
Valve body: Cast from ductile iron, the surface can be galvanized or sprayed with epoxy resin to enhance corrosion resistance;
Seals: Copper seals are commonly used for gray cast iron valves, and rubber (NBR, EPDM) or polytetrafluoroethylene (PTFE) soft seals are mostly used for ductile iron valves;
Drive components: The valve stem and handwheel are mostly made of stainless steel or carbon steel, suitable for manual, gear or electric operation.
3. Performance Advantages
Excellent mechanical properties:
The spheroidal graphite structure reduces stress concentration, and the impact toughness is 3-5 times higher than that of gray cast iron, which is suitable for pipeline systems with vibration or water hammer impact;
It has better wear resistance than ordinary cast iron and can withstand long-term erosion of sediment-containing media.
Corrosion resistance adaptation:
It is stable in water media with pH 6-9, and needs to be used with a galvanized layer (thickness ≥80μm) in a humid environment;
It is prone to pitting in sulfur-containing media and should be avoided in high-concentration acidic environments (pH <4).
Outstanding economic efficiency:
The production cost is 30%-50% lower than that of cast steel valves, which is suitable for budget-sensitive projects such as municipal engineering;
The maintenance cycle is as long as 5-8 years, and the cost of replacing seals is only 10%-15% of the valve body price.
4. Typical application scenarios
Municipal engineering:
Urban water supply network (DN50-DN1200), low-pressure (≤PN16) interception control in fire protection system;
Industrial field:
Petrochemical industry pipeline system containing weakly corrosive media (such as crude oil at room temperature);
Flow regulation of sediment-containing water flow in agricultural irrigation system;
Building facilities:
Opening and closing control of air conditioning circulating water system and drainage network, working temperature range -10℃~200℃.
5. Selection and maintenance points
Selection suggestions:
V-type ball valve or knife-type gate valve structure is preferred for medium containing particles to reduce sealing surface wear;
GGG40.3 (European standard) or QT400-18AL (American standard) materials should be specified for seawater or high humidity environment;
Maintenance specifications:
Check the valve stem grease status every 2 years, and EPDM rubber seals are recommended to be replaced every 5 years;
The valve stem needs to be manually rotated 3-5 times for the first use after long-term static to prevent jamming.