Production Process of Malleable Iron Pipe FittingsMalleable iron pipe fittings, also known as ductile cast iron fittings, are widely used in fluid transport pipeline systems due to their excellent mechanical properties, corrosion resistance, and ductility. The production process is rigorous and complex, mainly consisting of the following key steps:Step One: Melting and PouringAt the beginning of production, high-quality foundry pig iron, scrap steel, and iron alloys are carefully proportioned and charged into a cupola or electric furnace for high-temperature melting. During the melting process, the chemical composition must be strictly controlled, especially the carbon and silicon content, to ensure that the molten iron meets the material requirements for ductile cast iron. The qualified molten iron is then poured into pre-made sand molds to form the rough castings of pipe fittings. At this stage, the internal structure of the castings is brittle and hard, referred to as ‘white cast iron’, and cannot be used directly.
Step 2: Annealing TreatmentAnnealing is the key process that imparts “ductile” properties to the cast iron pipe fittings. The cleaned white cast iron blanks are loaded into an annealing furnace for a long-term graphitizing annealing treatment. This process typically lasts for several hours at high temperatures above 900°C, where precise control of the heating, holding, and cooling curves allows the brittle and hard cementite within the casting to decompose into flocculent graphite, significantly improving its toughness and plasticity to achieve true “ductile iron.”Step 3: Cleaning and ShapingAfter annealing, the surface of the casting has oxidation scale and sand residue, which need to be cleaned using a shot blasting machine to ensure a smooth surface. Subsequently, the casting enters the shaping process. Due to possible minor deformations during the casting and annealing processes, special shaping molds are used on a press to cold-correct the threaded interfaces of each pipe fitting, ensuring that their dimensional accuracy and roundness meet the standards, laying the foundation for subsequent processing.
Step 4: Machining The core of this stage is tapping, which involves processing precise pipe threads. Using qualified taps on a high-speed tapping machine, standard threads are cut at the socket or spigot of the fittings. The quality of the threads is directly related to the sealing and strength of the pipe connections, thus there are extremely high requirements for the precision and smoothness of the threads. Step 5: Surface Treatment and Inspection The finished fittings undergo surface treatment according to usage requirements. The most common method is hot-dip galvanizing, where the fittings are immersed in molten zinc, forming a dense layer of zinc plating that greatly enhances their corrosion resistance. Finally, a strict quality inspection must be carried out on the finished products, including dimensional accuracy, thread gauge tests, surface quality checks, and pressure testing, to ensure that each cast iron fitting meets national standards before it can be packaged and shipped. In summary, the production of cast iron fittings is a precise manufacturing process that integrates casting, heat treatment, machining, and surface treatment; each step is crucial in ensuring the reliability and durability of the final product.
Post time: Sep-25-2025