Presentation and suggestions of China's malleable cast iron pipe fittings in 2025

China's malleable cast iron production was successfully produced for the first time in March 1942 since the establishment of Shanghai Huafeng Iron and Steel Plant in November 1941. Over the past 70 years, the number of production enterprises has continued to increase, product quality has continued to improve, and the variety has continued to expand. China is one of the major producers of malleable cast iron pipe fittings in the world. At present, there are about 700 production plants with an annual output of more than 700,000 tons. 

Although there is still a large gap in product quality, specialized production, equipment utilization, process means, energy and raw and auxiliary material consumption compared with other industrially developed countries, my country's malleable cast iron pipe fittings industry has basically been able to meet the needs of various sectors of the national economy for pipeline connectors, and most of them have entered the international market.e cast iron production was successfully produced for the first time in March 1942 since the establishment of Shanghai Huafeng Iron and Steel Plant in November 1941. 

Over the past 70 years, the number of production enterprises has continued to increase, product quality has continued to improve, and the variety has continued to expand. China is one of the major producers of malleable cast iron pipe fittings in the world. At present, there are about 700 production plants with an annual output of more than 700,000 tons. Although there is still a large gap in product quality, specialized production, equipment utilization, process means, energy and raw and auxiliary material consumption compared with other industrially developed countries, my country's malleable cast iron pipe fittings industry has basically been able to meet the needs of various sectors of the national economy for pipeline connectors, and most of them have entered the international market.

Development Overview

Over the past 70 years, through the joint efforts of malleable cast iron workers, the cooperation of colleges and universities and scientific research institutions, the production process and production equipment have been continuously improved and improved, and the theoretical level has also made new developments. In the cupola smelting technology, the furnace type with two rows and large spacing was improved, the furnace incubation was promoted, the carbon and silicon content was increased, manganese was used to neutralize sulfur and harmful effects, and the problem of producing high-quality malleable cast iron with high sulfur was overcome. The statistical analysis method was used to optimize the chemical composition, so that the product quality was steadily improved and reached the high-grade level of the foreign double-link method. In the heat treatment graphitization process, the theoretical improvement process of low-temperature preheating treatment was used to increase the graphite core, shorten the time, and greatly save energy. The annealing box was changed from the original white cast iron to high-grade steel, which extended the service life of the annealing box by more than 10 times.

In terms of casting technology and tooling, manual demolding and large risers were used to compensate for shrinkage; it was improved to mold plate and sleeve plate tide core molding, leak mold molding, metal mold casting, and later developed to use plastic model plate molding. The pouring system uses small riser technology, edge pressure riser, and riser placement slightly away from the hot section, etc., which increases the process yield from <40% to about 70%.

The core-making process has developed from black sand dry core, tar mud core, rosin mud core, vegetable oil mud core, synthetic oil mud core, and residual oil mud core to clay sand tide core, furan resin hot core, and coated sand shell core. Some companies also use dry cores and coatings to improve surface quality.

In terms of machining technology, from the 1940s, the pipe thread was processed by a belt lathe with a single knife, and then improved to combing knife processing and tapping and threading of internal and external threads with taps and insert taps, special threading machines for flexible joints, and high-efficiency tapping machines without compressed air, etc., which increased production efficiency by dozens of times, and the thread quality and axis angle tolerance reached the international advanced level.

In terms of rust prevention technology, from oil immersion rust prevention to rust prevention liquid, diesel, bamboo shell oil, and varnish development to sealed oil rust prevention treatment, laying the foundation for the export of pipeline connectors. In terms of leak testing, it has also developed from single-piece manual water pressure testing to multiple-piece mechanical water pressure testing and air pressure leak testing, which has improved work efficiency.

In terms of the galvanizing process, in addition to the high temperature (580~620℃) of immersion plating, various elements such as aluminum, silicon, yellow passivation and white passivation are used to improve the quality of the coating and reduce costs, and good results have been achieved.

In terms of equipment, casting equipment has developed from manual and single-machine molding to mechanized molding, and a box turning mechanism is attached. Later, it developed into an automated production line, the control system has jet and contactless, and the compaction methods include shock, shock pressure, air cushion micro-vibration, micro-vibration compaction, shot pressure, extrusion and other machines, and gradually developed from low pressure to medium pressure and high pressure molding. Recently, it has developed a bench molding line suitable for small factories, which has the effect of saving investment, occupying less space and convenient maintenance.

Sand processing equipment has also been improved from manual single machine to continuous automatic sand mixing, belt conveyor, crusher, scale plate machine, suction and delivery, pressure delivery, magnetic separation, dust removal, molding sand cooling machinery and old sand regeneration treatment, etc., which are matched with molding automation. In terms of smelting equipment, most of them use large tuyere cupolas, which later developed into various furnace types, including multiple rows of small tuyeres, two rows of large spacing, waist-type, and closed cupolas. Some factories also use cupola-electric furnace duplex and electric furnace single smelting methods.

In the front of the furnace, there are fixed front furnaces, rotary front furnaces, and short coil insulation front furnaces. In the back furnace facilities, there are cold air, hot, and oxygen-enriched air supply, liquid oxygen and external heating wind furnaces are used to increase the temperature of molten iron, and various feeding equipment, automatic weighing equipment and other auxiliary machinery are used.

In terms of casting equipment, it has developed from workers carrying bags to handbags, hanging bags, ring rail casting, air pressure casting, synchronous platforms, and various iron pressing and box machines.

In terms of heat treatment, we started from improving the annealing furnace type to reduce the temperature difference, and adopted the coal grinding and powder spraying combined machine to promote high and low multi-tube double-layer combustion and hot in and hot out method to load the furnace, which has played a very obvious effect on improving quality and reducing coal consumption.

In the machining equipment, two-end and three-end thread processing machines, special threading machines, tapping and threading combined machines and high-efficiency tapping machines without compressed air are used, which greatly improves the work efficiency and product processing quality.

In terms of galvanizing equipment, the galvanizing furnace type has been improved from bottom heating to side heating and top heating, the galvanizing pot has been developed from gray cast iron pot to low-carbon steel plate pot and alumina cement refractory pot, and the pre-plating treatment equipment has been developed from sulfuric acid washing drum to shot blasting machine cleaning, which has contributed to improving the quality of the galvanized layer and reducing zinc consumption. So far, the advanced units have achieved a cupola furnace temperature of about 1500℃, the number of mechanical molding boxes per person per shift can reach about 400 boxes, the annealing cycle is <40 hours, the coal consumption is 150~200kg/T castings, and the machining production per person per shift is more than 7,000 pieces (taking 1/2 elbow as an example), and the hot-dip galvanizing zinc consumption is about 80kg/T plated parts.

Based on 70 years of technological accumulation, my country's malleable cast iron pipe fittings industry has built a mature manufacturing system. At present, more than 700 domestic production enterprises have achieved an annual output of more than 700,000 tons by relying on continuously upgraded process equipment and intelligent manufacturing technology. Core indicators such as annealing cycle (<40 hours), coal consumption (150~200kg/T casting) and machining efficiency (7000 pieces/shift) have reached new heights in the industry. While meeting the needs of national economic construction and the global market, it is accelerating the benchmarking of international leading standards through technological innovation and lean management, providing cost-effective Chinese solutions for global pipeline connection systems.