Deteriorating agents play an important role in the quality and cost of cast iron parts, especially for the development of high-grade cast iron parts. The cast iron parts have good comprehensive performance, low cost and can be recycled. Cast iron parts account for about 80% of the total casting output. Therefore, the development of cast iron modifiers has certain significance for sustainable economic development and is worthy of attention.
1. Demand situation
In 1997, China's casting output was second only to the United States, with 11.08 million tons, including 8.79 million tons of cast iron, 6.87 million tons of gray cast iron, 1.56 million tons of ductile iron, 350,000 tons of malleable iron and 10,000 tons of vermicular graphite iron. In addition to low grade grey cast iron, most of the cast iron parts are produced using inoculants. The annual consumption is 30,000 to 40,000 tons. The spheroidizing agent is used in an amount of about 4 to 45,000 tons per year. The amount of creeping agent and malleable cast iron modifier is very small, and the annual demand is about 200 tons each.
In the next five years, the proportion of ductile iron and high-grade gray cast iron in cast iron parts will increase, the number of malleable cast iron and vermicular cast iron will not increase, and even the specific gravity will decrease, and the proportion of low-grade gray cast iron will gradually decrease. As the production of automobiles will increase significantly, high-grade thin-walled gray iron castings and ductile iron castings will grow. The output of centrifugal ductile iron pipes will also increase significantly. Therefore, the demand for spheroidizing agents and inoculants will increase. It is estimated that the amount of inoculant used in 2005 will be about 50,000 tons, and the amount of spheroidizing agent will be about 60,000 to 70,000 tons. From the perspective of long-term development, the growth trend of China's nodular cast iron and high-grade gray iron castings will not decrease, and its proportion will increase year by year. The largest users of ductile iron castings are water and gas pipelines for various industries in the automotive industry and urban construction. In the next 5 to 10 years, China's automobile and infrastructure construction will have great development, and the growth of ductile iron castings is inevitable.
2. Inoculant development trend
From 1950 to 1970, China used 75 ferrosilicon for metallurgy as an inoculant. Ca and Al, which play an important role in the growth of the ferrosilicon, have no limited content range, and the inoculation effect is unstable. In the 1970s, the Shenyang Foundry Research Institute and other units developed silicon germanium and silicon germanium inoculants. Later, various units successively developed or introduced rare earth inoculants, carbon silicon inoculants, and stabilized inoculants.
Ten years of practice shows that China's inoculant series can meet the needs of the development of cast iron parts. The effect is significantly better than metallurgical ferrosilicon. The amount of ferrosilicon inoculant accounts for more than 80% of the total amount of cast iron inoculant. However, at present, quite a number of small and medium-sized foundries and castings with low quality requirements use ferrosilicon for metallurgy as an inoculant, and the effect is unstable. The second largest sales volume is bismuth-containing ferrosilicon inoculant, and again it is a ferrosilicon-containing inoculant. The use of carbon-silicon inoculants (including Inoculin 10 introduced from Foseco), rare earth-containing inoculants, and indole-containing ferrosilicon inoculants also increased significantly. These new inoculants play an important role in the production of high-grade cast iron parts, such as thin-wall water-resistant ash-casting iron engine block parts, thin-walled or thick spheroidal graphite cast iron parts. The development of inoculants has played an important role in improving the quality of cast iron parts. In recent years, electric furnace or cupola-electric furnace double-layer melting has gradually increased, and zirconium-silicon ferrosilicon and titanium-containing ferrosilicon inoculant are needed. However, the current two kinds of inoculants are not used much, and the demand is expected to increase in the future.
3. The development trend of spheroidizing agent
Since 1960, China has developed a unique rare earth magnesium ferrosilicon spheroidizing agent. At that time, magnesium silicate spheroidizing agent was mainly used abroad. The trend in China for 30 years is that the content of rare earth in the spheroidizing agent is gradually decreasing. Rare earths are also added to foreign spheroidizing agents. In the past ten years in China, the casting coke and the large double cupola have been promoted, and the amount of electric furnace is also increasing. The quality of the molten iron, including temperature and sulfur and oxygen content, has been significantly improved. Therefore, the content of rare earth and magnesium in the spheroidizing agent is gradually lowered. At present, most of the small and medium-sized cupolas have a tapping temperature of 1380 to 1420 ° C and a sulfur content of 0.08 to 0.12%, and a spheroidizing agent containing 8 to 10% of Mg and 6 to 8% of Re. Such spheroidizing agents account for about 60 to 70% of the total amount of spheroidizing agent. Large-scale hot-air cupola, desulfurization process, and the use of cupola-electric furnace double-melting process. The foundry that uses electric furnace melting requires the supply of a spheroidizing agent containing Mg and Re, such as Mg-containing 8%, Re0.5-1. % or 1 to 2% or 2 to 3% of the spheroidizing agent. The number of these foundries is small, but the output is very large, such as the Second Foundry of Second Automobile, the First Foundry, FAW, Nanqi and some centrifugal duct iron pipe plants. At present, its output accounts for about 25-30% of the total amount of ductile iron. In the future, the amount of such spheroidizing agents will gradually increase. As mentioned above, the production of ductile iron in China will increase year by year. At the same time, it should be pointed out that the quality requirements and cost indicators for castings will become increasingly strict. Therefore, the cupola-electric furnace double melting and desulfurization process is imperative. In addition, austempered (ADI) ductile iron will gradually develop, and the requirements for spheroidization grade will increase, of course, the requirements for spheroidizing agents will also increase.
Centrifugal ductile iron pipe is the largest output of ductile iron castings, which is ferritic-based ductile iron. The castings of the automotive industry are mainly chassis parts, which are ferritic-based ductile iron, and the crankshaft, camshaft and flat shaft are pearlite-based or austempered ductile iron. It is desirable to provide a dedicated spheroidizing agent that meets the requirements.
4. Other modifiers and treatment agents
The amount of creeping agent and malleable cast iron modifier is not large, and the dosage may be unchanged or reduced in the future. This article is not discussed anymore. It is worth mentioning that the demand for desulfurizers will increase. At present, the desulfurizing agent is mostly a mixture of calcium carbide, calcium fluoride and calcium oxide, and it is desired to further improve the reaction performance. The commercial supply of pretreatment agents such as silicon carbide is also worth considering.
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