Casting technology of the hottest ductile iron pis

2022-08-08
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Casting technology of nodular cast iron piston rings

Abstract: This paper focuses on the casting technology of producing high-quality monomer double piece nodular cast iron piston rings on the basis of advanced casting process design by strictly controlling the content of C and Si in the raw molten iron in front of the furnace, using special spheroidizing agent and inoculant, and under the condition of existing Mn, P and s ultra-high-tech pig iron in China

key words: single double piece piston ring; High quality pig iron; Spheroidizing treatment; Inoculation treatment

piston rings play the role of sealing, heat transfer and support in the engine, so piston rings are required to have good wear resistance, elasticity and thermal stability, especially for one ring. The development and application of nodular cast iron piston rings is a qualitative leap in the history of piston ring manufacturing. How to stably manufacture nodular cast iron piston rings is a difficult problem faced by the piston ring industry. In order to solve this problem, our factory imported all the technologies and related equipment of single body double piece ductile iron piston rings from goetzea, Germany

as shown in Figure 1, the design guideline of single body two-piece casting is to use milling cutters to mill the center of the billet and the upper and lower surfaces that are prone to pinholes and slag inclusions, so as to obtain excellent ductile iron piston rings. This casting method has been widely used abroad and has rich production experience. Many domestic manufacturers have also accepted and started trial production, but it is not very successful. The main reason is that the raw materials and the production process of nodular cast iron piston rings are too complex, so it is difficult to ensure the matrix structure of nodular cast iron piston rings and the qualification rate of castings. Although the factory has introduced all the casting software and hardware, there are still many problems in the supply of raw materials, production technology and so on. In the early stage of trial production, there are often cases such as low spheroidization rate and the qualified rate of ball number failing to meet the requirements. After trial production and exploration, we basically mastered the production process suitable for our factory, and comprehensively solved the technical problems of nodular cast iron piston ring casting, so as to ensure the qualification rate of nodular cast iron piston ring casting. The following is a brief introduction of how our factory trial produces nodular cast iron piston rings

1 process feasibility analysis

German experts have repeatedly stressed that "the key to the production of nodular cast iron piston rings lies in raw materials". It is difficult to produce nodular cast iron piston rings without qualified raw materials. They emphasized that the use of high-purity pig iron or synthetic pig iron, whose components are: 38% - 43% C, 02% - 04% Si, 04% - 015% Mn, P0 1%, will produce phosphorus eutectic at the grain boundary, reducing the strength, toughness and plasticity. ④ The sulfur content is higher than 0.016%. Higher sulfur content will directly consume the amount of spheroidizing agent, especially the influence of dissolved sulfur on graphite spheroidization during solidification, which will directly affect the effect of spheroidizing treatment, reduce the mechanical properties, apply to plastic plates, pipes, profiled materials, and increase casting defects (slag inclusion, subcutaneous pores, etc.)

the use of carbon sulfur analyzer creates conditions for timely mastering the sulfur content of raw molten iron and correctly controlling the addition amount of spheroidizing agent. At the same time, the use of M inoculant also plays an auxiliary role in the production of nodular cast iron piston rings. Through the above process analysis, it is possible to produce ductile iron piston rings that meet the requirements of foreign countries by using domestic raw materials

2 technological test and analysis

pig iron with 40% ~ 100% of the above components and less than 60% of the returned material are used. 7. Press the "reset" key on the operation timer and melt in a 150kg medium frequency furnace. Strengthen the operation process to ensure that the spheroidization temperature reaches 1500 ~ 1550 ℃, and the time from the discharge of molten iron to the completion of pouring is controlled within 10min to ensure the spheroidization effect

2.1 spheroidizing treatment

customized spheroidizing agent is used, and the composition is as follows: 38% ~ 48% Si, 50% ~ 65% Mg, re ≤ 10%, Al ≤ 10%. Particle size: 5 ~ 40mm. Compared with the domestic commonly used nodulizer of rare earth ferrosilicon magnesium alloy or rare earth ferrosilicon magnesium calcium alloy, the magnesium content of this nodulizer is lower than the former and higher than the latter. The spheroidizing reaction is relatively smooth, and the addition amount of spheroidizing agent can be well controlled on the premise of ensuring the spheroidizing effect, ensuring the absorption rate of spheroidizing agent, and better controlling the decrease of molten iron temperature. In addition, the content of rare earth elements in the spheroidizing agent used is very low, so that the residual rare earth in the molten iron after spheroidizing treatment is not too high and the formation of cementite is reduced; The trace rare earth elements remaining in the molten iron can not only inhibit the effect of spheroidizing interference elements, but also improve the nucleation rate during inoculation

after a series of tests, it is found that the addition amount of spheroidizing agent required by different v/o ratios (the ratio of cross-sectional area to perimeter) of piston rings is different; The addition amount of nodulizer required for different sulfur content of molten iron is also different. The addition amount of spheroidizing agent is the sum of burning loss, desulfuration magnesium consumption and residual magnesium

due to the original molten iron coming out of the furnace, but the development speed of the Indian market in the next 10 years will be 10 points. The temperature, the low profit of the main paper types of spheroidizing treatment, and the length of residence time will all affect the loss of magnesium. In order to correctly control the addition amount of spheroidizing agent, the factors that change greatly in production should be controlled. The spheroidizing temperature should be controlled at 1500 ~ 1550 ℃ (the best is 1530 ~ 1550 ℃), and the pit bottom punching method should be used for the addition of spheroidizing agent, The pouring time after spheroidizing treatment shall not exceed 8min (the best control is within 6min). Under the condition that the operation cycle and process are basically unchanged, it is considered that the burning loss of magnesium is basically the same

due to the high sulfur content of molten iron, it is impossible to reach 30000 pellets/cm2) before it is possible to reach cementite in the as cast matrix structure

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