Process for purification of molten iron using ceramic foam filter
The main features of the newly developed low-temperature sintering mullite foam ceramics are the application of foam ceramics in the purification of gray cast iron, ductile iron and alloy cast iron. The results show that the foam ceramic filtration process has the best purification effect. The low-temperature sintering type mullite foam ceramic is not only cost-effective but also can significantly improve the purity of molten iron and improve the mechanical properties of cast iron.
1Implications and significance of iron-fluid filtration and purification Most of the inclusions produced during the smelting and casting process of various liquid casting alloys deteriorate the casting process performance of the alloy and the machining performance of the castings, and reduce the mechanical properties of the castings and the casting process. rate. This effect is particularly severe in all kinds of non-ferrous alloys such as aluminum alloys and high-temperature alloys such as cast steel. In addition to the high economic value of the above alloys, the space for waste reduction and efficiency increase is large, prompting foundry workers to More emphasis is placed on the use of highly efficient and advanced ceramic foam filtration processes in these areas. However, due to people's concerns about the adverse impact of the high price of foam ceramic filter elements on production costs in cast iron, the extent of promotion and application of this technology in China has been low to date.
According to production statistics, the casting waste resulting from the adverse effects of cast iron inclusions is as high as about 50Z of the total number of waste products. The former's filtration efficiency, post-filtration casting tensile strength growth rate, and elongation growth rate are respectively the latter (double layer). 1.41 times, 45 times, and 3.43 times.
table! Bubble Ceramics and Fiber Filters Filter Comparison Tab.!
Inclusion Filtration Filtration After Filtration Casting Tensile Strength Filtration After Casting Elongation Efficiency Growth Rate Growth Foam Ceramic Fiber Filters (Double Layers) Seen from the Metallurgical Structure after Filtering Ductile Iron Crankshaft (QT800) with Two Filter Elements The distribution of spheroidal graphite after filtration using ceramic foam is more uniform than that of fiber filter, and the average diameter of 2002.1 modern cast iron is even smaller.
The comparative application of foam ceramics and honeycomb-shaped straight-hole ceramic filters in mass production of ductile iron also shows that when the former is used, the reject rate related to the purity of molten iron decreases from 3.6 when the latter is used to 1.79, and the rate of decline is 1.79. For 50.6; and the casting process production rate increased from 68.3 to 711 increased by 8; In addition, the consumption of cutting tools decreased by 58. The service life of the P-tools was increased by more than 1 times, and at the same time, the auxiliary time for tool replacement was reduced. Improve work efficiency.
Although the fire-resistant fiber filter is convenient to place, its use temperature is low and cannot exceed 14508, and its rigidity and anti-iron impact resistance are also low and it is easily damaged by the molten iron.
Although the strength of the honeycomb-shaped straight-hole ceramic filter is relatively high, its porosity is only 30040, which is about half of that of the ceramic foam, which results in a low liquid metal flow rate. In other words, in order to make the flow rate of the molten metal of the above two kinds of filter pieces comparable, the flow area of ​​the honeycomb-shaped straight-hole ceramic filter piece needs about twice as much as that of the ceramic foam filter.
The ceramic foam filter can generally withstand the over-flow of ductile iron 100: 00;. Based on this calculation, an average of 510 pieces of foam ceramics with a size of 100x100mm per ton of ductile iron castings will be required. If the price of foam ceramics is controlled at less than 500 yuan/m! Thickness is about), then the cost of foam ceramic per ton of cast iron parts can not exceed the main performance of low-temperature sintered mullite foam ceramic According to the above analysis, the technical benefit of the promotion and application of foam ceramic filtration purification technology in cast iron is so far The best problem in all filtration and purification processes, the first problem to be solved is to reduce the production cost of the foamed ceramic material as much as possible so as to increase the economic benefits of the process.
To this end, we have made further improvements in the following three aspects on the basis of the research results and production experience of the foam ceramic material production process for the past decade: The first is the use of a special refractory clay instead of ceramic ingredients. For the original clay, the sum of the B-water drying shrinkage ratio and the high-temperature sintering shrinkage ratio is only about 12 B, which is about 60 B of the original clay and the fire resistance is about 300 C higher than that of the original clay and the sintering point is not much different. The added amount can be increased by 23 times, thereby exerting a stronger sintering aid effect.
The second is the lower requirement for the refractoriness of foam ceramics based on the ferrofluid filtration conditions, and the third is the appropriate addition of a rare earth oxide as a sintering agent in the ceramic batch.
The above improvements all reduce the sintering temperature of the product. The main technical performance of this low-temperature sintered ceramic foam is shown in Table 2.
4 Application of foam ceramic filter in cast iron Application in grey cast iron We use low-temperature sintered ceramic foam filter with 10ppi pores and open porosity of > 0% under the actual production conditions. Purification of gray iron liquid The application of the system (samples are all from cast test bars) is shown in Table 3, and. From Table 3, it can be seen that: (1) After being filtered by the foam ceramic, the chemical composition of the gray cast iron is basically unchanged, and the foam ceramic has stable high temperature chemical properties and does not pollute the molten iron. (2) Foam ceramic can not only significantly reduce the non-metallic inclusions in gray cast iron, but also make the distribution of graphite sheet and matrix more uniform and refined. (3) Due to the above reasons, the ceramic foam filtration and purification will significantly improve the tensile strength, impact toughness, and hardness of gray cast iron (the tensile strength and hardness are equivalent to improving a brand, etc., the main technology of low temperature sintering type foam ceramics in Table 2). Performance Table 3 Chemical composition of the gray iron before and after bubble ceramic filtration (wf.%) Nominal number of holes Open porosity Normal temperature Compressive strength 1000C Compressive strength Refractoriness before filtration Filtration After filtration, the average value of the first group, the second group, the second group, the first group, the second group, the average growth rate of tensile strength (MPa) hardness (HB) (a) before the ceramic foam filter (b) inclusions in the gray cast iron after the filtration of ceramic foam And graphite sheet distribution 120; (a. before foam ceramics filter (b. metallographic structure of gray cast iron after filtration of foam ceramics) Table 5: Change in mechanical properties of ductile iron after filtration of ceramics after filtration Measured average of tested values ​​after filtration Value Growth Rate Elongation 1419 Table 8 Change in Mechanical Properties of High Chromium Alloy Cast Iron after Ceramic Filtering Filtration before Filtration Item Mean Test Mean Test Mean Average Growth Rate Resistance to Tenon (MPa) Impact Toughness (No Notched Specimen) Hardness Table 7 Change in Dispersion of Mechanical Properties of High-chromium Alloy Cast Iron after Filtering by Ceramic Filter Tab.7 Mechanical Project Filtration Reduction Rate after Filtering Maximum Dispersion Dispersion Maximum Dispersion Difference Dispersion Degree Anti-Rupture Strength Impact Toughness Hardness Level .
Application in Nodular Cast Iron The changes in the mechanical properties of castings after foam ceramic filtration and purification of ductile iron liquids are shown in Table 5. Tensile strength and elongation are increased by 15.3 and 12.5 respectively. This increases the grade of the cast iron grades at the same time. Elongation does not fall back.
Application in Alloyed Cast Iron The results of the filtration of high-chromium alloy wear-resistant cast iron in a ceramic foam filter under actual production conditions are shown in Tables 6 and 7 (the specimens are from the cast-in-place specimen). From Tables 6 and 7, we can see that: (1) Although the number of inclusions in the alloy cast iron is large, the filtering effect of the foam ceramic is also very significant, and most of the inclusions are removed.
(/) High-chromium alloy cast iron's bending strength, impact toughness and hardness are greatly improved after being filtered by ceramic foam.
(+) After filtration by ceramic foam, the dispersion of mechanical properties such as bending strength, impact toughness, and hardness of high-chromium alloy cast iron (ie, the percentage of the maximum deviation from the average value) is also significantly reduced, and the performance is more stable.
The distribution of inclusions after high-chromium alloy cast iron after filtration>30b (1) The effect of foam ceramic filtration process on the purification of liquid casting alloys is optimal in the currently used various filtration processes.
(/) The newly developed low-temperature sintering type mullite foam ceramics has a cost close to those of honeycomb-shaped straight-hole ceramics and filters, and its performance satisfies the requirements for iron liquid filtration and purification. ) The use of ceramic foam filter technology can effectively remove all kinds of debris in the cast iron, improve the metallurgical structure, improve the production rate of the casting process, and reduce the cost of casting cutting.
(4) The low-temperature sintering type foam ceramic filtration process should be promoted in the production of cast iron in order to create greater technical and economic benefits.
Causes and elimination methods of cracks in driving shell casting Zhuo Rongming (College of Engineering, Jiangxi Yichun University, Yichun 336000, Jiangxi, China) The driving shell is a stressed part of the wheel loader. The material disintegrates the cracked casting and observes the crack surface. The quality of the defect is QT500 -5. Because the product needs to have two drive shell models of 310mm and 280mm, the two models of the original casting process such as. Since the current process of driving the casing has been put into operation, there have been defects such as shrinkage holes and shrinkage, but there have never been any cracks. Recently, four consecutive cracks occurred in the four-girder 310 drive housing (the location shown), and the number of scrapped scraps accounted for 408 of the total number of castings, which affected the production schedule and economic efficiency.
2 Analysis of cracks 2.1 Micro-oxidation of cracking properties, resulting in thick and thin junctions in the casting, and almost all appear 23 Wang Weiwei and other cast iron with silicon carbide foam ceramic filter material should be developed with modern cast iron 2002.1 1 Ye Rongmao and so on. Discussion on Copper Alloy Filtration Technology (1). Thermal Processing Technology, 991 22001 -) Male, Man of Jiangxi Province, graduated from the Department of Mechanical Engineering of Jiangxi University of Technology in 1980, is a senior engineer. Now he is the vice president of Yichun College of Engineering.
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