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Resursosveregajuščaja technologija

Krutilin A. N.

Archives of Foundry Engineering

2010

Vol. 10, iss. 4

97--102

Поршневые кольца являются одними из наиболее ответственных тяжелонагруженных деталей двигателей, работающих на износ в условиях длительного воздействия знакопеременных нагрузок и повышенных температур. Ввиду несовершенства традиционных способов литья, постоянного повышения требований к качеству заготовок, необходимости экономии материальных, топливных и энергетических ресурсов, ведутся поиски новых прогрессивных технологических процессов производства высококачественных заготовок поршневых колец. В Белорусском национальном техническом университете разработан усовершенствованный способ литья погружением. Тонкостенные (5-10 мм) кольцевые одноместные формы, изготовленные из стержневой смеси, с помощью специального приспособления собирают в блоки. Заполнение и питание заготовок происходит при погружении предварительно нагретых форм в расплав через один или несколько литников, выходящих на наружную поверхность формы. Питание заготовок происходит непосредственно из ванны расплава до ее полного затвердевания, после окончания кристаллизации заготовки не затвердевший металл из питателей попадает обратно в печь. Значительно сокращаются безвозвратные потери металла, так как нет необходимости использовать большое количество отходов производства, составляющих более 50% при традиционной технологии литья. Замена традиционной технологии литья индивидуальных заготовок поршневых колец в песчано-глинистые формы на способ литья погружением позволяет при высокой производительности процесса, увеличить выход годного до 85-95%, значительно упростить и удешевить технологический процесс.

Piston’s rings are one of the most critical parts of heavy-duty engines for wear-work in conditions of prolonged exposure of alternating loads and high temperatures. Currently in the world production of billets for piston’s rings is dominated by the two methods of casting: production of individual and oiling billets of gray and ductile cast iron in green-sand mold and shell mold and centrifugal casting method (intended primarily for oiling billets of ductile iron); the technology for individual production billets for piston’s rings with a diameter up to 250 mm, from 250 to 450 mm with individual and oiling ways, over 450 mm - preference of oiling billet. The best parameters of physical-mechanical and operational characteristics piston’s rings are in the case of manufacture of billets to the maximum extent approaching the configuration to the finished product. The rings made of shaped billets are characterized by uniform distribution of properties from the perimeter, provide a given diagram of pressures and full fit to the cylinder. Because of deficiencies of traditional methods of casting, continuous quality requirements for billets, the need for economy of material, fuel and energy resources, are finding new progressive technological processes of production of high-quality billets for piston’s rings. One of the most promising for piston rings billet is a method of casting consists of immersing the sand molds into the melt. It is interesting idea, expressed by A. Sutherland and subsequently patented in several countries in the way of casting method, called "immersion pouring technology" (ICT-Immersion Casting Technique) [1]. Experiments, conducted in the laboratory of the Belarusian National Technical University, have identified significant shortcomings of immersion method of casting. When forms are immersing, have an intensive gassing in molten metal, and freezing of the metal on the out surface of the form. But despite some shortcomings, the proposed process is characterized by a significant reduction of laboriousness, improved working conditions, a significant decreasing of molding materials, decreasing of production areas, complete except flasks and ladles. In the Belarusian National Technical University was developed an improved method of casting immersion [2], schematic diagram of the process was shown in Figure 1. Thin ring single mould (5-10 mm), core sand - made, collect by means of a special device to the blocks. Pouring and filling billets are being when preheated moulds immersing in melt metal through one or more gatings, leaving the outer surface of the mould. Filling billet is directly from the molten pool until its complete solidification, after finishing of billet’s crystallization, non - solidified metal from the gatings goes back into the oven. For a long time, based on experimental investigation are identified optimal technological parameters of the process of casting billets of low-alloyed gray and ductile iron. Through the minimum time between the modification and pouring moulds of melt, graphitized items, in ligatures, have the greatest effect. Crystallization of the alloy is mainly running with the formation of austenite-graphite eutectic, which also has a positive effect on reducing marriage to porosity. Due to the active influence on the rate of solidification and cooling at different periods of the formation of the casting, provides technological process provide to obtaining billets without structurally - free carbides with the requisite level of physical and mechanical properties without the using of energy-intensive heat treatment. Optimal thermal conditions for the formation provide uniformity of hardness on the perimeter of billet. Physical-mechanical properties and microstructure satisfy the technical requirements for piston’s rings. Possibility to obtain a single cast billets of ductile iron with hypoeutectic composition, free shrinkage defects. Significantly reduces the deadweight loss of the metal, because there is no need to use big quantity of waste of production, accounting more than 50% with the traditional casting technology. Replacing the traditional casting technology of individual billets of piston’s rings in the green-sand moulds with casting by immersion, allows high-performance process, increase the yield of up to 85-95%, make technological process simplified and cheaper.

A concast billet caster and electromagnetic stirring of the melt

Stransky K., Kavicka F., Sekanina B., Stetina J., Dobrovska J., Stransky L.

Prace Instytutu Metalurgii Żelaza

2009

T. 61, nr 5

142-145

Electromagnetic stirring (EMS) suppresses the growth of columnar crystals of billets and reduces the tendency to cracking during casting and at low temperatures. A caster was used for the testing of two induction stirrers – one on the actual mould and the other beneath the mould – to determine the effect of EMS on the formation of the structure of non-alloy steel. As part of these tests, certain parts of the billets had been cast without the use of stirrers and other parts underwent alternate switching on and off of the stirrers for as many as nine combinations of modes. Samples were taken from the sections of these billets, fine-ground and etched in order to make the dendritic structure visible. The mode with the highest effi ciency was when both stirrers ran simultaneously. The growth of the columnar crystals, which pointed inward, was limited to 1/4 -to- 1/3 of the length of the case when there was no stirring. Experimental research was also confronted with results acquired from the application of the models of the temperature field and chemical heterogeneity and the physical-similarity theory. Statistical monitoring of the quality of concast billets has proven that stirring significantly reduces the occurrence of defects – in this case cracks.