RU2136440C1 - Method of centrifugal casting of blanks of cast iron cylindrical bushings - Google Patents

Abstract

FIELD: metallurgy, methods of centrifugal casting under flux. SUBSTANCE: method includes smelting of iron, pouring of iron into rotating mold of centrifugal machine, metering of inoculating and alloying mixtures onto metal stream. Iron smelting in furnace is carried out with copper content close to upper limit of its solubility in iron. Metal is poured into mold in volume equalling 0.6-0.8 weight of blank with use of inoculating mixture including ferrosilicon and flux in ratio of 2:1. Remaining part of blank is poured into mold with adding alloying mixture including copper scale and flux in ratio of 1: 1. EFFECT: provided uniform hardness across blank cross-section, improved machining.

Description

 The invention relates to the field of foundry, in particular centrifugal casting technology for billets under flux.

 The positive role of alloying gray cast irons with copper is known (Copper in Ferrous Metals, edited by I. Le Men and L. M. Shetki, M .: Metallurgy, 1988). With an excess of copper in cast iron above the solubility limit, antifriction properties increase and its workability improves. In addition, the thermal conductivity and heat resistance of cast iron increases under thermal cycling.

 However, during centrifugal casting of cast iron blanks with copper content above the solubility limit of it in the metal under the action of centrifugal forces, the elements are separated by specific gravity. The outer surface of the workpiece is enriched with copper, and the inner surface is depleted.

 Since the working layer of the cylinder sleeve is the inner surface, which is subjected to thermal cycling, the effect of copper separation during casting of the workpieces by centrifugal method does not allow casting with the copper content above its solubility limit in the inner metal layers. In addition, the method does not provide an impact on the crystallization of metals in the process of formation and solidification of the workpiece in the form (mold) of a centrifugal machine.

 A known method of producing centrifugal billets with alloying cast iron with copper in the process of pouring metal into a mold (ed. St. USSR, N 1294450, class B 22 D 13/00, BI N 9, 1987). According to the method, a mixture of copper oxide and flux is dosed from the beginning to the end of the pouring, and a copper reducing agent (carbon, silicon, manganese, chromium, and other elements) is dosed into cast iron when it is smelted in an oven above the required grade in quantities, necessary for the recovery of copper from copper scale. The method allows alloying the metal with copper, as well as affecting the crystallization of the metal during the formation and solidification of the workpiece in the mold to increase the physicomechanical properties of the metal.

 However, the method does not allow the use of fluxes and alloying additives in large quantities, since their distribution and recovery is due to the heat of the superheated metal. It has been established by centrifugal casting experience that mixtures of not more than 1.0 - 1.2% of the mass of the metal being poured into the mold can be added to the metal stream onto the trench of the casting device.

 Since the conditions of centrifugal casting do not allow the use of modifying or alloying additives in pure form, but only in a mixture with flux, to obtain a metal with a copper content of 1% or higher, in which under the conditions of thermal cycling the phenomenon of copper segregation on the interfacial and external surfaces of the metal is observed, centrifugal casting is not possible.

 The basis of the present invention is to create a method for centrifugal casting of billets of cylinder liners, providing casting with a copper content exceeding the limits of its solubility in metal in the inner (working) layers of the billet, eliminating the formation of segregation processes during the formation and crystallization of metal in the mold, providing uniform hardness metal cross-section and improving the conditions of machining and wear during operation.

 The goal is achieved in that the method of centrifugal casting of billets of cylinder sleeves, including metal smelting, pouring in a rotating form of a centrifugal machine and dosing of modifying and alloying mixtures onto the trench of the casting device, according to the invention is characterized in that the metal is melted in a furnace with a copper content close to the upper limit of its solubility in metal, and the metal is poured into a mold in a volume of 0.6 - 0.8 mass of the workpiece using a modifying mixture consisting of ferrosilic Ia and flux at a ratio of 2: 1, and the remaining mass is poured into the preform shape using a dopant mixture consisting of copper dross and flux at a ratio of 1: 1.

 When a modifying mixture interacts with a liquid metal during the formation of a centrifugal preform, ferrosilicon affects the graphitization of the metal, the flux component of the mixture covers the film with ferrosilicon particles and protects it from oxidation. Ferrosilicon together with flux intensifies the process of crystallization of metal in the form and eliminates segregation processes, including copper, helping to increase the physical and mechanical properties of the metal over the cross section of the workpiece.

 During the interaction of the alloying mixture with liquid metal in the process of forming a cast in the form of copper scale, metal elements are reduced, having an affinity for oxygen more than copper. Based on a number of metal activities, the elements carbon, silicon, manganese, chromium, etc., which are part of the metal, will restore copper from copper oxide.

 The intensification of the process of crystallization of the metal with a mixture uniformly fed to the metal stream, helps to obtain high-quality workpieces with a uniform distribution of copper along the thickness and length of the formed casting, improving the physical and mechanical properties of the metal.

 Billets are formed with a uniform distribution of copper over the cross section, the content of which exceeds its solubility limit in metal, as well as with high physical and mechanical properties.

 The mass of the metal, which is poured into the mold under the layer of the modifying mixture, is determined from the conditions for obtaining the inner diameter of the metal layer of the finished cylinder sleeve, in which the copper content is above the solubility limit of it in the metal. In addition, the size of this layer should be slightly higher than the allowable wear size of the sleeve before rejection.

 When pouring metal under a modifying mixture of less than 0.6 mass of the metal of the billet, the amount of interaction products between the metal and the alloying mixture increases with the formation of slag with low technological properties, and the consumption of expensive copper scale increases. In the case of pouring metal under the modifying mixture of more than 0.8 mass of the metal of the workpiece, the inner layer of the cylinder sleeve will have a copper content equal to the melting composition. The alloyed metal layer of the billet as a result of machining will be removed or it will not be of sufficient size to provide increased antifriction properties during the entire life of the cylinder sleeve.

 The flux of the alloying mixture, in addition to protecting copper scale from pelletizing on the trench of the casting device and its uniform distribution throughout the mixture, should assimilate the newly formed oxides as a result of the interaction between the components of the mixtures and the metal. To ensure the new flux composition (slag) of the required technological properties (low melting point, viscosity, refining ability, etc.), the amount of flux in the composition of the alloying mixture is increased compared to the modifying mixture. The ratio between flux and copper scale is 1: 1.

 The molten flux is carried out by centrifugal forces on the inner surface of the formed preform in the mold, facilitating directional crystallization of the metal.

 Example. In the conditions of the production of BMZ OJSC, work was carried out on casting billets of perlite cast iron of the following chemical composition on a centrifugal machine: percentage by weight C - 3.30; Mn 0.60-0.90; Si 0.80-1.40; P - not more than 0.20; S - no more than 0.15; Cr - 0.30 - 0.60; Ni - 0.30 - 0.40; V - 0.20 - 0.30; Ti - not more than 0.05; Cu - 0.30 - 0.70. Melting was carried out in an IST-016 induction furnace with acid lining in an amount of 190 kg. Metal was poured into a mold with a diameter of 360 mm and a length of 300 mm, lined with granular refractory material, in order to obtain a cast wall thickness in the range of 120 - 125 mm.

 To modify the metal, a mixture of fractions up to 1 mm of the following composition was prepared,% by weight: FS75 ferrosilicon - 65 and 35.0 flux. The flux component used was creolite, sodium fluoride, borax, boric anhydrite, slag ANF-29, etc.

The modifying mixture in the amount of 1.3 kg was dosed on a stream of metal on the trench of the casting device during pouring 125 kg of cast iron. During pouring the remaining portion of the metal into the stream, a doping mixture was dosed in an amount of 0.75 kg with a fraction of up to 1.0 mm, consisting of 50% copper scale and 50% of ANF-29 flux (slag). At a temperature on the inner surface of the workpieces of 650 - 700 ^o C stopped the rotation of the mold and removed the castings. The blanks had a high-quality outer surface. The inner surface of the workpieces is covered with a layer of slag with a thickness of 2-3 mm.

 Samples were cut from the blanks to study the micro- and macrostructure of the metal, layer-by-layer chemical analysis and hardness measurements. To identify the effect of thermal cycling on copper diffusion, chemical determinations of the metal composition were carried out near the grain boundaries of the surface of brittle interfacial fracture of the sample and the machined surface mechanically.

 An analysis of the results of metal research shows that with a melting copper content of 0.84% by mass in the iron - copper solid solution, no more than 0.6 - 0.7% is found. Excess copper is released on interphase surfaces along grain boundaries.

 The results of measuring the thermal conductivity of cast iron showed that copper interlayers on interfacial interfaces increase the thermal conductivity of the metal by 30 - 70% over its entire volume, and the antifriction properties of the metal on the wear or machining surfaces of cutting tools.

 Copper plays the role of a solid lubricant. The friction coefficient due to the selective mass transfer of copper atoms decreases by 20 - 25%. In addition, the machinability conditions of cast iron are improved. For example, cast iron with a copper content of up to 0.7 - 0.8% by weight and a hardness of 260 HB has the same machinability as cast iron without copper, but with a hardness of up to 200 HB.

 Under conditions of thermal cycling due to the mass transfer of copper to the friction boundary, the cylinder sleeve - piston ring increases the thermal conductivity of cast iron and its antifriction properties, which is directly related to a significant increase in its heat resistance.

Claims (1)

 The method of centrifugal casting of cast iron cylinder billets, including metal smelting, pouring it into a rotating form of a centrifugal machine, doping the alloying mixture onto a metal jet, characterized in that the metal is smelted with a copper content close to its upper solubility limit in metal, pouring metal into the form in the volume of 0.6 - 0.8 mass of the workpiece is carried out with a dosage of a modifying mixture consisting of ferrosilicon and flux in a ratio of 2: 1 on a metal stream, and the rest of the metal is poured with dosing per metal stream of an alloying mixture consisting of copper oxide and flux in a ratio of 1: 1.