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Centrifugal electroslag casting of tractor bushings of turning hinge.

Steel special-purpose parts having shape of bodies of revolution with through cavities of various diameters are often used in machine building industry. To the items of such type relate bushings of the K-700 tractor turning hinge from steel 40Kh with external diameter 306 and internal diameter 285 [micro]m. They are manufactured by machining of forged pieces or stamped parts, which causes high material and labor expenses.

Application of various methods of hot conversion is a forced measure, which is resorted to because of low quality of casting. That's why production of hollow cast billets, shape and size of which maximally approach those of ready items and quality of which would not be inferior to that of the deformed items, is an actual task.

Centrifugal electroslag casting (CESC) has great potential for solution of this problem [1]. Essence of the process consists in electroslag remelting of metal in a melting unit, which ensures accumulation of liquid metal and slag in necessary amounts and their subsequent pouring into a revolving mould. Consumable electrodes of any shape and section may be used as a remelted metal. This very process was used for manufacturing billets of hinge bushings.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Remelting of the consumable electrode was performed under the flux represented by a mixture of fluoric calcium, alundum, magnesite, silica, and manganese oxide. Such flux ensures refining and cleaning of liquid metal in the melting unit from sulfur and phosphorus and protection against harmful action of environment and significant yield at high cooling rate [2].

A set of equipment for performing mentioned process includes serial installation A-550U, a meting unit, a centrifugal machine with vertical axis of rotation, and a power source--transformer of TShS-3000-1 type (Figure 1).

Melting process was performed under the following conditions: working current was 2800--2900 A; voltage during the whole remelting process was constant and equaled 40 V; mass of a remelted electrode was 14 kg; duration of the remelting process was 7 min; mass of used flux equaled 6 kg. Remelting of the consumable electrode in the melting unit began from liquid start.

[FIGURE 3 OMITTED]

Accuracy of a produced casting is determined by a casting mould. That's why a built-up metal chill mould was used, which was manufactured by turning of annular billets, each of which repeated a portion of external configuration of a cast item (Figure 2). The chill mould consisted of a bottom 3, on which an intermediate side ring 2 was installed that formed external cylindrical part of a bushing, and a cover 1 of the cast mould. All these parts were fixed on faceplate 4 of the centrifugal machine. Than a plate 8 is installed, which pressed by means of studs 6 and wedges 7 all parts of the chill mould to the faceplate.

During pouring of slag-metaljet through the pouring hole it divides under action of centrifugal forces into flux and liquid metal, which forms body of the casting. Flux prevents sticking (welding) of a casting to the casting mould walls due to its arrangement in thin even layer over surface of the mould.

Speed of the centrifugal machine rotation is 400 rpm and duration of the pouring process is 5 s. By means of general reduction of the metal and the slag temperature slag skull forms on surface of the cast, which is separated from the billet only after it is removed from the mould.

[FIGURE 4 OMITTED]

In Figure 3 general view of the chill mould with the casting in skull is shown. Billets produced using this process meet all requirements established for the manufactured products (geometric accuracy of a casting and high values of the metal properties). So, allowance for machining of external side is 2--3 [micro]m,

for height--3--4 [micro]m, and for internal diameter--5--8 [micro]m. Metal utilization factor achieves 0.7 that significantly reduces metal consumption of the item and power consumption needed for its manufacture. General view of the casting cleaned of the skull and the bushing are shown in Figure 4.

Results of analysis of chemical composition and mechanical properties of steel 40Kh after CESC, in comparison with a forged metal, are given in Tables 1 and 2.

As one can see from Table 1, in CESC takes place significant reduction of the content of harmful impurities, which is explained by reduction and refining processes proceeding in the slag pool.

Ultrasonic testing and magnetic flaw detection of CESC castings showed dense cast structure and absence of micro-cracks or any defects. As a whole properties of the electroslag metal meet requirements of GOST 8479--70 established for forged metal of standard melting, which allows using cast electroslag billets instead of forged pieces. In addition, such process ensures high efficiency of producing items of different nomenclature and standard sizes.

[1.] Paton, B.E., Medovar, B.I. (1988) Electroslag crucible melting and pouring of metal. Kiev: Naukova Dumka.

[2.] Medovar, B.I., Tsykulenko, A.K., Shevtsov, V.L. et al. (1986) Metallurgy of electroslag process. Kiev: Naukova Dumka.

E.Nb. ERYOMIN and S.N. ZHEREBTSOV

Omsk State Technical University, Omsk, RF
Table 1. Chemical composition of steel 40Kh

Metal type Share of elements, wt.%

 C Mn Si Cr

Standard 0.36-0.44 0.50-0.80 0.17-0.37 0.80-1.10
Electrode 0.42 0.61 0.24 0.93
CESC 0.41 0.59 0.25 0.91

Metal type Share of elements, wt.%

 Ni S P

Standard [less than or [less than or [less than or
 equal to] 0.30 equal to] 0.035 equal to] 0.035
Electrode 0.12 0.019 0.017
CESC 0.12 0.009 0.015

Table 2. Mechanical characteristics of steel 40 Kh

Metal type [[sigma].sub.t], MPa [[sigma].sub.y], MPa

Standard on [greater than or [greater than or
forged piece equal to] 570 equal to] 315
CESC 932 794

Metal type [delta], % [psi], % [KCU.sub.+20],
 J/[cm.sup.2]

Standard on [greater than or [greater than or [greater than
forged piece equal to] 12 equal to] 25 or equal to] 40
CESC 14.2 49.6 62
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Title Annotation:ELECTROSLAG TECHNOLOGY
Author:Eryomin, E.N.; Zherebtsov, S.N.
Publication:Advances in Electrometallurgy
Article Type:Report
Date:Apr 1, 2006
Words:1016
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