外文翻译连铸的发展.docx

1、外文翻译连铸的发展The Development of Continuous Casting【连铸】中英文对照Continuous CastingFrom the Making, Shaping and Treating of Steel by William，McGrawHill Companies, Inc., 2002The Development of Continuous CastingContinuous casting was developed very rapidly after the Second World War. Steel-producers arc today

2、generally convinced that continuous casting is at least as economical as ingot production and can match the quality of the latter across much of the production spectrum for high-quality steels. Continual development of the technique aimed at improved steel characteristics is leading to increasing ad

3、option of the process in works producing special high-grade steels. The reasons for continuous-casting systems are: (1) lower investment outlay compared with that for a blooming train (mini-steelworks); (2) about 10% more productivity than with conventional ingot-casting; (3) high degree of consiste

4、ncy of steel composition along the whole length of the strand; better core quality, especially with flat strands; high inherent surface quality, leading to savings on an otherwise expensive surfacing process; (4) high degree of automation; (5) friendlier to the environment; (6) better working condit

5、ions. Types of Installation The first continuous-casting plants were aligned vertically; however, with larger cross-sections, increasing strand-length, and, above all, with increasing pouring-rates this type of construction leads to unreasonable building-heights. These factors also lead to a conside

6、rable increase in the length of the liquid phase which has metallurgical effects. The length of the liquid phase in a continuously-cast strand is determined by the following formula: L=D2/4x2Vc Where D =strand thickness (mm) x = solidification characteristic (mm / min1/2) These values amount to 2633

7、 for the whole cooling length. Vc = casting rate (m /min) Efforts to reduce building-height first led to continuous-casting systems in which molten metal passed into a vertical mould and solidified completely before being bent or where the strand has been in the liquid phase and later to the bow-typ

8、e installation which has a curved mould and is the system most used today. Vertical systems and those in which the strand is bent when completely solidified have long straight liquid phases and can lead to unacceptably high capital outlay. However, these systems have metallurgical advantages from th

9、e point of view of maintenance. A vertical system in which the strand is bent while still in the liquid phase has the advantage that the building need not be as tall as when the strand is bent after solidification; however, the liquid-phase bending system requires higher initial outlay and greater m

10、aintenance costs. The bow-type system represents a compromise between the costs of capital outlay and of maintenance and what can be achieved metallurgic ally. Continuous-casting is suitable for the production of almost any cross-section imaginable; square, rectangular, polygonal, round, and oval se

11、ctions are all available. There are also some instances of preliminary sections for tubes and slabs, blooms, and billets. Sections with a breadth /thickness ratio greater than 1.6 are normally described as slabs. Billet-machines produce square or nearly-square, round, or polygonal cross-sections up

12、to 160mm across. Larger sections and those with a breadth /thickness ratio less than 1.6 are cast in bloom-machines. Billets nowadays normally produced in this way range from 80 x80 to 300 x300 mm, and slabs are 50 - 350mm thick and 300 - 2500 mm wide. Continuous-casting output-rates have risen shar

13、ply, especially in the last few years. This is essentially because of increase in the breadth of the strand and in casting rate. The following outputs have been exceeded per section per minute: slabs 5 tones blooms 1 tones billets 350 kg Finally, we should mention horizontal continuous-casting syste

14、ms which are already used for non-ferrous metals and cast iron and which are being further developed for steel. R. Thieimann and R. Steffen have produced a comprehensive report about the state of development of horizontal continuous-casting systems for producing billets from unalloyed and alloy stee

15、ls. Horizontal continuous-casting systems have three important advantages over conventional continuous-casting system: (1) low height and cost of building; (2) simple means of protecting the melt against reoxidatioin; (3) no strand deformation because the ferrostatic pressure is much lower. Casting

16、Technique Molten steel is poured from a casting ladle via a tundish into an open water-cooled copper mould. At first the bottom of the mould is closed off by a starting-bar, which then leads transport of the hot strand from the mould into the continuous withdrawing rolls. The strand, which starts to

17、 solidify in the mould, passes through a cooling system before it finally reaches the withdrawing rolls, whereupon the hot strand takes over transport. The starting-bar is separated from the hot strand before or after it reaches the parting device. The latter, which may either be a flame-cutter or h

18、ot shears, moves at the same rate as the hot strand and cuts it into the lengths required. The purpose of the tundish is to feed a defined quantity of molten steel into one or more moulds. This can be done by using nozzles controlled by stoppers, slide-gates, or other means. The tundish may initiall

19、y be cold, warm, or hot according to the nature of its refractory lining. Where difficult steels are processed the pouring stream is protected against oxidation between the submerged boxes. The mould not only forms the strand section but also extracts a defined quantity of heat, so that the strand s

20、hell is strong enough for transport by the time it reaches the mould-outlet. The mould may be made from copper tube or hard enable copper alloy, depending on the shape and size of the strand to be cast. As a rule, tubular moulds tire used for smaller sections. The interior surface of the mould may b

21、e coated with chronic or molybdenum to reduce wear and to suit heat-transfer from the alloy being cast. The mould is tapered to match steel-shrinkage and casting-rate and the type of steel concerned. Moulds used today range from 400 to 1200 mm in length overall, but their usual length is between 700

22、 and 800 mm. The problem of steel adhering to the mould-sides is usually countered by oscillating the mould sinusoidally relative to the strand and by adding lubricant (oil or casting flux in an attempt to cut friction between the mould and the steel. The lubricant, particularly casting-flux, has an

23、 additional metallurgical function. The choice of lubricant depends on the qualities required and the casting conditions; it is particularly important that casting-flux should be chosen to match the quality-programme precisely. The level of steel in the mould may be controlled manually or by an auto

24、matic system. Either method may be used to keep the level constant or to match the incoming molten steel, i. e. to accommodate variations in casting rate. Manual control is affected via the stopper in the tundish or by varying the output rate. An automatic control system may meter radioactivity or i

25、nfrared radiation or measure temperature via a probe in the mould wall to determine the steel-level and compensate any changes by actuating the stopper-mechanism (for constant pouring rate) or controlling the speed of the withdrawing rolls (varying casting rate). The type of starting-bar used for co

26、ntinuous-casting depends on the type of installation. Rigid starting-bars can be used in vertical systems, while articulated dummy bars or flexible strip have to be used in bowed installations. The starting bar can be connected to the hot strand in different ways, one is by welding the fluid steel u

27、sing a jointing element (flat slab, screw, or fragment of rail) which is soluble in the starting-bar; another is by casting the connector in a specially shaped head in the dummy bar in a way that enables it to be released by unlatching. The thickness of the solidified strand shell on leaving the mou

28、ld depends first of all on how long the steel is in contact with the mould, but it also depends on the specific thermal conductivity of the mould and on the amount of superheat that steel has when it enters the mould. It can be determined with fair accuracy using the following parabolic formula: C=x

29、. T where C is the thickness of the strand shell (mm) x is the solidification characteristic (mm/min1/2) t is the solidification time (min) The solidification characteristic in and near the mould lies between 20 and 26, depending on the operating conditions; for the secondary cooling-area the figure

30、 is 29 -33. The thickness of the solidified strand shell on leaving the mould is about 8 10% of the strand-thickness, depending on casting rate. A secondary cooling-area under the mould speeds up completion of the solidification process. The coolant usually is water but a water / air mixture or comp

31、ressed air is also sometimes used. The secondary cooling area is divided into several zones to suit coolant flow rates. The necessary quantity of water is sprayed over the entire strand by spray-bars. The ferrostatic pressure may be so high in relation to the strand cross-section and the casting rat

32、e that the strand has to be supported to prevent buckling. The equipment for this is expensive in plants producing blooms and especially slabs. Process Control For productivity and quality reasons there is a trend in modern steelmaking to transfer time-consuming operations, such as temperature adjus

33、tment, deoxidation and alloying, from the furnace to the ladle treatment stations. These treatments are particularly important where the continuous casting process is involved because temperature and composition must closely be controlled. The temperature control of molten steel as it enters the mould nee