CONTINUOUS CASTING OF STEEL BOOK
From inside the book Metallurgical fundamentals of the CONTINUOUS CASTING. The presentday position of continuous casting of steel. This monograph provides university professionals and students, those working in the steel industry and steel plant suppliers in related activities. Front Cover. Iron and Steel Institute, - Continuous casting - pages. 0 Reviews. From inside the book QR code for Continuous Casting of Steel.
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CRC Press Published September 1, Reference - Pages ISBN - CAT# K Select Format: Hardback. Quantity: USD$ Continuous Casting of Steel by W. R. Irving, , available at Book Depository with free delivery worldwide. Book Reviews. Continuous Casting of Steel by W.R. Irving. This book is written to provide a detailed account of the development of continuous casting.
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Control Technology of Solidification and Cooling in the Process of Continuous Casting of Steel
Metal is drained from the tundish through another shroud into the top of an open-base copper mold. The depth of the mold can range from 0. The mold is water-cooled to solidify the hot metal directly in contact with it; this is the primary cooling process.
It also oscillates vertically or in a near vertical curved path to prevent the metal sticking to the mold walls. A lubricant either powders that melt on contact with the metal, or liquids is added to the metal in the mold to prevent sticking, and to trap any slag particles—including oxide particles or scale—that may be present in the metal and bring them to the top of the pool to form a floating layer of slag.
The shroud is set so the hot metal exits it below the surface of the slag layer in the mold and is thus called a submerged entry nozzle SEN.
Continuous Casting of Steel
In some cases, shrouds may not be used between tundish and mold 'open-pour' casting ; in this case, interchangeable metering nozzles in the base of the tundish direct the metal into the moulds.
Some continuous casting layouts feed several molds from the same tundish. In the mold, a thin shell of metal next to the mold walls solidifies before the middle section, now called a strand, exits the base of the mold into a spray chamber.
The bulk of metal within the walls of the strand is still molten. The strand is immediately supported by closely spaced, water-cooled rollers which support the walls of the strand against the ferrostatic pressure compare hydrostatic pressure of the still-solidifying liquid within the strand. To increase the rate of solidification, the strand is sprayed with large amounts of water as it passes through the spray-chamber; this is the secondary cooling process.
Final solidification of the strand may take place after the strand has exited the spray-chamber. It is here that the design of continuous casting machines may vary.
This describes a 'curved apron' casting machine; vertical configurations are also used. In a curved apron casting machine, the strand exits the mold vertically or on a near vertical curved path and as it travels through the spray-chamber, the rollers gradually curve the strand towards the horizontal.
In a vertical casting machine, the strand stays vertical as it passes through the spray-chamber. Molds in a curved apron casting machine can be straight or curved, depending on the basic design of the machine. In a true horizontal casting machine, the mold axis is horizontal and the flow of steel is horizontal from liquid to thin shell to solid no bending.
In this type of machine, either strand or mold oscillation is used to prevent sticking in the mold. After exiting the spray-chamber, the strand passes through straightening rolls if cast on other than a vertical machine and withdrawal rolls. There may be a hot rolling stand after withdrawal to take advantage of the metal's hot condition to pre-shape the final strand.
Finally, the strand is cut into predetermined lengths by mechanical shears or by travelling oxyacetylene torches, is marked for identification, and is taken either to a stockpile or to the next forming process. In many cases the strand may continue through additional rollers and other mechanisms which may flatten, roll or extrude the metal into its final shape.
Casting machines for aluminium and copper[ edit ] continuous hot vertical casting in process aluminum molten aluminum pours into this casting die top view of die bottom end of casting die the resulting Aluminum blanks after cutting to size Aluminium and copper can be cast horizontally and can be more easily cast into near net shape , especially strip, due to their lower melting temperatures.
Range of continuously cast sections[ edit ] Casting machines are designated to be billet , bloom or slab casters. Metal is poured into the mould and withdrawn with the dummy bar once it solidifies. It is extremely important that the metal supply afterwards be guaranteed to avoid unnecessary shutdowns and restarts, known as 'turnarounds'.
Each time the caster stops and restarts, a new tundish is required, as any uncast metal in the tundish cannot be drained and instead freezes into a 'skull'. Avoiding turnarounds requires the meltshop, including ladle furnaces if any to keep tight control on the temperature of the metal, which can vary dramatically with alloying additions, slag cover and deslagging, and the preheating of the ladle before it accepts metal, among other parameters.
However, the cast rate may be lowered by reducing the amount of metal in the tundish although this can increase wear on the tundish , or if the caster has multiple strands, one or more strands may be shut down to accommodate upstream delays. Turnarounds may be scheduled into a production sequence if the tundish temperature becomes too high after a certain number of heats or the service lifetime of a non-replaceable component i.
Many continuous casting operations are now fully computer-controlled. Several electromagnetic, thermal, or radiation sensors at the ladle shroud, tundish and mould sense the metal level or weight, flow rate and temperature of the hot metal, and the programmable logic controller PLC can set the rate of strand withdrawal via speed control of the withdrawal rolls.
The flow of metal into the moulds can be controlled via three methods: By stopper rods that descend through the tundish, By slide gates at the top of the mould shrouds, If the metal is open-poured, then the metal flow into the moulds is controlled solely by the internal diameter of the metering nozzles.
These nozzles are usually interchangeable.
Overall casting speed can be adjusted by altering the amount of metal in the tundish, via the ladle slide gate. The PLC can also set the mould oscillation rate and the rate of mould powder feed, as well as the flow of water in the cooling sprays within the strand.
Computer control also allows vital casting data to be transmitted to other manufacturing centres particularly the steelmaking furnaces , allowing their work rates to be adjusted to avoid 'overflow' or 'underrun' of product. Problems[ edit ] Contamination by oxygen[ edit ] While the large amount of automation helps produce castings with no shrinkage and little segregation, continuous casting is of no use if the metal is not clean beforehand, or becomes 'dirty' during the casting process.
To prevent oxidation, the metal is isolated from the atmosphere as much as possible. To achieve this, exposed liquid metal surfaces are covered — by the shrouds, or in the case of the ladle, tundish and mould, by synthetic slag.
In the tundish, any inclusions that are less dense than the liquid metal — gas bubbles, other slag or oxides, or undissolved alloys — may also float to the surface and be trapped in the slag layer.
While the tundish and mold fill for the first time at the start of a casting run, the liquid is badly contaminated with oxygen and the first items produced are typically quarantined or diverted to customers who do not require top-quality material.
Breakouts[ edit ] A major problem that may occur in continuous casting is breakout of the liquid metal: for whatever reason, the solid shell of the strand breaks and allows the still-molten metal contained within to spill out and foul the machine. A breakout is usually due to the shell wall being too thin to support the liquid column above it, a condition which has several root causes often related to heat management.
If the metal withdrawal rate is too fast, the shell may not have time to solidify to the required thickness even with enhanced cooling sprays. Similarly, the incoming liquid metal may be too hot and the final solidification may occur further down the strand at a later point than expected; if this point is below the straightening rolls, the shell may break from stresses applied during straightening.
A breakout can also occur as a result of physical irregularities or damage to the shell occurring within the mould during the initial seconds of solidification.
Excessive turbulence within the mold may cause an irregular shell pattern that grows abnormally or it may entrap slag droplets within the shell which reduces the wall strength. If the incoming metal is severely overheated, it may be preferable to stop the caster than to risk a breakout. Additionally, lead contamination of the metal caused by counterweights or lead-acid batteries in the initial steel charge can form a thin film between the mould wall and the steel, inhibiting heat removal and shell growth and increasing the risk of breakouts.
Other considerations[ edit ] Another problem that may occur is a carbon boil — oxygen dissolved in the steel reacts with also-present carbon to generate bubbles of carbon monoxide. As the term boil suggests, this reaction is extremely fast and violent, generating large amounts of hot gas, and is especially dangerous if it occurs in the confined spaces of a casting machine. Oxygen can be removed by "killing" it through the addition of silicon or aluminium to the steel, which reacts to form silicon oxide silica or aluminium oxide alumina.
However, too much alumina in the steel will clog the casting nozzles and cause the steel to 'choke off'. Computational fluid dynamics and other fluid flow techniques are being used extensively in the design of new continuous casting operations, especially in the tundish, to ensure that inclusions and turbulence are removed from the hot metal, yet ensure that all the metal reaches the mould before it cools too much.
Slight adjustments to the flow conditions within the tundish or the mould can mean the difference between high and low rejection rates of the product. Starter bar[ edit ] The starter bar, also called a dummy bar, has a free end portion which is flexible for storage and a substantially rigid portion at the end which plugs the mold.
The starter bar is constructed in discrete blocks secured to one side of a planar spine provided in segments and arranged end to end.If the metal withdrawal rate is too fast, the shell may not have time to solidify to the required thickness even with enhanced cooling sprays. Seller Rating: We can notify you when this item is back in stock. Besides, because the molybdenum has little impact on thermoplastic of steel and the data of nitrogen content is less than 0.
The tundish allows a reservoir of metal to feed the casting machine while ladles are switched, thus acting as a buffer of hot metal, as well as smoothing out flow, regulating metal feed to the molds and cleaning the metal see below.
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