Continuous Casting: Definition, Importance, How It Works, Advantages, and Examples

Continuous casting is widely used in steel production, nearing 95% of all products from strip and plate mills. The process is also widely used for non-ferrous metals and alloys. It is crucial in supplying the raw materials for most downstream manufacturing processes, including rolling, forging, and extrusion. It converts semi-finished products into various final profiles and cut lengths. This article introduces continuous casting, its applications and advantages, and its importance in certain areas of both raw material processing and finished or near-finished product manufacture.

What Is Continuous Casting?

Continuous casting is a metal casting process that produces continuous lengths of metal, with a constant (2D) cross-section. It's a highly efficient method for converting molten metal into long lengths of semi-finished product of a relatively small, potentially complex cross-section. Put simply… the process introduces molten metal into a mold that has the required profile. It allows the metal to solidify while continuously being pulled or pushed through the mold. Internal hollows of moderate precision can be seamlessly formed by the suspension of core features in the molten and early-cooling zone. The most common form has the casting tool mounted vertically on a tower, and the product is drawn from below the tool by rollers. However, increasingly, a horizontal system is being used: The tool is still mounted vertically, but rollers below it feed the not-yet fully hard profile through a 90° turn to run horizontally away.

Why Is Continuous Casting Also Called as Lost Wax Process?

No, continuous casting is not called a lost-wax process. The lost-wax process, instead, is also known as investment casting, precision casting, or cire perdue.

How Does Continuous Casting Differ From Other Types of Casting?

Continuous casting differs in most regards from all other casting types. While it does use a cavity to form liquid metal into a solid that reflects the shape of the cavity, it differs in almost every detail from all other casting processes. All other casting methods produce 3D profiles, or a 2D profile of predetermined lengths as a finished or partially finished object. In general, casting processes use a closed (or sometimes upper side open) cavity to form a part that accurately reflects this volume.

What Is the Importance of Continuous Casting in Manufacturing?

Continuous casting is of overwhelming importance in the manufacturing of high-quality and continuous-length bars and plate stock for follow-on manufacturing processes, particularly in the steel industry. It offers significant commercial benefits in cost reduction, quality, and energy consumption, compared with the more traditional open sand casting of billets that are then heavily hot and cold rolled to required profiles. 

What Are the Industries That Use Continuous Casting?

Some industries that use continuous casting are the: electrical, automotive, construction, and aerospace sectors. Continuous casting is widely employed in the production of prepared/processed raw materials for post-process finishing by forging, rolling, or machining. It is used to produce aluminum billets, slabs, and other shapes. These are later processed into products such as: sheets, plates, extrusions, and aluminum alloys for various applications. Continuous casting is employed to create copper rods, tubes, and other shapes for use in electrical applications, plumbing, and industrial components. This technique initiates most of the steel bulk raw materials used in the manufacturing of automotive components. The aerospace sector also uses continuous casting for raw materials of more exotic materials. Examples are the production of jet engine components including turbine blades.

How Does Continuous Casting Work?

Continuous casting is a metal manufacturing process that outputs semi-finished products like billets, slabs, and rods with a consistent cross-section. The key principle of the approach is to maintain a consistent flow of molten metal through the mold while ensuring gradual solidification to achieve an optimized and homogeneous structure.

Continuous casting uses a water-cooled 2D profile cavity that is mounted vertically and open at the top and bottom. This open channel accepts molten metal from a tundish feeder. The charge then cools and solidifies as it passes through the length of the water-cooled tool. As it emerges from the lower end of the casting tool, its profile is set and hardened enough to retain both shape and dimensional accuracy. 

This allows a continuous pour of molten metal to enter the cavity and feed through it as it cools and solidifies. In this way, the partially cooled cast can be pulled through the cavity at a rate that matches the liquid introduction at the other end of the tool. In vertical systems, the cast travels downwards to cutters that crop off the form to the required lengths. In more up-to-date horizontal setups, the cast is rolled through a 90º turn to run out horizontally and complete the cooling/hardening before cropping. 

What Is the Step-by-Step Process of Continuous Casting?

The process begins with melting the metal in a furnace, in which alloying and additive stages may occur. The step-by-step process is listed and discussed below:

1. Pour Liquid Alloy Into a Tundish To control the Flow

Transfer the molten metal from the furnace to a tundish. The tundish is the reservoir that holds the charge and regulates the flow into the mold.

2. Direct the Metal Into a Water-Cooled Mold To Partially Solidify and Form a Basic Grid Shape

Pour the metal from the tundish into the throat of the mold. The mold is typically cut from copper or another material with good thermal conductivity. This mold is an open, parallel form that matches the desired cross-section. It can contain internal cores to form hollows in the cast. It is drilled with water-cooling pathways.

As the melt contacts the cooled walls of the mold, solidification commences forming the grid. The cooling effect of the mold extracts heat from the metal, causing it to solidify. In general, a shell of solid metal forms against the mold walls while the core remains liquid for longer.

3. Send the Semi-Solid Grids Through a Strand Guide To Stretch and Cool Them Further

The charge is continuously pulled through the mold by rollers or other mechanical devices called strand guides. These strand guides often stretch the basic grid to improve straightness and dimensional accuracy. The pull rate and fill rate are carefully balanced to produce a consistent and steady finished material flow from the cool end of the tool. Cooling continues as the cast travels through and out of the tool.

4. Pass the Fully Solidified Grids Through Straighteners To Achieve the Final Dimensions

As the grid cools and hardens further, it is passed through straighteners that reduce the kinking that may have developed through non-uniform shape-induced cooling.

5. Wind the Finished Grids Into a Roll for Storage

Product from a strip mill will generally be wound onto a roller to make it compact and easy to store. The cut grid will be racked/stacked and kept straight.

What Are the Metals Used in Continuous Casting?

Some of the metals used in continuous casting are discussed below:

1. Copper

Continuous-cast copper is used as a source material in various sectors, to produce products such as: copper rods, tubes, bars, and the raw material for wire drawing. It allows for the efficient production of semi-finished copper materials that are used across various industries for electrical, cooling, and water-handling applications. To learn more, see our guide on Copper Applications.

2. Aluminum

Continuous casting is a widely used technique for casting aluminum alloys and pure metal into billets, slabs, ingots, and rods, often as source material for wire drawing. This process offers several advantages when applied to aluminum, in particular the consistent microstructure that results from highly controlled cooling. Semi-finished output is used for extrusion, forging, and machining of most finished goods in aluminum.

The process is the preferred method for high-quality aluminum raw material manufacture across diverse sizes and material-property requirements.

For more information, see our guide on What is Aluminum Used For.

3. Steel

Continuous casting is a widely used method for casting steel into various semi-finished forms, such as: billets, blooms, and slabs. This process offers high efficiency and productivity, with reduced energy use in producing high-quality steel products.

The process is the key initial step in the steelmaking process, providing the foundation for post-processing operations such as: rolling, forging, and machining. It's used to produce semi-finished steel forms that can be subsequently shaped and processed into finished products for various industries or used as-is in lower-precision applications. For more information, see our guide on the Description of Steel.

4. Copper Alloys

Continuous casting is a critical method for casting various copper alloys, including brass and bronze. Continuous casting offers: high productivity, low operational costs, and good energy efficiency. 

The process is used in the brass and bronze raw material sectors to produce semi-finished forms that are shaped and processed into finished products. These alloys find applications in various industries, including: automotive, electronics, and architecture, due to their attractive appearance, corrosion resistance, and good mechanical properties.

Is Nickel Alloy Suitable for Continuous Casting?

Yes, nickel alloys are suitable for continuous casting, and the process is commonly used to produce various semi-finished forms. Raw materials made in this way are used in the aerospace, chemical processing, and power generation sectors, among others.

The process offers the same general advantages of high productivity, consistent and high quality, and reduced energy consumption when applied to the manufacture of semi-finished nickel-alloy raw materials.

For more information, see our guide on Nickel Alloy Composition.

Can Zinc Be Used as Casting Material for Continuous Casting?

Yes, zinc can be used as a casting material for continuous casting, but this is not common. There are factors to keep in mind when considering zinc for the  continuous casting process. For example, zinc has a lower melting point than other continuously cast metals, making it relatively easy to process. Cooling and solidification require careful management to achieve useful casting quality. Premature cooling can result in microstructure problems and internal cracking. Alloy selection also has a big effect on casting behavior, so great care is required during setup to optimize for the chosen metal. Most continuous casting systems are established for higher-temperature operations, so some system adaptations will be required.

How Long Does It Take for Continuous Casting To Finish?

The time it takes for continuous casting to finish varies significantly depending on various factors such as: the metal being processed, the cross-section of the product, the optimal casting speed for a particular setup, and the technical standard of the equipment. It is a rapid and continuous process, but the speed of through-flow is highly variable.

In general, the time it takes for a single strand of metal to complete the continuous casting process can range from a few moments for thin sections to several minutes or more. Typical continuous casting is run at 1–3 mm/min for larger sections in steel, and up to 8–10 mm/min in some cases of higher conductivity materials and finer cross-sections. The continuous nature of the process in essentially 24/7 operation results in an output of product in high quantities and undisrupted flow.

How Accurate Is Continuous Casting?

Continuous casting can deliver a semi-finished product of high dimensional accuracy, allowing speed/stretch tuning to adjust section dimensions. For example, continuous casting of steels is reported as resulting in a dimensional error of around +/- 2% of linear sectional dimensions. Good mold design, well-executed and tightly controlled cooling, and precise casting speed all contribute to the accuracy and repeatability of the output from the process. It is important to note that achieving accuracy and consistency depends entirely on careful management of all aspects of the casting process. Modern equipment, advanced process control systems, skilled personnel, and ongoing process improvement efforts are needed for optimum results.

How Much Does Continuous Casting Cost?

The cost of implementing continuous casting varies a lot, based on several factors such as: the type of metal being cast, the section size and quantity of product required, the scale and capability of the casting facility, the currency of equipment, labor costs, energy costs, and a range of operational considerations.

Given the huge variability in factors, it's impossible to provide a specific cost figure for implementing continuous casting. As long as the volume of product required is sufficient to justify the investment in process and handling equipment, the cost per unit length of semi-finished output will be highly competitive with any discontinuous or batch production process.

Is Continuous Casting Cheaper Than Sand Casting?

The relative cost-effectiveness of the two processes depends entirely on the type of metal being cast, the size and complexity of the components, the net production volume required, and the availability of facilities and skills. Continuous casting and sand casting each have clear advantages and disadvantages. Process selection can only be based on the specifics of the product required, planned volumes, and quality requirements. Cost considerations are not the only factor in process selection. Product geometry, quality, dimensional accuracy, surface finish, and lead times also play a significant role in the choice of method. The cost/benefit comparison of continuous casting versus sand casting depends centrally on the specific details of your project and production strategy.

What Are the Advantages of Continuous Casting Products?

Continuous casting offers various advantages in the manufacture of appropriate metal products, including:

1. Allows for a continuous and efficient production process, increasing overall productivity.
2. Enables consistent quality and physical properties throughout the entire length of the cast output.
3. Delivers excellent dimensional accuracy and tight tolerances when tightly controlled.
4. Removes the need to recycle metal waste and removes all process waste.
5. Delivers a homogeneous grain structure and defect-free uniformity with potentially good surface quality.
6. Reduces heating and cooling cycles, relative to batch processes, reducing energy use per kg of cast.
7. The product serves as optimized feedstock for downstream processes, further enhancing manufacturing efficiency.
8. The process is well-suited for high-volume production, but tooling and parameter changes can allow quick switchover if the products are not excessively divergent.
9. It is applicable to a variety of metals and alloys, though setups tend to be material-class (temperature-range) fixed.
10. Continuous casting is amenable to automation and offers low operating costs per kg of output.

What Are the Disadvantages of Continuous Casting Products?

Although continuous casting has significant advantages, it is not suited to all production applications.

1. High initial setup costs.
2. More complex to set up and operate than some casting methods.
3. Only extended 2D profiles can be produced.
4. Unlike other casting methods with hard tools, the solidified casting slides against the tool, requiring lubrication and resulting in tool wear.
5. Surface finish issues can arise, harming the product’s cosmetics.
6. Material restrictions are implicit in the equipment setup—a steel continuous casting process cannot easily adapt to aluminum, or vice-versa.
7. Continuous casting equipment requires regular and costly maintenance to ensure good performance.

What Are Examples of Continuous Casting Products?

Continuous casting is used to produce large volumes of both semi-finished and finished metal raw materials with consistent cross-sectional dimensions and high quality. Below are some examples of continuous casting products:

1. Feedstock for rolling mills to create end-use steel strips, plates, and bars.
2. Copper rods and tubes used in electrical wiring, conductors, and water/coolant handling; copper is commonly drawn down in post-processing to make coarse and fine wire conductors.
3. Aluminum billets to be used as feedstock for follow-on extrusion processes to create aluminum profiles and components.
4. Aluminum strips and more complex sections.
5. Lead sheets for radiation shielding and construction.
6. Nickel alloy and titanium billets for precision machining and forging.
7. Magnesium alloy billets and slabs are used in die casting and extrusion processing for lightweight structural applications.

What Is the Life Span of Continuous Casting Products?

There is no definitive life span estimate for continuous-cast goods. The majority of such material processing is not for finished goods but to prepare precision raw materials for follow-on processes. Also, the variety of materials suitable for continuous casting is extensive, ranging from magnesium to a wide range of alloys including stainless steel. These have a wide range of applications that require varied resilience in mechanical and fatigue strength, corrosion resistance, and heat tolerance.

How Durable Are Continuous Casting Products?

It depends. The durability of continuous-cast materials is a function of the material properties and end-use applications. Failure modes for metal parts that result from follow-on processes are: fracture, fatigue, corrosion, and abrasion. For example, a fracture is due to shock or steady overload. This is a material and process selection and a design issue. For corrosion, selecting materials that are suitable for the operational environment or applying surface finishes that improve this property is key.

Are Continuous Casting Products Heat Resistant?

It depends. The heat tolerance of continuous-cast end products—or end products manufactured from them—will depend on the material used. It is a material selection criterion that must be considered from the start. For example, high-temperature stainless steel and alloy steels can handle 900 °C and more. 

Is Continuous Cast an Effective Mass-Production Tool?

Yes, continuous casting is a great option for mass production. This is specifically effective when the process is well established/operated and the volume is sufficient for the service to be commercially viable.

What Are the Alternatives for Continuous Casting?

There are a variety of casting processes that can be seen as alternatives to continuous casting. Selection of these depends on a number of factors—in particular, the required 2D nature of the outcome and the expected production volumes demanded. Listed below are some alternatives:

1. Sand Casting: A traditional and versatile casting method that is best suited to producing complex shapes and low to medium production volumes. The method was traditionally used for billet casting, in open cavities, until displaced by continuous casting in which volumes justify the investment.
2. Die Casting: Involves injecting molten metal into a two-part steel die under high pressure. It is not well suited to forming billets for follow-on processes, however.
3. Investment Casting: This is used to create intricate and detailed components. It requires creating a wax pattern, coating it with ceramic, melting out the wax, and pouring molten metal into the mold. It's ideal for high-precision parts with complex geometries.
4. Centrifugal Casting: Uses a top-poured rotating mold, allowing centrifugal force to distribute the metal evenly along the mold walls. It's used to produce hollow cylindrical shapes as finished goods, although continuous casting can also produce this profile for a limited number of applications.
5. Gravity Die Casting: Molten metal is poured into a permanent mold made of metal, usually cast iron or steel. This is a simple method for producing light metal billets in relatively low volume.

What Is the Difference Between Continuous Casting and Casting?

Continuous casting is differentiated from all other casting techniques in that it creates an elongated 2D casting as output that can be of essentially unlimited length. Many other differences in capability apply as shown in Table 1 below:

Summary

This article presented continuous casting, explained it, and discussed how it works and its advantages. To learn more about continuous casting, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including casting and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

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