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.