Aluminum Wire Rod Production Process via Continuous Casting

Introduction

Aluminum wire rod (Aluminium Wire Rod) is one of the basic and strategic products in the supply chain of wire, cable, overhead conductors, power cables, industrial wires, electrical components, and some mechanical products. This product is typically produced as continuous coils and later reduced to smaller diameters via cold drawing. The quality of aluminum wire rod directly affects drawability, breakage rate in wire drawing lines, final wire surface quality, electrical conductivity, tensile strength, elongation percentage, and service life of the conductor. Therefore, its production is not merely a simple melting and shaping operation but a precise metallurgical, thermal, mechanical, and control process.

In today’s industry, one of the most common and economical methods for producing aluminum wire rod is the continuous casting process combined with continuous rolling, known in industrial literature as Continuous Casting and Rolling or CCR Line. This method mostly uses reverberatory furnaces and holding furnaces with melt temperatures of 700–750°C. In this method, after preparation, refining, degassing, and chemical composition control, the molten aluminum enters the continuous casting machine and is formed into a continuous cast bar or strip. To remove hydrogen, oxides, and inclusions, degassers and ceramic filters are used. Poor performance in these steps may lead to porosity, reduced conductivity, and wire rod fracture. The hot section then passes continuously into rolling stands to be converted into a round wire rod, typically 9.5 mm or 12 mm in diameter. Companies like Southwire have stated that their aluminum SCR systems are designed for continuous production of 9.5 mm wire rod from molten aluminum, with capacities ranging from a few tons up to 15 tons per hour. Finally, the wire rods are collected into coils weighing 1.5, 2, and 2.5 tons.

Position of Aluminum Wire Rod in the Electrical and Cable Industries

The most important application of aluminum wire rod is in the electrical and cable manufacturing industry. Due to its low density, good electrical conductivity, more economical price compared to copper, good formability, and high-scale production capability, aluminum has become one of the main metals for producing electrical conductors. In overhead power transmission and distribution conductors, aluminum cables, self-supporting cables, reinforced aluminum wires, and certain electrical products, the quality of the primary wire rod plays a decisive role.

For electrical wire production, purer alloys such as the 1xxx series, especially 1350 aluminum, are widely used. ASTM B230/B230M, for example, covers 1350-H19 aluminum as hard-drawn round aluminum wire for electrical use, noting that 1350 aluminum was previously known as EC Aluminum. According to ASTM B193, electrical conductivity should be at least 61.0% IACS, with tensile strength between 80–120 MPa. This indicates that in producing wire rods for the electrical industry, not only the product shape matters, but also chemical composition, electrical resistance, mechanical properties, and final temper must be controlled.

In some advanced lines, it is possible to produce wire rod from different aluminum grades and various alloys. Continuus-Properzi, as a well-known supplier of aluminum CCR lines, has introduced lines for producing aluminum wire rod from different alloy series, including 1xxx to 8xxx. Therefore, although EC Grade wire rod is very common for the electrical industry, continuous casting technology can also be used to produce other alloy grades; however, each alloy has its own process window and metallurgical sensitivities.

Concept of Continuous Casting in Aluminum Wire Rod Production

In traditional casting, molten metal is poured into individual molds, and after solidification, a separate piece or ingot is obtained. But in continuous casting, the goal is for the melt to enter the mold or casting wheel without interruption and produce a continuous product. This product can be in the form of a strip, narrow ingot, trapezoidal section, or a section suitable for rolling. In aluminum wire rod production, continuous casting is usually the first stage of a combined line; the cast product is not yet the final wire rod, but a hot semi-finished section that must immediately enter continuous rolling.

In typical aluminum wire rod production lines, the melt from the holding furnace enters the gating system, tundish, or launder, and is then directed to the casting machine. In the casting machine, the metal contacts a cooled mold or wheel and transforms from liquid to solid. Controlling casting speed, melt temperature, cooling intensity, melt level, flow uniformity, and mold conditions are all important to prevent cracks, shrinkage, segregation, porosity, and surface defects.

Some industrial manufacturers introduce the steps of producing 9.5 mm wire rod as melting and melt holding, fluxing and degassing, continuous casting of a trapezoidal section, continuous rolling, and coiling. This sequence shows that the final quality of the wire rod begins from the melt stage, and rolling cannot correct all metallurgical problems created during casting.

Raw Material Preparation and Furnace Charging

The aluminum wire rod production process begins with selecting and preparing raw materials. Raw materials may include primary aluminum ingots, clean production returns, controlled scrap, alloying elements, and master alloys. For electrical wire rod production, using high-purity raw materials and controlling harmful elements is very important because elements such as iron, silicon, titanium, vanadium, or certain impurities can affect electrical conductivity and mechanical behavior.

After preheating, raw materials are charged into the melting furnace. The furnace can be flame, induction, gas, or a combination. After melting, the melt is brought to the proper temperature and usually transferred to a holding furnace. The role of the holding furnace is to stabilize temperature, homogenize composition, and provide a stable melt flow for the casting line. At this stage, the operator must avoid excessive oxidation of the melt surface, moisture ingress, scrap contamination, improper mixing, and temperature fluctuations.

One common error in low-quality lines is using contaminated scrap or returns containing oil, moisture, paint, coating, or excessive oxides. At high temperatures, these contaminants can generate gas, oxides, dross, and impurities. In producing wire rod suitable for drawing, even a small amount of contamination can cause frequent breaks in the drawing line, reduced surface quality, and loss of electrical properties.

Most Important Factors Affecting Wire Rod Quality

1. Hydrogen content of the melt: This is the biggest enemy of aluminum quality. Hydrogen dissolves in the melt but is released during solidification, causing internal porosity, microscopic voids, and loss of strength, leading to sudden breaks during drawing, internal failure, and reduced elongation.

2. Aluminum oxide (Al₂O₃): Aluminum oxides are very hard, and their entry into the wire rod causes die scratching, wire breakage, and increased scrap. These appear as lines or dark particles in metallographic examination.

3. Iron and Silicon: Two very important elements in EC wire rod. Increasing iron raises strength but lowers conductivity. Increasing silicon also reduces conductivity and decreases drawability.

Causes of Reduced Wire Rod Conductivity:
Conductivity is one of the most important quality indicators, and in standard wire rod, it should be about 61–62.5% IACS.
Factors reducing conductivity can include iron impurities, silicon impurities, copper, magnesium, and zinc elements, and finally improper cooling, which leads to an undesirable metallurgical structure.

Chemical Composition Control and Alloying

After melting, the chemical composition of the melt must be examined with precise analysis. A quantometer or spectrometry methods are typically used. If the final product is EC Grade wire rod, the main focus is on aluminum purity and limiting elements harmful to electrical conductivity. If the product is from alloy series such as 6xxx, 8xxx, or other families, alloying elements must be added and controlled within standard ranges.

Alloying must be performed so that added elements are completely dissolved and dispersed in the melt. Improper mixing can cause compositional segregation and property variations along the coil. For example, if one part of the coil has a higher amount of alloying element than another, its behavior in drawing, annealing, or final use will differ. Therefore, controlled stirring, sufficient holding time, proper temperature, and periodic sampling are essential.

In advanced lines, chemical analysis data is connected to the quality control system, and the heat number, coil number, chemical composition, casting temperature, line speed, and later test results are recorded in a traceability system. Such traceability is very important for sensitive industries, especially cable and conductor manufacturers.

Aluminum Melt Degassing

One of the most important steps in producing high-quality aluminum wire rod is melt degassing. Molten aluminum can dissolve hydrogen, and during solidification, the decrease in hydrogen solubility can cause porosity, shrinkage, and internal defects. Research published in Materials Science and Engineering: B explains that hydrogen is a harmful gaseous element in aluminum and its alloys, and high levels can cause porosity and reduced mechanical properties such as tensile strength, elongation, and fatigue resistance.

Degassing is usually performed by injecting inert gas such as argon or nitrogen through a graphite rotor. The rotor breaks the gas into very fine bubbles. As these bubbles rise through the melt, they absorb dissolved hydrogen and carry it to the surface. The finer the bubbles and the more uniform their distribution, the greater the gas-melt contact area and the higher the degassing efficiency.

Along with degassing, fluxing is also done to help separate oxides, impurities, and dross. However, flux use must be controlled because residual undesirable compounds or unwanted reactions can themselves become sources of defects. In modern lines, the goal is for the melt to be as clean, low-gas, and uniform as possible before entering the casting machine.

Melt Filtration and Inclusion Removal

Even if the chemical composition of the melt is correct, the presence of oxide inclusions, refractory particles, oxide films, fine dross, and non-metallic impurities can severely reduce wire rod quality. Inclusions may elongate during rolling and act as stress concentration points during cold drawing. The result can be wire breakage, surface lines, loss of ductility, and reduced surface quality.

To remove these impurities, ceramic filters, foam filters, online filtration systems, and proper melt flow path design are used. In some production lines, after degassing, the melt passes through a filter and then enters the tundish or feeding system of the casting machine. Articles related to aluminum defects have also emphasized that molten aluminum and its alloys are highly reactive, and the formation of oxide layers and defects such as bifilms can act as sources of cracks and hydrogen porosity.

Effective filtration depends not only on the presence of a filter but also on melt temperature, flow rate, avoidance of excessive turbulence, proper sealing, prevention of re-oxidation, and timely filter replacement. If the melt flow is turbulent, even after filtration, oxide films can reform. Therefore, the melt transfer path must be designed to be smooth, stable, and controlled.

Melt Entry into the Continuous Casting Machine

After melt preparation, the liquid metal is directed via a launder or refractory channel toward the casting machine. Temperature and flow control are very critical here. Excessively high temperature can increase oxidation, gas absorption, coarse structure, and shrinkage defects. Too low a temperature can reduce fluidity, cause premature solidification, flow instability, and surface defects or line stoppage.

In many CCR lines, the casting machine is of the wheel-and-belt type. The melt enters the groove of the casting wheel, and a steel belt or mold system creates a closed space for section formation. The wheel and mold are water-cooled, and the melt solidifies gradually along the wheel’s path. The output of this section is a solid, hot section, usually trapezoidal or near-trapezoidal, ready for rolling.

Solidification control at this stage is very important. If the initial solid shell is not strong enough, tearing, melt leakage, or deformation may occur. If solidification is too fast and unbalanced, thermal stress, surface cracks, internal cracks, or improper structure may result. The goal is to produce a cast section with uniform structure, proper surface, and adequate temperature for subsequent rolling.

Cutting, Straightening, and Preparation of the Cast Section

After exiting the casting machine, the cast section typically passes through auxiliary equipment such as shears, straighteners, descalers, or a guiding system. In some lines, the initial or unsuitable part of the product is cut off so that only the stable, sound section enters the rolling mill. If the section surface has burrs, thick oxide, cracks, or discontinuities, these defects will be elongated and exacerbated during rolling.

Straightening before entry into the rolling mill is important to prevent impact on the stands, abnormal roll wear, and dimensional fluctuations. The section must be centered in the roll pass and enter the first stand at the proper temperature. If the section temperature is below the optimal range, rolling force increases, and the risk of cracking or overloading equipment rises. If the temperature is too high, dimensional and surface control becomes more difficult.

Continuous Rolling and Conversion of Cast Section into Wire Rod

In the rolling stage, the hot cast section passes through several rolling stands, its cross-sectional area gradually decreases, and its length increases. Pass design must allow gradual, stable, and controlled deformation. At the end, the product is formed into a round wire rod of a specified diameter, typically 9.5 mm.

Rolling is not just a cross-section reduction operation; it also plays an important metallurgical role. Hot deformation can refine the cast structure, modify grains, partially compact very fine porosity, and improve mechanical properties. However, if defects such as large inclusions, severe porosity, severe segregation, or casting cracks exist, rolling cannot completely eliminate them.

In industrial lines, parameters such as entry temperature into the rolling mill, stand speeds, reduction per pass, interstand cooling, lubrication, roll condition, mechanical vibrations, and loop control settings must be precisely monitored. Any small fluctuation in these parameters can cause ovality, surface lines, diameter variation, waviness, or loss of drawability.

Cooling, Coiling, and Packaging

After the wire rod exits the last rolling stand, it must be cooled in a controlled manner. Cooling rate and method affect mechanical properties, residual stresses, and surface quality. Then the wire rod enters the coiling system. Coiling must be regular, uniform, and without severe twisting because an irregular coil will cause problems later, especially when payed off on a drawing machine.

After production, wire rod coils are typically weighed, labeled, sampled, strapped, and packaged. Care must be taken during strapping to avoid scratches and damage to the wire rod. Additionally, information such as heat number, coil number, alloy grade, diameter, weight, production date, test results, and customer name may be recorded on a label. In professional production, traceability from raw material to final coil is essential so that if a problem occurs, the root cause can be identified and corrected in subsequent production.

Quality Control of Aluminum Wire Rod

Quality control of aluminum wire rod must be multi-layered. The first layer is melt control: chemical analysis, melt temperature, hydrogen content, dross condition, melt cleanliness, and filtration quality. The second layer is process control: casting speed, casting temperature, cooling water pressure and flow rate, entry temperature to rolling, stand speeds, and equipment condition. The third layer is final product testing.

Typical tests include diameter measurement, ovality check, surface quality inspection, tensile test, elongation percentage, twist or bend test, electrical conductivity or resistance measurement, microscopic structure examination, and sometimes special tests for inclusions or porosity. For electrical products, electrical resistance and conductivity are especially important. Standards related to 1350 aluminum wire for electrical use impose requirements on dimensions, mechanical properties, and electrical resistance.

One important indicator of wire rod quality is its behavior on the drawing line. A wire rod that looks satisfactory but breaks frequently during drawing likely has an internal problem: inclusions, porosity, improper structure, non-uniform hardness, or surface defects. Therefore, professional manufacturers usually also consider feedback from cable manufacturers and wire drawers as part of operational quality control.

Common Defects in Aluminum Wire Rod Production

Aluminum wire rod defects can be divided into several groups. The first group is melt-related defects: inclusions, oxides, hydrogen porosity, dross, and out-of-spec chemical composition. The second group is casting defects: surface cracks, internal cracks, shrinkage cavities, segregation, section instability, and rough surface. The third group is rolling defects: surface lines, peeling, ovality, irregular diameter, deformation cracks, and roll marks. The fourth group is coiling and handling defects: twisting, crushing, surface contamination, and scratches.

To reduce these defects, a preventive approach is necessary. Clean charge, dry raw materials, furnace temperature control, proper degassing, effective filtration, smooth melt flow path design, precise mold cooling adjustment, regular roll maintenance, and controlled coiling conditions all play a role. Scientific articles on cast aluminum show that defects such as bifilms and porosity can have detrimental effects on the tensile and fatigue properties of aluminum components.

Main Causes of Wire Rod Breakage During Drawing

1. Porosity-induced breakage: Indications are rough fracture surface and voids in the fracture cross-section; the cause can be improper degassing.

2. Oxide-induced breakage: Indications can be brittle fracture and sudden breakage; the cause can be poor filtration.

3. Casting crack-induced breakage: Indications are breaks at recurring points; the cause is improper casting wheel adjustment and inappropriate speed.

4. Rolling-induced breakage: The main cause is excessive reduction in one pass and improper roll adjustment.

Advantages of Continuous Casting Production

Continuous casting has several important advantages over traditional methods. First, continuous production increases productivity and reduces line stoppages. Second, due to the elimination or reduction of intermediate steps, energy consumption and production costs decrease. Third, a product with long length and coiling capability is produced, which is very suitable for the wire and cable industry. Fourth, direct connection of casting to rolling allows use of the remaining heat of the cast section and reduces reheating requirements.

Another advantage is better product uniformity when the process is properly controlled. When temperature, speed, composition, and cooling are stable, the final product can have more repeatable properties. Southwire has cited advantages such as continuous production from melt, product quality, low operating cost, and the ability to produce EC and alloy grades for its aluminum systems.

However, this method requires high initial investment, skilled personnel, precise process control, and regular maintenance. If the line is not properly adjusted, the high production speed can produce a large volume of defective product in a short time. Therefore, the advantage of continuous casting is realized only when process control and quality control are developed to the same level as production capacity.

Role of Automation in Modern Lines

Modern aluminum wire rod production lines are heavily dependent on automation systems. Temperature control, melt level, casting wheel speed, cooling water flow rate, rolling stand speeds, system pressures, and coiling status are typically controlled via PLCs, sensors, and monitoring systems. Automation reduces human error, increases production stability, and records detailed process data.

Properzi, in introducing its aluminum lines, also mentions precise automation, technical support, and the ability to maintain stable parameters for wire rod and wire. In industrial production, it is this stability that makes the difference between a reliable coil and a high-risk coil. A manufacturer that records and analyzes line data can find the cause of defects more quickly and prevent their recurrence.

Today, some advanced lines use online monitoring systems for diameter, surface temperature, surface defects, and even data analysis for equipment failure prediction. Such tools allow the production line to move from a reactive to a preventive mode; that is, before a serious failure or defect occurs, early warning signs are identified.

Conclusion

The process of producing aluminum wire rod by continuous casting is a precise and continuous chain of metallurgical and mechanical operations. This process begins with raw material selection and melting, continues with chemical composition control, degassing, filtration, and controlled melt transfer, then solidifies into a cast section in the continuous casting machine, and finally is converted into the final wire rod through continuous rolling, cooling, and coiling.

Final wire rod quality does not depend on only one stage. If the melt is contaminated, if hydrogen is not properly removed, if inclusions enter the mold, if cooling is unstable, if rolling passes are not designed correctly, or if coiling is done improperly, the final product will have problems in the drawing line or in service. Therefore, producing high-quality aluminum wire rod requires a systemic view, proper equipment, skilled operators, precise quality control, and complete recording of production data.

In conclusion, continuous casting is not just a faster production method; it is an industrial technology for sustainable, economical, and controllable production of aluminum wire rod. This technology creates the most value when melt treatment, process control, precise rolling, quality tests, and data management are integrated.