Manufacturing & Processing

Manufacturing Processes

Basic Oxygen Steelmaking (BOS) Process

Basic oxygen steelmaking is a multistep process that involves the use of pure oxygen to produce steel from molten iron. Also known as oxygen conversion steelmaking, it leverages oxygen to change the carbon ratio of steel. Basic oxygen steelmaking involves blowing pure oxygen into molten pig iron. With a higher oxygen content, the ratio of carbon to other elements — including iron — drops.

How is basic oxygen steelmaking performed? This common steelmaking process begins with pig iron. The pig iron is smelted in a blast furnace, after which it’s poured into a ladle. From there, it’s blasted with oxygen as a form of pre-treatment. The next step of basic oxygen steelmaking involves charging.

Charging involves filling the furnace with ingredients. As you may know, steel contains more than just iron; it contains carbon, and in some cases, other elements. These ingredients are added to the furnace during basic oxygen steelmaking.

Now it’s time for the pure oxygen. The molten steel-filled vessel is raised and exposed to a lance that contains about a half-dozen nozzles, after which it’s injected with pure oxygen. The multi-nozzle lance essentially blows pure oxygen over the molten steel, thus allowing the carbon to dissolve while simultaneously creating excessively high temperatures. This step, in fact, can produce temperatures of over 1,700 degrees celsius.

Fluxes are then added to the steel-filled vessel, which are responsible for the slag. The slag essentially absorbs impurities from the steel. The slag is then separated from the steel. Lastly, the steel is allowed to cool. There are different types of basic oxygen steelmaking, but most of them involve these steps.

Steel manufacturing process

Recycling

42% of steel produced is recycled material
Re-melting proportion of steel scrap is constrained by availability. Availability can sometimes be defined as cost effective recovery.
Iron and steel are the world's most recycled materials, and among the easiest materials to reprocess, as they can be separated magnetically from the waste stream. Recycling is via a steelworks: scrap is either re-melted in an electric arc furnace (90-100% scrap), or used as part of the charge in a Basic Oxygen Furnace (around 25% scrap). Any grade of steel can be recycled to top quality new metal, with no 'downgrading' from prime to lower quality materials as steel is recycled repeatedly.
Globally around 85% of construction steel is currently recovered from demolition.

In 2013, across the world there was approximately 1606 Mt (that is 1 606 000 000 tonnes) of steel produced. To create 1 tonne of steel, approximately 18.68 GJ (that is 18 680 000 000 Joules) of energy is required. Approximately 70% of that energy is consumed using the Basic Oxygen Steelmaking Process.

This is a lot of energy. Steel making companies are developing new ways to reduce emissions during their steel making process. The video below explains current research in to more environmentally friendly methods of producing steel.

Steel making is responsible for around 8% of all global emissions

The method described in the video above is still in development. Here is what they have posted on their website about the importance of developing a more sustainable solution.

We know it can work in a lab, so our next step is to scale up from testing “grams” to “kilograms”. We have more work to do to prove it can work, but we’re optimistic this new technology could play an important part in reducing carbon emissions across the steel industry. Here are some of the reasons why:

It doesn't create fossil fuel emissions

In this new process, iron ore fines are mixed with sustainable raw biomass material (like agricultural waste) and heated using a combination of gas released by the biomass and high efficiency microwaves, turning the iron ore into metallic iron.

Fast growing biomass offers a carbon-neutral energy source

While the biomass will release carbon dioxide when it’s used, this is offset by using fast-growing plants as the biomass source. This is because about the same amount of carbon dioxide is absorbed in photosynthesis when the plants are regrown. If you just used plants and didn’t regrow them, or if the plants grew slowly – like trees in old growth forests – the CO2 would stay in the atmosphere. So using a fast-growing, sustainable biomass source is important.

If it's done right, it could be a truly sustainable solution

We don’t want to solve one problem and cause another. We know from talking to environmental groups that we need to consider the kind of biomass we use and how it’s produced and transported. So, we’re including this as part of our research too. And we would never use biomass that supports the logging of old growth native forests.

The biomass used in this process doesn't include food sources

Our process doesn’t, and can’t, use food such as sugar and corn. The parts you can’t eat – the straw, stalks and leaves – contain material called lignocellulose which has the type of carbon the process needs.

It could help our customers and the wider steel industry

It’s a global challenge and we want to play a part in finding solutions.

Hot Rolled vs. Cold Rolled

Hot rolled steel

Hot rolled steel is easier to make, to shape and form. It has its source in a mill process involving rolling the steel at high temperature. It starts from a piece of still billet which is heated up 1700 degrees Fahrenheit (926° Celsius) and then the steel is rolled through the mill into the particular shape. The whole process is done at high temperature and at the end is being cooled down. The cooling down may cause the steel to shrink and therefore there is less control over the final size and shape.

Hot rolled steel is commonly used when precise shapes and tolerances are not essential. Hot rolled steel comes with a scaly surface, slightly rounded edges and corners and the surface is non-oily. Cold rolled steel has an oily or greasy finish, very smooth surface, and very sharp edges.

Advantages

Easier to make: heat it up, push through, cool down and that’s it!
Cheaper than cold rolled
Hot rolled steel is allowed to cool at room temperature and it’s free from internal stresses that can arise from quenching or work-hardening processes
Most popular shapes are hot-rolled (UC, UB, SHS, RHS, PFC, flats etc.)

Disadvantages

dimensional imperfections caused by heating (expanding) and cooling down (shrink, warpage)
rough texture on a surface, need to be removed and buffed before painting
Slight distortions

Cold rolled steel

While hot rolled steel is heated then cooled, cold rolled steel is heated and cooled at the room temperature and then rolled after again. The steel is processed further in cold reduction mills, where the material is cooled (at room temperature) followed by forming the material by either press-braking or cold roll forming to achieve the desired shape.

The term “rolled” is often used just to describe a range of finishing processes such as turning, grinding, and polishing, each of which modifies existing hot rolled stock into a more refined product. Technically, “cold rolled” applies only to sheets that undergo compression between rollers. But forms like bars or tubes are “drawn” not rolled. Hot rolled bars and tubes once cooled, are processed into what we call “cold finished” tubes and bars.

Advantages

accurate shape (consistent and straight)
a wider range of surface finishes
a smooth and shinier surface
bars are true and square and have well-defined edges and corners
Tubes have better concentric uniformity and straightness.

Disadvantages

more expensive
fewer shapes available cold-rolled (sheets, box section shapes: CHS, SHS, RHS)
additional treatments can create internal stress within the material; this can cause unpredictable warping if the steel is not stress relieved prior to cutting, grinding, or welding.

Hot rolled vs. cold rolled

Aluminium Production

Aluminium is at the heart of modern life, from the smartphone in your hand, to the plane you fly in, to the buildings where you live and work. As economies grow and living standards rise, industry experts expect that demand for aluminium will increase.

You can learn more about Aluminium on the following website - https://www.ega.ae/en/products/

These are the basic steps for mining and producing Aluminium:

Step 1: Bauxite Mining - The production process for aluminium starts with the mining of bauxite ore. Layers of bauxite are generally found near the surface so it is extracted through open-cast mining. Around 90% of the world's resources are in tropical & sub-tropical regions
Step 2: Alumina Refining - Bauxite is refined into alumina using the Bayer process. Two or three tonnes of bauxite are required to produce one tonne of alumina. In the digestion stage, hot caustic acid is added to the bauxite to dissolve the aluminium-bearing minerals in the bauxite. Clarification separates bauxite solids from the pregnant liquor via sedimentation. In the precipitation stage, alumina crystals are recovered from the liquor via crystallization. Calcination is a roasting process to remove the remaining water.
Step 3: Aluminium Smelting - Alumina is smelted into aluminium using the Hall-Heroult process. It takes two tonnes of alumina to produce one tonne of aluminium. Alumina is poured into special reduction cells called pots with an electrolytic bath of molten salt called cryolite at temperatures around 960 degrees Celsius. An electrical current is then projected into the mixture at 400KA or above. This current then breaks the bonds between aluminium and oxygen atoms in alumina, resulting in liquid aluminium settling at the bottom of the reduction cell.
Step 4: Casting - Aluminium is then transferred to the cast house, where it is made into products using several different methods. Alloys are added into many products, according to customer specifications, before the solidification stage. In re-melt casting aluminium, at a temperature of 700 degree Celsius, is poured into moulds. The moulds are cooled and the aluminium solidified before being packed and shipped to the customer. EGA also supplies nearby customers in Khalifa Industrial Zone Abu Dhabi. Receiving aluminum as molten metal eliminates the need to use high energy to re-melt it before use. We transfer molten metal by truck in preheated 14.5 tonne crucibles which can keep the metal liquid for 18 hours at temperatures of around 780 degrees Celsius.

Bauxite Mining Process

Aluminium is the most abundant metal in the Earth’s crust, occurring as bauxite which contains aluminium oxide. The first step in producing aluminium is mining this ore. Bauxite occurs mainly in tropical and sub-tropical areas, like Africa, the Caribbean, South America and Australia.

Australia is the largest producer of bauxite, with five large mines supplying around 30 per cent of global production.

Bauxite mining has five steps:

Preparation of Mining Area - Pre-Mining Surveys are conducted in all new mining areas, to provide information on flora and fauna, to map the extent of any disease, such as dieback, and to identify any significant cultural heritage sites. If rare or protected species or significant sites are present, they are avoided, or management plans are developed to minimise the impact of mining on them.

Bauxite Mining - Scrapers and small excavators are used to remove the remaining overburden and expose the caprock. Depending on the depth of the caprock, it can be broken by blasting, or simply removed with scrapers and excavators. The bauxite is then mined using excavators or loaders to load the bauxite onto haul trucks and transported to the crusher. Several pits are usually mined simultaneously in order to produce a consistent grade of ore.

Crushing - A crusher is used to break the ore down to a smaller size suitable for transport. The crusher is made up of a number of components that include a vibrating screen, a jaw crusher and sizers. Fine material drops through the vibrating screen while larger material passes over the screen to the jaw crusher that breaks up the large rocks. The material that passes through the vibrating screen and jaw crusher is collected and passed through the sizer that further reduces the size of the material before it is transported via conveyor or ship to a refinery. The final size of the crushed bauxite ore is approximately 7.5cm or less in diameter.

Ore Conveyors - The crushed bauxite is transported via conveyor belts and railway systems, either to the refinery or shipping terminal.

Rehabilitation - After mining, the edges of the pit are smoothed. Topsoil and overburden are returned to the site and the earth is prepared to prevent soil erosion and for seeding and planting. The logs and rocks that were put aside during clearing are then returned to provide shelter and nesting sites for animals.

Alumina Refining

Alumina is a white granular material, a little finer than table salt, and is properly called aluminium oxide. Aluminium does not occur as a metal but must first be refined from bauxite into alumina. Approximately two tonnes of alumina are required to produce one tonne of aluminium.

Australia is the second largest producer of alumina in the world, with around 15 per cent of global production from six alumina refineries. As water is a key input for refining bauxite into alumina, Australian alumina refineries are located in areas with reliable water supply.

The Bayer Refining Process used by alumina refineries worldwide involves four steps:

digestion;
clarification;
precipitation; and
calcination.

Aluminium Smelting

Australia is the world’s sixth largest producer of aluminium and has 4 operating smelters. As electricity is a key input in aluminium smelting, smelters are usually located in areas with reliable, historically low-cost electricity.

The Australian industry continuously focuses on improving electricity efficiency, while also leading the global industry in controlling direct greenhouse gas emissions.

The Hall- Héroult process is the main method of smelting aluminium used today and consists of five steps:

Adding Bath and Alumina - Inside a pot, alumina is dissolved in a “bath” of molten cryolite (sodium aluminium fluoride) and other materials.
Potline - A pot is a large rectangular cell, lined with carbon blocks and insulating bricks. This lining forms the “cathode”. A potline is a long building, or collection of buildings, which contain a series of “pots”, or large electrolytic cells, in which aluminium is made.
Anode - Anodes are used to conduct electricity into the smelting cells/pots in the pot room. Anodes are consumed in the smelting process and the remaining portions (known as butts) are recycled. Anode Bake - Anodes are attached to rods and suspended into the electrolytic cells in the pot room where they are slowly consumed in the aluminium smelting process. Carbon anodes, made from petroleum coke and pitch, are often manufactured on site.
Electrolysis - A high electric current is passed through pots via the anode. The current flows continuously from the anode (positive) through alumina/cryolite mix to the lining of the pot (negative) and then onto the next pot.

Electricity maintains the temperature of the process at about 950°C and enables the alumina to split into aluminium and oxygen.
Tapping - At regular intervals the molten aluminium is tapped from the pots and transported to the casthouse.
Primary Casting - The molten aluminium is cast at a temperature of just over 700°C to form ingots, slabs, billots and t-bars.

Aluminium Recycling

Aluminium is the most abundant metal in the earth’s crust. It is strong, durable, flexible, impermeable, lightweight, corrosion resistant and 100% recyclable. Approximately 75% of the aluminium ever produced is still in use today as it can be recycled endlessly without compromising any of its unique properties or qualities.

Aluminium’s life cycle provides significant benefits through recycling, saving 95% of the energy it would take to make new aluminium metal.

New Scrap is surplus material that arises during the manufacture and fabrication of aluminium products, up to the point where they are sold to the final consumer. For example, offcuts of aluminium sheet or extrusions are considered new scrap. Sometimes, this new scrap can be safely recycled by aluminium smelters as its composition is known.

Old Scrap is material that has been used by the consumer and subsequently discarded. For example, used beverage cans, window frames, electrical cabling and car cylinder heads are all considered old scrap. Aluminium smelters are unable to safely accept this old scrap as its composition is usually unknown and it can be contaminated.

As aluminium smelters cannot safely accept general contaminated scrap, recycling in Australia is largely carried out by specialist metal recyclers. A list of specialist metal recyclers is shown below.

For more information about Aluminium production, follow the links below:

See Case Studies of where aluminium smelters have been trialling innovative recycling solutions, including Boyne Smelter which has innovated to become Australia’s largest aluminium can recycling facility.
The Australian Aluminium Council, as part of the International Aluminium Institute, contributes to the global effort to increase aluminium recycling rates and improve sustainability. For more information visit the International Aluminium Institute.
Here is a link to more information on Scrap Aluminium Recycling in Australia

2. Extruding vs. Drawing

Extrusion

Metal Extrusion is a metal-forming manufacturing process in which a cylindrical billet inside a closed cavity is forced to flow through a die of the desired cross-section. These fixed cross-sectional profile extruded parts are called “Extrudates” and are pushed out using either a mechanical or hydraulic press. The most commonly extruded materials are Aluminium, Copper, Steel, Magnesium, and Lead.

Extrusion, in the majority of cases, is a hot working operation but can also be carried out in cold mode. Hot extrusion is a process in which wrought parts are formed by forcing a heated billet through a shaped die opening.

As the name implies, the process is performed at high temperatures, which depend on the material being extruded. For steel the temperatures range from 1,100 deg C to 1,260 deg C, and for Aluminium alloys at around 450 deg C to 500 deg C. For hot working, the billet temperature is typically higher than that needed to sustain strain hardening during deformation. This is normally greater than 60 % of the absolute melting temperature of the metal.

Characteristics of metal extrusion

Able to create complex cross-sections and will be uniform over the entire length of the extrudates
Factors that affect the quality of extrusion are die design, extrusion ratio, billet temperature, lubrication, and extrusion speed. Check out the detailed design guide for metal extrusion, “How to design parts for direct metal extrusion”, to understand the 5 key design variables of metal extrusion and design for manufacture (DFM) extrusion design tips.
Like any other metal-forming process, it can be either hot or cold. However, the process is generally carried out at elevated temperatures to reduce the extrusion force and improve the material’s ductility.
Low cost due to reduced raw material wastage and high production rate
Brittle material can be deformed without a tear as it only exerts compressive and shear forces in the stock part

Parts that are formed have an excellent surface finish which minimizes post-processing machining
Metal extrusion tends to produce a favourable elongated grain structure in the direction of the material.
The minimum wall thickness of ~1mm (aluminium) to ~3mm (steel) could be achieved.

Extrusion Defects

Depending on the material condition and process variables, extrudates can develop many defects that could affect the quality of the end product. These defects can be grouped under the following three defects.

Surface cracking
Piping
Internal cracking

Extrusion process

Drawing

Among the most common metalworking techniques is metal drawing, a process that entails pulling a metal through a mold or die. Like the similar extrusion process, during which a metal is pushed through a die using a draw punch.

Metal drawing can result in a metal with a depth that equals or exceeds its width or radius. Sometimes referred to as deep drawing, this variation of metal drawing can produce high-strength, low-weight products while offering significant cost savings, making it an ideal solution for many manufacturers.

How does it work?

Metal drawing is generally performed cold, which means that the metal to be shaped is kept at room temperature rather than heated. A cold metal drawing process ensures greater accuracy in the drawn product’s tolerances, better grain structure, good surface finishes, and overall improvement in its properties.

During metal drawing the blank, is inserted through the die and mechanically gripped in order to pull it through. As it travels through the die, the workpiece will take the shape of a hollow box-shaped or cylindrical vessel. The sides may be straight, tapered, curved, or a combination of all three depending on the shape of the die. The workpiece can then be drawn through an additional series of dies in order to further reduce its diameter and increase its length with only minimal changes to the thickness of its walls.

Benefits

In comparison to other manufacturing processes, metal drawing much lower tool construction costs. Aside from its reduced operational costs, it also can yield lightweight products without compromising their strength or integrity. The process is also especially good for creating cylindrical parts and components.

Metal drawing is particularly well-suited to high-volume production runs. Because it can be performed with automated machinery, it can continue for long periods with little downtime and minimal upkeep.

3. Shaping

Forging

Forging is a manufacturing process involving the shaping of metal using localised compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it is performed: cold forging (a type of cold working), warm forging, or hot forging (a type of hot working). For the latter two, the metal is heated, usually in a forge. Forged parts can range in weight from less than a kilogram to hundreds of metric tonnes. Forging has been done by smiths for millennia; the traditional products were kitchenware, hardware, hand tools, edged weapons, cymbals, and jewellery.

Drop forging is a forging process where a hammer is raised and then "dropped" into the workpiece to deform it according to the shape of the die. There are two types of drop forging: open-die drop forging and impression-die (or closed-die) drop forging. As the names imply, the difference is in the shape of the die, with the former not fully enclosing the workpiece, while the latter does.

Drop forging process

Coining

The coining process is described as the squeezing of metal as it is held in closed dies. The work piece is placed in the die. A movable punch within the die cold works the material and forms intricate features. The coining process is typically used to produce coins, medallions and similar products.

Metal coining is a forging process by which very fine and intricate details can be created on the surface of a work piece. Coining may be used to control surface quality and detail on parts. Metal coining is often a finishing process for manufactured products. This is a flashless, precision forging operation, that due to the required accuracy of the process, is performed cold. Lubrication is not used, since any substance between the die and work would hinder the reproduction of the most accurate details that are to be formed on the work's surface. In the coining process, a large amount of force is exerted on the forging, over a short distance. Mechanical presses are often used for these operations.

Casting

In metalworking and jewelry making, casting is a process in which a liquid metal is delivered into a mold (usually by a crucible) that contains a negative impression (i.e., a three-dimensional negative image) of the intended shape. The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part (the casting) is extracted. Casting is most often used for making complex shapes that would be difficult or uneconomical to make by other methods.

Casting processes have been known for thousands of years, and have been widely used for sculpture (especially in bronze), jewelry in precious metals, and weapons and tools. Highly engineered castings are found in 90 percent of durable goods, including cars, trucks, aerospace, trains, mining and construction equipment, oil wells, appliances, pipes, hydrants, wind turbines, nuclear plants, medical devices, defence products, toys, and more.

Traditional techniques include lost-wax casting (which may be further divided into centrifugal casting, and vacuum assist direct pour casting), plaster mould casting and sand casting.

The modern casting process is subdivided into two main categories: expendable and non-expendable casting. It is further broken down by the mould material, such as sand or metal, and pouring method, such as gravity, vacuum, or low pressure

Expendable casting

Expendable mold casting is a generic classification that includes sand, plastic, shell, plaster, and investment (lost-wax technique) moldings. This method of mould casting involves the use of temporary, non-reusable moulds.

Non-expendable casting

Non-expendable mold casting differs from expendable processes in that the mold need not be reformed after each production cycle. This technique includes at least four different methods: permanent, die, centrifugal, and continuous casting. This form of casting also results in improved repeatability in parts produced and delivers near net shape results.

Die casting

The die casting process forces molten metal under high pressure into mold cavities (which are machined into dies). Most die castings are made from nonferrous metals, specifically zinc, copper, and aluminium-based alloys, but ferrous metal die castings are possible. The die casting method is especially suited for applications where many small to medium-sized parts are needed with good detail, a fine surface quality and dimensional consistency.

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