The Production Process
Our production process is clearly structured and efficiently designed.
On this page, we show you how we produce resource-efficient structural steel.
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The SWT Scrap Yard.
Scrap is the starting material
Our most important raw material for the production of steel beams is steel scrap.
Our section steel is produced 100% from scrap. It originates from within a 300 km radius around our plant – sustainably, efficiently, and regionally.
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Upon delivery, we inspect truck and railcar loads for potential contaminants. After this inspection, the scrap is moved to our scrapyard, where the technological process of steel processing begins.
Our scrapyard is larger than two football fields. With its storage capacity, it ensures the continuous supply of raw materials to our steel mill, which requires approximately 3,500 tons of scrap every day.
Huge grabs and magnets fill the scrap baskets with a mixture of different types of scrap. Each scrap basket has a filling capacity of approximately 110 m³. The scrap baskets are transported by radio-controlled rail vehicles. The rail vehicle then proceeds to the furnace hall lock. This is the gateway to our modern electric steel plant.
The Electric Steel Plant.
Welcome to the Melting Operation
The scrap is melted in the DC electric arc furnace for further processing. In doing so, we consume as much energy as a city with 100,000 inhabitants.
The next station is the ladle furnace. Here, by adding alloying agents, we produce the steel grade ordered by the customer.
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To produce a batch of liquid steel, the contents of two scrap baskets are charged into the electric furnace. We require electrical and chemical energy to melt the scrap. Our electric furnace operates on the direct current principle and produces approximately 120 tons of liquid steel in 50 minutes. The energy input is via a graphite electrode with a diameter of 750 mm. The furnace vessel itself has a diameter of 6.5 meters and is equipped with natural gas-oxygen burners to support the melting process.
During the melting of the scrap, slag is continuously generated in the so-called flat bath phase. This important by-product is separated from the steel and converted into an important substitute building material by an external service provider.
After reaching the tapping temperature of approximately 1,620 °C, the liquid steel is filled into a ladle. The adjustment of the steel composition then begins at the ladle furnace. For this purpose, samples are taken from the molten steel and analyzed with a spectrometer.
Depending on the steel grade, alloys are added. In addition to adjusting the analysis, the melting temperature is fine-tuned at the ladle furnace. For this purpose, three electrodes with a diameter of 400 mm operate on the alternating current principle. At the end of the ladle treatment, a melt ready for casting is transferred to the continuous casting machine.
The Casting Operation.
In the continuous casting machine, the liquid steel is distributed into four strands and continuously cast into beam blanks. The solidified beam blanks are cut into lengths between 4.50 and 11.50 meters for further production steps.
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Our casting hall houses the continuous casting machine as well as the facilities for the refractory linings of the casting ladles and tundishes.
A 190-ton overhead crane lifts the casting ladle with 120 tons of liquid steel from the steel transport car and places it into the ladle turret. The rapid change of ladles ensures our continuous casting operation. While the ladle turret rotates, the shroud tube is blown out and the casting ladle is changed. As soon as the final position is reached, the shroud tube is reattached to the filled casting ladle.
The liquid steel flows from the ladle through the shroud tube, which protects the steel from atmospheric oxygen, into the tundish. When the ladle is empty, the remaining slag is poured off, and the ladle is cleaned to prepare it for the next use.
We can cast the steel using two different casting methods.
For steel grades that are not susceptible to atmospheric oxygen, we use open casting. A defined amount of steel flows from the tundish into the so-called molds through precisely dimensioned, refractory nozzles. These are the casting molds for the liquid steel. These molds are elaborately manufactured copper tubes that correspond to the dimensions of the desired pre-block.
For steel grades that need to be protected from atmospheric oxygen, we use submerged casting. The liquid steel flows from the tundish through submerged entry nozzles into the mold. In the mold, the surface is protected by casting powder. The inflow of steel from the tundish into the mold is regulated by a slide gate system.
The mold is intensively cooled with water to extract heat from the liquid steel. A strand shell forms in the mold, which is guided downwards through the cooling chamber by a roller system. By adding casting powder or casting oil, we ensure uniform hardening of the outer strand shell. At the same time, we prevent the liquid steel from sticking to the mold wall. Sensors in the molds monitor the height of the casting level. The measurement results appear directly on the displays of the individual casting strands as well as on the monitors in the control station. At this point, all data important for our efficient process control is brought together. Above all, we regulate the casting speed, which depends on the fill level of the molds, here.
The strands solidified in the cooling chamber are now transported by the straighteners. They straighten each strand from its 8 m radius. Subsequently, the straightened steel strands reach the cutting system. At this point, automatic flame cutting machines clamp onto the strand. They cut it into the lengths ordered by the rolling mill with an exactly right-angled cut. The cutting process is monitored by a computer system. The cut blocks are transported by the cross-transport manipulator and via roller conveyors as hot input at approximately 600 °C directly into our rolling mill. Alternatively, the pre-bloom sections are moved to our warehouse, where they are temporarily stored until needed in the rolling mill.
The capacity of our modern continuous casting plant is approximately 150 tons of pre-bloom sections per hour.
Our pre-bloom sections have an unusual shape, the so-called “Beam Blanks”. We produce various formats of these. Thanks to the Beam Blanks, we have reduced our deformation work in the rolling mill and the passes at the rolling stands.
The Section Rolling Mill.
In the structural steel rolling line, steel is formed into sections
The technological line of our rolling mill begins at the reheating furnace. The Beam Blanks, i.e., the pre-bloom sections from the electric steel plant, can be fed to the furnace directly with residual heat from the continuous casting plant or in a cold state from storage.
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In the natural gas-fired furnace, the Beam Blanks are heated to temperatures of 1,250°C. After removal from the furnace, the Beam Blank is freed from oxidized deposits in a descaler using high-pressure water. Subsequently, the Beam Blanks are fed into the rolling process.
It is realized in our structural steel rolling line, which is among the most modern section steel rolling lines in Europe. Its capacity, depending on the shape and size of the section steel, ranges between 70 and 200 tons per hour.
In the section rolling line, steel sections are produced using both the duo and universal rolling processes. The section rolling line operates in reversing mode. The section bar is guided back and forth through the grooved rolls in several “passes”. Alternatively, the rolls operate according to the universal process.
Individual Rolling Stands Give the Shape
The rolling mill consists of three consecutively arranged groups of rolling stands: a roughing stand, the so-called Break Down, a tandem intermediate group, consisting of three rolling stands, and a finishing group, consisting of two rolling stands. As the rolling bar passes through these rolling stands, its cross-section is progressively adapted to the cross-section of the final product. This is achieved by mechanical deformation in the spaces between the rolls, known as grooves.
In the roughing stand, the original beam blank is reshaped into a pre-profile. This happens in several reversing passes, alternating forwards and backwards. The two rolls of the stand are driven by an electric motor with a power of 4,400 kW. The frame can generate a maximum rolling force of up to 10,000 kN.
The roughing stand is followed by the tandem group, whose three stands are arranged consecutively at short intervals. During deformation, the rolling bar is simultaneously in all three stands. Reversing operation is also used in the tandem group. After each pass, the distance between the rolls is reduced to achieve a reduction in cross-sectional area. After the final pass, the rolling bar proceeds to the finishing group, where the required final dimensions are produced.
Through continuous cross-sectional reduction, Beam Blanks initially up to 11.5 meters long are rolled into bars up to 100 meters in length. In the finishing stand, the steel beams receive their final shape. The operations in the rolling stands are fundamentally computer-controlled. Thus, the work of our rolling mill operators today primarily focuses on control and monitoring activities.
High Flexibility and Performance through Changeovers
The rolls are our tools for steel forming. In our roll turning shop, we either manufacture them ourselves from roll blanks weighing up to 22 tons or recondition rolls worn during operation on the rolling line. For this, we use CNC-controlled roll turning machines. Right next to the rolling line is the changeover hall, where we prepare the rolls and rolling stands for the subsequent rolling. To achieve high rolling performance through fast and flexible changeover times, we must work with extreme precision. We perform stand changes on all stand groups in less than 20 minutes. The new section is rolled shortly after the changeover.
Cooling and Measuring
After the forming process, the rolling bars, still approximately 950°C hot, pass through a measuring system where the geometry of the section is checked at several defined points using lasers. The rolling bars pass this profile measuring device at a speed of almost 10 m per second. They are slowed down on the roller conveyor before the cooling bed. There, material samples are taken for final analysis in the testing laboratories and workshops of our quality department.
Subsequently, the rolling bars are pushed onto the 100 m long cooling bed, which connects the rolling line with the finishing section. Through lifting movements of the movable part of the cooling bed, the hot rolling bars are gradually transported across the cooling bed. In doing so, they cool down to a straightening temperature of approximately 80°C with the help of air convection.
Intensively Tested Steel Quality
In our quality department, we test individual material samples using various sampling methods. We carry out these samplings in accordance with applicable standards and individual customer requirements. Test procedures employed by us include, for example, the tensile test and the Charpy impact test. All tests are part of our certified and integrated management system.
The Finishing Section.
Precisely straightened and cut section steel
In the straightening machine, several straightening rollers reduce the internal stresses in the rolled bars caused by rolling and cooling through targeted pressure.
This process is carried out using state-of-the-art straightening technology. The end product is standard-compliant, straightened rolled bars that leave the straightening machine at a speed of up to 6 meters per second.
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In the next step, the rolled bars are grouped into sawing layers on a collecting bed. They are then transported to the sawing system via roller conveyors. In the cold sawing system, the rolled bars are cut to the length desired by our customers with centimeter precision.
The profile bars cut to contract lengths finally reach the automatic stacking systems.
Material residues from sawing, such as chips and crop ends, are collected in containers and internally recycled.
This demonstrates the closed production cycle of our structural steel.
The Logistics.
Preparation for worldwide shipping
We stack the custom-cut profile bars variably and automatically into packages using several stacking systems. These are weighed, centered, and bound with steel straps in the binding lines. During this process, we label each package with customer-specific information.
The Shipping Hall and the Shipping Warehouse
After the binding line, the profile bar packages reach the transfer grids in the dispatch hall. Depending on customer requirements, color markings and stamps are applied here. Our computer-aided logistics system ensures that packages are loaded immediately according to the order. The dispatch hall has a storage capacity of 2,500 tons.
Additionally, we have an external warehouse where we can temporarily store another 10,000 tons of ready-to-ship steel profiles. Our products are transported to customers by rail and truck. In both cases, loading is done with magnetic cranes. We ensure transport safety using underlays and strapping systems.
Our Railway Undertaking (RU)
For reasons of sustainability and environmental protection, we prefer rail transport. That is why we operate the “Stahlwerk Thüringen Railway Undertaking (RU)”. A 28 km long rail network is available for internal transport.
Our RU includes diesel locomotives with radio remote control and freight wagons.
We deliver part of our production with our RU. On the way back, our trains usually load scrap, which then supplies our steel production with new raw material.
