TISCO achieves perfect surface finish on stainless steel plates

The vertical shot blasting system is 14m high and is placed in a pit with a depth of 2.5m. Four inspection platforms with stairways enhance the impressive appearance of the machine

Stainless steel is one of the most important raw materials for many industries such as medical engineering, shipbuilding and aerospace and accordingly, high volumes of stainless steel are used around the world. To cope with the ever-increasing demand, TISCO, one of the globally largest manufacturers of stainless steel, modernised the production line in its hot rolling mill for stainless steel plates. As partner in this challenging project, Rösler built the biggest vertical shotblast machine in the company’s history.

As part of the China Baowu Steel Group Corporation Ltd, the Taiyuan Iron and Steel Group Co Ltd (TISCO), is one of the largest suppliers of steel in the world. For a long time the company, located in Taiyuan in the Chinese province of Shanxi, has specialised in the development and production of stainless steel products such as plates and sheets. Since 2020 a huge modernisation project has been underway with the goal to update the production line in the hot rolling mill for stainless steel plates with ‘state of the art’ equipment, including a new shotblast and pickling line.

Once the project is completed, the entire system will run fully automatically. The technical specifications for the shotblast system, processing steel plates up to 4,100mm long, 160mm thick and with a maximum weight of 35 tonnes, were very detailed and strict; particularly with regard to the shotblasting results and the workpiece handling. The challenge for the Rösler engineers was to design and build a machine that guarantees a high-quality, high-precision finish in the micrometer range with high throughput. With regard to size and production speed the new shotblast system dwarfs the equipment that the company has ever previoiusly built.

Some of the TISCO requirements were that the steel plates must pass through the shotblast machine at a speed of 7m/min, the surface roughness cannot exceed Ra=4.0μm, and the surface finish must correspond to A/B Sa 2,5. To prevent even minimal damage on the workpiece surface by the transport rollers, the customer demanded the plates to be transported through the shotblast machine and the subsequent pickling system in vertical position. A challenge was that the plates are delivered horizontally and must be changed to vertical position before entering the machine.

To meet the customer’s surface quality requirements within the specified time frame, the Rösler engineers developed an innovative equipment concept. It combines two identical shotblast machines into one system, where the stainless steel plates are passing through the two machines sequentially, and each one uses a different blast media. The individual machines are equipped with 12 gamma 400G turbines with an installed power of 37kW per turbine.

A huge quantity
On each side of the blast chamber, six turbines are mounted at an angle. This turbine arrangement ensures that the plates are evenly covered by the blast media across their entire width. The total blast media throughput per machine amounts to 12,000kg/min — a huge quantity compared to the throughput of between 2,000 and 3,000kg in standard shotblast machines. The high media throughput posed a particular challenge for the wear protection of the two machines. This challenge was met by fabricating the blast chamber from manganese steel and lining it with 10mm thick, easily replaceable, wear plates, also made from manganese steel.

Pictured right: directly in front of the shotblasting system, the up to 160mm thick and 4,100mm long stainless steel plates are moved into a vertical position. They are then passing through the shotblast system and pickling line on special roller conveyors at a maximum speed of 7m/min

For shotblasting operations, where a higher surface roughness is specified, each machine can be run separately. In such cases the transport speed of the steel plates is reduced to 4m/min. To prevent media spillage, each machine is equipped with a high-performance blow-off system.

The large size of the steel plates and their high weight demanded an extremely sturdy design of the two shotblast machines. For example, the maximum load per running metre amounts to four tonnes. The overall machine dimensions are also impressive: The entire system is 17m long and 14m high. It was placed in a pit with a depth of 2.5m. The blast media cleaning system and media hopper were placed on the roof of each shotblast machine. For quick and easy maintenance the machines are equipped with four inspection platforms on different levels that can be easily reached by suitable stairways. This enhances the already impressive appearance of the shotblast system, designed for processing 315,000 tonnes of stainless steel plates.

The production unit consisting of the two Rosler shot blast machines and the pickling line is equipped with a level 2 control system. This upper-level system provides all the data required for the process, for example, the plate type and the required surface roughness. The information also specifies whether a special plate type must pass through both shotblast machines or just one. This ensures that the required surface roughness and finish values are achieved without any manual intervention whatsoever.

The entire vertical shotblasting system was designed and built in Germany. It was shipped to China by sea in 21 containers. Rösler service engineers, some of them from Germany, installed the system at the customer’s location. Another challenge was that the installation had to take place during a time of strict Chinese travel restrictions and quarantine regulations. In addition, the installation had to be carefully coordinated with the service engineers of the company supplying the pickling line.

Vasili Schaermann, global sales expert at Rösler Oberflächentechnik GmbH, said: “Only after the installation at TISCO could we test the entire system. Because of the extraordinary size of the shot blast system, such a test was not possible during the production phase at our Untermerzbach plant in Germany. Fortunately, the commissioning at the customer location was successful. Actually, the entire project went very well. In the future we will build other vertical shotblast machines, and I would like to point out that we are pleased with the cooperation between TISCO and Rösler.”