Blast cleaning of castings weighing up to 250 metric tons
The foundry of PJSC Energomashspetsstal specializes in manufacturing very big, heavy and complex castings. Considering the high value of the castings it is not surprising that they are subject to comprehensive quality controls including – among other criteria – the specified surface cleanliness. For this reason, the castings with dimensions of up to 12 (L) x 7 (W) x 5 (H) m, equivalent to 40 x 23 x 16 ft, and weights of up to 250 metric tons undergo an intensive blast cleaning process. The new custom engineered blast cleaning system, actually one of the biggest shot blast machines in the world, was designed by Rösler to fit precisely into the available space at the customer’s premises.
The facilities of the iron and steel works PJSC Energomashspetsstal (EMSS) are located in the Ukrainian town of Kramatorsk on an area of around 138 hectares (340 acres). Since 1964 this company has been manufacturing castings and forgings for the heavy, energy generating and nuclear industries as well as for marine and traffic engineering. Over the past years the company has specialized on components like steam and hydro turbine housings, steam turbine rotors, hydro rotors, trusses, ring gears, screw blades and hubs, support rollers for hot and cold rolling mills as well as die fixing blocks. Because of their unique function, as well as their size and weight these components are generally engineered and made as one-of-a-kind products.
EMSS has strict quality controls in place to ensure the extremely high quality and long service life of these components. For example, all external and internal surface areas of the castings are visually inspected. In addition, they undergo a magnetic particle test or an ultrasonic inspection to search for cracks in the material. This requires a clean surface free of any scale in compliance with the Swedish surface preparation standard SA 2,5. In the past this surface preparation operation was done manually. Igor Sapetko, foundry manager at EMSS comments: “We invested in this new shot blast system primarily because the stringent customer requirements for improved casting and surface qualities forced us to adopt the cold box casting method for castings with complex geometries. However, at the same time we wanted to improve the working conditions for our employees by eliminating the vibrations, the dust and noise caused by manual shot blasting. This, by the way, also contributed to a much cleaner environment.”
The technical challenge: Part size & weight and the on-site space restrictions
The work piece dimensions of 12 (L) x 7 (W) x 5 (H) m, equivalent to 40 x 23 x 16 ft, and weights of up to 250 metric tons posed a significant technical challenge for the Rösler engineers. But the engineering task became even more difficult, because the customer specifications called for integrating the shot blast system into the overall EMSS manufacturing line. The shot blast machine had to be placed on the foundation of an old water jet blast system in a building with numerous support pillars. At the same time, the Rösler engineers had to ensure that the machine design allowed utilization of the existing rail part transfer system with turn table for transporting the work pieces from the foundry through the blast machine to the quality control department. Because of the high weight of the castings a spinner/hanger shot blast system was not feasible. Igor Sapetko continues: “We looked primarily for a simple but effective shot blast system that guaranteed a high functional reliability and was easy to maintain.
Of course, economic aspects like the purchasing price and operating costs played also a significant role in our decision.”
With these requirements the project team at EMSS contacted six shot blast equipment manufacturers, among whom three companies, including the Rösler Oberflächentechnik GmbH, were pre-selected. In the end, after visits at the manufacturing facilities of the three suppliers, inspection of various reference shot blast installations and review of the different technical concepts, the customer decided to place the purchase order with Rösler. The comprehensive and extremely detailed layout of the RDS 80/70 shot blast system proved to the EMSS team at a very early stage that the Rösler concept met all its technical requirements.
Customer engineered to the very last inch
The Rösler continuous rail shot blast system RDS 80/70 is one of the biggest shot blast machines ever built in the world, and is certainly the biggest ever built by Rösler. It had to be placed in the building to fit exactly between the support pillars. To prevent spillage of blast media the blast machine inlet and outlet areas are equipped with double wing steel doors lined with wear resistant rubber. The inside of the 30 m (100 ft) long machine is divided into three sections: Inlet and outlet chamber and the actual blast chamber with inner dimensions of 10.5 (L) x 8 (W) x 7 (H) m, equivalent to about 35 x 26 x 23 ft. The large width of the blast chamber allows complete rotation of parts with a length of up to 7 m (23 ft) during the blast cleaning process. The RDS 80/70 is equipped with eight Hurricane H42® turbines mounted to the ceiling, respectively one side wall, of the blast chamber with an installed drive power of 22 kW each, throwing over 2,000 kg (4,400 lbs) of blast media per minute. After their first pass through the blast machine parts longer than 7 m are picked up from the transfer system turn table by the existing bridge crane, rotated by 180 degrees and placed back on the turn table for a second pass through the machine. This ensures all around blast cleaning of parts which, due to their length, cannot be rotated on the turn table. For optimum wear protection the blast chamber is fabricated from manganese steel and lined with easy to exchange overlapping manganese wear plates. To allow manual spot cleaning of critical surface areas the RDS 80/70 is equipped with a pressure blast system and lighting in the blast chamber.
A special technical feature of the EMSS shot blast machine is the extra large media hopper allowing the storage of 30 metric tons of blast media. This ensures that even in the case of work pieces which are extremely cup-shaped, the shot blast process must not be interrupted because of lack of blast media in the system due to media carryout.
A blast machine consisting of many more individual sections than other machines
The blast media thrown by the turbines is collected in two large hoppers placed in the foundation pit from where the media is transferred to the transport system of the media cleaning and classification unit. This posed another technical challenge, because the rails of the part transfer system allowed an access opening of only 2 x 2 m (6.6 x 6.6 ft) for placing all these equipment components in the foundation pit. For this reason, the media collecting hoppers below the blast chamber had to be fabricated in 15 individual sections instead of normally 4 sections.
A five storey high maintenance platform allows quick and easy access to all equipment sections requiring regular maintenance work. Another significant factor regarding maintenance is the fact that Rösler maintains a service center in the Ukraine.
Igor Sapetko concludes: “With the new shot blast system from Rösler we achieve the required surface cleanliness with the blast media consumption cut in half compared to our old manual blast cleaning system. In addition, we were able to significantly reduce the blast cleaning process times. Where previously several employees needed weeks of manual blasting, we are now completing the same blast cleaning process within a few hours.”