First Understand, then Optimize
Toshiba Uses MAGMA5 to Reduce Inclusions in its Steel Castings
With increasing quality demands on steel castings, steel carrier rings used in thermal power units are manufactured under very strict quality specifications. Toshiba Hydro Power has been producing these ring-shaped castings for over seven years for its parent company. One of their most significant challenges has been the presence of inclusions on the outer ring surface, which accounts for over 40% of the total defects.
Inclusions on the outer surface after machining (left) and perfect steel casting quality after being optimized using MAGMA5 (right).
Due to the high quality requirements, these inclusions had to be removed by polishing and subsequent welding. The cost for the welding electrodes alone was extremely high. The welding took roughly 12,142 total hours per year and about 2,600 kg of weld rods were used to achieve high quality castings for four projects during 2011. In order to find a solution that would decrease or eliminate this problem, a number of measures had been investigated over the years.
By mastering MAGMASOFT® the abilities and skills in understanding process knowledge were constantly enhanced and the foundry’s experts were convinced that they had to first identify the root causes of the problem in order to solve it. Before purchasing MAGMASOFT®, many different factors were suspected to be the cause of the inclusions, such as melt quality, molding materials and inclusion formation due to reoxidation. However, it had always been guesswork to predict which factor might have contributed most to the problem.
Inclusions predictions are similar to the findings in real castings
With the purchase and implementation of MAGMA5 in 2012, the foundry simulated their current casting layout using the “inclusion” criterion. The simulation clearly showed the potential endangered areas. The filling process was also evaluated in detail. It was determined that excessive turbulence at two main ingate areas resulted in an enlargement of the melt free surface and led to large amounts of entrapped air, which in resulted in the creation of reoxidation inclusions found on the outer surface.
Final version with a significant reduction in inclusion indications on the real casting.
Based on these findings, measures could be implemented to solve the problem. The key approach was to reduce the turbulence during filling and reduce the contact time between air and the melt. Any remaining inclusions would be moved into the risers.
With their growing confidence in MAGMASOFT®, the foundry experts at Toshiba investigated many other ideas, with MAGMA5 acting as a virtual foundry shop. During the simulation process, it was noticed that as long as ingates were located directly under the risers, inclusions would be pushed into areas between the risers. Their engineers used virtual experimentation with the gating system to move the gates between the risers with the idea to force the inclusions into the feeding system. The simulation results confirmed that this assumption was correct. Subsequently, two parts were produced with the new methoding. After performing all inspections, the castings were qualified with minimal amounts of inclusions.
Turbulent melt flow during the filling process
Through the application of MAGMA5 in the first year, the average weld rod consumption was reduced by 1/3 per cast ton. With continuous improvements resulting from using MAGMA’s software, the users expect the upgrading effort can be further reduced. Due to the reduction in the casting defects, the total production time could also be significantly shortened, increasing profitability. After a year of using MAGMASOFT® the engineers at Toshiba are convinced that they can make use of the program for the upfront optimization of many new castings due to their increased confidence by mastering MAGMASOFT®.
Toshiba Hydro Power (Hang Zhou) Co., Ltd. is a joint venture enterprise of Toshiba and Sinohydro Corporations. Its main activities are research and development, design, manufacturing, as well as installation and services in the hydro-electric equipment field. With over 110 years of history in the hydro-turbine and hydro-generator business, always engaged in the research and development of new technology, Toshiba Corporation provides the most advanced products to clients all across the world. Toshiba has been the vanguard in large capacity, high head, high speed pumped storage equipment, offering a large number of highly sophisticated record-breaking products and occupying the chief status in the market.
Text and images courtesy Toshiba Hydro Power (Hang Zhou) Co., Ltd., P.R. China