More than 45 % of the total electricity consumed in the United States is produced by coal burning power plants that rely heavily on large steel castings to help produce the pulverized or “powdered” coal. Columbia Steel, located in Portland, Oregon, takes great pride in the products that they provide to coal burning power plants for coal pulverization. In 2009, Columbia Steel took another step in their long history of continuous improvement when they purchased MAGMASOFT® to aid in their efforts to efficiently produce products that meet the ever increasing demands of their many loyal customers.
One of the key components in producing pulverized coal is a part known as the grinding table, which is the main support structure upon which coal is ground into powder using large wear resistant plates and rollers. One particular grinding table produced at Columbia Steel is a plain carbon steel casting that has a clean weight of 16 t and a pour weight of 28.4 t. Prior to acquiring a seat of MAGMASOFT®, the engineers at Columbia Steel designed a gating and risering system that produced castings free of solidification shrinkage indications. However, the parts made using this gating and risering system were spending more than 20 hours each in the cleaning room for repair work on gas pinholes, entrapped air or gas pockets, sand inclusions, slag inclusions, and sand penetration. In addition to the lengthy cleaning times, the machining times for this part were also being extended to perform repair work when additional defects were revealed during machining. Interrupted cuts caused by the defects were also leading to poor tool life and increased down time for making tool changes.
In an effort to reduce the number of defects on the grinding table casting, the engineers at Columbia Steel first simulated the filling using the original gating system. This baseline simulation revealed several undesirable conditions including a geyser effect that occurred as the metal shot into the mold cavity at velocities exceeding 420 cm/s The high velocity of the melt was causing excessive splashing and led to the formation of reoxidation inclusions and entrapped air and gases. In addition to the turbulence, the engineers noticed that while the cavity was filling from the two lowest ingates in the mold, it was also filling from the 4 elevated ingates, causing metal to cascade down from the top ingates to the metal level of the lower ingates.