ME Elecmetal pours abrasion-resistant white irons and pearlitic martensitic steels suitable for high impact applications.
Prior to the 2012 expansion, melt- ing was the main step that limited the rate of production, and the component of melting that caused the longest delay was melt down (Fig. 2). ME Elecmetal’s Duluth plant can
pour only one heat at a time, so only one heat is processed at a time. Ideally, a heat will be sent to pouring as soon as the prior heat finishes being poured. Tis allows continuous use of the pour- ing department while also maximizing output from the melt department. In a two-furnace process cycle, once a heat was finished being processed, the fol- lowing heat was not yet in melt down, resulting in a period of time where no processing occurred. Te third furnace was installed to eliminate this bottle- neck and allow continuous processing. Figure 2 shows the continuous process cycle. As soon as a furnace finishes being processed, melt personnel imme- diately move onto the next furnace to begin processing. Oxygen refinement occurs dur-
ing early stages of the processing step. After refinement, the heat is not allowed to sit idle for a specific length of time without additional refine- ment due to quality concerns, which constrains processing to a single heat at a time. Additional refinement incurs additional alloy cost for materials that
are oxidized out of the bath, so the practice is avoided. Because of the oxygen refinement constraint, multiple heats are not processed simultaneously. Any additional furnaces would only result in longer wait times until the cycle returns to processing; as a result, a fourth furnace would not increase production rates. In order to achieve a continuous
process in the three-furnace cycle time, the processing time of 65 minutes is staggered, causing a 15-minute wait time. Te primary reason for this is to level-load the plant and maintain low man-hours per ton. With the installation of the third
furnace, staff was increased by 35 employees. When the melt department operated just two furnaces, staffing was limited to five individuals: two operated cranes and three worked on the floor maintaining furnaces and processing heats. In the three-furnace process, staffing was increased to six individuals: two who operate cranes and four who work on the floor. Additionally, processing a heat requires two to three individuals on the floor, depending on the stage of processing, with the latter stages (tapping a heat) requiring three. Te majority of the additional staff hired for the expansion were directed
to molding and finishing to transition from two to three shifts per day and meet production demands. ME Elecmetal has explored opti-
mization to reduce the processing time by five minutes, which would result in a heat produced every 60 minutes and a drop in wait time. Te metalcasting facility has processed 24 heats in one day on occasion, but rate-limiting steps begin to appear, and often other depart- ments cannot keep up with this pace unless under near perfect conditions. With the described plant staffing and melt producing a heat every 65 minutes, the 160 ton/day goal is fairly easy to meet consistently. In 2013, the plant averaged 157.8 net good tons/ day with planned tons equal to 157.6 tons/day. Market demand decreased slightly toward the end of 2013 result- ing in lower production quotas.
Melt Process Optimizations for the Third Furnace
Prior to the third furnace being
installed, the melt department had to initiate changes to handle continuous processing and proactively targeted potential bottlenecks in the process. Scrap inventory is a function of the melt department, and the scrap bay has its own crane specialized for unloading scrap and alloy trucks. In addition, the
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