August 2022 Volume 4

MAINTENANCE

The subject of plant efficiency is an important one to consider, for in metal forming operations there is no greater ongoing cost than that of energy. Prior to the energy crisis of the 1970s, the energy consumed by a typical hot forging operation consisted of both electricity and a heating fuel, either gas or fuel oil. Following the oil embargo, many forging companies made the switch from gas- and oil-fired furnaces to electric radiant heated furnaces and newer solid-state induction heating furnaces. This switch enabled the forge to condense its energy bills into primarily electrical. Like the energy crisis of the 1970s, today's high energy prices are also the result of geopolitics. Today, forging producers are facing the conspicuous absence of new technologies offering high gains in efficiency, much as electric heating did in the 1970s. Additionally, the energy billing structure has become more complex, albeit creative, when it comes to ensuring that the utilities' costs of transportation (e.g. gas), generation and transmission are covered by the consumer. Thus, for the forging producer, the battle for profits and against inefficiencies is not to be won with the conventional weapons of capital expenditure, but the more subtle tools of strategy, innovation and most importantly, sheer determination. The Forge as An Energy Consumer: Typical Model The energy consumption of a typical forge can be broken down into three separate components. They consist of energy required for facility and lighting, material handling and manipulation, and to the heating of workpieces. Facility and Lighting -- To keep a commercial office suitably lit and warm in the northwest region of the United States requires on average of 0.28 electrical-watts per square-foot of space[1]. For a 20,000 square-foot office occupied 60 hours/week, approximately 17,470 kilowatt-hours (kWh) are consumed annually. Similarly, gas for heating approximates as an additional 30-50 percent relative to electrical consumption. Material Handling and Manipulation -- The energy required to saw, shear, upset, extrude, bend, or otherwise forge the workpiece is almost exclusively done with an electric motor providing the energy for the work. The motors and supporting electrical equipment to perform these operations range from less than 1 horsepower (hp) up to several hundred hp. The wattage of a 1 hp motor is 743 watts, a common 50 hp motor has a demand of 37.3 kW. Motor power consumption is directly correlated to press capacity, forging size, and forging rate. While the press is idle the motor may only demand 5 kW to maintain flywheel rotation. During a press stroke the motor could demand all 37 kW during the one-second press stroke plus an additional three seconds afterwards to regain press momentum. For a 37 kW (50 hp) motor driving a fly-wheel press The (In)Efficient Plant By Josh Carney

to produce 6 parts-per-minute, the energy consumption averages out to approximately 17.8 kWh. Based on the same 60-hour service week, the annual energy consumption of a single 50 hp forging press motor is approximately 55,500 kWh.

Figure 1. The kW demand of a press motor averages out over time. Energy Required for Material Heating -- Prior to hot forming/ forging operations, the temperature of the forging material must be increased to a suitable temperature for the operation. The target temperature depends on the forming process and the metallurgy of the forging material. The amount of energy it takes to bring the material to working temperature depends on many variables including target temperature, material dimensions, composition, forging rate, and thermal efficiency. For a modestly efficient induction setup the carbon steel billet heating rate is between 5.5 and 6.5 pounds of steel per kWh. As an example, to forge grade 1030 steel at a rate of 4,300 pounds per hour with an efficiency of approximately 5.5 pounds per kWh, requires approximately 782 kWh of electrical power[2]. Yearly consumption at this rate, based on the 60-hour week amounts to approximately 2,440,000 kWh annually. Where to Realize Cost Savings From these numbers, it is evident that the greatest volume of energy consumption, and hence most significant ongoing cost, goes into material heating prior to forging. If a company is to reduce its energy costs, it must either improve the efficiency of operations or reduce the energy cost. Production Efficiency -- In forging operations, it is possible to have two comparable forging plants operate at drastically different energy efficiencies and hence, cost of operations. Of the three components

FIA MAGAZINE | AUGUST 2022 13