The Iron Mountain Forge Press Cell at Jernberg Industries.
The Forging Unit 16 Lean Production Cell.
An operator oversees forging on the press at Jernberg Industries, in Chicago.
The heat-treating furnace at Jernberg Industries.
Jernberg Industries Inc. had begun the conversion from its traditional batch forging and finishing processes to a lean manufacturing operation when management decided to conduct a plant-wide energy assessment.
Jernberg was founded in 1937, and claims to have been the country's first independent press forging company.
The company's forging campus, located on the south side of Chicago, produces 170 million pounds of forged parts annually. Jernberg produces a wide variety of gears, yokes, hubs, and other parts for the automobile and motorcycle industries.
Steel bar is the primary raw material used in the forging operations. The bar stock is preheated with a natural gas-fired burner to drive off moisture and to facilitate shearing. The heated bar stock is fed into one of seven shear presses or saws, where it is cut into billets of 6-to 15-in. lengths. The billets are automatically deposited into metal boxes as they leave the shear press.
The billets are transported via forklift to one of 10 forging lines. Here the billets are manually charged into a conveyor that feeds the billets into a pass-through induction furnace. The heater rapidly increases the billet temperature to 2,200°F to 2,300°F.
The heated billet is discharged from the furnace and drops down a feed chute that serves the forging press. At the bottom of the chute, a worker lifts the billet from the chute and places it on the bottom die. The ram is activated to compresses the billet. Another worker then lifts the pressed billet and places it on the second-stage die where it is forged into its final shape. Once the billet has been forged, the part is ejected from the press and is conveyed to a trim press where flash is removed from the hot part.
Approximately half of the parts that are produced are also heat-treated. Heat treatment is accomplished in one of five batch furnaces. Jernberg employs several heat-treating methods, including water-quench, oil-quench, normalizing, and annealing.
Many parts undergo finishing operations, including shot blasting, drilling, grinding, Magnaflux testing, dimensional testing, and ultrasonic testing.
The lean manufacturing approach optimizes equipment utilization, maintenance programs, information flow through the plant, and workplace organization. Lean manufacturing also requires plant personnel to assess ways to eliminate waste, including work-in-process inventory, unnecessary movement of parts throughout the plant, over-production, machine downtime, etc.
The primary benefits of lean manufacturing include more efficient overall utilization of the plant, reduced inventory (and associated carrying costs), improved product quality, and improved equipment reliability.
Jernberg, like most industrial facilities, has traditionally produced parts using batch processes, which can lengthen a production cycle time by three to five times or longer.
With support from the Department of Energy BestPractices Plant-Wide Assessment Program (PWA, see p.23), the assessment team performed a process simulation to evaluate the impacts of converting existing batch production to a lean manufacturing operation. The team used the simulation to determine whether such models could predict the energyrelated impacts of modifying manufacturing processes, as well as to identify additional potential savings that might be achieved by eliminating production bottlenecks.
In this case, the heat-treating department was identified as a significant bottleneck, but using controlled cooling instead of batch heat-treating would largely eliminate the problem as well as save significant amounts of energy.
The assessment team used a systems approach to evaluate the plant's energy consumption. The team evaluated historical data for a two-year period to identify trends and energy use distribution for plant equipment. This allowed the team to identify systems to be targeted for further evaluation.
Once systems and equipment were identified and targeted, recommendations were developed that would be both technically and economically viable. These included recommendations that supported the conversion to lean manufacturing. The team also considered projects that would be applicable to conventional manufacturing operations.
In addition to targeting energy-intensive processes, the PWA evaluated the efficiencies of the primary support systems, such as compressed air and the cooling-water loop.
Results and projects identified
The assessment team identified seven projects during the Jernberg PWA. If all were implemented, Jernberg could save more than 64,000 MMBtu/yr in fuel and more than 6 million kWh/yr in electricity.
Total annual cost savings would be about $791,000. Total implementation costs would be about $2 million for all projects.
The team identified the following specific projects:
Repair recuperator — The existing recuperator on heat-treat furnace No. 5 was not being used. It appeared to have been taken out of service during a previous furnace rebuild. As a result, 1,400°F air is exiting the stack during furnace operation. By repairing the recuperator and returningit to service, the stack exit temperature could be reduced to 400°F, and the recovered heat could be used to preheat the combustion air in the furnace.
This would save an estimated 1,812 MMBtu/yr. The team estimated that the implementation cost for this project would be $25,000, assuming that the recuperator will need to be repaired before returning it to service. This project would yield an annual cost savings of $9,400, resulting in a 2.7-year simple payback period.
Recover waste heat — There are 14 cooling towers that provide process cooling for the induction heating furnaces, air compressors, and hydraulic systems on each forging line. Jernberg uses approximately 12,000 MMBtu of natural gas for space heating each year.
Most of the plant requires space heating, except for the forging department which relies on process heat to warm the area during the winter. Of the many cooling loops used in the plant, only the loop that serves the north air compressors is used consistently enough to provide a steady source of heat for the plant. This loop currently rejects 3,650 MMBtu of heat from two Ingersoll-Rand compressors.
By using this waste heat to warm the final processing department and displacing the existing gas-fired unit heaters that are only 80% efficient, 4,652 MMBtu/yr of natural gas can be saved. The annual savings would be $23,700. The estimated cost to implement this recommendation is $25,000, with a simple payback of 1.1 years.
Eliminate billet reheats — The induction heaters operate on an openloop control to heat room-temperature billets to 2,300°F, before delivering them to the forging press. When a downstream process (such as the forging press) goes down, the heated billet stock is diverted to totes where it cools to room temperature before being reheated.
The furnace has no automated controls, so an operator must shut down the charging system that feeds the billet stock into the furnace to reduce waste heating of billets when the line goes down. Therefore, the assessment team proposed a closed-loop control system for each line. This control system would allow the induction furnaces to react to downstream variations and speed up or slow down as needed to match production requirements more closely.
This type of control would fit with the lean manufacturing process very well, because it allows all processes in the forging cell to balance. Because billet heating is by far the most energy-intensive step in the manufacturing process, eliminating these reheats would have a significant impact on energy consumption.
This recommendation would save the company about 4.1 million kWh/yr of electricity, with an annual cost savings of $247,700. The cost to retrofit all 10 lines would be $500,000, including the installation of controls, queue sensors, and programming logic to operate the furnaces. The simple payback for this recommendation would be two years.
Install air compressor controls — Currently, the Ingersoll-Rand compressors are base loaded while the Fuller rotary-vane compressors operate partially loaded in throttle modulation. Like rotary-screw compressors, throttle modulation of vane compressors is an inefficient method of control. Plant personnel turn compressors on and off as needed. In most cases, this causes more compressors to be on than needed, particularly during shift change and when process lines are shut down early.
An integrated control system would remove the human factor from compressor control and ensure that the vane compressors are base-loaded when they are online by using the reciprocating compressors as swing machines. These electronic controls would also allow the compressors to maintain system pressure at ±1 psig. This allows the compressor pressure set-point to be reduced safely to within 2 psig of the plant's minimum pressure requirement.
The combined savings associated with pressure reduction and capacity control would be about 1.8 million kWh/yr, with a cost savings of $76,900 per year. Based on an implementation cost of $270,000, the simple payback would be 3.5 years.
Convert heat treat process to controlled cooling — Currently, forged parts are allowed to cool for a minimum of 24 to 48 hr, and then reheated to 1,500°F in the heat treat furnaces.
Controlled cooling would take the hot forged parts and carefully cool them in a closed chamber. The cooling profile would be designed to make certain the parts' microstructure is properly developed to ensure proper hardness. This would be accomplished using the residual heat from the forge process.
Jernberg currently uses a type of controlled cooling on some of its parts by using vanadium-alloyed steels. Implementing controlled cooling on other parts would require significant research and development to model and develop a normalizing chamber to achieve desired results.
Such a system could save Jernberg 57,700 MMBtu/yr by using the process heat (currently wasted) for heat-treating parts. This system would also fit well with lean manufacturing, because the forged parts would be fed via conveyor directly through the cooling chamber.
The estimated cost for this project is $1.1 million. This includes approximately $600,000 to model the cooling profiles for the parts plus $500,000 to construct two chambers that would provide the cooling process.
Based on an annual natural gas savings of $352,000, the simple payback for this project would be 3.2 years. Installing this system would remove a production bottleneck in the heat-treat department and increase the plant's capability such that raw materials could be converted into finished product in only one workday.
Replace air compressors — The four existing Fuller compressors are at the end of their service life. These machines are two-stage rotary vane compressors that are controlled much like a rotary screw compressor. Because of the age and wear on the compressors, the maintenance costs are high (approximately $10,000 per year for materials alone), and the machines' capacity has degraded because of increased blowby between the vanes and the chamber wall. Also, the compressors are watercooled so there are costs associated with cooling tower evaporation and drift.
By replacing the machines with new, two-stage rotary-screw compressors, the specific power of the compressor (measured in cubic feet per minute per brake horsepower [cfm/bhp]) could be increased from the current 4.3 cfm/bhp to 5.3 cfm/bhp at the application conditions. This improvement in efficiency would save 143,100 kWh/yr, and save $74,000 per year.
The cost of four new compressors would be approximately $280,000; therefore, the simple payback associated with this recommendation would be 3.8 years. Jernberg has already started to replace two air compressors. The new compressors are also being relocated to further optimize the air system in conjunction with plant layout changes associated with lean manufacturing.
Reduce forge press downtime — When dies are changed on the forge presses, the new dies are heated using a natural gas torch that is sandwiched between the die cavities for approximately 20 minutes. When die changes are required during production hours, this time represents lost productivity.
By installing an infrared dieheating station, the same die-heating process could be accomplished in 4 to 5 minutes, allowing the crew to change a die and return the press to production more quickly.
While some energy would be saved by eliminating the torch, the primary savings (approximately $7,200 per year) would occur because less press downtime would reduce billet-heater losses. An infrared die-heat station could be purchased for $5,000, yielding a simple payback of 0.7 years.
Industrial Technologies Program, A Public-Private Partnership
The U. S. Department of Energy's (DOE) Industrial Technologies Program (ITP) cosponsored the Jernberg Industries assessment through a competitive process. DOE promotes plant-wide energy-efficiency assessments that will lead to improvements in industrial energy efficiency, productivity, and global competitiveness, while reducing waste and environmental emissions. In this case, DOE contributed $100,000 of the total $212,000 assessment cost.
In addition to Jernberg Industries, project partners were ComEd, Oakbrook Terrace, IL; and Taratec Corp., Columbus, OH. Additional assistance was provided by the Forging Industry of America, and the City of Chicago, Dept. of Environment.
Industrial Technologies Program. BestPractices is an Industrial Technologies Program initiative that supports the DOE Industries of the Future strategy. This strategy helps the country's most energy-intensive industries develop ideas and projects that have potential to improve their competitiveness.
BestPractices brings together emerging technologies and energy-management best practices to help companies begin improving energy efficiency, environmental performance, and productivity right now.
BestPractices emphasizes plant systems, where significant efficiency improvements and savings can be achieved. Industry gains easy access to near-term and long-term solutions for improving the performance of motor, steam, compressed air, and process heating systems. In addition, the Industrial Assessment Centers provide comprehensive industrial energy evaluations to small-and medium-size manufacturers.
|This article is adapted from a report issued by the U.S. Department of Energy's Industrial Technologies Program. A copy of the report is available at http://www.oit.doe.gov/bestpractices/fa ctsheets/jernberg_steel_cs.pdf|