This article was originally published in April 2014.
The international ISO 50001 standard puts forth ambitious goals to reduce CO2 emissions and increase the generation of electricity from renewable energy sources. Energy-intensive manufacturing industries, such as forging, can reduce electricity costs and improve their competitive position through ISO 50001 certification. This first of two articles highlights energy savings available to energy-intensive businesses in the forging industry.
The ISO 50001 standard prescribes management-system standards to achieve continuous improvement in energy performance. It focuses on the processes within an organization to reduce CO2 emissions, energy costs and other environmental impacts. Global application of this standard could contribute to the efficient utilization of available energy sources and improved competitiveness. Essentially, the stated intent of ISO 50001 is improved energy efficiency, which is defined as the relationship between a plant’s performance and the energy used to achieve it.
The standard defines energy-management systems to promote energy efficiency and stewardship while reducing energy costs and achieving financial benefits through compliance with statutory requirements. It encompasses all forms of energy, but this article focuses on electrical, which is the primary form of energy used in induction heating for closed-die forging.
Apparent power (S), or connected load, is the electric power being fed to an electrical consumer. It is taken from RMS values of the electrical current (I) and voltage (U), and it is made up of the actual applied active power (P) and an additional reactive power (Qtot) as shown in Equation 1 (top slideshow).
It is not just the active power that energy-intensive businesses such as forges are interested in but also the reactive power, which is generated when the current and voltage are not in phase with each other. In Figure 1, the portion of active power is shown over the cosine of the phase angle (cosf), also called the power factor. The following rule of thumb applies: A power factor cos ø of 0.9 roughly corresponds to "reactive power = 50% of the active power."
Active power (P) is taken from the supply network if the voltage and current have the same sign. It is fed back into this supply network as a function of the working point of the electrical consumer, either fully or in part, as reactive power (Q) when the signs are opposing. To counteract the reactive power-related losses in the network supply, larger wire sizes are required in the supply lines, together with larger generators and transformers.
Industrial electrical consumers pay for the reactive energy they use as well as the active energy they use. Therefore, it is in the interest of energy-intensive businesses to minimize the reactive power they use. Reactive-power compensation systems can be used, but a better option is working point-independent optimization of the consumer power factor cos fto a constant value close to 1 (barely any reactive power) by choosing suitable circuit topologies to achieve a lasting increase in energy efficiency.
Impact of ISO 50001 on the Forging Industry
The forging industry is one of manufacturing’s most energy-intensive sectors. The proportion of energy costs relative to the industry’s added value is significant. To ensure long-term survival in today’s world of rising costs, plant operators would be well advised to control and optimize energy usage.
Although induction furnaces are inherently energy-efficient compared to other technologies, they account for the majority of closed-die forging energy cost. Therefore, forge operators want to ensure that their plants are making the best use of that energy. In practical terms, the following questions often arise:
• What definition of energy efficiency applies to the specific production framework?
• How and at what point is energy consumption measured?
• What influence does the product range and throughput have on energy consumption, and what opportunities does an optimum production strategy offer?
An induction-related energy audit takes into account the overall production situation, identifying the optimum machine setup and providing information on the best production sequence – from an energy point of view – for the various material dimensions. Data generated by the installed energy meter(s) are the basis for this evaluation. The induction-related energy audit also examines the induction furnace design and the components that have a lasting influence on energy consumption.
Work on the efficiency of induction heating has resulted in a system called iZone (see sidebar). In the next and final installment of this article we will examine the systematic efficiencies of the induction heating of forging billets and bars. Additionally, the results of an induction audit will be considered.
Co-author Dirk M. Schibisch is vice president of sales for SMS Elotherm GmbH, Germany. He can be contacted at email@example.com. Co-author Loïc de Vathaire heads the service spare-parts department for SMS Elotherm, Germany. He may be reached at firstname.lastname@example.org. This article was adapted for publication in FORGE by George Burnet, SMS Elotherm North America. He may be reached at email@example.com or 724-591-0252.
iZone – Intelligent Zone Control of Forge Heating Plants
The overall concept of this system is based on zone heating control, which SMS Elotherm calls iZone. It was developed for the process control of modern induction heating plants. An integrated computer system controls the continuous heating process. Heating coils can be controlled individually, resulting in lower energy consumption rates, consistent with ISO 50001 requirements for energy savings.
The database-supported expert system automatically calculates the parameters required for the heating process to improve energy efficiency and reduce scale formation. The resulting process parameters are then transferred directly into the plant system.
The graphics function integrated into iZone safeguards the process. Using the heating curves individually generated by the operator, the system automatically calculates the process parameters and transfers these directly into the machine control system. Optimized production can then be started straight away at the push of a button.
Another advantage is the running of bars with residual heat. Until now, one had to wait until the bars cooled down to room temperature before they could be reheated to the forging temperature. iZone technology allows warm charging (i.e. the reheating of partially heated bars). For this, the warm bars are automatically transferred back to the induction heating system and the amount of energy required for through-heating is calculated and applied, saving time and energy while reducing scale formation.
SMS Elotherm uses this control system in both billet and bar heating plants and in large-scale quench-and-temper lines for heat treating long products and tubular products.