May 2024 Volume 6

EQUIPMENT & TECHNOLOGY

Key Areas That Affect Electrical Efficiency in Induction Billet Heating Systems By Brian Lockitski

Operating electrical efficiency of an Induction billet heating system is a major discussion point when reviewing applications with all forging companies. This article will present the key areas that affect the elec trical efficiency of an induction billet heater and discuss methods for improving its efficiency. Being price competitive in the forging market encompasses many different factors, such as employee wages, material costs, plant expenses and operating costs. One large expense for all forging companies with induction heating systems is the electrical cost of running these energy intensive systems. For forging companies, maximizing the efficiency of these units can lead to large cost savings, but it starts by understanding the key areas that affect operating efficiency. Material Before the design of any induction billet heater begins, an estimated equipment efficiency can be determined by acknowledging the type of material to be heated. Figure 1 provides an estimated efficiency for heating different material types with a wide range of material properties. Since most induction billet heaters are designed to heat carbon steel material, this article will focus primarily on the effi ciency measures of this material.

Estimated Efficiency

Material

Final Temp.

750˚C

80-90% 65-70% 60-65% 40-50% 30-40%

Carbon Steel

1250 ˚C 1250 ˚C 550 ˚C 900 ˚C

Stainless Steel

Aluminum (pure)

Copper (pure)

The two critical properties of materials that affect induction heating efficiency are electrical resistivity and relative magnetic permeability. Materials with higher electrical resistivity tend to heat more effi ciently than those with lower electrical resistivity. This is why carbon steel will heat more efficiently than aluminum or copper. As for relative magnetic permeability, an induction billet heater will be more efficient when heating a magnetic material than a non magnetic material. For carbon steel, the material will transition from magnetic to non-magnetic when the material is heated above the Curie temperature point. This can be seen in Figure 1 when carbon steel is heated to a warm forming temperature below the material Curie temperature (750˚C) instead of a hot forming temperature (1250˚C) above the Curie temperature. Figure 1: Approximate maximum efficiencies for various materials (from ambient temperature)

FIA MAGAZINE | MAY 2024 12