FORGING NEWS

Are you looking to expand in-house heat treat operations on a brownfield industrial site? These sites can bring complications due to a more restrictive footprint combined with other fixed process conditions. In today’s Technical Tuesday installment, the authors of this case study reveal how to consider available footprint and conveyance mechanism options in a continuous steel reheat furnace, as well as the key design variables for industrial furnaces.

On the research team are the following: Michael K. Klauck, P.Eng., President; Robin D. Young, P.Eng., Vice President — Mechanical Engineering; Gerard Stroeder, P.Eng., Manager — Sr. Technology Specialist; and Jesse Marcil, E.I.E., Project Manager — Mechanical Engineering, all from CAN-ENG Furnaces International.

This informative piece was first released in Heat Treat Today’s February 2025 Air/Atmosphere Furnace Systems print edition.

Introduction

A manufacturer with in-house heat treating had the need to develop a custom furnace for a critical step in the forging process. Specifically, this furnace would be for reheating bottom poured ingots and/or continuously cast round blooms to forging temperatures.

Like all industrial furnaces, the design for such a furnace takes into consideration many factors, including but not limited to:

• Production throughput/capacity
• Product configuration/condition
• Material composition
• Target product temperature uniformity
• Soak time
• Cycle time
• Serviceability
• Upstream and downstream process integration
• Automation

Continuous reheat furnaces that supply steel rolling mills (slabs, blooms) are often designed for very large capacities up to 500 TPH (tons per hour). However, this client’s site was in the 15–30 TPH capacity range. For an open die forging application, this would be considered a low to medium capacity range.

Another consideration was that this was a location with already existing buildings. “Greenfield” sites are undeveloped areas free from prior industrial use; thus, they impose very few restrictions on the layout of the reheating furnace and overall forging cell. In this case, the manufacturer was developing on a “brownfield,” a place with evidence of prior industrial production. Places like these often have the blessing and curse of existing, vacant structures. So, in addition to the design considerations listed above, the physical limitations of a brownfield places constraints on what technology can meet the key performance deliverables.

In this article, we will review how this manufacturer with in-house heat treat was able to customize their furnace to successfully adapt it to the constraints of a brownfield location. The key: An appropriate conveyance mechanism.

Continuous Furnace Design for Cylindrical Round Reheating

The client’s product was a cylindrical “as cast” (continuous casting or static cast) round of approximate weight 1.5–2 tons with required reheating at 2300°F. With a design production capacity of 15–30 TPH, batch reheating was not a viable option; the main choices for continuous furnace reheating are either a walking hearth or rotary hearth furnace (“ring furnace”).

The scope of plant equipment that had to be installed in custom forging cells consists of the following:

1. Incoming raw material preparation and cutting
2. Reheat prior to forging
3. Forging
4. Post-forging operations — trimming, shearing, and heat treatment (normalizing, tempering)
5. Machining and finished goods

For a recent reference site, the incoming raw material preparation, the cutting facility consumed approximately 30% of the overall floor space and the forging machine consumed 35% of the footprint, leaving approximately 35% of the available area for the reheating furnace. A comparison of the advantages and disadvantages of the walking hearth technology and rotary hearth technology was made and presented to the end user.

Some of the advantages of the rotary hearth design included the following:

• A smaller overall footprint/lower consumption of building length
• Non-water-cooled hearth
• Positive product positioning with low risk for movement during conveyance
• No complicated pits/foundations
• Less complicated drive system

For this reason, the end user opted for the rotary hearth furnace design over the walking hearth system. A traditional rotary hearth furnace design incorporates two gantry style units, one for loading and one for unloading (see Figure 1). There is a “dead zone” of 10–20° between the charge and discharge which does not contribute to the overall effective heated length.

Alternatively, the CAN-ENG design employs a single door vestibule for both charging and discharging. Instead of dedicated mechanical systems with limited degrees of freedom, this design uses a pedestal-mounted, purpose-built furnace tending robot with a 270° axis slew (see lead article image). The result of these design changes is a more effective utilization of the building width for reheating with no dead zone combined with a robot that has considerable freedom when transferring products from furnace elevation to discharge conveyor elevation.

The robotic feature is particularly important when considering pass line differences for various pieces of equipment in a production cell. Some installations cannot have pits due to high water table considerations, and so the flexibility of robot reach combined with the 270° of axis slew yields fewer restrictions for the end user.

This rotary hearth furnace can be configured for loading a single long piece or two shorter pieces, one charged towards the furnace inner ring, and one charged to the furnace outer ring, with a suitable gap between the pieces and the refractory walls. This provides considerable flexibility for piece size which is accommodated by the furnace tending robot. Had gantry style loaders/unloaders been used for the charging/discharging functions, the requirement for charging an inner and outer ring of the furnace would have been significantly more challenging.

The overall diameter of a typical steel rotary furnace for 15–30 TPH of production capacity is in the 55’–65’ diameter range (outside of steel service platform). This is dependent on the soak time specified by the end user and the heat up time for the cast or wrought steel
product that is charged.

There are many aspects of industrial furnace design that are not covered in this article, and they would include at a minimum:

• Refractory — hearth, wall, roof and flue areas
• Flue design
• Burner type — heat-up zones (both above and below auto-ignition), holding zones (i.e. soak zones
• Physical zone separation vs. soft zoning
• Drive configuration/drive synchronization
• MES or Level II automation and controls
• Incoming raw material cutting — carbide-blade, band saw and torch
• Downstream post-forge heat treatment — normalizing, normalizing & tempering
• Integrated machining operations
• Integration with end user’s ERP system

A full article could be dedicated to each of these subjects. Many details are considered confidential design aspects of the furnace builder.

To speak just on support pieces (piers/bunks), nearly all refractory pier compositions are subject to interaction between the scale that is formed during heating (Fe2O3/Fe3O4) and silicates in the refractory matrix, particularly at reheating temperatures of 2300°F or higher.

Under the conditions of pressure and extremely high temperatures, a low melting point liquid compound of fayalite (iron silicates) is formed at the contact point between the workpiece and refractory pier. This is very undesirable and severely limits the overall pier life. Nickel- and cobalt based super alloys have been used successfully at temperatures up to 2450°F, but these materials can be cost prohibitive, especially considering that 70 or more product locations/pier placements may be required. Unless the product requires very restrictive uniformity in reheating (i.e., titanium ingots), consideration of nickel- or cobalt-based work support pieces is not economically feasible.

The most important consideration for the forging cell downstream of the reheating furnace is the uniformity of the bar, ingot, bloom or mult as delivered for forging. Accurate determination of the temperature uniformity is often misleading by infrared radiation (IR) methods since primary scale is removed in the breakdown passes and secondary scale reforms in its place. Workpiece thermocouple measurements at defined locations in predrilled test pieces under full load conditions yield the best results for determining product uniformity prior to furnace discharge.

Conclusion

The modern rotary hearth ring furnace at low to medium production capacities of 15–30 TPH offers a compact footprint that has many advantages compared to water cooled beam walking hearth type reheating furnaces. This is particularly important to brownfield sites which need to adapt the existing industrial layout to current production needs. When combined with automated saw cutting and forging cells, an integrated manufacturing solution results in very low man-hour/ton of labor input. As seen in this article, recent reference sites where material handling conveyors, robots, descale units, vision systems and Level II MES (Manufacturing Execution Systems) were supplied have allowed U.S.-based end users to achieve the lowest total production costs, allowing them to be competitive with India and China.

About the Authors:

Michael K. Klauck, P.Eng., has nearly 40 years of working in the foundry, steel, commercial heat treating and industrial furnace businesses. He started at CAN-ENG in the year 2000 and has been president since 2012.

Robin D. Young, P.Eng., joined CAN-ENG in the year 2000 and has held progressive positions with the company since then. In his current role, he is responsible for departmental oversight of all aspects of Mechanical Furnace Design as well as the Field Service Team.

Gerard Stroeder, P.Eng., joined CAN-ENG METAL TREATING in 1984, a commercial heat treater, moving over to CAN-ENG FURNACES in 1991. With four decades of process and industrial furnace knowledge, Gerard has expert knowledge of industrial furnace costing and ERP business systems.

Jesse Marcil, E.I.E., is a mechanical engineer working on his Professional Engineer Certification (P.Eng.). Prior to joining CAN-ENG in 2021, he worked in the Engineer, Design — Build of Commercial and Industrial buildings. In his four years with the company, he has now completed several large custom ETO (Engineered To Order) furnace projects.

For more information: Contact the team at www.can-eng.com.

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