Industrial furnaces are used widely in industries and fields of study, from automotive manufacturing to chemicals to sustainable packaging and beyond. They work with a range of materials, including solid and powdered metals, organic fibers, ceramics, and others.
Depending on the application, furnaces are designed in different sizes and shapes to produce a range of temperatures, atmospheres. Examples include lab and factory use for research or manufacturing, checking for combustibility of chemicals, hardening metals for use in bearing balls, or uniform drying of paper pulp.
In this post, we’ll take a closer look at what goes into an industrial furnace.
What are the Parts and Features of an Industrial Furnace?
From the outside, an industrial furnace looks deceptively simple, but there are many complex processes going on inside. Variations in furnace anatomy and features allow many options for heat treatment and thermal processing applications.
These common components and technologies are used in most industrial furnaces:
Single or double chamber design. In a single chamber furnace, heating and cooling take place in the same chamber, while in a double chamber furnace there are separate, contained areas for heating and cooling. A door separates the two chambers to keep temperatures and atmospheres from mixing. Double chamber design helps to retain heat generated within the heating chamber instead of losing it every cycle as the chamber cools back down. For this reason, a double chamber furnace may be more efficient and cost effective because only the load is heated each cycle, not the entire chamber. It is also possible to provide two different atmospheres in each chamber.
Muffles. Muffles are used to create separate chambers for fuel combustion and for heating. This is especially important for avoiding contamination from combustion byproducts. They can also be used as preheating or cooling zones, or as an area to hold materials or parts at high temperatures. Muffles can be metal or ceramic.
Flat or humpback shape. In a humpback furnace, the heating chamber is elevated several inches higher than the entrance and exit doors of the furnace. Parts are conveyed inside on an upward sloping mesh belt. This configuration is used to control the internal atmosphere of the chamber, especially when a hydrogen atmosphere is needed. Because hydrogen is very lightweight, the raised ceiling in the humpback chamber keeps heavier oxygen molecules from interfering with the flow of hydrogen gas.
Atmosphere/moisture controls. Sometimes parts must be held under specific atmospheric conditions to promote or inhibit chemical processes, produce desired changes to the material surface, or aid in delubrication. In these cases, a special chamber can be constructed to maintain a specific chemistry at the correct concentration. Examples include dissociated ammonia, nitrogen bubblers for wet nitrogen, or steam from water. It’s important to monitor parameters, including dew point, gas output, temperature, and pressure.
Heat source. Most furnaces can be heated with natural gas combustion, electric boilers, or electrical heating coils. Depending on the temperature, furnace size, and process time required, one option may be more cost effective than another.
Temperature regulation. Furnaces are equipped with specialized controls to raise, maintain or “soak,” and lower temperatures within a specific range. Used in conjunction with a mesh belt or pusher conveyor, parts stay in different heat zones or chambers for the precise amount of time needed for the desired effect, such as delubrication, sintering, brazing, annealing, or drying.
Control systems. There are many ways to monitor and adjust conditions inside the furnace with data collection and testing software. It’s also possible to track performance trends like temperature fluctuations, belt speed, or fan speed over time. Reports and alerts can also be sent to operators, along with reminders for system testing.
Conveyance. Options for moving parts through the furnace include:
- Roller hearth. This option works well with heavy loads and when high-volume throughput is desired. It’s also useful for long parts and situations where it may be necessary to reverse the direction parts move.
- With this type of conveyance, parts sit in baskets or trays on skids as they move through the chamber(s). Pushers can operate manually or continuously.
- Mesh belt. This type of continuous conveyor system is more efficient than batch processing. The belt’s speed can be changed to control the amount of time parts remain in each chamber.
Types of Industrial Furnaces
Most of the components listed above appear in every type of furnace. What makes a furnace optimized for a specific application is how those standard components are configured or constructed. This includes things like temperature range, belt speed, atmospheric composition, and the size or shape of each chamber.
Common processes for which industrial furnaces are used include:
Annealing. This process is used to heat metals to very high temperatures to improve machinability and decrease brittleness. It creates a uniform internal structure that adds strength to finished parts. Timing is important so that part temperatures are raised, held, and lowered at the correct rate.
Brazing. This process joins metal components with a dissimilar filler metal at temperatures up to 1288 ̊C / 2350 ̊F. It is often used with base metals including copper, carbon steel, stainless steel, and brass and filler metals including copper, silver, and nickel alloys. Controlled Atmosphere Brazing (CAB) using a noncorrosive flux, is the preferred process for manufacturing aluminum heat exchangers, such as radiators, oil coolers, condensers, charge air coolers, and evaporators in the automotive industry. Read more about the process here.
Pulp drying. Drying ovens are used to dry items made from molded paper pulp, such as packaging materials. These low-temperature furnaces typically have a continuous mesh belt that carries pieces through the heating chamber and operate in the 400˚F to 500˚F temperature range. Drying can take anywhere from a few minutes to an hour or more depending on things like pulp thickness, temperature, and part geometry.
Heat treatment. These furnaces can be custom designed for various heat treatments followed by rapid quenching and annealing. They are commonly used for the tempering of austenitized and quench hardened steel or iron at temperatures generally below 1300°F and hardened steel around 300°F.
Sintering. This method of heat treatment is often used with powdered metal manufacturing, in which metal powders are mixed with wax lubricants and then compacted into desired shapes. Sintering improves part strength and conductivity while reducing porosity by joining the individual metal particles without melting them. Prior to sintering, lubricants must be removed without forming excess soot/carbon. Some sintering furnaces can complete both steps in a single piece of equipment. Read more about sintering here.
Steam treatment. The steam treatment process is the controlled oxidation of metals to produce a thin layer of oxide on the surface of a component. This process can be used to provide a component with increased corrosion resistance, better wear resistance, increased surface hardness, an attractive surface finish, and, in the case of porous materials such as powder metal, seal the part porosity and increase the density.
Abbott can Build a Furnace to Suit Your Unique Needs
The Abbott team brings over 35 years of combined research and engineering experience to furnace design and manufacturing. From established processes like annealing or sintering to new approaches to applications like powdered metal manufacturing or pulp drying, we can work with you to create the right furnace for the job. Please contact us.