Industrial ovens are batch or continuous process insulated enclosures or tunnels used for thermal processing. Ovens are lower temperature (usually <1400 degrees F) thermal processing units, usually without refractory insulation.

Thermal processing in industrial ovens takes place in varied atmospheres including pressures above and below the standard atmospheric pressure of 14.7 psia or 760 torr. In a vacuum oven, the heat-treating process takes place inside a vessel that is airtight, allowing low pressures to be generated. Heat treating under vacuum can: prevent surface reactions, such as oxidation or decarburization; remove surface contaminants such as oxide films and residual traces of lubricants; add a substance to the surface layers of the work; remove dissolved contaminating substances from metals by means of degassing.

Applications

Industrial ovens are used in a wide range of industries from chemical processing to semiconductor manufacturing for many different applications, including the following.

Aging describes a time/temperature-dependent change in the properties of certain alloys.

Annealing is used to treat work-hardened parts made out of low-carbon steels (< 0.25% carbon). This allows the parts to be soft enough to undergo further cold-working without fracturing.

Baking involves heating to a low temperature in order to remove entrained gases.

Brazing is a method of joining metal parts together by fusing a layer of brass between the adjoining surfaces. A red heat is necessary, and a flux is used to protect the metal from oxidation.

Burn-off removes cured paint, epoxies, and plastics from metal parts and other materials.

Curing uses temperature to alter heated media by chemical or physical processing changes.

Drying uses temperature to remove moisture from object within oven / furnace.

Firing / sintering bonds adjacent surfaces of particles in a mass of powder or a compact by heating. Sintering strengthens a powder mass and normally produces densification and, in powdered metals, recrystallization.

Foundry furnaces are used for metal melting applications for jewelry manufacturing, mining, and die casting operations, production aluminum foundries, and fine arts studios. They typically have a tilting mechanism, which can be manually operated (e.g., handwheel) or powered (e.g., hydraulic tilt).

Heat treating is a combination of heating and cooling operations applied to a metal or alloy in the solid state to obtain desired conditions or properties. Heating for the sole purpose of hot-working is excluded from the meaning of this definition.

Hot pressing is a method used to densify a material, whereby heat and pressure are applied simultaneously and the pressure is typically applied unidirectionally via rigid tooling.

Preheating involves heating to an appropriate temperature immediately prior to austenitizing when hardening high hardenability construction steels, many of the tool steels, and heavy sections.

Quenching furnaces are used for rapid cooling of heated media. These furnaces are typically identified by the more specific technology utilized: direct quenching, fog quenching, hot quenching, interrupted quenching, internal quenching, selective quenching, slack quenching, spray quenching, and time quenching.

Sterilizing ovens heat objects to temperatures high enough to kill bacteria and germs.

Validating temperature uniformity of an industrial oven. Video credit: Despatch Industries

Heat Sources

Industrial ovens generate heat through a variety of means, such as:

Arc - An arc between graphite electrodes and metal generates heat. Both carbon and alloy steels are produced in electric arc furnaces. Scrap, rather than molten metal, is used as the base material.

Combustion - Some ovens and kilns use heat generated by combustion of gas, oil, biomass, waste products, or other fuels. The combusted gas may heat the material being processed directly or indirectly.

Natural gas - Natural gas is a hydrocarbon used in some combustion ovens.

Propane - Propane, sometimes indicated as liquefied petroleum (LP), is a catchall term for propane, butane, and mixtures of the two. It also includes propylene and butylene, which are sometimes included in blends, mostly outside the United States and Canada. In North America, propane is the most likely to be available in industrial quantities. Nearly any natural gas burner will operate on propane with little or no sacrifice in performance.

Oil – Some ovens are powered by oil or petroleum.

Electric / resistance - Electricity, typically utilizing existing factory voltages, is the power source for some ovens.

Indirect / contact / conduction - Walls, tubes, jackets, or discs are heated by steam, gas, thermal oil, or hot air. These heated elements transfer their heat to materials that come in contact with them via conduction.

Induction - Induction is a widely used process for the surface hardening of steel. The components are heated by an alternating magnetic field to a temperature within or above the transformation range followed by immediate quenching. The core of the component remains unaffected by the treatment and its physical properties are those of the bar from which it was machined, whilst the hardness of the case can be within the range 37/58 Rc. Carbon and alloy steels with carbon content in the range 0.40-0.45% are most suitable for this process.

Infrared / radiant - Some ovens or kilns use radiant heat generated by electric- or gas-fired infrared heaters. Radiant heat units are useful for processing surfaces, flat products, or web materials where clear line of sight can be provided.

RF / microwave / dielectric - In a radio frequency drying system, an RF generator creates an alternating electric field between two electrodes. The material to be processed is conveyed or placed between the electrodes where the alternating energy causes polar molecules in the material to continuously reorient themselves to face opposite poles, much like the way bar magnets behave in an alternating magnetic field. The friction resulting from molecular movement causes the material to rapidly heat throughout its entire mass. Areas in the material with greater moisture content heat up and dry faster.

Steam - Steam is a heat source used in some ovens, typically tapping off existing factory steam lines.

Image credit: Terra Universal, Inc.

Configurations

Industrial ovens are available in a number of common configurations, although custom and specialized models may be designed in conjunction with a supplier.

Cabinet or bench ovens are small batch equipment typically mounted on integral stands. Batch ovens are typically suited for processing quantities of a given product in a single batch.

Continuous or conveyor oven units are oriented toward automated production of mass quantities of small-to-medium-sized product. The type of conveyance system used depends on the product line, volume of work to be produced, and temperature to be obtained.

Front load (walk-in or truck-in) ovens are often larger size batch equipment, typically with double doors and integral carts, shelves etc. As with cabinet and bench ovens, these ovens are typically used for processing large quantities of a given product in a single batch.

Top load ovens will load material by placing it down into the heating area. A crucible may be used to convey the material and the unit will likely have a cover.

Vertical load ovens have a space-saving configuration where entry is gained from a platen that is either raised into the heating area or, as in a bell-lift configuration, the heating area is lowered onto a platen.

Standards

The International Organization for Standardization (ISO) provides the standard ISO 13577-1 that specifies general safety requirements common to industrial furnaces and associated processing equipment.

The National Fire Protection Association (NFPA) provides the standard NFPA 86 that states requirements for the safe design; installation; operation; and inspection, testing, and maintenance of Class A, B, C, and D ovens, dryers, and furnaces, thermal oxidizers, and any other heated enclosure used for processing of materials and related equipment. Provisions are also provided for furnace heating systems, safety equipment and application, and fire protection.

Image credits:

IEEE GlobalSpec | Terra Universal