When describing how an industrial oven works, the first thing to be considered is the type of fuel used to heat the oven, which can be hot water, direct and indirect gas, ultraviolet light, steam, and electricity.
The second consideration, and essential factor, is the industrial ovens airflow pattern, which can be:
- Horizontal – for products loaded on shelves or hung
- Horizontal/Vertical – Air is returned through ceiling ducts
- Vertical/Horizontal – The air supply comes from the ceiling and exits through return ducts on the walls.
- Vertical/Top Down or Bottom Up – Parts are hung or on perforated shelves. Air flows from the ducts to the return supply.
The airflow has to move with minimal obstructions and at a constant rate to maintain uniform oven temperature.
The National Fire Protection Association (NFPA) divides industrial ovens into classes A and B, where Class B ovens do not process volatile materials or solvents and Class A ovens can process volatile materials and solvents. Industrial oven manufacturers are required to follow the NFPA guidelines outlined in the NFPA 86 Code Book.
Industrial Oven Power
The types of fuels an industrial oven uses determines how it operates. Below is a description of the most common fuels.
Gas ovens – Direct and Indirect
Gas ovens are Class A and transfer heat directly or indirectly.
In a direct gas oven, a fan distributes the heat from a gas burner, which can reach temperatures of 1000° F. Under normal conditions, gas ovens operate at temperatures between 180° F and 500° F. Heat is distributed rapidly by convection using propane or natural gas as fuel. Their initial cost is more expensive than electric ovens but have low operating costs. The image below is a tunnel oven with direct gas heating.
Indirect gas ovens use a stainless steel heat exchanger heated by gas or propane. Air is circulated through the heat exchanger to radiation tubes that heat the product, as can be seen in the diagram below.
The gas burner in the diagram is to the right of the oven with the circulating fan to its right. The circulating fan pushes air through the burner to the radiant tubes. Indirect gas industrial ovens keep combustion away from the work area.
Steam ovens
Steam ovens heat water to the boiling point and release the steam to heat the oven. They are used in applications where time and speed are not important. Their range of temperatures is limited to 212° F, the boiling point of water.
Hot Water Ovens
Hot water ovens operate on the same principles as steam ovens at a lower temperature range, which is 160° F or lower. Hot water moves through radiator coils to emit heat that warms recirculating air that is carried to the work area. As with steam heated industrial ovens, the hot water process is slow and time consuming.
Ultraviolet ovens
Ultraviolet UV ovens use UV light to quickly dry substances that have been applied to the substrate. UV ovens use mercury vapor, fluorescent, and light emitting diode (LED) lamps. The UV process is used to cure coatings on cars, boats, planes, missiles, and skis. Pictured below is a UV industrial oven for curing resins.
Electric ovens
Heat in an electrical industrial oven is powered by Incoloy sheathed heating elements and is a Class B configuration. The flow of electrical current controls the temperature in the oven. Electric ovens are less expensive and do not produce pollutants or emissions. They heat-up faster and have a long life. Heat is radiated, which eliminates the need for fans, blowers, or other moving parts.
Microwaves
In a microwave system, microwaves penetrate the material directly and heat it. The process does not require additional pressure and involves the inertia-less heating where the oven is no longer being heated. The microwave heating method generates a high heating rate in the component with low energy consumption.
The key to microwave heating is homogeneity where the microwaves are evenly and uniformly distributed over the product being processed.
Chapter Four – What are industrial ovens used for?
Industrial ovens are used for large and small applications from applying coatings to small electronic components to baking finish coatings on parts for airplanes and trucks. In cleanrooms, they remove moisture to help remove and contain contaminants.
Uses for Industrial Ovens
The list of uses of industrial ovens is very long and extensive. They have become an essential part of every form of manufacturing for the improvement of product performance and reliability. Described below are a few of the more common uses.
Sterilization
Industrial ovens are used to sterilize medical devices and instruments as can be seen in the dry heat sterilizer pictured below. The medical industry requires equipment with precise temperature control for the removal of bacteria, microbes, and viruses. The precision controls of industrial ovens ideally fit the required conditions.
Pharmaceuticals
Industrial ovens are used to bake coatings on pills and as an oxidizer to remove excess chemicals and waste from the coatings.
Burn-In Testing
Industrial ovens do static and dynamic burn-in testing for integrated circuits and electronic devices such as laser diodes. They provide harsh and hazardous conditions for the detection of any problems in a product, especially electrical circuits. Pictured below is a burn-in testing industrial oven and a burn-in board.
Sintering
Industrial ovens compact and bond materials below their melting point, a process that is used in injection molding and metallurgy. The sintering process increases a material’s strength and density. Pictured below is a sintering oven for a heat treatment of Teflon coated pipes and pipe fittings.
Heating Treating
Heat treating includes tempering, aging, stress relief, and annealing of metals at controlled temperatures. Tempering lessens a metal’s brittleness. Stress relief relieves structural, residual, and thermal stress. Aging simulates the effects of use, while annealing increases a metal’s ductility. Pictured below is a heat treatment oven from Wisconsin Oven.
