by Marjorie Steele, Editor at IQS
There’s no question that fire was man’s first great invention. Before Homo sapiens discovered how to create and harness fire, we were in most ways more like our closest primate ancestors, the chimps, gorillas and orangutans who spend over half their waking hours just chewing. Not only did fire give Homo sapiens the ability to break down food into more digestible forms, it also gave sapiens the key ingredient for forming metals: heat.
Since man’s discovery of fire somewhere around 800,000 years ago, we’ve made a lot of progress in harnessing heat’s energy. We’ve discovered forging and casting, giving rise to the Iron Age, followed by our learning to alloy stronger metals such as steel. Our knowledge of curing, tempering and baking has given rise to tools, cars, skyscrapers, utensils, polymer-painted furniture and all manner of processed foods. Food production and metallurgy, two of civilization’s most essential processes, are dependent on heat energy, and today we are more dependent on food processing and metallurgy than any of our ancestors. Ovens are key to these processes, being essential in nearly every type of food processing, metal heat treating and polymer binding. In manufacturing, industrial ovens catalyze the curing, tempering and sintering which cause metal parts and polymers to become solid, strong and resilient.
Since industrial ovens have such an extensive range of applications, we’ll review their main types and applications with a list:
Curing ovens – Harden or toughen polymers (powder coating), metals or rubber through the application of heat. Metals can be stress relieved, cured or tempered to fuse internal cracks and stresses and to improve the strength of a part’s molecular structure. Rubber curing, referred to as vulcanization, causes rubber to become extremely tough, and polymer curing causes powder coatings to fuse and harden through the cross-linking of polymer chains at the molecular level.
Drying ovens – Remove excess moisture from a product or coating, such as in textile painting or the production of crackers, cereal and other dry foods.
Baking/Convection ovens – Bake materials or food in order to change the material’s molecular structure. This is done by transferring heat from hot circulated air (gas) to an object (solid). Food production most commonly uses baking ovens, although metal and plastic parts requiring low-temperature curing also use baking ovens.
Conveyor/Continuous ovens – Usually use convectional heating, moving objects through the heating process on a conveyor belt. Conveyor ovens are often called “continuous” ovens because objects can be continually taken through the oven as the conveyor rolls. While continuous ovens are often necessary in food production and textile painting, a major drawback of conveyorized ovens is that the entering and exiting end of the conveyor must be open, allowing heat energy to escape and causing the oven to produce more heat than is actually used on products. Heat regenerators and recuperators are often used to recycle this “waste” heat energy.
Batch ovens – Convection or baking ovens designed to process one batch at a time. Unlike continuous ovens, batch ovens are filled, allowed to process its contents, then the contents are removed and the oven is refilled with another batch. Batch ovens can be smaller than ovens designed for larger processes; booth ovens are a type of table-top oven designed to process very small batches.
Powder coating ovens – Booth, closet or walk-in ovens which employ convection or infrared heat to cure powder coating polymers onto an object. Infrared heat is most energy efficient in this process, although infrared beams cannot penetrate complex 3 dimensional shapes and for this reason are often combined with convectional heat.
Sintering ovens – May be batch or continuous. Used to sinter powdered metal parts, a process which melts powdered metal particles which have been shape-pressed into a solid metal part.
Walk-in ovens – Have size capacity for larger tempering, heat treating and powder coating applications. Large equipment, such as jet engines, cars or cargo containers may be loaded by cranes and personnel for stress relieving or powder coat curing.
Vacuum ovens – Airtight enclosures in which the pressure level remains lower than atmospheric pressure, or the pressure outside. Vacuum ovens guard against undesirable effects of heat processes such as oxidation and contamination.
Infrared ovens – Use electromagnetic radiation to transfer heat directly to an object without using gas-to-solid transfer like convectional heating. Infrared radiation is transferred directly to an object through a beam without heating the air around it. While infrared heating is extremely energy efficient and precise, it must have direct contact between the beam and the object, making the infrared curing of complex 3 dimensional objects difficult to achieve through infrared heating alone.
While there are many processes, such as powdered metal parts sintering and powder coating, which require industrial ovens, there are other processes for which heat treating is optional. Forgings and castings don’t have to be put through a curing oven in order to be fabricated, but being stress relieved or tempered in an oven can dramatically improve a cast or forged part’s structural integrity and strength. Some industrial businesses specialize in these processes, offering facilities with walk-in ovens, powder coating ovens and curing ovens which can heat treat a range of metal and plastic parts. If fractures and stresses are a problem in your metal fabrication facility, perhaps it’s time to consider investing in a curing oven or soliciting the services of facility that offers heat treating.
There have also been many advances made in the process heating industry in the last several years. Infrared technology is a major advancement for green technology and energy efficiency, but other technologies have arisen in this field as well. Heat recuperation and regeneration technology recycles wasted heat energy, helping the environment as well as energy costs. It’s never a bad time to look at upgrading a facility with leaner equipment, even – or especially – in tough economic times. Just as Homo sapiens in the distant past learned to harness fire as technology, modern engineers and manufacturers are learning to harness heat energy with precision and efficiency, continuing the evolution of technology into a greener and more advanced future.