Temperature, Range, Uniformity, and Control Top Feature List
Ovens are found in almost every industrial, research, and development laboratory. Applications include drying lab ware and keeping it ready for use; sterilization; conducting above-ambient, constant-temperature experiments; drying reagents and desiccants; annealing and curing materials; component and materials testing; and many others.
“Nobody gets excited about lab ovens,” comments Frank Brombley, general manager at Jeio Tech (Seoul, South Korea), “but ovens are definitely essential lab components.”
What to look for
The most important characteristics of lab ovens are temperature range, temperature uniformity, size, ergonomics, energy consumption, and price.
Temperature range, the most important oven property, refers to the highest reliable operating temperature above ambient. Common ranges are 250ºC, 300ºC, 400ºC, etc., up to 1000ºC.
Temperature uniformity is arguably the most important oven property after temperature range. “Uniformity and accuracy have always been the key specifications for heating and cooling instruments,” says Mr. Brombley.
Until relatively recently, lab oven manufacturers adhered to an ASTM standard for temperature uniformity that was based on the temperature at nine locations within the oven chamber. This standard served the industry well for many years, but its shortcomings became obvious as experimentation and processing requirements increasingly demanded highly uniform temperatures throughout the oven.
“You want the temperature at every point inside the oven to be the same as the number on the unit’s temperature display,” Brombley tells Lab Manager Magazine.
Top oven manufacturers, including Binder, ESCO, Memmert, Jeio Tech, and Thermo Fisher, have adopted a more rigorous temperature-uniformity standard, DIN 12880, for some of their products. Instituted in 2007 by a German standards agency, DIN 12880 uses 27 measurement points to provide significantly improved temperature uniformity.
The DIN 12880 standard is as much a corporate-cultural statement as an absolute requirement. Brombley believes that the use of DIN 12880 conveys that manufacturers are making extra efforts to guarantee the quality of their products.
Measurement points are just one aspect of uniformity, however. To achieve the goals of DIN 12880, ovens must circulate air constantly and uniformly. Binder ovens, for example, use mechanical convection and proportional- integral-derivative control. “Mechanical convection provides greater consistency and more rapid recovery after oven doors are opened,” says Uwe Ross, president, BINDER Inc. (Great River, NY).
Oven size is a major consideration for laboratories that are short of space or concerned about energy consumption. Those considering the purchase of new or used units following the older, ASTM standard should know that temperature control is somewhat more difficult in larger ovens.
Ergonomics has become a factor for many larger, stationary lab items such as refrigerators, ovens, and constanttemperature baths. Oven controls are not particularly difficult to navigate, but they should be readily viewable and accessible on a front panel and should not require the operator to bend or reach. Nearly all lab ovens are used by more than one person, so workers should be able to access their materials or experiments easily, without disturbing those of their colleagues.
Labs concerned about operating costs can now select ovens that minimize electricity consumption. A highly efficient oven in constant use can save thousands of dollars over the life of the appliance. Energy efficiency is a complex characteristic based on type of heating and circulation, anticipated usage, temperature range, insulation, door closing and gasket options, and other factors. Note that insulation also provides a measure of safety for operators.
Despite the simplicity of lab ovens, manufacturers compete on numerous second-tier features, according to Mr. Ross, who lists “accurate temperature without overshoot,” time to heat up, reliability, and independent temperature safety or shutoff on his list of desirables, because, “you don’t want to burn the lab down.” Temperature programmability, cooling-down capability, alarms, shelving options, monitoring, and data logging round out the features list.
Specialized oven types
The term “kiln,” an alternative name for oven, is usually reserved for hightemperature ovens operating above 1,000ºC to about 2,300ºC. Kilns are normally working ovens used to process materials such as wood (lower temperatures) and glass or ceramics (higher temperatures).
Another specialized oven type, the autoclave, is used for fixed-time sterilization of laboratory and medical instruments or lab ware. Autoclaves work by bathing objects in steam at 121ºC or higher, followed by a purge or drying cycle. At any given temperature, steam is significantly more effective at sterilization than hot air.
For additional resources on lab ovens, including useful articles and a list of manufacturers , visit www.labmanager.com/lab-ovens
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