Basic Utilities for Heating, Drying, Processing
Most laboratory workers view ovens almost as utilities, using them principally for drying glassware and heatresistant equipment, regenerating desiccants and catalysts, gently heating samples (and sometimes whole experiments), and curing or preparing materials and composites.
Common laboratory ovens maintain temperatures ranging from just above ambient to about 300° C and are ubiquitous in chemistry, biology, pharmaceutical, forensics, and environmental labs. Units operating at temperatures above 300° C are normally dedicated to specialized applications in physics, engineering, electronics, and materials processing.
Typical lab ovens take up four to six cubic feet of space and are located on benchtops or stacked atop another oven; other units, particularly for centralized glassware washing and storage, may be much larger.
Oven applications are expanding beyond simple drying: chemists use ovens for thin film battery drying and solvent removal; the food industry desiccates samples inside ovens to determine moisture content; electronics and defense labs process integrated circuit boards and other components inside ovens; materials, pharmaceutical, and nanotechnology labs use ovens to remove solvents or waters of hydration from powders or chemicals; mechanical engineers subject parts to heating and stress to test durability and service life in temperature-programmed ovens; and optics and glassware labs subject parts to annealing in tightly temperature-controlled ovens.
“Lab ovens have evolved to suit the demanding needs of end users who require even more precise temperature control, heat distribution, and added safety features,” explains David Craig, North America sales manager at Binder (Great River, NY). “Laboratory oven purchasers can work in a variety of industries and utilize ovens in many different ways.”
Temperature control, precision temperature distribution, and temperature ramping/programming are desirable features in an oven but not required for common drying applications. Highend ovens control temperature at 27 points inside the box, whereas ASTM standards require only nine-point control. Similarly, temperature control may be as narrow as a fraction of a degree or can span several degrees.
According to Mr. Craig, the single most important consideration for a potential oven purchaser is the type of temperature controller employed. Simple on-off controllers work through a thermostat to turn the oven on and off when the temperature is below or above the setpoint temperature, respectively. Proportional controllers are sophisticated versions of on-off controllers that slow down heating as the setpoint temperature is reached, thereby preventing the unit from constantly turning on and off.
By far the most sophisticated controller is the PID (proportional integral derivative) controller. PID controllers are highly desirable for applications that demand precise temperature control and uniformity.
PIDs measure the discrepancy between the actual temperature and the setpoint, then calculate how long to keep the heating element on to reach the setpoint temperature without overshooting it. While PID controllers take a bit longer to bring the oven to the desired setpoint, they do not constantly overshoot the target temperature as less sophisticated controllers do.
Other influencing factors
Beyond—perhaps before—considering choice of controller, buyers need to assess which features they absolutely need. An oven dedicated to simple drying of lab equipment does not require sophisticated controls, temperature ramping, or precise temperature distribution. However, ovens used for high temperatures should be capable of low-temperature operation as well. “It’s possible for one oven to do the work of several ovens, saving money and lab space,” Mr. Craig observes.
Where lab space is at a premium, purchasers should also consider the unit’s size and stackability. But perhaps the most often overlooked features are related to safety, for example, automatic turnoff if the unit overheats, susceptibility to corrosive materials when applicable, and flaps for venting solvent and chemical fumes.
Thermo Fisher Scientific (Asheville, NC) recently surveyed their oven customers to ascertain their preferences and usage. According to Konrad Knauss, oven product manager, Thermo’s study uncovered a features wish list with at least one surprise.
“Until recently almost nobody cared about energy efficiency, but today it’s high on the list of desirables,” says Mr. Knauss. “Perhaps not for end users, but definitely for lab supervisors and facility managers.” Another emerging trend, according to Mr. Knauss, is increasing demand for high-temperature ovens from engineering and materials processing labs.
Other features cited were small footprint, the ability to conduct sophisticated heating protocols (“particularly in pharmaceuticals, where everything is documented”), monitoring, and data logging. Yet, despite the call for more features, users valued a straightforward user interface. User-friendliness is a common trend in lab instrumentation and will grow in importance as labs are increasingly staffed with students, interns, and contract personnel, Mr. Knauss tells Lab Manager.
Price is naturally a decision point for ovens, but the importance of acquisition cost depends on who is being queried. Since ovens are considered utilities, end users tend to have less sway in purchase decisions than they might for spectrometers or chromatographs.
For additional resources on lab ovens, including useful articles and a list of manufacturers, visit www.labmanager.com/ovens
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