Ovens -

Most laboratory workers view ovens almost as utilities, using them principally for drying glassware and heat-resistant equipment, regenerating desiccants and catalysts, gently heating samples, 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 use four to six cubic feet of space and are located on benchtops or stacked atop another oven; other units 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; and there are many more applications.

“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).

Temperature control, precision temperature distribution, and temperature ramping/programming are desirable features in an oven but not required for common drying applications. High-end 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 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.

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.

Konrad Knauss, oven product manager at Thermo Fisher Scientific (Asheville, NC) said other features are gaining in popularity.

“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 is increasing demand for high-temperature ovens from engineering and materials processing labs, he adds.

ED Series

• Allows for routine drying and sterilization applications up to 300 °C
• Fast, even tempering
• Wide temperature range
• Thanks to the gravity convection, thermal processes are highly efficient

BINDER
www.binder-world.com

Isotherm ® Series

• Provide multiple redundant over-temperature protection systems for maximum sample and user protection
• Feature electrogalvanized steel with white oven-baked epoxy antimicrobial powder-coated finish
• Comprised of a single piece stainless-steel chamber with rounded corners

ESCO
www.escoglobal.com

TR 60 – 1050

• Features forced air circulation and a maximum working temperature of 300°C
• Stainless steel interior chamber is easy to clean and resistant to rust
• Suitable for various applications, including drying, sterilizing and warm storing
• Features consistent temperature uniformity

Nabertherm
www.nabertherm.com

Heratherm

• Provides gentle heating and drying with minimal air turbulence
• Microprocessor controls deliver detailed information on current temperature and set points
• Allows users to set the temperature from 50 to 330 C and store the setting in memory while the oven is off
• Features a visual over temperature alarm and built-in safety backup

Thermo Scientific
www.thermoscientific.com