Controlling Temperatures to a Fraction of a Degree

Most basic lab uses employ oven temperatures from just above ambient to several hundred degrees Fahrenheit, although ovens used for materials processing reach temperatures in excess of 1000ºF. Kilns, specialty ovens used to process ceramics, may reach 2400ºF.

Basic components common to all general-purpose lab ovens are an electrical heating coil, insulation, temperature measurement and/or recording, and a circulation mechanism that provides even temperature distribution. Advanced features include double doors, digital control, and temperature recording (useful for regulated industries requiring documentation).

Cabinet ovens are used for batch processing, while conveyor designs—common with mediumto- industrial-sized process applications— provide continuous heating of many samples.

Circulation ovens (the most common in labs) come in two types: gravity convection or mechanical (forced) draft. The former often suffer from temperature inhomogeneities and stagnation, which is why ASTM and AASHTO standards call for forced draft ovens.

Larger labs primarily interested in glassware drying are better served by large ovens with customizable configurations than by hightech units with advanced controls. Materials testing or pharmaceutical development groups involved in drying or curing should focus on temperature stability/uniformity and perhaps automated recording and diagnostics. Users should modestly overbuy on temperature range to ensure that their applications will easily be covered.

However, for a given heat rating, oversized ovens consume considerably more energy than compact designs, have a larger footprint, and may require specialized electrical hookups. Smart buyers whose oven volume and application needs vary often purchase several smaller ovens rather than one large one. Lab ovens range in size up to capacities of 25 cubic feet, but most applications employ units of 6 cubic feet and smaller.

Other features to consider are general location, exhaust capabilities, mounting (floor or tabletop), fire/explosion protection, ambient or inert atmosphere, and controls/displays. Location is connected with unit size, ease of use, compatibility with other equipment, exhaust, and access to electric utilities.

Uwe Ross, executive VP at Binder (Great River, NY) notes that in recent years, users’ preferences have shifted from gravity ovens without fans to fan-based forcedair units. Fans distribute heat more rapidly on startup, and “people are becoming less willing to wait for units to heat up,” Ross observes.

Fans provide more even heating by minimizing temperature variability within the oven, to the point where temperature distribution becomes a selling point. ASTM, for example, specifies an oven’s temperature deviations by measuring at nine locations inside the oven, while the newer DIN (Deutsches Institut für Normung) standard uses 27 points. Vendors supply temperature specifications, which vary from fractions of a degree in high-end ovens to several degrees. “Users will tell you that an application works great— on the middle shelf in the rear left corner—but nowhere else,” comments Ross.

Little SHOT III™ Medium Hybridization Oven

• Provides rapid heat-up, excellent temperature stability, and efficient mixing
• Suited for all types of hybridization and incubation applications
• PID controller enables heat-up from ambient to 65°C in 20 minutes with a stability of + 0.5°C
• Forced air convection maintains excellent uniformity throughout the heating chamber

Boekel Scientific
www.boekelsci.com

SHEL LAB Model 1425 Vacuum Oven

• Sizes range from 0.6 to 9 cu. ft.; include three shelves, seamless welds and strong bracing
• Features solid brass vacuum valves with Teflon seats to prevent leaks
• Features positive latch handles with spring-loaded glass for a good vacuum seal
• Temperature range is 10°C above ambient to 240°C

Sheldon Manufacturing
www.shellab.com

OF-G Series Forced Convection Oven

• Temperature range is 10°C above room temperature to 250°C
• Features an over-temperature limiter and door opening alarm
• Optional adjustable fan speed helps to prevent powder sample blowing
•Dual-wall door opens to 180° and features a double-rack door handle

Jeio Tech
www.jeiotech.com/eng

FD Series Drying Ovens

• Available in four models, sizes ranging from 0.7 cu. ft to 8.6 cu. ft.
• Feature temperature range from 5°C above ambient to 300°C
• Include digital temperature setting with accuracy of one degree
• Feature homogeneous temperature distribution and rapid dynamic response

BINDER
www.binder-oven.us