Laboratory ovens are convection appliances for general purposes in the scientific and manufacturing industries. Applications include sterilization, experiment management, drying, processing, and testing.

 

Operation

 

Selecting laboratory ovensA laboratory oven heats its contents via the principle of convection. The heating element is not located within the specimen chamber of the oven, but in a separate external envelope. This prevents radiant heat from affecting the specimen, but the resulting temperature of the oven walls is enough to heat and dehydrate a specimen.  

 

Convective heat transfer is achieved by gravity or mechanical convection. In the former, cooler air is displaced by warmer air and directed towards the heating element until the entire chamber is up to temperature. Since this method has poor uniform heat distribution, energy waste, and a longer preheat time than mechanical convection, mechanical convection lab ovens are favorable. These types heat quicker and more evenly due to blowers and baffles in the oven chamber.

 

Air intakes and exhausts can be adjusted to withhold or release humidity, and are necessary to expel VOCs and fumes. Insulation reduces the rate of thermal transfer and is responsible for the energy efficiency of the oven. The oven itself is typically steel in construction which helps prevent radiant heat from the oven exterior. A locking door with robust gaskets provides user access to the oven chamber.

 

The essential functions of a laboratory oven are:

 

  • Drying: removing the moisture from the specimen and chamber as efficiently as possible.
  • Baking: heating a substrate without dehumidifying it.

  • Curing: the sample is physically or chemically altered by a slow baking and drying process.

Types

 

These ovens have a specialized application or characteristic which separates them apart from general-purpose lab ovens.

 

Name

Description

Image

Vacuum ovens Vacuum ovens typically process metal components. Brazing, sintering, heat treatment, and case hardening applications are most common. There are no gases in the oven chamber, which prevents convection and oxidation. These ovens are capable of temperature distribution exceeding 1100° C. Metals quench quickly in the oven when an inert gas is introduced after processing. Vacuum ovens are common for batch processing.

Selecting vacuum laboratory ovens

Image credit: Binder Inc.

Clean process oven These stainless-steel, HEPA-filtered lab ovens assist in medical equipment manufacturing (syringes, catheters, stents, pacemakers, and eyesight lenses). They also participate in semiconductor wafer production. Temperatures commonly exceed 260° C. Batch processing and conveyor processing are common.

Selecting clean process ovens

Image credit: Despatch

Burn-in Burn-in ovens heat soak semiconductors and microprocessors in temperatures over 260° C, often in a nitrogen or air atmosphere.

Selecting cleanroom ovens

Image credit: Despatch

Reach-in Horizontal airflow creates uniform heating cross all shelves, whereas most lab ovens utilize vertical airflow. This type of oven is excellent for applications which require 100+ air exchanges each hour, but can also be used for general laboratory purposes.

Reach in oven diagram

Image credit: Despatch

  

Specifications 

 

Size

 

Oven volume and mounting are of critical importance. The internal cubic volume of the oven chamber must suit the spatial needs of substrates, and can ideally accommodate multiple samples during a single oven cycle. An adjustable shelving system can be invaluable to utilizing all of the available space. Control mechanisms are easily located and articulated by the operator.

 

Selecting truck-in walk-in lab ovenAdditionally, lab ovens are manufactured in three mounting varieties.

 

  • Benchtop: the lab oven is installed upon a workbench or counter for easy access. These models often include hardware for stacking several lab ovens upon each other.  
  • Cabinet: the oven is a free-standing item of laboratory furniture, typically with a larger capacity or a specialized application.

  • Truck-in/walk-in: the oven (pictured right) is large enough where substrates are carried into the chamber by the operator or with material handling equipment.

Temperature

 

Lab oven selectionUniform temperature throughout the entire oven chamber is the most important aspect regarding operation. Standards bodies assess spatial temperature accuracy by testing the oven chamber at 9 or 27 separate points within a time frame.

 

Most laboratory ovens have a temperature range of just above ambient temperature to 300° C; those ovens which exceed this range are application specific. Ovens also have a temperature tolerance, which references the accuracy to which the oven preheats; increments of fractions of a single degree to tens of degrees are common.

 

Temperature is regulated by one of three technologies.

 

  • Thermostat: a simple on/off switch engages the heating element to maintain a set temperature. Typically, temperature briefly exceeds this value before settling, and ultimately fallins below the threshold.
  • Proportional control: a thermostat monitors oven temperature, but eases heating as it approaches the preheat value to prevent any overheating.
  • Proportional integral derivative (PID) control: a processor calculates the amount of energy needed to maintain a temperature, and considers it against the rate of heat loss. This prevents over- and underheating, and is typically the most energy efficient means of temperature regulation.

Controlled Atmosphere

 

Some lab ovens are compatible with equipment which inserts a specific gas or gas compound into the lab chamber, or removes the atmosphere of the oven chamber altogether (vacuum oven). These ovens typically have flow meters and solenoid valves to control fluid flow, as well as internal sensors to register atmosphere particulate. It is most common to insert an inert gas such as argon or nitrogen into the oven chamber at a pressure of five to ten times the volume of the oven. This blankets the specimen and prevents oxidation and condensation from forming in the chamber.  

 

Energy Efficiency

 

A lab oven requires considerable quantities of energy to heat the chamber. It is common for ovens to be left on for long periods, sometimes for days, to reduce preheating times. For clear reasons, reducing thermal egress from the oven can result in measurable cost savings. Ovens with a boost feature incorporate an accelerated preheat to limit long operating periods.

 

The oven shell is typically steel in construction and underlying layers of insulation reduce thermal transfer rates. An efficient oven quickly reaches uniform temperature by thorough circulation. Door gaskets help retain heat around door tolerances. Many ovens are able to compensate for ventilation of the chamber. Recovery time is how long it takes an oven to recuperate to the preheat value after the chamber has been ventilated, such as by a door opening.

 

Maintenance

 

On average, lab ovens are obsolete every seven years. This is in part due to design innovations, but mostly because defective lab ovens can be costly and difficult to repair. Many lab ovens never return to specification after the malfunction is addressed, and a new lab oven typically costs less than refurbishment.

 

Oven maintenance should be conducted at routine intervals. Ventilation ports, gaskets, sensors, controls, heating elements, and blowers should be reviewed for faults. The oven should also be temperature calibrated on occasion.  

 

Features

 

  • Alarms: audible tones signal the oven has reached operation conditions which require operator attention.
  • Auto shut-off: an idle oven shuts off after a preset period has elapsed.
  • Boost: the oven's preheat time can be shortened by briefly increasing energy consumption.
  • Blow out panel/door: special panels or the oven door eject from the oven in the event a specimen explodes. This directs the concussion in a single direction to limit peril to personnel and equipment.
  • Conveyor: a conveyor mechanism translates the specimen through the oven, with a finished specimen emerging from the output.
  • Data logging: the lab oven is compatible with mechanisms which strictly record the lab oven's every operation. This is particularly important in pharmaceutical and biological applications.
  • Overtemperature protection device (OTPD): a mechanism automatically shuts down the oven if a maximum temperature has been exceeded.
  • Quick start: the oven begins a preheat cycle without input operation parameters.
  • Temperature monitoring: the oven or connected equipment records the temperature of the oven chamber at intervals, and informs the operator as necessary.
  • Temperature ramping/programming: the preheating cycle can be extended, or the oven can be instructed to change temperatures at a preset time.
  • Timed: the oven is instructed to shut down after a preconfigured time has passed.

  • Viewing window: the oven construction contains a window to observe specimens within the oven chamber.

Standards

 

The following standards may prove serviceable when considering laboratory ovens.

 

ASTM 5374 Testing forced-convection laboratory ovens

DIN 12880 Electrical laboratory ovens

BS 2648 Performance of laboratory ovens.

 

Applications

 

Lab ovens are prevalent in chemistry, biology, pharmaceutical, forensics, and environmental laboratories. Common applications for lab ovens include:

 

Resources

 

Lab Manager—Lab Ovens

 

Shel Lab—Ovens 

 

Images credits:

 

Trent Heat | Despatch | Elve Flow | Lab Manager


Related Products & Services

  • Autoclaves and Sterilizers

    Autoclaves are used for applications requiring constant pressure and temperature for long periods of time.  Common applications include the sterilization of instruments and polymerization of rubbers and plastics.

  • Ovens (industrial)

    Industrial ovens are batch or continuous process enclosures or tunnels that are insulated and used for thermal processing. Ovens are lower temperature (usually < 1400° F) thermal processing units, usually without refractory insulation.

  • Vacuum Ovens

    Vacuum ovens are heat-treating ovens that use a low atmospheric pressure instead of a protective gas atmosphere. This helps to alleviate surface reactions.