Laboratory ovens have material testing applications in multiple industries, so there are a lot of factors to consider when choosing a lab oven to purchase. This blog post lays out some of the most important features to consider when you’re looking for an oven for aggregate, soils, concrete or asphalt testing.
Look for a model with a maximum temperature rating higher than required in your tests. This assures greater accuracy and uniformity during operation, as well as longer service life since the thermostat, controller and heating elements don’t have to work as hard or cycle as often.
Heat is distributed throughout a laboratory oven’s chamber either by gravity convection or mechanical draft (forced draft) to heat the contents.
- Gravity ovens rely on temperature and density differences in the air for circulation in the chamber, and this can result in dead spots. These ovens are ideal for simple drying applications or in cases where strong air currents may displace lightweight sample materials. They are often more economical to purchase and operate.
- Mechanical or forced-air ovens have fans that actively distribute air through the oven chamber to produce even heating. Many ASTM and AASHTO standards require use of a forced draft oven. Applications with multiple samples, higher moisture contents, and a required level of accuracy may call for forced-air convection.
The internal dimensions of the chamber are an important factor to consider. The chamber needs to accommodate the size and shape of your samples, and you should think about the number of samples you would need to load in at a given time. If you select a chamber size based on a number that is too small, your work flow is hampered. A chamber that is too large means wasted space in your lab and higher operating costs to heat unused chamber area. Externally, the oven needs to fit available floor space and ceiling clearances, and you must be able to move it in through available door openings. Most models have additional shelves available with interiors designed for mounting.
Uniformity in a lab oven is a measure of how consistent the temperature remains at various points in the chamber. Cold or hot spots affect overall accuracy and may affect test results. All reputable oven manufacturers will indicate uniformity ratings of their models.
You should know the capacity and configuration of your electrical supply and the type of hook up the oven requires before purchasing. You may need to factor in electrical upgrades or modifications before installation. For some ovens, amperage draw may be increased during the start-up period. Gas-fired ovens may also be an option when large capacity chambers or continuous operations are anticipated, and when reduced uniformity can be tolerated.
If fumes from heated samples are undesirable or hazardous, the oven’s air must be vented to the outside. In some cases, the oven can be positioned under a fume hood with adequate capacity, but many ovens have options for direct forced-air exhaust through built-in ports and some models include options for explosion-proof motors. Samples with high moisture contents may also require ventilation. Safe and effective ventilation may require the services of an HVAC professional to design and install an optimal system.
Opening the oven door frequently to add or remove samples puts an additional load on the system as it tries to make up lost heat. A short temperature recovery time is a desirable performance feature, but it does require additional energy. If your specifications call for a high level of uniformity and accuracy, shorter recovery time will be important to you. Otherwise, heat loss can be controlled satisfactorily by limiting door opening frequency and keeping an adequate sample load in the chamber.
Many laboratory ovens feature stainless steel interiors and shelf construction to resist corrosion and deterioration. If your materials are not particularly corrosive, you could consider a model that has an interior of plated or galvanized steel as an economical option. Double-wall construction and good insulation make an oven more economical to operate, more uniform, and operate with a cooler exterior surface for added safety.
Many controller options are available ranging from simple analog dial controllers with bimetallic thermostats to high-accuracy programmable digital models with self-diagnostic, logging and calibration functionality, some even with remote web access. Cool stuff, but you’ll have to balance the cost of the features with the benefits. If your lab is “lightly staffed”, it’s going to be helpful for an oven to have timed, automatic, or even remote operation and temperature protection set-points. If the oven will be in use by entry-level technicians, maybe simpler is better. The point is to think it through and make an informed decision. Gilson Customer Service and Technical Support Staff are always here to help you make those decisions.