Convection Ovens.


Convection ovens use convective heat transfer, whether the energy source is gas, electric, or steam. Convection is the indirect transfer of thermal energy by the circulation of a heated carrier, such as air. The greater the air velocity and the turbulence in a convection oven, the faster the transfer of heat.

Convection ovens supply air at temperatures not far above the desired curing temperature of the part or coating. That is, the part or coating is typically heated to an equilibrium temperature, usually between 150°F to 1000°F, depending on the application: 400°F is common for many coating applications. The rate of heat transfer is often 500 to 2,000 BTUs per hour per square foot, far less intense than most infrared ovens, but far more uniform.

High velocity convection.

High velocity convection is a unique form of forced convection. In contrast to natural convection ovens, where air flows incidentally as the result of the heat, forced convection is the intentional flow of air provided by fans and blowers. One step further, high velocity convection uses large amounts of air to create velocities at the upper limit that the process will allow. Where forced convection is like a breeze at the beach, high velocity convection is like a tornado. High velocity convection is ideal for many preheating and drying applications.

Advantages of convection. Convection ovens are ideal for uniformly transferring heat to a part. Convection is the most common type of oven. The advantages include accurate control of temperature, simplified burner control, uniform, consistent heating regardless of part size or shape, low capital expenditure, and low maintenance cost.

Disadvantages of convection. The primary limitations of convection ovens result from its low rate of heat transfer and its inherent requirement for rapid air movement, which is unacceptable for powder applications. These characteristics can result in slow start up, slow line speeds, greater need for oven space, and possibility of disturbing or contaminating unfused powders.

Well designed convection ovens exhibit many of the following characteristics:

• Large blower capacity to provide high velocity air and uniform heating. Heat transfer is accelerated by air velocity. Large blowers provide the flexibility to optimize airflow with little effort. A high rate of air circulation insures uniform temperatures throughout the oven.

• Air plenums for uniform air distribution. Perfectly and flexibly designed plenums to distribute air accurately and uniformly at ± 2°F.

• Air seals and heavy insulation to contain heat. To operate efficiently and economically.

• Inverter controlled blower for air velocity control. To provide adjustment of air velocities simply and easily by the push of a button, manually or automatically.

• Proper exhaust. Designed and balanced to meet the specific exhaust needs of the powder or finish being cured.

See also infrared and combination ovens.