Continuous Airflow Styles
Figure A – Top Flow with bottom return
There are five (5) standard types of airflows used in conveyor ovens: Top-Down, Bottom-Up, Top & Bottom, Horizontal, and Combination. Horizontal and Combination airflow are least common in conveyor ovens, but are used in batch ovens quite often.
Whether the product is conveyed by an overhead conveyor, a flat belt conveyor, or a spindle (chain-on-edge) conveyor, these type of air flows are industry standards and provide various advantages as described hereafter.
Top-down air flow is very popular for flat belt and spindle (chain-on-edge) conveyors when the product height is less than 39" (1 meter). The relationship from the top of product to the bottom of supply duct is very important and should be considered especially in powder coating applications. Belt conveyor ovens typically utilize a return air duct below the conveyor belt (see Figure A) to ensure the air passes through the conveyor belt. Spindle conveyor ovens usually have the air returned along the sides (see Figure B).
Figure B – Top Flow with side returns
We do not recommend Top-Down air flow for overhead conveyor ovens. Generally, the product height prohibits good air control. The hot air, lighter than the cold air, loses velocity after leaving the duct and doesn't fully engulf the load, causing cold areas at the bottom of the work.
Bottom-up air flow is an excellent choice for continuous conveyor applications, both belt type (see Figure C) and overhead (see Figure D). The air is supplied below the work area, allowing the air to flow naturally upward, through and past the product, ensuring proper heating (as long as the belt and/or product does not impede the airflow as it travels vertically upward). We highly recommend Bottom-Up air for overhead trolley conveyor ovens. Regardless of the product height, the hot air fully bathes and engulfs the product as it naturally rises.
Figure C – Bottom-Up Flow
Top and bottom air flow is primarily used in flat belt conveyor applications. This type of air flow is particularly effective with densely packed small parts of heavy loads. As you can see in Figure E, supply ducts are located above and below the load, and air is delivered equally to the work chamber.
These are the three most common types of air flow for conveyor applications. Choosing the best air flow configuration for your application is very important and can make or break the process. However, air flow type is only one of the design parameters important to the success of an oven's performance and Wisconsin Oven will be glad to discuss your specific heat process needs.
Figure D – Bottom-Up Flow
Figure E – Top & Bottom Flow