Air Knife. Image Credit: haug-static
Air Knives are pressurized air plenums containing a series of holes or continuous slots through which pressurized air exits in a laminar flow pattern. The exit air velocity then creates an impact air velocity that can range from a gentle breeze to a powerful stream.
Air knives are also known as air curtains, air jets or precision drying systems. All the terms describe a device which uses air to blow a substance from a substance. The advantage of using an air-knife is it is faster, takes up less space, and dries oddly shaped parts completely as well as removes solid debris.
How Do Air Knives Work?
Air knives create a high intensity laminar air flow across the length of an object. Laminar flow means the airflow is a balanced and uniform layer of air that does not mix with other later layers nearby. Air knives generally have a specially designed nozzle in order to use low-pressure air and will need a reliable supply to work properly. Low pressure air is less expensive, and safer for workers than high-pressure systems.
Air knife systems consist of an air supply such as a low pressure blower and a nozzle. The blower air pressure varies by application but is usually less than 15 PSI and supplies a large volume of air. The nozzle is designed to provide a long, wide path through which air is dispersed.
Air knives can be made out of aluminum, steel or plastic.
Cross section of air-knife. Image Credit: Health and Safety Executive
Types of Air Knives
There are several types of air knives available depending on the specific application,
High-performance blowers- use high velocity air and are commonly used in food industry applications because the sound enclosures act as a splash guard.
Side channel blowers - are used in applications that require a higher pressure than high-performance blowers.
Straight air-knives- have adjustable slot widths for optimum power and air diffusion. They are used in drying processes on a variety of materials.
Special high-performance air knives- are large extruded aluminum devices with adjustable slot widths for optimum performance and energy efficiency. They can be unique to a system.
Small Section air- knives- are ideal for use in confine spaces because they have a lower air volume and medium power requirement.
Circular air- knives- have many applications including drying continuous extrusions, cables, tubes, rods and to remove coolant from wire drawing. They are designed to replace compressed air-systems in the continuous extrusion industry.
They are used to clean, dry or cool components, webs and conveyors from substances such as water, oil, dust and even more viscous contaminants from a surface.
Conveying systems to clean continuously produced parts and clean the conveyor mechanism to prevent build-ups and clogs.
Video Credit: NEXFLOWAIR
Part washing and process dip tanks use air knives to dry products between dragouts to prevent tank contamination down the line.
Reduce friction by blowing air beneath material sheets.
Cooling or heating of materials
Material sorting by weight or size
Provide an air cushion or barrier.
A two step process is used for drying, cleaning or material removal. First, a high velocity air stream is directed to roll the liquid or material back. This creates a standing wave at the point of a shear and leaves a thin, residual layer. Second, as the "point of impact" of the impinging air flow passes over the residual layer. If liquid, the layer is shattered or atomized to form minute liquid droplets which are carried away by the air stream to leave a clean, dry surface. Other substances such as dust are removed in the second phase.