An air knife is a tool used to blow off liquid or debris from products as they travel on conveyors. Air knives are normally used in manufacturing or as the first step in a recursive recycling process to separate lighter or smaller particles from other components for use in later or subsequent steps, post manufacturing parts drying and conveyor cleaning, part of component cleaning. The knife consists of a high intensity, uniform sheet of laminar airflow sometimes known as streamline flow.
An industrial air knife is a pressurized air plenum 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 onto the surface of whatever object the air is directed. This impact air velocity can range frosm a gentle breeze to greater than Mach 0.6 (40,000 ft/min) to alter the surface of a product without mechanical contact.
Air knives remove liquids, control the thickness of liquids, dry the liquid coatings, remove foreign particles, cool product surfaces or create a hold down force to assist in the mechanical bonding of materials to the surface. Electrical currents from anti-static bars can also be injected into the exit air knife stream to neutralize the static electricity charge on some surfaces.
In the majority of manufacturing applications for air knives, the air knives are stationary while the product passes through the air velocity air stream. In other circumstances, the product is stationary and the air knives moves (reciprocate or rotate) over the surface of the stationary product. Although there are very few applications where an air knife can actually cut a product (break mechanical bonds between two points), air knives are often the most efficient method of removing or controlling unwanted or foreign substances on any surface.
In conveying systems air knives are used on continuously produced parts or products. For instance in the cement industry air knives can be used to remove dust and gravel from the conveyor. In the case of a high tech product like printed circuit boards that go through many chemical baths during production, air knives speed up the production process by drying the printed circuit boards after each chemical bath. Rubber extrusion used in making seals for car doors and windows require a dip in hot salt potassium nitrate to give it a gloss. An air knife can be used to blow off the excess salt to restore the gloss.
An air knife can also be used to remove viscous contaminants from a surface. Cutting oil used in the production of threaded metal rods can be blown away by an air knife.