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Air knife


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 from 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 move (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 the 1950s and 60s, the term "air doctor" was first used to refer to the non-contact method of debris blow-off using compressed air. The printing and textile industries were some of the largest users of air doctors at that time. They often needed wide paths of air from a compressed air system to control the thickness of liquids on a surface, or to blow debris off the surface of materials prior to the next process. Other terms used were air bar, air squeegee, air curtain, air jet, air blast, air blow off, air nozzle, air comb, air blade and air doctor blade. Today the most commonly used term is simply "air knife".

Although air knives powered by compressed plant air are used in a wide variety of industrial applications, industrial blower-powered air knives have proven to reduce the energy usage versus compressed air knives by 50–75% for most applications. Blower-powered air knife systems came of age with the advent of the 1987 , which started the clock on the worldwide phase-out of atmospheric ozone depleting CFC’s (chlorofluorocarbons) then used as cleaning agents in many industries.


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