What is an air-knife ?

Air-Knives deliver a continuous sheet of precisely controlled high-velocity air for stripping away moisture and debris. To work successfully, they need a reliable supply of low-pressure air. To meet this need, Engineers have developed a unique range of Centrifugal Blowers with their performance optimised for Air-Knife applications. The phrase "air knife" is a fancy name for using air to blow a substance from a surface. A crude example can be seen in many machine shops. A machine operator will blow metal chips and oil from a newly machined part using a nozzle attached to a high pressure (100 PSI) air line. The same effect can be achieved by using a properly designed nozzle using low pressure air to remove water, oil, dust, and even more viscous contaminants from a surface. Most air knives use low pressure air because it is much less expensive to produce, much safer for workers, and just as or more effective than high pressure air. High pressure air is used in some applications where lower pressures do not supply enough force. Air knife systems consist of an air supply such as a low pressure blower and a nozzle. Blower air pressures are varied depending upon application but are usually less than 15 PSI. Higher pressures supplied by an air compressor are sometimes used. Low pressure blowers typically supply a large volume of air. Most nozzles are designed to provide a long or wide path through which air is dispersed. Outlet velocities of 35,000 feet per minute (400 miles per hour) or higher are possible, providing considerable force for cleaning or drying. Higher velocities create greater pressure drops requiring larger motors and high­pressure blowers. Air-Knives used for drying, cleaning or material removal accomplish their work in a two-stage process: First, a high velocity air stream is directed to roll the liquid or material back, creating a standing wave at the point of shear and leaving a thin, residual layer. Second, as the "point of impact" of the impinging air flow passes over the residual layer, this layer (if liquid) is shattered or atomized to form minute liquid droplets which are carried away by the air stream to leave a clean, dry surface. Non-liquids are also blown away and removed in this second phase.

A common problem.

In many manufacturing processes, moisture or particles can become deposited on plant or product. These need to be continuously removed quickly and cleanly, but with minimal cost and maintenance requirements. A further complication is that debris often becomes lodged within isolated areas of machinery.Air knifes are frquently used as a solution to common production headaches in food & beverage indstries.

Testing
Trials and testing is essnetial to evaluate your process requirements as each application has unique conditions.

High-performance blowers
High velocity blowers are specifically designed for Air-knives. They are available with or without stainless steel sound enclosures, which also act as splash guards for food industry wash down areas.

Side Channel Blowers
Side Channel Blowers are ideally suited for use in applications where a higher pressure is required than that supplied by a high velocity blower.

Straight air-knives
Used for drying a wide variety of sheet materials, boards, extrusions, bottles, jars, cans, components & castings. They have adjustable slot widths for optimum power and a unique air diffuser system. Single, multiple and special entry ports as required.

Special high-performance air-knives
• Large bodied, energy efficient extruded Aluminium. Hard Anodised, excellent air handling properties.
• Adjustable slot width for optimum performance.
• Unique air diffuser system
• Stainless Steel Air-knives are also available.

Special small section Air-knives for constricted areas
• Lower volume air knife.
• Medium power, available in short to medium lengths.
• Adjustable slot width.
• Ideal for use in confined spaces

Circular air-knifes
Circular for drying stainless steel circular air-knives for continuous extrusions, cables, tubes, rods, etc.
Designed to replace compressed air-systems in the continuous extrusion, industry.
Used after water chillers, or to remove coolant from wire drawing.
Ultra low energy system for fast payback.
Wide diameter for Plastic extrusions, under sea cables and large diameter continuous strips.Stainless steel circular body, with adjustable apperture to suit production speeds. Special designs on request.
Narrow diameter for Rubber extrusions, plastic coated wire, and small dia continuous strips. Stainless steel circular body, with adjustable apperture to suit production speeds.

APPLICATIONS

Uses in Conveying Systems

Typically air knives are used on conveyor systems to clean continuously produced parts. For example, air knives might be used to remove machining chips from aluminum extrusions before anodizing or painting as the extrusions are carried past on a conveyor belt. They might be used after painting to decrease drying time by blowing air onto the parts as they pass by on a hook­chain conveyor. Air knives can also be used to clean open web conveyor belts to prevent product or debris from clogging the openings. Scrapper knives are sometimes used to remove stickies from conveyor belts. The knife scrapes the stickies off the belt and an air knife blows them into a bin.

Uses In Parts Washing and Process Dip Tanks

As parts are lifted from a washing or plating bath, cleaning or plating solution adheres to the parts. This is called dragout. The wash solution can cause contamination of downstream processes or rinse tanks. Air knives can be used to blow solution from the parts back into the process tank as they are lifted from the tank. This reduces the need for rinsing further downstream and reduces contamination of downstream processes. If air knives reduce dragout by 50 percent, rinsing requirements are reduced by 50 percent. Additionally, if wastewater from rinsing operations is treated to remove suspended solids or metals, sludge generation from wastewater treatment could be reduced by 50 percent and the costs associated with treating downstream rinsing could be reduced by 50 percent.

Shape of Parts Suitable for Use with Air Knives

The effectiveness of using air knives is highly dependent upon the shape of the part being cleaned and the type of contamination being removed. A flat, smooth part is much easier to clean with air than a complex three­dimensional item. Additionally, air knives work well for cleaning internal passages, and open, flat meshes can be easily cleaned with an air knife by blowing air through the mesh.

Other Uses

Air knives can be used to reduce friction by blowing air beneath paper or steel sheets, thus providing an air cushion on which they can ride. Also, air knives are often used as a barrier between two areas to prevent mixing of air. For example, where doors are not practical, blowers with nozzles can be used to blow air across a doorway, such as a fork truck entrance, to prevent hot or cold outside air from mixing with conditioned air.

Drying / removing liquid films from surfaces
Controlling the coating of surfaces
Blowing off / removing dust and debris
Impregnation of surfaces
Conveying, holding down or cushioning materials with air
Cooling or heating of materials
Providing an air curtain or barrier
Separating different weights or sizes
Conveyor line speeds to more than 2,000 feet per minute are easily accommodated.

Following are some of the key factors to consider in the design of your Air-Knife system:

The Air-Knife system's objective(s).
Direction of material flow and posture of the material: Horizontal / Vertical / Inclined
Product temperature.
Speed of the line.
Arrangement of product or material on conveyor, i.e., single file, rows, etc.
Dimensions of product(s) involved.
Description of surfaces, including cavities and difficult areas.
Conveyor dimensions .
Temperature limitations, and heat sensitivity of materials.
Drying requirement, and whether product is to be treated (dry, stripped, cleaned).
Types of fluids involved (wash, rinse, treatments,
coatings, acids, plating or printing).

Should you require more information contact Secomak for assistance.