Airless atomization

A variation of airless atomization is called air-assisted airless. A small amount of compressed air at 35—170 kPa (5—25 psi) is introduced adjacent to the airless nozzle and impinges upon the thin sheet of fluid as it exits from the nozzle. This air aggravates the turbulence in the fluid and results in improved atomization at lower fluid pressures. Often, material that caimot be properly atomized using straight airless atomization can be using the... 

An aerosol container can be considered a special appHcation of airless atomization (see Aerosols). The pressure is usually suppHed by a Hquefied gas in the container at its equiUbrium pressure. The material being sprayed has a very low viscosity to provide easy material flow through the feed tube and to permit fine atomization. 

Airjet spinning, cotton yarn, <5 17 Airjet textured yarn process, 20 19 Airjet texturing, 19 753 Air-knife chemical finishing, 17 513 Air knife coating, 7 10-11 method summarized, 7 5t Air-laid processes, 11 179-180 Air legislation (EU), 23 121 Airless atomization, in spray coating, 7 69-70... 

Brooks, W.R., "Advantages of New Airless Atomization Spray Gun Explained", Journal of Cellular Plastics, 1(3) 419 (July... 

Air atomization, airless atomization, and ultrasonic atomization are some of the methods used to create atomized spray. While these methods differ slightly, they all are generally less selective than film coating and the... 

In conventional spraying, atomization is the result of external mechanical forces, i.e., the exchange of momentum between two free jets (air and paint). Atomization may be classified as compressed air atomization (air 0.02-0.7 MPa, paint 0.02-0.3 MPa), airless atomization (paint 8 40 MPa), air-assisted airless atomization, also termed airmix process (air 0.02 0.25 MPa, paint 2-8 MPa), and special technologies (Table 8.3). 

Conventional nitrocellulose lacquer finishing leads to the emission of large quantities of solvents into the atmosphere. An ingeneous approach to reducing VOC emissions is the use of supercritical carbon dioxide as a component of the solvent mixture (172). The critical temperature and pressure of CO2 are 31.3°C and 7.4 MPa (72.9 atm), respectively. Below that temperature and above that pressure, CO2 is a supercritical fluid. It has been found that under these conditions, the solvency properties of CO2 ate similar to aromatic hydrocarbons (see Supercritical fluids). The coating is shipped in a concentrated form, then metered with supercritical CO2 into a proportioning airless spray gun system in such a ratio as to reduce the viscosity to the level needed for proper atomization. VOC emission reductions of 50% or more are projected. 

Airless spray uses hydrauHc pressure to deUver the paint. Paint is brought to the spray gun under 7—40 mPa (1000—6000 psi), where it is divided into small separate streams and forced through a very small orifice to produce the spray. Airless spray is faster, cleaner, and less wasteful than air atomization, but demands good technique because it deUvers paint very quickly. 

The principal factors affecting transfer efficiency are the size and shape of the object, the type of apphcation equipment, the air pressure to the spray gun, and the distance of the spray gun from the object. The transfer efficiency becomes lower as the object becomes smaller or more complex. The transfer efficiency increases when the spray gun is brought closer to the object and when the atomizing pressure is reduced. The transfer efficiency of different types of apphcation equipment in descending relative order is manual > electrostatic spray > airless spray > conventional atomized air spray. 

Air-Atomized Spray Airless Spray Pressure-Atomized Electrostatic Spray... 

The cost savings in 2007 USD for airless spray and pressure-atomized electrostatic spray are as follows14 ... 

A method for atomizing and spraying a liquid, suspension, or emulsion by high pressure, without using compressed gas at the spray nozzle. Also termed hydraulic spraying . Airless spraying is used for paints and urethanes among others. 

Spray coating is used before and after a product is assembled particularly if already assembled and has complex shaped and curved surfaces. Many different types of spray equipment are in use to handle the different forms of paints used. They are classified by their method of atomization (airless, air, rotary, electrostatic, etc.) and by their deposition assist (electrostatic or nonelectrostatic, flame spray, etc.). Spraying techniques may fall into several of these categories. They range from simple systems with one manual applicator to highly complex, computer-controlled, automatic systems. They can incorporate hundreds of spray units. Automatic systems may have their applicators mounted on fixed stands, on reciprocating or rotating machines, on robots, and so on. 

The use of supercritical carbon dioxide (CO2) as a component in a solvent mixture is another ingenious technique to reduce VOC emission by 50 percent or more. This technique takes the advantage of the fact that CO2 is a supercritical fluid below its critical temperature (31.3°C) and critical pressure (7.4 MPa). Sohd coating and supercritical CO2 are metered into a proportioning spray gun in such a ratio so as to reduce the viscosity to the level needed for proper atomization. Airless spray guns are used. 

Application. Cellulose acetate butyrate lacquers are usually applied by spraying (air atomization, airless, spinning disk). Application by brush or dip is possible but less commonly used. 

Suitable for special-effect paints Airless (hydraulic) atomization ... 

In airless hydraulic) atomization the paint is forced through a slit nozzle of hard metal under high pressure (8-40 MPa). On account of the high degree of turbulence, the paint stream disintegrates immediately after leaving the fluid tip. A similar atomization process occurs in spray cans where the paint pressure is produced by the propellant gas. 

The combined airmix process operates at a lower paint pressure (2-8 MPa). Additional low-pressure air jets (0.02-0.25 MPa) from the air-cap bores impinge on the spray jet to mix and homogenize it. In addition to the atomizer and a compressed air generator (airless pump), the airmix unit therefore also requires compressed air for postatomization. Advantages over the airless method are the less sharply defined spray jet and the smaller droplet size. Compared with compressed air atomization, a low-mist coating is possible. 

Electrostatically assisted compressed air, airless, and aiimix atomization... 

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