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What is the benefit of positive displacement? How do atomized air spray systems work?


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Air-Atomized Precision Spray Systems

In many manufacturing operations, fluids need to be applied in a distributed manner. One way of achieving this is to utilize an air atomized precision spray system. This type of spray product uses air flow to atomize or break up the fluid and propel it to the substrate. The atomization air flow can be shaped to distribute the liquid into any number of desired spray patterns. This type of system will use a fluid delivery system with an air flow metering system to deliver fluid and air to a nozzle where they will mix and will be dispersed by the nozzle tip. Spray coating this way allows for very low volumes of fluid to be evenly distributed.

creating an atomized spray
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How do atomized air spray systems work?

Air atomized spraying systems use nozzles that typically have two inlet ports; one for the atomization air and one for the fluid. The fluid flow rate can be adjusted through a number of means, depending on the nozzle.

  • Pressure based fluid delivery systems can use metering screws, fast acting pulse width modulated valves, needle valves, or adjustable pressure regulators to control the flow of the fluid.
  • Pump based fluid delivery systems can deliver the precise flow rate via a continuous flow positive displacement pump to control the flow of fluid.

The air and fluid is atomized by means of the nozzle tip. Air flow can be controlled by a needle valve, metering screw, or by pneumatic pressure regulator. The nozzle tip is responsible for shaping the flow of the air into the desired shape or spray pattern coverage. Precise spray control is achieved by careful adjustment of both the flow of air and fluid.

The air and the fluid typically mix at or very close to the nozzle spray tip. This helps provide crisp operation with little to no dripping. Some nozzles are classified as internal mix and some are an external mix. The type required usually depends on the desired spray pattern.

  • Internal mix air atomized spray nozzles combine the air and fluid before exiting the nozzle tip. The air and fluid mix and then together exit the nozzle orifice as an atomized spray.
  • External mix air atomizing spray nozzles combine the air and fluid after exiting the nozzle tip. The air and fluid exit the nozzle separately and mix outside of the nozzle into the atomized spray.
atomization of a fluid via separate air and fluid channels
conical vs. fan spray patterns

What are all the elements to an atomized air spray system?

A typical air atomized spray system will require a compressed air supply, a fluid supply system, the nozzle, tubing, valves, and adjustment devices. Fluid supplies can be either pressure or pumped based and can incorporate closed loop feedback controls if extreme precision spray control is required. Nozzles can be configured with onboard metering adjustments for both air and oil or the controls can be remotely mounted for easy adjustment away from the nozzle. Valves for actuating or starting the flow of air and fluid are also required for the system. These can be manual or electrically controlled for process automation. Some special systems utilize electrostatic spraying systems in which the particles and the substrate receive opposite charges to ensure excellent transfer ratios.

What are the benefits of atomized air spray systems over other dispensing methods?

  • More control over spray pattern
  • Atomization can happen without the need to increase fluid pressure
  • Can produce much finer droplets than air-only(hydraulic) atomization
  • Not as prone to clogging as air-only nozzles
  • Can atomize a wider range of fluid viscosities

The main benefit of atomized air precision spray equipment is that a small volume of fluid can be evenly distributed over a relatively large surface area. This makes this system ideal for applying thin film coatings in an efficient manner. Liquid only atomized nozzles just take a much larger volume of fluid to produce an even spray pattern. There are a lot of adjustments available to dial in the correct amount of coating. An air atomized spray nozzle is usually a bit more expensive than a fluid only atomized nozzle and is also much less expensive than an ultrasonic atomizer nozzle.

Another advantage is that air atomized nozzles can be used to spray fluids with a wide range of viscosity. Thin fluids such as water or isopropyl alcohol can be sprayed as well as thicker fluids such as heavy oils, lubricants, and even grease. Various applications are candidates for air atomized spray systems such as coating in food processing, lubrication for metal forming, applying lubricants during product assembly, applying rust preventative and many others.

What are the downsides or challenges compared to other methods?

  • Produces large volumes of air turbulence which can prevent droplets from settling in corners and recesses
  • Prone to fogging when set up incorrectly
  • Requires compressed air

The amount of air flow propelling the fluid to the substrate should be carefully adjusted to maximize the transfer efficiency of the fluid to the target. With too much atomization air flow, the fluid can be over-misted or fogged causing excess overspray or drift off. Usually this can be controlled with careful adjustment or sometimes with an overspray shield or vacuum system.

Unist products for atomized air spray-based systems

Several Unist products are available for precision spray and coating in both continuous spray and intermittent spray applications. Both with pressure-based fluid delivery sources and pump based. Contact us today to discuss your spray application needs.