Chapter 4: High Pressure Airless Spray Method
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Airless Spraying
It is a paint spraying which use high pressure (more than 40 Bar) to push material paint out of nozzle without air pressure to mix in paint. The surface object are covered by material paint only. No air bubble to mix and make damage surface to be not smooth. Low spread rate to avoid disturb environment. Spraying with high speed and also deliver large quantity paint in the same time to complete work in a few time.
Airless spray gun and airless feeding unit of WAGNER are compatible to use under maximum pressure around 110 Bar to 400 Bar.
Characteristic of Airless Spray
The below picture are the example of airless spray procedure. The main principle, free air to mix in spray pattern. First step, material paint are delivered out from nozzle (1) with high speed. Second step is the paint disruption (2) to atomize (3). All procedure are done by high pressure spraying and use a few second for all process. Importantly, the high speed flow are danger to physical user so you may see tip guard in example picture (The cap which hold the nozzle) to protect finger from paint touching.
Example of Airless Spray Gun
Droplet size on surface object
Droplet size determine the resolution of paint atomizing. Large provide resolution less than small size but it depend on job specification and 3 factor are following below;
1. Nozzle Size
Nozzle bore is similar to exit gate from spray gun. Droplet will be larger by following widely size of gate.
2. Material Pressure
It is the push force which move paint out of spray gun. More pressure, spray will be faster but droplet size will be smaller as pressure reduce droplet size.
3. Paint Viscosity
Viscosity affect to deliver hardly paint out of spray gun. High viscosity will make matterl paint to be materialcked sitr and increase droplet size. Using unsuitable nozzle and pressure will be spray slowly paint or unable to spray.
From above table, the information will be used to select the suitable nozzle for job requirement. Please see below link
Airless Spray Pattern
Spray pattern deliver only material paint because using pressure to push paint out from spray gun. With this reason, airless nozzle size must be separated in each size and can not be adjusted by itself because it must built from robust material so it need to change nozzle if it need to be changed nozzle size. Airless nozzle have various type to compatible with many type of job requirement and paint viscosity.
Airless Spray Goal
Main objective of airless spray is quantitive spraying and minimize working time. Spray performance may lower than air spray type but it is compensated by less working time, reduce material consumption rate. For paint spraying in industry, it is suitable to spray with large object or smooth surface subject. For example, roof tile, wood sheet, container box which need to deliver larger quantity paint and finish in a few time and. For architectural coating, it is suitable for wall painting, roof painting and ground painting which deliver a large quantity paint to surface. Unlike air spray, it focus on quality of work or spray with small object.
Workpiece example
Convoy or truck body
Workpiece Example
Smooth Wood Sheet
