Metal Finishing Guide Book

2013

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Table I. Spray Application Processes Figure No. 2.2 2.3 3. 3.1 3.2 3.3 170 Process Advantages Limitations Air-assisted airless–lower fluid pressures than airless (normally below 1,000 psi); low pressure is added via the air nozzle to further atomize the ready preatomized spray. Used by furniture and industrial finishers. Air-assisted airless (heated)–uses same principle as 2.2 with the addition of heat to reduce viscosity and improve flow. Electrostatic atomization– voltage difference between paint dispenser (low-speed rotating disc or bell) and work causes paint to be attracted to the grounded work. Used by most appliance manufacturers. High production of uniformly shaped parts. Electrostatic attraction– material is atomized using convention air, airless, or air-assisted airless principles; particles are electrically charged and attracted to the work. Electricity may be turned off to permit normal spraying. Electrostatic attraction (heated materials)–same as 3.1 except materials are heated. High speed rotation atomizers–high speed (10,000–70,000 rpm) rotating disc or bell gives exiting paint particles velocity and direction. Voltage differential then takes over and allows electrically charged paint particles to attract themselves to a grounded part. Material savings 50% better than air spray plus lower overspray and fog. Less tip wear; longer pump life than airless. Higher film build per pass than air spray. Atomization not as fine as air spray. Hydraulic injection may occur. Tip plugging. Strict maintenance is required. Better flow of material. Strict maintenance. Same Higher solids per pass of gun. limitations as 2.2. Viscosity control. Finer atomization than 2.2. High transfer efficiency at 65–95%. "Wrap around" effect, coating other surfaces. Minimum overspray. Parts must be conductive. Limit to shapes that may be coated. High production rate required. High voltage and spinning cup or disc may be hazardous. "Wrap around" effect. Material savings through minimized overspray. Use with or without electrical charge. Some conductive materials will require special equipment. Parts must be conductive. Difficult to penetrate cavities or recesses with power supply on. Ability to use the systems coupled together to get all the advantages as in 1.5, 2.1, 2.3, and 3.1 High transfer efficiency. "Wrap around" effect, coating other surfaces. Works well with high solids coatings. Minimum overspray. Same limitations as in 1.5, 2.1, and 3.1. Parts must be conductive. Limit to shapes that may be coated. High production rate required. High voltage and spinning cup or disc may be hazardous.

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