• Back Ionization: An excessive build up of charged powder particles which may limit further powder being deposited on the substrate. The electrical charge on the surface layer may be reversed, repelling additional powder. Bulk Density: Mass per unit of volume in powder form including the air trapped between particles.
• Cartridge Filter: A cylindrical filter unit used to separate oversprayed powder from air for recovery and reuse.
• Corona Charge: The process of inducing a static electric charge on powder particles by passing the powder through an electrostatic field generated by a high voltage device.
• Cure Schedule: The time/temperature relationship required to properly fuse a powder coating.
• Cyclone: A type of recovery unit using a centrifugal process to separate oversprayed powder particles from an air flow.
• Delivery: The process of moving the powder through the application equipment to the end product.
• Edge Coverage: A powder's ability to flow over, build and adhere to sharp corners, angles and edges.
• Electrostatic Spray Technique: A deposition method of spraying and charging powder so that it is deposited on a grounded substrate. (See Corona charging and Tribo charging.)
• Faraday Cage Effect: A condition that may exist on a substrate due to its geometric configuration that may inhibit the electrostatic deposition of powder particles at a specific localized area.
• Film Formation: The forming of a continuous film by melting powder particles and fusing them together by the application of energy.
• Fluidizing: The process of suspending the powder in a continuous stream of air giving it "fluid" characteristics. Used to facilitate transfer of the powder to the application device.
• Fusion: The melting and flow of individual powder particles when heated to form a continuous film.
• Grounding: The electrical grounding of the item to be coated.
• Impact Fusion: The combining of powder particles to form a solid mass during the delivery and application process.
• Lower Explosive Limit (LEL): The lower point for a range of concentrations of organic particles suspended in air which can be ignited by a sufficient energy source.
• Micron/Mils: Common unit of measurement of coating thickness. 25.4µ (microns or micrometers) = 1 mil (one thousandth of an inch)
• Particle Size: Average diameter of an individual, irregular powder particle.
• Recovery: The process of removing non-deposited powder from the air prior to reclaiming it for reuse.
• Spray Booth: A specially designed enclosure in which powders are introduced, contained and recovered during the coating process.
• Surface Appearance: Generally refers to the smoothness and gloss of powder coating films and the presence and degree of surface defects.
• System Utilization or System Efficiency: The combined efficiencies of each component in the powder coating system resulting in total material usage compared to the amount of material entered into the system.
• Transfer Efficiency: The ratio of the powder deposited on the workpiece compared to the amount of powder sprayed during a fixed time period.
• Transfer Efficiency: The ratio of the powder deposited on the workpiece compared to the amount of powder sprayed during a fixed time period.
• Tribo Charging: Process of creating a static electrical charge on powder particles by creating friction between them and a nonconductive material.
• Virgin Powder: Powder that has not been previously sprayed as opposed to reclaimed powder.
• Wrap: A characteristic of electrostatic application for the powder to seek out and adhere to parts of the substrate not in direct line of sight of the delivery point.

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For a quality compressed air supply, maintain the correct volume of air available for the powder paint system. Clean, dry air is important. The compressed air supply feeding the powder system needs to be conditioned. This is accomplished with a properly sized air dryer. Either a refrigerant or regenerative air dryer is acceptable. When the air volume required is 500 SCFM or greater, a regenerative unit may be preferred. Other items required with the air dryer are a particle filter and a coalescing filter. It is best that the filters in the system be set up with automatic drains or flags that indicate when service or replacement is required.

Air quality requirements are three-fold: maximum oil content of 0.1 ppm, dew point of 35oF or lower, and a particulate matter no large than 10 microns. By keeping the powder free of moisture, oil and ther dirt. Powder fluidizes more evening and the pump can lift the powder through the suction tube easier and transport it to the gun more efficiently.  
 

• Inconsistent compressed air supply or quality from the plant air source can cause pump delivery rates to increase or decrease.
• Tubing and powder hose lengths can affect the ability to provide consistent delivery rates.
• Wear of the powder pump parts can cause poor powder delivery.
• Maintain a good blend of reclaim and new powder to help control the powder particle size distribution.

Another issue associated with the powder pump is "surging." This typically is the result of an inconsistent compressed air supply or blockage in the powder pump or feed line, causing the powder to puff, or surge, out of the powder feed line and cause a reject. When powder feed surging occurs:

• Check powder feed hoses to determine if they are pinched, routed correctly, excessively long or kinked.
• Check for impact fusion inside the hoses or on the gun components that can impair flow and cause powder surging. Performing periodic maintenance of the equipment can avoid this problem. Follow the manufacturers' guidelines for regular checks and cleaning of the components in the powder path. This includes the gun tips, electrodes and pump inserts. To prevent additional build up, never leave the powder hoses full of powder at the end of shifts or overnight. Before shutting down the system, use compressed air to blow the liens and guns free of residual powder. This should be done at the end of each shift and before breaks.
• Check fluidization that may cause powder surging. Uneven fluidization can cause too little or too much air in the mixture at the suction tube. Fluidization should be an even and uniform soft boiling in the feed hopper.

To avoid back ionization, try the following:

• Lower the voltage setting. But be aware that reduced voltage may lead to unacceptable penetration and/or coverage.
• Optimize the gun-target distance for coating the desired part and attempt to maintain that distance at all times.
• Use a grounding ring as a ground source to reduce the voltage strength.

When a part cannot make good contact with the hanger or transporting rack, then only a small amount of powder will be attracted to the part surface. To avoid this problem, the following solutions may help:

• Clean hangers regularly.
• Make sure the part is making good connection with the hanger each time a part is loaded on the line. A good hanger design allows for good contact surface between the part and the hanger.
• Check ground strength periodically. By using a megaohm meter, the ground strength can be measured and should be no greater than 1-million ohms of resistance.
• Maintain the ambient conditions in the room to the recommended levels suggested by the materials and equipment suppliers. Typical humidity in the room should range from 45 to 60 percent relative humidity.
• Investigate the power supply for a failure if poor charging cannot be traced to a grounding issue. Powder equipment manufacturers offer some type of high-voltage gun meter. Including the meter in a preventative maintenance program will minimize poor charging.

Most problems of penetration are caused by the "Faraday cage effect".  The Faraday effect occurs when an electrical cage is created by the part configuration.  Edges and shapes that create deep recesses are attractive antennae for the charged particles, inhibiting the penetration into the corners.  The charged powder particles always want to take the path of least resistance.  To overcome this problem, several techniques may be employed: 

• Try various nozzle tip designs.  Different tips produce a different and particular spray pattern and some are designed specifically to increase penetration.  Tips best suited to penetration typically have narrower pattern or focus and as a result higher forward velocity.
• Another method, often combined with tip design, is to decrease the gun to target distance.  By bringing the gun closer to the part, the powder is forced into the recessed area that is to be coated.  This works well for manual application and may serve well in automatic applications.  In automatic applications, the adjustment should be tested to ensure that coverage is not lost somewhere else on the part by relocating the guns.  In automatic applications the right gun target distance is very important.  By moving the gun in or out relative to the product coated causes the effective pattern size to change.  This will change the ability of the powder to cover the part.  If the penetration area can be made repeatable by hanging configuration an additional target gun may be used to improve the performance.
• Gun target distances for manual applications may be from 2" to 6" away from the substrate.  For automatic applications, a target distance of 8" to 12" from the substrate is common.
• Increase the spray velocity by increasing the supplemental air or possibly increasing the powder delivery.  Increasing delivery air pressure will give the powder particles more forward velocity in an attempt to overcome the Faraday area.  Because there is more forward velocity it is important that the angle and target location of gun is set to reduce the possibility of the powder simply blowing back out of the area being addressed.  The drawback to higher velocity is often more powder being sprayed.  This can cause additional build on the edges and surfaces surrounding the penetration area.
• Voltage and current of the applicator can often be used to manipulate penetration performance.  Often it is best to turn the voltage down to penetrate a recessed area.  Minimizing the voltage achieves better penetration by reducing the effects of the electronic cage created.  To improve penetration of the guns output voltage by 30 to 50%. 

For a quality compressed air supply, maintain the correct volume of air available for the powder-paint system. Clean, dry air is important, too. The compressed air supply feeding the powder system needs to pass through an air-drying unit. Either a refrigerant or regenerative air dryer is acceptable. When the air volume required is 500 scfm or greater, a regenerative unit is usually needed. Other items required with the air dryer are a particle filter and a coalescing filter.

Typical air quality requirements are three-fold: maximum oil content of .1 ppm, dew point of 35°F or lower, and particulate matter no larger than 10 microns.

By keeping the powder free of moisture, oil and other dirt, the powder pump can lift the powder through the suction tube much easier and transport the powder to the gun more efficiently.

Other items to consider:

• Check powder feed hoses to determine if they are pinched.
• Check for impact fusion inside the hoses or on the gun components that can cause powder surging. Performing periodic maintenance of the equipment can avoid this problem. Use compressed air to blow the lines out at the end of each shift and before each employee break.
• Check fluidization that may cause power surging. A minor adjustment in the fluidization pressure corrects the problem.

• Reduced cycling and degradation of powder.
• Reduced wear on pump and delivery components.
• Less frequent rejects due to inconsistent coverage.
• Less wear in the recovery and recycling system.

Some other factors affecting the powder delivery rate:

• Inconsistent compressed air supply from the plant air source can cause pump delivery rates to increase and decrease.
• Tubing and powder hose lengths can affect the ability to deliver consistent delivery rates.
• Wear of powder pump parts is critical to achieving good powder delivery.
• Maintaining a good blend of reclaim and new powder helps to control the powder-particle-size distribution.

Another variable affecting powder delivery is the temperature and delivery of the ambient conditions. Powder systems may or may not be located in an environmental room and are therefore, subject to problems occurring due to humidity and temperature. Consistent powder-delivery rates are best achieved when the temperature is between 60°F and 80°F and the relative humidity is between 45 percent and 60 percent.

Moist powder can create a blockage in the powder pump, causing the powder to puff or surge out the powder feed line and onto the part.  This surging leads to rejected parts, higher rework rates, wasted powder and ultimately wasted time and money.  So, save your powder from a rainy day by storing it in a clean dry, air-conditioned environment.
 

Appearing as a pock-marked finish, orange peel usually occurs as a result of back ionization.  Back ionization is a condition in which an excessive buildup of charged powder particles on a part limits additional powder from being applied.

But there is good news!  It is possible to minimize or eliminate orange peel with the proper tools and techniques.  Here are a few tips that might help:

1. Proper ground is integral to all powder applications, so first check to see if your equipment is sufficiently grounded.

2. Check the powder manufacturer's data sheet for recommended film thickness.  Try to keep the film thickness down.

3. Make sure the powder is not damp.

4. If your unit allows you to reduce current, lower the current setting to between 5 and 22 micro amps and keep Kv maximized as high as possible.  If your system does not allow you to adjust current then reduce the Kv level to a lower voltage (40-60Kv maximum)

5. Trigger off the part until a soft cloud of powder stabilizes, then move onto the part and begin coating.  (This step is unnecessary if your are using an ITW Gema Optiflex^TM Unit due to its superior air regulation.

6. Keep the gun 8 to 10 inches from the part and coat in a smooth, uniform manner.

7. Lastly, be sure your oven is heated to the powder manufacturer's recommended temperature so parts can heat fast enough for good flow prior to cross-linking.

Orange peel belongs in the kitchen, not on your parts!  By following the manufacturer's recommendations and using proper techniques, you should be successful in eliminating the orange peel effect and producing higher quality finishes.

ITW Gema produces a SuperCorona ring (also called a "corona ring") for every model of gun we sell.  Adding this accessory to your gun might make it possible for you to produce smoother finishes and get better penetration into parts with deep crevices.

If your parts require a heavy film build, a SuperCorona ring can help you apply a smoother finish and minimize the occurrence of back ionization.  Conversely, if you require a thinner coating, but a combination of flat surfaces and recesses make it impossible to accomplish without creating a heavy film build around the recessed areas, a SuperCorona ring could make a significant difference.  How?  The corona ring draws some of the free ions away, minimizing the available charge on the powder.  This enables you to achieve increased penetration and a smoother finish.

The simple attachment of a SuperCorona ring to your existing powder gun results in visible improvement to the surface quality of your parts; particularly where orange peel and back ionization is a problem. 

Two common methods of water purification are Deionization (DI) and Reverse Osmosis (RO).  DI units work by utilizing a process known as "ion exchange".  DI systems do not produce totally pure water, but the output is sufficiently clean for most applications.  RO systems, on the other hand, push water through membranes that trap impurities.  RO systems are much more effective than DI systems and can remove up to 99% of the impurities.  The type of membrane used will determine how pure the output of the RO unit will be.  RO and DI systems are often used in conjunction with each other to obtain the purest water possible.  Water is first sent through the RO system and is then processed by the DI unit for further purification.

The truth is that for most pre-paint applications, either will work.  An exception is for electro-coat operations, where DI water purification is required. RO has gained favor recently because it is perceived to provide more consistent quality output over time. Also, the extra cost and hazard associated with the chemicals in a DI unit are eliminated when using RO.  But don't be fooled into thinking an RO system has no cost to operate.  The membranes in an RO system must be replace, on average, every 3-5 years.

• Powder Chemistry - Make sure you follow the powder supplier's recommendations. If powder is not cured for the specified time and temperature, you may experience rejects.
• Pretreatment - If there is oil, water or other debris on a part, there is a strong likelihood you will see defects after curing.
• Grounding - Without proper grounding, a good transfer of powder from gun to part cannot be achieved.  Clean hangers and check grounding regularly. 
• Training - Your personnel should be proficient at using the various techniques required to get adequate coverage on a variety of part geometries.  This will prevent the orange peel effect, fatty edges, and other defects.
• Gun Placement - On automatic systems, guns that are not properly placed can cause parts to e coated too lightly or too heavily in spots.
• Maintenance - Simple maintenance issues such as worn nozzles and pump inserts can cause a wide variety of defects.  A regular regimen of cleaning and maintenance can greatly improve the life and performance of your equipment.

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