Monthly Archives: June 2016

Understanding Powder Coating Gun Settings

When you first start powder coating, adjusting your powder coating gun settings can be confusing. We’ll cover the most important terms and settings for everyday powder coating situations and addresses some common issues you may encounter. Once you understand how electrostatic powder guns work and know what the basic gun settings do, you can improve your powder coating results quickly and confidently.

Author’s Note: All examples in this article use the Wagner EPG controller for illustrative purposes, but other brand-name professional quality guns have similar controls.

Powder Coating Gun Settings # 1: Kilovoltage (kV)

Powder Coating Gun kV Meter“kV” is the symbol for kilovolt. One kilovolt = 1000 volts. It is a unit of measure indicating how much electrical charge an electrostatic powder gun can produce.

The kV adjustment changes the amount of voltage charging the powder particles as they pass through the gun. The higher the setting, the stronger the charge. High settings are great for flat panels and the outside of box-like parts. A high kV setting can improve your transfer efficiency (more powder sticks to the part) and also allow you to increase the distance between the gun and the part. This can help you get very uniform coverage on flat surfaces. In some cases, excessively high kV settings can cause tiny pits or dimples in the finish due to “back-ionization.”

Lower kV settings are best for Faraday cage areas and when working with some specialty powders, such as metallics. As a general rule, the more detailed and complex the part, the lower the kV setting. Professional quality powder guns from companies like Gema, Nordson and Wagner typically have a maximum voltage setting of 100 kV. A good starting point is a setting of 50 to 80 kV for applying a single coat (or the first coat) to an uncoated part. When working with Faraday cage areas, turn down the voltage. When applying a second coat, a lower kV setting can give the best results.

What is the Faraday Cage effect? This describes what happens when you are trying to powder coat into a recessed area like the inside of a box. Highly charged powder particles are attracted to the closest grounded metal surface–the sides of the box–so they have a difficult time penetrating into the corner. This often happens with parts that have tight corners, angled features, prominent bends or recessed areas. Window and door trim, frames, boxes, wire racks, I-beam sections, angle iron, conical parts, u-shaped channels, uni-strut, grids, and other unusually shaped parts can be tough to coat without adjusting the gun’s output. By reducing the electrical charge (lowering the kV setting), you can help sprayed powder penetrate Faraday cage areas more effectively.

It is important to have a good ground. This is the physical connection that allows an electrical current to follow a path to earth. A ground is needed for the charged powder particles to effectively be drawn to the metal part. The stronger the ground, the more effectively the electrostatic process works. We recommend the use of a dedicated grounding rod. Get a copper grounding rod of at least 8’ length from an electrical supply company. Drive the grounding rod into a spot as close to your powder spray booth as possible (yes, you will have to penetrate your concrete floor if you have one). Using a good quality grounding strap of 14 gauge or heavier wire (heavier is better) and a well-made clamp, connect the ground rod to the rack or hook that is supporting your part. This will dramatically improve the performance of your coating gun, especially when dealing with complex parts. In some areas, you may need to pour a few ounces of water into the hole around the grounding rod to improve the quality of your ground.

Another way to improve results in Faraday cage areas is to aim the gun near the corner or detail area, but not directly at it. Wrap is the term that describes when sprayed powder is attracted to the back side of the part. Wrap means that the gun delivers powder to areas of the part that aren’t directly in front of the gun’s output. By having a good quality ground, you can get improved wrap on panel-shaped parts and improved penetration into Faraday cage areas.

Remember, voltage and amperage are not the same thing, so it may be important to also adjust the amperage at which the powder is being sprayed.

Powder Coating Gun Settings #2: Microamperage (µA)

Powder Coating Gun Microamperage Meter“µA” is the symbol for microampere. One microampere = 1/1,000,000th of an ampere. It is a measurement of electrical current. It indicates how much charge is moving from the gun’s electrode to the cloud of air and powder exiting the gun, and then onto the surface of the part being coated. This may be the hardest gun feature to understand.

Voltage and current (measured in microamperes) have an inverse relationship when you’re talking about powder coating guns. Voltage is a measurement of electrical “potential to do work,” while current is a measurement of the actual movement of electricity–“the work being done.” When some of the potential energy is used, it becomes current. As current increased, there is less potential (unused energy) left. A gun’s current feedback system can indicate to the operator what the electrostatic charge is doing. It is, in some ways, more useful than just looking at the kV setting. This is because the microamperage reading tells you how much of the charge is working, instead of just indicating the charge’s maximum potential like the kV setting does. On powder guns like the one shown from Wagner, you can see the effectiveness of the charge and limit how much current is possible. This allows you to understand and control how much energy is being used.

The kV setting is, in part, restricted by the power supply. While spraying a part, the load on the power supply limits the actual output, so the voltage may be lower than the setting. The current load increases as the gun gets closer to the part being sprayed. On a gun with an adjustable current limiter, when the current load reaches the set limit, the kV will quickly decrease. This helps prevent problems from too much voltage (like dimples in the coating from back-ionization), especially when the gun is too close to the part. Also, if the amperage is not limited to a certain range, the transfer efficiency may suffer in Faraday cage areas or the powder may not coat evenly if the gun-to-part distance is inconsistent. Setting the µA range to 20-25 can help with difficult to coat areas.

Powder Coating Gun Settings #3: Air-Flow/Powder Volume Dial

Powder Coating Gun Air-Flow DialWagner powder application guns automatically balance the powder output with the airflow via the main dial. The number selected is the actual maximum percentage of powder that can be used. Typically, 70% is the highest you would want to go. When working with intricate parts, this number can be much lower.

 

 

Powder Coating Gun Settings #4: The Factory Presets

Powder Coating Gun Factory PresetsThese are settings pre-determined by the gun manufacturer or the operator. They are intended for the most common scenarios encountered by typical gun users.

Flat Panel Setting: This setting provides maximum kVs and a high volume of powder being sprayed. This is for large flat panels and will provide a lot of powder wrap.

Repaint Setting: This setting is for a previously painted part that needs more powder for cosmetic or performance reasons. The kVs are reduced, as is the powder volume, since there is already powder on the part.

Faraday Cage Setting: This setting lowers the kVs, restricts current µAs, and reduces the powder flow percentage to allow powder to penetrate difficult-to-reach corners and angles.

Custom Settings: These are the settings that you use with a specific powder or part. The fourth preset is reserved for custom settings. (On the Wagner controller, you have up to 50 available custom settings that can be saved.)

My Powder Coating Gun Is Set, Now What?

Once you’ve got your powder gun adjusted correctly, you are ready to start spraying powder. Before you begin coating a part, look at the part and figure out how you will get the best and most efficient coverage while spraying. As your part becomes coated with powder, a charge will build up on the surface. It will make the Faraday areas even more challenging to coat. Therefore, it is best to coat the Faraday areas first, then spray the flat surfaces of the part.

After rehearsing what you are going to do, you need to get the powder flowing smoothly through your gun. Spray the powder coating gun away from the part until a uniform cloud is coming out with no sputtering or surging. This may take up to a second or two. Move the gun to the part and move it in a slow, controlled motion across the part, keeping a gun-to-part distance of around 8”. Keep the gun triggered and spraying until the part is done—don’t start and stop. If possible, try to get full coverage with a single pass across the entire part. Often you will need to move the gun in a controlled back-and-forth motion, starting with side-to-side movements and then switching to up-and-down passes if needed.

Inspect the coated part with a bright light to help detect thin spots. Touch up any spots you see before curing the part, but be careful not to add too much powder or to let the gun puff powder onto the touch-up areas. These common mistakes happen when you become impatient and blast the part with a heavy fog of powder or don’t let the gun’s powder flow stabilize before attempting touch-up work.

What Else Do I Need To Know?

Air Supply Problems are not uncommon. It is critical that you use only cool, dry, oil-free compressed air to power your powder application guns. Make sure you have an accurate in-line pressure gauge and a regulator that can restrict the amount of pressure reaching your gun. You may need to use a powered air dryer, and you will definitely need a filter system that traps moisture and oil.

Fluidization is what we call the small amount of air movement that aerates and fluffs the powder around the pick-up tube on a box-feed unit. An adjustable valve controls how much air is provided. The air helps break up clumps of powder before they are pulled into the pick-up tube and pumped through the gun. It is also the term used for the air movement that mixes the powder in a hopper container. In the hopper unit, there is a plastic membrane at the bottom with lots of tiny holes that allow the air to condition the powder. When adjusted correctly, it will look like the powder is slowly boiling.

Impact Fusion describes what happens when partially gelled powder sticks to sharp areas in the gun and inside the powder pump. This problem is more prominent in hot shop environments and when working with poorly conditioned powder. The stuck-on powder can be removed with a clean, fresh shop towel and denatured alcohol.

Mil Thickness is the term used when talking about the thickness of the powder coating material that has been cured over the surface of a part. One mil = 1/1,000th of an inch. A healthy human hair is about one mil thick. Most powder coated finishes are between 2 and 4 mils thick, with some finishes up to 6 mils or thicker. Achieving ideal powder thickness and uniform coverage takes practice. Make sure to keep good notes. Some coating instructors have their students spray test parts to learn about adequate powder coverage. A student sprays a part while the instructor illuminates the surface of the part with a bright pocket flashlight. Once the flashlight no longer reveals any bare metal spots, the student stops spraying. This method typically results in a finished coating that is about 2 mils thick.

Orange Peel describes the uneven, “wrinkled” finish that can happen after curing if the painter sprays too much powder on the part in some places. You can end up with areas of heavily concentrated powder that flow out into wavy sections that have something of an orange peel texture. The excessively thick powder in these areas will also make the finish more prone to chipping. If the applied powder is under-cured, especially as the result of the oven temperature being too low, the powder can also fail to flow out properly, even if it’s not too thick, causing the same type of textured defect in the finish.

Powder “Starved” Finish/Light Powder are terms used to describe the grainy texture that a defective finish can have after it is cured if the part does not get adequate powder coverage. If there wasn’t enough powder on the part for it to flow together and create a uniform coating, it can have an odd, textured appearance. Even worse, the part will likely start to rust or oxidize in these textured areas because the part’s surface isn’t fully covered by the coating material. Using a powerful flashlight or LED inspection tool can help prevent this by allowing the painter to see areas that need more powder.

A professional powder coating gun can make a huge positive impact on your operation, allowing you to coat with more accuracy, better efficiency and higher quality. Reliant Finishing Systems only offers professional powder guns from companies like Wagner. Need a new powder application gun or a complete powder coating system? Our powder coating specialists are ready to help – give us a call today!

The Basics Of Powder Coating Coverage

Powder Coating Gun And PartKnowing how much powder you need for a particular job is critical when determining cost. Without that information, it is easy to make pricing mistakes that can drain your profits or run off potential clients due to pricing that isn’t competitive.

However, calculating powder cost can be a little confusing. We’re going to show you how to calculate powder coating coverage and how to gather the information necessary to give an accurate prediction of cost per square foot.

 

The Data You Need To Calculate Powder Coating Coverage

Before you start calculating coverage costs, these are the values that you will need to know :

  • Powder Specific Gravity
  • Cost Per Pound of Powder
  • Transfer Efficiency
  • Dry Film Thickness
  • Square Footage of Metal To Be Coated (Per Part)

Powder Specific Gravity: This is usually supplied by the powder coating manufacturer on their technical data sheet. Remember that not all powders of the same color have the same specific gravity.

Cost Per Pound of Powder: Check your invoice or get the cost from your powder manufacturer or sales representative.

Transfer Efficiency: Transfer efficiency is the percentage of the powder that is being applied to the part instead of being wasted as overspray. Transfer efficiency is almost always an estimated figure and the most difficult one to determine when estimating coverage costs. It is hard to get an accurate percentage of how much powder is being applied to the part and how much is going in the filters, on the floor, on the rack, and getting stuck to the booth’s walls.

Powder Coating Gun Overspray

Transfer efficiency is directly impacted by how much powder the operator is using.

Transfer efficiency is directly related to the way the operator is applying the powder. If there is a giant cloud of powder in the booth or a heavy fog of powder blasting out of the gun, you can bet that there is more wasted powder than if the operator is spraying lightly enough to coat the face of the part and still get a gentle wrap of powder moving around the part to partially coat the other side.

Proper ground and powder coating gun quality can have a significant effect on transfer efficiency. A shop with a dedicated ground rod that is connected to the parts rack or hooks, or to an uncoated portion of the parts, can always get better transfer than one that doesn’t. Likewise, a shop using a professional quality electrostatic gun with adjustments for powder flow, voltage and current can get better results than one using a hobby gun.

For estimation purposes, if this is a new operation with untrained painters, the transfer efficiency can be as low as 25%-30%. After proper instruction, experience, gun adjustment, and proper ground, the transfer efficiency can reach 70%. If you are reclaiming the powder by collecting and reusing the powder, you could possibly reach 85%.

One way to calculate transfer efficiency percentage is to determine how much powder is applied to a part in the time necessary to fully coat that part. You will need a high quality digital scale and a timer to do this. First, weigh your part before you spray it. Get your timer ready and spray the part until it is fully coated and ready to cure. Record the time it took to coat. Now, weigh the part again to learn how much powder was deposited. Next, turn off the gun electrostatics but do not adjust the powder flow or air and spray the powder gun into a porous filter bag that will trap the powder but allow the air to flow through (you can get these online or from your powder supplier). Spray powder for the same length of time it took to spray the part. Weigh the bag before and after to measure how much powder was applied. Then apply the following formula:

Powder Deposited (the weight of the powder on the part) divided by Powder Applied (the weight of the powder in the bag) multiplied by 100 will give you the basic transfer efficiency percentage.

Powder Coating Gun Applying PowderDry Film Thickness: This is the amount of powder you would like to apply to the part, measured in terms of coating thickness. You can measure a part with a DFT gauge to get an average of the mil thickness across a section of the part’s surface. You should take as many readings as possible, then average them, to get the most accurate estimate of the overall average thickness.

Square Footage of Metal in Your Part: This might take a bit of calculation but it will give you the cost per part at the end of this exercise.

Powder Coating Coverage Formula

Now that you have all the data you need, you can apply the powder coating coverage formula.

Assumption: The Powder Coating Industry standard is 192.3 square feet of coverage per pound of powder. This pound of powder would be at 1.0 specific gravity and applied at a thickness of 1 mil with 100% transfer efficiency. In other words, this is how much surface a common powder could cover if no powder was wasted and you only needed a thickness of 1/1000th of an inch.

So the formula would be:

Actual Coverage Rate (ACR) = 192.3/Specific Gravity/Mils x Transfer Efficiency (as a decimal)

Example: Powder A has a 1.5 specific gravity and is being sprayed at 2 mils with 50% transfer efficiency. The powder cost is $5.00 per pound. The part being sprayed has 3 square feet of surface area.

ACR = 192.3/1.5 (specific gravity)/2 (mil thickness) x .50 (transfer efficiency)

ACR = 32.05 square feet per pound of Powder A

Next, take your cost per pound and divide it by your ACR.

Cost per square foot = $5.00 (cost of one pound of powder)/32.05(ACR) = cost is $0.16 per square foot of coverage by Powder A

Multiply this cost by the square footage of your part’s surface area and you’ll know the cost of the applied powder.

Cost Per Part = 3 (square feet of part) x $0.16 (cost per square foot) = $0.48 per part in powder cost

Now that you know how to do this by hand, Interpon has a nice online calculator that you can use here: http://www.interpon.us/our-coatings/powder-coverage-calculator/

Knowing what your cost is for powder coverage will prevent you from making costly budgeting mistakes and keep your prices competitive.

Powder Coating Gun For All ApplicationsIn order to maximize your profits you have to maximize your transfer efficiency, and the best transfer efficiency comes from professional powder coating guns. Professional guns provide multiple settings and factory-presets to get the right amount of powder onto your parts without excessive waste. Reliant Finishing Systems only provides professional quality powder application guns from industry-leading companies like Wagner. When you buy from Reliant, you know you’ll be getting the gun you need to get the job done right.

Looking for a new powder coating gun or new powder coating system? Give us a call today – our systems specialists are standing by to answer your questions and help improve your operation.

Manual Powder Coating Gun Comparison: Box-Fed vs Hopper-Fed

Venturi Pump - Wagner Manual Powder Coating Gun

Typical venturi pump from a Wagner manual powder coating gun system.

If you’ve been shopping for a manual powder coating gun, you’ve already seen the terms “box-fed” and “hopper-fed.” In this article, we’ll explain what those terms mean, how they affect your powder coating process and how picking the right gun configuration can dramatically improve your results.

Every professional quality manual powder coating gun has an integrated delivery system for preparing the powder and bringing a steady stream to the application gun. The powder flows through the hand-held application gun as it is sprayed onto the part being coated. Both box-fed and hopper-fed delivery systems provide powder to a venturi-type powder pump, but these two preparatory feed systems have different attributes. You’ll need to consider which system will work best for you before buying a new powder coating gun.

[Author’s note: We’re showing Wagner products for this article, but other brands look very similar.]

Box-Fed Powder Coating Guns

Wagner Box-Fed Manual Powder Coating Gun

Wagner box-fed powder gun with pick-up tube shown outside of a box of powder.

A box-fed powder coating gun draws powder coating media directly from the box provided by the powder supplier. A platform holds the powder box at an angle on a stand below the gun’s controls. A powder pick-up tube is then inserted into the powder in the box. The pick-up tube hangs vertically and usually has a small amount of compressed air delivered to the tip area to break up any compacted or clumpy powder. This helps assure uniform powder flow. The tube routes the powder up to the venturi powder pump, which sends the powder to the gun itself.

During operation, the platform which holds the box constantly vibrates. This vibration causes the powder to shift around inside the box. The powder in the box moves constantly and replaces the powder that is being pulled up the tube. This prevents “rat holes” from developing in the powder still in the box. Without constant vibration, the powder would be supplied in surges, which would create problems during application and degrade the finish.

Advantages of Box-Fed Powder Coating Guns

1) Fast Start-Up: Grab a box, open it up, put the pick-up tube in and start coating!

2) Quick Color Change: It takes as little as 3-5 minutes to change colors when using a box-fed gun with air pulse cleaning. Less expensive models may require up to about 10 minutes. You simply clean or swap the hoses, switch to a different box of powder and go back to work.

3) Lower Initial Investment: If you spray a variety of colors and textures each week, the cost of buying multiple hoppers can really add up. Since the powder you buy already comes in a box, there is no extra cost associated with dealing with lots of different powders.

4) More Mobile: There’s less weight to move around your shop when working with a box instead of a hopper on the gun cart.

Disadvantages of a Box-Fed Powder Coating Gun

1) Special Effect Powders Won’t Work: Since the vibratory box feed system tends to cause larger or denser particles to settle to the bottom of the box, any powder that has distinct particle size differences can have consistency issues, especially as you get closer to the end of the box.

2) Humidity Can Cause Problems:  To get best results and prevent powder from degrading while in storage, you should keep your powder in a cool, dry, climate-controlled area. If you are starting a new project and you bring powder into a hot and humid shop environment, you can encounter troublesome powder clumping due to condensation occurring when the cool powder is exposed to the humid air.

IMPORTANT:  When working in hot or humid environments, bring out a box of powder a couple of hours before you need it and open the top to allow the powder to acclimatize to the environment before you start spraying with it.

3) Spillage And Contamination: Although it isn’t easy to do, you can tilt the gun cart by accident and spill the powder out of the box. You can also get contaminants in the powder if you try to reuse spilled powder, or if you have a dirty shop environment and leave the opened box of powder in use for a long period of time.

Hopper-Fed Powder Coating Guns

Powder Coating Gun - Wagner Hopper Fed Gun

Wagner hopper-fed powder gun with powder pump attached to a 60-liter stainless steel hopper.

A hopper-fed powder coating gun holds the powder in a sealed (usually stainless steel) container that has a perforated plastic membrane on the bottom. This membrane has tiny holes in it that allow compressed air to enter the container and constantly fluff the powder so that it flows around inside the hopper. This process is called fluidization. When you look at the top surface of the powder in a hopper that is being fluidized by compressed air, it should look like it is boiling. If you put your hand in the powder while it is being fluidized, it should feel silky smooth.

The compressed air supply to the hopper should be adjusted so that powder isn’t wasted due to excessive agitation/over-pressurization of the container. While some powders require a small amount of venting, you should adjust your system for minimal powder loss, especially if you are reclaiming the powder as an on-going process.

Specific Advantages of Hopper-Fed Powder Application Guns

1) Conditions The Powder: The fluidization process helps remove moisture in humid environments by introducing clean, dry air from the bottom of the hopper.

IMPORTANT: Never stir the hopper with a stick! It can damage the plastic membrane on the bottom of the hopper, reducing the effectiveness of the fluidization airflow.

2) Mixes The Powder: Fluidization also insures that the powder is thoroughly mixed. This is important if you are regularly spraying river textures or bonded metallic powders, or making a transition from one batch of the same powder to the next.

3) Less Chance of Powder Contamination: The hopper is sealed off from the surrounding environment and each hopper is typically used for only one type of powder.

4) Less Surging: Because the powder is better conditioned, the pump picks up the powder more consistently and the gun delivers it more uniformly.

Disadvantages of Hopper-Fed Coating Guns

1) Increased Cleaning Time: If you have only one or two hoppers for all of your colors and textures, it can take a significant amount of time to switch between colors or textures—up to one hour per change if done meticulously.

2) Cost/Storage Issues: If you buy multiple hoppers to accommodate all of your most commonly sprayed powders, it can be costly. It can also be challenging to store hoppers when they are not in use. You may end up using valuable floor space to store empty hoppers, particularly if you don’t normally carry some common powders in inventory and get them on demand from your powder vendor.

3) Reduced Throughput: If you commonly have to move the cart around a good bit because of the size or complexity of what you are coating, having a hopper-fed gun can slow you down. A gun cart loaded with a full 60-liter hopper (the most popular size) can be a bit unwieldy.

Which Powder Coating Gun Is Right For You?

Depending on your work environment, getting the right configuration can make a significant impact on your performance. If speed (how fast you can get started on a new project), agility (how fast you can change colors or textures) and lower cost are key concerns, a box-fed gun may be the right choice for you. If premium finish quality is the most important goal, a hopper-fed gun is probably the right tool for the job.

Box-fed powder coating guns are best suited for:

1) Job Shops: If you spray different powders for different jobs, guns that are box-fed let you change colors quickly between projects.

2) Regular Powder: If you don’t do a lot of special effects, box-fed guns work fine with most single color powders.

3) Small Powder Runs: If you only powder coat a small number of parts the same color during the week, a box-fed unit is perfect for projects where you’ll only be running a few pounds of a specific powder at a time.

Hopper-fed powder guns are recommended for:

1) Limited Color Applications: If you only use a handful of different powders, a hopper-fed gun is usually a better value.

2) Special Effects: As noted before, if a special effect powders are an important component of your process, having a hopper dedicated to each of these powders would be best. Special effect powder must remain fluidized to be applied properly, and a box-fed system simply won’t cut it if you need professional quality results.

3) Reclaim: If you reclaim your powder, you’ll need a hopper-fed gun. The hopper-fed system enables you to mix reclaimed powder with new virgin powder perfectly.

IMPORTANT – If you are new to reclaiming spent powder, a ratio of 60% virgin to 40% reclaimed powder is a good starting point.

4) Humidity Issues: If your powder’s characteristics or your shop environment causes clumping due to humidity, using fluidized hoppers will usually cure this issue if you have an air dryer attached to your shop’s compressed air supply.

With either feed system, you can be successful powder coating a wide range of substrates with multiple types of powders. If you decide on a box-fed system first, you can always add a hopper later. With most professional quality systems, a hopper can be attached right to the box feed controller and only requires a small fluidizing air tube attachment. Although it may cost a little more to have your gun configured this way, it enables a single gun to give you the benefits of both systems.

Have questions about powder coating guns? Looking to add a new gun to your existing coating operation? Feel free to give us a call. Our systems specialists will be happy to help you get the powder coating gun you need.