Once you’ve completed a powder coating job, your next step is quality control testing. Whether the coating has to withstand harsh environments or resist normal wear and tear, you – and your customers – need to know what to expect from your coating work.
Profitable job shops make sure they meet their customers’ coating specifications. Successful manufacturers also perform rigorous testing to ensure that their powder coated products meet pre-set standards. If you want to retain customers and expand your powder coating business, you need to focus on the quality of your work. The same attention to quality is critical if you want to keep an in-house coating department on the right track.
Flexibility, color, gloss, adhesion, corrosion resistance, chemical resistance, durability, film thickness, proper curing and overall appearance are all things you can test for as part of a quality assurance program.
Practical Quality Control Testing Methods
No matter what you are coating, there are a few tests you need to add to your daily process. The most common areas to test for basic powder coating functionality are:
- Film Thickness
- Uniformity/Proper Curing
Because proper quality control testing is so important to your success and reputation, we recommend these tests be performed daily, or at least once with every batch of products–and any time you change your coating products or processes.
Powder Coating Film Thickness Testing
A film thickness test determines the thickness of the powder on the part once it’s been cured. This is generally confirmed with a Dry Film Thickness gauge. These gauges are fairly affordable and easy to use.
A common range to look for is 2-3 dry mils (thousandths of an inch). A coating of 2-3 mils usually provides complete coverage of the powder over the metal.
Remember: Make sure that if you powder coat both steel and aluminum, you purchase a gauge that will measure both ferrous and non-ferrous metals.
If you are getting less than 2 mils, you are at risk of not providing full coverage on the product. If you are over 5-7 mils in a single coat, you could be wasting powder or causing surface appearance defects like “orange peel” or runs. In either case, adjustment of the powder coating application is needed.
Powder Coating Uniformity/Cure Testing
When we talk about “cure” in quality control, we’re talking about the correct temperature and dwell time that allows the powder to achieve it’s formulated hardness and chemical resistance properties. When testing for cure, you want to make sure that there aren’t any areas of overbake (where the powder has cured in a dry and brittle fashion) or underbake (where the powder has not completely cured).
A cure test is easy to perform. Proper curing is confirmed by rubbing a methyl ethyl ketone-soaked cotton swab lightly over a cured panel or part (in an inconspicuous area if the part is to be used if acceptable). Application of 20 double rubs (back and forth over the same spot) is a common standard for checking cure, but you will usually see failure after about only three or four passes. If the finish deteriorates to the point that you expose bare metal, your cure is lacking or the powder is defective. If the coating softens but then recovers, you are fine. Some color may transfer to the cotton swab, but that is normal, especially with hybrid powder coatings.
If your parts are failing their cure tests, temperature in the oven or dwell time in the oven may need to be increased. Be careful when adjusting your process not to overcure, as that can cause issues like adhesion failure; dulling of gloss; or yellowing and browning of the color, especially if you are coating white.
Powder Coating Adhesion Testing
Adhesion testing measures how well the powder sticks to the part once it is fully cured. As with the cure test, your adhesion test results can be affected by overbake or underbake.Generally, adhesion testing kits are available for specific testing requirements.
You can perform a simple adhesion test on your powder coated products using some common tools you likely already have at your shop – but remember, the adhesion test is a destructive test. Do not do this on parts you want to use because this test will ruin the finish.
To perform the adhesion test, you will need some sticky clear tape and a utility knife. You will also want at least one test panel that you have already coated and cured.Make sure the part or test panel is clean and dry.
Again, this is a destructive test, so make sure you test adhesion on a part you won’t mind throwing away or completely reworking.
Next, using the utility knife, scribe a section of the part five times one way and then again 5 times perpendicular to the first scratches.This will give your part’s coating a grid-like appearance. Make sure you cut through the coating to the metal.
After making the cuts, put a piece of tape over the grid and smooth out any air bubbles. The tape should completely cover the grid. Pull the tape off aggressively and look at the tape and the part. An acceptable result will show only a little of the powder coming off from the grid cuts. If a square or two of coating is removed, adhesion can be suspect. If your coating comes off in a sheet, then you have adhesion failure.
Adhesion failures can be caused by several factors. One of the first places to look is metal preparation. If the metal is too slick or oily, powder will not be able to stick to the surface. Make sure the substrate is clean and etched/abraded. Overcure can also cause the powder to become so brittle that it will easily pull away from the metal. Old powder may have issues that can cause lack of adhesion as well. Proper process evaluation will lead you to the cause of the failure.
Powder Coating Appearance Evaluation
One of the advantages of powder coating is how good the finished product looks. All your products should be inspected before shipment to make sure that there aren’t gaps in coverage, bubbles, warping or poor coating application. If your quality assurance manager is actively looking for defects, problems with the powder or the product can be fixed before delivery.
The second part of your appearance testing routine involves taking time to communicate with your customers. Every customer should have an idea of what he or she considers to be an acceptable finish, but it may take some discussion to determine what’s realistic and measurable. A finish standard can be as simple as no more than two visible surface imperfections per square foot. Or it can be no blisters or pinholes visible on the primary surfaces. Gloss and color standards may also be included. If a customer has very precise requirements, we recommend investing in a gloss meter/color eye (spectrophotometer or similar) to make certain the customer receives exactly what they expect.
Appearance issues can be caused by many factors. Contamination is usually the biggest problem. Shop dirt, welding debris, sanding dust or other airborne contaminants can get on the parts. These substances can cause the powder to react negatively or simply fail to cover the contamination. Proper cleaning and pretreatment can address these issues.
Unfortunately, improper cleaning contributes to many appearance issues. Ignoring rust or residue can prove costly in the long run. The use of poorly mixed or overly-diluted chemicals, the application of inappropriate detergents, and other pretreatment shortcomings related to carelessness can also cause significant finish problems.
Sometimes water in compressed air lines or high humidity in the shop environment can cause powder to clump and generate unwanted appearance issues. Evaluating your process by eliminating one variable at a time is crucial for discovering what’s causing the issue.
Generally speaking, the four basic tests discussed in this article should be included in any powder finishing process. Other periodic laboratory tests may be needed. These include salt-spray, UV exposure, QUV, taber abrasion testing, etc. Most of the lab testing can be done by your powder supplier. Be sure to communicate fully with your customer, as well as your powder media and pretreatment chemistry suppliers, to clarify what testing is required and what standards the finished parts must meet.
Need Help Getting Your Line Back Into Shape?
Reliant Finishing Systems manufactures all types of powder coating equipment and offers a wide variety of repair and troubleshooting services for the powder coating industry.
Need equipment? Reliant builds blasting enclosures, gas and electric ovens for parts drying and powder curing, environmental rooms, powder application booths, spray walls, multi-stage parts washers, and manual wash stations. Our systems specialists have years of experience with the design and installation of powder coating lines of all sizes.
If you already have equipment in place, Reliant can help. Whether you need a line audit to help you increase throughput or simply need to run a Datapaq to diagnose possible hot spots in your oven, our team of experienced technicians can help. Give us a call today.
Regardless of what you’re powder coating, there will likely be an area on your part where you DO NOT want any powder coating to be applied. Screw holes, pipe fittings, precisely machined surfaces and sleeves or cylinder interiors are some of the places where powder will interfere with the fitment needed during assembly. If powder gets in the wrong place, it can definitely cause problems down the line.
Thankfully, there are a couple easy techniques you can use to prevent powder from going where you don’t want. By using “masking” and “plugs,” you can get the results you need. This article explains when to use masking and plugs for powder coating and also describes the supplies you’ll need in order to use either method. Follow these simple tips and you’ll soon be producing incredible-looking finishes that fit together perfectly during assembly.
Masking For Powder Coating
Masking is the term we use when we want to shield fairly large areas of a part during the powder coating process. For powder coating masking, a high-temperature masking tape is required. Some companies use the term “high-temperature masking film,” especially for larger tape sizes or material that can be cut into sheets.
Remember: Powder curing typically takes place between 380° F and 450° F, so be sure that your masking material is rated for those temperatures before using.
Masking is usually done after the chemical pretreatment stage of your coating process. Follow your pretreatment steps as normal and allow the part to dry fully before applying the high-temp tape to any areas that require masking. The pretreatment process will provide the uncoated metal with some amount of corrosion protection prior to assembly.
If the metal requires blasting prior to coating and needs to be masked before blasting, you will need a different, more durable tape. Resilient high-temp tapes can be left in place, but they are usually fairly expensive. Alternatively, you can also use a thicker version of normal masking tape. You would apply it for the blasting process, remove it after the part has been blasted, and then apply high-temp tape over the areas you want to shield. If you use chemical pretreatment after blasting a part, be sure all tape is removed before the part is treated. Mask the part with high-temperature tape only after it has dried fully and you’re ready to coat.
When working with high-temp masking tape, the tape stays in place while the part is being sprayed and cured. You should be able to coat and cure the part as usual after the tape has been applied. Once the part is fully cured, you remove the tape.
TIP: When removing the tape, try to take it off while the part is still fairly hot. Around 200° F is the optimal temperature to remove the tape. If you take it off too early, while the part is too hot, it can cause strings of powder to pull off at the edge of the tape and result in a defective finish. If you wait until the part is too cool, there can be chipping or a rough line along the edge of the coating when the tape is removed.
Advanced Masking Technique: Two-Tone Powder Coating Finishes
Two-tone and multi-color finishes are achieved when two or more different colors of powder are applied to the same part. High-temperature tape and/or masking film is used to achieve this type of finish. A two-tone finish is applied like any other powder coating that requires masking, but special care should be taken to ensure that the results are acceptable.
When applying two-tone or multi-color finishes, you may need to use slightly different masking, coating and curing techniques than you normally would. You’re still dealing with a situation where you’ll be spraying a part and some portion of the part shouldn’t have any powder applied to it, but you will need to spray and cure the part more than just once.
Recommended Rules For Two Tone Application
When masking the part, always try to limit skin contact on the bare metal. Your skin has oils that can cause issues later when you apply the remaining color(s).
As with normal masking, take the tape off of the part when it is around 200° F. A handheld laser-pointer IR temperature gauge is good enough for checking the metal temperature after curing, once the part is outside of the oven.
Make sure the first coat is fully cured and cooled before re-taping for the second color. The adhesive on the tape can cause finish problems if the powder has not fully cured. Also, you may want to wipe the remaining bare metal surface with alcohol before coating just to make sure no contaminants are still on the surface from the previous masking. For multi-color finishes, you’ll re-mask the part after each coat has been applied and cured.
Check with your powder provider in advance to be sure that the powder you’ll be working with is appropriate for two-tone or multi-color applications. You’ll also want to consider just how long to cure the part each time you spray a new section. You may need to adjust the curing temperature to assure that each coat is adequately cured without becoming discolored. It is easy to under-cure the last coat if you become concerned about over-curing previously applied powder. Remember that most powders are hard to over-bake if you are careful.
Two-tone finishes require extra care to get right, especially if the line between one color and the other is on a flat or oddly contoured surface. Extra care when masking can make the difference between a great finished product and a reject, so take your time.
Plugs For Powder Coating
Remember: Just like masking, make sure your high-temperature plugs are rated for the appropriate oven temperature. Always check the temperature rating on the plug before using.
Like tape, plugs are also used after pretreatment. Prior to inserting the plugs, blow out the holes with compressed air to ensure all moisture is out of the part. Trapped moisture in hard-to-reach areas can cause surface defects if the moisture leaks from the part during the curing cycle.
Plugs can be reused, as long as they do not get impregnated with powder. When reusing plugs, try to remove as much old powder as possible from the plug to keep from contaminating the next part.
TIP: When removing the plug, try to remove it when the part is around 200° F for the same reason as when using tape. You’ll get cleaner edges and have fewer defects.
Improve Your Powder Coating With Quality Equipment
Your finish quality is tied directly to the tools you use. If you’re going to be doing professional quality work, you need professional quality powder coating equipment. Reliant Finishing Systems only partners with premium quality, brand-name powder gun manufacturers like Wagner. We only integrate premium component for use with powder coating booths and powder curing ovens.
Looking to upgrade your powder coating results? Let Reliant help you with the equipment and support you need. Give us a call today.
(Be sure to check out our article What Size Powder Coating Oven Do You Need? for more information on matching your powder coating equipment for best results.)
Just like with your powder curing oven, your powder spray booth needs to be large enough to accommodate either the largest product you will routinely be coating or the largest batch of products you must coat in order to meet your shop’s throughput requirements. Your booth may need to be a bit larger than your oven if you are dealing with large parts, or it may be possible to use a smaller booth if you coat multiple small racks of parts before curing them all in one large batch. Regardless of the booth’s size, you need an appliance that is large enough to hold your products and provide enough space for the operator(s) to move and work efficiently.
Although this article focuses on batch coating processes, many of the concepts also apply to powder coating in a constant-process environment where parts are moved via conveyor instead of on rolling racks or carts. With both batch and automated lines, it is not uncommon for booths to be open-faced or to have ware openings instead of doors that seal the parts inside the powder coating booth. Unlike with conventional wet paint processes, contamination by airborne dust or debris is usually less problematic when powder coating.
Prevent Powder Contamination In Your Work Environment
During powder application, the powder that does not adhere to the part is called overspray. Overspray generally falls to the ground or is moved by the booth’s airflow and pulled into the filtration system, but only if the powder is sprayed inside the booth while the exhaust is operating. Spraying powder outside the booth or away from the filters can lead to powder contamination of nearby appliances (including your curing oven). The airborne powder is a nuisance dust that can travel throughout your workspace.
When sizing your powder spray booth, make sure that the booth is large enough to completely enclose the largest product you’ll be coating. This ensures that all the powder is being sprayed inside the booth, which eliminates powder contamination of the shop environment.
Add Interior Space To Improve Efficiency
The largest product you are coating should easily fit inside the booth with extra room for each operator to both move himself and the powder coating gun around the part. Adding additional space gives your operator adequate room to work without jostling or bumping the product that is being coated. Prior to curing, applied powder media is fairly easy to remove. Any accidental contact with the part will require touch-up if not a total rework.
Besides adding room for the painters, you also need to allow room for your racks. Let’s say you have a 6’ tall part and you want to coat it in an 8’ tall booth. If the rack and hook cause the part to hang about 1’ from the ceiling of the booth, the painter is going to end up having to paint a portion of the part that is only 1’ off of the floor. To do this effectively can be slow and tedious, and this type of cramped working space contributes to fatigue.
Another issue is maintenance. In the scenario above, the top surface of the part being coated is only 1’ from the ceiling. This means that the booth’s ceiling and ceiling-mounted lights will be coated with powder overspray. After an hour of painting, the lights will have a film of powder over them—reducing illumination in the booth and causing the light coming from the fixtures to be tinted by the thin layer of powder as it passes through. This makes it harder for the painter to gauge coverage. Greater contamination by overspray also translates to greater cleaning costs and more down time as the booth must be frequently cleaned with compressed air or wiped down. The same problem can occur when spraying parts that are too close to the walls. It’s easy to dislodge accumulated powder and contaminate fresh parts, especially if the old powder on the wall is a significantly different color or gloss compared to the powder being applied to the parts.
If you are going to be using a single large rack per batch, we recommend that the powder spray booth be an additional 2′ – 6′ wider than the matching powder coating oven. This gives your painters room to work. We also suggest that you consider a booth that is 2’ taller than your oven to reduce cleaning hassles associated with powder covering your light fixtures. One of Reliant Finishing Systems’ most popular batch equipment packages is sold with an 8’H x 8’W x 25’D (interior) curing oven and an 8’H x 10’W x 25’D or 10’H x 10’W x 25’D (interior) powder spray booth for this very reason.
Determining Your Powder Spray Booth’s Footprint
Make sure you have enough available floor space to put the right size booth in your facility. Note any low ceilings, structural supports, posts or columns, or other obstructions that might restrict where your powder spray booth can be installed. Carefully planning the layout of your booth, oven (https://www.reliantfinishingsystems.com/powder-coating-equipment/powder-coating-ovens/) and pretreatment appliances before you buy them can prevent headaches later.
While the overall footprint of most powder booths is similar to their listed interior dimensions, there are a couple things to keep in mind. Every powder spray booth comes with at least one integrated, attached or separate exhaust chamber that houses the filters and the exhaust fan system. Depending on the powder spray booth’s configuration, these exhaust chambers are attached to the rear of the booth or to one or both of the side walls. These exhaust chambers usually add an additional 4’ to 5’ of depth if attached to the rear, 4’ to 5’ of width if a single side wall has an exhaust, or 8’ to 10’ of additional width if both walls have exhaust units attached.
As an example, a standard model PSE81025 from Reliant Finishing Systems is a powder spray enclosure that is approximately 8’H x 10’W x 25’D inside. It comes with an exhaust chamber that is built into the rear of the booth enclosure. The overall exterior length of the booth is 28’10” including the exhaust unit.
Another space consideration is the header panel. The header panel is usually about 2’ tall and is added to the front of spray booths in order to keep airborne powder from drifting over the top of the booth and into the light fixtures. The header also assures that the light fixtures are adequately isolated from the booth interior to meet national codes, such as NFPA 33. The header panel is installed on the very front of the spray booth, above the main opening, and is typically only a couple inches deep, so you won’t have to account for its additional height over the entire appliance.
In addition to the total exterior dimensions of the powder spray booth, we suggest that you allow for at least 3’ of clearance around the booth in order to make installation and maintenance less costly and to meet common codes and regulations once the booth is installed.
Adjust Workflow With Different Booth Models
The type of powder spray booth you decide on can also greatly influence your powder coating system’s layout and workflow. Reliant Finishing Systems provides three different configurations of powder spray booths, shown below.
A STANDARD powder spray booth has an enclosed cabin with a filtered back wall. Many batch powder operations use standard booths and install them side-by-side with their powder coating oven (again, allowing for at least 3′ between appliances and the walls).
Remember: Some companies, especially those that primarily deal with wet paint booths like those used in automotive body shops, this design may be called a “crossflow” configuration to differentiate it from “downdraft” designs where the air travels from the ceiling into a metal basement or excavated pit under the booth before being exhausted.
A CROSSFLOW powder spray booth usually does not have a back wall. Instead, it has the exhaust filters installed on one side wall. This creates a tunnel-style configuration that allows you to move whatever you are coating in one end and out the other.
A DOUBLE-CROSSFLOW powder spray booth is also tunnel-style booth. It is similar to a crossflow configuration, but has an exhaust system mounted on each side wall. One benefit of this design is that it allows the painter to stay clean and work quickly. He can move the rack slightly and always be painting into the exhaust filters—as opposed to spraying powder onto the part while the exhaust is behind him, causing the overspray to cover him as it is pulled out of the booth by the fan. A double-crossflow booth also allows two painters to work effectively at the same time, especially when the exhaust units are mounted in a diametrically-opposing position. In that configuration, each painter deals with only one part of a large part or rack full of parts and is always spraying into the exhaust filters. As the rack moves through the booth, each painter sprays only a designated portion of the parts being coated.
In nearly all types of automated systems, a tunnel-style powder spray booth is paired with a tunnel-style powder coating oven with track running through both appliances so a continual coating process can be maintained. In a batch setting, the booth configuration should help improve coating workflow and maximize use of available floor space.
Plan For Staging Areas Around Your Coating Equipment
Another thing to consider when planning for your powder spray booth (and your coating line in general) is staging. A staging area refers to the additional shop space you’ll need for storing racks and parts as they move through the pretreatment, coating and curing processes. Even if racks are only going to be parked in a spot for a few minutes, it is important that the spot is clearly defined and kept clean.
Make sure you have a staging area where the parts can be prepared before they enter the powder spray booth. Whether you use blasting, chemical pretreatment, or simply a wipe-down before the parts are coated, you need to be able to stage parts after they’ve been prepped. This staging area is where your racks will be loaded with clean products, and may be where empty racks are returned. This staging area needs to be large enough to accommodate at least one typical batch of products.
In some batch operations, a second staging area is placed between the powder spray booth and the curing oven. In most batch operations, the powdered parts go directly into the curing oven. But, if your coating throughput is very high or you’re curing something that requires a long dwell-time, you may need this second area to store your previously coated parts away from shop traffic before they are placed in the curing oven.
IMPORTANT: Don’t let your powder coated parts wait too long before curing. Powder does not immediately fall off once a part has been coated. Good adhesion isn’t hard to achieve as long as you have a proper ground during application. Typically, uncured powder coating will adhere to the part for several hours with no ill effects. However, the longer you leave the powder uncured, the more exposure it has to moisture, handling damage, dust and airborne contaminants that cause imperfections in the cured finish.
Once you remove the cured objects from the oven, the racks and parts must have a place to cool before being handled. This final staging area is where the parts can adequately cool before assembly or packing. It’s very important to stage cured parts away from pretreatment areas and powder spraying operations to prevent accidental contamination of the powder finish before it has cooled and fully hardened.
A Custom Solution For Your Exact Needs
Reliant Finishing Systems manufactures over 250 standard powder spray booths, as well as fully custom booths built to client specifications. Our booth configurations are also available with matching powder curing ovens, wash stations, dry-off ovens and blast rooms. Our modular, perfectly-matched appliances are easily configured for a fully integrated powder coating line. Regardless of your finishing equipment needs–from a small batch oven or booth to a complex automated powder coating line–the specialists at Reliant Finishing Systems can help you determine exactly what equipment you need to get the best results. Let us provide you with a list of some of our very happy customers. We’ve worked with hundreds of unique layouts and design requirements, and our technicians have installed countless coating systems across the U.S.A. and abroad. When you’re ready for a new booth, oven or complete powder coating system, give us a call!
Whether you’ve just started coating or have been operating a batch powder coating system for years, you know that the coating oven is an expensive appliance and a vital part of your coating operation. Keeping your batch oven in good working order is critical to long-term success. A well-maintained powder coating oven can last for over a decade, produce thousands of high-quality parts for your customers and be a considerable source of income for your business.
However, a batch oven that is operated incorrectly can be a serious safety hazard that’s unreliable and can cause you nothing but problems and headaches. To help you avoid making a costly – and potentially dangerous – mistake, here are five things you should NEVER do when operating a powder coating oven.
1) Don’t Run The Oven Above The Recommended Temperature
Most batch powder coating ovens are rated for sustained operation at temperatures of up to 450° F, while some more expensive models are rated up to 500° F or higher. If you own a conventional 450° batch oven, jumping up from 380° to 480° in an attempt to save a few minutes of cure time will harm the equipment, possibly trip the safety devices (leading to downtime) and potentially damage the finish on your parts. Every powder is rated for a specific temperature range. Going above this range will make the finish brittle and less durable, and can cause discoloration issues. This is especially true with glossy white finishes. Also, the few extra minutes you might save aren’t worth voiding your warranty or damaging costly components, especially on a critical piece of equipment like a batch curing oven.
2) Don’t Reduce The Exhaust Airflow In An Attempt To Save On Heating Costs
All professional-grade gas fueled ovens are built to exhaust a certain amount of air whenever the oven is in operation. The exhaust causes the air to move in a particular pattern within the oven cabin, keeping the cabin a stable temperature throughout. If you reduce or eliminate the exhaust airflow, you can create hot and cold spots that weren’t there before. These temperature changes will cause the powder to overbake or underbake, resulting in poor finishes and lots of reworks.
You’ll also have problems with safety devices. If you disable the safeties to keep them from tripping, you are violating important safety codes and you’ll void your warranty, no matter who built your oven. Another problem is that if there isn’t enough air being exhausted from the oven, you can have significant heat loss at the doors or oven panel seams. You may also have problems getting the doors to latch properly.
3) Don’t Overload The Oven Trying To Increase Throughput
If too many objects and racks are added to the oven, there’s a high probability you will accidentally block the oven exhaust or airflow ducts inside the cabin. If the exhaust is blocked, it adds stress to the exhaust fan and can shorten the service life of both the fan and the drive motor. It can also promote hot spots inside the oven that can damage parts, rolling racks or the oven cabin itself. If the supply ducts from the heater are obstructed, the powder can get blown off the parts. A bigger problem arises if the airflow through the heat unit gets reduced. This not only kills fuel efficiency but it also causes the temperature inside the heat unit to skyrocket. This can result in the heat unit’s fan failing, reduced service life from the motor, erratic operation due to safety circuits being tripped and even structural damage to the heat unit.
4) Don’t Skip Maintenance
No matter how busy the coating line is, skipping scheduled maintenance will shorten the service life of important oven components and can lead to critical failures. The majority of service calls we receive regarding older ovens are linked to poor maintenance practices. Most of these calls come from successful powder coating shops that use their equipment daily and stay busy–but they learn the hard way that “we’ve been busy” is no excuse for avoiding routine maintenance procedures. Keep your oven clean. Service the burner regularly. Lubricate bearings as directed. Check ductwork for obstructions. Don’t let a nuisance issue, like a noisy exhaust fan or a worn-out door latch, result in costly downtime because you were too busy to deal with it when you first noticed it.
5) Don’t Install The Oven Too Close To Other Equipment Just To Save Shop Space
From time to time we encounter a situation where a customer has installed his oven too close to his powder booth, his welding operation, a clean-up station, his blasting operation or some type of chemical pretreatment wash station. Not only does this violate safety codes, but debris, fumes or even powder from other appliances can cause problems with your oven or your finishes.
We were recently asked to troubleshoot problems with a high-end oven from another manufacturer. We discovered that the oven worked fine, but the parts were being exposed to WD-40 fumes during both the coating and cool-down stages—resulting in unacceptable finishes. Although this wasn’t damaging to the oven, similar exposure to airborne grit from blasting or pretreatment chemistry from a washer could have been.
Another common problem is when the “guts” of a powder coating oven get coated with a layer of powder over and over again during operation because of powder overspray from a nearby booth (usually one that needs a filter service). The burner safeties can cause the oven to shut down, the fan can come out of balance due to an uneven layer of melted powder and ductwork can become restricted. All of this can be prevented with proper planning and equipment placement.
Routine Maintenance and Scheduled Service Can Keep You In Operation For Years To Come
At Reliant Finishing Systems, we pride ourselves on providing some of the best and most efficient batch coating equipment on the market. By following these tips, making sure you’re following a set maintenance schedule and contacting us for service visits when you have problems, you can help increase the lifespan of your equipment and maximize your ROI.
Have any questions about powder coating equipment or need to schedule a service visit? Give us a call today.
If you use a walk-in sized batch powder curing oven for your powder coating operation, you may have questions about how to consistently get the best results from your equipment. The oven’s performance–particularly the air temperature and airflow inside the oven–can make or break the quality of your finished products.
These important tips can help you get the best finish possible from your curing oven:
Make Sure The Oven Is Sized Correctly For The Project
Powder coating ovens can be built to nearly any height, width or depth. The ideal size for your project is dependent upon what you are going to be coating. No matter what you want to coat, the entire object needs to fit inside the oven with room to spare. For more information on oven sizing guidelines, click here.
Keep Parts Away From Walls, Doors, Ductwork And Ceiling
Depending on which brand of oven you have, heated air is usually blown into the oven via ducts in the ceiling or wall, or sometimes both. When curing, make sure you have enough space between the ductwork and the parts. If the parts get too close to the ducts, the powder can get blown off and you will have to rework the part.
Likewise, if a part touches the oven’s interior, the powder is likely to either rub off completely or flake away during curing. In order to get a proper finish, the parts can’t touch the ceiling, ductwork or walls, and they can’t impede the operation of the doors or rub against them.
Also consider how the parts will be carried in and out of the batch powder curing oven. Most parts are hung on rolling racks (also called parts carts), so there has to be enough room for the rack to fit into the oven once the parts have been hung. If your rack bumps into the walls of the oven, the powder you applied can get knocked off.
Keep Parts Off The Ground
Just like you will need to allow for room near the walls, ceiling, doors and ductwork, you also need to avoid hanging parts so that they nearly drag the ground. If possible, the lowest part of the biggest parts should be 10” or more off the floor. This makes the temperature of the parts more uniform and allows the powder to cure more evenly. It also helps prevent dust contamination if the oven’s heat system blows dust and dirt from the floor onto the parts.
Routinely Check Your Batch Powder Curing Oven’s Temperature
Some ovens have better temperature uniformity than others, but none are perfectly uniform. Ovens with ceiling ducts are usually cooler at the floor than elsewhere. Ovens with wall ducts may be cooler in the corners, and possibly near the floor. It is recommended that you routinely check your oven’s temperature with an oven data recorder (a Datapaq or similar) and keep a log of the results. Get professional help fine tuning your oven and adjust your curing practices as needed.
Check Your Shop For Airflow Issues
Although it might not be obvious, drafts and air currents in the shop influence the way an oven operates. Some days there may be giant wall-mounted vent fans in operation to help keep the shop cool or get rid of welding fumes. Other days there may be one or more heaters in operation to keep office or shop space warm. Many shops have roll-up doors that are constantly being opened and closed. Wind can blow into the building or move across openings and create an imperceptible vacuum or pressurize a shop in ways that can easily overcome a powerful fan system. All of these things can impact your oven’s performance.
If you notice a change in your oven’s performance, check for changes in the way air moves through your building. Is air blowing in from outside that wasn’t a few days ago? Were the building exhaust fans turned off but the vents left open? Have you started using an AC system or have you cranked up heaters that weren’t in use until recently? Does the oven only have problems when a roll-up door is opened or closed? Examining the airflow within the shop can often help you pinpoint oven operation issues.
Check Your Fuel Source When Local Usage Changes
Another factor that can make a huge difference in the way an oven runs is fuel supply. Whether your oven is burning LP or natural gas, changes in the fuel supply can cause problems that are almost impossible to trace. These issues can be due to weather changes, new construction near your shop, changes within your building, or changes to your style of use.
If an oven is calibrated during the summer, the gas supply may decrease during the winter because of increased demand. This may be due to your neighbors (especially if located near a hospital, apartments or a large office complex) or may be because you’re using more fuel to run heaters or gas-fueled appliances within your own building that are tied in to the same line feeding your batch powder curing oven.
A similar problem can occur if new apartments or other types of high-demand buildings are constructed near your building. Once occupied, they may cause changes to the fuel supply coming into your building. Along the same lines, if you add shop heaters, steam units, or additional ovens, it may reduce the amount of available LP or natural gas fuel.
Remember, gas pressure and gas volume are not the same thing. It is possible to have a situation where the pressure gauge shows plenty of pressure when the oven is at idle or turned off, but then have performance issues once the oven goes to high fire. This usually happens when the supply line or regulator is too small. The oven can also have problems if the supply has enough volume, but the pressure is too high (dangerous and can cause the safeties to trip) or too low (can cause the oven to fail to ignite or to take too long to get to curing temperature). For best results, the oven needs an adequate volume of gas delivered at just the right pressure.
Always Follow Safety Procedures
IMPORTANT: If your shop’s work schedule becomes busier or you change operators, it is possible to have oven issues crop up because of the way the oven is being used. One common problem is caused by operators opening the oven doors for loading/unloading while the oven is running. This is unsafe and can lead to property damage, serious injury or death. It also causes the heat system to burn a large amount of fuel as it tries to maintain curing temperature while heat is rapidly escaping from the oven through the open doors. Not only does this waste fuel, it can reduce the service life of expensive oven components because of the burner’s extremely high output. When you’re ready to open the oven doors, shut down the burner but leave the fans running. Turning off the fans while the oven is at curing temperature can cause them to warp or can cause related parts to fail prematurely.
Follow Factory Maintenance Recommendations And Usage Guidelines
Every powder coating oven manufacturer provides a maintenance schedule which outlines the safest and most effective ways to operate their equipment. These factory-recommended “best practices” describe the style of use that is safest, most efficient in terms of manpower, least expensive in terms of fuel use, least likely to result in down-time due to equipment repair, and most likely to prevent unusable powder coated parts that are rejected due to poor finish quality.
There’s a reason why successful shops that are noted for premium quality work or incredibly high throughput keep their equipment in top shape and operate it properly. Having a set schedule for cleaning, maintenance and lubrication of your batch powder curing oven and related equipment will help you get consistent, high-quality finishes. Similarly, only running the oven within recommended temperature ranges is not only more fuel-efficient, it is safer for your operators and less likely to damage parts. Oven providers typically offer strict guidelines designed to assure that you get the best results from your equipment and the highest level of efficiency. Following those guidelines will help save you from expensive equipment repairs and costly parts reworks due to bad finishes.
Need An Equipment Check-up?
Reliant Finishing Systems batch powder curing ovens are always set up by our factory-authorized technicians to provide performance that is well balanced. We want our ovens to reach operating temperature quickly, while burning as little fuel as possible, and we are committed to helping shop owners keep our equipment in the best operating condition possible.
If you have any service or maintenance issues, please give us a call today. Scheduling a visit from one of our factory-authorized technicians can help solve curing issues, improve your efficiency and increase the lifespan of your equipment. Available services include troubleshooting, Datapaq recording and line audits, preventative maintenance, and both routine and emergency repairs. Call today for more information or to schedule an appointment.
One of the keys to successful powder coating application is proper grounding. A good ground acts like glue to the powder being sprayed on the part, making it easy to get a uniform, high-quality finish with high transfer efficiency. A weak ground can cause a host of issues, such as light coverage areas, Faraday cage problems, larger hook marks, generally uneven powder application, dirtier spray booth filters, and poor transfer efficiency. In extreme cases, improper grounding can cause the operator to get shocked.
How to Get Proper Grounding for Your Powder Coating Gun
There are four main areas where your grounding technique needs to be addressed:
Grounding Rod. We have mentioned in previous articles that the best starting ground for manual spray applications is a 6’ to 10’ copper grounding rod installed just outside of the powder spray enclosure. Permanently attach a ground strap of at least a 14-gauge wire with a good clamp on the end that will be used to ground parts. When the ground rod is in rather sandy or dry soil, a small amount of water can be poured into the grounding rod hole and allowed to soak in prior to powder coating.
When using this grounding method, the powder will stick to the part like glue. The powder will resist being shaken off when moved or when encountering mild air movement.
IMPORTANT: Using just the grounding clamp supplied with the gun unit is inferior to using a grounding rod, but it’s better than nothing until you get your grounding rod installed.
Parts Rack or Cart. You will need good metal-to-metal contact from the grounding rod clamp to the part. If you clamp the cart in the same place each time, be sure to blow or wipe off the powder around the clamp attachment area each time BEFORE the cart enters the curing oven. This will prevent you from having to grind off this area every time you use the cart.
When parts are attached directly to the rack or cart frame, metal-to-metal contact is usually achieved by the part shielding the rack’s contact points. It’s important to note that if you do not hang parts on every contact point, powder will accumulate on the exposed points and will have to be removed before using the rack again. Some operators use high temp tape or other masking agents to protect areas of the rack from powder that can become baked over the exposed metal.
If you use racks that have movable hooks to attach the parts using a bar or similar contact points, you need to grind the tops of the bars every 5-6 coating cycles. This will ensure a good ground and proper transfer efficiency. If you hear popping sounds while applying the powder or see small instances of electrical arcing from hook to rack, flag that rack to be cleaned via grinding or stripping before using it in the next coating cycle.
Racks can usually be manufactured by any local metal fabrication shop. Many job shops make their own. When designing racks or carts, remember to concentrate parts so they are two feet from the floor to about six feet high. This will allow the operators to spray all areas fairly easily.
Hooks. As with the cart, you need good metal-to-metal contact with the cart and the parts. Most shops can get 5-6 uses from a hook before it starts becoming insulated by baked-on powder. Some powder coaters just replace the hooks with new ones, but others have them cleaned. Cost analysis will tell you which is more efficient. If you are getting arcing and the rack has been cleaned, then you need to clean or replace your hooks. Mighty Hook is a great source for hooks, plugs, and tape. http://www.mightyhook.com/default.aspx
Parts. Not all parts ground well. Because of their mass, some parts can be tough to ground properly. Also, if parts have been coated before, they can be more challenging to ground. Sometimes the racks don’t ground parts adequately because the parts hang too far from the grounding point. In these cases, you can clamp directly to the part in question. After spraying the powder, just remove the clamp and spray the clamped section last to keep from getting surface defects.
If you’re worried that you might not be getting a good ground, use a megohmmeter (often called a “megger” after the company that makes these types of test instruments: http://us.megger.com/) to check the resistance from area to area. If the resistance exceeds 1 megohm from ground to part, work backwards at all the contact points to determine where the loss of ground is occurring.
Using professional quality powder coating equipment can solve many of your coating issues. All of Reliant Finishing Systems’ equipment is designed to provide the best finishes possible for today’s powder coating operations. Find out more about Reliant equipment here, or give one of our systems specialists a call today.
One of the many advantages powder coating has over wet paint is the variety of ways you can fine-tune and rework a powder coated finish. This article discusses some of the different touch-up techniques you can use to clean up your work and get the best overall quality for your powder coating projects.
Why Should You Touch-Up Your Powder Coated Finish
Visual Appeal. This is the obvious reason for fixing a powder coated finish. To most customers, if it doesn’t look right, it isn’t acceptable.
Performance. Some powder coatings are purely functional, so they don’t need to be aesthetically perfect. Usually there are one or more standards (such as corrosion resistance) that have to be met. A defect can compromise the finish integrity and cause a part to fail to meet a specific customer’s standards.
Warranty. If the powder coated part has any sort of warranty, then special care should be made to make sure the part passes end-of-the line QC testing. A part may look great and have no apparent defects, but if it does not pass the customer’s minimum testing standards, a repair or rework is needed.
When Is The Right Time To Do Touch-Up Work?
The best time to catch your coating mistakes is prior to curing the powder. The powder can easily be blown off with compressed air or wiped off and then reapplied with very little hassle. Get in the habit of checking your parts for application errors before you start the curing process. Every mistake you catch here will save you time, effort and money later.
Common Powder Coating Touch-up Techniques After Curing
It’s not always possible to catch coating errors, especially if there are overbaking or underbaking issues with your oven. When dealing with a defective finish, you should ask yourself: will a touched-up surface be acceptable -both visually and from a performance standpoint-or should you repaint? In either case, if you have to resolve a finish problem, here are some of the most effective techniques to use once a powder coated part has been cured using Reliant’s products:
Liquid Paint Touch-Up
Many manufacturers use color-matched liquid enamels to cover hook marks, missed areas, Faraday areas, re-welds, sanded spots, handling damage and other defects.
Pros – cheap, fast, least labor intensive, little skill required
Cons – not visually appealing on a class A part, visual “halo” around repair, repair is not as durable as the rest of finish, repair may fade or chalk faster than surrounding powder coated finish
Usable with most decorative finishes. This repair method is fine except for on the primary surface a customer can see.
In some instances, your powder process can allow for a repainted finish to go over a previously painted part with no prep work. Usually the part must be freshly powder coated with no contamination on the surface.
Some chemistry is not compatible with this method and the surface will need to be abraded (blasted with abrasive grit or scuffed with sandpaper) and then wiped down with alcohol. If the part has been cured for more than a week, it will almost always need to be abraded and cleaned before re-coating.
Pros – Less expensive and faster than stripping, better corrosion protection than liquid enamel
Cons – Adhesion risk (always do a test part and check adhesion), too much film build-up could cause issues (weight, measurement tolerances, extreme temperature checking)
Many small parts manufacturers will re-run parts after inspection if they have light powder coverage or other easily repaired surface defects. In the closet hardware and racking industries it is especially common for facilities to repaint parts once or twice if they are having an acceptable amount of rejects.
Tip: Remember to use your powder gun’s re-coat settings to properly apply a second coat
Sanding And Buffing
Sanding and buffing the powder finish can eliminate surface trash and some defects. This also helps smooth out orange peel that naturally occurs with most powder coatings on parts where the powder thickness is excessive in a particular area. Sanding companies like 3M have a series of abrasive and buffing compounds that allow shops to sand out defects and then bring the surface back to a smooth shine.
Pro’s – Mirror-like finish, faster to buff than to repaint
Con’s – Burn-throughs will need to be repainted or touched up with a liquid paint, labor-intensive, requires moderate skill
In the automotive and other transportation industries, manufacturers will sometimes sand and buff out Class A type parts such as hoods or panels that need to have a mirror-like defect free finish. This is similar to work done with wet paint. It takes some experimentation to develop a successful sanding and buffing process.
Tip: The sooner you buff after curing, the easier it is to work with the finish. Power coating gets very hard 1-3 days after curing.
IMPORTANT! Be sure to have the buffing operation isolated from the finishing operation. Many of the waxes and compounds used for buffing and polishing do not react well with painting and powder coating processes and can cause defects like “fish-eyes.”
Fillers And Putties
There are many products like Bondo and Lab-metal that can be used to fill gaps and seal holes prior to powder coating. Before adding a filler to your process, make sure it is compatible with 400° to 450° F curing temperatures and that it is recommended for powder coating.
Pros – Eliminates re-welding for small areas, surface defects are much less noticeable if repaired prior to powder coating, parts do not need to be taken off-line for repair
Cons – Powder may have trouble being electrostatically attracted to the repair, in a large area adhesion can be suspect, may cause powder finish to “shimmer” or look different over repair
Trailer companies often use filler-putty to bridge gaps in their dump-style trailers. Tiger Drylac has a two-component filler that has some conductive elements for good results when used under a powder coated finish. Here is a link to their data sheet:
Total Strip And Repaint
If there is a catastrophic finish failure, starting over after taking the finish off down to the bare metal can sometimes be the only solution. Major powder coating issues, like severe adhesion problems in high-performance parts, often require a total repaint. Pretreatment failures, parts contamination after pretreatment, underbaking, and overbaking can also cause problems that are so bad that the only answer is to totally strip the coating off and redo the process (after you have identified and corrected the fault in the process). Remember, the finish is only as strong as its weakest layer, so if you notice flaking once the finish is cured, it will need to be completely redone.
Pros – Once the process is fixed, you have high quality parts going to the customer and you don’t have to worry about field failures and the possibility of costly claims in the future
Cons – Costliest and most time-consuming solution
For demanding projects like government contracts, high-performance industrial components, engine parts, military equipment, parts that will be exposed to a highly corrosive environment or impact/abrasion in the field, the only way to insure quality compliance for parts that have badly defective finishes is to re-work the parts down to the metal.
The Nail Polish Fix
We’ve just outlined the most common touch-up and re-work methods, but there is another technique that can sometimes get positive results. An uncommon method for fixing small finish imperfections is to put a small amount of the powder in a clear lacquer and use it as touch-up paint. It’s possible to use hair spray, nail polish and other lacquers in a hobby situation, but bulk materials will be needed in a professional environment. Although the touched-up area will visually match the cured powder paint, the repaired area will not have the same durability as the cured surface. Remember, if you need the same surface integrity and durability in your touch-up areas as you do with the powder coated finish, you will probably need to use a two-component catalyzed topcoat and possibly a zinc-rich epoxy primer for appropriate corrosion resistance.
Meet Expectations With The Right Powder Coated Finish
To retain business and keep customers happy, you need to know exactly what each customer expects from the powder coated finish you are providing. Once you know that, you can develop a process that includes a repeatable touch-up system that addresses defective finishes of all types. Proper touch-up and re-work techniques help ensure great finished products.
Using professional quality equipment can solve many of your coating issues, including overbake and underbake problems associated with outdated or inferior quality ovens. All of Reliant Finishing Systems’ equipment is designed to provide the best finishes possible for today’s powder coating operations. Find out more about Reliant equipment here, or give one of our systems specialists a call today.
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)
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)
“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
Wagner 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
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!