If you’re running a successful powder coating shop that uses “batch” powder coating equipment, you need to move parts quickly and efficiently between the various stages of the coating process: loading, parts cleaning and preparation, powder application, powder curing, cool-down, and unloading. Well-designed parts racks can make the problem much easier to tackle. A parts rack (also called a parts hanging rack or a parts cart) is a sturdy metal rack on wheels. Parts are typically hung from the rack using slender metal hooks. Once they have been hung in place, the parts can easily be moved from one stage of the powder coating process to the next.
To maximize your shop’s efficiency, is important that you build or buy good quality powder coating parts racks that are suitable for the way your shop is laid out. Unless you have experience working with a particular type of rack and know exactly what you want, you may need to start out by testing just one rack at a time and refining the design as you go. If you already have orders that need to be filled and you want to hit the ground running with your new powder coating equipment, then building multiple racks that can be stationed at every stage of the coating process might be the best solution.
Whether you buy or build racks—one rack at a time or in multiples—these 10 tips will help assure you get the right racks for the job:
1.) Don’t Use Fancy Wheels
The wheels (also known as casters) will need to withstand 400°F or higher temperatures, day-in and day-out. Cast steel or aluminum wheels work best and are easy to find at industrial supply houses and home improvement stores.
If possible, avoid the expensive models that have ball bearings. Very few of them can withstand extended exposure to high temperatures without the bearing grease leaking out and making a mess or the bearing assemblies seizing up due to expansion and contraction as they are repeatedly heated and cooled.
Other wheels, like glass-filled nylon, phenolic resin, and high-temp polypropylene might seem attractive, but they are difficult to clean without damaging them, especially if you blast your rack to clean it. They also serve as insulators, preventing grounding of the rack via the wheels (more about that in tip #9).
2.) Don’t Use Small Wheels
Try to use only 6” or larger wheels. The rack’s wheels will pick up powder overspray from the floor. Small wheels clog up faster with powder build-up and require more frequent maintenance. Because of the increased space between the wheel and the wheel’s mounting plate, large wheels don’t clog as fast and are easier to clean. Smaller wheels also tend to be harder to steer when the rack is loaded with parts. It’s no fun fighting with a set of wheels that won’t turn smoothly or that wander back and forth under heavy loads. To prevent the rack from constantly trying to spin as you move it, mount wheels that turn only on one end of the rack and attach wheels that track straight on the other end.
3.) Build A Sturdy Frame
Make sure the frame of the rack is sturdy and can safely support the load of the parts. A frame made from angle iron or square tube stock usually works best. Mild steel is easier to ground and takes a charge better than aluminum.
When designing your rack, remember that sharp corners, clean edges, and notches make excellent ground contact point with the hooks the parts will be hung from.
4.) Make A T-Shaped Rack
A T-shaped rack design prevents parts from accidently bumping into the frame of the rack. It also keeps the frame out of the way of the operator trying to spray the parts. To prevent fatigue, joints at 90° angles need to be cross braced. It will see plenty of use, so make sure your rack has only good welds. If you are spraying very heavy parts, you may need a square cage type rack, but try to design a T-rack whenever practical, even if you have to use much heavier material for the rack itself.
5.) Understand Your Coating Zone
The “ideal” spraying zone for manual powder application is somewhat limited in size. Loading parts into this zone whenever practical will assure good throughput, high powder transfer efficiency, and consistent results. While standing on the floor, an operator can typically spray in a rectangular area that extends from about 2’ off the floor up to about 6’ from the floor. He can do this comfortably and with good visibility of the powder on the part. Side to side, the operator can spray in sections of about 4’ before having to change foot position. Imagine a 4’ x 4’ active coating area in front of the operator where he can do his best work without using a ladder, kneeling down, or having to move his feet side to side. Hanging parts in this zone will net optimum results. For longer parts, imagine another 4’ X 4’ area beside the first one, creating a 4’ X 8’ ideal coating zone. The operator can cover this entire zone by slightly changing his foot position as he applies powder. This approach to racking and coating parts will provide optimal throughput and prevent operator fatigue. There may be times when a part must be hung with the bottom close to the floor or the top surface near the ceiling of the booth. These parts can still be coated, but the amount of time it takes to apply an acceptable finish will be much longer than with parts that are hung so that it is easy for the operator to coat them without climbing a ladder or having to kneel down.
6.) Understand Your Curing Zone
Hanging parts between about 2’ and 6’ off the floor also helps keep the parts in the ideal curing zone for most walk-in sized batch ovens. Factor in your hook lengths and try to keep parts in this optimal curing zone whenever possible. When measuring temperatures inside a curing oven, the temperature at the floor is usually a little lower than average. This is especially noticeable during the first batch in the morning or after a cold start.
Parts hung near the floor may need extra dwell time to cure adequately. The temperature at the top of the oven may also be a bit hotter than average, especially on warm days where the oven sees non-stop use. You need to be on the lookout for color consistency issues or other signs of overbaking if you have parts near the ceiling of the oven. With parts that are so large they extend both above and below the ideal curing zone, you will probably have to tweak your curing routine to get top-quality results.
7.) Consider Removable Hanging Bars
The bars that your hooks hang from will need to be cleaned from time to time. Removable bars make this easier. If they are bolted on or slide into support channels instead of being welded in place, they can be taken off to strip, blast, or grind when they get powder built up on them.
Unless you are using a chemical stripping agent, square tubing is simpler to clean than round tubing or angle iron because the flat surfaces can be ground/wire-brushed/blasted more easily than round stock and you don’t have any recessed corners to deal with like you do with angle iron.
8.) Make Sure It Fits
It should be obvious what will and won’t fit in your booth and oven, but sometimes people don’t consider what will actually work best with their shop layout. It’s important to think about the turning radius of the rack. More than one business has fabricated their own racks without testing them, only to find out the racks couldn’t turn sharply enough to move from appliance to appliance because the shop was so crowded.
We’ve also encountered shops where the racks were based on the equipment’s internal dimensions and ended up having to be cut down to work properly. Don’t get carried away trying to fill every inch of your appliances when you build or order racks.
The rack will need to be at least 1’ away from all surfaces inside the oven. If not, your operators will spend too much time trying to avoid bumping parts into the walls or discharge ductwork as they move the rack in and out of the oven.
Keeping the rack smaller than the oven is also a good idea because you want to avoid jamming parts against the wall or floor-mounted ductwork (or ceiling in ovens with overhead discharge of heated air). You risk having the powder blown off the parts or impairing the performance of the oven’s recirculation or exhaust fans, which can cause the oven to shut down. Your rack will also need to allow 2’-3’ or more of working space inside the powder booth. If the rack fills the booth, there’s no place for the operator to work. Multiple small racks give you more flexibility when coating and can be stacked into the oven side by side or one in front of the other when you want to do several parts in a single cure cycle.
9.) Get A Good Ground
Don’t rely on your cart’s wheels for grounding. Weld a beefy grounding tab to the bottom section of your cart. You may want to also weld a small shield a few inches above the tab to prevent falling powder from quickly coating it. This tab is where a grounding clamp will attach. When planning your grounding tab, remember it will need to be easy to clean because powder overspray will build up on it over time. Having a grounding tab on your cart only makes sense if you have a good grounding point in your booth. Don’t count on the wimpy ground that is integrated into your powder gun and don’t hook your ground strap to the wall of your booth. Install a grounding rod near the wall of your booth. Install two or more in a large booth so your operators don’t have to deal with dragging around a long ground strap. If possible, use an 8’ long copper rod, as opposed to a shorter one or one made from a cheaper material. Use 14-gauge or heavier wire and a stout spring-loaded clip to make your ground strap. Permanently attach the ground strap to the grounding rod and use the clip to attach to your cart’s tab. This grounding method will improve powder transfer efficiency, saving you time and money. Remember to keep your racks clean. Don’t saddle operators with racks that are so badly caked with baked-on powder that the parts can’t be properly grounded. Good rack maintenance practices will improve throughput and reduce powder waste.
10.) Don’t Skimp on Racks
This isn’t a design tip, but it is just as valuable. One of the most frustrating things we encounter when talking to a customer who needs more throughput from their batch powder coating shop is a rack shortage. Racks are one of the cheapest components you can get for your powder coating process, yet smaller shops sometimes treat them like gold. In fact, one of the biggest differences we see between shops that are thriving and those that seem to be struggling with throughput is the way they go about racking and staging their parts.
Successful shops don’t let themselves get delayed by having their operators waiting around for racks. Once you build or buy a rack that works well for your shop, get enough of them to let your business thrive!
Spending time to design and build racks that work well in your shop environment will increase your productivity and save you from headaches down the road. If you have experienced operators, get feedback from them, especially workers who have a good bit of powder spraying experience. They can add valuable input and you can learn about the challenges they’re facing by working alongside them as they test new rack designs.
Need Help? We’re Here for You!
In addition to manufacturing, installing, and supporting our own powder coating equipment, Reliant also provides a wide range of services to help your existing finishing operation run smoothly–from on-site troubleshooting to training, equipment refurbishment, and more. Call us today at (877) 418-5550.