By the time your pretreatment equipment, dry-off oven (if you’re going to use one), spray booth, powder gun(s), and curing oven are installed and operational, it’s natural for you to want to dive in and start batch powder coating right away. However, make sure you’ve received training on how to operate and maintain all of your new equipment before you start using it.
If you haven’t received equipment training, we recommend that you either attend an established powder coating training class or hire a consultant/on-site trainer to help you. If formal training is impractical, ask your powder and chemistry suppliers to send technicians to help you get off to a good start.
Understanding how the equipment works and how to maintain it will help you navigate the key steps in your coating process: application, product flow, process and preventative maintenance.
Batch Powder Coating Application
Before any powder coating application begins, the parts need to be clean and ready for powder. This sounds simple, but you may have to try a couple different chemicals/detergents before you get the right fit for your situation. Your parts need to be clean, streak free, fiber free (note— shop towels and tack rags leave fibers), and dry in order for the surface to be ready to accept powder. Depending on your finish, you may need to blast or phosphatize your part. Remember, streaks, oily spots or wet parts can cause finish problems, so make sure you run a (clean) hand over the parts before you start coating to check their surface.
Here are some things to consider if you are having application problems:
Insufficient Ground: The powder won’t uniformly stick to the parts, or won’t go into the corners of certain parts. This can be solved by burying a 6’ to 10’ grounding rod close to the spray booth and using a heavy gauge ground strap attached to it to assure that parts are well-grounded. You need clean hooks and a clean rack if you are clamping the ground strap to your cart.
The Powder Gun Won’t Spray Evenly: If an inconsistent amount of powder is spraying out of the gun, or you are getting the wrong amount of air, check the gun manufacturer’s recommended settings or ask your powder supplier’s tech for recommendations. Incorrect settings can be troublesome and easy to overlook.
Bad Finish Due To The Amount Of Powder On The Part: The typical mil thickness of applied powder is 2-3 mils after baking. This can be achieved by spraying powder evenly with about a 50% spray overlap as you cover the part. You are trying to make the freshly applied powder look like felt. If it looks like chalk on a chalkboard or it seems like you can see through it, then you need to apply a heavier coating for best results. If it looks like moss, then you may have applied too much and may get an orange-peel look after baking.
Clumpy Powder: Weather conditions can affect powder application. Rainy, damp or high-humidity weather can cause powder to clump and spit from the gun, especially if your shop that isn’t heated or cooled. Storing your powder in a cool, dry environment may help reduce this problem.
Finish Seems Inadequately Cured: Extremely cold temperatures outdoors can give your parts a lower temperature. Colder parts may require extra baking time or a slightly higher curing temperature. Consider storing your parts in a climate controlled area (for at least an hour) before being sprayed.
Fish-eye Or Other Surface Defect Issues: Airborne contaminants are often the culprit to surface defects. Make sure the compressor is supplying dry, oil-free air to the powder gun. Look for work stations near the coating line that have WD40, caulk or other products that emit solvent vapors. Isolate your coating equipment from blasting, sanding and welding stations. Check the air that is flowing through the spray booth. If the booth has diesel fumes coming into it from a generator, welding rig or forklift–or if new asphalt is being poured nearby–the fumes can cause temporary problems that may be hard to trace.
Racks and holding areas should have been planned for in advance, but sometimes you have to adjust your thinking once you see your coating process actually taking place. You will need to be flexible with your rack design and keep in mind the need for staging areas for parts that are in-process.
Initially, small production runs will help you develop a process that can be repeated with consistent results. Don’t overdo it—if you can’t get great results on a small scale, you certainly can’t get them on a large scale. Production can be increased after employees are comfortable with the coating process and understand each of the steps. Don’t expect to do 5,000 flawless parts your first week after start-up. It’s much easier to increase throughput slowly than to be stuck with a large number of re-works right from the start.
The desire to go fast can cause unique problems related to product flow. One common issue is handling damage to the finish of parts that would have otherwise been acceptable. This is usually caused by workers unloading the parts before they’ve cooled enough to safely be handled, often in an attempt to meet throughput goals. Keep your expectations realistic and avoid quality problems that are easily preventable.
Batch Powder Coating Process
This goes hand-in-hand with product flow, but you must to adhere to the powder coating and pretreatment chemistry manufacturer’s specifications if you want your process to work correctly.
This includes following the recommended specifications for dwell times for chemicals, mil thickness guidelines for powder, cure time/temperature for powder, and cool-down requirements before packing.
The provided guidelines will help you troubleshoot your process flow. By following the experts’ recommendations, you will start to see how much time it actually takes to produce a good part with a quality finish. By working closely with the production schedule, you can find out where your bottle necks are taking place and where you may need to move employees around to help with issues like excessively long rack loading and unloading times.
Cure times can vary depending on your metal thickness, outside temperature, and powder specifications. Be smart about batching your jobs. Thin metal may only need 12 minutes at curing temperature, while ¼ inch steel rebar might take up to 30 minutes. Although it might not seem like a big deal, 18 minutes of variance is a hefty difference if you intend to cure both parts at the same time. You may run into over-bake issues with the thinner parts. You’re better off batching similar parts together for curing. Bake all the small or thin parts at one schedule, and then do the thicker parts with a different one. Remember, it may take much longer for the surface of heavy parts to reach curing temperature than it does for the powder to cure once that temperature is reached.
Testing your parts on your own is a great idea if you want to understand the quality of the finish you are providing. Mil thickness, adhesion, MEK rubs (for cure), and impact resistance are all good tests that can be done in-house to insure the parts are good before they go to the customer. Any adjustments to your process should be cleared through the powder manufacturer’s technical rep.
Quality assurance is a process all its own and should be developed hand-in-hand with your finishing process.
Preventative Equipment Maintenance
This is an area where we see an alarming number of shops struggle. A company will invest considerable capital on new equipment and then suffer a major setback by failing to invest in their maintenance plan. Filters, bearings and the recommended lubricant is relatively inexpensive and easy to get from your equipment provider Proper maintenance isn’t always cheap, but it is always much cheaper than new equipment.
When you get new powder coating equipment, there are usually a number of PM routines that need to be adopted. If you don’t have a maintenance department, you need to designate an employee as the maintenance supervisor for your new coating equipment and keep that position responsible for maintenance-related downtime and issues.
Keeping your powder coating equipment clean and well maintained is the key to your system’s longevity. Proper maintenance can help a system last 3-5 years longer, with 20-30% less downtime during regular production hours. It can also significantly reduce costs associated with finish quality issues caused by poorly maintained coating equipment.
If you want to get the most from your equipment and expendables, take care of them and stay organized:
Keep critical spare parts on hand for emergencies, as well as small parts and expendables like filters, grease, and belts.
Store your powder in a climate-controlled environment and routinely rotate stock.
Keep all of the contact information for your suppliers’ technical support personnel in one easy-to-access location.
Stick to a schedule for everything from filter changes to lubrication to booth cleaning to rack and hook burn-off.
Don’t wait for something to break before instituting a good PM program.
By preparing for these challenges and educating yourself on equipment maintenance and proper process, you will be able to skip many of the growing pains and get your coating off to the right start.