Technology Interchange—Improving Powder Utilization, Reducing Rejects, and Saving Money
Posted on Monday, March 21, 2022
By David Merritt
Let’s face it, if we’re looking for cost savings, we often think about efficiency. Time is money, as they say. We all know that powder coatings are an outstanding coating choice, delivering a gorgeous finish, technical advantages over traditional liquid paints, and an unbeatable sustainability footprint. Ensuring an efficient powder operation will not only lead to beautiful finishes and happy customers but can also lead to cost savings.
Maximizing your powder utilization is one way of improving efficiency and maximizing savings throughout your operation. It will also come as no surprise that many factors, from the type of system used and the maintenance of application equipment, to the quality of the powder itself, can affect powder utilization. Let’s delve into some simple ways to maximize efficiency, powder, and savings.
Powder coating booths have evolved over the years to enable shorter down times during color changes and greater utilization of the reclaim material. Some booths are strictly spray-to-waste, while others, such as cartridge and cyclonic recovery booths, can and do recover powder efficiently. Like any other system, these booths must be maintained to the manufacturer’s specification and preventive maintenance must be performed at the suggested intervals to ensure optimum performance. For proper utilization of powder, check these simple system requirements to maintain an efficient system.
- Grounding of the booth and application equipment is essential for optimum safety and efficiency. The booth should be checked with a megohmmeter to be sure that the resistance to ground falls within the manufacturer’s requirements. Ground rods should be installed around the booth, and the track, load bar, racks, and hooks should also be well grounded. Maintaining clean tracks, load bars, racks, and hooks is essential to ensuring a good ground and improves transfer efficiency. More powder on the part means less waste.
- The air flow into a booth should be checked and maintained per the manufacturer’s specifications. Magnehelic® gauges are frequently installed to show the air pressure flowing through the cartridge and final filters. These filters help remove the overspray powder from the air stream and allow it to be reclaimed for reuse. The Magnehelic® gauges should be marked with the equipment manufacturer’s recommended minimum and maximum settings for proper operation.
The utilization of overspray powder, and the resulting booth development, is a key factor influencing the growth of powder over the past four decades. The two most used powder booths are cartridge booths and cyclonic recovery booths.
Cartridge Booth System
A cartridge booth typically has a slightly higher powder utilization rate than a cyclonic system. Cartridge booths are good for coaters using fewer colors, so the large cartridge housings do not have to be switched out as frequently.
However, if not maintained properly, fines can start to build up inside the cartridge collectors, which can lead to poor transfer efficiency. In some cases, it is a good idea to send samples of powder from the cartridge recovery system to the powder manufacturer to have the particle size checked. If the volume of fines is getting too high, virgin powder can be added to the feed hoppers to shift the particle size closer to the virgin powder. If the air flow entering the booth drops too low, powder can escape from the booth. Again, it’s worth stating that maintaining the filtration system is important for the efficient use of a cartridge booth.
Cyclonic Powder System
Cyclonic powder systems have become very popular over the last ten years, mainly due to their quick color change capabilities. These systems can be changed over in minutes versus the hours required for a cartridge system. The overall powder utilization can be a little lower than a cartridge system, but the color change speed can offset this. The cyclone used in these systems can also separate the fines from the larger particle reclaimed powder. Maintaining the manufacturer’s recommended airflow through the system is very important for reclaiming and achieving maximum utilization of the overspray powder through the system.
Line Management and Quality Control Checks
In both cartridge and cyclonic booths, the incoming air quality is very important for good powder and system utilization. If air quality is poor or compromised, a whole host of issues can occur. For example, if oil or water are allowed to enter the compressed air lines, the powder can become contaminated and show signs of craters and fisheyes. It can cause premature blinding of the cartridge filters and final filters. Oil and water can blind the fluidizing membranes inside the feed hoppers, causing fluidization problems. Impact fusion inside the feed pumps, hoses, and application guns can also occur. This can cause the application equipment to spit and surge, increasing the reject rate of parts being coated, and increasing your powder usage, time, and energy in recoating.
Checking fluidization pressures is also important. Different powder coating chemistries and colors have different specific gravities, so they may require different pressures to properly fluidize. It’s also worth remembering that the relative humidity and temperature can affect the fluidization of powder if the powder is not stored and applied in an environmentally controlled space.
As disruptive as it may seem to adjust cure oven settings, understanding the optimal cure conditions and thermal stability of the parts being coated can save time and costs in the long run. A simple check to ensure proper cure is running a data oven recorder through the cure oven at regular intervals. This can potentially catch any malfunctions in the oven before they cause multiple part rejects. Also, any time a new part is run, it is important to consider the type and gauge of metal used. Does it have thin spots that may be sensitive to high oven temperatures? Is it a part with very thick profiles that may need increased heat or bake time to achieve the proper peak metal temperature? After these questions are assessed, it may be necessary to review the powder being used. Many powders are available in standard cure and low temperature cure formulations. Depending on the part, a low temperature cure powder may be ideal. Of course, the performance of the powder in application must be maintained.
It sounds obvious but developing standard operating procedures (SOP) can alleviate many of these issues. SOPs should include, but not be limited to, the kV, micro amp, powder feed and atomization pressures used, as well as ideal gun to part distance. This should include regular film build testing to ensure proper application amount and any other physical testing (these will vary depending on the end use of the product) that might lead to rejects or quality concerns.
Establishing a documented color change procedure is a good practice for a powder coating operation of any size. It is particularly necessary when making a change from a light color to a dark color. A checklist detailing each piece of equipment used in the application that needs to be cleaned or checked for wear will help to reduce the possibility of cross contamination from one color to the next. A timeline for checking wear parts on a regular basis should also be part of this standard operating procedure document.
A preventive maintenance plan and spare parts list are also useful and time-saving tools. Pretreatment, application equipment, powder booths, conveyors, and ovens should all be checked regularly for signs of wear that could result in the system shutting down. System shutdowns equal skyrocketing costs. Equipment suppliers can usually provide a list of wear parts and replacement parts. Check the operations manuals for parts that should be kept in inventory.
Choosing the Right Powders
These procedures should also be used when going from one powder vendor to another. Different powder suppliers may use different types of raw materials that can cause technical issues such as incorrect gloss, or craters and fisheyes when mixed together, even at low mix ratios. An often overlooked consideration that affects powder utilization is the quality of the powder coating being used. A more resin-rich powder will deliver better utilization. A powder heavy with fillers will deliver poorer utilization.
There are numerous types and chemistries of powder coatings available in today’s market. Most vendors have information posted on their websites detailing the chemistries they have to offer, primer and topcoat suggestions, and applied cost information. It is important to partner with a powder supplier that has proven products and provides access to qualified salespeople and technical service staff who can help you iron out any issues, help keep costs down, and have the ability to supply your powder coating needs in a timely manner.
In conclusion, there are multiple factors in any powder coating operation from the smallest shop to the largest, high volume manufacturing facility that can help improve efficiency and reduce costs. All powder coating operations are built on a powder, a line, and are built on a powder, a line, and a process. Optimizing all three will ensure smooth operations, flawless finishes, and efficient powder utilization, and ultimately cost.
David Merritt is technical service manager for IFS Coatings.