Sustainability in Powder Coating
The view from one experienced (meaning old) equipment designer.
Sustainability is a buzzword that has been around since the late 1960s. Even going back further, that renowned engineer and quality guru, W. Edwards Deming, had a well-circulated quote: “One must learn to do more with less.” When presented with the concept and benefits of sustainability, practically everyone agrees it is a great idea. It is not even a new idea. So, why is there still so much talk — and relatively little action — on sustainability in the manufacturing sector?
The Environmental Protection Agency defines sustainability in manufacturing: “Sustainable manufacturing is the creation of manufactured products through economically sound processes that minimize negative environmental impacts while conserving energy and natural resources.”
“Economically sound” … “minimize negative impact” … “conserve energy” … What’s not to like? Many of the practices that have evolved in the powder coating industry have increased the potential for implementing sustainable practices. Here is a quick rundown of these practices.
Powder coating was developed in Europe as an alternative to high solvent content liquid coatings. (See an abbreviated powder coating timeline in the sidebar.[3 ]) With the advent of electrostatic spray guns, powder became as easy to apply as liquid paint. In addition, factors such as better control of coating thickness, performance features based on advances in powder coating formulation chemistry, and the overall downward pressure on material costs have helped powder coatings come a long way as a replacement for conventional and compliant VOC-based liquid coatings. More low-cure-temperature powders also are available.
Powder coating is economically sound, and it certainly minimizes negative environmental impacts.
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Cleaning and Surface Preparation
As most are aware, proper surface cleaning and preparation prior to applying a powder coat is critical for coating performance. The cleaning can be done with media blasting, but most production applications use a spray washer.
When I started in the business of spray-washer design, a five-stage iron-phosphate wash system was considered top of the line for surface preparation of steel parts. Seven-stage washers with zinc phosphate were few and far between. Heated wash tanks were designed to operate at 180°F (82°C), and the phosphate application tanks were designed to 160°F (71°C). Even some of the rinse tanks were heated to 140°F (60°C). Products like Alodine, Granodine and Bonderite were what people used —along with hexavalent chrome sealers. Some of those products are still around and being used regularly. Luckily for us, hexavalent chrome sealers seem to be a thing of the past.
Washer chemistry has advanced through the last few decades with a definite trend toward lower-temperature cleaners and pretreatments as well as less phosphates. A technological jump occurred about 10 years ago with the advent of zirconium-based conversion coatings. Using an ambient-temperature non-phosphate product like that rather than a modern phosphate conversion coating can save $25,000 per year just in natural gas. That swap does not even take into consideration the reduction in sludge buildup that must be handled as a hazardous waste.
There also are single-stage ambient nonaqueous cleaner/pretreatment options that have been around for some time. This type of chemistry can give exemplary results under the right conditions. Overall, the newer chemistry is economically sound, minimizes the negative environmental impact and conserves energy.
There have been a few attempts at standardized powder coating system design that incorporates lean manufacturing principles and sustainable manufacturing concepts.
As an equipment designer over the last 30 years, I have seen some advances in sustainability in the washer, oven and spray booth designs that are offered.
Washers. When I started, most washers were made from carbon steel. Today, almost all washers are stainless or plastic. Those old washers had two or three (or five) heated stages. Many modern washers are unheated or use minimal heating. CPVC pipe and clip-on adjustable nozzles have replaced steel or stainless pipes with fixed nozzles.
In the past, chemical-concentration monitoring and automatic dosing systems were rare and expensive. Today, filter systems and close monitoring of fresh-water fill helps maintain the effectiveness of the solution in the various tanks. If you are still using a spray washer that is 30 years old, it is time for an upgrade.
Ovens. Oven technology has made modest improvements over the last few decades. Ovens used to have the minimum amount of insulation that the manufacturer thought could meet OSHA hot-surface limitations at the maximum operating temperature of the oven. Today, there are low NOX burners with sophisticated combustion-control systems available. One caveat is ovens with such controls can be expensive and are more often used in states or municipalities that have stricter requirements than the federal government.
Oven heating and heat recovery technologies have seen changes as well. Infrared technology is viable under the right circumstances, but it seems to come in and out of fashion like a fad in alternating generations. Air seals on the oven entrance and exit openings are still problematic. And, with the relatively low cost of natural gas, I cannot remember the last time I saw a heat exchanger on an oven exhaust fan on a paint line.
There is room for improvement in oven design. Too often, the customer is not willing to take the long view when evaluating capital cost versus operating cost. If you have existing ovens, you might consider upgrades and retrofits as a cost-effective alternative to buying new ovens for your paint line.
Application Equipment. The use of electrostatic spray is widespread, which results in good transfer efficiencies of powder to the parts. I also have noticed more dedicated-color booths — or at least dedicated-color reclaim-collection modules — both of which contribute to improved powder efficiency. Unfortunately, many operations still operate as spray-to-waste powder application. A fluidized-bed application provides an excellent alternative to such spray-to-waste operations if the circumstances are right.
Powder coating was developed in Europe as an alternative to high solvent content liquid coatings. With the advent of electrostatic spray guns, powder became as easy to apply as liquid paint.
System Design. There have been a few attempts at standardized powder coating system design. Such concepts incorporate lean manufacturing principles and sustainable manufacturing concepts. Many such systems designs are compact, modular and energy efficient. They can incorporate single-stage, nonaqueous cleaning and pretreatment, and they may include a convection dry-off oven and an infrared cure oven with heat recuperation. While some of these modular, compact systems have been built, the overall concept has never really gotten off the ground.
Achieving sustainability is like personal improvement. You never quite get there, so there is always room for progress. A few of the items to concentrate on include:
- Reducing your carbon footprint.
- Reducing energy usage.
- Reducing water effluent.
Let’s take a closer look at each.
Reducing Your Carbon Footprint. Your carbon footprint is the total amount of greenhouse gases produced (directly or indirectly) during the performance of the manufacturing process, expressed in equivalent tons of carbon dioxide (CO2 ) emissions. The gas burners on your washer and ovens produce CO2 as a byproduct of combustion. Using powder coating rather than solvent-based coatings reduces the carbon footprint by 50 percent. So, you are off to a good start.
Reduce Energy Usage. As previously mentioned, there are more powder coatings with low cure temperatures being developed. If you can clean and surface prep with ambient chemistry, you will save a significant amount of energy. If you can cure your powder at 375°F (190°C) instead of 450°F (232°C), you are saving nearly 20 percent of the energy usage just in your cure oven. Other variables to examine are the exhaust rates in your dry-off and cure ovens, part-opening sizes and conveyor-line density.
Reduce Water Effluent. Fresh water is — or is going to become — a hot-topic conversation in many areas of the United States. It seems silly to allow a constant overflow of washer tanks. Just one gallon per minute of water going down the drain equates to about 125,000 gal annually for a single-shift operation. Having to periodically dump and refill tanks also adds to the effluent. As a reminder, the nonaqueous cleaners/pretreatment options do not release effluent.
Surface cleaning and preparation prior to applying a powder coat are critical for coating performance. The cleaning can be done with media blasting, but most production applications use a spray washer such as this one.
Sustainable manufacturing — and more specifically, sustainable powder coating — is just one small effort we can make to minimize environmental effects. Several sources are available to help you improve the sustainability of your thermal processes. For instance, ASTM has published three standards to evaluate, characterize and document KPIs for sustainability. (See sidebar on ASTM sustainability standard guides.[7,8,9])
The time of doing nothing is past. “By the end of this century, if emissions keep rising, the average temperature on Earth could go up another four to eight degrees,” Bill Nye the Science Guy explained while setting a globe alight during Last Week Tonight on May 12, 2019. “What I’m saying is, the planet’s on f%#@ing fire.”
ASTM Sustainability Standard Guides
ASTM E2986-18 Standard Guide for Evaluation of Environmental Aspects of Manufacturing Processes
This guide provides guidance to develop manufacturer-specific procedures for evaluating the environmental sustainability performance of manufacturing processes. This guide introduces decision support methods that can be used to improve sustainability performance.
ASTM E3012-16 Standard Guide for Characterizing Environmental Aspects of Manufacturing Processes
This guide defines a process characterization methodology that uses graphical and formal representations to support the construction of unit manufacturing process unified modeling language (UMP) information models. They characterize the environmental aspects of manufacturing processes as being comprised of four elements (input, output, product and process information, and resources) that support manufacturers in systematically identifying, collecting, structuring and visualizing manufacturing information.
ASTM E3096-18 Standard Guide for Definition, Selection and Organization of Key Performance Indicators for Environmental Aspects of Manufacturing Processes
This guide provides a procedure for identifying candidate key performance indicators (KPIs) for environmental aspects of manufacturing processes. The KPIs can be derived from existing sources, or the guide defines a methodology for selecting effective KPIs from a list identified or defined by the user.
- Doug Beloskur, “How to Become a Dryer Energy Guru,” Process Heating, June 2009, accessed July 1, 2019. https://www.process-heating.com/articles/87279-how-much-energy-should-an-efficient-dryer-consume.
- “Sustainable Manufacturing,” Environmental Protection Agency website, accessed July 1, 2019, https://www.epa.gov/sustainability/sustainable-manufacturing.
- “Powder Coating: The Complete Finisher’s Handbook,” Second Edition, Powder Coating Institute, 1999.
- Gary Nelson, “Advanced Pretreatments: It’s Time to Get Off the Fence,” Materials Today, April 7, 2010, accessed July 1, 2019. https://www.materialstoday.com/metal-finishing/features/advanced-pretreatments-its-time-to-get-off-the/.
- “Single and Available,” Products Finishing, July 2009, accessed July 1, 2019. https://www.pfonline.com/articles/single-and-available.
- Steven Onsager and John Hober, “Improving the Performance of Existing Industrial Ovens,” Process Heating, October 2018, accessed July 1, 2019. https://www.process-heating.com/articles/92811-improving-the-performance-of-existing-industrial-ovens.
- ASTM Standard E-2986-18. https://www.astm.org/Standards/E2986.htm
- ASTM Standard E-3012-16. https://www.astm.org/Standards/E3012.htm
- ASTM Standard E-3096-18. https://www.astm.org/Standards/E3096.htm