CARC Powder Topcoat: Bring it on

By: Paul Mills

While CARC powder coatings have been approved for some time, until now powder has made up only a tiny fraction of overall CARC use. In many cases, powder coatings have frequently served only as a primer for CARC liquid top coats. The project talked about here really changes the game. Instead of being a specialty item, CARC powder is now an off-the-shelf product.

U.S. military vehicles are painted for many reasons—from concealing them with desert colors and camouflage patterns to providing special infrared (IR) signatures that reduce detection in the field. Military coatings also protect the vehicle’s metal surfaces from the attack of nature’s elements. But, in 1974, the U.S. Army began to develop coatings with a new attack in mind—to protect the American warfighter from harmful chemical and biological agents. Chemical Agent Resistant Coatings (CARC) resist the absorption of chemical agents, making decontaminating a vehicle easier so it can be returned more quickly to combat and improve the readiness of our forces. CARC’s ability to conceal and transport tactical vehicles prompted the Army to require CARC coatings since 1983.

Traditionally, CARC coatings have been liquid solventborne and waterborne paints. But according to Department of Defense (DoD) reports, liquid topcoats contribute roughly 2.3 million pounds of volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) per year. So, like many manufacturers in the private sector, the DoD has aggressively pursued alternative coating technologies, including powder coatings, to reduce the environmental impact of CARC coatings. The key challenges to developing powder coatings for CARC topcoats have been achieving resistance to a wide range of chemical agents and providing superior durability at extremely low gloss levels.

One of the most popular applications for CARC coatings in recent years has been for high-mobility multipurpose wheeled vehicles, or Humvees. Due to the increased use of weapons such as mines, roadside bombs and other improvised explosive devices (IEDs), the DoD began adding additional armor to Humvees to protect them in battle. This summer, the Army began to “up armor” Humvees with powder coated CARC top-coat armor plating for the first time.

“We are coating armor plates to go primarily on transport and tactical vehicles,” says Shivie Dhillon, president of SunDial Powder Coating, Los Angeles, Calif. “They are thick steel plates weighing hundreds of pounds. They are large pieces of metal that protect against shrapnel, gunfire, explosions, IEDs, and are integral to protecting the passengers.” Dhillon’s company is now refurbishing armor plates for Humvees using a CARC approved powder coating manufactured by Hentzen Powder Coatings.

“These are armor plates typically ranging from a half-inch to threequarters- inch thick steel that get bolted over the outside of a Humvee to add to the integrity of the vehicle,” explains John Mort, managing director of Global Sales for Aerospace & Defense Products at Hentzen Coatings.

“After vehicles have been in action for a while, the armor gets pretty beat up. That could cause the old CARC coating to fail. They are in horrid shape and need to be fixed up,” adds Dhillon.

SunDial refurbishes truckloads of parts each week. The armor gets taken down to bare metal, repainted with CARC powder coatings, and returned to the Army depot so they can be sorted into kits and returned to military bases all over the world where they are reinstalled on combat vehicles.

While CARC powder coatings have been approved for some time, until now powder has made up only a tiny fraction—estimated at perhaps 5 percent—of overall CARC use. And, in many cases, powder coatings have frequently served only as a primer for CARC liquid top coats.

“The size and scope of this up-armor project is a giant step forward,” says Mort. “These parts are not like little metal fasteners; they are substantial pieces of metal often weighing hundreds of pounds each, making this one of the largest ongoing CARC projects I know of— whether liquid or powder.”

“Early in the process, we went to the Army depot for a site visit,” remembers Dhillon. “When we saw the material for the first time, it was a little nerve-racking. There were millions of pounds of steel that needed to be refurbished and put back into service. Some people have been powder coating things like small boxes here and there but this was the biggest, the first, ...the everything.”

Mort agrees. “This project really changes the game. Instead of being a specialty item, CARC powder is now an off-the-shelf product. It’s mainstream.”

Because SunDial is located on the West Coast, they first reached out to powder suppliers they have worked with on prior industrial projects. “We called around looking for CARC powder, and there were suppliers who said they would be ready,” recalls Dhillon. “But the reality was that when we got the order, they weren’t ready.” Mort adds, “Some of the suppliers working on CARC powders couldn’t get approved product in time. SunDial approached us because Hentzen already had approval on the colors they needed in order to meet the Army’s schedule.”

Hentzen has been a leading supplier of both liquid and powder CARC coatings since the late 1970s. “Military coatings have been a niche for us,” says Mort. “The CARC liquid specifications were in large part written around some of our products. While a lot of time and money has been invested by the government to try and stimulate CARC powder research, we have been working on CARC powder as a self-funded, non-government effort to remain as innovative and agile as possible. So we are very proud to be involved in this, the most visible application of CARC powder coatings.”

“When we first talked to Hentzen about the project, I got the feeling they thought this was just going to be another project requiring a couple of boxes, or maybe a few hundred pounds of powder,” recounts Dhillon. ”I said, ‘look we’re going to need 5,000 pounds of CARC powder pretty regularly,’ and they nodded and said, ‘yeah, sure, no problem’. After the first week, we depleted them. You could say things were a little crazy at the start.”

Hentzen reacted quickly, adding production capacity, expedited materials, and building inventory to satisfy the demand from SunDial. “We were officially out of the crawling phase and into the walking phase with CARC powder coatings,” reflects Mort.

“The depot wanted material ‘now’ and weren’t willing to wait.” says Dhillon. “They moved their timelines up, tripling their delivery requirements. Everything was moving at an accelerated rate.”

One of SunDial’s initial bottlenecks was removing the old liquid CARC coating from the armor. “We first need to take the parts down to bare metal,” explains Mike Campisi, project manager for SunDial. “So we prepare the armor using a manual aluminum oxide shot blasting process.” To achieve the required production rate, SunDial operates three large blasting chambers. Two of the blast chambers measure 8'x8'x40' and the third, largest enclosure is 10'x10'x20'. To meet the delivery schedule, SunDial began blasting around the clock, moving from three to nine shifts a day, five days a week. After removing the old CARC liquid coating, the parts are recoated using a two-coat process that requires a powder primer, followed by a powder top coat.

The blasted metal parts are manually loaded onto the powder coating line, sometimes with the help of a mechanical hoist for the heaviest parts. “The parts mountings have holes in them that we can use for hanging them,” explains Campisi. SunDial’s conveyor is a heavy-duty I-beam monorail design with trolleys spaced one foot apart. Since each trolley has a load capacity of 250 pounds, the system has no problem transporting the bulky 300-400 pound parts.

The blasted parts need to be cleaned and pretreated prior to powder coating. “Just because a part has been blasted down to bare steel doesn’t mean it’s ready to be coated,” says Frank Thompson, technical sales manager for Chemetall US.

CARC powder has stringent performance requirements. Chemetall worked closely with SunDial over the summer of 2016 to replace its existing iron phosphate system and install a new pretreatment process that uses inorganic Silane-Zirconium chemistry to provide the needed performance and durability.

“We had worked with a few other military installations on CARC over the past few years, but this is the first powder coating application for CARC we have worked with,” says Thompson.

“SunDial uses our Oxsilan 9810/2 product which is approved for TT-C- 490, the federal specification for cleaning methods and pretreatment of iron surfaces. This means that Oxsilan 9810/2 is a viable replacement for zinc phosphate pretreatment approved by the military,” says Gary Nelson, manager of Portfolio Management for Chemetall. “This comes after the completion of an exhaustive three-year testing program that began in 2009,” explains Nelson.

The Army has tested and approved Chemetall’s Oxsilan 9810/2 for adhesion, flexibility, water resistance, salt spray, cyclic corrosion, outdoor exposure and hydrogen embrittlement. “Used together with our Gardoclean S 5219 silicate-free alkaline cleaner, Oxsilan provides a great foundation for powder coating,” says Nelson.

“We have worked on military applications that have required zinc phosphate, and this new chemistry is much easier to run than zinc phosphate,” says Thompson. But the pretreatment process is carefully monitored. “If the pretreatment system is not properly maintained, you could get oxidation and have a hard time keeping the pH right,” notes Campisi. So, the SunDial operators perform regular titrations, and monitor conductivity while the system uses an electronic metering system to replenish chemicals.

“Converting to a new process always requires effort,” says Thompson, “and you have normal growing pains.” Campisi explain. “In terms of switching from iron phosphate to the new Silane-Zirconium technology we had to descale our system and tighten up controls compared to how you can run an iron phosphate system.”

The six-stage pretreatment system consists of an alkaline cleaning stage, followed by two rinses with a deionized water (DI) halo rinse at the end of the third stage. The cleaned parts are then treated in stage four with the Oxsilan 9810/2 Silane-Zirconium coating, followed by two additional rinse stages and a second final DI halo.

The clean, pretreated parts are dried using heated forced air to remove any excess water from their surface. The warm, dry parts enter the powder primer booth. The spray-to-waste, cross-draft design manual spray booth is 7 feet tall and approximately 10 feet long. Two operators standing at openings on opposite sides of the spray booth powder coat armor plates using Gema electrostatic spray guns as they pass continuously through the booth. The CARC powder primer, a modified epoxy powder coating, must be applied uniformly at a coating thickness of approximately 2-3 mils.

Following application of the primer, the powder coated parts pass through a convection ‘gel oven.’ In this step, heated convection air melts and flows the powder coating. “We deliberately under-cure the powder at this stage to get better adhesion of the top coat to the primer. This allows the two coatings to lock together,” explains Campisi.

Next, the partially cured primed parts are coated with a modified polyurethane top coat to a total film thickness of approximately 5-8 mils. The top coat powder booth is similar in design to the primer spray booth, using a manual cross-draft spray-to-waste design with two opposing manual spray stations and Gema application equipment.

Currently, the armor parts are all coated with a tan-colored top coating intended for mountainous and desert terrain, “but we have approvals on all three colors needed for the project,” says Mort, “including tan, green and black.”

After applying the CARC top coat, the parts enter a 100-foot long convection cure oven where they bake at temperatures in excess of 340°F, allowing the top coat and primer to cure completely. Finally, after the powder is fully cured, ambient forced air is used to cool the parts as they are inspected for defects before the refurbished parts are unloaded for shipment.

“The SunDial system is the most advanced CARC powder coating facility we’ve worked with in terms of its ability to handle this kind of size and volume of parts,” says Mort. “Besides, even if they had this capacity, most other job shops use iron phosphate, and so to do what SunDial can do, they would have to change to a new and more stringent process.” “It probably took us a good month to get the cure process nailed down,” says Campisi. “It is dialed-in now. Interestingly, we went through a few pallets of parts that we coated, had to blast and then recoat in order to work out some of the bugs. That let us see first-hand how tough the powder coating really is. It takes our operators about 6 to 10 minutes to blast the old liquid coating off the parts when we get them in. But it takes a good 30 minutes to blast a fully powder coated part.”

“We’ve been crawling with the technology since 2014 when we got the first Army approval on the powder topcoat,” says Mort. “Of course, powder had been approved as a primer for almost 4 to 5 years prior to that. But the real holy grail was getting the Type 3 (top coat) approval. Hentzen was the first to do that in July 2013. Nevertheless, things move slowly—the government needed to address a lot of details on approvals and drawings before we got to this point. Now since we have the tan, green and black colors approved, it makes converting to powder for larger CARC projects more feasible.” Another challenge for Hentzen was formulating its powder top coat with field repair and maintenance in mind, because the powder has to accept a liquid coating so that it can be reworked or refinished in the field.

“It’s been amazing,” says Dhillon. “The powder shoots really well. The depot is extremely pleased with the quality and beyond pleased with our service. We’re just a small little drop in the pond. But ManTech International, the government’s prime contractor, has worked really well with us. The team has worked hard to get it right, and now it’s time to ‘bring on more.’”

Paul Mills is a marketing and business development consultant to industry chemistry and equipment suppliers. He has been a writer for the powder coating industry since 1994. Paul can be reached at 440-570-5228 or via email at pmillsoh@aol.com.