Study group develops guide to aid in working with trailer customers and suppliers of coatings

May 1, 2010
THE National Association of Trailer Manufacturers (NATM), working with paint and trailer manufacturers, has compiled a guide to use for working with potential

THE National Association of Trailer Manufacturers (NATM), working with paint and trailer manufacturers, has compiled a guide to use for working with potential customers as well as working with suppliers of coatings.

It's meant to educate all involved on criteria used in determining what type of standard processes are utilized in testing as well as how they may relate to the finished product.

“We all agreed there are standard methods that just about all paint companies use to test paints,” said Ron Yarnell, OEM sales manager of PPG Industries Inc.

The American Standard Test Method (ASTM) has established testing for most of the criteria used in today's coatings. Although there are multiple test criteria that could be explored, the group agreed on four main areas, and attempted to include, for reference, other test methods that may relate to special circumstances in particular markets: ASTM D3359 (scribe adhesion), ASTM D3170 (gravelometer test), ASTM B-117 D1654 (salt-spray testing), and ASTM D4587 (QUV-B 313, accelerated weather testing).

Agreeing on minimum requirements, the study group put standards into classifications. Although standards are grouped, a company's needs may call out for a higher standard for one area and not in another area. For example: A company that produces a product that goes into a mining industry — never seeing the light of day — may not need a high QUV (accelerated weather test) but may need a high adhesion (gravelometer).

The classifications for scribe adhesion:

  • 5B: The edges of the cuts are completely smooth, and none of the squares of the lattice are detached.

  • 4B: Small flakes of the coating are detached at intersections, but less than 5% of the area is affected.

  • 3B: Small flakes of the coating are detached along the edges and at the intersection of cuts. The area affected is 5%-15% of the lattice.

  • 2B: The coating has flaked along the edges and parts of the squares. The area affected is 15%-35% of the lattice.

  • 1B: The coating has flaked along the edges of cuts in large ribbons and whole squares have detached. The area affected is 35%-65% of the lattice.

  • OB: Flaking and detachment is worse than 65% (or grade 1B).

The classifications for gravelometer are based on pictorial standards. A rating of 7-8 is very good; there are very few 9 or 10 ratings in this market. Conversely, a rating of 4 or below is an indication that low performance is anticipated with respect to chip resistance.

Visual standard examples: Basically coating suppliers run a test at a specified time and count the amount of chips in a specified area and report a rating of 1 to 10 as called out for in ASTM.

Salt spray

Classifications for salt spray:

  • D714: Reported as scribe blisters rated in size and frequency along the scribe. Reported as the same as D3359 (scribe adhesion/humidity adhesion) after a predetermined time in a salt-fog tank. Usually reported after 100/250/500 or 1000 hours.

  • D1654: Scribe adhesion/corrosion creep from a set procedure. The panels are rinsed off, and the scribe is scraped while under the water stream. This test is done within 15 minutes of panels being removed from the salt-spray cabinet. Examples: 9A= 0.0-0.5 mm creepage; 5A= 3.0-5.0 mm creepage; 2A= 10.0-13.0 mm creepage.

“Is it a perfect science?” Yarnell said. “It really isn't. We had to start somewhere and give a baseline. We thought it was an educational function to put it out there.”

The classifications for accelerated weather testing:

  • D523: Typically reported on 60° gloss, and DOI (Distinction of Image) if required. Clear coats usually will not see gloss loss at 1000 hours, while alkyds will often have poor gloss retention in as little as 100 to 250 hours. Classifications were grouped in hours exposed in ratio to loss of gloss.

The group decided to use the “UVB” bulb as the standard for the trailer market.

Color shift, usually expressed as Delta E, is a relatively complicated formula that considers the changes in the L-Scale, A-scale, and B-scale. As a rule of thumb, Delta E's of less than 1.0 are considered very good, and are usually un-noticed by the untrained eye.

The group developed standards for four different classes:

  • Class 1 standards: ASTM D3359, humidity adhesion test 2B-3B; ASTM D3170, gravelometer test, less than 4 (visual reference standards published in ASTM); ASTM B117/ D1654, salt spray, 200 hours with less than 5mm creep manufacturers reference 30-180 days); ASTM D4587 QUVB, accelerated weather, 0-200 hours with little or no effect.

  • Class 2 standards: ASTM D3359, humidity adhesion test, 3B-4B; ASTM D3170, gravelometer test, less than 4 (visual reference standards published in ASTM); ASTM B117/ D1654, salt spray, 300 hours with less than 5mm creep (manufacturers reference 12-18 months); ASTM D4587, Accelerated weather test, 200 hours with little or no effect.

  • Class 3 standards: ASTM D3359, humidity adhesion test, 4B-5B; ASTM D3170, gravelometer test, 4 to 6 (visual reference standards published in ASTM); ASTM B117/ D1654, salt spray, 400 hours with less than 5mm creep (manufacturers reference 36-60 months); ASTM D4587, accelerated weather test, 400 hours with little or no effect.

  • Class 4 standards: ASTM D3359, humidity adhesion test, 5B consistently; ASTM D3170, gravelometer test, greater than 6 (isual reference standards published in ASTM); ASTM B117/D1654, salt spray, 500 hours with less than 5mm creep (manufacturers reference 60 months); ASTM D4587, accelerated weather test, 1000 hours with little or no effect.

“Class 1 would be the minimum standards for what you would want on a trailer,” Yarnell said. “Believe me, I would have disagreements in some areas. But the message is, ‘Partner with your supplier and start to know what these things mean so everybody's on the same page and we understand where we're at in this market. Work with your supplier and talk with him.’ All of us as paint companies have historical information. We know by history what they're going to do. We already have historical data, and this is what you can expect.”

Prep the surface

He said coatings can help suppliers design processes and products that can meet classifications in many ways, and these ratings are to be used for guidance purposes only. Choice of specific substrate can have a significant impact on final performance as well as preparation and pretreatment of that substrate before painting. It is highly recommended that surfaces to be painted be free and clean of all oils, dirt, weld spatter, and rust before applying any coatings. He said the better the prep of the surface to be painted, the better the coating system will perform.

“There are some manufacturers of trailers who would like to know how abrasion-resistant their trailer is,” he said. “We run into that and are asked to test for that from time to time.”

The abrasion test is usually seen in appliance or floor coating markets and involves a taber abrader. The specs for ASTM D4060: wheel, CS10; weight, 500 grams; revolutions 1000.

This test is often reported in different ways: weight loss to a predetermined number of revolutions as well as number of revolutions before hitting substrate. A full cure for coatings is recommended prior to testing, according to published supplier literature. Taber wheels must be resurfaced periodically. Loading is indicated when the wheels take on the color of the test coating. It is suggested to resurface the wheels every 500 cycles, which consists of 50 cycles with an S-11 abrasive disk, each of which is to be used only once. Wheels should always be resurfaced prior to the start of testing.

Other ASTM test to consider:

  • ASTM D1308: 02 (2007) standard test method for effect of household chemicals on clear and pigmented organic finishes test for determining resistance to various household cleaning materials.

  • ASTM D6486: 01 (2005) standard practice for short term vehicle service exposure of automotive coatings. This is an actual road test of the coating in real-world conditions.

  • ASTM D6943: 03 standard practice for immersion testing of industrial protective coatings. This test is intended for testing storage-vessel linings but may apply in some instances.

  • ASTM D5402: 06 standard practice for assessing the solvent resistance of organic coatings using solvent rubs. This test describes the process to measure the resistance to a particular solvent being tested for.

Chemicals that may affect a particular market: anti-freeze, battery acid, chlorine, brake fluid (DOT4/5, Skydrol), diesel fuel, calcium/magnesium chloride, fertilizers, motor oiltransmission fluid, gasoline herbicides, livestock excrement, silage effluent (the liquid that forms from fermentation of silage for livestock feed).

“What does that mean in real terms?” Yarnell said. “There's no book on this that says if you do this a certain way, it will last a certain amount of time. We tried to break it down into each class on what products typically are in each class and what your expectations would start to look like in terms of years lasting. There's no golden rule, but the group decided manufacturers needed some benchmark for what it would look like.”

  • Class 1: Minimal prep, enamel or alkyd paint; no primer with a direct-to-metal paint lasting up to a year.

  • Class 2: Washing high pressure; possible etching chemical, primer, and paint with a mid-range paint, possibly catalyzed one to two years; medium to good gloss.

  • Class 3: Full prep or blast as needed; acid wash phosphates' sealer, prime, paint, polyurethane, or similar two-component prime and paint; two to three years higher gloss.

  • Class 4: Paint before assemble possible if powder coating; full prep typical as in Class 3; full blast also possible; paint sealer after wash sealer; also possible baking after paint; three years or more, depending on conditions and use.

Rick Achterhof, industrial product manager

Diamond Vogel Paints

Gary Sales, OEM business manager

Diamond Vogel Paints

Sales said that over the past 10 to 15 years, the market has experienced a marked increase in corrosion, especially in the over-the-road trailer market and the infrastructure.

“In the over-the-road trailer industry, the expectation level for the life of the trailer was typically 9 to 10 years,” he said. “Recent studies are showing that with the same trailer going over the same roads with new corrosive de-icing agents, the life expectancy is down to 6½ to 7 years. It affects wiring and brakes. One study said we used to get 60,000 miles out of brakes, and now it's 20,000.

“We've been looking at some of the foreign steel coming into the marketplace. There are different coatings on that steel, and it's very tough to get it off without blasting or using a hard chemical. And some steels have a lot of impurities, which affects the integrity of the coating and primer.

“Two-and-a-half years ago, we had a call from one of our largest trailer manufacturers. They had trailers in Pennsylvania for a little over a year. Pennsylvania is one of the leading states for magnesium chloride. These trailers came back with a lot of corrosion, particularly where the coatings on laser-cut edges were thin.”

Achterhof said after de-icers were applied to roadways, there was an 80% reduction in accidents.

“It's very important that de-icer technologies keep improving,” he said. “Four percent of the roads are interstate highways and carry 40% of the total traffic in the US, and 75% of the total truck traffic. Interstates are where de-icers are being used the most.”

He said that involves the most common de-icer, rock salt, along with sodium chloride, calcium chloride, and magnesium chloride. He said mag chloride is starting to take over the market because it's much more effective at lower temperatures and lasts longer on the roadways.

Other benefits: reduced labor and materials; reduced abrasives on roadway; reduction in environmental impacts and accident rates.

The costs: dramatic increase in wiring failures; brake system component and lining failure; fouling and pitting of aluminum wheels; and failure of coatings on steel by galvanic corrosion.

How can coating failure be predicted? Achterhof said ASTM B117 has been in the industry since 1939, but “the problem is, there is no correlation to real-world corrosion. In fact, it can give you the opposite results to what real-world corrosion will do.”

He said ASTM G85, a cyclic test that came from Europe in the 1960s, is much more effective.

Different corrosion mechanisms are involved under immersion condition and wet condition for sodium chloride and mag chloride. Under high-humidity conditions (wet), mag chloride tends to cause higher levels of corrosion; and under dip conditions (immersion), sodium chloride results in a higher level of corrosion.

How is the industry addressing the corrosion problem?

  • Stainless or galvanized steel is an option. “It's very expensive, and galvanized has its own issues.”

  • Improved pretreatments, including abrasive blasting. “Out of all testing, abrasive blasting gives you a good anchor pattern. If have a good anchor pattern and have good adhesion, you have good corrosion resistance.”

  • Removing sharp edges and laser scale.

  • Sealing seams, joints, and welds (in product design). “Areas on a trailer that hold water are a huge problem. Water sits there and has time to work through the coating. All coatings are permeable over time.”

  • Soft and flexible undercoats.

  • Metal conversion coats, which react with oxidized metal.

  • Multi-coat primer/topcoat systems in both liquid and powder. “It's still the best visual product to put on there.”

Liquid-coating systems:

  • High-build zinc dust primer system allowing for quicker recoats and “sacrificial” corrosion protection.

  • High-build sealer/primer that cures quickly for “sand-ability,” barrier-corrosion protection, and stone-chip resistance.

  • Acrylic urethane topcoats.

Powder-coating systems:

  • Rust inhibitive primers. “Fifteen years ago, powder was a one-coat process. Everybody said it was the best thing since sliced bread. Within the last five to 10 years, the significant trend is to go to priming under powder topcoats. One coat of powder just is not the answer anymore.”

  • TGIC polyester or urethane topcoats. “They give long-term gloss retention and good stone-chip resistance.”

  • Edge coverage is critical. “We see powder manufacturers restricting flow and getting the powder to lock up quickly so it doesn't have time to move away from the edges.”

About the Author

Rick Weber | Associate Editor

Rick Weber has been an associate editor for Trailer/Body Builders since February 2000. A national award-winning sportswriter, he covered the Miami Dolphins for the Fort Myers News-Press following service with publications in California and Australia. He is a graduate of Penn State University.