FEATURE

Recent advances inammunition coatings

By Pauline Smith, KestutisChesonis, John Escarsega,Christopher Miller

INTRODUCTION

The U.S. Army Research Laboratory(ARL) Coatings and Corrosion Teamhas the Department of Defense (DOD)lead responsibility in the development,formulation and implementation ofChemical Agent Resistant Coating(CARC) systems. These responsibilitieshave led to numerous enhancementswith regard to environmental compli-ance, durability and survivabilityrequirements for the military. ForFY04, the removal of Volatile Hazar-dous Air Pollutants (VOHAPs) hasbeen paramount in order to complywith upcoming Environmental Protec-tion Agency (EPA) Clean Air Laws.The EPA has been working with aServices Steering Committee (SSC)and the steering committee has suc-cessfully been able to establish aNational Emission Standard forHazardous Air Pollutants (NESHAP)rule referred to as the Defense LandSystems and Miscellaneous Equip-ment (DLSME NESHAP). This rulingis the catalyst to eliminate VOHAPSfrom topcoats and primers while stillmaintaining or improving durability inthese materials. To date numerous top-coats and primers have been reformu-lated without VOHAPs.

Increasingly stringent environmen-tal regulations have forced ammuni-

Pauline Smith, Kestutis Chesonis,John Escarsega, Christopher Millerare affiliated with U.S. Army ResearchLaboratory, Materials Division,Bldg. 4600, Deer Creek Loop,Aberdeen Proving Ground,MD 21005-5069, USA(e-mail: pmsmith@arl.army.mil).

14 � Division of Chemical Health and Safety of the

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tion manufacturers and maintenancefacilities to reconsider their traditionalcoating processes. The demands onthe ammunition coating specificationshave changed over the years. Treat-ments of hazardous emissions andwaste generation at all levels of pro-duction are very costly, and any reduc-tion in emissions through improvedcoatings will save money. The currentcoating system for high explosive (HE)ammunition is an alkyd enamel top-coat that contains high levels of Vola-tile Organic Compounds (VOCs).

ARL’s Coatings Technology Team,in conjunction with ArmamentResearch Development and Engineer-ing Center (ARDEC) Munitions MetalParts Team, developed a UniversalAmmunition Coating (UAC) for muni-tions systems. Prior to the develop-ment of this novel coating system,ammunition coatings were subject topremature and severe film failures, suf-fered from poor corrosion resistance,were incompatible or reactive withenergetic materials, and failed to meetNESHAPs. To enhance and improvethe overall coating performance, weincorporated a new class of corrosioninhibiting pigments into an alkyd poly-mer system consisting of durable fast-drying chain stopped alkyd (drying oilmodified polyester) (Figure 1).

In addition to meeting the require-ments for substrate adhesion and pos-sessing long-term storage stability withenergetic materials, the UAC providesvastly improved corrosion resistance,eliminates the primer coats on certainmunitions applications, and is ‘‘a dropin replacement’’ for existing materials.After extensive laboratory evaluations,the UAC was qualified on artillery andmortar projectiles at Scranton ArmyAmmunition Plant (AAP) and CraneArmy Ammunition Activity (AAA)munitions manufacturing and mainte-nance sites. The benefit of this newcoating to the Army is superior singlecoat performance providing enhanced

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durability, environmental compliance,elimination of production rejects andreworks.

The impact of UAC implementationincludes a cumulative reduction of250,000 pounds of Hazardous Air Pol-lutants (HAPs), a cost avoidance ofover$2 million and $800K annual savings.Developmentof thisUACwillbeapplic-able to all munitions systems and willprovide essential payoffs in superiorcoating performance, corrosion resis-tance, and enhanced durability.

BACKGROUND

The U.S. Army has a need for advancedcoating materials to meet military per-formance requirements and increasingstringent environmental regulations.The ARL and ARDEC established amajor collaborative effort to solvemajor Army ammunition coating pro-blems and to meet the requirement forHAPs replacement. Military coatingshave unique requirements: harsh ser-vice conditions, demanding multifunc-tional performance requirements,chemical agent resistance, low specu-lar reflectance, cost effectiveness, long-term stability, and long service life. As aresult, the coating system has a directimpact on environment, economics,force readiness and force survivability.The Clean Air Act and its Amendmentsseverely restrict the VOC content ofprotective coatings in order to reducethe occurrence of photochemical smogformation. In addition, the EPA hasdeveloped a list of HAPs that imposesfurther restrictions on coating compo-sition in order to comply withNESHAP requirements, for paintingMiscellaneous Metal Parts and Pro-ducts (MMPP).

Ammunition coatings are used toprovide easy identification and corro-sion protection during long-term sto-rage stability of munitions. Due todimensional tolerance limitations,

1074-9098/$30.00

doi:10.1016/j.chs.2004.09.015

Figure 1. Formation of an Alkyd or Polyester.

Figure 2. Pigment Volume Content of UAC.

ammunition coatings require topcoatsand primers, and in certain cases,munitions can only be top coated tomeet restrictions. High rate productionrequires these coatings to be fast dryingwith a maximum of 12 minutes to dryhard. Additionally, during the projec-tile loading process, shells can be con-taminated and stained by moltenexplosives that are melt-poured intothe casings. Subsequent cleaning bysolvent solutions can adversely affectcoatings and deteriorate performance.

Traditional protective coatings formortar and artillery projectiles arebased on quick drying enamels thatwere developed over time from mili-tary and federal specifications. Histori-cally, coatings on these variousammunition components typicallycontained pigments and surfactantsthat were toxic containing high levelsof VOCs, HAP solvents, hexavalentchromium, lead, and other heavymetals. Furthermore, new coatingsshould be compatible with highvolume and low pressure (HVLP)spraying equipment and reduce envir-onmental emissions by more than 50%without adverse affects on productionrate or quality of paint.

The research and development goalof the team was to produce a uniqueammunition coating by combining theproperties of the primer and topcoatinto one coating. In all cases, this fast

Chemical Health & Safety, March/April 200

drying coating would meet the currentspecifications, providing improveddurability and performance. The useof environmentally friendly corrosioninhibiting pigments in the topcoatspecification was successfully demon-strated, as well as, excellent propertiesdemonstrating resistance to cleaningsolvents and explosives.

The new, highly specialized, anti-corrosive pigments were developedsolely for use in the primer. Knowledgeof their low solubility level that isnecessary for metal surface passivationwhen formulated into a coating wasrequired. The approach was to employ

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a new class of anti-corrosive pigmentsinto a durable fast drying alkyd poly-mer system. After incorporating theseanti-corrosive pigments into the top-coat package, thorough testing wasperformed, including weatheringtests, the UAC exceeded the existing120 hours with minimal 240 hourscorrosion protection requirementsper ASTM B 117.

The main challenge was to optimizethe level of the color pigments, exten-ders, and the anti-corrosion pigmentsas shown in Figure 2. There is a narrowwindow in the Pigment Volume Con-tent that maximizes the ability of the

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pigmentation to minimize formation ofgalvanic cells that lead to corrosion.

The coating formulated with thesenew highly specialized anti-corrosivepigments were held at 40–45% PVC toavoid porosity and rusting. The UAC isnon-reactive, compatible with ammu-nition explosives, highly corrosionresistant, fast curing, economical andcan be used as a single coat for mediumand large caliber ammunition systems.The UAC complies with environmen-tal regulations including NESHAPseliminating the use of HAP solventsand reducing VOCs to meet local reg-ulations.

The in-house pigment and polymerselection process and formulationdesign permitted the development ofa unique chemistry with unparalleledperformance. The formulation is com-pleted for a corrosion resistant UACcoating and incorporated into MIL-E-11195 as TYPE II. A 100% improve-ment in salt spray resistance is evi-dence of improved durability, andproduction line results indicate lesshandling damage. These coatings weretransitioned to production facilities inless than one year from the projectinception. Currently, UAC is beingused on the 155- and 120-mm projec-tiles. Successful qualified productshave been produced in all camouflagecolors including: Olive Drab, Green,White, Black and Blue. The solventsystem is HAP-free, environmentallyacceptable, yet exceeds critical Armymission requirements. The productprovides improved durability withoutrequiring specialized applicationequipment.

TECHNICAL APPROACH

The initial effort consisted of evaluat-ing various coating candidates in alaboratory environment and selectinga suitable candidate for field-testing ata renovation facility. The CoatingTechnology Team at the ARL con-ducted the laboratory testing usingcold rolled steel (S36 and D36) panelsfrom the Q-Panel Company. Theselected coating candidates wereapplied in the de-painting and re-painting line at a renovation facilityusing empty ammunition metal parts

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(specifically the 155 mm and M795 HFsteel bodies) to ensure the technicalpracticability. The coated metal partswere then sectioned by the renovationfacility and sent back to ARL for finaltesting and evaluation.

EXPERIMENTAL

The standardized test surface was ColdRolled Steel (CRS), Type R and Type Dpanels 4 in. � 6 in. � 0.0‘32 in. fromthe Q-Panel Company. Type R panelshave a dull matte finish while the TypeD has a ground side that imparts ascratched surface. For comparison, alimited number of coatings were testedon panels with a Bonderite B952, zincphosphate pretreatment. The test spe-cimens were horizontally oriented dur-ing paint application. A conventionalair-atomizing HVLP spray gun wasused to apply the candidate paints tothe appropriate substrates. They wereallowed to cure at ambient tempera-ture (approximately 75 8F) and 50%humidity for seven days. The groupof candidates was generated basedon general use, labeled Sample Athrough Sample M. Sample A was usedas control. The pretreatment wasapplied at 0.3–0.5 mils, while the pri-mer was applied at 0.9–1.1 mils andthe topcoats were applied at approxi-mately 1.2–1.5 mils (Table 1).

RESULTS AND DISCUSSION

Spraying Properties

All individual coatings when sprayedwere given a satisfactory or a passingrating, presenting uniform films with-out of any surface defects.

Hydrocarbon Fluid Resistance

After exposure for 7 days to a mixtureof 75% isooctane and 25% toluene,ASTM D 1308 and ASTM 609 wereused to evaluate of the coatings follow-ing chemical immersion exposuretests. All coating systems passed exceptfor Sample B and Sample J. Sample Bsoftened after exposure and exhibitedwrinkling on the exposed panel sur-face. Sample J showed color and glosschanges and did not recover after

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24 hours. These two coatings wererated unsatisfactory for gloss andcolor. Samples F, G, H and I showedsome wrinkling but recovered after24 hours. The remaining Samples A,C, D, E, and K, satisfied the specifica-tion requirements, displaying no coat-ing defects upon exposure followinghydrocarbon fluid immersion test.

Water Immersion Resistance

ASTM D 1308 involves exposing anorganic coating to a de-ionized reagentto determine adverse affects. Thecoated panels were immersed halfwayin de-ionized water at room tempera-ture (23 � 5 8C) for 7 days. The panelswere examined immediately uponremoval and after a 24-hour recoveryperiod, for any defects, such as blister-ing, loss of adhesion, color and glosschange. All panels passed the waterimmersion test.

Flexibility

The Mandrel Bend Test was performedon all coatings in accordance withASTM D 522. The purpose of this testis to rate each coating’s resistance tocracking and to rate the flexibility ofeach coating. Except for Samples J andF, this test demonstrated that the coat-ings were generally flexible, and whenbent over a 1/4-in. mandrel diameter,did not show any signs of cracking.However, coatings J and F had finecracks within the paint after being bentover the 1/4-in. mandrel. Sample F didnot show cracks through to the metal.Sample J coatings could be bestdescribed as brittle, since crackingwas evident through the entire thick-ness of coating.

Impact Resistance

The standard test for resistance todeformation (impact) was performedusing an impact tester. Impact resis-tance can be described as a paint prop-erty that quantitatively characterizesthe durability of a coating with respectto a rapid impact event. After curingseven days at ambient laboratory con-ditions, reverse impact resistance testwas performed on all coating, based onASTM D 2794. All coatings passed at40 lb/in. At 60 lb/in., Coatings A, B, C,G, H and K maintained relatively high

ical Health & Safety, March/April 2005

Table 1. Samples For Testing

Samples for M549A1

Sample ID Pretreatment Primer Topcoat

A (Control) DoD-P-15328 None MIL-E-52891Wash primer—SW(VOC non-compliant)

Ammunition topcoat(VOC non-compliant)

B E61G520 None 12997567Commercial wash primerpretreatment—(VOC compliant)

MIL-E-11195F93GC353 (TYP 11)

C None None 12997567MIL-E-11195F93GC353 (TYP 11)

D None 12991256 12997567MIL-P-11414 (E90R351) MIL-E-11195VOC compliant/HAPS free) F93GC353 (TYP 11)

E None TT-P-664 TT-E-516Red oxide alkyd primer(VOC compliant)

Ammunition topcoat(State VOC exempt—CAAA)

F None MIL-P-11414D TT-E-516Ammunition topcoat(State VOC exempt—CAAA)

G 02887GWP None 12997567Universal pretreatmentHentzen (low VOC)

MIL-E-11195F93GC353 (TYP 11)

H 02887GWP None MIL-E-52891Universal pretreatmentHentzen (low VOC)

Ammunition topcoat(VOC non-compliant)

I None MIL-P-11414E 12997567E9962 MIL-E-11195Low VOC, HAPS free F93GC353 (TYP 11)

J None MIL-P-11414E TT-E-516E9962 Ammunition topcoat

(State VOC exempt—CAAA)Low VOC, HAPS freeK DoD-P-15328 None MIL-E-52891

Wash primer(VOC non-compliant)

Ammunition topcoat(VOC compliant)—Experimental

L None None MIL-E-52891

impact resistance. Coating J failed forcracks while Coatings I, F and Dshowed fine cracking but were ratedborderline/satisfactory.

CROSS HATCH ADHESION TESTINGASTM D 3359 METHOD B

The ASTM Cross Cut Adhesion testingwas performed with 2 mm line spacing,appropriate for dry film thicknessbetween 2 and 5 mils (1 mil = 0.001in.). All samples passed the dry adhe-sion test.

Accelerated Corrosion Testing

Accelerated corrosion testing was per-formed using both neutral salt spray

Chemical Health & Safety, March/April 200

test per ASTM B 117 and acceleratedcyclic corrosion test per GM9540P.

Salt spray resistance is widely usedby the paint industry as a quality con-trol test and is not necessarily indica-tive of long-term performance of acoating. Our test used three steelpanels for each system with two inter-secting scribes (‘‘X’’) through the coat-ings to the substrate. The panels were‘‘X’’ scribed using a standard carbide-tipped hardened steel scribe. Thepainted panels (3 each) for each coat-ing were exposed for 168 hours of saltspray. All the painted panels appearedvisually identical before testing. Panelswere evaluated using ASTM D 1654for Evaluation of Painted or CoatedSpecimens Subjected to Corrosive

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Environments and ASTM D 714 forEvaluating Degrees of Blistering ofPaints. Final detailed ratings for the168-hour duration using ASTM D1654 quantitatively indicates thedamage caused by pitting or delamina-tion outwards from the scribe.

General Motors (GM) Standard Test9540P is an accelerated cyclic corro-sion test that was developed by theautomotive industry to provide moreaccurate replicates of long-term out-door performance of coatings thanthe conventional salt spray test. A cyc-lic corrosion test chamber (CCTC) wasused to perform the GM 9540P test.The test consists of the repetition ofone cycle with 18 separate stagesincluding salt (1.25% by mass: 0.9%

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Table 2. GM 9540P Cyclic Corrosion Test Details

Interval Description Interval Time (min) Temperature (+/�3C)

1 Ramp to salt mist 15 252 Salt mist cycle 1 253 Dry cycle 15 304 Ramp to salt mist 70 255 Salt mist cycle 1 256 Dry cycle 15 307 Ramp to salt mist 70 258 Salt mist cycle 1 259 Dry cycle 15 30

10 Ramp to salt mist 70 2511 Salt mist cycle 1 2512 Dry cycle 15 3013 Ramp to humidity 15 4914 Humidity cycle 480 4915 Ramp to dry 15 6016 Dry cycle 480 6017 Ramp to ambient 15 2518 Ambient cycle 480 25

Figure 3. Control Rounds (Set A) after 168-Hour ASTM B 117 Exposure.

NaCl, 0.1%CaCl2, 0.25% NaHCO3)water mist, humidity, drying, ambient,and heated drying. The environmentalconditions and duration of each stagefor one complete 9540P cycle are givenin Table 2. The above process repeated80 times to a scribed panel is claimedby industry to be equivalent to 10 yearsof field exposure in South Florida. Forthis test, the groups of scribed couponswere exposed until failure or comple-tion of 80 cycles.

The criterion for failure was eithercreep from scribe of greater than10 mm (ASTM D 1654 rating of lessthan 3) or an ASTM D 714 rating forblistering in excess of 6M in theunscribed regions. Upon removal,coupons were rinsed in deionizedwater. In addition, standard plaincarbon steel calibration couponsdescribed in GM Standard Test9540P and supplied by GM were initi-ally weighed and subsequently mon-itored for mass loss at intervals set bythe specification. Mass losses mea-sured for steel coupons used for thistest were within parameters stated inthe GM specification. For each coat-ing tested, three panels were sub-jected to CCTC testing. As in saltspray, the panels were ‘‘X’’ scribed.The scribed panels were placed intothe chamber and tested using GMStandard Test 9540P, Method B10,which provides a more realistic accel-

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erated environmental test than con-ventional salt-spray.

The analysis of the panels exposed inthe B117 for 168 hours indicated thatthe rating was greater than 5, meaningthat creepage at the scribe was lessthan 3 mm. The only exceptions wereSample C and Sample H, which failedon both CRS substrates. Sample Cpasses on zinc phosphate panels. At

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the final inspection at 168 hours, Coat-ings A, B, D, E, G K, L, and M per-formed the best, with the least amountof creep from the scribe and no blisters.Coatings F, J and I trailed behind withincreased creep and blister formation.Coating H also showed small blisters.

The analysis of the panels exposed inthe GM 9540 for 38 cycles indicatedthat most samples passed the criteria.As with the salt spray results, an excep-tion was Sample C, which failed onboth CRS substrates. Sample C passeson zinc phosphate panels. At the finalinspection Coatings A, B, D, and Gperformed the best, with the leastamount of creep from the scribe andno blisters. Initially Coating B lookedthe best, but after scraping the scribedareas with a blunt knife, Coatings A, B,D, and G were visually equivalent.

SUMMARY

ARL and ARDEC have recently quali-fied and implemented the UAC intolarge-caliber ammunition production.Timely implementation of the ‘‘dropin’’ UAC has allowed for continuous,uninterrupted production of 120- and155-mm projectiles at AAP and AAA.If the UAC were not implemented in a

ical Health & Safety, March/April 2005

Figure 4. Rounds Coated with MIL-DTL-11195 Following 500-Hour Exposure toASTM B 117.

timely manner, Scranton AAP wouldhave been required to incorporateexpensive emission control equipmentto meet local environmental regula-tions, costing an estimated $300K.Implementation of the UAC will allowrenovation facilities to meet localenvironmental regulations during therenovation of artillery projectiles. TheUAC test results indicated outstandingperformance and suitability as a repla-cement for the current system. Figures3 and 4 show assessment of the partsthat were shipped to the ARL facilityfor final evaluation. Based upon expo-sure of truncated 155 mm roundscoated with MIL-DTL-11195 to asmuch as 500 hours of ASTM B 117,the following can be supported: MIL-

Chemical Health & Safety, March/April 200

DTL-11195 outperforms the legacysystem by at least a factor of three.

References1. American Society for Testing and Ma-

terials. ASTM B 117 Standard Methodof Salt Spray (Spray) Testing; Philadel-phia, PA, 1990.

2. General Motors, Accelerated Corro-sion Test. GM 9540P. General MotorsEngineering Standard GM 9540P; De-troit MI, 1997.

3. American Society for Testing and Ma-terials. ASTM D 1654 Standard Meth-od for Evaluation of Painted or CoatedSpecimens Subjected to Corrosive En-vironments; Philadelphia, PA, 1984.

4. American Society for Testing andMaterials. ASTM D 3359 Standard

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Test Method for Measuring Adhesionby Tape Test; Philadelphia, PA, 1998.

5. American Society for Testing and Ma-terials. ASTM D 714 Standard TestMethod for Evaluating Degree of Blis-tering of Paints; Philadelphia, PA,1987.

6. American Society for Testing and Ma-terials. ASTM D 609 Standard Practicefor Preparation of Cold-Rolled SteelPanels for Testing Paint, Varnish, Con-version Coatings, and Related CoatingProducts; August 2000.

7. American Society for Testing andMaterials. ASTM D 522-93 StandardTest Methods for Mandrel Bend Testof Attached Organic Coatings; July1993.

8. American Society for Testing and Ma-terials. ASTM D 2794 Standard TestMethod for Resistance of OrganicCoatings to the Effects of Rapid Defor-mation (Impact).

9. American Society for Testing and Ma-terials. ASTM D 1308-02 Standard TestMethod for Effect of Household Che-micals on Clear and Pigmented Organ-ic Finishes; July 2002.

Specifications

MIL-E-52891B: Enamel, Lusterless, ZincPhosphate, Styrenated Alkyd Type.

TT-E-516: Enamel, Lustreless, Quick-Dry-ing Styrenated Alkyd Type (No. S/SDocument).

MIL-E-11195E: Enamel, Lusterless, FastDry, VOC Compliant, Supersedes MIL-E-11195D.

MIL-P-11414: Primer, Alkyd, Fast Dry,Corrosion Inhibiting, Lead and Chro-mate Free, VOC Compliant.

TT-P-664: Primer Coating, Alkyd, Corro-sion Inhibiting, Lead and ChromateFree, Voc-Compliant (S/S by Sspc-Paint25).

DOD-P-15328D: Primer (Wash), Pretreat-ment (Formula No. 117 For Metals)(Metric).

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