N241-028 TITLE: High Volume Low Pressure (HVLP) Style Spray for Rapid Cure Ultra-High Solid (UHS) Coating Systems

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials

OBJECTIVE: Develop paint spray equipment for ultra-high solid (UHS) coatings that allow application at low thickness for specific, targeted areas such as propulsors or geometrically complex superstructure.

DESCRIPTION: The application of Type VII UHS epoxy coatings for naval applications relies entirely on commercially available airless coating spray equipment. The equipment used to spray the UHS coatings consist of a single or plural component mix pneumatic pumping/proportioning unit, in-line heaters for viscosity control, high pressure hoses and static mixers followed by a spray whip connected to a spray gun. Because of the viscosity of the UHS coatings system, it is typical for heat to be applied by the inline heaters to reduce the viscosity to achieve a properly atomized spray pattern at the tip of the spray gun. Various spray tips are used as well to properly atomize the spray fan or cone shape of the coating being delivered to the surface being painted. The current systems deliver the coating at high pressure and high volume, which causes difficulty in controlling film build and spread during application. For most of the work performed where UHS systems are employed, the result of coating application does not require a finished surface akin to an evenly spread, uniformly thick coating without surface flaws.

In an ever-growing need, the maintenance community relies on MIL-PRF-23236 Type VII UHS coatings for corrosion control in areas where legacy thin film coatings were historically applied in multiple thin layers to achieve the desired surface finishes and thickness. Transitioning to UHS coating applications increased the difficulty of achieving the surface finish and increased dry film thickness (DFT) that affect ship component fit of covers, plates, and other equipment assemblies in new ship designs. Controlling the volume of flow and spray pattern of UHS coatings in many applications will dramatically improve production efficiency when preserving naval assets.

Developing a spray gun that can achieve adequate volume and tailored spray capabilities is not trivial. To achieve the atomized spray desired, the developmental spray gun will have to control incoming pressures up to 7250 psi (50MPa), meter coating volume to a level to achieve control of spray atomization, pattern, and thickness control while allowing sufficient flow and productions levels as not to allow the rapid cure nature of the UHS coating to solidify within the application equipment past the static mix blocks or in the lines due to too slow coating deposition. The gun should be light enough for use by the applicator for long periods, handle the heat generated by fluid temperatures used to modify coating viscosities, and be able to spray coating film metered between 2 – 10 min/max mils wet film thickness, (WFT) per pass with an average targeted range of 2 – 5 mils per pass by an applicator.

Existing UHS spray technology is not well suited for applications where highly detailed work is required. Technologically advanced structures continue to be developed for marine service using light weight corrosion prone materials in seawater. When the structure being coated is geometrically complex, it becomes difficult to apply coatings properly and with any level of detail. Developing the capability to tailor spray parameters will provide significant advantages for controlling the application of UHS coatings, providing the asset with the necessary corrosion protection and functionality to operate as intended in a highly corrosive seawater marine environment.

The Naval Research Enterprise (NRE) produced an in-house prototype spray gun using existing commercially available gun bodies and was successful at achieving and demonstrating basic spray capabilities. However, the prototype was highly dangerous as the components were not designed for such high fluid pressures. Additionally, the ability to fully realize the desired performance of the gun itself was never met. Development was necessary with respect to flow, volume control, and atomization behavior of the coating. The science behind the operation and thus the ability to tailor to a wide range of spray conditions were not addressed since a production problem with a new Navy asset necessitated a hastily designed and constructed spray gun prototype for just that application. NRE engineers surveyed commercial industry manufacturers that supply coating equipment and were not able to identify such a spray gun with the desired capabilities. Discussions with equipment manufacturers indicated they had no desire to invest in such a design since their customer base was satisfied with the existing technology. However, as with the development of UHS coatings, the Navy’s need drove UHS development, and the commercial sector followed suit as the demand began to increase. It is likely the same process will play out for this effort. When applicators who routinely use UHS systems have an alternative spray gun that allows them to control their application parameters to a higher degree, the equipment manufacturers will likely follow suit. The Navy currently has several designs for autonomous vehicles in operation and under development which require controlled coating applications. Over the past few years, the need has grown significantly.

To properly spray high solids/rapid cure coatings, a balance of pump pressure, temperature, flow rates, distance from pump, and a host of other factors need to be met. Existing commercial products are designed to meet a wide range of capabilities. However, the need to restrict many of these parameters will cause significant issues and are counter to how both the equipment and coatings were designed for use. R&D and innovation is needed to address how to change the parameters to achieve desired properties; (tightly controllable surface thickness and finish) over a wide variety of applications where a high-volume coating is being applied in a low volume situation without affecting coating cure properties or performance. Additionally, a new spray gun must be developed to ensure applicators can safely apply the coatings which are under high pressure metered down to some working pressure while having the ability to adjust the spray to geometrically complex structures in the field. The Navy needs a method to apply existing high-performance coatings in a way to achieve asset operation that supports asset design.

On average, the cost of such equipment is dictated by the complexity of the design, required machining, and availability of incorporated parts. Sales of spray guns assumed to be within the same complexity of design range from $3K to $7K each. The design should weigh no more than a comparable style commercial gun because weight and balance affect the applicator’s ability to spray for long durations. Physical weight should not exceed 3 lbs. and fall within a box 8" W X 8" L X 2.5" D dimensionally. In addition, the design should account for ease of use when spraying in tight geometries, for example, in a rectangle that is 12" W X 14" D X 72" L. Supply lines for fluid and potentially compressed air should be attached in a way that they allow flexibility at the applicator’s wrist. The gun should be able to sustain continuous spray for several hours at a time, and not suffer from any internal erosion of moving parts or fluid pathways.

To date no Commercial Item Description, (CID) exists for such a spray gun. CID A-A-50310 is a spray gun CID however it is not applicable to this design and should not be used as a reference. However, the pumping system to which the gun will attached falls under the CID A-A-59780 accessible through Assist Online at Defense Logistics Agency https://quicksearch.dla.mil/quicksearch.aspx. During the demonstration phase, the prototype gun will be attached to a plural spray pump that meets this CID. Coatings that will be sprayed through this prototype are qualified to MIL-PRF-23236, Type VII, Class 5, 5/18, 7, 7/18, &13 Grade C. All the specifications listed are available as Distribution A to the public and can be found at the DLA quick search website mentioned above.

The product shall be a packaged spray gun with all the necessary components for operation and connectivity to plural component spray equipment, like that of existing commercial spray gun sales. If adapters or any component deemed proprietary is needed for use, it shall be included in the end products inventory. The company identified for commercialization shall have the ability to provide repair and maintenance components and services as necessary to support end user needs. Beyond the immediate need for GFE components, the military industrial complex has immediate needs for coating specific equipment and designs for UHS coatings that require detailed spray capabilities. Those organizations both government and commercial will require this equipment. In addition, some of those commercial entities rely heavily on outside commercial coating applicator companies to perform the applications. Many of these companies also perform routine maintenance on military assets e.g., surface ships, submarines, barges, etc., and will likely adopt the use of this product to other activities as it will improve their ability to provide a level of control over the process they struggle to manage. In many instances coating appearances plays a larger role in acceptance of the final coating product, than intended coating performance. Coatings companies strive to perfect the applications so the job can be accepted by the owners of the assets they were hired to coat.

PHASE I: Define and develop a concept for an UHS delivery system that meets the specifications identified in the Description. Modeling and simulation should be used to articulate the feasibility of the design features and functionality, and to provide a computerized working model and detailed diagrams. The concept for a working prototype shall be at a level so that prototype construction and operation methodology are well defined. The Phase I Option, if exercised, will require the small business to provide a written report detailing the design concept, proposed functionality, construction methodology and materials, and marketing strategy to develop the desired product. The report shall include the initial design drawings and specifications with sufficient detail to complete construction of the working prototype in Phase II.

PHASE II: Develop and deliver a working spray gun prototype that meets the requirements detailed in the Description. The prototype will be required to function as designed and be demonstrate using a plural component proportioning pump like that used in industry. Recommendations will be made to identify such equipment if necessary. Demonstrate performance in house prior to demonstrating to the government. Upon completion of the government demonstration, the prototype shall be delivered to the government for additional testing if the prototype has met the performance criteria. A total of four prototypes units will be required to be constructed for field testing at industrial sites specified by the Topic Author.

PHASE III DUAL USE APPLICATIONS: Assist the Navy to transition from prototype to full production. In the early stages the Phase III product will initially role out to specific Navy organizations that currently require coatings applications which are driving the spray gun development. The spray gun will be introduced into the system that supports GFE. It will be through this effort that the Navy will validate performance during complete preservation of GFE components and certify it for Navy use.

Commercial interest will be driven by the need for controlled coating application where high volume deposition fails. The polyurea/insulation community has high volume and low volume spray guns (e.g., GX-7 vs GX-8 respectively) where controlling the volume of coating being deposited is driven by application requirements and type. Industrial coating application such as refineries and chemical plants where complex structure is involved would benefit from tighter application controls to reduce overspray and film build. It would also reduce the cost of materials through wastage.

REFERENCES:

1. Sanchez-Amaya, J.M., Osun, R.M., Bethencourt M., and Botana, F.J. "Monitoring the degredation of a high solids epoxy coating by means of EIS and EN." Science Direct Progress in Organic Coatings Volume 60, Issue 3, October 2007: 248-254. https://doi.org/10.1016/j.porgcoat.2007.07.020
2. Webb, Martin, Groeninger, Slebonick, Lucas, and Hogan. "Reducing Corrosion Control Cost with Rapid-Cure Coatings." Naval Research Laboratory Review 2007: 63-69
3. MIL-PRF-23236D AMD/1 March 2023, via Assist Online Quick Search https://quicksearch.dla.mil/qsSearch.aspx using Document number 23236

KEYWORDS: UHS thin film deposition; Airless spray guns; UHS coatings application; Marine coating anticorrosive coatings; Tunable spray atomization and thickness control; Low volume rapid cure spray gun

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