Archive: Mar 2021

Special Coatings Support Mars Rover

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Ever wondered how rovers can survive the harsh environments of space? Liquid coating.

According to Products Finishing Online:

“NASA’s Mars 2020 mission successfully launched on July 30 and is currently on its way to the red planet. Known as Perseverance, the Mars rover’s mission is to search for signs of ancient life and cache rock and soil samples for possible return to Earth.

“To protect Perseverance, a special paint job is needed. Chris Salvo of NASA’s Jet Propulstion Laboratory (JPL) who manages the team who puts together the rover’s mechanical subsystem, explains the role the paint job plays in standing up to the extreme temperatures of space travel and the harsh environment of the red planet. A special reflective white paint is used to reflect sunlight and prior to painting, the aluminum surfaces of the rover chassis are scuffed and carefully cleaned to ensure the paint adheres correctly. Detailed masking is required to make sure areas requiring paint are coated precisely and operational surfaces are left unimpeded.

“’This very special formulation of paint has to live through all the difficulties of getting to Mars, shaking on the launch vehicle, as well as existing on the surface of Mars in the hot and cold cycles,’ Salvo says in a video released by JPL.

“Once painted, the rover’s chassis is then baked in a thermal vacuum chamber to remove any volatile materials such as water particles that might be drawn out of the paint by the vacuum of space and cause problems.

“Various components within the rover also require special coatings. A proprietary impingement lubricant coating process known as Microseal developed by Curtiss-Wright’s Surface Technologies Division (Parsippany, N.J.) has been used on numerous components for NASA’s Mars 2020 Mission, many within Perseverance’s sample caching system.

“Curtiss-Wright Surface Technologies has a long standing relationship with NASA. Microseal was selected for the Perseverance mission because of its friction reduction properties under a wide range of temperatures from cryogenic temperatures to over 1,000° F, and its ability to perform in hard vacuum conditions.

“’High performance in harsh conditions typical to space applications demands a reliable solution like Microseal,’ says David Rivellini, senior vice president and general manager, Curtiss-Wright Surface Technologies. ‘The Microseal process outperforms conventional lubricants as it remains stable under extreme conditions and is resilient to shock, radiation, vibration, acceleration and electrical discharge.’

“The Microseal process creates an ultra-thin adherent film that fills voids on the surface of components. The film is designed to perform within a vacuum and in extreme temperatures ranging from -423°F to 2000°F (-253°C to 1093°C). The company says the process creates a continuous lubricating surface that reduces friction and prevents galling and seizing. It also dissipates heat, remains stable under extreme environmental conditions, and does not attract contaminant particles.

“According to Pierce Cleary, director of business development, Curtiss-Wright Surface Technologies applies the Microseal process to surfaces using a specially designed, patented air tool that mixes micro-size particles. Particles leave the tool at speeds of nearly 600 feet per second, depositing a firmly adherent thin film that fills the surface voids.

“’Regardless of the surface geometry of the treated part, once the coating reaches a thickness of fifty to eighty millionths of an inch, no further coating will be accepted,’ explains Cleary, ‘Coverage is uniform on all surfaces the air tool can reach, and the process is burnishable to original dimensions, eliminating the need for special machining or tolerance allowance.’

“Due to the complex and proprietary nature of the equipment, Microseal application takes place at one of Curtiss-Wright Surface Technologies’ worldwide facilities. The company inspects incoming parts for cleanliness and freedom from surface defects and closely monitors the entire application process.

“The latest Mars rover mission includes numerous new technologies including a robotic helicopter that will mark humanity’s first attempt at flight in an alien atmosphere. Perseverance is scheduled to arrive on the red planet on February 18, 2021.”

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Thermoset Powder Coating

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New to thermoset powder coating? Here is a breakdown.

According to Thomas Net:

“Thermoset materials are used for the majority of powder coating processes because they can provide a surface layer that is both durable and decorative. Most thermoset powders have a molecular weight lower than that of thermoplastic materials and higher than that of liquid coatings. Thermosets are solid resins that, when heated, melt, flow, and—unlike thermoplastics—can crosslink with one another or other reactive substances to form compounds with higher molecular weights. After curing, a thermoset coating remains thermally stable, meaning it cannot be melted back into a liquid from further heating.

“In a powder coating system, the more brittle thermoset resins can be broken up into a very fine powder that can then be fabricated into an exceptionally thin, paint-like film. This film exhibits chemical and physical properties comparable to those of liquid-based coatings. In addition, advancements in thermoset technology have continuously increased the versatility of this material group, allowing for more customization options. Many standard thermoset materials can now be chemically altered to provide the specific characteristics required for a given application.

Thermoset Powder Coating Properties

“The most commonly used thermoset powder coating resins derive from the epoxy, hydroxyl or carboxyl, acrylic, and silicone groups. They generally require lower curing temperatures than thermoplastics, and manufacturers often introduce additives to accelerate or delay the curing reaction. It is important to subject a powder-coated product to thorough heating and allow the thermoset to flow evenly over the targeted surface because once the thermoset powder has completed crosslinking, it cannot be reflowed to correct any flaws in the coating. To achieve successful coating results, it also necessary to match the thermoset formulation with the product’s intended corrosion resistance, curing cycle, texture, and aesthetic properties.

“One of the most significant developments in thermoset powder coating involves the capacity to engineer resin types with variable properties designed to complement metal finishing treatments. This broader range of characteristics has led to an increase in specialized roles for thermoset powders, with polyesters and acrylics finding greater use in the automotive and appliance industries despite the traditional reliance on epoxy-based coatings. Most thermoset powders can provide a high level of corrosion, temperature, and impact resistance. They can also be designed with a wide range of colors, glosses, and surface finishes. Coating texture can be wrinkled, smooth, or matte, while film thickness is highly adjustable.

Epoxy-Based Powder Coatings

“Epoxies are the most common thermoset resins used in industrial powder coating, and they have a wide range of formulation options. Different types of epoxy can be fabricated into functional thick film or more decorative thin film, while their crosslinking properties are similar to those of epoxy adhesives and paints. Most epoxy-based materials are crafted to be thermally stable at room temperature. Some standard epoxy powder coatings include:

“Functional Film: Thick, functional film epoxies are often employed for electrical insulation and corrosion resistance applications. As insulation, epoxy powder bonds to a surface and follows its contours with relatively few voids or other defects. This is useful for devices such as electrical motors, switch gears, and automotive alternators. Anti-corrosion epoxy provides low cost and long-lasting protection for products in chemically hazardous environments, such as underground gas and oil pipes.
Thin Film: Thin film coatings are typically designed to provide specific decorative results while preserving the durability and resistance characteristics of other epoxy groups. They are generally restricted to interior coatings, as de-glossing and chalking are frequent risks for thin exterior layers. Thin epoxy film coatings are commonly found in fire extinguishers, furniture, hospital equipment, and a wide number of household appliances.
Epoxy-Polyester Blends: An epoxy resin crosslinked with a reactive acid polyester will form a blend, or hybrid, material that has flexibility and impact resistance qualities similar to those of other epoxies, but provides a higher level of ultraviolet light protection. These blends are effective when applied as an electrostatic spray and have a range of applications similar to those of thin film epoxies.

Acrylic Powder Coatings
“Acrylic powder coatings are beneficial for their high level of exterior durability and relative ease of application. Acrylics require curing temperatures close to those of hydroxyl polyesters, and they combine high quality surface aesthetics with flexibility and impact resistance. They also exhibit excellent alkali resistance, making them well-suited for use on appliances, such as ovens and washing machines. Acrylic powder coatings can be effectively applied through electrostatic spraying and have adjustable thin film characteristics. However, acrylics are more responsive to substrate attributes than most other powder coatings, making them incompatible with certain chemical compounds. Aside from their use in appliances, acrylic powder coatings can also be found on aluminum extrusions, automotive trim components, and tractors.

Hydroxyl and Carboxyl Polyester Powder Coatings
“Hydroxyl polyester powder, also known as urethane, provides both a high quality surface finish and resistance to wear. It is usually fabricated as thin film because its thick film form exhibits lower impact resistance and flexibility. A hydroxyl polyester coating has aesthetic qualities comparable to those of liquid paint, and it is commonly used for coating light fixtures, furniture, automotive components, wheels, and appliances. During curing, some hydroxyl polyesters release an emission that needs to be vented away from the cure oven to prevent defects or contamination.

“Carboxyl polyesters have durability characteristics similar to those of epoxy-polyester blends and weathering resistance comparable to urethane. They have consistent mechanical properties across a range of standard coating thicknesses and provide a high level of flow, glossiness, and material strength. However, their resistance to chemical solvents can be lower than that of hydroxyl coatings. Carboxyl polyester powder coating is commonly used on irrigation pipes, outdoor furniture, fences, aluminum extrusions, and steel wheels.”

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