The history and evolution of thermal spray coatings show that the thermal spray coating industry is far from sedentary. Numerous thermal spray coating techniques have been developed since thermal spraying was discovered in the 1900s. The development of these new techniques has significantly widened the range of applications of thermal spray coatings.
Origins of Thermal Spraying
- Thermal spraying started in the early 1900s when Dr. Max Ulrick Schoop of Zurich realized it was possible for “a stream of molten particles impinging upon themselves” to create a coating. During that period, engineers were conducting experiments to break up liquids into fine particles or powders using high-pressure gas.
- Dr. Schoop’s discovery led to the development of the first thermal spray process. Dr. Schoop and his German engineer collaborators or associates, Felix Meyer and Franz Herkenrath, were able to develop processes and equipment to produce coatings from molten and powder metals. This development, in turn, led to the establishment of the first stationary metal spraying plant in 1910.
- It was 1912 when Dr. Schoop and his associates were able to create the first instrument for spraying wire-form solid metal. Metallizing was the technique behind this instrument. The principle of metallizing was that “if a wire rod were fed into an intense, concentrated flame, (the burning of a fuel gas with oxygen), it would melt and, if the flame were surrounded by a stream of compressed gas, the molten metal would become atomized and readily propelled onto a surface to create a coating.”
- What was known then as metallizing is now known as oxy-fuel or flame spraying. There is now a wide range of oxy-fuel techniques that involve ceramic powder, ceramic-rod, detonation, high-velocity oxy-fuel (HVOF), metallic powder, molten metal, and wire.
Emergence of New Thermal Spraying Processes
- Problems associated with the use of liquid metal led to the use of fine metal powder.
- Cold spraying, which is known today as the process of throwing cold metal powder onto a surface to coat it, was actually attempted more than a century ago. Engineers knew then that this process would create layers of maximum protection.
- The attempt failed, however, as conditions back then made successful cold spraying impossible. This failure then served as an impetus for the development of the powder flame spraying technique, which is still in use today.
- Thermal spraying eventually scaled up to an industrial level where coating plants that converted wires into coating materials were established. It was during this time that the wire flame spraying and arc spraying coating techniques came into existence.
- This development was followed by the creation of the laser spraying, plasma spraying, and detonation spraying techniques in the 1950s. These techniques were widely used in the aviation industry.
- Additional techniques or processes were developed in the 1980s. The 1980s saw the development of the vacuum plasma spraying, low pressure plasma spraying, and HVOF spraying techniques.
- The latest major development in the industry is the creation of the cold spraying technique. Although the name cold spraying seems incongruous with thermal spraying, it is considered by the International Thermal Spray Association as one of the thermal spraying techniques.
Current Thermal Spraying Processes and Applications
- Key thermal spray coating processes at present are categorized by their heat source schematic. Molten metal flame spraying, powder flame spraying, wire flame spraying, ceramic rod flame spraying, detonation flame spraying, and HVOF spraying techniques are considered flame spraying techniques, while non-transferred plasma arc spraying, electric arc spraying, and radio-frequency (RF) plasma spraying are considered electrical techniques. Cold spraying is in a category of its own.
- Thermal spray coatings have applications in the following industries: aero gas turbine, stationary gas turbine, hydro-steam turbine, automotive engine, diesel engine, transportation non-engine, agriculture implementation, railroad, iron and steel manufacture, steel rolling mils, iron and steel casting, forging, copper and brass mills, ship and boat manufacture and repair, oil and gas exploration, mining, construction, and dredging, rock products, screening, cement and structural clay, chemical processing, rubber and plastic manufacture, textile, food processing, electrical utilities, pulp and paper, printing equipment, defense and aerospace, nuclear, medical, business equipment, electrical and electronic, architectural, and glass manufacture.
- The oxy-fuel spraying techniques, especially HVOF, and the air plasma spraying technique appear to be the most widely used thermal spraying techniques. These techniques are used by the majority of the aforementioned industries.
- Iron and steel, self-fluxing materials, nickel alloys, cobalt alloys, and non-ferrous alloys appear to be the most widely used coating materials. Chrome carbide is used by the aero gas turbine, stationary gas turbine, hydro-steam turbine, automotive engine, diesel engine, defense and aerospace, architectural, and glass manufacture industries.
- Thermal spray coatings are applied to surfaces to give them properties such as wear resistance, abrasion resistance, erosion resistance, corrosion resistance, temperature resistance, and low friction.
- Emerging thermal spray techniques include the high-velocity air-fuel (HVAF) spraying technique and the liquid feedstock thermal spraying technique.
Trends in the Thermal Spray Coating Industry
The development of new or proprietary thermal spray coatings, the use of robotics, and the exploration of anti-virus, anti-bacteria, and anti-fungus applications are three trends in the United States thermal spray coating industry.
1. Development of New or Proprietary Thermal Spray Coatings
- The development of proprietary thermal spray coatings seems to be an ongoing trend in the United States thermal spray coating industry. Players in the industry appear to be in a continuous search for high-performing and cost-effective thermal spray coatings.
- These new or proprietary thermal spray coatings appear to be designed with specific industries or desired properties in mind.
- For example, A&A Coatings, a New Jersey-based key market player, has developed three proprietary thermal spray coatings, namely the Cerami-Pak, the Wirewear Protective Coating, and the Microcoat.
- Cerami-Pak coatings are coatings specifically designed for the packaging industry that are made of ceramic fluorocarbon composite materials and have superior properties. Wirewear coatings are non-sticking, hard, and abrasion-resistant coatings that have low coefficients of friction, while Microcoat coatings are coatings that are specifically designed for ion implanting and dry-etching in the electronics industry.
- F.W. Gartner Thermal Spraying, a Texas-based key market player, has also developed its own proprietary thermal spray coatings. It can be seen from the company’s website that the company has the following proprietary thermal spray coatings: Rokide™, JP-5000™, Jet-Kote™, and Diamond Jet®. Unfortunately, the company has not shared details about these proprietary coatings on its website.
- Following are examples of processes and materials that players and researchers in the market are currently exploring:
- Oerlikon Metco (United States): Suspension feed thermal spray of sub-micron powders
- Saint-Gobain (United States and France): Thermal-spray barrier coatings from rare earth silicates
- Stony Brook University’s Center for Thermal Spray Research (United States): Thermal spray coatings for compression engines
- Fisher Barton Technology Center (United States): Thermal spraying of polymer matrix composites
- University of Connecticut, Solution Spray Technologies (United States): Yttrium aluminum garnet thermal barrier coatings
2. Use of Robotics
- Thermal spray coating providers in the United States appear to be increasing its usage of robotics to improve the accuracy, efficiency, consistency, and flexibility of their operations. They recognize that robots allow for the accurate and precise setup of process parameters.
- ASB Industries, an Ohio-based key market player, recently shared that it has bought a new addition to its robot family. It has bought a new thermal spray robot manipulator from ABB for added accuracy, efficiency, consistency, and flexibility in the types of process fixtures it could use. What makes this robot manipulator special is its small footprint and its ability to adapt to various kinds of spray guns.
- BryCoat, a Florida-based key market player, also touts on its website that it uses robots in the application of coatings to ensure coating quality and process repeatability. It shares that its coatings are robotically controlled for both consistency and uniformity.
- According to BryCoat, its thermal spray guns are controlled by industrial robots so that coating properties and process parameters such as stand-off distance, traverse rate, number of coating passes, and coating angle can be accurately controlled, and the process can be repeated in a precise manner.
- TST Coatings, a Fisher Barton company and a Wisconsin-based key market player, also shares that the Fisher Barton Technology Center has a robotic plasma transferred arc system that is capable of producing high-purity, low-porosity thermal spray coatings.
3. Exploration of Anti-Virus, Anti-Bacteria, and Anti-Fungus Applications
- Players in the thermal spray coating space seem to be exploring the anti-virus, anti-bacteria, and anti-fungus applications of thermal spray coatings.
- Anti-virus, anti-bacteria, and anti-fungus applications are the topic of the ITSC 2021 Preview organized by the Ohio-based Thermal Spray Society. ITSC stands for the International Thermal Spray Conference and Exposition.
- The fact that these applications are the subject of the ITSC 2021 Preview suggests that anti-virus, anti-bacteria, and anti-fungus applications are a hot topic in the industry during this time of the COVID-19 pandemic.
- Industry experts are exploring how thermal spray techniques can be utilized in depositing antimicrobial compounds on various high-touch surfaces. In the preview, industry experts will discuss how biocidal thermal spray coatings can be implemented and utilized in a large scale to lower the risk of virus or bacteria transmission in high-touch places such as hospitals and public transportation.