Metals, plastics and wood – many materials today are powder-coated. Paints and lacquers are applied as powders, melted by the introduction of heat and finally cured. Electrical infrared emitters transfer large amounts of energy in a short time without the need for a contact medium. As a result, the oven length can be reduced or the production rate speeded up compared with conventional methods. Moreover, rapid melting of the powder helps to improve the surface quality of the coating. The example of a manufacturer of metal parts for technical consumer products shows how companies in China utilize the advantages of infrared technology.
Powder coating on flat metal parts is cured quicker and on less floorspace than with a gas-fired oven. Copyright Heraeus Noblelight 2007
Saving space was a key argument when a manufacturer of metal plates for technical consumer products in China compared gas-fired and electrical infrared technology for its new plant in Fujian province. As the market for these powder-coated products is very competitive and downward cost pressure is huge, the floorspace has to be used in the best possible way. After testing electrical infrared emitters in the Heraeus test center in Shanghai, the company was impressed by the speed of curing which made a much more compact design of the line possible. Compared to a convection oven, the line speed could be increased by more than 50%. The coating line contains two infrared sections: drying of the uncoated parts before coating and curing the powder at approx. 200OC after coating. Both process steps use medium-wave infrared modules which were built and equipped with emitters by Heraeus Noblelight. They can be controlled in different zones to save power when smaller parts are running through the curing oven. The power of the infrared heaters can also be easily adjusted to the different colors of coating, dark coating requiring less energy than light coating.
Further benefits of infrared technology became obvious when the line started operation. The quality of the coated products improved further because the powder is cured faster, without time to flow down the plates. “We have not had a single complaint since the new line started operation” says the Engineering and Maintenance Manger of the company. The company was further able to take advantage of lower off-peak electricity rates, keeping the energy bill at a comparable level as for a gas-fired oven. Absolute energy consumption is even lower for electrical infrared because the heat can be better targeted, which reduces the heat load in the production building and is in line with China’s policy of efficient and clean energy usage.
Electrical infrared emitters transfer heat without the need for a contact medium, where electromagnetic waves generate heat in the material to be heated. Infrared radiation is absorbed very well by powder, so that the powder mass heats up very quickly. Powder is gelled significantly faster than in a convection oven, and the transmitted power is higher than for gas-fired infrared ovens. Fast melting improves the surface quality and increases the throughput speed. In most cases, ovens are significantly shorter or the product speed is higher.
Infrared radiation offers many more advantages for power coating applications. Speed and space-saving have been demonstrated in the case study above. For flat parts like the metal plates mentioned above, it heats the surface evenly. But also round parts can be cured by rotating the part in front of the infrared heaters.
In comparison with hot air ovens, the powder is not disturbed or blown about. With no air movement, dust inclusions are also eliminated, so that quality is improved.
Compared to gas-fired infrared heaters, electrical infrared eliminates potentially dangerous gas supply in the factory. Electrical infrared systems also can be easily integrated in existing drying lines. This helps when upgrading existing hot air ovens in order to speed up production.
However, knowledge and experience is needed when designing an infrared system. There are many different types of infrared emitters, from short-wave and halogen heaters to medium-wave heaters. Each one has specific advantages that depend on the specific application of the customer. For example, using the wrong emitter for powder coating can easily lead to over-cooking the coating instead of curing it properly.
This is why Heraeus Noblelight operates test centers in five countries around the world, including the one in Shanghai. Here, customers can conduct experiments with their own materials together with the Heraeus experts. Thus, the customer can be sure that he selects the best-suited emitter for his application.
Heraeus Noblelight GmbH with its headquarters in Hanau and with subsidiaries in the USA, Great Britain, France, China, Australia and Puerto Rico, is one of the technology- and market-leaders in the production of specialist light sources. In 2006, Heraeus Noblelight had an annual turnover of 88 Million € and employed 651 people worldwide. The organisation develops, manufactures and markets infrared and ultraviolet emitters for applications in industrial manufacture, environmental protection, medicine and cosmetics, research, development and analytical laboratories.Heraeus, the precious metals and technology group headquartered in Hanau, Germany, is a global, private company in the business segments of precious metals, sensors, dental and medical products, quartz glass and specialty lighting sources. With revenues of more than EUR 12 billion and more than 11,000 employees in over 100 companies, Heraeus has stood out for more than 155 years as one of the world’s leading companies involved in precious metals and materials technology.
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