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Manufacturing is challenging in terms of technology, energy and cost-efficiency. Modern infrared systems offer advantages for many heating and drying processes. Infrared radiation can provide energy-efficient heating because the thermal energy transfers directly from the heater to the body to be heated via electromagnetic waves in the infrared spectrum. Infrared energy can be emitted in a well-controlled manner, meaning it is transferred only where it is needed and only for as long as necessary.

The characteristics of the product and process can help inform the selection of infrared emitters and modules in terms of wavelength, power and emitter shape. Product testing can help identify which heating sources are best suited to the process and material. Careful heater selection can help processors achieve increased production speed, improved quality and reduced reject rates — all of which contribute to lower manufacturing costs.

This article will describe four real-world examples of how infrared technology helped improve industrial heating processes.

Saving Time with Partial, Intermediate Drying

Car manufacturer Audi relies on a process that produces two-tone contrasting paints in a single pass. An important component of the concept is an infrared module that follows the geometry of the vehicle and realizes the necessary partial intermediate drying.

Traditionally, two-tone paintwork on cars required a multistep process: masking, pre-masking and fine masking; sanding of the areas to be painted; and a second painting pass. After the necessary cleaning, the contrasting applications were applied and sealed with clear lacquer. Then, the car body was run through the dryer a second time. Finally, unmasking and a final check would be carried out. A time-consuming and cost-intensive process with a high workload, this approach also caused a high material consumption because foils and adhesive tapes were required.

The infrared heater used at Audi enables intermediate drying of the two-color coating, which reduces the amount of work and material consumption. Photo credit: Audi

Overspray-free painting (OFLA), which is being used in series production for the first time at Audi, transforms this time- and material-intensive process. After the base coat is applied, the roof is partially dried. Subsequently, the contrast color is applied directly in line with the car body by means of an applicator without overspray. In this way, a roof contrast paint finish can be achieved by lining up individual stripes with sharp edges, without any overspray. Masking the body is no longer necessary. After the contrast paint has been applied, the body goes into the convection oven.

An important component of the new approach is the intermediate drying of the basecoat before the OFLA application. This is carried out with the help of an infrared module. Its carbon emitters follow the course of the roof height. In this way, the first coat of paint is dried only on the roof. The carbon emitters can be switched quickly on and off so that heat is applied in a targeted manner.

The carbon infrared emitters used at Audi combine the medium infrared wavelength with high surface powers and short response times. The infrared drying can be switched on in cycle mode. In this way, contrast-painted cars can be produced in line with the monochrome models, and they do not have to pass through the convection oven twice.

For Audi, a change to medium-wave carbon infrared emitters should help to save considerable amounts of energy. Tests have shown that carbon emitters require up to 30 percent less energy for drying water-based paints and varnishes than conventional short-wave emitters. In the event of an unexpected conveyor stop, conventional medium-wave emitters also must be swiveled away or shielded to prevent damage to the surfaces of fabric webs.

While solutions of this kind have a performance of up to 60 kW/m² and are associated with reaction times of up to 3 minutes, carbon emitters should be able to achieve a performance of up to 150 kW/m². They counteract within seconds and can be switched off immediately in the event of a malfunction.

Tailored infrared heat ensures the least possible residual moisture and the highest possible adhesion during slurry drying for electrode production. Photo credit: Heraeus Noblelight

Infrared Heat Optimizes Electrode Production

Lithium batteries are found in e-cars, electric scooters and other modern means of transportation. Their production is booming and, with it, the manufacture of the necessary electrodes. For this purpose, metal foils, usually made of copper, are coated with a paste called slurry. Drying the slurry on the metal foils is not simple; instead, it involves a complex interplay between drying temperature, energy input and time. It is important to dry the slurry with as little residual moisture as possible to ensure maximum adhesion.

In the past, the electrode slurry was dried by hot air, but infrared heat technology is becoming increasingly established. Because infrared heat radiation has a higher heat-transfer capacity than air, the drying step can be accelerated significantly. A series of intensive tests by one infrared heating equipment manufacturer showed that the wavelength and power of the infrared emitters, combined with the optimum drying time, have a major influence on the drying result. Binder crosslinking and residual moisture content can be strongly influenced by these parameters, so it is worth taking a close look at the design of the infrared drying system.

This is confirmed by field tests at customer facilities. Retrofitting infrared emitters to existing hot-air drying systems accelerates the production speed, almost doubling it.

Practical test series and computer simulations can be used to optimize the system. To identify the interaction of the various parameters and understand their influences, the infrared equipment manufacturer conducts drying trials with different radiation sources and outputs at its application center. In addition, the process from coating to drying to analysis can be simulated on a laboratory scale.

For battery production, a film applicator precisely coats the substrate films with electrode paste in different layer thicknesses. After infrared drying, residual moisture is determined, and adhesion tests are carried out. In this way, the relationships between film thickness, drying speed and adhesion can be identified. Infrared emitters are adapted to the required parameters in the wavelength range and also in the power density.

Such process optimization also can be conducted at the infrared equipment manufacturer using numerical simulation via computer-aided engineering. Production systems can be analyzed and optimized using virtual product data models. This involves simulating information about the temperature distribution in the coated foils; feedback from environmental influences; and airflow for the removal of moisture or water vapor.

Drawing tests confirm high adhesion after infrared drying. Photo credit: Heraeus Noblelight

Infrared Heat and UV Technology for Decorative Plastic Parts

Decorative moldings in cars, metal-look switches or high gloss fittings are made from injection-molded plastic and coated on the outside. Often, this is accomplished using the in-mold decoration (IMD) process or film back injection. A specialist for thin-film technology, Leonhard Kurz Stiftung & Co. KG worked with an infrared equipment manufacturer to optimize infrared heating technologies for its IMD technique.

In the IMD process, a carrier product with decorative lacquer is placed inside the injection mold. As the mold is filled with plastic, lacquer or paint adheres to the surface of the plastic castings. When the mold is opened, the lacquer then detaches from the carrier and remains on the plastic part. The coated part then can be removed.

The entire process benefits from infrared and ultraviolet curing technology. The coated transfer product can be processed better if it is preheated by infrared radiation, making it moldable. After injection molding, the coating is cured by ultraviolet radiation and thus becomes particularly resistant to scratches.

The IMD process benefits from the infrared system’s ability to preheat the coated transfer product. Photo credit: KURZ

Infrared Booster Prevents Powder Carry Over

Aluminum profiles for buildings are powder coated before use. By installing an infrared booster in the vestibule of an existing infrared oven, Smart Architectural Aluminum, the largest manufacturer of aluminum profiles for windows, doors, facades and conservatory roofs in the United Kingdom, was able to increase the speed of its coating line by 20 percent. The booster helps to avoid powder carryover, additionally improving the quality of the aluminum profiles.

Aluminum profiles are coated in three lines: two vertical and one horizontal. The products are first powder coated and then passed through infrared gas catalytic ovens to gel the powder before passing through the convection oven for final curing. Over time, the efficiency of the infrared oven had suffered from free powder that had migrated from the vestibule of the furnace. This caused quality problems in the production process.

Instead of simply renewing the gas catalytic panels, an additional electrical infrared booster in front of the furnace could provide a decisive improvement. (See the photo at the top of the article.) The booster quickly brings the applied powder into a gel state, thus avoiding any powder carryover onto the panels in the gas catalytic furnace. Complete gelling then can be achieved in the furnace before the coated parts are transported into the convection furnace for final curing.

The infrared booster was mounted on the existing steel structure in the vestibule of the gas catalytic furnace. Since the installation of the medium-wave infrared emitters, the system has been working successfully.

Michael Coles, the paint plant manager at Smart Architectural Aluminum, said: “The infrared booster, which was retrofitted easily into the existing space in the vestibule, has provided us with a simple, but elegant solution to a possible contamination problem, increasing panel working life and improving product quality.”

In conclusion, as these examples show, infrared radiation can help ensure energy-efficient heating processes.