Curing a finish means to bring it to its intended degree of hardness and luster. Before this last decade, we might have been dealing strictly with “baking”. Heat is still the primary method of curing a finish. But today’s finishes can also be water-based, and heat, although helpful in accelerating the drying of waterborne finishes, is not as effective as air movement.
The newest technology involves the use of light without heat to cure the finish
Curing by Heat
Heat curing is accomplished either by heated or super-heated air, or by radiant heat emitted from infra-red lights. Both methods are used in both industrial and refinish situations to cure finishes. Powdercoat and e-coat finishes are cured through a heat cycle, as well as painted finishes.
In most cases, when talking about heat curing, the temperature required is referring to the substrate – the surface being painted. For example, in a refinish situation, the heat specification refers to the vehicle’s body metal temperature, rather than air temperature, being raised to a specific degree.
In refinish terminology, the term “bake mode” is often used to describe the period of time required for curing the paint applied to the vehicle. During this phase, the control unit maintains the operator’s pre-selected temperature (up to 199°F) to obtain the standard 140°F surface temperature.
The “cool down” phase is the period of time required to cool down the heated vehicle and the booth. This phase starts automatically upon completion of the bake period, and can take as much as 30 minutes for a car.
When cured by heat, additional time may have to be allowed for the finish to reach its full hardness. The finish on cars fresh out of a cure cycle is still soft enough to be dented with a fingernail or scratched by buffers. The need for post-cure cut-and-buff can be dramatically reduced through diligent shop cleanliness and contamination control.
Downdraft airflow is generally accepted as the best type of airflow for a paint booth, and generally speaking this is correct. It does an excellent job of controlling overspray and contamination, and provides a safe, clean environment in which to paint. However, there is one limitation that downdraft airflow just cannot avoid. This limitation is the creation of ‘laminar air’ and ‘boundary air’. Laminar air is created as air passes in one direction over a solid object in a paint booth. Boundary air is a low-pressure layer of slow moving air immediately below the laminar air and above the surface of the vehicle.
When looked at under a microscope, even the most perfect paint jobs are not entirely smooth. They have tiny bumps, dips and ridges that are inperceptible to the naked eye. These tiny imperfections slow down the air enough to create a layer of slow-moving air referred to as the ‘boundary air’. During the paint drying process, this boundary air becomes saturated with water molecules from the paint, and limits the speed of evaporation that can take place. It is this boundary air that prevents the airflow from drawing water molecules out of the wet paint.
In order to achieve the fastest drying times possible, this boundary air must be disrupted and dispersed. This disruption is accomplished by creating turbulent airflow on the surface of the vehicle, which is what AdvanceCure does. It breaks up the slow-moving boundary air and rapidly speeds up the drying process.