Abstract
The life time of some thermal sprayed coatings is limited. Flaking or partial removal of the coating reduces its protective effect. To allow further use of the component the coating has to be reworked before the part gets heavily damaged. The damaged coating must be removed with minimum impact on the surface of the component. Many removal methods as chemical, electrochemical or waterjet techniques have to be used with great care to prevent damaging of the substrate or are environmentally hazardous. An alternative technique which removes the coating selective with minimum impact on the substrate is the use of dry ice. Pellets of solid carbon dioxide are accelerated by means of compressed air. During the impact the carbon dioxide sublimates at a temperature of –78°C. The sublimation generates a large expansion (~600 times) of the carbon dioxide. The coating is strongly cooled while the shock wave of the sublimation destroys the cohesion. To support this process and to enlarge the thermal stresses in the coating a laser can be used. In this contribution the pellet velocity is measured and compared for three different dry ice jet devices by particle image velocimetry. Analysed parameters which are supposed to have an influence to the particle velocity are the mass flow of the compressed air, nozzle geometry and the working principles of the devices. The pellet velocity and the resulting kinetic energy are important process parameter. The results are used to optimise the laser assisted dry ice jet process.
