ISO 14917:2017 pdf free

ISO 14917:2017 pdf free.Thermal spraying一Terminology, classification
Injection of the suspension (radially or axially) into the spray gun depends on its construction principles;axial injection can be more easily realized for HVOF processes. The general principle is that the liquid is fragmented through an atomization process into small droplets. The liquid is then evaporated and the resultant particles are melted or partially melted and accelerated onto the substrate where they will form the coating. These fine particles show a different behaviour concerning splat formation as compared to traditional thermal spray materials. See Figure 5.
In detonation spraying, the gun contains a chamber into which certain quantities of a powder are injected. The gas mixture in the chamber is detonated at controlled intervals at frequencies of a few Hertz. This creates a hot, high velocity gas stream that heats the powder to its plastic or partially or completely molten state and accelerates the particles as they leave the gun barrel.
The detonation gun consists of the barrel and the gun chamber. The injected gas and powder mixture are ignited by an electric spark. The resulting shock wave generated in the barrel accelerates the particles, which are further heated in the flame front and are propelled in a directed jet onto the prepared substrate. Nitrogen is used to flush clean the gun chamber and barrel after every detonation.See Figure 6.
In the cold spraying process, a gas (nitrogen or helium) is accelerated to supersonic velocity in a de-Laval type nozzle. The acceleration is driven by letting the gas expand from very high pressure (up to 50 bar) to the surrounding atmosphere. The spray material is injected into the gas jet in powder form upstream of the nozzle and then propelled with high kinetic and relatively low thermal energy onto the substrate. Above a certain particle velocity which is characteristic of the respective spray material,the particles form a dense and solid adhesive coating upon impact. External heating of the gas jet, e.g.in an electric-heated continuous heater, increases the flow velocity of the gas and also the particle velocity. The related rise in particle temperature assists the deformation upon impact. However, the gas temperature is clearly below the melting temperature of the spray material, which means the particles
cannot be melted in the gas jet.ISO 14917 pdf download.