Cooling requirement for thermal spray equipment: With a high power input to the various processes and high temperatures resulting from the heat source (e.g. fuel, plasma) cooling of the nozzle (and other equipment) is crucial for a number of thermal spraying processes. Heat is removed from the nozzle, the anode etc. by means of water. Proper cooling leads to a high process stability regarding in general avoidance of clogging at the nozzle, avoiding damage to nozzle or anode by melting and considering influence from the boundary layer at the gun's inner surface on the trajectory of the powder that is injected into the gun. Proper cooling in this case is an intersection of mainly the parameters: coolant temperature and temperature stability, pressure and the "water quality" in terms of dissolved solids or hardeners. Temperature should be high enough to avoid condensation at any surface, the pressure high enough to avoid local boiling and the water should be kept "soft" enough to avoid lime precipitation and - for the plasma process - have a conductivity that will not lead to any short circuit. Although "city" water is widely available, there are some reasons to not use it for the cooling of thermal spray equipment. Temperature varies with the seasons and depending on the origin of the water, dissolved solids might lead to an inferior quality in terms of scaling of the heat transfer surfaces in the gun. Finally, using city water is not favorable in terms of environmental protection, sustainability and also cost need to be factored in.
展开▼
