How does tempering occur in flame spraying?

       The so-called tempering is the phenomenon that the flame during spraying goes from the nozzle to the inside of the spray gun until the acetylene tube burns back. Taking the SQP-1 wire flame spray gun as an example, when the spray gun switch is turned on 90° during ignition, the acetylene gathers on the outer ring of the nozzle, and is sprayed from the nozzle through the mixing chamber alone, but the pressure and flow rate are very low. When the switch is in the fully open position after ignition, oxygen is rapidly ejected from the nozzle, which makes the acetylene nozzle form a negative pressure and sucks the acetylene out. Oxygen and acetylene are mixed in a certain ratio (usually 1:1.25) through the mixing chamber, and then sprayed from the nozzle, making it a heat source for melting the spraying material. If the injection velocity of the mixture is less than the combustion velocity of the mixture,



That is, when the spray speed is slow and the burning speed is faster, the flame will inevitably fall back into the spray gun and the hose to produce backfire. When the seal of the mixed gas path components in the spray gun is not tightly sealed, it is also one of the reasons for the tempering. Due to operational reasons, such as insufficient air supply, overheating of the nozzle, heating and expansion of the mixed gas to increase the internal pressure, increasing the flow resistance of the mixed gas, the nozzle being blocked by molten metal or solid carbon particles, making it difficult for the mixed gas to flow out, etc. cause backfire. Improper handling after tempering may result in an explosion hazard.