| Thermal spray technology constituted by coating material, spraying process and spraying equipment. And most of the coating material is present in the form of powder. As one core component of thermal spray system, it’s role is convey powder into the gun. The uniformity and stability in the process of powder feeding directly affect the performance of the coating.Screw powder feeder was based on the principle of screw conveyors and solid flow theory to achieve powder feeding function. In order to constitute a complete HVOF system which to accomplish spray job with the existing supersonic flame spray gun, the main control cabinet and cooling device, a prototype of screw powder feeder was developed by studying the key technology of screw conveyance.According to the functional requirements for powder feeder, the overall mechanical design of prototype of screw powder feeder, gas and circuit design and related components selection were completed. In order to further improve the uniformity of powder feeding in the process of screw conveyance, a serrated double thread screw was used. And the main parameters of screw designed were calculated. Chain drive was chosen as gearing because it has advantages of simple structure, smooth transmission, the average transmission ratio is high and absorbing cushioning. Virtual prototype assembly of powder feeder mechanical structure was completed to ensure reasonable structure design and no motion interference between parts. In order to protect the motor, the gas pressure switch was selected to ensure that carrier gas into the case before screw rotates. AC servo motor which was commonly used in material metering industry was used to drive the screw to ensure uniform rotation speed of the screw.As a key part of powder feeder, screw plays an important role in the entire process of powder feeding. Static analysis and modal analysis of screw were done by using finite element analysis software ANSYS Workbench14.5. The simulation results of static analysis showed that screw deformation that occured under the action of various force within the range of permit value. The simulation results of modal analysis showed that the designed screw speed was reasonable and the frequency corresponding to each mode wasn’t equal to the value of the outside frequency. It will not resonate. So the selected material of screw and design of the screw speed were reasonable.The test results showed that powder feeding accuracy of the prototype of screw powder feeder was within 5% when the amount of powder feeding was 30～60g/min by using NiCrAlY powder and WC-12Co powder which were commonly used in HVOF. The powder feeding parameters of NiCrAlY powder and WC-12Co powder were assured by studying the impact of carrier gas flow rate, screw speed and amplitude of the vibration on powder feeding rate. HVOF system consisted of prototype of the powder feeder, HVOF gun, the main control cabinet and cooling devices. NiCrAlY coating and WC-12Co coating were prepared by using the system.The powder feeding process during the test was continuous and stable. The error of coating thickness was within 10% by measuring and observing the cross-sectional shape of the sample. It can satisfy production requirements.The test results of prototype of screw powder feeder achieved the desired requirements. Its design is reasonable and it has practical value. |
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