Abstract
With the development of the plastic industry, the plastic foam sheet is widely applied. However, the further development of the plastic foam sheet is still limited by the drawback of the plastic foam sheet surface’s mechanical property. In this paper,using the plastic sheet’s surface thermal spraying technology, with the polypropylene and polyethylene sheet which was widely used in foam sheet as the matrix, and the iron and copper powder as the spraying material, through the thermal spraying method to improve the mechanical properties of the plastic sheet surface.
Based on the heat transfer theory and the law of energy conservation, creating a mathematical model of the heater's heating process, the final calculation is to determine when the substrate is polypropylene and polyethylene, the heater one’s temperature is 214℃ and 151℃, the heater one’s power is 3.3KW and2.7KW, the heater two’s temperature is 218℃ and 162℃, the heater two’s power is1.7KW. And according to the extrusion sheet’s width and thickness and the size of the heater, a heater bracket which can easily regulate the heater’s height and horizontal position and a conveyer roller which can make it more convenient to convey the plastic sheet is designed.
using the transient thermal analysis module of ANSYS software to simulate and analyze the temperature field in the plastic sheet’s thickness direction and finally determined the heating time is 60s when the plastic sheet was in transportation, so as to verify the reasonableness of the heater’s design, and after the experiment proved that the heated plastic sheet surface’s soften layer can achieve the required thickness.
On the basement of hydromechanics theory, based on the gas’s actual flow in the nozzle to establish mathematical model when the gas flowed in the nozzle during the spraying and calculate to determine the structure and size of the nozzle, and finally produced the required spraying device, according the experiment verified the spraying devices can form a good surface coating of plastic sheet.
Take the polypropylene and polyethylene foam material as substrate, using the iron and copper powder as spray material to carry on spraying experiment, and ultimately acquired a more ideal metal coating. And then carry on mechanical experiments to the plastic sheet before and after spraying, founded that the hardness, strength, wear resistance have a considerable increase.
According to the characteristics of the technology of polyolefin plastic sheet’s extrusion molding process, the thesis designed the appropriate heating and spraying devices. Through adjust the extrusion parameters, finally acquired dense metal coating on the plastic sheet surface, played a positive function to improve the performance of the plastic sheet surface and better to do “take plastic to replace steel”.
Key words: foamed sheet; heater; powder feeding; spray nozzle; ANSYS thermal analysis; thermal spray; surface properties
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