Tham khảo tài liệu 'coatings technology handbook episode 3 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 101-2 Coatings Technology Handbook Third Edition zinc oxide surface as the zinc layer becomes thinner. The white zinc oxide has substantial water solubility and washes away in rain. The zinc surface is often painted to give protection against these losses. Flame Plasma Spray Although all the flame and plasma spray processes project liquid metal droplets through the air to the substrate each starts with a solid metal wire or solid molten powder. The solid is taken into a device which heats it to the molten state breaks it into microscopic droplets and propels the droplets at the substrate. Longo edited a reference book on this The flame or thermal spray uses a modified oxyacetylene torch as the heat source. After the flame has been adjusted to its hottest additional compressed air is blown into the flame. The wire or powder is then fed in via a funnel and the blast of liquid metal particles is pointed at the substrate. The plasma spray uses an electric arc as the heat source to melt the wire or feed powder into the compressed airstream. The distance between the molten metal s origin and the substrate will determine the type of coating obtained. The close approach of the nozzle means that most particles will hit the substrate surface as a liquid. Many will stick and transfer their heat to the substrate but some particles will bounce off. If the nozzle is further away the smaller liquid particles will solidify and bounce off the substrate while the larger particles will still stick. If the nozzle is too far from the substrate none of the particles will stick because they will have cooled too much. Losses from bounce-off or from premature cooling will be on the order of 25 of the weight of the metal sprayed. The metals most commonly sprayed include copper zinc iron and aluminum. Alloys and even metal oxides can also be sprayed provided there is enough heat in the flame to make the particle soften. Since the sprayed metal is of lower density than the .
