Coating flame-spraying

Although the above applications consume over 90% of the polyethylene produced there are a number of other important end-uses. Filament for ropes, fishing nets and fabrics are an important outlet for high-density polyethylene powdered polymers are used for dip coating, flame spraying, rotational moulding and other outlets, whilst fabricated sheet is important in chemical plant. 

Extrusion coating Flame-spray coating Flocking Flow coating Fluidized-bed coating Friction calendaring... 

See also coating spray, airless spray, electrostatic spray coating, flame spray coating and plasma-spray coating. 

Flame spray metallising is widely used for the protection of metal against corrosion, especially for in situ protection of stmctural members. The principal metal used for spraying of plastics is sine. Aluminum and copper are also used. If the distance from the part is too great, the zinc solidifies before it touches the part and adhesion is extremely poor. If the molten zinc oxidizes, conductivity and adhesion are poor. If the distance is too short, the zinc is too hot and the plastic warps or degrades. These coatings are not as dense as electrically deposited coatings because of numerous pores, oxide inclusions, and discontinuities where particles have incompletely coalesced. 

Powder Coating. Nylon-11 and nylon-12 are used in powder form for anticorrosion coating of metals. Dip coating and electrostatic and flame spraying are used. Dip coating, which involves immersing a preheated article into fluidi2ed nylon powder, is most suitable for automation. 

Flame spraying is no longer the most widely used melt-spraying process. In the power-feed method, powders of relatively uniform size (<44 fim (325 mesh)) are fed at a controlled rate into the flame. The torch, which can be held by hand, is aimed a few cm from the surface. The particles remain in the flame envelope until impingement. Particle velocity is typically 46 m/s, and the particles become at least partially molten. Upon impingement, the particles cool rapidly and soHdify to form a relatively porous, but coherent, polycrystalline layer. In the rod-feed system, the flame impinges on the tip of a rod made of the material to be sprayed. As the rod becomes molten, droplets of material leave the rod with the flame. The rod is fed into the flame at a rate commensurate with melt removal. The torch is held at a distance of ca 8 cm from the object to be coated particle velocities are ca 185 m/s. 

The expander turbine is designed to minimize the erosive effect of the catalyst particles stiU remaining in the flue gas. The design ensures a uniform distribution of the catalyst particles around the 360° aimulus of the flow path, optimizes the gas flow through both the stationary and rotary blades, and uses modem plasma and flame-spray coatings of the rotor and starter blades for further erosion protection (67). 

Zinc, aluminum, nickel alloys, cobalt alloys and tungsten carbide are applied for sprayed coatings, which are slightly porous. Flame-sprayed zinc coatings are used for corrosion protection of steel and provide similar properties for galvanized coatings. 

Flame sprayed molybdenum articles have poor corrosion resistance, no doubt owing to the porosity of the coating. However, modern plasma spraying techniques produce a dense coating and this should lead to more widespread use of clad materials such as molybdenum clad steel where the clad product should have the same corrosion resistance as the solid material. 

Fischer, K. P., Thomason, W. H. and Finnegan, J. E., Electrochemical Performance of Flame Sprayed Aluminium Coatings of Steel in Water , Paper No. 360, Corrosion/87, San Fransisco, USA, March (1987)... 

Corrosion Tests of Flame Sprayed Coated Steel-19 Year Report, American Welding Society. Miami (1974)... 

Copper coatings are usually applied by electrodeposition (Section 12.1), although for more limited purposes electroless or immersion deposits are used. Less frequently, copper may also be applied by flame spraying. ... 

Finely divided aluminium powder or dust forms highly explosive dispersions in air [1], and all aspects of prevention of aluminium dust explosions are covered in 2 recent US National Fire Codes [2], The effects on ignition properties of impurities introduced by recycled metal used to prepare dust were studied [3], Pyrophoricity is eliminated by surface coating aluminium powder with polystyrene [4], Explosion hazards involved in arc and flame spraying of the powder are analysed and discussed [5], and the effect of surface oxide layers on flammability was studied [6], The causes of a severe explosion in 1983 in a plant producing fine aluminium powder are analysed, and improvements in safety practices discussed... 

Flame-retardant silicone rubber, 22 584 Flame spray coatings, 5 665 Flame temperature, 12 322 Flame temperature, 7 443 Flame throwers, 5 824 Flame working, of vitreous silica, 22 415-416... 

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