THERMAL SPRAY SYSTEM
FAMILIARIZATION WITH THERMAL SPRAY SYSTEM by MEHUL N. DAVE
INTRODUCTIONWear and Tear caused due to abrasion, corrosion and impact cause damage of billions of money every year worldwide, could be avoided if the proper preventive measure of wear and corrosion protection were taken. These preventative measures also mean precautions to regenerate the equipment, which means repair and re-integration into the economic cycle.MAJOR INDUSTRIES SERVICEDSteel IndustriesPaper PlantsThermal ,Hydro Power PlantsRefineriesSugar IndustriesChemical And Fertilizers PlantsCement PlantsMining Industries And Equipment ManufacturersOEMs Of Steel, Power, Cement,General Engineering Industries
ApplicationsCirculating Fluidized Bed Boilers (CFB) Pulverized Coal Fired Boilers Biomass Boilers Black Liquor Recovery Boilers Digesters Evaporators Flash Tanks Process Vessels Tanks Roller Journal/Shaft Pump Sleeve Steel Structures Dimensional Restoration
WEAR
Wear is the progressive damage, involving material loss, which occurs on the surface of a component as result of its motion relative to the adjacent working parts.
OCCURRENCE OF WEAR DEPENDS ON
Geometry of the surface Applied load The rolling and sliding velocities Environmental conditions Mechanical, Thermal, Chemical and Metallurgical properties
Physical, Thermal and Chemical properties of the lubricant
METHODS TO IMPROVE WEAR RESISTANCE
Geometry of the surface Alloying Heat Treatment Weld Overlays Surface Coatings (1) Cold Repair Products (2) Thermal Spray
PROBLEMS
Erosion:- Erosive nature of sorbent Lime stone in fuel particles at high velocity go and hit the combustor major up to one meter & at the corners of boiler at 18 to 22 meter elevation above refractory transit zone during the process of combustion leads to sever erosion of combustor tubes. This causing tubes failure at early stage.
WHAT IS THERMAL SPRAYThermal spraying, also known as metal spraying or metallizing is a surface engineering / coating process where a wide range of metals, carbides and ceramics can be applied (sprayed) onto the surface of a component.
CONVEYANCE TECHNOLOGY OF THERMAL SPRAY
Oxygen/Acetylene Wire & Powder Process
TWIN Wire Arc Spray Process
Plasma Spray Process HVOF (High Velocity Oxy-Fuel)
TWIN Wire Arc Spray Process
Two wires of desired materials act as electrodes when they're fed thru a spray gun. The gun is connected to a high-current (DC) power source to facilitate an arc between them. An air stream thru the back of the gun atomizes and propels the molten particles towards a prepared surface. With adjustable parameters including voltage and amperage arc temperatures can reach 5000C, enough to melt any material, at the same time the part surface remains cool. The process is considered energy efficient because all of the input energy is used to melt the spray materials.
SCHEMATIC OF TWIN WIRE ARC SPRAYING SYSTEM
Steps of TWASSurface preparationThermal sprayingSurface preparation
Alumina Al2O3 Grit Blasting (16 Grit)RLA (roughness value = 50 before blasting, approx 250 after blasting of water wall tubes)This stage involves exposure to high velocity Alumina grit particles. This stage is essential to remove the worn out tube particles and to judge the adherence of the coating on the Boiler tube material.This also enables removing corrosive media from the tubes. Alumina Grit Blasting is done by projecting a stream of Alumina Grit with high pressure compressed air.Blast cleaned steel surfaces shall not be touched by bare hands.Image of surface preparation/Blasting
ALUMINA GRIT IMAGES
ALUMINUM GRIT BLASTING
BEFORE BLASTING TUBE
FURNACE AREA WERE COATING APPLY
Location where coating process carriedout
Thermal sprayingArmour 63 Twin wire Arc Spray CoatingChemical Composition: Fe Bal C