Er. P. Sathiyaprathap

Introduction(thermal spraying) Various types Flame spraying High velocity oxy-fuel spraying Properties, benefits & application Introduction(hard facing) Hard facing process Gas metal arc welding and its advantages Applications

Thermal spraying techniques are coating processes in which melted (or heated) materials are sprayed onto a surface.coating The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame). Thermal spraying can provide thick coatings (approx. thickness range is 20 micrometers to several mm, depending on the process and feedstock), over a large area at high deposition rate as compared to other coating processes such as electroplating, physical and chemical vapor deposition.electroplatingphysical chemical vapor deposition

Coating materials available for thermal spraying include metals, alloys, ceramics, plastics and composites Coating quality is usually assessed by measuring its porosity, oxide content, macro and micro hardness, bond strength and surface roughness. porosityoxidemicro hardness bond strengthsurface roughness Generally, the coating quality increases with increasing particle velocities.

Flame spraying High-velocity oxy-fuel coating spraying (HVOF) Plasma spraying Warm spraying Wire arc spraying

Flame spraying is the oldest of the thermal spraying processes. A wide variety of materials can be sprayed by this process, and the vast majority of components are sprayed manually. Flame spraying uses the heat of combustion of a fuel gas (usually acetylene or propane) and oxygen mixture to melt the coating material, which can be fed into the spraying gun in two forms, either powder or solid wire/rod. The two consumable types give rise to the two process variants: powder flame spraying and wire flame spraying

... Schematic of Flame Spraying System

During the 1980s, a class of thermal spray processes called high velocity oxy-fuel spraying was developed. A mixture of gaseous or liquid fuel and oxygen is fed into a combustion chamber, where they are ignited and combusted continuously.fueloxygen The resultant hot gas at a pressure close to 1 MPa emanates through a converging–diverging nozzle and travels through a straight section. The fuels can be gases (hydrogen, methane, propane, propylene, acetylene, natural gas, etc.) or liquids (kerosene, etc.).

The jet velocity at the exit of the barrel (>1000 m/s) exceeds the speed of sound.speed of sound A powder feed stock is injected into the gas stream, which accelerates the powder up to 800 m/s. The stream of hot gas and powder is directed towards the surface to be coated. The powder partially melts in the stream, and deposits upon the substrate. The resulting coating has low porosity and high bond strengthporositybond strength

HVOF sprayed Tungsten Carbide / Chromium Nickel Coating (WC/20Cr7Ni )

Tribological (wear, resistance). Corrosion resistance. Heat resistance. Thermal barrier. Electrical conductivity or resistivity Abradable or abrasive. Textured surfaces. Restoration of dimension.

Comprehensive choice of coating materials: metals, alloys, ceramics, cermets and carbides. Thick coatings can be applied at high deposition rates. Coatings are mechanically bonded to the substrate— can often spray coating materials which are metallurgically incompatible with the substrate, e.g., materials with a higher melting point than the substrate.

Components can be sprayed with little or no pre- or post-heat treatment, and component distortion is minimal. Parts can be rebuilt quickly and at low cost, and usually at a fraction of the price of a replacement. Thermal spray coatings may be applied both manually and automatically.

Crankshaft reconditioning or conditioning Crankshaft Corrosion protection Corrosion Fouling protection Fouling Altering thermal conductivity or electrical conductivitythermal conductivityelectrical conductivity Wear control: either hardfacing (wear-resistant) or abradable coatinghardfacing abradable coating Repairing damaged surfaces Temperature/oxidation protection (thermal barrier coatings) Medical implants

Hard facing is a metalworking process where harder or tougher material is applied to a base metal. A Hard Facing Process consist of adding some cast material along the cutting area on the part surface. The additional material is from 1,3 mm to 1,6 mm thick and it is made of the following basic elements: CARBON: 4 % CHROMIUM: 30 % MANGANESE: 1,5 % SILICIUM: 4 % It is welded to the base material, and is generally takes the form of specialized electrodes for arc welding or filler rod for oxyacetylene and TIG welding.arc weldingoxyacetyleneTIG.

HF THICKNESS 0,4 mm to 1,8 mm

HF THICKNESS 1,3 mm to 1,6 mm

Hard facing may be applied to a new part during its production, or it may be used to restore a worn-down surface. Hard facing by welding is a surfacing operation to extend the service life of industrial components, pre-emptively on new components. Hard facing processes are very useful for improving wear and corrosion resistance to selected areas of machinery, such as cutting edges of earth-moving machinery. Common hard facing techniques include arc, torch, and other processes. Various types of welding processes are used including SMAW, FCAW, SAW, GMAW, GTAW

Submerged Arc Welding (SAW) – uses a continuous, consumable bare wire electrode, and arc shielding is provided by a cover of granular flux. Low-carbon, low alloy, and stainless steels can be readily welded by SAW. Electro gas Welding (EGW) – uses a continuous consumable electrode (either flux-cored wire or bare wire with externally supplied shielding gases) and molding shoes to contain the molten metal. Shielded Metal Arc Welding (SMAW) (stick) – arc is struck between the rod (shielded metal covered by flux) and the work pieces to be joined, the impurities rise to the top of the weld in the form of slag Gas metal arc welding (GMAW) – (metal + inert gas) electrode is continuously fed through the welding gun and is shielded by an inert gas

The heat is produced by an electric arc between the continuously fed metal electrode and the base metal. Both the base metal and the filler are melt. The weld area is protected by inert shield gases. Weldable metals: -steel carbon - steel low-allow - steel stainless - aluminum - copper and its allows - nickel and its allows - magnesium - reactive metal (titanium, zirconium, tantalum) Characteristics of the weld joint by GMAW (Modern Welding (p63))

- The method used to transfer the metal across the arc. -There are four metal transfer methods (short circuit, globular, spray, pulsed spray). -Each one requires different settings and has divers use interests. - The shielding gas. - The electrode size. - The electric parameters: voltage and current (the GMAW use the continuous current). - The feed rate (speed of filler supply). - The travel speed.

- Torch - Electric power source - Shielding gas source - Wire spool with wire drive control Equipment required for the GMAW (Modern Welding (p63))

- wide range of wieldable metals (high-quality welds on all commercially important metal) - easy to learn - can be used in all welding position - low in cost (the equipment costs less than 3000 dollars) - can be easily automated - rapid, economic - high level of productivity

Mining- shovel teeth, draggling chain Deep mining- conveyor parts, crushing hammer Construction and earth moving equipments- cutting edges, grader blade Drilling- drill bits, tool joints Processing equipment- screw conveyors, mixing and blending parts Agriculture- sugar mill roll, injectors