Thermal spray - Overview

IMPORTANCE OF THE SURFACE MODIFICATON TEHNIQUES:

In the modern Industrial world, engineering components are prone to more rapid surface degradation due to mechanisms such as wear, oxidation, corrosion or failure under an excessive heat load. As a consequence, in an effort to achieve enhanced performance in terms of productivity, efficiency etc., surface modification technologies have been attracting a great deal of attention as they present a cost-effective way to combat degradation modes such as above without sacrificing the bulk properties of the component material. Thermal spraying is one of the most versatile coating technique and finds wide ranging applications in numerous industry sectors.

THERMAL SPRAY PROCESS

In the thermal spray processes, electrical, chemical or mechanical energy is used to produce a high velocity gas jet. The coating material is introduced into this gas jet, usually in powder form. Particle-gas interaction lead to heat and momentum transfer from the gas jet to the particles and these accelerated particles are sprayed onto the substrate surface. On impact, thermal and kinetic energies of the particles are used for the formation of splats. These splats adhere to the substrate, and subsequently to each other to form the coating.

BENEFITS OF THERMAL SPRAY COATINGS

DIRECT COST SAVINGS

• Very dense coatings (porosity less than 1%)
• No problem of hydrogen embrittlement like Hard chrome platting
• Increase in life of component.
• Reduction in maintenance costs.
• Decrease in equipment downtime.
• Increase in operating efficiency.
• Use of less costly material for bulk of component.

DESIGN IMPROVEMENTS

• Utilization of surface design engineering.
• Extending operating range of equipment.
• Improvement of manufacturing methods.
• Use of less dense base material.

Thermal spray processes available

• Detonation spray process
• HOVF spray process
• Cold spray process
• Plasma spray process
• Electric arc spray process
• Powder/ Wire/ Rod Flame spray process

Hvof Process

High Velocity Oxy Fuel Spray System

HVOF system used to develop wear resistant coatings for Aero engine, Power, Paper, Oil & refinery Sectors.

Process description

In High Velocity Oxy Fuel (HVOF) Spray System, Continuous combustion of the oxygen and fuel gas occurs in the combustion chamber and the resulting hot, high pressure gas is allowed to expand and accelerate through orifices into the nozzle. A carefully measured flow of powder is introduced axially into the nozzle, allowing sufficient heating and acceleration of the powder particles. The powder is heated and accelerated by the products of the combustion, usually to temperatures above its melting point and to velocities approaching supersonic velocities.

Sailent Features

• Coatings are very hard, clean and dense
• Coatings has low compressive stresses
• Coatings has very high bond strength
• Coatings has high surface finish
• Coating characteristics are superior than Flame spray , Wire arc and Plasma spray coatings

Typical Coatings

• Anti – Wear Coatings
• Anti - Corrosion Coatings
• Metallic Coatings

Electric Arc Wire Spray System

Electric arc wire spray system uses only electricity and atomized air to deposit metallic coatings.

Process description

In Wire arc spray system, two metallic wires are fed into a "gun" where they are electrically charged with opposing polarity and directed together to create an arc. The resulting heat (Nearly 4,000°C) melts the metallic wire, forming droplets that are propelled (Particle velocity will be up to 150 m/s) by compressed air or gas onto the work piece surface to form the coating.

Powder/wire/Rod Flame Spray System

The main advantage of Powder flame spray over the wire flame spray is that a much wider range of materials can be easily processed into powder form giving a larger choice of coatings such as metals, alloys, carbides, polymers and ceramic powders.

Spray and Fuse Process

Spray and Fuse coatings has virtually no porosity and bond strength comparable to welding.

Process description

Coating material in a powder form is fed into an oxygen-fuel gas combustion flame, melted and projected by the gas stream onto a prepared substrate. This process requires a fusing process after being sprayed. This is done by using a torch to bring the part up to approximately 1100 degrees Centigrade.

HORIZONTAL TIG WELDING EQUIPMENT

This Equipment very useful for carrying narrow groove welding to join thick sleeves, long tubes and to carry cladding on large components. The welding principle of this equipment is Tungsten Inert Gas Welding (TIG) principle.

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