Role of Thermal Spray Coatings in Steel Industry

WHAT IS THERMAL SPRAY COATING : Thermal spray coating is the process of deposition of a thin layer of coating material on to a prepared surface for special surface properties. The coating material in either powder or wire form is melted in a heat source and then propelled at a high velocity to impact on to a prepared substrate to form a thin dense protective coating.
TYPES OF THERMAL SPRAY COATING PROCESSES : Based on the coating material form and the heat source the thermal spray coating processes are classified as … • Detonation spray coating • Plasma spray coating • Wire arc spray coating • Wire flame spray coating • Powder flame spray coating • HVOF spray coating
SPECIAL PROPERTIES PROVIDED BY THERMAL SPRAY COATINGS : Thermal spray coatings are used to achieve the following special surface properties .. Wear resistance - Abrasion resistance - Erosion resistance - Cavitation resistance - Adhesion resistance - Fretting resistance - Fibres & threads resistance Corrosion resistance - Atmospheric corrosion - Immersion corrosion Electrical properties - Conductive coatings - Resistive coatings Heat & oxidation resistance Abradable & abrasive coatings Restoration of dimensions
TYPES OF COATING MATERIALS : • Ceramics • Carbides • Cermets • Metals & Alloys
APPLICATIONS OF THERMAL SPRAY COATINGS IN STEEL INDUSTRY : Thermal spray coatings find wide applications in the steel industry due to its typical work environment. Different thermal spraying processes are used to apply coatings on different components considering the typical service conditions of the component. Steel industry, one of the most important infrastructure industries, is plagued by many problems. Heavy wear rates, corrosion and subsequent poor product quality are some of the major problems faced by the industry. Over a period of time it has been proven worldwide that coatings deposited with Detonation Spray Coating technology are most effective in meeting the challenging surface properties requirements of the steel industry.
ADVANTAGES OF DETONATION SPRAY COATING (DEE GUN) TECHNOLOGY : In this process the coating material in powder form is injected in the detonation of oxygen and fuel gas, where it gets melted and is propelled through the long gun barrel at very high velocities, to impact on the surface to be coated to form the coating. Due to the very high impact velocity, the resultant coatings are very dense ( porosity < 1 %), hard , wear resistant and have excellent adherence with the base material. The substrate temperature during detonation spray coating never exceeds 150° C and as such there are no metallurgical changes in the base material nor is there any distortion in the component.
PLASMATRON SOLUTIONS FOR STEEL INDUSTRY : Here we consider some of the most critical applications from cold rolling, annealing and galvanizing departments of the steel industry and the coatings to increase the service life of these components. The approach is to consider the requirement and the solution thereof.
BRIDLE ROLL : The most important bridle roll surface requirements are. • Resist material pick up between the roll and the coil. • Keep the roll surface free from wear / defects so that these are not transferred to the coil • Resist working temperature (about 550°C) without losing its hardness, oxidation and other adverse effects of high temperature. • The capacity to grip the coil with controlled friction and surface finish. It should not allow any coil slippage, which leads to marks on the coil surface.
PLASMATRON SOLUTION : DEE-GUN APPLIED TUNGSTEN CARBIDE COATING : Special Tungsten Carbide coating deposited by the Detonation Spray Coating (Dee-Gun) process. Detonation spray coating process yields the most tenaciously bonded coatings which are very dense ( porosity < 1 %) and as a result are highly wear resistant. The as sprayed texture of the coating is quite fine and can further be finished as per requirement. Normally the surface finish for bridle roll is kept between 2 – 5 microns Ra Due to this high wear resistance, the original surface profile of the bridle roll is maintained over a longer period as compared to hard chrome plated or similarly treated bridle rolls. This results in no slippage of the coil and leads to better productivity and product quality. The coating composition is such that the coating resists the working temperature, avoid oxidation and not lose its hardness. Because of the galling resistance, high hardness and inertness of the carbides there is no material pick up between the roll and the coil, resulting in good consistent product quality. Coating Properties : Hardness : 1150 Hv Tensile Bond Strength : > 10,000 psi Thickness : < 0.1 mm Porosity : < 1 %
FURNACE ROLLS : Furnace rolls surface requirements are … • Resist oxidation and wear which lead to spalling , which reduce the roll dimensions, resulting in low roll life • Resist material pick up between the roll and the annealed coil • Should not allow any slippage of the coil, which occurs on account of non-uniform wear.
PLASMATRON SOLUTION : DEE-GUN APPLIED COATINGS : Depending of the location of the rolls in the various temperature zones of the furnace, PLASMATRON offers two different coatings for furnace rolls .. • Chromium Carbide Coating • High Temperature Alloy with Cermet Additions Chromium Carbide Coating This Dee-Gun deposited chromium carbide coating has the following special properties • Wear resistance • Temperature resistant (up to 750°C approx.) • Oxidation and spalling resistance • Cracking resistance at operating temperatures and normal cycling • Resists material pick up between the roll and the coil • No reaction with steel or alloying elements Coating Properties : Hardness : 775 Hv Tensile Bond Strength :> 10,000 psi Thickness : < 0.1 mm Porosity : < 1 % High Temperature Alloy with Cermet Additions This Dee-Gun applied coating exhibits the following properties … • Wear resistance • Temperature resistant (up to 1100°C approx.) • Oxidation and spalling resistance • Cracking resistance at operating temperatures and normal cycling • Resists material pick up between the roll and the coil • No reaction with steel or alloying elements Coating Properties : Hardness : 800 Hv Tensile Bond Strength : > 10,000 psi Thickness : < 0.1 mm Porosity : < 1 %
SINK (POT) ROLLS : Sink roll immersed in the molten zinc bath is affected by the dross picked up by the coil. Also it is attacked by the molten zinc leading to pitting and build ups. All these factors affect the coil surface.
PLASMATRON SOLUTION : DEE-GUN APPLIED CARBIDE COATING The carbide coating selected for the sink roll exhibits the following properties .. • Resistance to molten zinc • Resistance to wear by dross • Resistance to material pick up The life of the sink rolls thus coated can be expected to increase multifold as compared to uncoated rolls. Coating Properties : Hardness : > 1000Hv Tensile Bond Strength : > 10,000 psi Maximum Temperature Resistance : 550°C Thickness : < 0.1 mm Porosity : < 1 %
Conclusion : It is now possible to overcome various wear & corrosion problems faced by the steel industry with Detonation Spray (Dee-Gun) coatings. In addition to the coating solutions mentioned above, the company is in process of developing many other challenging coating solutions for steel industry components. Associated Plasmatron Pvt. Ltd., an ISO 9001 – 2000 certified thermal spray coating company offers solutions to these wear problems faced by the steel producers. Established in 1988, the company has proved its competence in providing feasible solutions to various wear & corrosion problems faced by the industry. As part of its expansion program PLASMATRON has introduced the DETONATION SPRAY COATING (DEE-GUN) technology. With availability of this Detonation Spray Coating technology PLASMATRON now provides comprehensive solutions to the wear and corrosion problems faced by the steel industry.