Metal spray rebuilding
Engineering components can fail due to one or a combination of several mechanisms. They are: wear, corrosion, fretting, galling, erosion, cavitation or high temperature oxidation. In the majority of the cases, the component may be structurally sound but its surface properties have deteriorated or the clearances between mating parts have increased. The cost of replacing the part is usually much greater than the cost of the part itself. The increased cost of maintenance because of unwanted shut downs reduces profits.
The base material is usually chosen for its structural properties such as tensile strength, elasticity, ductility, density etc. But when the parts move relative to other mating parts, their surface properties such as hardness, galling resistance etc become crucial. It is nearly always impossible to match the combination of the structural properties and surface properties in a single metal or alloy. This is where Metal Spray surface coating technology provides solutions by combining various base materials and coatings to give optimum core and surface properties. Metal Spraying does not produce distortion and does not damage the base metal as in welding.
Sometimes technological progress and manufacturing efficiency may be constrained solely by surface requirements. For example, the fuel efficiency and power output of gas turbines or diesel engines are limited by the ability of key components to withstand high temperatures. However, it is often impractical, inefficient or uneconomical to manufacture components from a bulk material simply for its surface properties - far better to use a cheaper, more easily formed underlying material and coat it with a suitable high performance film. The resulting product performs better than the original and may be cheaper..
Surface engineering is relevant to all types of products. It can increase performance; reduces costs and control surface properties independently of the substrate, offering enormous potential for:
- Improved functionality
- The solution to previously insurmountable engineering problems
- The possibility to create entirely new products
- Conservation of scarce material resources
- Reduction of power consumption and effluent output Thermal spraying processes are used in all industry sectors for component protection and reclamation. It is a well established technology for applying wear, corrosion and heat resistant coatings in Marine, Steel, Power Generation, Petrochemical, Offshore and Aerospace Industries.
Benefits of Thermal Spraying: Worn shafts can be rebuilt to original size without distortion or loss of strength. Coating alloy is vastly superior to the base metal. Hence refurbished shaft lasts two or three times longer than a new replacement. Ceramic Coatings on shafts increase their wear resistance and reduce corrosion. Repairs can be done in hours instead of waiting for days for replacement parts. Very wide range of coatings solve problems of erosion, corrosion, wear and high temperature. Components can be sprayed with no pre- or post-heat treatment. Hence parent metal microstructure is unaffected. Component distortion is minimal. Parts can be rebuilt quickly and at low cost, and usually at a fraction of the price of a replacement. By using a premium material for the thermal spray coating, coated components can outlive new parts.
Metallising is a fast technique for salvaging worn parts. A shaft, worn beyond use at the bearing journal or seal area can be brought back to its original size within hours, using a high grade alloy steel. It is vastly superior to welding because there is no risk of cracks or distortion. The shaft never gets hotter than 100 C through out the process.
Metals with melting points as low as lead (333°C) and as high as molybdenum (2500°C) can be sprayed. Metallising is performed without overheating the basic part (generally less than 100°C) which avoids distortion. It is an excellent method to salvage worn or corroded parts. The repairs can be done in hours/ days at a fraction of the cost of a new replacement part. Delivery of new parts may take weeks.
Almost any material available in wire form may be applied. Examples are stainless steels, Babbitt, bronzes, molybdenum, aluminium, etc. The composition of sprayed metal is chemically and physically different from the original wire. Generally it is harder and more porous than its equivalent in cast or wrought form.
This combination of hardness and microscopic surface porosity which tends to hold lubricants makes the metallised coating an ideal bearing surface, much superior to the same metals in its original form. Another enhancing feature of metallising is the fact that almost any thickness of overlay may be applied with very good results.