Now, let’s explore each of them in details.
What is overlay welding technology?
Case study: as a vital spare part of steel rolling mill, in the process of steel rolling consumption, China’s annual production of steel has more than 600 million tons, the value of the consumption of rolls in the 17 billion yuan. Therefore, the use of welding methods to repair the old rolls and extend the service life of the rolls has become China’s steel rolling enterprises to reduce production costs and improve the economic efficiency of a necessary measure. When the original rolls used to the end of the period, can be welded repair. After welding repair of the rolls, with low cost, long life, good results, etc., by the steel rolling enterprises generally welcomed, but also in line with China’s energy-saving, clean production, the fundamental national policy of circular economy. The figure below shows the use of welding methods to repair the old rolls.
With the increasing progress of science and technology, a variety of products and machinery and equipment gradually to large-scale, high-efficiency, high-parameter direction, the reliability of the product and the use of performance requirements are increasingly high. Surface overlay welding of materials as a branch of welding technology is to improve the performance of products and equipment, an effective means of extending service life. In addition to metals and alloys, ceramics, plastics, inorganic non-metals, and composite materials can be used as overlay alloy materials. Therefore, overlay welding technology can make the surface of the parts obtain wear resistance, heat resistance, corrosion resistance, high temperature resistance, lubrication, insulation, and other unique properties. Currently, overlay welding technology is widely used in machinery manufacturing, metallurgy, electric power, mining, construction, petrochemical, and other industrial sectors.
Overlay welding characteristics and classification
(1) Characteristics of overlays
overlay welding is a process in which materials with specific properties are deposited on the surface of workpieces using welding methods. The purpose of overlay welding is different from the usual welding methods, not to join the workpiece. But to modify the workpiece’s surface to obtain a deposited layer with unique properties such as wear resistance, heat resistance, corrosion resistance, etc., or to restore the workpiece due to wear or machining errors caused by dimensional deficiencies. Both of these applications are referred to as repair and enhancement in surface engineering. The figure below shows the surface of a part after overlay welding.
The advantages of the overlay welding method over other methods of surface treatment are.
(1) the combination of the overlay welding layer and the base metal is a metallurgical combination, combined with high strength, excellent impact resistance.
(2) the composition and properties of the metal of the overlay welding layer are easy to adjust. Generally, the electrode arc welding electrode or flux-cored electrode to change the formula is very convenient; you can design a variety of alloy system, to adapt to different working conditions.
(3) the thickness of the cladding layer, the general thickness of the cladding layer can be adjusted in 2 ~ 30mm, more live together in severe wear and tear conditions.
(4) cost savings, a good economy. When the workpiece matrix is made of ordinary materials, surface with high alloy overlay welding reduces the manufacturing cost and saves a lot of precious metals. In the workpiece repair process, the reasonable choice of overlay welding alloy, the surface of the damaged workpiece to be overlaid welding repair, can significantly extend the service life of the workpiece, extend the maintenance cycle, reduce production costs.
(5) The overlay welding technology is through the welding method to increase or restore the size of parts or parts surface with unique properties of the alloy layer, so those who can master the welding technology are not very difficult, operable durable.
(2) Classification of overlay welding
overlay welding is a type of fusion welding technology, and any method that falls under the category of fusion welding can be used for overlay welding. The classification of commonly used overlay welding methods is shown in the table. Currently, the most widely used are electrode arc welding and oxyacetylene flame overlay welding.
Overlay welding applications
As a branch in the field of welding, overlay welding technology has a wide range of applications. Overlay welding technology is used in almost all manufacturing industries. Such as mining machinery, conveying machinery, metallurgical machinery, power machinery, agricultural machinery, automotive, petroleum equipment, chemical equipment, construction and tools, molds and metal structural components for the manufacture and repair. The overlay welding can repair the appearance of substandard metal parts and products, or manufacturing bimetallic parts. The use of overlays extends the service life of components, reduces costs, improves product design, and is particularly essential for the rational use of materials (especially precious metals).
According to the application and the working conditions of the workpiece, overlay welding technology is mainly manifested in the following areas.
(1) Restoration of workpiece size overlay welding
Undersized workpieces due to wear and tear or machining errors are common problems encountered in factories and mines. Overlay welding method to repair the workpiece mentioned above is a standard process, after repair of the workpiece, it can not only be regular use. In many cases, the original workpiece can also exceed the service life because the new technology, new materials for overlay welding repair, can significantly improve the performance of the original parts. Such as cold rolls, hot rolls, and profiled rolls surface welding repair, agricultural machinery (tractors, farm vehicles, transplanters, harvesters, etc.) wear parts of the overlay welding repair. According to statistics, the amount of overlay welding alloy used to repair the old workpiece accounted for 72.2% of the total amount of overlay welding alloy.
(2) wear-resistant, corrosion-resistant overlay welding
Wear and corrosion are the main factors that cause the failure of metal materials, to improve the wear resistance and corrosion resistance of the surface of metal workpieces to meet the requirements of working conditions and extend the life of the workpiece. The surface of the workpiece can be surfaced with one or more layers of wear or corrosion-resistant coatings. The choice of materials with different properties for the base and surface overlay welding of the workpiece allows the creation of bimetallic workpieces. As only the surface layer of the workpiece with the required wear-resistant, corrosion-resistant, and other unique properties, so give full play to the role of the material and working potential and save a lot of precious metals.
(3) Manufacture of new parts
Bimetallic machine parts with integrated performance can be produced by overlay welding an alloy on a metal substrate. The base of the piece and the overlay alloy layer have different properties and can meet the two’s diverse performance requirements. This allows the full working potential of the material to be utilized. For example, the turbine blade, matrix material for carbon steel, may occur cavitation part (more in the edge back lower half of the section) overlay welding a layer of stainless steel, making it resistant to cavitation of the bimetallic blade. In the manufacture of metal abrasives, matrix requirements are strict, choose relatively cheap carbon steel, low alloy steel manufacturing. And the blade requirements of high hardness, wear resistance, wear-resistant alloy overlay welding in the mold blade parts can save! The consumption of large amounts of precious alloys significantly extends the life of the tooling.