The operating conditions of materials in aggressive environments inevitably make users think about the special protection of target objects and structures. This can be construction, production, as well as domestic technical and other objects that require resistance to hostile influences. One of the most effective ways to solve this problem is cladding. This is one of the methods for the external coating of parts and structures, which in our time is undergoing a new round of development.
Technology Overview
The main purpose of cladding is to create a coating on the surface of the workpiece, which could provide the protective functions specified by the project. Among the latter can be called refractoriness, biological resistance, frost resistance, etc. In some cases, new properties are added, such as insulating qualities or increasing electrical and thermal conductivity. What is cladding in terms of practical implementation?
This is the process of building up new technological and functional layers on the surface, which can be performed in different ways. It can also be a direct coating or overlay, but the fundamental difference is precisely the way the layers are formed. Classical approaches to cladding presuppose thermomechanical formation of a protective shell, but today, with the advent of new materials, the methods of structural arrangement of protective coatings are changing.
Cladding Features
To form on the surface of the conditional product a functional coating allows ordinary paint with one or another set of properties. Cladding also refers to external protection methods involving intrusion into the structure of the target surface. This effect of the merger of the functional layer and the base material is just achieved by the thermal effect, which can be expressed in different forms. For this reason, cladding of metal surfaces is often accompanied by temperature-time welding with subsequent deformation of the workpiece.
Another fundamentally important feature of cladding is its layering. The structure is formed not by a homogeneous layer of one or another protective material, but by several heterogeneous layers, which have different functional directions. Moreover, part of the layers can have a general functional purpose (fire resistance, temperature resistance, biosecurity), and the other part performs special tasks inside the coating structure, for example, creates an adhesive base for bonding cladding layers.
Cladding Technique
The cladding operation can be performed both in a separate format and within the framework of the general technological process of production or processing of a part. In both cases, the basic method for implementing the technology involves layer-by-layer deposition of alloys on the target surface. For metals, this operation is performed during hot rolling, drawing or pressing. At the stages of formation connection, cladding technology provides for thermal deformation, under which conditions are created for the diffusion of the hot workpiece.
In this way, whole groups of metals can be superimposed and fused, including steel, copper, aluminum, corrosion-resistant alloys, etc. At the current stage of technology development, the inclusion of polymer independent layers and modifiers that improve the individual properties of the applied coating is also practiced.
Cladding tape application
In order to optimize the cladding process, the concept of laying the finished multilayer coating was developed. It is represented by a bimetallic tape, which contains in its structure several heterogeneous layers obtained as a result of cold rolling. The basis of this blank is made up of both ferrous metals and composite materials, which are used in pure form by engineering, electrical, food, chemical and other industries.
Low-carbon steel is almost always used as the basis for the tape, due to which the main cladding process is carried out - this is a kind of intermediate binder, the melt of which connects the workpiece and the functional coating of the tape. By the way, the differences of multilayer tapes of this type are not limited to the approach to the structural structure of the coating and cover the range of tasks of new layers. On the cladding shell, work units and parts, such as current-carrying circuits, tips, bimetallic contacts, disconnecting knives, electrical clamps, etc., can initially be placed.
Laser cladding technique
A promising area for the technical implementation of cladding with the principles of gas welding. A laser beam is used as a thermal source, which ensures the melt state of the workpiece and the active material. The raw material for laser cladding is usually powder, which can be compared with the flux used in gas welding. This is the basis of the melt, forming a thin functional layer as a result of laser exposure. As for gas mixtures, their supply plays an auxiliary role to protect the working area from the negative effects of oxygen.
Powder Cladding
Bulk mixtures of chromium, tungsten and nickel can also be considered as an independent base for cladding, optionally associated with laser melt technology. Combined powder mixtures specially selected for a specific set of functions are applied to the metal by chemical cladding. This is a transport reaction of particle transfer in an alkaline ionic melt.
The process of coating with molten powder is carried out directly for 30-40 minutes at a temperature of about 700 ° C. The complexity of this technology in production conditions is the need to connect large-sized specialized equipment with crucibles and high-temperature furnaces.
Cladding restoration
Like many other types of coatings, the cladding base collapses over time, requiring restoration or repair. Partial correction of multilayer coatings is carried out by means of gas thermal, electrothermal or plasma spraying. The base for spraying may be the same flux of composite materials or metal alloys. Liquid-reducing cladding agents are also becoming more widespread.
These are special compounds that contain ultrafine or soluble metals, their compounds or alloys. After application under the influence of certain temperatures or chemical reactions, the solution polymerizes, and after a few hours the updated coating can be put into full operation.
Conclusion
In many areas of the national economy, industry, and construction, a special modification of the materials used is required, however, due to economic and organizational conditions, not all methods for improving the characteristics of the target stock can be used. Modern cladding methods also remain unavailable to many potential consumers due to the high cost and technological complexity of their implementation.
On the other hand, the example of a multilayer tape shows that it is quite possible to simultaneously increase the performance of the coating and simplify the process of its formation on the surface of the final product. However, such innovations so far are found only in certain industries related to the production of electrical products.