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Surfacing coatings - a process of coating the molten material onto a heated surface to the melting temperature of the recoverable parts.
Coatings produced by welding , characterized by the absence of pores , high values of elastic modulus and tensile strength. Bond strength of the coating to the substrate is commensurate with the strength of the workpiece material .
If the mechanical production surfacing used to improve the wear resistance of the rubbing surfaces , the repair production mainly for subsequent remediation of the location, shape and size of worn parts . Reconstructive surfacing while also provides a new surface properties : corrosion , erosion , cavitation . abrasion , heat resistance , etc.
Win complexity of welding and surfacing is ~ 70% of all ways of creating repair blanks when restoring items. Surfacing worn surfaces occupies a leading position due to its versatility .
Surfacing methods are divided into groups depending on the species used heat sources , and the nature of the doping method of protection from the effects of the formed coating of oxygen and nitrogen in the air .
Arc welding has many kinds . In their classification into account the following classification criteria :
- The level of mechanization (manual , semiautomatic, automatic );
- Kind of applied current ( DC, AC , pulsed , special characteristics);
- Type of electrode ( consumable , non-consumable );
- Electrode polarity at DC (direct , reverse );
- Form of an arc ( direct, indirect );
- Mode (stationary or non-stationary );
- Way to protect the area from surfacing air atmosphere ( in shielding gases , water vapor , liquid , submerged arc , combined) ;
- Doping of weld metal ( coated electrodes , flux, electrode material , combined) .
Arc welding is most prevalent in the repair of machines coating methods . This method is compared with the other by methods of creating the repair pieces allows to obtain layers with high productivity of almost any thickness and of different chemical composition of the high physical and mechanical properties. Hardfacing coating deposited on the cylindrical surface of a diameter > 12 mm.
Technological features arc welding is used to loosening unwanted related phenomena, such as the oxidation of the metal , nitrogen absorption , burning dopants and heating the material above the details of phase transformations . These phenomena lead to a reduction in the strength of the weld heat treatment of the material breach , three-dimensional, structural and phase changes and warpage parts. Stirring base materials and coatings degrades its properties .
For arc surfacing used mainly melting electrodes are . Non-consumable carbon electrodes with the introduction of the filler material used in arc welding sheet steel and lead and hardfacing pochvorezhuschih details. Welding with non-consumable tungsten electrode is used for TIG welding.
Arc welding Submerged in fact, is the development of a manual on - melting electrodes coated with thick quality . Electroslag cladding characterized in that the heated surface of the part of the flux of the molten bath formed , in which the electrode is inserted , and the workpiece and the electrode voltage is applied . The current flowing from the electrode through a molten slag parts , generates heat sufficient to melt the slag and the metal electrode .
ESHN used to prepare bimetallic products and recovery of worn surfaces of large parts subject to wear > 10 mm. Thus reduced road wheels tracked vehicles , track link , operating in abrasive environments , tools , gears, transmissions and other parts. ESHN method is useful for large batches of parts and significant amounts of surfacing works .
SUMMARY welding shielding gas consists in the fact that the zone of the electric arc is fed by the shielding gas pressure , whereby the pole arcs and welding bath are isolated from the oxygen and nitrogen of air.
To create a protective atmosphere is used : inert gases (argon , helium, and mixtures thereof ) , reactive gases (carbon dioxide , nitrogen, hydrogen, steam , and mixtures thereof ), and mixtures of inert and reactive gases . A variation of the process is the gas-flame protection from combustion of flammable gases or liquid hydrocarbon fuel . The best protection for the metal cladding provides inert gases , but their use is limited by high cost.
Application of flux or shielding gas in arc surfacing associated with certain technological difficulties. Using the flux-cored wire or tape with the necessary structure eliminates the core flux and shielding gas.
The composition of the cores of the electrode material powders other than the alloying components are introduced gas and slag formers , which protect the molten metal against the atmosphere and enhance the stability of deposition process .
Vibrodugovaya surfacing : the electrode and the workpiece are melted during arc discharge , while at the end of the electrode metal droplet is formed . Atomized metal transfer on the item occurs mainly during the short circuit . Since the length of the arc is ~ 20% of the cycle time , the penetration of the base metal is shallow , with a small heat-affected zone .
Pulsed- arc welding is a kind of arc welding. In this case, the main current continuously burning arc generator with a special impose short current pulses which accelerate the transport of metal droplets and reduce their resolution.
Plasma surfacing - a process of coating the plasma jet , when the item is included in the main power circuit . In this case, the plasma arc heats the surface of the restored parts and material damage . Material moving the plasma jet . Its temperature can exceed 20 000 K.
In plasma surfacing unlike TIG welding arc is compressed by the water-cooled walls of the nozzle. Gas blown through this do -gu, acquires the properties of plasma - ionized and becomes electroconductive schim . The gas layer in contact with the walls of the nozzle is intensively cooled , loses its conductivity and serves as an electric and thermal insulation, which leads to a decrease of the plasma jet diameter which is 0.7 the diameter of the nozzle. As the plasma gas is increasingly used argon. Surfacing with replacement of argon with air ( 90%) significantly reduces the cost of repairing the parts.
SUMMARY electromagnetic welding is applied from a powder coating on the workpiece surface in a magnetic field while passing the DC power through a large contact area between particles of the powder itself and the workpiece .
A magnetic field is produced in the gap between the workpiece and the pole piece . It builds bridges between the ferromagnetic powder particles specified elements . In a magnetic field , in turn , impose an electric field by applying a voltage to the workpiece and the pole piece . Reductive coating is obtained by heating the powder particles in the gap , their fusion and attachment to the restored surface.
Laser cladding uses as a heat source concentrated laser beam.
Using lasers operate : surfacing , melt sprayed surfaces, surface alloying , surface hardening and amorphization of the material. Laser type of heating can also repair damage such as cracks in high- detail mode with irregular loading , linking parts in remote places and ceramic products . After laser machining with cracks on the regime , which ensures their partial melting , with subsequent normalization of the work of destruction detail details 30% higher compared with samples having initial cracks .
SUMMARY electron beam welding consists of heating the material and the workpiece surface the flow of electrons . Way to provide a highly concentrated energy input into the heated surface.
Gas welding : welding this kind has spread in the coating of ferrous metals in the form of a solid wire and alloys in powder form. Despite the low power of a gas flame , it gives a soft and local heating allows to apply coatings on small parts with little deterioration in remote