Ceramic Fused Fluxes
The key feature of ceramic fluxes is the way of their production, in many respects similar to the method of manufacturing high-quality coatings of electrodes for manual welding, as described above.
Flux parts finely shredded, mixed in appropriate proportions and kneaded in an aqueous solution of sodium silicate into a thick paste, as to cover the electrodes way crimp. Wet weight of granulated, that is, converted into grain size of 1-3 mm, then dried, calcined for 2 h at a temperature of 300-400 ° C to remove residual moisture and improve the mechanical strength of grain by setting the reaction of sodium silicate with a particle flux. Calcination ends production of ceramic flux, which does not require smelting furnaces and the high cost of fuel or electricity to the melting of average bulk density of ceramic fluxes of about 1.0 g/cm3. Each grain of ceramic flux is composed of many thousands of small particles mixed in appropriate proportions and securely fastened.
Ceramic fluxes do not have the major disadvantages inherent in conventional fused fluxes. Mechanically stable grain size necessary to provide sufficient gas permeability of a layer of flux and gases blown arc. Strong bonding of particles eliminates the possibility of separation and segregation of the individual particles of flux and change in the feeding zone of welding and cleaning, which is one of the major drawbacks of fused fluxes. Fine grinding of the components ensures complete fusion reactions and the flow of steel, as in the electrode surfaces.
The disadvantages of ceramic fluxes compared to fused is less mechanical strength, water absorption and high grain flux. Ceramic fluxes have opened up new possibilities for automated arc welding and greatly expanded its scope. To create a slag of the ceramic fluxes are introduced various minerals. The principle is a very important advantage of ceramic flux is to introduce into their substance, decomposing at high temperatures with the formation of gases, protecting the welding zone. For this purpose, injected calcium carbonate CaCO3 in the form of marble, decomposes at high temperatures to form carbon dioxide. During the welding process, particularly important is deoxidation of the metal. For this purpose, ceramic fluxes introduce such strong deoxidizing agents, as metallic titanium, silicon and sometimes aluminum. It is often possible to simultaneously remove most of the sulfur content or reducing it to a few thousandths of a percent, which is attached to the main character of the slag by increasing the content in the calcium oxide CaO.
Ceramic fluxes provide a wide range of doping weld metal flux through the weld metal to give special properties. Ceramic fluxes reduce the consumption of expensive alloy welding wire, and in most cases of doping in flux with the use of low-cost low-carbon wire Sv-08. Doping is possible to implement all elements, including carbon, it is difficult in other cases. Ceramic fluxes can modify the weld metal, ie, to improve its structure, weld metal during solidification in the process of primary crystallization often takes on a coarse dendritic structure in the form of long crystals, elongated in the direction of heat removal during solidification, normal to the surface cooling. In the area of the meeting of the dendrites growing from opposite sides of the bath, replaced metal pollution, and therefore the strength of the metal is reduced, it is easy to form hot cracks; area became known as the "zone of slack," and most of the dendrites is the phenomenon of joint transcrystallization. The advancing further cooling became secondary crystallization caused by the collapse of the austenite, often masks and makes unobtrusive primary dendritic structure, which can be detected only by special deep etching. In the poor are often the primary structure is the cause of reduced mechanical properties of weld metal. Modification of the dendritic structure is destroyed, even during the primary crystallization of the metal solidifies with the formation of equiaxed fine grains. This metal has high mechanical properties. For a suitable modification of the smallest non-metallic inclusions which serve as crystallization centers and surface-active substances that alter the surface tension of the metal. A good modifier in a welding titanium. The modification is carried out during welding electrodes with high-quality coating and a ceramic fluxes. When welding under fused fluxes modification typically is weak as a modifier, such as titanium, is introduced into the electrode wire. Intensive modification of the metal to produce a fine-grained equiaxed structure during the primary crystallization is the advantages of ceramic-tion fluxes. Elements necessary for deoxidation, alloying, and modification of the metal is usually introduced into the ceramic fluxes, as in the electrode coating in the form of ferroalloys.
Advantage of ceramic fluxes for welding carbon steels is the low sensitivity to various contaminants and rust the metal surface, thus reducing the requirements for surface cleaning , to carry out welding outdoors in wet weather, this gives a dense pore-free metal with high mechanical properties.
For the welding of low-and medium-high-strength structural steels, a series of special ceramic fluxes for the production of critical parts. Ceramic fluxes are also used for welding high-alloy steels, such as austenitic chromium-nickel stainless and heat-resistant steels. In this case, is alloyed austenitic wire. Ceramic flux produces only the necessary additional doping. When welding stainless steel is a high resistance of the welding zone against intergranular corrosion.
Known successful use of ceramic fluxes for the welding of copper, nickel and their alloys for surfacing work and semi-automatic welding is a welding wire, low carbon alloy with ceramic fluxes, containing increased amounts of ferroalloys.
See also:
Automatic Arc Welding
Automatic ADS
Machines with a Constant Feed Rate of Electrode
Flux Equipment
Settings for Automatic Arc Welding
Automatic Submerged Arc Welding Introduction
Fluxes for Automatic Arc Welding
Processed Fluxes
Ceramic Fused Fluxes
Semi-Automatic Arc Welding
Arc Welding with Flux Cored Wire
No comments:
Post a Comment