Flux, broadly defined, includingMolten salt, organic matter, active gas, metal vapor, etc., i.e. removalBase metalandSolderIn addition, it generally refers to the third kind of material used to reduce the interfacial tension between base metal and solder.
Chinese name
flux
Foreign name
flux
Boiling point
280 ℃
Definition
Materials to reduce the interfacial tension between base metal and solder
Function 1
removeoxide, reduce the surface tension of melting point
During welding, it can melt to form slag and (or) gas to protect the molten metalMetallurgical Physical ChemistryA substance that functions.
The flux is granularwelding material 。During welding, it can melt to form slag and gas, which plays a protective and metallurgical role in the molten pool.When welding, it is a substance that can melt and form slag and gas to protect and metallurgical treat the molten metal.be used forSubmerged arc weldingSubmerged arc flux.
classification
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There are many classification methods for flux, including usage, manufacturing method, chemical composition, welding metallurgical performance, etc., as well as the pH and particle size of flux.No matter which classification method, it only reflects the characteristics of the flux from one aspect, and cannot include all the characteristics of the flux.The classification methods commonly used in Zhongyuan Welding Material and Electrode Recycling Center are as follows:
The flux can be classified into neutral flux, active flux and alloy flux according to the addition of deoxidizer and alloy flux, which are also commonly used classification methods in ASME standards abroad.[1]
1. Neutral flux Neutral flux refers to the flux that has no obvious change in the chemical composition of the deposited metal and the chemical composition of the welding wire after welding. Neutral flux is used for multi pass welding, especially for the base metal with welding thickness greater than 25mm.Neutral flux has the following characteristics:
a、The flux basically contains no SiO2, MnO, FeO and other oxides.
b、Flux has no oxidation effect on weld metal.
c、Porosity and weld bead crack will be produced when welding seriously oxidized base metal.
2. Active flux Active flux refers to the flux added with a small amount of Mn, Si deoxidizer.It can improve the anti porosity and anti crack ability.Active flux has the following characteristics:
a、Because of the deoxidizer, Mn and Si in the deposited metal will change with the change of arc voltage.The increase of Mn and Si will increase the strength of the deposited metal and reduce the impact toughness.Therefore, the arc voltage should be strictly controlled during multi pass welding.
b、Active flux has strong anti porosity ability.
3. Alloy flux Alloy flux is added with more alloy components for transition alloy elements. Most alloy fluxes are sintered fluxes.Alloy flux is mainly used for welding low alloy steel and wear-resistant surfacing.
4. Melting flux Melting flux is to mix the raw materials of various minerals according to the given proportion, heat them to more than 1300 degrees, melt and stir them evenly, and then take them out of the furnace, and then quench them in water to granulation.Then it is dried, crushed, sieved and packaged for use.The brand of domestic melting flux is represented by "HJ". The first digit after it represents the content of MnO, the second digit represents the content of SiO2 and CaF2, and the third digit represents different brands of the same type of flux.
5、Sintered fluxAfter batching according to the given proportion, dry mixing is carried out, and then binder (water glass) is added for wet mixing, and then granulation is carried out. Then it is sent to the drying oven for curing and drying, and finally sintered at about 500 degrees.The brand of domestic sintered flux is represented by "SJ", the first digit after it represents the slag system, and the second and third digits represent different brands of the same slag system flux.
component
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The flux is composed of marble, quartz, fluorite and other ores, titanium dioxide, cellulose and other chemicals.Flux is mainly used forSubmerged arc weldingandElectroslag welding。When welding various steels and non-ferrous metalsWelding wireSatisfactory welds can be obtained by reasonable cooperation.
effect
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Effect of flux:
1. Remove the oxide on the welding surface to reducesolderMelting point and surface tension shall reach the brazing temperature as soon as possible.
2. Protect the weld metal from harmful gases in the surrounding atmosphere when it is in liquid state.
3. Make the liquid solder flow at a proper speed to fill the solder joint.
Role of flux in submerged arc welding:
one
Mechanical protection: flux inelectric arcMelt into the surface layer under the action ofslag, protectionweld lineWhen the metal is in liquid state, it will not be invaded by the gas in the surrounding atmosphere, so as to avoid porosity inclusion in the weld.
The weld surface shall be smooth and straight. The melting point of well formed flux shall be 10-30 ℃ lower than that of solder. In special cases, the melting point of solder can also be higher than that of solder.If the melting point of the solder is too low, it will melt prematurely so that the flux component will lose its activity when the solder melts due to evaporation, interaction with the base metal and other reasons.The choice of flux usually depends on the nature of the oxide film.Acidic boric anhydride (BtwoOthree）And slightly acidic oxide film, for example, to deal with cast iron containing high SiOtwoThe oxide film commonly contains alkaline NatwoCOthreeThe flux oftwoSiOthreeAnd into the slag.somefluorideThe gas of is also commonly used as brazing flux. They react evenly and leave no residue after welding.BFthreeConstant sum NtwoMixed use brazing stainless steel at high temperature.The flux used for brazing below 450 ℃ is soft flux, which can be divided into two types:Water solubilityIt is usually composed of single hydrochloride and phosphate or aqueous solution of sog salt, with high activity and strong corrosiveness, and needs cleaning after welding.The other is organic flux insoluble in water, usually based on rosin or artificial resin, with organic acid, organic amine or its HCl or HBr salt added to improve the ability and activity of removing film.
Flux control
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1. Flux drying and heat preservation control
The flux shall be baked according to the flux specification before use. This drying specification is the correct data with quality assurance obtained from the test and process inspection control. It is an enterprise standard, and the specifications required by different enterprises are also different. Secondly, the recommended drying temperature and holding time of the flux shall be in accordance with JB4709-2000<<Steel Pressure Vessel Welding Procedures>>.Generally, when the flux is dried, the stacking height shall not exceed 5cm,The number of welding material warehouses dried at one time is often more than one generation, and the stacking thickness is more than one generation. This should be strictly controlled to ensure the drying quality of welding flux.Avoid stacking too thick, and ensure the flux drying thoroughly by extending the drying time.[2]
2 On site treatment and recovery and disposal control of welding flux
The welding position shall be cleaned, and sundries shall not be mixed into the flux, including the flux used for the flux pad shall be distributed as required, and it is better to use it at about 50 ℃, and the flux shall be recycled in time to avoid pollution;8 mesh and 40 mesh sieves shall be used to screen the flux that has been continuously used for many times, and impurities and fine powder shall be removed. The flux shall be mixed with three times of new flux before use.Before use, it must be dried at 250-350 ℃ and kept for 2 hours. After drying, it must be stored in 100-150 ℃ incubator for future use. It is forbidden to store it in the open air.When the site is complex or the relative humidity is high, timely manage the operation site, keep it clean, carry out necessary tests on the moisture resistance of welding flux and mechanical mixture, control the moisture absorption rate and mechanical inclusions, and avoid disorderly stacking and mixing of welding flux.[2]
3 Flux particle size and distribution requirements
The flux shall have certain particle size requirements, and the particle size shall be appropriate to make the flux have certain permeability. The welding process shall not emit continuous arc light, so as to avoid air pollution and formation of pores in the molten pool.Fluxes are generally divided into two types, one with a common particle size of 2.5-0.45mm (8-40 mesh), and the other with a fine particle size of 1.43-0.28mm (10-60 mesh).The fine powder smaller than the specified particle size is generally not more than 5%, and the coarse powder larger than the specified particle size is generally more than 2%. The detection test and control of the flux particle size distribution should be done well to determine the welding current used.[1-2]
4 Control of flux particle size and stacking height
If the flux layer is too thin or too thick, it will cause pits, spots and pores on the weld surface, forming an uneven weld bead shape. The thickness of the flux layer should be strictly controlled within 25-40mm.When usingSintered fluxDue to low density, the height of flux stack is 20% - 50% higher than that of melting flux.The larger the wire diameter is, the higher the welding current is, and the higher the flux layer thickness is;Due to the non-standard operation in the welding process and improper disposal of fine powder flux, intermittent uneven pits will appear on the weld surface. The NDT is qualified, but the appearance quality is affected, and the shell thickness is weakened locally.[2]
