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Brazing knowledge summary(6)

Jan 28, 2019

Inspection method editing

The inspection methods for brazed joint defects can be divided into non-destructive testing and destructive testing.

1. Visual inspection

The visual inspection is to check the surface quality of the brazed joint with the naked eye or a low magnification magnifying glass. If the brazing filler fills the gap, whether the exposed end of the brazing joint is rounded, whether the rounded corner is uniform, whether the surface is smooth, whether there are cracks, pores and Other external defects.

2. Surface defect inspection

Surface defect inspection methods include fluorescence inspection (coloring inspection) and magnetic particle inspection. They are used to inspect the appearance and to inspect surface defects such as cracks, pores, etc. that are not visible to the eye. Fluorescence testing is generally used for inspection of small workpieces, large workpieces are examined by coloring (partial inspection of workpieces), and magnetic powder inspection is only used for metals with magnetic properties.

3. Internal defect inspection

Mainly used for radiographic inspection, ultrasonic inspection and compactness inspection.

Radiation inspection (divided into X-rays and gamma rays according to the type of source) is a common method for testing internal defects of important workpieces. It can show pores, slag inclusions, unbrodded and cracks in the brazing joint and the base metal. The range of defects that can be found by ultrasonic inspection is the same as that of the ray inspection. Common methods for testing the compactness of brazed structures include general hydraulic testing, airtight testing, gas permeation testing, kerosene leakage testing, and mass spectrometry testing. Among them, the water pressure test is used for high pressure vessels, the airtight test and the gas permeability test are used for low pressure vessels, the kerosene penetration test is used for pressureless vessels, and the mass spectrometry test is used for vacuum sealed joints.

Common brazing editor

1. Brazing of carbon steel and low alloy steel

The oxides on the surface of the carbon steel are FeO, Fe2O3 and the like. In addition to iron oxide, low alloy structural steel surfaces may also form oxides of alloying elements. In addition to the large influence of chromium and aluminum oxides, other oxides are easier to remove.

(1) solder

When soldering carbon steel and low alloy steel, various solders can be used, of which tin-lead solder is the most widely used. The low carbon steel joint brazed with HISnYb10 tin-lead solder has a tensile strength of 93 MPa and a shear strength of 37 MPa. When HlSnrbs8-2 solder is used, it is increased to 113 MPa and 49 MPa, respectively. When brazing is performed using copper, copper-based brazing filler metal and silver-based brazing filler metal, a higher joint strength can be obtained.

For example, when using HUL solder, the tensile strength of the joint is 323 MPa, and the shear strength is ao When using BAg40Cuf-nUd solder, it is increased to 385 MPa and 203 MPa, respectively.

(2) flux

For soldering, the flux is a zinc chloride aqueous solution or a zinc chloride or ammonium chloride aqueous solution. When using a copper-based solder, a borax borate flux or Q7301 is used. When using a silver-based solder, QJ101, QJ102, etc. are used.

Second, stainless steel brazing

Since stainless steel contains metal elements such as Cr, Ni, Ti, Mn, N, Nb, Mo, Si, Cu, etc., there are many kinds of surface oxides, and chromium and chin oxides have the best chemical stability. It is necessary to use a highly active flux and a protective gas or a high vacuum brazing method.

(1) solder

Different solders and brazing filler metals can be used depending on the requirements of the brazing member, the performance of the brazed joint, the brazing temperature, and the like.

(2) flux

Since chromium forms a stable oxide, a highly active flux should be used. For soldering, a zinc chloride hydrochloric acid solution, a zinc chloride monoammonium chloride hydrochloric acid solution or phosphoric acid must be used. [4]

For brazing, Q7101, QJIV2 can be used when using silver-copper-zinc, silver-copper-tin-tin solder. When brazing with copper-based solder, QJZOOo containing calcium fluoride should be used.

Solder selection editor

(1) The solder should have a suitable melting temperature range, at least tens of degrees lower than the melting temperature of the base material.

(2) At the brazing temperature, it should have good wettability to ensure that the gap between the brazing seams is fully filled.

(3) The solder and the base material should have a diffusion effect to form a strong bond.

(4) The brazing material should have a stable and uniform composition to minimize the loss of alloying elements during the brazing process.

(5) The brazed joint obtained shall meet the technical requirements of the product and meet the requirements of mechanical properties, physical and chemical properties and performance.

(6) The economics of the brazing filler metal is better. Minimize or contain rare metals and precious metals. It should also ensure that the productivity of brazing is high.

(7) The brazing material should have a processing deformation ability to facilitate various shapes.

Second, the classification of solder

1. According to the melting temperature range of the solder

(1) A solder having a melting point of lower than 450 ° C is called a solder such as a gallium base, a ruthenium base, an indium base, a tin base, a lead base, a zinc base or the like.

(2) Solder having a melting point higher than 450 ° C is called brazing filler metal (commonly known as refractory brazing filler metal) such as aluminum-based, magnesium-based, copper-based, silver-based, manganese-based, gold-based, nickel-based, palladium-based, and Chinky. .

2. According to the main alloying elements of the solder

The brazing filler metal can be divided into tin base, lead base, aluminum base and the like according to its main alloying elements.

3. According to the shape of the bran

The brazing material can be divided into wire, rod, sheet, foil, powder or special shape brazing material according to its shape (for example, ring solder or paste solder)