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Vacuum brazing flux

The function of soldering flux is to reduce the oxide on the surface of tool rod and hard alloy, so that the metal can be well wetted. Usually, the melting point of filler metal is below 100 ℃ above the melting point of the filler metal, and it has better liquidity and lower viscosity. The flux melted during brazing heating protects the filler metal and brazing surface while reducing oxides.

The main requirements for cemented carbide solder are as follows.

(1) the filler metal shall have good wettability to brazing hard alloy and steel matrix to ensure good fluidity and permeability of the filler metal.

(2) a characteristic of cemented carbide is its high red hardness, so it must be ensured that the brazing joints have sufficient strength at room temperature and high temperature.

(3) the melting point of solder should be as low as possible, to reduce soldering stress, prevent craze, but should be higher than the melting point of solder weld the working temperature of 300 ℃, in order to ensure the normal work of tool in high speed cutting.

(4) the filler metal shall not contain elements with low evaporation points to avoid the influence of element evaporation in the filler metal on joint quality or harmful to human health.


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The blades are made of 40Cr steel and tungsten cobalt titanium carbide.

Filling materials for the BCu (Cu99.95 %), thickness of 0.1 mm, melting temperature of 1083 ° C, brazing temperature is 1100-1150 ° C.

Soldering flux for YJ1 and main ingredients for borax, brazing temperature is 800-1150 ℃. Hard flux QJ201 can also be used. The flux consists of 80% boric acid, 14.5% borax and 5.5% calcium fluoride. The brazing temperature is 850-1150 ° C.

Borax is the most commonly used brazing flux for cemented carbide and steel. More attention should be paid to the application of borax.
(1) industrial borax (borax) should be dehydrated before use. Because industrial borax contains 10 parts of crystal water (na2b4o7.10h2o), and a large amount of water is absorbed in the air, a large amount of foam will be generated in the brazing process, which will not only make brazing operation difficult, but also affect the quality of the weld.

(2) dehydrated borax (Na2B4O7) can be used for brazing various brands of hard alloys. Brazing temperature range of 850 to 1150 ° C. It is suitable for brazing flux, such as copper, brass, copper, zinc and silver solder, but is not suitable for brazing solder melting point below 800 ° C. When storing dehydrated borax, care must be taken to prevent moisture. If wet, dry before use.

The dewatering treatment of borax is to put industrial borax into steel crucible. The crucible can be heated at 850 degrees in a resistance or coke oven. During the heating process, the borax in the crucible will produce a large amount of white foam. As the heating temperature increases, the foam gradually decreases until the foam disappears. When all borax melts into liquid, the heating stops. Pour the green transparent liquid borax from the crucible into the tin. When it cools, it breaks into pieces of green glass. The color of dehydrated borax is related to melting time. The longer the melting time, the darker the color of borax, but it has no effect on the quality of brazing. Crush the melted borax blocks and sift them in a 60 to 80 mesh sieve.

(3) the mixed flux of dehydrated borax (85-90%) and potassium fluoride (10%-15%) is mainly used for brazing YT60 and YT30 cemented carbide. Due to the toxicity of potassium fluoride, strong ventilation equipment must be installed near the heating equipment during the brazing process, and harmful gas must be discharged in time.

Fluoride and chloride are highly absorbent. Dehydration should also be carried out when fluorides and chlorides are prepared. Dehydration is a ceramic or stainless steel crucible heated to about 270 ℃, fluoride and chloride in last three to four hours, until don't smoke. The dehydrated fluoride and chloride should be stored in a sealed glass container.

When using fluoride or chloride flux, pay attention to ventilation and eliminate harmful gas in time. After brazing, weld components shall be cleaned in time to avoid corrosion of the weld and residual flux of the base metal. Most fluxes absorb water easily and we should take care to seal and preserve them for use.

Flux can also be prepared in advance into paste, flux is made by adding a small amount of alcohol, rosin oil, petroleum jelly oil and other flux paste, coated on the surface of the workpiece to be welded. When cryogenic silver filler metals are used, the filler metals can also be used in a paste form with water. Now you should prepare the paste to fill the metal.

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