Hard Alloy hammer Vacuum Brazing Solution

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The alloy hammer is a hammer head formed by welding hard alloy hammer grains and the base metal together.

Its main function is to dent the finished concrete structural surface every day, usually in the cast-in-place structure. After pouring the cast-in-place slab, it is necessary to chisel the hair and cast the next layer of concrete. Let the concrete bond firmly. Simply put, the concrete (concrete surface) is roughened with a drill, and then rinsed with water, mainly to increase the adhesion of the post-cast concrete and it.

The role of chiseling:
The reason for chiseling is not only to roughen the surface, but also to remove the scum on the surface of the concrete, so that the concrete at the new and old joints is dense and the joint is firm.

Take the bridge analogy:
1. The broken pile head of the bridge’s pile foundation can also be regarded as chiseling, the purpose is to chisel out the dense concrete to ensure the quality.
2. The chiseling of the pier-column joint is for the purpose of solid concrete connection, and it can also play a role in eliminating joints;

The purpose of chiseling the top surface of the beam is to firmly bond with the pavement layer. Because the thickness of the pavement layer is thin, it is easy to cause peeling without chiseling.

Alloy hammers play an important role in chiseling. The hammer head is the core component, and its quality and stability directly affect the use.

The hammer head is obtained by welding hard alloy and base metal by adding solder and flux.

Cemented carbide
Cemented carbide is a tool material with high production efficiency, which has excellent properties such as high strength, high hardness, wear resistance and good red hardness. It is used to make knives, molds, measuring tools, mining tools and various parts with wear resistance as the main performance. It is widely used in industrial fields such as mechanical processing, geological exploration and mining.

Cemented carbide is expensive and has poor toughness, making it difficult to produce large-size and complex-shaped products. And many parts do not need to be made of cemented carbide as a whole, so it is of great value to connect cemented carbide with steel with good toughness, high strength, excellent processing performance, and cheap steel.

The brazing method is currently the main welding method of cemented carbide and steel. In the past ten years, some new welding methods such as vacuum welding, sinter diffusion welding, inert gas shielded welding, and laser welding are also under active research and exploration. It is widely used in the welding of cemented carbide.

Brazeability:
The hard solderability of the cemented carbide is because the carbon content of the cemented carbide is higher, and the uncleaned surface often contains more free carbon, which hinders the wetting of the solder. In addition, the hard alloy is easily oxidized to form an oxide film at the brazing temperature, which will also affect the wetting of the solder. Therefore, the surface cleaning before brazing is very important to improve the wettability of the brazing material on the cemented carbide, and if necessary, measures such as surface copper plating or nickel plating can also be taken.

Another problem in cemented carbide is that joints are prone to cracking. This is because its coefficient of linear expansion is only half of that of low-carbon steel. When brazing carbide and the base of such steel, it will produce a large thermal stress in the joint, which will lead to cracking of the joint. Therefore, when brazing hard alloys with different materials, measures should be taken to prevent cracking.

Brazing material
Cemented carbide usually uses pure copper, copper zinc and silver copper solder.
Pure copper: Pure copper has good wettability to various cemented carbides, but the best effect can be obtained only in the reducing atmosphere of hydrogen. At the same time, due to the high brazing temperature, the stress in the joint is large, resulting in an increased tendency to crack. The shear strength of joints brazed with pure copper is about 150MPa, and the joint plasticity is also high, but it is not suitable for high temperature work.

Copper-zinc solder: Copper-zinc solder is the most commonly used solder for cemented carbide. In order to improve the wettability of the solder and the strength of the joint, alloy elements such as Mn, Ni, Fe, etc. are often added to the solder. For example, B-Cu58ZnMn is added with w(Mn) 4%, so that the shear strength of the hard alloy brazed joint reaches 300~320MPa at room temperature: it can still maintain 220-240MPa at 320C. Adding a small amount of Co on the basis of B-Cu58ZnMn can make the shear strength of the welded joint reach 350MPa, and have higher impact toughness and fatigue strength, which significantly improves the service life of cutting tools and rock drilling tools.

Silver-copper solder: The melting point of silver-copper brazing material is low, and the thermal stress generated by the brazing joint is small, which is helpful to reduce the cracking tendency of hard alloy brazing. In order to improve the wettability of the solder and increase the strength and working temperature of the joint, alloy elements such as Mn and Ni are often added to the solder. For example, B-Ag50CuZnCdNi solder has excellent wettability to cemented carbide, and the brazed joint has good overall performance.

Preparation before welding
① Before welding, check whether the cemented carbide has cracks, bends or uneven uneven defects. The brazing surface must be flat. If it is a spherical or rectangular hard alloy brazing surface, it should also meet a certain geometric shape to ensure good contact between the alloy and the substrate to ensure the brazing quality.

② Grit blasting the hard alloy. If there is no sand blasting equipment, you can hold the hard alloy in your hand and grind the oxide layer and black brand letters on the brazed surface on the rotating green silicon carbide grinding wheel. If the oxide layer on the gold brazed surface is not removed, the brazing material will not easily wet the hard alloy. Experience has shown that if there is an oxide layer or black brand letters on the brazed surface, sandblasting should be performed, otherwise the brazing material is not easy to wet the hard alloy, and obvious black letters will still appear in the brazing seam, which reduces the brazing area and occurs. Desoldering phenomenon.

③ When cleaning the brazed surface of cemented carbide, it is better not to use chemical mechanical grinding or electrolytic grinding, because they all rely on the binder (cobalt) that corrodes the surface layer of the cemented carbide to speed up the grinding or improve the grinding efficiency After the cobalt on the surface of the cemented carbide is corroded, it is difficult for the brazing material to wet the cemented carbide, which can easily cause de-soldering. In special cases, when the brazing surface of the cemented carbide must be treated by the above method or wire EDM, the treated cemented carbide can be sandblasted or ground with a silicon carbide grinding wheel. The blasted carbide can be cleaned with gasoline and alcohol to remove oil stains.

④ Before brazing, you should carefully check whether the groove shape on the steel substrate is reasonable, especially for hard alloys with cracked grades and hard alloy workpieces with large brazed surfaces. The knife groove is also sandblasted and cleaned to remove oil stains. When the cleaning volume is large, the alkaline solution can be used for boiling for 10-15 minutes. For high-frequency or copper-immersed multi-blade cutters and complex measuring tools, it is best to boil them in saturated borax aqueous solution for 20 to 30 minutes, remove and dry them before welding.

⑤Clean the brazing material with alcohol or gasoline before use, and cut and shape it according to the brazing surface. When brazing a general hard alloy tool or mold, the thickness of the brazing material is about 0.4 to 0.5 mm, and the size is similar to the brazing surface. When heating with a coke oven, the brazing material can be increased appropriately. When brazing hard alloy multi-edged tools, measuring tools and other workpieces, the area of the brazing sheet should be reduced as much as possible. Generally, the brazing sheet can be cut to about 1/2 of the brazing surface. The brazing sheet is reduced to 1/3 or less of the brazed surface. Reducing the brazing material can make the appearance of the workpiece after welding beautiful and sharper.

Flux and shielding gas
Flux: The choice of flux should be matched with the base metal and the selected brazing material. When brazing tool steel and cemented carbide, the flux used is mainly borax and boric acid, and some fluorides (KF, NaF, CaF2, etc.) are added. Copper-zinc brazing filler metal is matched with FB301, FB302 and FBl05 flux, and silver-copper brazing filler metal is equipped with FBl01~FBl04 flux. When using special brazing filler metal to braze high-speed steel, borax flux is mainly used.

Shielding gas: In order to prevent the oxidation of tool steel during brazing heating and to eliminate the cleaning after brazing, gas shielding brazing and vacuum brazing can be used. Vacuum brazing can be a working vacuum of 10-3pa in the heating chamber, which protects the workpiece from oxidation.

Brazing process
The surface of the hard alloy should be sandblasted before brazing, or polished with silicon carbide or diamond grinding wheels to remove excess carbon on the surface, so as to be wetted by the brazing material during brazing. Cemented carbide containing titanium carbide is relatively difficult to wet, by coating copper oxide or nickel oxide paste on its surface, and baking in a reducing atmosphere to make copper or nickel transition to the surface, thereby enhancing the solder Wettability.

When welding cemented carbide tools, uniform heating of the arbor and cemented carbide sheet is one of the basic conditions to ensure the welding quality. If the heating temperature of the cemented carbide sheet is higher than that of the cutter bar, the melted brazing material wets the cemented carbide sheet and cannot wet the cutter bar, the strength of the joint will be reduced. When shearing the alloy sheet along the welding layer, the brazing material does not Destruction, and with the alloy flakes off. On the welding layer, traces of the milling cutter on the support surface of the cutter bar can also be seen. If the heating speed is too fast and the temperature of the cutter bar is higher than that of the alloy sheet, the opposite phenomenon will occur.

The placement order and mutual position of flux, brazing filler metal and cemented carbide have a direct impact on the brazing quality. The correct placement method is: place the brazing filler metal on the knife groove, sprinkle the flux, then put the cemented carbide, and spread a layer of flux on the top surface of the cemented carbide along the side weld. In this way, it is easy to grasp the brazing temperature during brazing, and reduce the excess brazing material adhering to the weld.

The brazing temperature of the workpiece must be correctly controlled during the brazing process. If the brazing temperature is too high, the zinc element in the zinc-containing solder will evaporate; if the brazing temperature is too low, the weld will be thick due to the poor fluidity of the brazing material. There are a lot of pores and slag in the weld. This is the main reason for desoldering. The brazing temperature should be 30-50°C higher than the melting point of the brazing material. At this time, the fluidity and permeability of the brazing material are good, and it is easy to penetrate the entire welding seam.

The cooling rate after brazing is one of the main factors affecting brazing cracks. The instantaneous tensile stress is generated on the surface of the cemented carbide sheet during cooling, and the tensile stress of the cemented carbide is much lower than the compressive stress. Especially for workpieces with large brazing area such as YT60, YT30, YG3X, and large substrates, and small substrates with large carbides, more attention should be paid to the cooling rate after brazing. Usually the workpiece is inserted into the lime trough or charcoal powder trough immediately after welding to cool the workpiece slowly. This method is simple to operate, but the tempering temperature cannot be controlled. If conditions permit, the workpiece can be placed in a furnace at 220 to 250°C and tempered for 6 to 8 hours immediately after brazing. The use of low temperature tempering treatment can eliminate part of the brazing stress, reduce cracks and extend the service life of cemented carbide tools.

Selection of brazing furnace
Brazing is a very important step in the manufacturing process. The quality of brazing directly determines the quality, wear resistance, hardness and other properties of the product.

Brazing in the atmosphere furnace, by filling the protective gas to exhaust the gas inside the brazing furnace, can effectively protect the product from oxidation.

Vacuum brazing in a vacuum brazing furnace. The vacuum furnace evacuates the heating cavity before heating, which can reach a high vacuum of 10-2-10-3pa. At this time, the brazing environment is very guaranteed to ensure the quality of the product brazing. , You can get higher performance quality.

As a professional vacuum furnace manufacturer, SIMUWU has 20 years of production experience. Vacuum brazing furnace is the main research and production field of SIMUWU. It has established good cooperative relations with many countries in the world. SIMUWU vacuum brazing furnace is aimed at Vacuum brazing of various products can be customized to meet every key point in the user’s product manufacturing process.

Edited by: Ryan Wu
Copyright: SIMUWU Vacuum Furnace

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