FAQ about silver brazing

Release time: 2019-11-06

Scientists and archaeologists have confirmed that brazing is one of the oldest methods of connecting materials. Back to 1500-2000 BC, ancient brazing was first used to make jewelry and handicrafts, but it was found in metals such as gold and silver that welding existed in natural form and produced new metals, and then alloys were derived.

Now, from household tools to high-tech aviation facilities and equipment, silver brazing has been widely used in various fields as a science. Silver brazing was originally used to weld metals and metal alloys, but now it has been expanded to connect other uses besides metals, such as ceramics and cermets. When a new material or a new use of the existing material appears, silver brazing often acts as the main welding work; In this regard, the operator or the person preparing to perform brazing should understand the basic principles of welding to help select the correct solder alloy to successfully complete the welding work. In order to help readers get more information about this aspect, we have listed the following common questions and answered them:

1. How to distinguish brazing from other welding methods?

By definition, the American Welding Association stipulates that the filler metal (solder alloy) melts below the melting temperature of the workpiece to be welded and above 450 ° C, and the alloy fills the workpiece and forms a joint through capillary action, which is brazing.

2. What are silver solder and hard solder?

The above two terms are used to describe solder containing silver, but both are slang or non-standard expressions. The welding conducted at a temperature higher than 450 ° C is soldering, and the welding conducted at a temperature lower than 450 ° C is soldering.

3. Is there any other metal besides silver that can be used as filler material (filler metal)?

In addition to silver, common alloys include copper, copper phosphorus, nickel, aluminum and gold.

4. Why is silver solder so popular?

Because silver solder can connect many different metals, alloys and other materials, and its lower melting temperature makes it easier to use.

5. What is capillary action?

According to the American Welding Association, capillary action refers to the phenomenon that molten solder flows against the gravity on the surface of closely spaced workpiece and finally forms a joint.

6. What will affect capillary action?

There are many factors that will affect the capillary effect. The size of the gap in the welding device is the main factor and the contact area of the welded workpiece.

7. What is the appropriate welding gap?

For most standard types of joints, the filler metal is silver and copper-phosphorus alloy, and the recommended welding gap is 0.002-0.005 inch. Of course, if you have any questions, please contact our technical experts.

8. Common types of brazed joints?

There are mainly three types of welded joints: butt joint, lap joint and embedded joint, as well as different mixed types of the three types of joints.

9. What are the main factors affecting the surface energy of the base metal?

Dirt and oxide

10. What dirt does it contain?

The most common pollutants include drawing lubricant, cutting fluid, polishing agent, engine oil and lubricating oil.

11. How to remove oxides?

The use of flux during welding is the most effective method to remove oxides.

12. Are there different types of fluxes?

have According to the classification of soldering fluxes, there are three types: chemical, reducing air and vacuum. When copper-phosphorus alloy is used to weld copper and copper workpieces, phosphorus can replace flux to remove oxides.

13. Can flux be used to remove other contaminants?

may not. Solder flux is not detergent, solvent, degreaser, and cannot be used to remove other dirt.

14. Should the paste flux be removed after welding?

Paste flux should be removed. Because all paste fluxes contain fluoride, staying on the workpiece will weaken its joint strength.

15. The importance of heating in the welding process?

Improper heating is the main problem of silver brazing, which can affect the integrity of the joint.

16. What is the most difficult part in the heating process?

It is the most difficult to know when the inner surface reaches a uniform and appropriate temperature in the heating process, because the operator cannot see the inner surface and it is also difficult to measure the surface in mass production.

17. Why is uniform temperature important?

Capillary action is the action mechanism of filling metal melting and forming contact. When the temperature under the whole capillary zone reaches uniform, the filler metal (filler metal) can be drawn to the hottest surface.

18. Can uniform heating ensure filler metal alloy filling and joint formation?

No. Uniform heating alone is not enough to ensure the smooth flow of solder and the final formation of joints. Brazing requires a variety of technologies to complete. The operator's professional skills are extremely important for welding a good joint. In addition, the area under the action of capillary may not be uniformly heated. In this case, the filler metal is pulled to the nearest mating surface under the action of capillary.

19. What is the difference between silver solder and silver-containing copper-phosphorus alloy?

Copper-phosphorus alloy (with or without silver) is not as widely used as silver filler metal. It is mainly used to weld metal materials with copper as the base material. Phosphorus element in copper-phosphorus solder also plays a role in soldering flux. The silver filler metal can be used not only for the metal welding of copper-phosphorus alloy, but also for the workpiece with other metal as the base metal.

20. Besides copper, is there any other base metal suitable for copper-phosphorus alloy?

Copper-phosphorus alloy can also be used for the connection of brass, silver, tungsten and molybdenum. However, these materials need to be welded with flux.

21. Why is copper-phosphorus alloy not suitable for welding with iron and nickel as the base metal?

Iron and nickel elements will react with phosphorus to produce brittle phosphide and weaken joint strength.

22. What is the solid phase temperature and the liquid phase temperature?

When brazing, the solid phase temperature is when the solder reaches a certain temperature and begins to melt; When the alloy reaches a certain temperature and completely becomes liquid, it is the liquid phase temperature.

23. What is hypoeutectic/eutectic?

Low eutectic/eutectic is a term used to describe the transformation of alloy or alloy to liquid when the temperature reaches a certain temperature. The common silver eutectic alloy contains 72% silver, 28% copper, and the eutectic temperature is 1435F

24. What factors should be considered when selecting silver solder?

Workpiece material, heating method, automation, strength, internal pressure, working temperature, corrosive environment/medium, fusibility, ductility, conductivity and cost are all important considerations. For more information, please contact our technical experts.