Copper Brazing

Brazing is a process of joining two or more pieces of metal by melting a filler metal into the joint. Copper is a common metal used in brazing because of its high thermal conductivity, excellent corrosion resistance, and good electrical conductivity.

This article provides a guide on how to properly braze copper, as well as safety precautions that should be taken.

• Guide to Silver Brazing

What are the key steps in the copper brazing process?

The copper brazing process typically involves the following steps:

1. Surface preparation: The mating surfaces of the components to be joined must be clean and free from oxides, dirt, and contaminants.
2. Application of flux: A suitable flux is applied to the joint area to promote wetting and prevent oxidation during heating.
3. Assembly: The components are positioned together, ensuring proper alignment and fit.
4. Heating: The assembly is heated uniformly using a torch, furnace, or induction heating to reach the melting point of the filler metal.
5. Brazing: Once the filler metal melts and flows into the joint, it is allowed to solidify, creating a strong bond between the components.
6. Cleaning and inspection: After brazing, the joint is cleaned to remove any residual flux or oxides, and the quality of the joint is inspected for defects.

Filler Metals for Copper Brazing

Copper brazing involves the use of filler metals to create strong and reliable joints between copper and copper alloy components. The selection of the appropriate filler metal depends on various factors such as the base metal composition, operating temperature, joint design, and desired joint properties.

Silver-based Filler Metals

Silver-based filler metals are widely used in copper brazing due to their excellent flowability and corrosion resistance.

These alloys typically contain silver as the main component along with other elements such as copper, zinc, tin, and sometimes cadmium. The silver content in the filler metal contributes to its low melting point and improved wetting properties.

Silver-based filler metals offer high strength, ductility, and thermal conductivity, making them suitable for a wide range of copper brazing applications.

Phosphorus-based Filler Metals

Phosphorus-containing filler metals, often referred to as "phosphorus bronzes," are commonly used for brazing copper and copper alloys.

These alloys contain copper as the main component along with phosphorus, and sometimes small amounts of other elements like tin and zinc. Phosphorus-based filler metals provide good wetting properties and high strength joints.

They are particularly suitable for brazing copper to copper without the need for additional flux, as the phosphorus acts as a self-fluxing agent.

Nickel-based Filler Metals

Nickel-based filler metals are used when brazing copper to stainless steel or other dissimilar metals.

These alloys typically contain nickel as the main component along with other elements such as chromium, iron, and manganese.

Nickel-based filler metals offer good strength, corrosion resistance, and compatibility with different base metals.

They are especially useful for applications that require joining copper to stainless steel components, as they provide a reliable bond between the dissimilar metals.

Other Filler Metals

In addition to the silver, phosphorus, and nickel-based filler metals, there are various other filler metals available for specific applications.

Copper-zinc alloys, commonly known as brasses, are used in brazing copper and copper alloys with good strength and corrosion resistance.

Copper-tin alloys, or bronzes, offer excellent wear resistance and are suitable for applications such as tool brazing. Copper-silicon alloys provide a lower melting point compared to other filler metals and are often used in electronic and delicate component brazing.

It is essential to carefully select the appropriate filler metal for copper brazing based on the specific application, joint design, and desired performance.

Consider factors such as the base metal composition, melting point, mechanical properties, and compatibility with other materials. Consult industry standards, filler metal manufacturer recommendations, and expert advice to ensure the correct choice of filler metal for your copper brazing needs.

What are the key factors affecting the quality of copper brazed joints?

The quality of copper brazed joints can be influenced by several factors, including:

• Surface cleanliness: Proper surface preparation, including removal of oxides and contaminants, is crucial to achieve good wetting and bonding.
• Flux selection: The choice of appropriate flux is essential to promote wetting, prevent oxidation, and ensure a clean joint surface.
• Temperature control: Achieving the correct brazing temperature is critical to ensure the filler metal melts and flows properly without overheating the base metal.
• Joint design: The design of the joint, including clearance, gap size, and fit, can impact the capillary action and strength of the brazed joint.
• Heating technique: The heating method, such as torch brazing, furnace brazing, or induction brazing, should be selected based on the size, complexity, and material of the components.
• Brazing time: Sufficient time must be provided for the filler metal to fully flow and solidify, ensuring a strong and reliable bond.

Fluxes for Copper Brazing

Flux is a chemical compound that helps remove oxides and other impurities from the metal surface, allowing the filler metal to flow properly. The flux used for copper brazing should be specifically designed for use with copper alloys, as other types of fluxes may cause corrosion or weaken the joint.

Some of the commonly used fluxes for copper brazing include:

• Borax-based fluxes
• Fluoride-based fluxes
• Phosphate-based fluxes

Copper Brazing Applications

Copper brazing is commonly used in various industries, such as HVAC, plumbing, electrical, and automotive. Some of the common applications of copper brazing include:

• Joining copper pipes for plumbing and HVAC systems
• Manufacturing electrical components, such as transformers and motors
• Joining copper components in automotive radiators and air conditioning systems
• Manufacturing heat exchangers for various industrial applications

Copper Brazing Safety Precautions

When performing copper brazing, it is important to take appropriate safety precautions to prevent injury and damage to equipment. Some of the safety measures that should be taken include:

• Wear appropriate personal protective equipment, such as gloves, safety glasses, and heat-resistant clothing.
• Ensure adequate ventilation in the brazing area to prevent exposure to fumes and gases.
• Keep a fire extinguisher nearby in case of accidental fires.
• Use caution when handling hot equipment and materials.
• Follow proper disposal procedures for flux and other hazardous materials.

Why is copper brazing used?

It is commonly used in a variety of industries, including HVAC, plumbing, and automotive, for several reasons:

• Strength: Copper brazing creates a strong bond between two metals, which can withstand high temperatures and pressures.
• Corrosion resistance: Brazed joints are less susceptible to corrosion, as the filler metal creates a barrier between the base metals and the environment.
• Cost-effective: Brazing is a relatively low-cost method of joining metals compared to other methods such as welding or soldering.
• Versatility: Brazing can be used to join a wide range of metals, including copper, brass, steel, and aluminum, making it a versatile joining method.
• Cleanliness: Brazing produces a clean joint with no excess material or slag, making it suitable for applications where cleanliness is important.

Overall, copper brazing is a popular method of joining metals due to its strength, corrosion resistance, and cost-effectiveness, making it an ideal choice for a variety of applications.

What temperature is copper brazing?

The temperature of copper brazing varies depending on the type of brazing and the material being brazed. Generally, copper brazing is done at temperatures ranging from 1100 to 1500 degrees Fahrenheit (593 to 815 degrees Celsius).

Some Questions and their Answers

What types of filler metals are used in copper brazing?

Various filler metals can be used for copper brazing, including:

• Phosphorus-based alloys: Phosphorus-copper alloys are commonly used for copper brazing due to their low melting points and good flow characteristics.
• Silver-based alloys: Silver-copper alloys are often used when higher strength and better corrosion resistance are required.
• Other alloys: Other filler metals, such as gold-copper and nickel-copper, can also be used for specific applications.

Can copper brazed joints be disassembled?

Copper brazed joints are typically permanent and not designed for disassembly. Brazing creates a strong metallurgical bond between the components, making it difficult to separate the joint without damaging the parts.

Can copper brazing be used for dissimilar metal joining?

Yes, copper brazing can be utilized for joining dissimilar metals. By using appropriate filler metals and fluxes, it is possible to create strong bonds between copper and other metals, such as brass, bronze, stainless steel, and even some non-ferrous materials.

What are some common filler metals used in copper brazing?

Common filler metals employed in copper brazing include:

• Silver-based alloys: Silver brazing alloys are often used due to their excellent flowability and corrosion resistance.
• Phosphorus-based alloys: Phosphorus-containing brazing alloys are commonly used for joining copper and copper alloys, offering good wetting and capillary action.
• Nickel-based alloys: Nickel brazing alloys can be used for joining copper to stainless steel or other dissimilar metals.

What factors affect the choice of filler metal for copper brazing?

The selection of the appropriate filler metal for copper brazing depends on factors such as:

• Base metal composition
• Operating temperature
• Strength requirements
• Corrosion resistance
• Joint design and clearance

Consulting industry standards, filler metal manufacturer recommendations, and expert guidance can assist in choosing the most suitable filler metal for specific copper brazing applications.

Related Post:

• Working With Braze Aluminum
• Guide to Metal Brazing
• How to Braze Cast Iron
• Magnesium Brazing and Soldering
• https://copper.org/publications/pub_list/pdf/soldering_brazing_ads.pdf