• SkillCat Team

Metal Joining: Brazing vs Welding vs Soldering

Updated: Jun 23

Brazing & Soldering: Chapter 2


Introduction to Brazing and Soldering


In this module, we will introduce three metal-joining techniques. These techniques are welding, brazing and soldering. Skip to quiz!


Metal-Joining Techniques


We join two similar or different types of metals using the metal-joining techniques. It involves the use of high heat to join metals.


In this module, we will come across the following terms:

  • Base Metal,

  • Joint, and

  • Filler Metal

Let’s take a quick look at what they mean before learning about the metal-joining processes.

Base metals are the pieces of metals that we join together. A joint is the gap formed between two pieces of the base metal when we push them together to join. We need to fill this gap to join the base metals permanently.


We join the base metals with the help of a filler metal. This metal acts as a glue that we use to fill the gap in the joint. It holds the base metals together just like a glue holds two pieces of paper together.


Welding


Welding is a metal-joining technique. It uses high heat to join the same type of metal together.

This means that you can only weld steel to steel, or aluminum to aluminum.


Welding can produce temperatures up to 5,660°F. That is almost as hot as the sun! Recall that metals can withstand such high temperatures.


Welding is done by creating a lot of heat using electricity. It uses an electrode to carry the electricity. The electrode heats up as electricity flows through it, just like the filament in a light bulb.


The electricity creates an arc, which is like a very hot spark between the electrode and the base metal. This arc melts the electrode and the base metal. It creates a pool of mixture of hot liquid metal.


The melted metals begin to mix in the weld pool, much like any two liquids would mix. These mixed metals will then begin to cool down. Once the weld pool is fully cooled, the metals will be permanently combined.


When we weld, we are creating what is known as a state change in the metal. As we heat metal, it turns from a solid state to a liquid state. And as it cools, it turns from a liquid state back to a solid state.


Recall that welding produces a lot of heat. Non-metals have a very low melting point, which means they will melt at low temperatures. If you try to weld a non-metal, like plastic, it will melt and catch fire!




Brazing


Brazing is another metal-joining technique. Brazing can be used to join two similar metals. Unlike welding, brazing can also join two different types of metal. Recall that we can only join two similar metals by welding.


When brazing, a filler metal is melted between two pieces of metal. The filler metal acts as a glue that holds the pieces of metal together.


Brazing is different than welding because it does NOT melt the base metals. Base metals are just the two metals being joined. Instead, brazingonly melts the filler metal.


In brazing, the base metals are heated to about 840 °F. The filler metal is then placed on the heated surface of the base metals.


The heat from the base metal is what causes the filler metal to melt. The liquid filler metal leaks into the joint created by the two metals being joined.


The filler metal must melt at a lower temperature than the base metals. This means that the filler metal will melt first, before the base metals. Otherwise, the base metals will melt and you will NOT be able to apply the filler metal.


Once the liquid filler metal is in the joint, it begins to cool. After the filler metal cools in the joint, it becomes a solid and permanently combines the pieces of metal.Recall that this change from a liquid to a solid is a state change.


Much like welding, brazing is not suitable for many non-metals. Non-metals such as plastic and wood can melt and catch fire when exposed to high heat. That is why we do not braze non-metals.




Soldering


Soldering is another metal-joining technique. Soldering occurs at temperatures below 840 °F. This means it occurs below the brazing temperature.


Soldering occurs by heating the solder until it melts. The melted solder is applied over the parts being soldered. Unlike brazing, the base metals are NOT heated during the soldering process.


The melted solder is applied over the parts being soldered. Once the solder cools these parts are permanently joined.


Soldering is similar to brazing as it also uses a filler metal to join two metals. The filler metal used in soldering is called a solder. Much like in brazing, the solder has a lower melting point than the metals being joined together.


We use two types of solder in soldering:

  • Soft solder, and

  • Hard solder

They are classified based on the temperature they melt at.


Soft solder is a low-temperature tin-based solder, which means it melts at a lower temperature than hard solder. These are available in lead and lead-free options.


Soft soldering is used for joining electronic components. It uses soldering iron to heat the tin based solder.


Hard soldering creates a stronger bond compared to soft soldering and involves higher temperatures to melt the solder material. This material is normally brass or silver. It is similar to brazing process and requires the use of a blowtorch to melt.


When we use silver as the solder material, hard soldering may be referred to as silver soldering or silver brazing.This method is used for joining copper tubes used in HVAC system because it creates stronger bond than soft soldering.


One of the dangers of joining metal is poisoning. When the lead in the filler metal or solder is heated it can release toxic fumes. We will look into detail at the precautions to follow while joining metals in the next module.


Welding, brazing, and soldering are metal-joining processes used in industries for joining base metals. We join the base metals with the help of a filler metal. Filler metal fills the gap to join the base metals permanently.




Metal-Joining Techniques - Precautions


In this module, we will identify the dangers of metal-joining techniques. We will look at the precautions to follow to avoid them. We will also discuss their applications in brief. Skip to quiz!


Welding, Brazing and Soldering


Recall that welding, brazing and soldering are all metal-joining techniques. They all form a permanent joint between the base metals.


The difference between these metal-joining techniques are based on the following:

  1. Temperature,

  2. The metals being joined, and

  3. Their application.

Welding produces heat as high as 5,660 °F. It is used to combine similar metals, typically steel and cast iron. We use welding in the automobile industry and building structures.

Brazing produces heat over 840 °F. It is used to combine similar as well as different metals. Brazing is typically performed on copper, brass, and aluminum. We use brazing to create a leak proof joint while joining two pipes.


Soldering produces heat below 840 °F. The low heat allows metals like copper, brass, silver, and gold to be soldered. We use soldering in electronics mainly on circuit boards.


Recall that these metal joining techniques require a lot of heat and are not suitable for many non-metals. The high heat can not only melt or catch non-metals such as plastic on fire. It can also damage the surrounding area.


Precautions


There are various dangers associated with joining metal. These dangers include shocks, burns, and even poisoning.

Recall that welding produces temperatures as high as 5,660 °F. At these high temperatures, ultraviolet and infrared rays are created. These rays can cause burns to your skin and even your eyes.


Another danger is poisoning. Recall that filler metals like solder contain lead which is toxic. Poisoning is caused by toxic fumes released by filler metals.


Although welding, brazing and soldering can be dangerous, there are ways to prevent harm. This first step to avoiding harm is to always follow the recommended procedures when using the equipment. These procedures are normally provided by the manufacturer.


Wearing proper protective equipment is another way to avoid injury. This equipment includes face shield, safety goggles, and flame-resistant clothing. These keep you safe from shocks, burns, and even toxic fumes.


We should avoid welding, brazing, and soldering:

  • near flammable materials, and

  • in a poorly ventilated area.

We should always have a fire extinguisher readily available.


Welding, brazing, and soldering differ from each other based on the metal being joined, temperature, and application. These techniques can be dangerous and so proper precautions must be taken.




Filler Metals


In this module, we will cover filler metals and how they are used. We will explore the different types of filler metals and their drawbacks. Skip to quiz!


Filler Metal


Recall that in brazing and soldering, we use a filler metal to join two metals. A filler metal acts like a glue that holds the two base metals together. Recall that the base metals are the two metal parts being combined.

Recall that the melting point is the temperature at which a solid becomes a liquid. Filler metals typically have a lower melting point compared to the base metal. This is because we want the filler metal to be melted rather than the base metal when we apply heat.


The filler metal is melted by a torch or electricity into a joint between the two metal parts. Recall that a joint is the gap created when two pieces of metal are touching.


In most cases when using a filler metal, it is important to heat the base metal first. After the base metal is heated, you then apply the filler metal.


Gently drag the filler metal along the joint between the base metals. The heat from the base metals will melt the filler metal, and it will fill the joint. When the filler metal cools, the base metals will be permanently combined.


Types of Filler Metals


Filler metals are typically made from a variety of alloys. Recall that alloys are made by mixing two or more metals to create a new and improved metal. These alloys are used in welding, brazing, and soldering process.


Alloys are generally more useful than pure metals. Pure metals are normally weak, they rust easily, and are too soft to hold a shape.


Recall that electrodes are used as filler metals in the welding process. This filler metal comes in the shape of a rod, and is heated by passing electricity through it.


The electricity creates an extreme amount of heat, just like an electrical heater. The heat melts the electrode much like a hot glue gun, while also melting the base metals. When the filler metal cools, the base metals are permanently joined.


There are three different types of electrodes used in the welding process:

  • Covered electrode,

  • Bare electrode, and

  • Tubular electrode wire

The covered electrode is an electrode covered in an alloy powder. As the electrode melts and forms the joint, the alloy powder creates a protective coating on the joint called slag.

The slag floats on top of the molten joint and protects it from oxidation. Recall that rust is formed during oxidation when metal reacts with oxygen. This slag is like a protective metal skin that covers the joint.


Bare electrodes have no protective coatings and can easily react with the air and other gases. This limits their applications and makes a weak joint.


Tubular electrode wire comes in a coil and is fed through the welding machine. Much like the covered electrode, the wire produces a protective coating around the weld.


Depending on the application brazing and soldering use different alloys as a filler material. They are mainly classified based on the materials used for rods.


Braze alloys and Solder alloys are available in powder, paste, foil, rods, bars and wires. Typically, wire and rod forms are used with torches as they are easiest to apply while heating.


Filler metals used for brazing are silver, copper, and aluminum alloys. They are also called braze alloys. Some of the common types of braze alloys used are:

  • Aluminum-Silicon

  • Copper-Tin (Bronze)

  • Copper-Zinc (Brass)

  • Gold-Silver

Recall that soft soldering uses lead and lead free solder. The solder having lead in it is composed of about 60% tin and 40% lead. Lead-free solders have tin, silver, and phosphorus in them. The silver content is lesser in soft solder,


Recall that silver brazing, known as hard soldering, uses a silver alloy based filler metal. The silver content is much higher in hard solder compared to hard solder. It contains other metals such as copper, zinc, and cadmium.


Almost all filler metals have flux in them. Flux helps the filler metal flow better and protects the metal from rust. Flux can be applied to the surface before heating or can be found in the filler metal itself.


One filler metal that does NOT have flux in it is silver based alloy. So, we need to apply flux when joining metals using silver-based alloys.


Flux is not required when we are joining copper pipe to another copper pipe. This is because the phosphorus present in soft solder allows the rod to self-flux on copper. Recall that refrigerant lines in HVAC system are made of copper. Soft soldering is best suited for soldering copper pipes.


If we overuse flux, it can get in the system and cause more harm than good. Soft soldering and brazing reduces the chance of flux getting stuck in the HVAC pipes and blocking the refrigerant flow.


Common Filler Metals


In HVAC, rods for soldering and brazing are classified based on the percentage of silver content in the rod. They are:

  • 0% Silver Alloy,

  • 5% Silver Alloy, and

  • 15% Silver Alloy

0% silver alloy does not have silver present in it. This alloy is used for brazing.

Silver alloy can be expensive depending on how much silver is in the filler metal. 5% silver alloys are cheap but create weak joints. This is because they do not flow as easily as the 15% silver alloys.


15% silver alloys contain the maximum amount of silver. This alloy is more expensive and creates strong joints. These alloys are used in HVAC systems because they need strong and trustworthy joints.


Filler metals are used to permanently combine pieces of metal. They are melted into a joint and cooled. They come in various shapes and sizes and have their own advantages and disadvantages.





Question #1: Welding is done by creating a lot of heat using a electricity, and this electricity creates an _________.

  1. Plug

  2. Arc

  3. Bond

  4. Filler Metal

Scroll down for the answer...












Answer: Arc

Recall that electricity creates an arc, which is like a very hot spark between the electrode and the metal.


Question #2: Welding can produce temperatures up to _________.

  1. 5,660°F

  2. 3,222°F

  3. 1,789 °F

  4. 7,351 °F

Scroll down for the answer...

















Answer: 5,660°F

Recall that welding can produce temperatures up to 5,660 °F.


Question #3: Brazing can be used to join two different metals together.

  1. True

  2. False

Scroll down for the answer...








Answer: True

Recall that brazing can be used to joining two or more different metals together.


Question #4: Why is it important that the filler metal has a lower melting point than the base metals?

  1. So that the filler metal will melt before the base metals

  2. So the filler metal can become a solid

  3. The base metals will melt first

  4. So the metals can break apart

Scroll down for the answer...












Answer: So that the filler metal will melt before the base metals.

Recall that the filler metal must have a lower melting temperature than the base metals so that it will melt before the base metals.


Question #5: Soldering is carried out at a temperature above brazing temperature.

  1. True

  2. False

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Answer: False

Recall that soldering occurs at temperatures below 840°F.

In brazing, the base metals are heated to about 840 °F.


Question #6: In soldering, we melt the filler metal and base metal to form a joint.

  1. True

  2. False

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Answer: False

False! Recall that soldering occurs by heating the solder until it melts. he melted solder is applied over the parts being soldered.


Question #7: We use torch for hard soldering the base metals.

  1. True

  2. False

Scroll down for the answer...







Answer: True

Recall that hard soldering is similar to brazing process and requires the use of a blowtorch to melt.


Question #8: What are the main differences between welding, brazing, and soldering? (Select all that apply)

  1. Metals that are joined using these processes are different

  2. Only welding uses heat to join metals

  3. Temperature of all processes are different

  4. Number of people required for carrying these processes are different

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Answer: Metals that are joined using these processes are different

Temperature of all processes are different

The difference between welding, soldering, and brazing metal-joining techniques are based on the following:

  1. Temperature,

  2. The metals being joined, and

  3. Their application.

Question #9: Which process do we use for joining cast iron?

  1. Soldering

  2. Welding

  3. Brazing

  4. Metal Fusing

Scroll down for the answer...












Answer: Welding

Recall that welding produces heat as high as 5,660 °F. It is used to combine similar metals, typically steel and cast iron.


Question #10: What are the main dangers associated with Welding, Brazing, and Soldering? (Select all that apply)

  1. Shock

  2. Fall

  3. Poisoning

  4. Burns

Scroll down for the answer...













Answer: Shock

Poisoning

Burns

Recall that there are various associated with these techniques such as Shock, Burns and even Poisoning.


Question #11: Which safety gear should we wear during welding to prevent injury?

  1. Hard hat

  2. Safety glasses, gloves, flame-resistant clothing and face shield.

  3. Gloves, hard hat

  4. Flame-resistant clothing.

Scroll down for the answer...








Answer: Safety glasses, gloves, flame-resistant clothing and face shield.

Recall that wearing proper protective equipment is another way to avoid injury. This equipment includes face shield, safety goggles, and flame-resistant clothing.


Question #12: Compared to the base metal, the filler metal has ______ melting point.

  1. High

  2. Low

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Answer: Low

Filler metals typically have a low melting point than the base metals they join.


Question #13: Pure metals are stronger than alloys.

  1. True

  2. False

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Answer: False

False! Recall that Pure metals are weaker than alloys.


Question #14: What does slag prevent?

  1. Light

  2. Melting

  3. Oxidation

  4. Electricity

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Answer: Oxidation

Recall that slag protects the metal from oxidizing with the air. This prevents rust formation.


Question #15: Which of the following electrode is covered in alloy powder?

  1. Covered electrode

  2. Bare electrode

  3. Tubular electrode

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Answer: Covered electrode

Recall that the covered electrode is an electrode covered in an alloy powder.


Question #16: Which of the following filler metal is NOT used for brazing? (select all that apply)

  1. Covered electrode

  2. Bronze

  3. Brass

  4. Bare electrode

Scroll down for the answer...








Answer: Covered electrode

Bare electrode

Recall that the common types of braze alloys used are:

  • Aluminum-Silicon

  • Copper-Tin (Bronze)

  • Copper-Zinc (Brass)

  • Gold-Silver0


Question #17: Soft solder and hard solder has same content of silver in it.

  1. False

  2. True

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Answer: False

Recall that the silver content is much higher in hard solder compared to hard solder.


Question #18: Which of the following does not have flux in them?

  1. Braze alloys

  2. Silver based solder alloys

  3. Aluminium alloys

  4. Welding electrode

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Answer: Silver based solder alloys

Recall that one filler metal that does NOT have flux in it is silver based alloy.


Question #19: One drawback to 5% silver alloy is that it creates a ______ joint.

  1. Expensive

  2. Cheap

  3. Strong

  4. Weak

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Answer: Weak

Recall that 5% silver alloys are cheap, but they create weak joints.


Question #20: One drawback to 15% silver alloy is that it is ______.

  1. Strong

  2. Weak

  3. Expensive

  4. Cheap

Scroll down for the answer...












Answer: Expensive

Recall that 15% silver alloy alloy is more expensive and creates strong joints.




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