Brazing and Soldering: Chapter 1
Review: Metal Properties
In this module, we will explore common types of metals used in HVAC along with their properties. We will also review how metals melt to form alloys. Skip to quiz!
Metals in HVAC
Most components of the HVAC systems are made of metals. The most commonly used metals in HVAC systems are:
Copper,
Aluminum, and
Steel
Copper, aluminum, and steel are great at transferring heat. This means they heat up and cool down quickly. They are used to carry the refrigerant in HVAC systems because of their ability to transfer heat.
Recall that refrigerant is a material that can easily change from a liquid to a gas and back again. This change is done by applying heat or taking heat away from the refrigerant. This is known as heat transfer.
When a material changes from a solid, liquid or gas, it is known as a phase change. Think of an ice cube. It melts into liquid and boils into steam when heat is applied.
Every material has its own properties. Recall that properties are characteristics of a material. Think about how a rubber band can stretch. This is a characteristic of the rubber band.
The following properties are useful in an HVAC system:
Ductility,
Malleability,
Heat Transfer,
Melting Point, and
Corrosion Resistance
Ductility is when a material can be stretched out when pulled. This is like a rubber band being pulled. Copper is very ductile and is often used to create wire because it can be pulled into thin strands.
Malleability is when a material can be formed under pressure. Think about how a blacksmith hammers red-hot metal into shape. Copper, aluminum and steel are easily worked into shapes used in HVAC systems.
Heat Transfer is when a material can heat up or cool down quickly. Recall that copper, aluminium and steel are great at transferring heat. That is why they are used to carry the refrigerant.
Recall that melting point is the temperature at which a solid becomes a liquid. Metals have a high melting point. This means they will not melt until temperatures reach above 1,000 °F in most cases.
Non-metals like plastic have a low melting point. This means that plastic will melt before metal. We use metals in HVAC systems because they can withstand the high temperatures without melting.
If a material does not react with the air, it is corrosion resistant. This means the material will NOT rust when it is exposed to air. Copper, unlike steel, is highly resistant to corrosion and used in areas that are prone to rust.
Other non-metal materials such as plastic and wood do NOT have the same properties as metal. Plastic and wood are prone to melt or even catch fire at the high temperatures used in HVAC systems. That is why we do not use these materials in an HVAC system.
Melting of Metals
Metal can withstand a lot of heat before melting. When enough heat is applied to a solid, it will break down and begin to act like a liquid. Anything can melt; for example, lava is just melted rocks.
Every material is made up of tiny things called molecules. In solids, these molecules are very close together and tightly packed. In liquids, these molecules are far apart and loosely packed.
When you apply heat to a solid, the molecules being to move away from each other. As this happens, the material begins to look and act like a liquid. Think about how ice cream will turn from a solid to a liquid on a hot day.
Melting is important because we can combine different metals together. We mix different melted metals together as we would with any two liquids. When we combine these metals, we get a new metal called an alloy.
An alloy is a combination of two or more metals. Alloys are created so we can combine the properties of different metals into a single metal. Steel is an alloy and it is a combination of carbon and iron. It is much stronger than either one.
Alloys are useful because we can combine properties we like from different metals into a new metal. We can combine a metal that is strong with a metal that is lightweight. This will make a strong and lightweight alloy.
When we melt things, we have to heat them, but eventually, these metals will cool down. The heating and cooling of metal in this way can cause it to change. These changes can be good, but they can also be bad for the metal.
One of the changes that can occur when a metal is cooled is distortion. Distortion is an unwanted change in the metal’s shape. This is similar to how cooking pans will warp and pop when heated in the oven.
Cooling can cause unwanted changes to the structure of the metal. The molecules in the metal are re-arranged. This change in the position of the molecules can cause the metal to become weak and break easily.
Types of Metal
Recall that the most common types of metal are
Copper
Aluminum
Steel
These metals are commonly used because of their properties.
Copper is not as strong as the other metals, but it is highly resistant to corrosion. It is also very ductile and can be formed into many shapes and pulled into thin wires. Like aluminum, copper is a great conductor of heat.
Copper can be found in the following HVAC components:
Condenser coils,
Evaporator coils, and
Refrigerant lines
Many of these components utilize copper's ability to transfer heat.
Aluminum is a strong and lightweight metal. It resists corrosion and is highly malleable.
Recall that it is also great at transferring heat.
Like copper, aluminum can be found in the following HVAC components.
Condenser coils
Evaporator coils
Ductwork
We use aluminum in ductwork as it is lightweight.
Steel is one of the strongest metals. However, steel is prone to rust and must be covered in a protective coating. It is also poor at transferring heat.
Steel is used to create the compressor casing. The casing is subjected to high forces and vibrations. It needs to be made of a strong material like steel.
Properties of metals can help us determine which metal should be used for a task. If a metal is prone to rust, like steel, it should not be used where it is likely to rust.
In this module, we have reviewed the common types of metal found in the HVAC system. We have seen how metals can be melted and used to create new alloys. Or how we can utilize the different properties of metal depending on the task we wish to accomplish.
Question #1: If a material can be stretched out when pulled, it is considered to have which property?
Malleability
Heat Conductivity
Ductility
Corrosion Resistance
Scroll down for the answer...
Answer: Ductility
Recall that Ductility is when a material can be stretched out when pulled, much like a rubber band. Copper can be pulled into thin lines to create a wire.
Question #2: What does Heat Transfer mean?
Creates Heat
Able to heat up and cool down quickly
Flow of Electricity
Able to withstand more weight
Scroll down for the answer...
Answer: Able to heat up and cool down quickly
Recall that metals can heat up and cool down faster than other materials like wood or plastic, and that is known as heat transfer.
Question #3: Copper is highly resistant to corrosion.
True
False
Scroll down for the answer...
Answer: True
Recall that Copper, unlike steel, is highly resistant to corrosion and used in areas that are prone to rust.
Question #4: Plastic and wood are not used in HVAC systems because they can easily melt and catch fire?
False
True
Scroll down for the answer...
Answer: True
Recall that plastic and wood are prone to melt or even catch fire at the high temperatures used in HVAC systems.
Question #5: What is an alloy?
A material found in the ground
A property
A mixture of two or more metals
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Answer: A mixture of two or more metals
Recall that an alloy is the mixture of two or more metals.
Question #6: Metals can become weak and break easily when the position of its ______ are re-arranged?
Energy
Molecules
Properties
Distortion
Scroll down for the answer...
Answer: Molecules
Recall that the change in the position of the molecules can cause the metal to become weak and break easily.
Question #7: What does Malleable mean?
Able to heat up and cool down fast
Can be pulled into thin strands
Flow of Electricity
Can be hammered into shape
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Answer: Can be hammered into shape
Recall that malleability is when a material can be formed under pressure.
Question #8: What does Corrosion Resistant mean?
Can be hammered into shape
Able to heat up and cool down fast
Can be pulled into thin strands
Does not react with air to form rust
Scroll down for the answer...
Answer: Does not react with air to form rust
Recall that Corrosion Resistant is when a material does not react with air to form rust.