• SkillCat Team

The Soldering Process in 5 Simple Steps

Brazing and Soldering: Chapter 5


Soldering


In this module we will learn about steps to carry out soldering process. We will also learn about how to inspect the joint after soldering. Skip to quiz!


Soldering Set Up


Recall that soldering is a metal-joining technique used to join both similar metals and different types of metals. Soldering is used for joining electrical parts and electrical wires in the circuit.

Electronic connections may be hand-soldered with a soldering iron.


Recall that soldering can also be used for joining copper pipes used in HVAC system. This is similar to brazing process. We need to use torch for heating the pipes to soldering temperature.


Recall that a joint is the gap formed between two pieces of the base metal. Recall that a clean joint is required for good capillary action. We need to clean the joint with the help of a sandpaper, a wire brush, or a sand cloth before soldering.


A fitting is used to connect two pipes together. We also need to clean the fitting before connecting to pipes. We should never touch metal to be joined with bare hands. Moisture, oil, or dust particles on our hands can prevent solder from flowing completely.


After successfully cleaning the pipe, the next step is applying flux using flux brush. This is because filler metals used for soldering do not have flux present in it. Recall that flux helps the filler metal flow better and protects the metal from rust.


We use a brush to apply flux. It is similar to flat head paintbrush. Its purpose is to apply the flux perfectly in smaller areas for soldering easily. We need to apply flux only on ends of pipe that we are going to connect.


We can start applying a thin layer of flux on the ends of pipes and the insides of the pipe fittings. Connect the pipe ends using a fitting. If any excess amount of flux is present, it will come off the joint. Wipe it off using a rag or cloth.



Soldering the Joint


Once the metal is fluxed and torch is set up, it is time to heat the joint. Before we start heating the joint, we heat the pipe by using neutral flame. Recall that a neutral flame is used for uniform heating. Recall that a neutral flame is produced by adjusting the supply of oxygen.

We heat the joint from the opposite end to where we apply solder. This will enable the solder to get pulled to the front because of capillary action. Recall that capillary action draws molten filler metal through the gap between the metals to be joined.


We can check whether soldering temperature has reached by touching the solder on the joint to see if it melts. The heat present on the joint will help the solder to melt and create a bond between the two parts. Continue the joining operation until a silver ring is formed around the joint.


Checking the Joint


Sometimes, the joint formed using soldering has extra filler metal and uneven finish. We need to clean the solder joint when it is completely solidified. The solder joint can be easily cleaned by sand paper or abrasive cloth.


Recall that the next step after cleaning the joint is inspecting the joint. We need to examine the joint visually for any cracks and pinholes. Much like brazing, nitrogen leak test can also be used for checking soldered joint.


Recall that before starting nitrogen leak detection test, the system must be isolated. For isolating the system turn OFF the system and close all the valves connected to the piping.


As shown in the video, we need to test the system at the minimum allowable system pressure to avoid damage to components. Pressure limit for testing is specified by the manufacturer.

The least pressure limit in HVAC system is evaporator pressure and it is 500 psi as per manufacturer recommendation.


Recall that we use purging in brazing to remove impurities inside the pipe. As the soldering temperature is lower than the temperatures for brazing, soldering does not oxidize the inside of a copper pipe. So, we don’t need to purge the pipe with gas when we are soldering.


The stepwise process for soldering the joint is as follows:

  • Cleaning the joint,

  • Fluxing the joint,

  • Heating the joint, and

  • Applying filler metal

Cleaning and nitrogen leak test is carried out to inspect leak present in the pipe joint.





Silver Soldering


In this module we will learn about steps to carry out silver soldering process. We will also discuss their application in brief. Skip to quiz!


Basics


Recall that silver soldering, also known as hard soldering, uses a silver alloy-based filler metal.

As this silver solder contains silver about 45% or higher, it is also known as a hard solder. Because of the higher percentage of silver, the temperature we will need to melt this solder is more.


Recall that ductility is when a material can be stretched out when pulled. The silver increases the ductility of the filler and allows it to flow at a slightly lower temperature. This results in a better flow of solder into the joint.


Recall that lead used for soft soldering is harmful. Silver solder or hard solder is lead-free. This makes them safe to work with.


Since the temperature for silver soldering is higher, silver-soldered joint is very much stronger than other soldering methods. The joints cannot crack due to high temperature and vibration.

We can use them for high temperature applications.

Recall that soft solder has phosphorus in it. Phosphorus does not react with steel properly.

This creates a weaker joint. Silver solder does not have phosphorus and can be used to solder copper to steel.


The advantages of silver solder makes them suitable for many application. They are used for joining metals in HVAC, automobile, and aerospace industries.


Recall that HVAC system works on refrigeration cycle that includes temperature changes and pressure changes. A compressor used for residential unit often specifies a maximum temperature of 225 °C. If you use soldering method that cannot sustain this temperature, joint will break.


Recall that silver based alloy does not have flux in it. We need to apply flux when we are joining metals other than copper. For example, ducts used for HVAC application are made of galvanized iron. Here, we use flux before silver soldering.


Recall that flux helps the filler metal flow better and protects the metal from rust. Silver flux is available in paste or powdered form. Silver flux is useful for temperature of about 600 ℃. That is why it is used only for silver soldering.


Silver flux will successfully flux all the common engineering materials. The residues of silver flux are soluble in hot water. This makes them easier to clean with water after metal is soldered.


Recall that the stepwise process for soldering the joint is as follows:

  • Cleaning the joint,

  • Fluxing the joint,

  • Heating the joint, and

  • Applying filler metal

Similar process is followed for silver soldering.


We will start with cleaning the pipe. The next step is application of flux on the pipe in an adequate amount. Recall that excess flux can be harmful. It can get into the system and block the pipe.


After applying flux we connect fitting to join pipe ends and start heating the joint. Recall that for soft soldering copper pipe we use flux-free joint and start heating from one end and apply solder on the other end.


When we are silver soldering with flux, we must heat the metal on both sides of the joint. We need to start heating the pipe first. This will boil off the water in the flux.


We now start heating the fitting evenly. When the flux starts to take watery, runny appearance, that is the correct time to apply silver solder. We only need to touch the silver solder till it melts and fills the joint. Holding too long will cause unnecessary wastage of silver solder.


Recall that flux residue has a corrosive nature that can lead to joint failure. Flux residues will remain on the joint after soldering.If they are not removed, it forms small holes in the pipe that eventually lead to leakage.


We need to wipe the flux off with a wet rag, after the joint is dry to avoid contaminating the joint with water. Recall that residues are soluble in hot water. We can also remove them by inserting the fitting into hot water.


Silver soldering is used for joining metals in HVAC, automobile and aerospace industries. Silver flux is available in paste or powdered form. Flux residue has a corrosive nature that can lead to joint failure. So, we need to remove flux residues after soldering.




Soft Soldering


In this module we will learn about steps to carry out soft soldering process. We will also discuss their application in brief. Skip to quiz!


Basics


Recall that soft soldering differs from hard soldering by the type of filler metal used. The filler metals used for soft soldering can be classified as:

  • Leaded, and

  • Lead-free

The solder having lead in it is composed of about 60% tin and 40% lead. We cannot use lead for pipes that carry water through them because lead is poisonous and can make the water unsafe to use. This is why we use leaded solder only for joining electronic components.


The soft soldering for joining electronic components is carried out using soldering iron. The soldering iron uses electricity to melt the filler metal.The video shows complete soldering process for electronics.


Many lead-free solders have tin, silver, copper, and phosphorus in them. Recall that hard solder has 45% or higher amount of silver. A lead-free soft solder contains about 5% to 30% of silver.


Recall that if the percentage of silver is lower, the temperature we will need to melt lead-free solder is less. The temperature required for soft-soldering is lower than silver soldering.

The temperature is below 400°C.


Due to low working temperature, soft soldering is best suitable where the joint is not exposed to high heat, and vibrations. For example, soft soldering is used to join electronic components and small copper tubes for refrigerants. In HVAC system, we use soft soldering for connecting thermostatic expansion valve.


Valves have rubber bushings that help prevent damage to the valve due to vibration. We cannot use brazing or other soldering methods for pipes connected to valves, and expansion valves. This is because rubber bushings can catch fire at high temperatures required for these methods.


Soft solder has poor wetting property. Recall that wetting is the ability of a liquid to maintain contact with a solid surface. This property helps the filler metal to flow better.


Recall that silver alloy does not contain flux. Recall that flux helps the filler metal flow better.

So, we need to add flux during soft soldering.



Soft Soldering the Joint


Recall that the stepwise process for soldering the joint is as follows:

  • Cleaning the joint,

  • Fluxing the joint,

  • Heating the joint, and

  • Applying filler metal

Similar process is followed for soft soldering.

Recall that valves have rubber bushing that can catch fire when heated. Soft soldering is used for connecting piping to valves. We need to keep the flame away from valve and cover valve body with wet rag to avoid damage to rubber bushings.


We need to connect the solder to the tubing before we start heating. Then we can start heating the tubes that we want to connect. We then apply flux and continuously heat the joint.

The filler metal melts and joint is created.


Soft soldering is carried out at much lower temperature than silver soldering. Soft soldering is best suitable where the joint is not exposed to high heat and vibrations. Soft soldering is used for joining metals in connecting valves and electronics components.



Question #1: What do we use for soldering? (select all that apply)

  1. Torch

  2. Soldering iron

  3. Welding electrode

  4. Metal powder

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Answer: Torch

Soldering iron

Recall that electronic connections may be soldered with a soldering iron and copper pipes can be soldered using torch.


Question #2: We should clean the joint with hands so that no dirt is present.

  1. True

  2. False

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Answer: False

False! We should never touch metal to be joined with bare hands. The moisture, oil or dust particles on our hands can prevent solder from flowing completely in the joint.


Question #3: What do we use for cleaning the joint?

  1. Sandpaper, a wire brush

  2. Soldering iron

  3. Flux

  4. Metal powder

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Answer: Sandpaper, a wire brush

Recall that we need to clean the joint with the help of an sandpaper, a wire brush or a sand cloth.


Question #4: What is one of the advantage of using flux?

  1. It is used for reducing capillary action

  2. It is used for heating the joint

  3. It protects the metal from rust

  4. It control pressure inside joint

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Answer: It protects the metal from rust

Recall that flux helps the filler metal flow better and protects the metal from rust.


Question #5: We should apply excess flux for strong joint.

  1. False

  2. True

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Answer: False

False! We should apply a thin layer of flux and wipe off excess flux from joint.


Question #6: We should heat the joint from all sides.

  1. True

  2. False

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Answer: False

False! We need to start heating the joint from opposite end of applying solder. This will enable the solder to get pulled to the front because of capillary action.


Question #7: If we exceed the pressure limit, it will damage the components of system.

  1. False

  2. True

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Answer: True

True!

We need to test the system at the minimum allowable system pressure to avoid damage to components.


Question #8: Where do we connect red high side hose from gauge manifold?

  1. Oxygen cylinder

  2. Nitrogen Cylinder

  3. Indoor unit

  4. Outdoor unit

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Answer: Outdoor unit

Recall that outdoor unit is at higher pressure compared to indoor unit. The red high side hose from gauge manifold is connected to the outdoor unit.


Question #9: What is the use of gauges?

  1. Create vacuum

  2. Change temperature

  3. Show pressure reading

  4. Control pressure

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Answer: Show pressure reading

Gauges indicate pressure. They are present on the regulator to verify the pressure of nitrogen that is going to be inserted into the piping.


Question #10: How do you ensure there is leakage present by monitoring gauges?

  1. Gauge show leakage message

  2. Pressure fluctuation indicate leakage

  3. Pressure limit for leakage is noted

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Answer: Pressure fluctuation indicate leakage

Monitor the low pressure and high pressure side gauges. If two reading dont match there is leakage present.


Question #11: How do you recognize the leakage during nitrogen leak test?

  1. Using temperature sensor

  2. Bubbles coming out after applying soapy water

  3. Measuring nitrogen volume

  4. Measuring nitrogen mass

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Answer: Bubbles coming out after applying soapy water

Soapy water is used to identify the leak point.

Leaks present in the material will cause gas bubbles to form at defective spots.


Question #12: Why the system is not purged with nitrogen while soldering the joint?

  1. Soldering is leak proof process

  2. Purging requires high temperature

  3. Purging can cause failure of soldered joint

  4. Soldering does not oxidize the inside of a copper pipe

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Answer: Soldering does not oxidize the inside of a copper pipe

Recall that the soldering temperature is lower temperatures than brazing, and it does not oxidize the inside of a copper pipe.


Question #13: What percentage of silver is present in silver solder?

  1. 40 to 60

  2. 45 or higher

  3. 15 to 30

  4. 5 to 15

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Answer: 45 or higher

Recall that a soft solder contains about 45 percent silver or higher.


Question #14: The strength of silver soldering is more than brazing and welding process.

  1. False

  2. True

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Answer: False

Recall that silver soldering is carried out at lower temperature than brazing and welding. The strength of silver soldering is less compared to brazing and soldering but it is more than other soldering methods.


Question #15: Where do we use silver soldering for joining metals? (select all that apply)

  1. Electronics

  2. Automobile industry

  3. Aerospace industry

  4. HVAC industry

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Answer: Automobile industry

Aerospace industry

HVAC industry

Silver soldering is used for joining metals in HVAC, automobile and aerospace industries.

We use soft solder for electronics.


Question #16: Which process do we use for joining copper to steel.

  1. Soft soldering

  2. Silver soldering

  3. Electronics soldering

  4. Soldering iron

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Answer: Silver soldering

Silver solder does not have phosphor and can be used to solder copper to steel.


Question #17: Silver flux is used for joining low temperature soft soldering.

  1. True

  2. False

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Answer: False

False! Recall that silver flux is useful for temperature of about 600 ℃. That is why it is used only for silver soldering.


Question #18: What is the correct order of performing silver soldering?

  1. Cleaning, Heating, Applying filler metal, Fluxing

  2. Cleaning, Fluxing, Heating, Applying filler metal

  3. Fluxing, Heating, Applying filler metal, Cleaning

  4. Cleaning, Heating, Fluxing, Applying filler metal

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Answer: Cleaning, Fluxing, Heating, Applying filler metal

Recall that the stepwise process for silver soldering the joint is as follows:

  • Cleaning the joint

  • Fluxing the joint

  • Heating the joint

  • Applying filler metal


Question #19: How to remove flux from joint? (select all that apply)

  1. Using paint remover

  2. Using wet rag

  3. Using pipe dope

  4. Inserting the joint into hot water

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Answer: Using wet rag

Inserting the joint into hot water

Recall that we can wipe the flux off with a wet rag after the joint is dry.We can also remove them by inserting the fitting into hot water.


Question #20: What is the composition of lead solder?

  1. 60% tin and 40% lead

  2. 60% silver and 40% lead

  3. 60% aluminum and 40% lead

  4. 60% copper and 40% lead

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Answer: 60% tin and 40% lead

The solder having lead in them are composed of about 60% tin and 40% lead.


Question #21: Flux does not help while soldering electronics components using soldering iron.

  1. False

  2. True

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Answer: False

False! Oxide layer present on copper wire is barrier for bonding solder and copper. Flux removes the oxide layer and helps bonding of solder and copper.


Question #22: Flux removes oxide layer on copper wires at room temperature.

  1. True

  2. False

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Answer: False

False!

Flux starts to show its action when it is heated to melting temperature of solder.


Question #23: How do you clean burnt mark or flux residue from electronic component formed due to soldering.

  1. Using hot water

  2. Using acids such as isopropyl alcohol

  3. Heating the component

  4. Using teflon tape

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Answer: Using acids such as isopropyl alcohol

Recall that black spots formed on electronic component after soldering are flux residues. We can clean them using isopropyl alcohol and scrub it off using brush.


Question #24: What percentage of silver is present in soft solder?

  1. 40 to 60

  2. 45 and above

  3. 5 to 30

  4. 5 to 15

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Answer: 5 to 30

Recall that a soft solder contains about 5 to 30% silver.


Question #25: Soft soldering is used for joints subjected to high heat and vibration.

  1. False

  2. True

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Answer: False

False! Recall that soft soldering is carried out at much lower temperature than silver soldering.

Due to low working temperature, soft soldering is best suitable where the joint is not exposed to high heat, and vibrations.


Question #26: Flux is not required for soft soldering.

  1. True

  2. False

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