What is Welding?

Have you ever wondered how the body of a car gets attached together? Or how builders combine huge pieces of metal to make giant skyscrapers?

These feats of engineering are possible because of welding. Welding is a method of heating pieces of metal until they melt and fuse into one piece.

Making or fixing many everyday objects involves welding. Ships, airplanes, and train tracks all rely on welding. Even the pipes that bring water to your shower were probably welded together!

Image - Text Version

Shown is a colour photograph of a car going through an assembly line. The bare metal body of the car takes up much of the frame. The car does not have a trunk door, so the entire rear section of the car interior is visible. A robotic welding arm creates a shower of sparks from the trunk section on the right passenger side.

 

History of Welding

People use welding techniques to make many modern technologies. But humans have been welding for thousands of years. People began welding at the beginning of what’s known as the Bronze Age around 3300 BCE. Around this time Egyptians used charcoal to heat and fuse pieces of metals.

Image - Text Version

Shown is a colour photograph of hot molten bronze being poured into a mold. The mold looks a bit like a brick with a cylindrical hole down the centre. A red hot cup-shaped container holds the liquid metal. It is being held by a pair of sturdy metal tongs. The two sides of the mold are held together by two sturdy sticks which are tied together with leather strapping. The bottom of the mold is in a barrel containing sand.

 

Did you know?

Bronze is an alloy made of the chemical elements copper and tin.

Since then, people have been refining new welding techniques. People developed forge welding in the Middle Ages. This involves heating pieces of metal and then hammering them together.

Image - Text Version

Shown is a colour photograph of the Iron Pillar of Delhi. The 7.3 metre iron pillar is a dark rusty grey colour. Most of the pillar is cylindrical and unadorned, but the top metre has bands of decorative elements. Pillar stands alone in an empty courtyard. A small decorative pale yellow metal fence surrounds the decorative base of the pillar.

 

In the 1800’s, people began developing new welding techniques involving electricity. People began using electric arcs to heat and melt metals. Arc welding uses an electric arc to fuse metals together. Many of the welding techniques that we use today involve arc welding.

Image - Text Version

Shown is a colour photograph of a person arc welding. The person is wearing dark grey coveralls and an elaborately decorated welding face shield. Blue sparks and white light are coming off the piece of metal where the electrode touches the base metal.

 

These techniques were further improved throughout the 20th century. Even more recent welding techniques involve magnetic pulses, lasers, x-rays and automated robots.

Chemistry of Welding

Think about how you would attach two pieces of paper together. You might use tape, staples or glue. Even after attaching them, the paper is still paper and the tape is still tape, even if the paper-tape seems to be one thing. But what if you wanted to attach two metal bars together. Would you use tape or glue now? Probably not. Especially if you did not want the metal bars to come apart! This is where welding comes in. Welding is not like glue. It combines two pieces of metal into one. This makes for a very strong bond between pieces. But how does it work? We can use chemistry to help us understand the process.

Solid metals have organized structures made of atoms. These atoms are held together with metallic bonds. Metallic bonds are very strong and hold atoms together tightly. This is because the atoms share electrons. Lots of energy is needed to break metallic bonds.

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Shown is a colour illustration showing the arrangement of atomic nuclei and electrons in a metallic bond. The nuclei are represented by red circles with black plus signs on them to indicate their positive charge. There are twenty nuclei arranged in four rows and five columns.
The electrons are represented by blue circles with black minus signs on them to indicate their negative charge. Encircling each nuclei is a translucent pink area. This represents the area where the electrons can be found. The blue electrons are scattered throughout this pink region.

 

These strong bonds explain many of the properties of metals. Metals generally have high melting points. They are also malleable and ductile. This means that they can be stretched and formed into different shapes without breaking. We can weld metal because of these properties.

Did you know?

Tungsten has the highest melting point of all pure metals. Its melting point is 3422 °C.

Heating a metal to a very high temperature changes it from a solid to a liquid. The metallic bonds are not completely broken, but there is more space between the atoms. When welding, liquid metals combine. It would be kind of like melting together cheddar and mozzarella cheese in a grilled cheese sandwich.

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Shown is a photograph of a grilled cheese sandwich. The slices of bread are toasted, and slightly burned. The sandwich is cut in half diagonally. Gooey melted white and orange cheese is oozing out of the sandwich and onto the surface below.

 

In their liquid form, atoms from both pieces of metals would move around and their electrons would overlap with each other. When the metal cools, a solid is once again formed.

The atoms of one metal may replace the atoms of the other metal (top image) or they may fit around the atoms of the other metal (bottom image).

Image - Text Version

Shown is a colour illustration showing the arrangement of atomic nuclei when two metals are melted together. The nuclei of one metal are represented by red circles with black plus signs on them to indicate their positive charge. The nuclei of the other metal are represented by yellow circles with black plus signs on them to indicate their positive charge.
There are twenty nuclei arranged in a pattern with four rows and five columns. There are 15 red nuclei and five yellow nuclei. The yellow nuclei are randomly located in the pattern.

 

Image - Text Version

Shown is a colour illustration showing the arrangement of atomic nuclei when two metals are melted together. The nuclei of one metal are represented by red circles with black plus signs on them to indicate their positive charge. The nuclei of the other metal are represented by yellow circles with black plus signs on them to indicate their positive charge.
There are twenty red nuclei arranged in a pattern with four rows and five columns. There are five yellow nuclei randomly located in the spaces between the red nuclei.

 

Types of Welding

To get metals to melt, you need high temperatures. Generating a high temperature can come from using energy sources such as:

• Electricity
• Gas
• Lasers
• Sound (ultrasound)
• Friction

Arc Welding 

welding is a very common type of welding. In this form of welding, an electric current is used to heat up the metal. This type of welding is generally inexpensive and fairly easy to do, even for beginner welders. It also has the advantage in that it can be done indoors and outdoors or in closed spaces since no fumes are given off. As with other types of welding, hot metal and very bright light is involved. This is why wearing protective equipment is very important!

Image - Text Version

Shown is a colour photograph of a person arc welding a long metal pipe. In the foreground is the welder. The person is wearing bright red coveralls, a black welding face shield and bright blue welding gloves. A bright light is coming off the pipe where the electrode touches it. Bluish smoke is swirling into the air above the welding area. In the background is a blurred out workshop.

 

It is very important while arc welding that the surfaces being welded are very clean. This is to prevent things like rust and corrosion from weakening the joint. To make and keep the surfaces clean, welders use a shielding gas. The shielding gas is a bit like a “force field” that protects the welding area from being contaminated by stuff in the air. So, where does this gas come from?

If you check out the image above, you will notice something called “flux coating” on the outside of the electrode. When the flux is heated up, it produces gases and also forms a slag that covers and protects the molten metal in the weld. It can also act as an oxygen barrier, preventing the surface from reacting with oxygen in the air.

Metal inert gas (MIG) welding gets its shield gas in a slightly different way. Along with the wire electrode is a tube that sends out the shield gas from a high-pressure gas cylinder, instead of the gas coming from flux.

Not just any wire is used in MIG welding. The production process of this wire makes MIG welding possible. Wire is made using a process called Wiredrawing. In this process, metal is pulled through the holes of a die where it is strained into the correct size.

As part of the welding process, the wire travels from spools through as much as 5 metres (15 feet) of tubing to reach the welder. To make sure that the wire does not get stuck in the tube, a lubricant is used during the drawing process. The lubricant leaves a residual film on the surface of the wire. Lubricants help the wire feed through the tube smoothly and easily. Since there is also air in the tube, the film of lubricant must also protect the wire from being exposed to oxygen.

But not just any lubricant will do. Welding wire requires special lubricants. These lubricants leave a residue that helps with the melting process and improves the stability of the arc. However, these lubricants are often toxic and harmful to people and the environment.

Blachford supplies wire drawing lubricants and surface treatment products to the global welding wire industry. Blachford has developed a new safe and effective lubricant to solve this problem. Their new water-based formula contains a soap for making the wire slippery, compounds for corrosion protection, special additives, and emulsifiers for combining the two things together.

We may think about welding or welding wire rarely. However, these processes are central to many of the technologies that we rely on everyday. Understanding these techniques can help us build safer and better functioning technology.

Let’s Talk Science appreciates the work and contributions of H.L Blachford Ltd. in the development of this Backgrounder.

About H.L Blachford Ltd.

H.L Blachford Ltd was founded in Montreal in 1921 by Henry Lloyd Blachford and has grown its operations to include manufacturing sites in the USA, Canada, and the UK. Blachford manufactures stearate based products for a variety of industries including rubber, tire, powdered metal, plastics, PVC, food, wire drawing and metal working. Blachford is also a leading manufacturer of noise and vibration control technology, heavy duty rubber mats and headliners for the transportation and agricultural equipment industries.