Nowadays, the construction industry is experiencing significant growth worldwide, and Vietnam is among the countries at the forefront of this development. The period from 2010 until now is considered a pivotal time for the construction sector, and Vietnam ranks among the top countries with a fast-paced economic growth in the Asian region.

Bolted connections are essential components in construction projects, especially in industrial facilities, industrial constructions, and machinery. There are many more applications of bolts that we may not be aware of. The following article will provide you with an overview of bolts as well as their important applications in daily life.

What is a 'Bolt'?

Bolts, also known as "bulong" in Vietnamese, are an integral part of secure fastening systems. They are mechanical components that consist of two parts: the head, which can come in various shapes such as hexagonal, cylindrical, square, or even custom shapes, and the body, which is a cylindrical shape with threads throughout its length (see Figure 1).

Bolts are assembled with other components such as nuts and washers to form a complete fastening system (see Figure 2). The assembly process follows specific thread types (metric, inch, fine thread, coarse thread), product grades, manufacturing standards, ensuring that the bolt assembly matches the nuts with corresponding internal threads. This allows for easy disassembly, adjustment, or removal when necessary (see Figure 3).

Some important applications of bolts in daily life

Although bolts are small components, their role and position are crucial in many activities and applications in various fields such as:

• Mechanical assembly and machine fabrication in engineering.
• Construction projects, both civil and industrial, including steel structures and workshops.
• Transportation infrastructure projects, such as bridges and railways.
• Electro-mechanical systems, including HVAC systems, high-pressure pipelines, and more.
• Bolts also contribute to the convenience and ease of everyday life activities.

Bolts also contribute to making daily activities more convenient and user-friendly.

The working principle of a bolt

A bolt operates based on the friction between the external threads of the bolt and the internal threads of the nut. These threads are designed and calculated to have high tensile strength and shear strength, enabling them to withstand significant pulling and cutting forces. This ensures a secure connection between components. Additionally, the continuous thread design of the bolt allows for effective adjustments when needed.

Common shapes of bolts

Bolts come in various common shapes, but they fundamentally consist of a cylindrical body with continuous threads. The differences lie in the bolt heads. They can have an external square shape, an external hexagonal shape, or a circular shape with a recessed square or hexagon inside, commonly known as countersunk hex bolts. Among the different types of bolts, hex bolts with hexagonal heads are the most popular and widely used due to their aesthetic appeal and the convenience of accompanying tools.

Classification of bolts

Bolts can be classified in several ways, such as by function, material, field of use, and manufacturing method.

• Classification by function includes anchor bolts, connecting bolts, and structural bolts.
• Classification by strength grade includes common bolts with widely used grades such as 4.5, 5.6, and 6.8, as well as high-strength bolts with popular grades such as 8.8, 10.9, and 12.9.
• Classification by material includes carbon steel and corrosion-resistant alloy materials.
• Classification by bolt grade includes A/B/C grades.

Some common types of bolts include:

• Anchor bolts: These are fixed at one end into concrete to provide a protruding threaded end for connecting other components.
• Carriage bolts: They have a round smooth head and a square neck to prevent rotation.
  Hexagon bolts: The head of the bolt has a hexagonal shape.
• Square bolts: The head of the bolt is square.
• T-head bolts: The head of the bolt is shaped like the letter "T." J-bolts: These bolts have a shape resembling the letter "J."
• U-bolts: These bolts have a shape resembling the letter "U."
• ….

Some criteria used to evaluate bolts

• Complete and well-managed bolt manufacturing process without skipping steps.
• The input materials used for bolt manufacturing must be controlled in terms of mechanical properties and chemical characteristics (C, Mn, S, P, Cr, Al, etc.) to meet standards, facilitate machining, and enable easy welding.
• Bolts should undergo experimental testing based on various criteria such as minimum tensile strength, minimum yield strength, and impact testing for ductility and toughness.
• Bolts should have resistance to wear, oxidation, and corrosion, with hardness ensuring the required performance.
• The finished surface of the bolt must withstand environmental factors without rusting, corroding, or oxidizing. They should be able to withstand high-temperature environments.
• Bolt dimensions should comply with regulations and standards to ensure compatibility with various types of machinery and equipment available in the market.

We hope that the information provided by CTEG above will help you gain a better understanding of bolts and make informed choices based on your specific needs.