Bolts, or "bu lông" in Vietnamese, are products frequently mentioned in the field of mechanical engineering. They come in a circular shape, feature meticulously-cut threads, and are used in conjunction with nuts.

Bolts are designed to join and assemble small components into a sturdy system, such as frames, cylinders, or buildings. The fundamental principle behind bolt operation lies in the engagement of threaded connections, creating a reliable bond.

These bolts come in various head shapes, including square, round, external hexagonal, and internal hexagonal. However, the most widely used type of bolt today is the external hexagonal bolt.

Bolts vary in type and shape, making them suitable for different applications, depending on the level of demand. Primary materials used in bolt manufacturing include copper, regular carbon steel, high-quality carbon steel, and alloy steel, such as C35, 30CrMnCA, 40CrNiMnA, C45, and 38CrA.

To understand the classification of bolt products, let's explore the following categories:

1. Classification by Material Composition:

• Bolts can be categorized into three main types based on the materials used:
  • Bolts made of regular carbon steel and alloy steel:
    • High-strength bolts: Grades 8.8, 10.9, 12.9. These bolts are produced from alloy steel materials with equivalent strength or materials with lower strength, which are heat-treated to meet the product's required strength.
    • Bolts without heat treatment: Mainly regular bolts or low-strength bolts. These bolts are manufactured from materials with equivalent mechanical properties, and after processing, they do not require heat treatment. They include Grade 4.8, 5.6, and 6.6 bolts.
  • Stainless steel bolts (Inox): These bolts have the ability to resist chemical corrosion and electrochemical corrosion from the environment. Commonly used materials include INOX 201, INOX 304, INOX 316, and INOX 316L.
  • Bolts made of colored metals and colored alloys, such as copper, aluminum, and zinc. These bolts are primarily manufactured to meet the specific needs of various industries, including electrical, aviation, water processing, etc. This classification depends on chemical composition, mechanical properties, heat-treating capabilities, and resistance to chemical corrosion.

2. Classification by Corrosion Protection Method:

• Black bolts: Made from regular carbon steel.
• Black-dyed bolts.
• Zinc electroplated bolts, hot-dip galvanized bolts, rainbow-colored plated bolts, and anchor bolts.
• Stainless steel bolts (INOX 201, INOX 304, INOX 316, INOX 316L).

3. Classification by Manufacturing Method and Precision Machining:

• There are specially produced bolts that require precise machining and meet strict requirements for dimensional accuracy. These bolts are used in special joints where small tolerances, particularly in mechanical engineering, are essential.

4. Classification by Functional Use:

Based on their intended use, bolts can be divided into two main categories: Connecting Bolts and Structural Bolts. This classification has a direct impact on the strength, shape, and size of the bolts.

Connecting Bolts: These are bolts with the primary purpose of connecting various components to each other. The primary load these bolts carry is axial, and they do not play a decisive role in bearing shear forces. Connecting bolts are mainly used in static structures, where they experience minimal dynamic loading, and in fixed machine parts.

Structural Bolts: These bolts are used in components that frequently endure dynamic loads. They are designed to handle both axial and shear loads. Structural bolts find application in structures like frames, beams, and large machine parts, where the connecting elements must bear both axial and shear loads.

Classification by Various Industries:

In this classification method, bolts are categorized based on their application in various manufacturing industries:

• Bolts used in the construction sector for connecting structural frameworks.
• Bolts used in railway projects, including cut bolts and high-strength bolts.
• Bolts used in marine and offshore structures.

III. Applications:

Bolts play a vital role in various industries and can be found in numerous applications:

• Bolted joints can withstand a range of loads, including tension, bending, shear, and wear, providing long-term stability. They also offer ease of disassembly and adjustment without the need for complex technology.
• Bolts are ubiquitous across different fields, including mechanical engineering, assembly, industrial equipment manufacturing, civil construction, industrial workshops, and transportation infrastructure such as bridges and culverts.