Detailed explanation of flange bolts: definition, type, characteristics, application and processing

In various types of mechanical equipment, automotive parts, steel structure buildings and pipeline systems, the role of bolts is crucial. Among the many types of bolts, flange bolts have become an ideal choice for many industries due to their excellent force-bearing characteristics and convenient installation methods. Unlike ordinary hexagonal bolts, flange bolts come with a flange plate, which can provide a larger contact area and improve the stability and anti-loosening ability of fasteners.

This article will explore the definition, classification, characteristics, application scenarios and manufacturing process of flange bolts in depth to help you more comprehensively understand the wide application of this fastener in the industrial field.

1. What is a flange bolt?

A flange bolt is a fastener with an integrated flange plate, which is mainly used for flange connections (such as pipelines, mechanical equipment, steel structures, etc.). It is characterized by an enlarged flange surface under the bolt head, which can replace the combination of ordinary bolts + gaskets, providing better sealing, vibration resistance and load-bearing capacity.

2. Main types of flange bolts

According to the design and purpose of the flange surface, they are mainly divided into the following categories:

3. Core features of flange bolts

(1) Structural features

Integrated flange: integrally formed with the bolt head, providing a larger pressure-bearing area (1.5D~3D). This overall design ensures uniform force and is particularly suitable for high-pressure sealing occasions.

Contact surface treatment: serration (30-45° bevel teeth to prevent loosening), flat surface (high-precision matching), sandblasting (increase friction). Different treatment methods meet the needs of various working conditions.

Thread type: full thread (uniform force) or partial thread (shear resistance), adapted to different load characteristics.

(2) Performance advantages

Anti-vibration and anti-loosening: serration mechanical interlocking design, anti-loosening performance is improved by more than 50%, especially suitable for vibration environment.

No gasket required: integrated design simplifies assembly, saves 15-20% installation time, and avoids the risk of gasket displacement.

Uniform load: effectively reduces stress concentration by 30%, significantly extending the fatigue life of the connector.

(3) Mechanical properties

Strength grade: 8.8 (general purpose), 10.9 (heavy load), 12.9 (aviation grade), to meet the needs of different working conditions.

Surface hardness: HRC22-32, balance strength and toughness, can be adjusted by heat treatment.

Tensile strength: 800-1200MPa, with ≥8% elongation, to ensure high strength and toughness.

4. How to choose the right flange bolt?

(1) Size matching

1) Flange diameter ≥ 1.3 times the hole diameter of the connected part (to ensure sufficient pressure bearing area). Specific considerations for selection:

●For ordinary steel structure connection, it is recommended to use a 1.5D flange diameter

●For high pressure sealing occasions, it is recommended to use a flange diameter of 2D or above

●For special heavy load conditions, a 3D oversized flange design can be used

2) Thread length ≥ 1 times the bolt diameter (to ensure sufficient engagement length). In practical applications, the following should be noted:

● Thermal expansion factors should be considered in high temperature conditions, and the thread engagement length should be appropriately increased

● Full thread design is recommended for dynamic load situations

(2) Material selection

(3) Installation requirements

● Preparation: Clean and wash the joints to be bonded to ensure cleanliness.

● Alignment: Ensure that all components are properly aligned to reduce stress caused by misalignment.

● Tightening: Ensure that the bolts are properly tightened according to the torque specifications. Over-tightening or under-tightening will have adverse effects as it will affect the structure of the joint.

(4) Anti-loosening measures:

Serrated flanges or nylon pad flanges are suitable for vibration environments. Things to consider when selecting:

● Ordinary vibration occasions: Use 30° serrated flange bolts

● Strong vibration environment: Recommend 45° serration or nylon locking pad design

● Extreme vibration conditions: It is recommended to use serrated flange + thread lock glue for double anti-loosening

● Parts with high disassembly frequency: It is advisable to use reusable metal locking structure

5. Application scenario analysis of flange bolts

(1) Pipeline connection

In oil, natural gas, water treatment and chemical pipeline systems, flange bolts are used to fix flange connections to ensure the sealing and pressure resistance of the pipeline system.

Because flange bolts can evenly distribute pressure, they can effectively reduce the risk of leakage and improve system safety.

(2) Automobile manufacturing

Widely used in high-strength connection parts such as engines, gearboxes, and chassis suspension systems.

The flange surface can prevent the nut from loosening and improve the vibration resistance, making it suitable for parts with large engine vibration.

(3) Mechanical equipment assembly

In machine tools, heavy machinery, mining equipment and other fields, flange bolts are used to fasten key components to ensure that the equipment remains stable under high load and high vibration environments.

The structure of the flange can reduce the loosening of bolts and improve the reliability and service life of equipment.

(4) Construction and steel structure engineering

It is used as a connecting component in construction projects such as bridges, steel structure workshops, towers, etc., to withstand wind, vibration and load.

Flange bolts can enhance the shear strength of the structure and improve overall safety.

(5) Wind power and new energy equipment

In new energy equipment such as wind turbines and photovoltaic brackets, flange bolts are used to fasten blades, towers and other key components.

Its high strength and high corrosion resistance ensure the long-term stable operation of the equipment in harsh environments.

(6) Shipbuilding and marine engineering

It is suitable for ship engines, deck equipment and offshore drilling platforms, and bolts are required to have high corrosion resistance and fatigue resistance.

Due to long-term exposure to humid or high-salt environments, galvanized or stainless steel flange bolts are often used to improve corrosion resistance.

(7) Rail transit

In the chassis and body connections of high-speed railways, subways and rail vehicles, flange bolts are used to withstand large dynamic loads and impact forces.

Its high-strength bolts can improve the stability and safety of train operation.

6. Processing technology of flange bolts

The production of flange bolts involves multiple precision manufacturing processes to ensure that they have sufficient strength, accuracy and durability. Its main processing processes are as follows:

(1) Material preparation

Select suitable metal materials, such as carbon steel, alloy steel, stainless steel, etc.

The raw materials are generally metal bars or round steel plates, and are cut into appropriate lengths.

(2) Cold heading

The metal bars are extruded into the basic shape of the bolt, including the screw and flange, by a cold heading machine.

Cold heading can improve the density and mechanical properties of the material while reducing processing loss.

(3) Turning

If the bolt has a special shape or requires high-precision dimensions, it is necessary to use a CNC lathe for processing to trim the shape of the screw and flange.

(4) Rolling thread

The screw part is threaded using a thread rolling machine.

Rolling thread has more advantages than cutting thread, which can enhance thread strength, reduce material loss, and improve the fatigue resistance of the bolt.

(5) Heat treatment

High-strength flange bolts are heat treated, such as quenching + tempering, to improve their hardness, strength and toughness.

The choice of heat treatment process depends on the material and application requirements of the bolts. For example, 10.9 and 12.9 grade high-strength bolts must undergo strict heat treatment processes.

(6) Surface treatment

Surface anti-corrosion treatment is performed to improve the corrosion resistance of the bolts. Common processes include:

●Electroplating: such as galvanizing and nickel plating to improve rust resistance.

●Blackening: used to improve wear resistance and oxidation resistance.

●Dacromet coating: used for high-strength bolts, with excellent corrosion resistance.

●Hot-dip galvanizing: suitable for marine environments or outdoor applications, to improve corrosion resistance.

(7) Quality inspection

Use professional inspection equipment to inspect the size, strength, thread accuracy, etc. of flange bolts to ensure that they meet international standards (such as ISO, DIN, ANSI, GB, etc.).

Common inspection methods include hardness test, tensile test, thread gauge test, salt spray test, etc.

7. Summary

From traditional manufacturing to high-end equipment, flange bolts have proven with their excellent performance that even seemingly simple parts can become a key support for industrial progress.