Combination screw is a type of fastener composed of a bolt, a washer, and a spring washer. It is widely used in fields such as machinery, electronics, and construction.
Its features include easy installation and excellent anti-loosening performance, making it suitable for situations where frequent disassembly is required or where it needs to withstand vibrations.
Combination Screw
Main features of GB/T 9074 three-piece screws
Structural composition:
Screw: Usually a hexagonal head screw, the material can be carbon steel, stainless steel, etc.
Flat washer: Used to distribute pressure and protect the connection surface.
Spring washer: Provides elastic preload force to prevent loosening.
Loosening resistance:
The elastic deformation of the spring washer can effectively resist vibration and impact, ensuring the reliability of the connection 27.
Installation convenience:
The three-piece combination screws are pre-installed at the factory, reducing the steps and time required for on-site installation.
Material and surface treatment:
Material: Carbon steel (such as grade 4.8, grade 8.8), stainless steel (such as A2-70).
Surface treatment: Galvanization, Dacromet, blackening, etc., to enhance corrosion resistance.
GB/T 9074 Specifications and Parameters of Sems Screw
1. Common Specifications
Screw diameter (d): M4, M5, M6, M8, M10, etc.
Screw length (L): Customized according to requirements, common range is 12mm to 100mm.
Gasket size: Inner diameter matches the screw diameter, outer diameter and thickness are in accordance with standard regulations.
2. Mechanical Properties
Grade 4.8: Tensile strength ≥ 400 MPa, yield strength ≥ 320 MPa.
Grade 8.8: Tensile strength ≥ 800 MPa, yield strength ≥ 640 MPa.
3. Surface Treatment Options
Galvanizing: Ordinary galvanizing (general corrosion resistance), hot galvanizing (strong corrosion resistance).
Dacromet: Suitable for high-corrosion environments (such as marine, chemical).
Blackening: Aesthetically pleasing and has certain rust prevention capabilities.
Application Scenarios of GB/T 9074 Sems Screw
Mechanical Equipment:
Used for motors, pump valves, transmission devices, etc. in situations requiring anti-loosening.
Electrical and Electronic:
Suitable for circuit board fixation, equipment shell connection, etc.
Construction Engineering:
Used for steel structure connections, curtain wall installation, etc.
Automotive Industry:
Used for chassis, engine, etc. parts’ tightening.
Selection and Usage Notes
Selection Suggestions:
Choose the strength grade based on the load requirements (e.g., 4.8 grade, 8.8 grade).
Select the surface treatment based on the environment (e.g., galvanized for general environments, duralumin for highly corrosive environments).
Installation Notes:
Ensure that the bolts, washers, and spring washers are properly matched.
Use a torque wrench to tighten according to the standard torque, avoiding over-tightening or under-tightening.
Maintenance and Inspection:
Conduct regular checks on the tightness, especially in environments with vibration or shock.
Replace damaged or corroded screws to ensure the reliability of the connection. Summary
GB/T 9074 Three-piece combination screws are an efficient and reliable fastener suitable for various industrial applications. Their anti-loosening performance and ease of installation make them an ideal choice for vibration environments.
When selecting, it is necessary to match the strength grade and surface treatment according to specific requirements to ensure optimal performance and service life.
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