Atlas Copco fastener
I. Basic Parameter Meanings
M12: Indicates that the nominal diameter of the bolt is 12mm (the major diameter of the thread, which is the maximum diameter of the outer thread).
1.5: Indicates that the pitch is 1.5mm (the axial distance between two adjacent threads), which is a fine-threaded type (the major pitch of M12 is 1.75mm).
Fine-thread characteristics: Compared to coarse threads, M12×1.5 has more thread teeth and better self-locking performance, suitable for scenarios requiring anti-loosening, sealing, or where space is limited (such as the connection of high-pressure components in air compressors to reduce loosening caused by vibration).
II. Common Materials and Strength Grades
Air compressor bolts need to withstand vibration, temperature changes (from normal temperature to above 150℃), and a certain preload. The selection of material and strength is crucial:
Material:
Normal conditions: Low-carbon steel (such as Q235), medium-carbon steel (such as 45 steel), suitable for non-corrosive and low-vibration areas.
Severe conditions (high temperature, humidity, oil mist): Alloy steel (such as 40Cr, 35CrMo), high strength, fatigue resistance; Stainless steel (such as 304, 316), corrosion-resistant, suitable for oil-free air compressors or food-grade air compressors.
Strength grades:
Example marking: 8.8 grade, 10.9 grade (the bolt head usually has a marking).
Meaning: The number before the decimal point ×100 is the tensile strength (MPa), the number after the decimal point ×10 is the yield ratio (yield strength / tensile strength).
8.8 grade: Tensile strength 800MPa, yield strength 640MPa, suitable for medium loads (such as connection of air compressor housing).
10.9 grade: Tensile strength 1000MPa, yield strength 900MPa, suitable for high loads (such as connection of cylinder head and cylinder body at high pressure positions).
III. Head type and anti-loosening method
Head type: Select based on installation space and tool compatibility:
Hexagon head (most common): External hexagon head (GB/T 5782 full thread, GB/T 5783 partial thread), suitable for tightening with a wrench, widely used.
Internal hexagon head: Head is an internal hexagonal hole, suitable for areas with narrow space (such as internal pipeline fixation of air compressor), with greater tightening torque.
Anti-loosening measures: During air compressor operation, vibration is large, additional anti-loosening is required:
Spring washer: Relying on elastic deformation to generate preload, preventing loosening (commonly used in simple conditions).
Anti-loosening nut: With nylon ring (nylon locking nut) or metal insert, through friction force to prevent loosening, suitable for high-frequency vibration positions.
Thread adhesive: Apply anaerobic glue (such as Loctite 243) on the thread surface, after curing, forms adhesive force, detachable and reliable anti-loosening.
