Small knowledge about expansion anchor bolts

1、 Classification system
Divided by materials
Metal Expansion Bolts: Carbon Steel (Conventional Galvanized), Stainless Steel (304/316 Corrosion Resistant), Alloy Steel (High Bearing Capacity)
Non metallic expansion bolts: Nylon (insulated and shock resistant), chemical anchor bolts (epoxy resin bonded porous substrate)
Divided by expansion structure
Mechanical expansion type
Internal expansion bolt: expands the internal expansion plate by screwing in the bolt (such as metal sleeve type)
External expansion plug: The outer sleeve expands under external force (such as with a casing structure)
Sleeve type: Expansion after tapping (commonly used concrete)
Chemical bonding type
Anchoring through resin curing (such as injection type chemical anchor bolts)
Divided by application scenarios
Architectural use: seismic and fire hydrants for curtain walls
Mechanical use: heavy-duty anchor bolts (bearing capacity>50kN), precision micro expansion bolts
Home use: Self tapping plastic bolt (gypsum board/wood)
2、 Working principle
Mechanical expansion type
Using conical slope to generate radial expansion force:
During installation, the bolt is pulled out or pushed, forcing the expansion sleeve/sheet to form a frictional grip with the substrate hole wall;
A typical structure includes an outer sleeve with a cut or an internal wedge-shaped structure, such as an outer expansion bolt relying on an outer sleeve for expansion, and an inner expansion bolt supporting an internal metal sheet through a screw cone head.
Chemical bonding type
By injecting resin glue to fill the gaps in the substrate and curing it to form a solid anchor, it is suitable for porous brittle materials.
3、The difference between internal expansion and external expansion plugs
Internal expansion bolt: only includes the bolt body, with a wedge-shaped structure or expansion plate inside; Expansion occurs inside the hole, with a flat surface; No additional components required, easy to operate; Stronger radial support; Suitable for moderate loads; Scenarios that require a smooth surface (such as precision equipment installation).
External expansion bolt: including bolt and detachable outer sleeve; Expansion occurs on the outside of the hole, and after installation, some components are exposed; Simultaneous installation of sleeve and core shaft is required, with multiple steps involved; The outer sleeve has a larger contact surface with the substrate, resulting in better shock resistance; Application scenario: Vibration environment or scenarios that require post adjustment (such as steel structure connections).
4、 Typical examples of internal and external expansion fasteners
External expansion fastener
Bite type expansion sleeve
Structure: The sleeve body is rolled from a plate body, including barbed, stamped grooves, and bite teeth. After installation, the outer sleeve forms frictional resistance with the hole wall.
Application: Suitable for scenarios that require anti slip and high structural strength, such as concrete fixation.
Sleeve type external expansion bolt
Structure: Includes a bolt body and a detachable outer sleeve, which expands by compressing the sleeve with a nut during installation.
Application: Commonly used in seismic resistant scenarios such as air conditioning outdoor units and steel structure bridges.
Galvanized external expansion bolt
Structure: Standard bolts are paired with an external expansion tube, and the sleeve is expanded by tightening the nut.
Application: Fixed light equipment (such as lamps, pendants).
Internal expansion fastener
Implosion expansion screw
Structure: Contains screws, springs, and an internal conical structure, triggered by an expanding agent to expand the hollow rod outward.
Application: Ceiling fixation or furniture installation in construction projects.
Stainless steel internal expansion bolt
Structure: It contains a metal sleeve inside, suitable for deep anchoring, and has strong resistance to breakage of the substrate.
Application: Reinforcement of heavy machinery bases or concrete structures.
Key Differences Comparison
External expansion core components: outer sleeve/casing; Expansion triggering method: external force squeezing the sleeve for expansion
Internal expansion core components: built-in conical structure/expansion sheet; Expansion triggering method: internal cone head or expansion agent drive
5、 Typical application examples
External expansion plug: fixing of air conditioning external unit, anchoring of bridge steel structure
Internal expansion bolt: installation of curtain wall keel, calibration of machine tool base
Chemical anchor bolt: hollow brick wall equipment fixation, installation of electrical boxes in humid environments