What are the matching requirements for building fasteners and steel pipes?
The matching between building fasteners and steel pipes is a core requirement for ensuring the reliability and overall stability of scaffold connections. It requires strict matching from multiple aspects such as dimensional accuracy, material performance, and connection strength. The specific requirements are as follows:
1、 Dimensional accuracy matching
The size is the basis for matching the two, directly affecting the tightness and fit of the connection:
Match the diameter of the steel pipe with the size of the fastener buckle:
The commonly used specification for scaffold steel pipes in China is φ 48.3mm × 3.6mm (outer diameter 48.3mm, wall thickness 3.6mm), and the corresponding standard fastener clamp inner diameter needs to be accurately matched with the outer diameter of the steel pipe (usually designed as 48-51mm), to ensure that the cover plate and base arc-shaped groove of the fastener can tightly fit the surface of the steel pipe, with a gap of no more than 1mm. If the diameter deviation of the steel pipe is too large (such as outer diameter>48.6mm or<48mm), or the size of the fastener clamp does not match (such as non-standard fastener clamps that are too wide/narrow), it will cause loose fitting or forced clamping, resulting in fastener deformation.
Bolt and nut specification matching:
Fastener bolts usually use M12 specifications (diameter 12mm), and nuts need to be matched with them. The thread accuracy should meet the standard (such as 6g/6H). If the specifications of the bolt and nut do not match (such as using M10 bolts with M12 nuts) or the thread processing is rough, it will cause the connection to become loose, the thread to slip, and the specified clamping force (40-65N · m) cannot be achieved.
2、 Material performance matching
The two materials need to be coordinated in strength and toughness to avoid premature local damage caused by performance differences:
Strength matching:
Steel pipes are generally made of Q235 low carbon steel (yield strength ≥ 235MPa), and the main body of the fasteners (cover plate, base) needs to be made of malleable cast iron (such as KT33-8, tensile strength ≥ 330MPa) or cast steel (such as ZG230-450). Bolts need to be made of Q235 steel or 4.8 grade high-strength bolts (tensile strength ≥ 400MPa). If the material strength of the fastener is lower than that of the steel pipe (such as using gray cast iron instead of malleable cast iron, with a tensile strength of only 150-250MPa), it will fracture due to insufficient strength when the steel pipe transfers load; On the contrary, if the strength of the fastener is too high and the strength of the steel pipe is insufficient, it may cause the steel pipe to deform first, indirectly causing abnormal stress on the fastener.
Resilience matching:
Steel pipes have good plasticity (elongation ≥ 26%), and fasteners need to have a certain toughness (malleable cast iron impact toughness ≥ 8J/cm ²) to avoid brittle fracture under impact loads (such as pipe shaking) due to excessive rigidity (such as high brittleness of gray cast iron). The coordination of toughness between the two can reduce stress concentration failure during load transmission.
3、 Connection method matching
It is necessary to ensure that the connection method is compatible through structural design to achieve effective clamping:
Match the fastener type with the steel pipe connection requirements:
Right angle fasteners are used to connect two vertically intersecting steel pipes, rotary fasteners are used to connect two intersecting steel pipes at any angle, and butt fasteners are used to butt two steel pipes in the same straight line. If right angle fasteners are used instead of rotary fasteners to connect diagonal steel pipes, insufficient clamping force may occur due to the inability of the cover plate to fit the curved surface of the steel pipe, resulting in sliding; On the contrary, if the docking clip is used for cross connection, it will completely lose its connection function.
Matching clamping method with force direction:
The fasteners tighten the steel pipe tightly between the cover plate and the base through bolts, generating frictional force to transfer the load. Therefore, the tightening direction of the bolt should be perpendicular to the axis of the steel pipe to ensure that the clamping force is distributed radially along the steel pipe. If the fasteners are skewed during installation (such as bolts not perpendicular to the steel pipe), it will cause the clamping force to be dispersed, resulting in ineffective friction and loose connections.
4、 Use environment adaptability matching
In special environments, additional consideration should be given to the impact of the environment on matching:
Anti corrosion performance matching:
In humid, coastal and other corrosive environments, steel pipes are usually treated with galvanizing (zinc layer thickness ≥ 85 μ m), and fasteners need to be galvanized (zinc layer thickness ≥ 55 μ m) or painted for corrosion prevention. If the steel pipe is galvanized but the fasteners are not corrosion-resistant, electrochemical corrosion will occur due to the potential difference, accelerating the corrosion of the fasteners and damaging the size matching; On the contrary, both anti-corrosion coatings have the ability to prolong the retention time of compatibility.
Load condition matching:
Scaffolding that can withstand vertical loads (such as masonry frames) and scaffolding that can withstand horizontal loads (such as formwork support frames) have different clamping force requirements for fasteners. It is necessary to select matching fastener specifications based on load calculations (such as heavy-duty fasteners used in scenarios with large loads) to avoid overload damage caused by "small fasteners subjected to large loads".
