Building fasteners are key components that connect scaffold steel pipes, and their performance directly affects the overall stability and safety of the scaffold. During use, the following forms of damage often occur due to factors such as material, installation, load, and environment:
1、 Structural fracture
This is the most serious form of damage that directly leads to fastener failure, mainly including:
Brittle fracture: It is often caused by casting defects such as high carbon content, pores or cracks in the material of the fastener. When subjected to impact loads (such as steel pipe shaking or sudden stress), the bolts, cover plates or bases of the fastener suddenly fracture, and the fracture surface is rough without obvious plastic deformation.
Fatigue fracture: Long term repeated exposure to alternating loads (such as scaffold vibration, stress changes caused by frequent trampling by construction personnel), micro cracks gradually appear in key stress bearing parts of fasteners (such as bolt necks, connection points between cover plates and bases), and eventually propagate into macroscopic fracture, with obvious fatigue lines on the fracture surface.
2、 Deformation
The shape of the fastener changes and loses its normal connection function due to exceeding the yield strength of the material under stress:
Deformation of cover plate or base: During installation, if the fastener is forcefully knocked to clamp the steel pipe, or if the diameter deviation of the steel pipe is too large, causing the fastener to be forced to open, it will deform the arc-shaped contact surface of the cover plate and base, making it unable to tightly fit the steel pipe, resulting in loose connections.
Bolt bending: When tightening the bolt, excessive force (exceeding the specified torque, usually requiring 40-65N · m) or insufficient strength of the bolt material can cause the bolt rod to bend, affecting subsequent disassembly and reuse, and reducing clamping force.
3、 Wear and corrosion
Wear and tear: mainly occurs at the contact area between fasteners and steel pipes, as well as at the threads of bolts and nuts. When setting up or dismantling scaffolding, the relative sliding between steel pipes and fasteners can cause wear on the contact surface and increase the gap; Repeated tightening and disassembly of bolts can cause thread wear, resulting in thread slippage and ineffective clamping.
Corrosion: In damp, rainy, or corrosive environments such as cement slurry and acidic or alkaline environments on construction sites, the rust proof layer on the surface of fasteners is damaged, and the iron matrix undergoes oxidation reactions, forming rust. Corrosion will weaken the cross-sectional size of fasteners, reduce strength, and cause bolts and nuts to get stuck, making it difficult to disassemble.
4、 Loose connection
Although no obvious damage occurred, the connection function failed mainly due to the following reasons:
Untightened bolts: During installation, the bolts were not tightened to the specified torque or the wrench specifications were not met, resulting in insufficient tightening force. Under the load, the bolts gradually loosened, causing a decrease in the clamping force of the fasteners on the steel pipe.
Thread damage: The threads of bolts or nuts may experience slipping due to low machining accuracy, poor material quality, or repeated wear and tear, resulting in ineffective engagement and loss of clamping force.
Elastic failure of cover plate: The cover plate of high-quality fasteners has a certain degree of elasticity and can clamp steel pipes through deformation. If the material of the cover plate is brittle cast iron (rather than malleable cast iron), or if plastic deformation occurs after long-term stress, it will lose elasticity and cannot continuously hold the steel pipe tightly, causing loose connections.
5、 Explosion or fragmentation
Commonly seen in inferior fasteners, due to the use of brittle materials such as gray cast iron for casting, and the existence of defects such as shrinkage holes and sand holes. When subjected to large loads (such as scaffold overload or concentrated stress), the base or cover plate of the fastener will suddenly burst, causing fragments to splash and seriously endangering construction safety. This type of damage is directly related to the unqualified material, and it is rare for malleable cast iron fasteners that meet the standards to encounter such problems.
summarize
The damage of building fasteners is often related to substandard materials (such as using gray cast iron instead of malleable cast iron), non-standard installation (such as excessive tightening, failure to operate according to torque requirements), improper maintenance (such as failure to remove rust in a timely manner, repeated use of worn parts), and exceeding load limits. Regular inspection, selection of qualified products, standardized installation and maintenance are key to reducing damage and ensuring the safety of scaffolding.
