Office Chair Wobble and Weld Seam

The main reasons for office chair wobble related to weld seams are metal fatigue, potential defects in the welding process, and the accelerating effects of environmental factors.

Metal Fatigue

During normal use, if an office chair is subjected to weights exceeding its design capacity for an extended period or frequently experiences dynamic loads, such as when the user frequently rocks the chair, microscopic cracks gradually form at the welded areas. These cracks tend to appear and propagate more easily at stress concentration points, such as right-angle connections. As usage time increases, these microscopic cracks accumulate and eventually develop into visible cracks, reducing the connection strength of the weld seams and causing the office chair to wobble.

Potential Defects in the Welding Process

• Improper Temperature Control: During the welding process, if the local temperature is too high, it can cause the metal grains to coarsen. Coarsened grains reduce the metal's strength by approximately 30%, making the structure at the weld seams unstable and unable to effectively withstand the various forces encountered during normal use of the office chair, leading to wobbling.
• Insufficient Solder Penetration: If the solder fails to fully penetrate the metal parts to be connected during welding, partially fused solder joints will form. These partially fused joints are prone to peeling when subjected to external forces, severely affecting the connection strength of the weld seams and ultimately causing the office chair to wobble.
• Cooling Rate Issues: After welding is completed, if the cooling rate is too fast, internal stresses can develop at the weld seams. These internal stresses, equivalent to a continuous pressure of 50 kg, may cause deformation at the weld seams, disrupting the original structural stability and leading to office chair wobbling.

Accelerating Effects of Environmental Factors

• Humid Environment: In humid conditions, metal solder joints undergo electrochemical reactions with oxygen and water vapor in the air, resulting in corrosion. This corrosion reduces the strength of the welded areas by about 5% annually. Over time, the stability of the weld seams is compromised, leading to office chair wobbling.
• Temperature Changes: In winter, when temperatures drop, metals contract, generating tensile forces equivalent to applying an additional load to the solder joints. If the weld seams already have minor defects, this extra load can cause problems at the seams, triggering office chair wobbling.
• Long-term Vibration: If an office chair is placed in a vibrating environment for an extended period, such as in an office near a subway, the lifespan of its solder joints may be reduced by 40%. Long-term vibration can destabilize the weld seam connections, resulting in office chair wobbling.