Welding Office Chairs

Key process aspects such as heat input control, weld leg size design, welding sequence planning, and post-weld treatment must be emphasized when welding the metal frames of public seating chairs.

1. Heat input control is a core parameter
During welding, the current intensity and welding speed jointly determine the 'heat input' value, directly affecting weld quality. Excessive heat input can lead to excessive weld penetration, metal overheating, and welding deformation upon cooling. It may even cause stress concentration due to an overly large heat-affected zone, resulting in cracks. Insufficient heat input, on the other hand, leads to inadequate fusion, making it easy for unfused areas or porosity to form inside the weld. Given that public seating chairs are used frequently and must withstand repeated sitting pressure and movement, a moderate heat input is typically used, combined with a multi-layer, multi-pass welding process. This approach reduces heat accumulation through layered welding, preventing local overheating.

2. Weld leg size requires precise calculation
The connection points between the legs and crossbeams of public seating chairs are mostly fillet welds, and the weld leg size must be determined based on load calculations. A size that is too small results in insufficient weld strength, unable to withstand the loads during use. A size that is too large increases the total heat input, raising the risk of deformation. The standard practice is to take 0.7 to 1.0 times the thickness of the thinner plate as the weld leg height. For example, if the thinner plate has a thickness of 5mm, the weld leg height should be controlled between 3.5-5mm to balance strength and deformation risk.

3. Welding sequence affects overall deformation
The frames of public seating chairs are mostly symmetrical structures, and the welding sequence must be reasonably planned to reduce deformation. The correct sequence is to weld symmetrically from the middle to both ends or use the skip welding method (interval welding) to distribute heat evenly and control overall deformation. If the sequence is improper, it may lead to frame distortion or dimensional deviations, affecting the stability and service life of the chairs.

4. Post-weld treatment ensures long-term performance
After welding, an overall heat treatment (annealing) is required to eliminate residual stress. The annealing temperature is typically controlled between 600 and 650 degrees Celsius, with the holding time calculated as 1 to 2 minutes per millimeter of plate thickness. For example, a 10mm-thick plate requires a holding time of 10-20 minutes. Additionally, weld slag and spatter on the weld surface must be cleaned; otherwise, they can damage the coating's adhesion, leading to local rusting. Rusting can spread along grain boundaries, accelerating structural failure. Therefore, the welding area usually requires grinding to achieve a surface roughness below Ra3.2 micrometers before applying an anti-corrosion coating to extend the service life of the chairs.