Solder spot spacing of LPG Cylinder Spot Welding Machine
The spacing between welds and the strength of the LPG cylinder spot welder is nonlinearly related, and a balance needs to be achieved between stress distribution and heat-affected zone control. When the spacing is in the range of 30-50mm, adjacent welds can form a "stress synergy effect". For example, when a 15kg cylinder (3mm plate thickness) uses a 40mm spacing, the tensile shear force of the weld group can be increased by 20%-30% compared to a single weld, because a reasonable spacing can evenly distribute the load to each weld. However, if the spacing exceeds 60mm, the intermediate metal is prone to plastic deformation due to lack of support, resulting in a 15%-20% decrease in overall strength; and when the spacing is less than 20mm, the overlap of the heat-affected zone will cause the grains to coarsen and the tensile strength to decrease by 10%-15%. Especially when welding galvanized sheets, too close spacing will aggravate the evaporation of the zinc layer, forming a brittle and hard phase at the weld interface, which will reduce the fatigue strength by more than 30%.
From the perspective of process matching, the plate thickness and spacing need to be adjusted accordingly: 25-35mm spacing is recommended for 2-2.5mm wall thickness, and 35-50mm for 3-4mm wall thickness. At this time, the molten core needs to be strengthened by adjusting the current. For large spacing (>45mm), the current needs to be increased by 10%-15% and the welding time needs to be extended to avoid insufficient melting depth due to excessive heat dissipation; for small spacing (<30mm), the current needs to be reduced by 5%-8%, and pulse welding is used to reduce heat accumulation. In actual verification, when shearing tests are carried out according to ISO standards, the reasonable spacing should make the fracture occur at the parent material rather than the weld interface. For example, through finite element analysis, it can be seen that if the spacing of a 50kg steel cylinder is reduced from 60mm to 55mm, the stress concentration factor can be reduced from 2.3 to below 2.0, meeting the safety threshold. In engineering, 15kg steel cylinders often use a spacing of 35-40mm, and with a current of 80-85kA, the shear force of the weld can reach more than 3800N, and the fatigue life decay rate is less than 5%.
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