1.Why does welding cause the coating to peel off/become damaged?
Instantaneous ablation of the coating: The coating (including the primer) at the weld point will directly vaporize and carbonize, completely disappearing.
Damage to the galvanized layer: High temperatures cause zinc to evaporate, losing its cathodic protection to the steel substrate.
Formation of the heat-affected zone (HAZ): The area around the weld point will also be heated (potentially reaching 200-400℃), causing the coating in that area to:
Blister, discolor, and age: The polymer structure of the coating is destroyed.
A sharp decline in adhesion: Even if it doesn't peel off immediately, it is very easy for it to peel off from the edges of the HAZ later.
The creation of a new "exposed metal area": After welding, the weld point and its surrounding HAZ effectively become exposed steel or a fragile coating area with no coating, becoming the weakest point in the entire component most susceptible to corrosion.
2.What are the advantages of avoiding welding and using mechanical connections?
Typical methods:
Self-tapping screw/rivet connection: Secured using self-tapping screws or blind rivets with sealing washers. Quick installation and low cost.
Interlocking connection: For roof and wall panels, specialized standing seam or interlocking systems are commonly used, achieving connection through mechanical interlocking, completely eliminating the need for perforations.
Snap-on/bolt connection: Secured using bolts to the matching steel structure.
Advantages:
Protective coating: Does not disrupt the continuity of the coating and galvanized layer.
Easy installation: No professional welder required; simple tools.
Removable: Facilitates future maintenance or modification.
3.What is the welding process plus post-weld local repair?
Standard Procedure:
Welding: Complete welding.
Cleaning: Thoroughly remove weld slag, spatter, and damaged coating in the heat-affected zone using tools such as wire brushes and grinding wheels.
Surface Treatment: Grind the exposed steel surface; if necessary, apply a special epoxy zinc-rich primer for rust prevention.
Coating Repair: Apply a layered repair paint using a special repair paint that matches the color and performance of the pre-coated steel sheet. The repair paint typically needs to have good rust resistance and weather resistance.
Disadvantages:
Complex Process: Increases the number of steps and time required.
Perfect Repair Results: Color, texture, and thickness may differ from the original panel, posing a risk that the repaired area will age before the original panel.
Weak Points in Corrosion Protection: Even after repair, the overall protection level of the area is lower than that of the original panel.
4.What are some special welding processes?
Cold welding: Using special low-temperature welding electrodes and precisely controlled equipment, welding is performed at relatively low temperatures, resulting in better control of the heat-affected zone. However, it can still damage localized coatings, usually requiring subsequent repairs.
Laser welding: Low heat input and narrow heat-affected zone, but the equipment is expensive, and it also damages the coating in the weld area.
5.What are some things to keep in mind?
Regarding the food cart partition walls you are concerned about: Mechanical connections (self-tapping screws + sealant or a dedicated clip system) should be the absolute priority. This is not only industry standard practice, but it also maintains the overall cleanliness, corrosion resistance, and ease of cleaning of the partition wall, fully complying with hygiene regulations. Welding should be avoided at all costs.
If welding is unavoidable due to structural reasons:
Welding must be considered a "destructive process," and subsequent "repair processes" must be strictly planned.
The technical requirements and construction specifications should clearly specify the processes and material standards for post-weld cleaning, grinding, primer, and topcoat repair.
Welded areas and repaired areas should be the focus of future maintenance inspections.