Which method is better for galvanizing guardrail mesh?

As a protective product, guardrails are subject to long-term outdoor use, necessitating long-term corrosion protection. Generally speaking, the primary method used for surface galvanizing for highway and railway guardrails is hot-dip galvanizing. However, some smaller manufacturers also utilize cold-dip galvanizing. Here, we'll explain the differences between the two.
Hot-dip galvanizing is a relatively old galvanizing method, having been used in industry for 170 years since France first introduced it in 1836. However, hot-dip galvanizing of guardrail mesh has recently become widely used by major guardrail manufacturers in Anping.
The production process for hot-dip galvanized guardrail mesh primarily includes: mesh preparation → pre-galvanizing treatment → hot-dip galvanizing → post-galvanizing treatment → finished product inspection. Conventionally, the pre-galvanizing treatment is often used for the production of hot-dip galvanized guardrail mesh. As a protective product, guardrails are subject to long-term outdoor use, necessitating long-term corrosion protection. Generally speaking, hot-dip galvanizing is the primary method used for surface galvanizing of highway and railway guardrails. However, some smaller factories also utilize cold-dip galvanizing. The senior engineers at Anping County Ruixiang Guardrail Factory will explain the differences between the two methods.
Off-line annealing for hot-dip galvanizing involves recrystallization annealing of the guardrail mesh in a bottom-type or bell-type annealing furnace before entering the hot-dip galvanizing line. This eliminates the need for an annealing step on the galvanizing line. Prior to hot-dip galvanizing, the mesh must maintain a clean, pure iron surface free of oxides and other contaminants. This method involves first removing the surface oxide scale from the annealed mesh using pickling, followed by a protective coating of zinc chloride or a mixture of ammonium chloride and zinc chloride to prevent further oxidation.
If wet hot-dip galvanizing is used, the mesh is dipped into a molten zinc bath before the solvent has dried off (i.e., while still wet). This method has the following disadvantages: It can only be galvanized in a lead-free environment, resulting in a thick alloy layer with poor adhesion. Any zinc slag that may form accumulates at the interface between the zinc and lead baths and cannot settle on the bottom of the bath (because the zinc slag has a higher specific gravity than the zinc bath but lower than the lead bath). This contaminates the surface of the fence mesh by penetrating the zinc layer. This method of hot-dip galvanizing has been largely phased out in recent years.
Second, the single-sheet method: First, the annealed mesh is sent to a pickling workshop, where sulfuric or hydrochloric acid is used to remove the oxidized scale from the steel surface. After pickling, the mesh is immediately immersed in a water tank for galvanizing to prevent further oxidation. After pickling, rinsing with water, squeezing, drying, and hot-dip galvanizing, it is placed in a zinc bath (maintained at 445-465°C) and then oiled and chromized. The hot-dip galvanized mesh produced by this method has significantly improved quality compared to wet-galvanized products, and is only of certain value for small-scale guardrail production.