Achieving optimum results of steel structures galvanization depends on the method their design and execution. Elements subject to galvanization should have such a shape that will allow them immersion in a bath and reaching each galvanized surface and then free drainage of residual zinc.
At the stage of designing, one must consider:- dimensions of plating bath,
- all thermal consequences,
- individual features of an element subject to galvanization,
- expected methods of the galvanized structure installation,
- condition of steel elements surface before galvanization.
Guidelines concerning designing of the constructions are given in PN- EN ISO 14713.
Structures subject to hot galvanization should meet the following conditions:
- Seams should be made using semi-automatic method with the aid of shielding gases. It is not recommended to weld with covered electrode due to poor quality of zinc coating on seams.
- Surface of the structure should free from: lapping, scale, welding spattering, sharp edges, paints, oils, emulsions and other materials used during machining, marking, welding, drilling, etc. In case of welding with an electrode, it is necessary to carefully remove the welding covering in order to eliminate coating defects. After galvanization, surface quality defects will be highlighted, e.g. lapping, machining and grinding scratches, pores, welding spattering, defects of seams.
- Structural elements should have proper technological holes for venting, free flow of zinc outside and inside the element and for suspension purposes (holders of metal sheet with holes can be welded).
- Box-type cross-sections and overlapping surfaces exceeding 400 cm2 are not recommended. In case of surfaces welded with overlapping, seam should be tight from all sides (welded all around), and the overlaps should tightly adhere to the structure. Box-type cross-sections and overlapping surfaces may cause damage to the structure – welds breaking.
- Each structural element should be made of a single steel grade.
- Structures should not have small gaps or cavities. Seams should be tight and closed around the element, otherwise, after welding, residues of flux and acid may flow out and deteriorate the coating quality (so called “bloody leaks”).
- Dimensional allowance concerning bolt holes should be 1 – 2mm.
- Thermal impact of the zinc bath releases internal stresses in the elements, which may lead to deformations. This is particularly noticeable in welded elements. This also applies to welded I-beams, deformation of which may exceed admissible standards after galvanization as well as not stiffened metal sheets and open bent sections.
In doubtful or individual cases we propose consultation of technical documentation with our technology engineer.