Preparation for galvanizing

Products must have holes or elements that allow them to be hung on a wire from transport traverses. The placement, dimensions and feasibility of technological holes or loops for hanging must be agreed and approved by the galvanizer before the products are manufactured.

Each element of the product must have technological holes that allow for free and rapid flow of molten zinc to all parts of the product surface and for air to escape during the dipping process. To do this, it is necessary to adhere to the data from the table on the minimum required diameter and number of holes depending on the profile cross-section:

The diameter of the technological holes for air outlet and zinc melt drainage must be at least 8 mm. The actual area of ​​the holes in structures made of long hollow profiles must be at least 1/7 of the cross-sectional area of ​​the profile from which the structure is made. The larger the technological holes, the better the galvanizing process will be.

The diameter of the technological holes must be no less than the thickness of the metal.

At the point where the three metal planes meet, a technological hole must be made to accommodate the cutout.

The product must not have “pockets” in which molten zinc can remain or air can be trapped.

The product cannot have closed cavities, as they can damage the product during galvanizing and injure workers.

Internal and external ribs, partitions, and lintels must have bevels or cutouts sufficient for the flow of molten zinc and the escape of air and must be visible through the technological openings.

The metal product should not have joints with overlapping surfaces of rolled metal. If such joints are present, the internal surfaces of these joints will not be galvanized and therefore rust streaks are possible during operation.

In the case of joints with overlapping surfaces, welding should be performed with an interrupted seam or a hole should be made.

Correct product design:

The dimensions of products or structural elements to be galvanized must not exceed the technological dimensions of the galvanizing bath: 6.5×1.5×2.5 m !

The design of products for hot-dip galvanizing should include appropriate design solutions that take into account the specifics of hot-dip galvanizing to obtain a high-quality zinc coating, prevent structural deformation and destruction of welds.

Before signing a contract for galvanizing, the customer must provide product drawings to assess the possibility of applying a coating by hot-dip galvanizing.

Products that have internal stresses after preliminary processing, such as welding, rolling, bending, stamping, etc., may deform during the galvanizing process. This is especially true for products with an asymmetric design and product elements made of sheet metal up to 2 mm thick (inclusive). The Customer must subject such products to heat treatment to relieve stresses before galvanizing. The Contractor is not responsible for product deformation caused by the release of physical stresses.

To ensure zinc flow, the distance between parallel surfaces of the product must be at least 3 mm, otherwise non-galvanized surfaces and crevice corrosion are possible.

Hollow products, products with long welds, products of complex shape, products made of various rolled products, as well as products made of cast iron are subject to trial galvanizing to determine the possibility of high-quality galvanizing of a series of products!

To avoid deformation of the metal product, it is undesirable to use metal that differs in thickness by more than 2 times. Also, if possible, the products should be symmetrical.

The following shall not be allowed on the surface of metal products to be hot-dip galvanized: scale, organic films (including residues of lubricant after rolling), other types of embedded mechanical contaminants, oils, fats, paints, primers, welding slag, labels, glue, in particular adhesive tape glue. Excessive corrosion, manifested by the formation of pores or delamination of the metal, shall also not be allowed.

It is not recommended to use metal that has been in use and is significantly corroded for the manufacture of products for galvanizing. Such metal, even after shot blasting, cannot be properly etched during pre-treatment of the product and, accordingly, ensure good quality galvanizing.

Welds must be continuous, uniform, without pores and without slag inclusions. The use of welding spray is not allowed, except for spray specifically intended for hot-dip galvanizing. The presence of metal drops formed during welding is not allowed.

Welding in a carbon dioxide or inert gas environment is recommended. When performing conventional welding, the slag should be thoroughly cleaned, preferably by sandblasting or shot blasting.

All defects on the metal surface that are invisible to the naked eye, such as micro-scratches and micro-pores, appear after hot-dip galvanizing. Areas of the surface of products that have been cleaned appear after galvanizing.

Due to the peculiarities of hot-dip galvanizing technology, threads and moving elements are “filled” with zinc. The customer must take into account the result of immobilizing such elements. The customer must perform thread stripping work independently, at his own expense.

Sharp corners and edges must be rounded off with a radius of at least 1mm.

Coating adhesion on parts that have been flame, laser or plasma cut may be poor. The galvanizer is not responsible for this.

The customer must inform the galvanizer of the intention to paint the products after galvanizing.

The quality of the zinc coating (gloss, smoothness, thickness, adhesion) is significantly affected by the chemical composition of the steel from which the product is made, and especially the content of carbon, phosphorus and silicon.

Products must be made of steel (casting), the chemical composition of which meets the following requirements: the silicon content (Si) must not exceed 0.03%, the phosphorus content (P) must not exceed 0.025%, and the carbon content (C) must not exceed 0.24%.

To obtain a high-quality coating with the same appearance, the product must be made of steel of the same grade or grades that are close in chemical composition. When using metal with different chemical composition and manufacturing method in the construction of products, a significant difference in the appearance of the coating is possible.

The material of the welding wire should be as similar in chemical composition as possible to the material of the elements being welded.

When galvanizing cast iron products, it is necessary to conduct trial galvanizing of samples after shot blasting to agree on an acceptable quality of galvanizing.

Below are photos of galvanized products that were made from steel of inappropriate chemical composition: