Advice on galvanizing
Quality and standardization for hot dip galvanizing
Quality management systems: the ISO 9000 system
The needs of today’s market, for which customers ask that the products offered meet high performance standards, together with the effects of the increasingly pressing competition between the companies themselves, have also determined the need to evolve in the hot-dip galvanizing sector, focusing on quality control as a characterizing element of its commercial strategy. This has made it possible to increase profitability and competitiveness to those who have adopted production schemes based on the continuous improvement of results.
Today almost all of the hot dip galvanizers belonging to the Italian Galvanizing Association meet high quality standards by adopting the management system required by the international and Italian UNI EN ISO 9000 standards.
Operating according to this quality management system means paying attention to all stages of the production process and the compliance of the final result with the rule of the art. This takes place with a view to continuous improvement to be sought in the progressive and systematic elimination of any cause of non-compliance. The presence of a certification body guarantees that the procedures are carried out scrupulously and that the desired effect is actually achieved, which must correspond to the total satisfaction of the customer of the zincheria. From this point of view, the quality certification, that is the implementation of the production management system, does not mean for the galvanizing company the possibility of boasting a mere static mark on the headed paper, but it is testimony of a global and indefinitely.
It is easy for the galvanizing customer to find plants in their geographical area that are attentive to quality management and certified by independent bodies, accredited and in charge of certifying compliance with regulatory provisions. In the hot-dip galvanizing sector, it is possible to obtain coatings that meet the required standards through different techniques, which may be different for each plant. The individual procedures and characteristics must be reported in the company manual.
Natural complements of the quality management system are the ISO 14000 and EMAS environmental management systems, which in the latter period are spreading dynamically among galvanizing companies and have beneficial effects in reducing environmental loads. But we will talk about this at length in one of the next chapters.
From 1966 until the end of the 1980s, the rule of art in the field of hot dip galvanizing was dictated by the UNI 5744 \ 66 standard.
The first steps towards modern legislation were taken at the end of the 1970s, when the existing international specifications, called ISO 1461, began to prove inadequate, like the numerous national standards inspired by them. & nbsp; The development experienced by the sector had changed the needs of galvanizers and users, the minimum thicknesses envisaged did not correspond to what was practically obtained. Many points appeared ambiguous, others even lacking the information necessary to obtain a coating that meets the demands of the sector.
In 1978 the ISO 1461 standards were therefore revised. However, the process of developing the new legislation required an extremely long period of time. submit it for review. Once the new version was finalized, however, its publication was suspended, since the European Normative Committee (CEN) had in the meantime started the procedure for the development of a European standard. Pending the presentation of the new European standard, it was decided to print a specification in the form of a project with the initials: pr.E.14.07.000.0 on the basis of which we operated until the end of the 1990s.
In 1999, thanks to the joint commitment of ISO and CEN, integrated the works developed separately by their respective technical committees, a single document was published, which includes the specifications relating to hot dip galvanizing. , also published in Italy by the UNI – National Unification Body and indicated by the initials UNI EN ISO 1461, for the application of galvanized coatings on steel products constitutes the unitary reference for all the member countries of ISO. 2001, the guidelines, UNI EN ISO 14713, entitled: “Metal coatings for the protection of iron and steel in structures” were added. The standard has the status of a guideline and suggests which solutions to adopt in the choice of the metal coating by fusion between dip galvanizing and thermal spray metallization with zinc or aluminum.
As extensively described in chapters 3 and 6, it constitutes an information manual which, in addition to indicating the duration of the protective coatings according to the different degrees of environmental aggressiveness, includes suggestions for the design and implementation of construction details to adapt in the best way to the chosen coating.
The two international standards EN ISO 1461 and EN ISO 14713 represent the best response to the transformation of the market towards an increasingly global dimension, a process that has highlighted the need for unification of specifications. In this way, the compliance of supplies with the law is guaranteed in any European country and in all ISO countries and the user will have the security of a certified product that meets the required service performance.
The UNI EN ISO 1461 standard
To obtain galvanized products in compliance with existing regulations, it is sufficient to indicate in the order the words “Galvanized according to EN ISO 1461”. Further requirements must be previously assessed in agreement with the galvanizer who will perform the work.
The document opens with the definition of hot dip galvanizing which is indicated as “the formation of a coating of zinc and / or an alloy of zinc and iron on iron and steel objects, obtained by immersing the treated steel or the casting of iron in the molten zinc “. & nbsp; The standard defines the minimum coverage thicknesses foreseen, shown in the table according to the different thicknesses of the galvanized steel artifact, for different types of structural elements treated. The test methods for the verification of such thicknesses and the relative sampling procedure are also indicated. & Nbsp; Normally these measurements are carried out by means of a magnetic flux meter. This method has the advantage of being easy to apply and not destructive. In cases where you want to proceed with further investigation, chemical methods are used that calculate the weight of the deposited coating. The standard establishes that only the UNI ISO 1460 method is considered reliable, which is very accurate but involves the dissolution of a layer sample. & Nbsp; Since the coating obtained by hot dip galvanizing cannot be absolutely uniform between an area and the other than the surface, the standards establish methods for detecting thicknesses that express a value that is effectively representative of the average thickness.
The standards then indicate the minimum number of samples on which it is necessary to check and the number of individual areas to be estimated based on the overall size of the item under examination. In a completely similar way, the number of products on which to inspect and measure the thickness of the coating is defined, in relation to the size of the lot subjected to hot dip galvanization. This table is particularly important for series including small parts, such as bolts, nuts, hooks, etc.
In addition, the appearance and final characteristics that the galvanizing must have are established: obviously, there must be no bubbles, tips, uncovered areas, excessive roughness, flux residues on the coating; any presence of ashes or zinc drops, which must necessarily be contained as far as processing difficulties allow, must be in positions that do not interfere with the effective use of the product. Small surface roughness, small zinc nodules are usually tolerated. Any sharp parts that may pose a risk can and should be removed. The legislation clearly establishes the concept of a significant surface for which the coating is essential for its appearance and functionality, and reminds the reader that hot-dip galvanizing has corrosion protection as its fundamental purpose. Consequently, particular degrees of surface finish must be agreed in advance with the galvaniser.
As already reported, some anomalies found in the coatings and considered as defects are due to particular surface conditions and / or under the skin of the steel. The galvanizer, despite all his expertise and the attention paid to the various stages of processing, is unable to foresee and prevent similar problems. The regulations, even the most modern ones, cannot enter into these details which would involve previous processing technologies and techniques and, therefore, unrelated to galvanizing.
It should be the responsibility of the user-builder to ensure that the steel starting products for the production of products that must be protected with hot dip galvanizing are of excellent quality and free from superior defects occult surfaces that are highlighted with galvanization. To allow the achievement of a satisfactory product, the customer should provide additional information for the composition and any properties of the steel that may affect the galvanizing, identify the significant surfaces and generally indicate the desired level of finish on particular areas of the product. (for coupling or interlocking needs with other details, for example, or for particular uses involving those areas).
The UNI EN ISO 1461 standard also regulates the quality of the zinc used and the purity of the zinc coating. For zinc, it specifically refers to the requirements set out in the corresponding standard EN 1179 on the composition of ingots intended for hot dip galvanizing. present in solution) and tin. However, overall the purity of the zinc in the bath must not be less than 98%. , or due to technical difficulties encountered in dipping pieces with slight design defects. In this case, the area affected by the retouching must not exceed 0.5% of the total area of the item and, individually, must be less than 10cm2. Otherwise the piece must be reprocessed.
It is possible that the galvanized products have a color tending to gray. This aspect complies with the specifications of the legislation, being solely due to the composition of the steel. If there are elements that accelerate the galvanizing reaction, the layers of zinc-iron alloy, which are created during the process, rise to the surface, giving a grayish appearance to the product. This cannot be a cause of rejection of the material, since these coatings still guarantee the required anticorrosive performance.
However, to be sure that the elements retain a brilliant aesthetic and to guarantee a galvanizing result that adheres to your expectations, it is always advisable to contact your trusted galvaniser or to the experts at the Italian Zinc Plating Association in advance. . It is preferable that these experts are consulted already in the early design stages, as suggested several times. They will be able to recommend the characteristics of the steel to be indicated on the order in order to obtain normal coatings both in terms of appearance and thickness and the best solutions for both the project and the manufacturing phase of the product in the workshop.
The UNI EN ISO 14713 standard
As required by the UNI EN ISO 14713 standard, reference is made to the specific paragraphs of chapter 3 and chapter 6. They highlight the indications relating to the behavior of galvanized steel in different corrosive environments (cf. chapter 3) and the best design requirements (see chapter 6) suggested in the standard.