Joseph Ash Galvanizing

Technical information

A coating that lasts up to 170 years.

When clean steel is immersed in molten zinc, which is at a temperature of about 450°C, the iron in the steel begins to react with the zinc to form zinc/iron alloy layers. As the steel remains immersed, so the growth of alloy layers progresses, each forming with reducing iron content as they build up to form the base of the coating. Finally, when the steel is slowly withdrawn from the galvanizing bath, unalloyed ‘free’ zinc is also drawn out and solidifies over the alloy layers. This forms the smooth, bright finish that is characteristic of hot-dip galvanizing.

The end result of this process is a coating that not only has great abrasion resistance but one that according to the most recent exposure tests* lasts between 34 and 170 years before the base steel is exposed and with S02 levels in the atmosphere reported as continuing to decline this should further increase the life of galvanized coatings in the years to come

* source ADAS zinc millennium map 2000 (right-click to download the map).

The galvanizing process, process control and technical support.

The Galvanizing Process

Applying the hot dip galvanizing process to steelwork provides fabrications with a robust, durable and corrosion protective finish that under normal conditions will last for many years without maintenance of any sort. The process itself has a number of stages that are required to achieve the final finish. These are all by immersion and they may be summarised as follows (rinse stages omitted):

Degreasing – This may be carried out using either acid or alkaline based proprietory products and they may be heated or used at ambient temperatures. The target is to produce a surface, which is not contaminated with oil, or grease based products.

Pickling – This is carried out in dilute hydrochloric acid which dissolves rust and scale and produces a ‘chemically clean’ surface which will react with the molten zinc.

Fluxing – A mixture of zinc chloride and ammonium chloride in solution is the standard fluxing agent of choice. This is normally used at between 50°C and 70°C, which helps the steelwork to dry after it is withdrawn. Drying is important as it helps prevent zinc splash and a separate drying stage is sometimes employed.

Zinc Immersion – This ‘final’ stage utilises a special bath holding molten zinc at 450°C. The clean steel is immersed in the zinc and while it is submerged it alloys with the iron in the steel to form zinc/iron alloy layers. These layers form the basis of the coating, which is then overlain with free zinc, as it is withdrawn from the galvanizing bath. The coating that is formed offers cathodic protection to the steel to which it is alloyed. As such, it will corrode preferentially to the steel extending its life by many years.

Process Control

The key to consistent product quality is control of the process. At Joseph Ash our process control is of paramount importance and all process stages are operated within set parameters, which are strictly managed. Analysis of process liquids and zinc is carried out frequently and control equipment is serviced and calibrated on a regular basis in accordance with manufacturers recommendations.

Process test data and performance are reviewed on an on-going basis to ensure ‘Right-First-Time’ processing is delivered at every one of our operating divisions such that customers get the consistent quality they expect from Joseph Ash.

Standards and Environmental Policies

All galvanizing supplied by Joseph Ash conforms fully to the coatings requirements of BS EN ISO 1461.1999 and is also quality assured to BS EN ISO 9000 specifications. In addition, Joseph Ash is working hard to protect the environment through an ever-growing list of recycling activities with processes supported by both an Environmental and Sustainability policy.

Technical Support

As part of our focus on customer service Joseph Ash offers its customers a high level of technical assistance by way of its Technical Support Department, staffed full time by qualified personnel who have a wealth of experience in the galvanizing industry. The department is always available to discuss customers’ technical and/or quality requirements and queries, particularly with regard to design for galvanizing, venting, and the steel chemistry and grade necessary to give optimum finish quality. They have access to a technical library and a large database of galvanizing information, much of which can be made available to our customers. Our Technical Support staff, Terry Felton and Stuart Cobourne, are also available to answer customers’ queries after galvanizing has been completed and when necessary will attend meetings, carry out site inspections and provide detailed advice.