Case Studies

Wedge Group Galvanizing was started by John Wedge in Willenhall, West Midlands (circa) 1869 as a backyard workshop and has grown to become the largest UK hot dip galvanizing organisation in the UK. They have 14 plants spanning the UK from Glasgow to Exeter, operating 16 galvanizing baths to service a broad range of industries including construction, industrial plant and equipment and transport.

What is Galvanizing?

Galvanizing is the application of a zinc coating to iron or steel to prevent rusting. The most common method of galvanizing is hot dip, where the iron or steel parts are submerged in molten zinc.

Prior to hot dip galvanizing, the metal article is pickled (cleaned) using Hydrochloric Acid and then rinsed before being immersed in the flux treatment tank containing a hot solution of Zinc Chloride and Ammonium Chloride. Through the pre-treatment process the flux becomes contaminated with iron released from the articles to be galvanized, which has a negative impact on the quality of the galvanizing and consequently increases operating costs.

Reliable, steady concentrations of flux give the best galvanizing results; the conventional process is to treat the flux in the treatment tank to reduce the iron content to an acceptable level. This is achieved with the addition of Ammonium Hydroxide. The iron oxidises becoming an insoluble thick brown sludge settling at the bottom of the flux treatment tank. 

Maintaining the process is a fine balance, if any of the metal articles touch the thick iron sludge a residue can form and the flux is unable to form a consistent coating, so the article may require rework. Also, should the flux become too concentrated in iron the whole flux tank needs deep cleaning, with the flux being pumped out by tanker and the brown iron sludge removed by sludge gulper, both then needing specialist disposal. The tank would then need cleaning and refilling, with the final costs reaching in excess of £50,000, depending on plant size.

Process Challenges

Wedge Group Galvanizing had previously purchased a system for the Worksop site to continually treat and recirculate the flux. The system was designed to circulate the flux from the treatment tank through a mixing tank, then a filter press before the cleaned flux is transferred back to the treatment tank as a recirculating, linear process. 

Unfortunately, the system was unable to cope with the demands and volumes generated by the size of the Worksop operation, with the filter press becoming a bottleneck. The filter press would frequently block causing the iron rich flux to be passed back into the treatment tank further increasing the concentration and risk of issues with zinc coating. The costs of increased chemicals to regulate the flux plus costs and time for maintenance and downtime led to the system being taken offline and condemned to “good idea but…”.

The system was manufactured from thermoplastics, so in 2022, aware of Chem Resist’s expertise in the design and use of these materials, Wedge asked for help to improve the process. 

Process Improvements

After detailed discussions and investigations, we recommended redesigning the treatment tank and the process by introducing an additional stage to the system, a clarifying tank. The mixing tank introduces Ammonium Hydroxide to the flux; once mixed, the flux slowly passes into the new clarifying tank where, due to the induced low flow rate, the iron solids settle on the tank floor whilst the cleaned flux rises to be recirculated back into the treatment tank. The settled solids are then transferred to the filter press, now capable of handling the reduced volumes of sludge.

A prototype Flux Regeneration System, incorporating the improved mixing and new clarifying tank was designed and built for the Wedge site at Worksop providing significant improvements. Further development and refinement led to fully specified, modular plug and play systems with control panels available in two volumes, 4m3 and 2m3, with pipework pre-assembled in skids to minimise installation time on site. 

The Benefits for Wedge

The Flux Regeneration System has delivered significant benefits for Wedge. A consistent flux regeneration cycle of 20 hours, with the flux maintaining a steady iron concentration of 0.5% (reduced from circa 2.0%) and the galvanizing process now producing a more consistent quality and finish. This has delivered savings in terms of rework and chemical costs to treat and regulate the flux, plus there has been service improvements to customers. 

The Flux Regeneration System now operates continuously without shut down or downtime, and the transfer of Ammonia from an IBC is automated through the control panel, a Health and Safety improvement on the previous manual handling.

The introduction of the System has also contributed to Wedge moving closer to their sustainability goals, consuming less raw material, particularly Hydrochloric Acid, reduced raw material and energy consumption driven by reductions in rework, plus less waste as now only the solid filter cake is produced. 

The Wedge sites at Wednesfield and Willenhall are due to have systems installed in 2025, with several other Wedge sites looking to adopt the new system in the future. 

Simon Hewitt. MD at Chem Resist comments,

“This project was a great opportunity for Chem Resist to enhance the basic chemistry involved in the galvanizing process with our years of process experience and expertise in thermoplastics. We were able to bring a new perspective, and the clever addition of the clarifying tank has brought significant improvements. Wedge now have a reliable, ready to install system they can roll out across their multiple sites and their customer benefits from consistency of service and product finish.” 

David Nobes, Technical Services Director for Wedge Group Galvanizing adds,

‘’The new flux treatment unit from Chem Resist is working incredibly well for us. The Team at Chem Resist worked tirelessly with us to design a solution to our flux regeneration needs and delivered a design that integrates well with the size and scale of our Worksop operation. The new unit has proven to be both effective and reliable and has helped us achieve our ambitions to not only reduce costs and improve the quality of our galvanizing finish for our customers, but also to support our sustainability goals as the new flux treatment unit significantly reduces both the frequency of chemical change in the tank and the amount and type of waste sent for disposal. Following the effective design and performance of the Chem Resist system, the Group have now placed further orders for additional locations across our UK network of plants’’.