Problems With Welding Zinc Coated Surfaces
Zinc melts at 420°C and boils at 907°C. Steel melts at around 1400°C. You can see then how trying to weld a part consisting of both steel and a zinc coating will cause the zinc coating to vaporise. This is an occupational health hazard because the welder risks breathing in this vaporised zinc. It also means that you do not benefit from the zinc coating in the area that you have welded and the surrounding zinc plating is likely to also be degraded.
Metal Fume Fever
Metal fume fever is an industrial disease caused by inhaling welding fume. Perhaps the most common or most well known cause of metal fume fever is welding zinc coated articles (zinc plating, galvanised, zinc spray etc.). The acute symptoms of metal fume fever are usually similar to flu or other lung related discomfort. While the flu-like symptoms often only last for a few days, exposure to welding fume can cause long-term damage or increase susceptibility to other illnesses.
We recommend that anyone undertaking welding (regardless of whether zinc coatings are involved) should consult an occupational hygienist. Welding can produce many hazardous substances and employers have a duty to assess and control these risks under the COSHH Regulations. The British Occupational Hygiene Society is the professional body for occupational hygienists/industrial hygienists in the UK.
Reducing The Hazard
To reduce the hazard posed by welding, we recommend that parts are welded before they are zinc plated. However, we realise that this is not always possible. If a surface has already been coated with zinc, then we recommend removing the zinc before welding. You can locally remove an area mechanically or we can remove the coating from the entire part using our hydrochloric acid pickle. If you only locally remove the zinc, then be careful to make sure that surrounding areas do not get too hot.
If you are determined to weld on to zinc coated surfaces, then you should ensure that you use suitable local exhaust ventilation (LEV). When considering LEV engineers, you should look for ILEVE membership as a mark of competency. Drinking milk before welding is not a valid COSHH control and will not protect welders. The HSE publishes information on illness caused by welding fume.
This page is provided for information only, it should not be considered advice and we cannot accept any responsibility or liability for your use of the information on this page. The information on this page is used and relied on at your own risk and you bear the sole responsibility for any outcomes. E&OE.