Bob Kilby, head of health and safety/quality and environment at ArcelorMittal’s plant in Birkenhead, explains how Western Air Ducts helped the company solve the problem of extracting the dust, fumes and sparks generated by plasma cutting heavy plate steel

Health and safety is at the top of the list of priorities at the steel plate stockholding and processing plant at ArcelorMittal operations in Birkenhead. Thirty-five staff handle and cut plates up to 12m long by three metres wide for a wide range of applications, ranging from shipbuilding to the creation of the new gates to the vegetable plots at Kew Gardens.

It is a major undertaking to cut steel to these dimensions and the plant has invested in major machine tools to tackle the job, including an ESAB plasma cutting machine on a 28 x 7m bed.

High temperature operation

The plasma technology necessary to achieve this high speed, accurate cutting heats the steel plate to temperatures of 2,000°C, causing the steel to vapourise. The resulting fumes and dust are extracted through slots in the machine bed, into an under floor duct from where they are carried outside the building. Here the air is filtered and cleaned before being emitted to the outside air via a chimney. The correct and efficient functioning of the extraction system is therefore a vital part of the plasma cutting operation for the plant.

The high temperature of the process generates sparks. In order to avoid these sparks reaching the air filters  (even though these are themselves fire retardant) Western Air Ducts installed its Flashback Box, between the extract duct and the filters, to ensure that all sparks are extinguished before they reach the filters, therefore avoiding any possibility of a fire hazard.

The series of 15 filters serving the plasma machine are replaced on an annual basis, but during the intervening 12 months, as part of the planned maintenance procedures, they are refreshed by a ‘reverse pulse’ mechanism, which literally blows the dust off the filters and into a holding tray (from which it is extracted) leaving the filters clean once again. This process is planned in such a way that the filters are cleaned in sets, so that machine production is not disrupted.

One of the effects of this planned cleaning process is that the airflow through the extraction system varies week by week and even day by day, as air is extracted more rapidly through the cleaned filters. Western Air Ducts therefore proposed the incorporation of an inline device to measure the flow rate, together with a system of dampers which can be opened and closed to exactly regulate the air flow.

Bob Kilby explained, “Being able not only to know the exact air flow rate at all times, but also to regulate it easily, enables us to fine-tune the system so that it operates at optimal efficiency. Our plasma cutting machine represents a major investment for this plant and our board was naturally keen to have it operating at maximum efficiency. The Western Air Ducts extraction system enables us to achieve this, while maintaining our ongoing commitment to health, safety and the environment.”

Western Air Ducts

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