TPT July 2015

Article

Huntingdon Fusion Techniques

Flexible enclosure welding By Dr M J Fletcher, Delta Consultants (Huntingdon Fusion Techniques)

For many years the cost of metal enclosures precluded all but the major companies taking on work involving fabrication of nickel and titanium alloys. To the rescue came Huntingdon Fusion Techniques HFT ® , a decade or so ago, with the introduction of flexible enclosures that exploited the opportunities offered by advanced engineering polymers. These innovative products offered significant attractions over both vacuum and glove box alternatives: a significant reduction in cost, very small floor footprint and availability of a range of sizes from stock. Since that time the HFT ® product has been developed and is rapidly becoming the preferred alternative enclosure. Technical specification The vertical sides are made from translucent material and the top is constructed using optically clear sheet. Ultraviolet stabilised engineering polymers are used throughout during manufacture. Material thickness is nominally 0.5mm (480 microns). A principal access zip is fitted and this has a total length typically 60 per cent greater than the enclosure diameter, ie a 900mm enclosure will have a 1,400mm-long main zip.

Introduction Control of contamination can be effected in the majority of cases by shielding the local welding area with a protective inert gas such as argon, as in GTAW (TIG welding) or by introducing a protective slag as in MMAW (stick electrode welding). Withmany metallic materials, however, including some titanium and nickel alloys, more stringent precautions are necessary, and to ensure satisfactory weld quality the entire joining process needs to be undertaken inside a vessel from which all potential contaminating products have been removed. A glove box also provides the means of providing protection against contamination by using an inert gas such as argon to replace air by ‘flushing’ or ‘purging’. Purging has become the preferred term in this context. However these are still relatively expensive to manufacture. Many of the metallic materials in common use now are prone to contamination when in contact with atmospheric gases, such as oxygen, nitrogen and hydrogen. This is particularly the case when this contact occurs at the high temperatures prevailing in fusion welding.

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J uly 2015