TPT July 2015

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90 July 2015
Article Huntingdon Fusion Techniques
Flexible enclosure welding
By Dr M J Fletcher, Delta Consultants (Huntingdon Fusion Techniques)
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.
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.