Page 10 - Enclosure_Spring-Summer_2023

continued from page 8

terity while trying not to damage a glovebox glove. With process inside of a glovebox, pay attention to all your
that image and understanding in mind, it is quite common feedthroughs.
to see custom tools and widgets for electrode change out,
wire cutting, and torch adjustment designed specifically to Arc Starting
avoid sharps exposure while performing common tasks. Be aware of arc starting, which is common for GTA pro-
The time spent on developing special tooling or processes cesses, and required for the PAW process. The arc start
referred to here is that split second high frequency or ca-
pacitive discharge arc start, a commonly found feature on
most modern GTA welding equipment. The intent of these
arc starters is to jump the gap or start the arc without ever
actually touching the electrode to the part. This method of
arc starting is preferable to most weld engineers who may
be concerned with the potential of tungsten inclusions in
the weld deposit. Modern arc starters work great, they have
been on the market for decades, and they are reliable. The
arc starter is intentionally designed to force an electrical
discharge which is all well and good in most cases. Howev-
er, if your system is poorly grounded, or if there is an easier
pathway to ground anywhere in the torch, that arc start will
be more than happy to jump that gap instead and will cause
havoc with instrumentation or anything else available.
The working gas for most inert gloveboxes is argon,
which has a dielectric strength about one-fifth that of
Figure 3, Glovebox Feedthroughs air. The welding arc starter will easily cross small gaps

to mitigate sharp items is well spent when compared to the
recovery time of puncturing a glove. In many nuclear ap-
plications, a glove puncture is simply not tolerable.

Feedthroughs
Welding applications bring all the traditional feedthrough
issues, plus their own unique challenges. Traditional
sealed feedthroughs can be used for welding applications
without modification. Special care should be taken to
select appropriately rated high current feedthroughs for
both electrode power and weld ground. Water cooled
torches will require their own sealed feedthrough for
water supply and water return. Weld shielding gas is also
typically needed and ran through a separate feedthrough.
Pay attention to the fittings used on your GTA or PAW weld
torch. The weld industry will commonly use inert arc fittings,
which are somewhat specialized and unique to the welding Figure 4, Arc View Camera Image
industry. You may need fittings or adapters to something
more universal, such as a pipe thread, for the glovebox or exploit cracked or damaged cable insulation. Proper
feedthrough. grounding and bonding are essential when welding inside
a glovebox to ensure noise free instrumentation and arc
Pay particular care to any feedthrough sensitive to
electrical noise such as camera systems, instrumentation, starting issues. Seek advice from someone familiar with
and data acquisition systems. Even if these systems are not high frequency electrical noise if problems persist.
associated with the welding equipment, they can (and will) Arc starting and weld arc electrical noise can also affect
be affected by the electrical noise of the welding arc. For systems in close proximity but not inside the glovebox.
example, it’s pretty common to see noisy instrumentation Video systems, instrumentation, and nearby electronics
signals as soon as you start welding. This is a sign that your are particularly problematic. Ensure any sensitive systems
feedthroughs are poorly isolated and incorrectly grounded in close proximity to the arc start are well shielding and
or shielded. Bottom line is, as soon as you run a welding grounded.

continued on next page

10