By Tim Heston
Assist gas generation for laser cutting has come a long way during the past decade. As more shops expand their laser cutting
capacity, they o;en take another look at assist gas
consumption. More operations are looking at alternatives for delivered gas, and this includes generating gas on-site—specifically, nitrogen.
Purity in on-site nitrogen generation has reached
so-called “five-nines levels”— 99.999+ percent pure.
According to Jordan Messick, industrial sales mar-
ket manager at Wilmington, N.C.-based South-Tek
Systems, “The latest nitrogen generation systems
can be tuned to the flow rate and purity level an ap-
Five-nines nitrogen purity may be overkill for
typical laser cutting assist gas applications, but
certain machine elements can benefit from such
purity. Some cutting heads on the market require a
nitrogen purge gas that’s 99.999 percent pure, and
according to Messick, some smaller, dedicated ni-
trogen generation systems have been designed to
supply that purge gas.
If you’re cutting thick stainless, 99. 99 percent
purity (four nines instead of five) will help prevent
discoloration on the cut edge. Some less critical
applications—say, thin-gauge mild steel—probably
wouldn’t need such a high purity level.
“From what we’re seeing, 99. 99 percent would be
a fairly standard purity requirement for most applications,” said Mike Montesi, commercial sales manager for On Site Gas Systems, Newington, Conn. But
he added that purity requirements do vary, depending on the laser machine and application.
What about oxygen? Oxygen generation systems
are on the market, though they usually aren’t de-
signed for laser cutting. On Site has systems that
generate 95- and 99-percent pure oxygen. According
to the company website, the system has been used
to generate oxygen in medical applications and
even for the International Space Station. In a Sep-
tember blog about its booth at this year’s FABTECH®
show in Chicago, the company stated, “Our 95 per-
cent and 99 percent oxygen PSA generators are ideal
for oxyacetylene cutting and welding purposes.”
So is this good enough for laser cutting? “The pu-
rity is too low,” said Montesi. “You still need 99. 95
percent oxygen purity. We sell a lot in the laser cut-
ting market for nitrogen generation. We tested oxy-
gen generation with a laser machine manufacturer
about a decade ago, but the oxygen generation
technology just isn’t there for laser cutting.”
Regardless of how technology progresses, one
thing is for sure: Fabricators are looking for ways to
reduce the cost of laser cutting—and this includes
generating assist gas in-house.
Nitrogen Generation Basics
Although nitrogen and oxygen sit next to each other
on the periodic table, the two elements behave very
di;erently under pressure, which is basically what
makes shop floor nitrogen generation possible for laser cutting. Gas generation technologies take advantage of this di;erence to separate the nitrogen molecules and send them on to a laser cutting machine.
Industrial applications accomplish this separation
in two common ways. One way uses a membrane
of permeable hollow fibers. Gas flows through hollow fibers and oxygen permeates outward through
pores in the fiber. Nitrogen molecules, which can’t
fit through the pores, continue flowing to the nitrogen storage tank.
A membrane system controls the flow rate by re-
stricting the outlet flow, building more pressure and
forcing more oxygen out. The drawback, however, is
that flow can be constricted only so much, so there’s
a limit to how much oxygen can be drawn out of the
The nitrogen generation systems growing more
common on the fab shop floor use another technology. It’s called pressure swing adsorption, or PSA.
(Di;erent from absorption, adsorption is a process
in which molecules adhere to a surface of the adsorbent.) At the heart of it are two pressure vessels filled
with what’s called a carbon molecular sieve, or CMS.
This material performs the gas molecule separation.
“If you look at CMS under a microscope, it looks
like a small piece of charcoal that’s very porous,”
Here’s how it works. Compressed air is pushed
A pressure swing adsorption nitrogen generator can be
tuned to meet the purity and flow rate requirements a
fabricator needs. Photo courtesy of South-Tek Systems.
In-house assist gas generation picks up steam