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The Art of Manufacturing Neon
Neon Signs, Neon Art
Neon art and signs are luminous-tubes that contain neon
or other inert gases at a low pressure. Applying a high
voltage (usually a few thousand volts) makes the gas glow
brightly. They are produced by the craft of bending glass
tubing into shapes. A worker skilled in this craft is known as
a glass bender, neon or tube bender.
The finished glass pieces are illuminated by either a transformer or a
switching power supply running at voltages ranging between 3,000 and
15,000 volts and currents between 20 and 60 mA. These power supplies
operate as constant-current sources (a high voltage supply with a very
high internal impedance), since the tube has a negative characteristic
electrical impedance. The most common current rating is 30mA for
general use, with 60mA used for high-brightness applications like channel
letters or architectural lighting. 120mA sources are occasionally seen in
illuminating applications, but are uncommon since special electrodes are
required to withstand the current, and an accidental shock from a 120mA
transformer is much more likely to be fatal than from the lower current
supplies. Neon signs are a type of cold cathode lighting..
Glass tubes with external diameters ranging
from about 8 to 15 mm is most commonly used. The tube is heated
in sections using several types of burners that are selected according
to the amount of glass to be heated for each bend. These burners
include ribbon, cannon, or crossfires, as well as a variety of torches
that run on a simple combination of natural gas (butane or propane
work better, however natural gas is cheapest) and air.
A section of the glass is heated until it is malleable; then it is bent
into shape and aligned to a pattern containing the graphics or lettering
that the final product will ultimately conform to.
An electrode is melted (or welded) to each end of the tube as it is
finished. The electrodes are also lead glass and contain a small metal
shell with two wires protruding through the glass to which the sign wiring
will later be attached. All welds and seals must be perfectly leak-proof
before proceeding further.
The tube is attached to a manifold which is itself attached to a high
quality vacuum pump. The tube is then evacuated of air until it reaches
near-vacuum. During evacuation, a high current is forced through
the tube via the wires protruding from each electrode (in a process
known as "bombarding"). The current depends on the specific electrodes
used and the diameter of the tube, but is typically in the 500mA to
1000mA range, at an applied voltage usually between 15,000 to 25,000V.
The bombarding transformer acts as an adjustable constant current
source, and the voltage produced depends on the length and pressure
of the tube. Typically the operator will maintain the pressure as high as
the bombarder will allow to ensure maximum power dissipation and
heating. This very high power dissipation in the tube heats the glass to
a temperature of several hundred degrees Celsius, and any dirt and
impurities within are drawn off in the gasified form by the vacuum pump.
The current also heats the electrode metal to over 600 degrees Celsius,
which activates a special coating that scavenges unwanted contaminants
in the tube and reduces the work function of the electrode for cathodic
emission. When completed properly, this process results in a very clean
interior at a high vacuum.
Neon Manufacturing process
While still attached to the manifold, the tube is allowed to cool while
pumping down to the lowest pressure the system can achieve. It is then
filled to a pressure of a few torr with one of the noble gases, or a mixture
of them, and sometimes a small amount of mercury. The required
pressure depends on the gas used and the diameter of the tube, with
optimal values ranging from 6 torr (for a long 20mm tube filled with
argon/mercury) to 27 torr (for a short 8mm diameter tube filled with pure
neon). Neon or argon are the most common gases used; krypton, xenon,
and helium are used by artists for special purposes but are not used alone
in normal signs. A premixed combination of argon and helium is often
used in lieu of pure argon when a tube is to be installed in a cold climate,
since the helium increases voltage drop (and thus power dissipation),
warming the tube to operating temperature faster. Neon glows bright red
or reddish orange when lit. When argon or argon/helium is used, a tiny
droplet of mercury is added. Argon by itself is very dim pale lavender when
lit, but the droplet of mercury fills the tube with mercury vapor when sealed,
which then emits ultraviolet light upon electrification. This ultraviolet
emission allows finished argon/mercury tubes to glow with a variety of
bright colors when the tube has been coated on the interior with ultraviolet
sensitive phosphors after being bent into shape. Plain argon/mercury
fill in clear glass is used for a bright but pale blue (or bluish white) color
often seen in signs where cost is a major factor.
Source: Wikipedia The free encyclopedia
Applications:
Neon Signs, Neon Art, Neon Lighting & Architectural accents
