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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


Neon Signs, Neon Art, Neon Lighting & Architectural accents