How Neon Sign Is Made

The Neon Manufacturing Process

Manufacturing neon signs is largely a manual process. It consists of bending the tubing and attaching the electrodes, removing any impurities from within the tubing, then evacuating the air and adding the gas. The following process is typical.

Preparing the tubing

• 1 Lengths of glass tubing are cleaned and placed vertically in a coating machine. The machine blows a liquid phosphor suspension upwards into the tube and then lets it drain back out the bottom. The tubes are placed vertically in an oven which dries the coating. Color tints are applied in a similar manner. Tubes that are to be filled with neon to form a red or orange light or argon to form a blue light are left clear.

Bending the tubing

• 2 The design of the sign is laid out in full size on a heat-resistant sheet of asbestos. The glass tubing is carefully heated and softened using a variety of burners. Gas-fired ribbon burners 24 inches (61 cm) or longer are used to make curves in round letters and the sweeping curves of script. Smaller hand torches are used to heat shorter lengths. Using the asbestos template as a guide, the tubing is bent by hand. The tube benders do not wear protective gloves because they must be able to feel the heat transfer and the degree of softening in the glass to determine the right moment to make the bend. To prevent the softened tubing from collapsing, the tube bender attaches a short length of flexible hose, called a blow hose, to one end. While the glass is still soft, the tube bender gently blows into the hose to force the tubing back to its original diameter. Tubes with restricted diameters will not operate properly.
• 3 Most large neon signs are made of several sections of glass tubing. A length of 8-10 feet (2.4-3.1 m) for each section is considered a practical limit. To make each section, the ends of two lengths of tubing are heated and spliced together. When the shape of the lettering or design has been formed for a section, an electrode is heated and fused onto each end. A small port, called a tubulation, is added to allow the tubing to be evacuated with a vacuum pump. This tubulation port may be part of one of the electrodes or may be a separate piece joined into the tubing.

Bombarding the tubing

• 4 A process known as bombarding is used to remove any impurities from the glass, phosphors, and electrodes. First the air inside the tubing is evacuated. After the vacuum reaches a certain level, dry air is allowed back into the tubing until the pressure is in the range of 0.02-0.04 inches (0.5-1.0 mm) of mercury. The longer the tubing, the lower the pressure may have to be. A very high-current transformer is connected to the electrodes. For a length of tubing that may normally run on 30 milliamperes, 400-750 milliamperes may used for the bombarding process. The high current heats the glass to about 420°F (216°C), and the metal electrode is heated to about 1400°F (760°C). This heating forces the impurities out of the materials, and the vacuum pump carries the impurities out of the system.

Filling the tube

• 5 Once the tube has cooled, the gas is inserted under low pressure. The gas must be free from impurities in order for the sign to operate properly and have a long life. The normal fill pressure for a tube 0.6 inches (15 mm) in diameter is about 0.5 inches (12 mm) of mercury. The tubulation port is then heated and sealed off.

Aging the tube

• 6 The finished gas-filled tubing is put through an aging process. Sometimes this process is referred to as "burning in the tube." The purpose is to allow the gas in the tube to stabilize and operate properly. A transformer, often rated slightly higher than the normal operating current, is attached to the electrodes. The tube should come to full illumination within 15 minutes if neon is used. It may take up to a few hours for argon. If a small amount of mercury is to be added to an argon tube, a droplet was first placed into the tubulation port before it was sealed. The droplet is then rolled from one end to the other to coat the electrodes after the aging process. Any problems such as a flicker in the gas or a hot spot on the tube indicate the tubing must be opened and the bombarding and filling processes repeated.