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Neon signs use a straightforward high intensity discharge approach to creating light. But how on earth do they make those signs? Electric By JULIAN EDGAR Lighting Pt.15: Making A Neon Sign The different coloured neon tubes that are commonly available. The colours can be created in one of three ways – different fill gases, different fluorescent coatings, or different coloured glass. The most common technique for generating the different colours is to use tubes with different coloured fluorescent coatings with a fill gas of argon and mercury vapour.  November 1999  39  When the different colours are created by the colour of the fluorescent coating, the unexcited tubes all look white – irrespective of the colour they later glow! This can lead to problems when some of the tubes within a pack are mislabelled. Neon tube is available in 9, 15 and 18mm diameters, and made from soda or lead glass. The soda glass lengths are five feet long, while the lead glass tubes are four feet long.  The layout of the sign is provided as a sketch on paper, which is then transferred to a fibreglass mat. The mat provides a template against which to compare the glass tube bends. The next step is to select a piece of tube and soften it over a heater that uses a flame fed with natural gas and compressed air. The width of the flame can be adjusted to suit the length of tube to be heated and the temperature of the flame can also be changed. Take note of the single, four-foot length of tube that you see here – it ends up a very different shape!  The hot tube is bent to the shape shown by the marked template. The need for a fibreglass mat (as opposed to a paper plan) can be seen here – the tube is hot enough to cause a paper plan to burst into flames! Every bend that you see in a neon sign is formed individually, being compared with the template at each step. It is a time-consuming task that requires patience and skill. ING NEON SIGNS MAKING NEON  Because the letters of the sign are made from the continuous length of tube, often the tube needs to wrap back on itself. Using the least amount of tube and the smallest number of bends means that the sign maker needs to have a complete mental picture of where the tube is to go. Sometimes, this requires that the bending starts from one end; at other times the bending begins in the middle of the length of tube. 40  Silicon Chip  After each couple of bends are formed, the bent tube is heated with a ‘cool’ flame. This removes any built-up stresses within the tube. If this is not done, the tube can crack as it cools. The tube is quite fragile – it can be broken by as little force as being placed firmly on a bench. When mounted in the signs, the tube is supported on sprung fittings so that undue stress isn’t placed on it.  Here’s what that straight section of tube that we saw a few pictures ago now looks like! Remember, each bend that you can see here was formed individually. The cork in the end of the tube closest to the camera is so that the sign maker can blow air into the tube to expand the glass at the bends. Note how closely the tube follows the template. As the tube is bent, it tends to close up. So that the original tube diameter is re-formed, the bender (having corked the other end of the tube!) blows into it. The hot, softened part of the tube then returns to its original diameter. Too much air pressure would balloon the tube out at the bend, so this, too, is an operation requiring a deft touch.  Where a bend is needed near to the end of the tube, another section of tube is joined to provide a convenient handhold. This tube will later be removed, so cheaper clear glass can be used. The ends of both pieces of tube are heated with a natural gas and oxygen flame until just molten and then the tubes are pushed together. It’s quite amazing watching how well they join – much easier than welding steel tube!   Here the new clear section of tube is being used as a handhold while the tube is again heated in preparation for making another bend. Since the beginning of this sequence, about 30 minutes has passed – it’s a slow and careful process. The fluorescent coating on the inside of the tube stays attached, despite the heat that is applied. N SIGNS MAKING NEON SIGNS  This particular assembly (the last three letters of a ‘Pokies’ sign) is formed from two four foot long lengths. The tubes therefore need to be joined, with the join placed so that it falls behind part of another letter. It will be later blacked out by paint, so the change in illumination caused by the disruption to the fluorescent coating won’t be visible.  The ends of the assembly where the electrodes will be located need to be cut to size. The tube is heated with a direct flame and then stretched to narrow the wall thickness of the tube. After that, a nick from a normal metal-cutting file creates a weak spot, with the tube breaking cleanly at that spot when struck. It was obvious that extreme care was now being taken – it’s apparently easy to destroy the 2 hours of concentrated work!  The electrode comes as a preformed assembly. The tube diameter closest to the camera matches the diameter of the neon tube being used, while the smaller diameter tube is used to evacuate the tube and fill it with gas. Two conductors are connected to the electrode and these are wired to the test transformer in parallel. November 1999  41  The electrode is attached to the tube in the same way as the clear glass extension piece was previously attached. The flexible plastic tube (visible at the top left) connects the upper glass extension of the electrode assembly to the sign maker’s mouth, allowing him or her to suck on the neon tube. With a cork located in the other end, the maker can sense when the electrode join is airtight.  The neon tube is then ready to be filled with gas. Those tubes using just neon require no addition of mercury but those using fluorescent coatings (such as the sign we have watched being made) use a fill gas of argon, with mercury then added. A syringe is used to place the mercury in the glass bulb assembly in the foreground.  At left is the electrode of the neon tube, with the mercury bulb tee’d off from the evacuation/gas fill tube, which leads off at the right to the machine that is used. During both the evacuation and gas filling procedures, the mercury remains in the bulb. However, after these operations are completed, the glass is sealed to the right of the bulb, allowing the mercury to be then added to the neon tube. GNS MAKING NEON SIGNS MAK  When the tube is being evacuated, sheets of mica are placed between adjoining parts of the tube. This is done in case the tube should get so hot that it distorts, allowing adjoining parts to touch and so cause cracking. The charred paper test strip can be seen on the right. 42  Silicon Chip  Once the tube has been evacuated, filled with argon and then disconnected from the machine, the mercury remaining in the bulb is added to the tube. This is done by simply tilting the sign so that it flows out of the bulb and into the main body of the tube.  The tube is then connected to a high voltage source and energised on the bench. The sections of the tube where mercury has mixed with the argon are glowing brightly; the sections it is yet to reach are dull. As the tube heats up, the mercury vaporises and fills all sections of the tube evenly. The neon tube is evacuated by the machine in the background. During this process, 20kV is applied at currents of up to an amp, causing the electrodes to glow red hot. The tube also gets hot; a strip of paper is placed across the tube and when it starts to char, the tube is hot enough! Even though it is not filled with a gas, the tube still glows brightly during this process.  As indicated earlier, either neon or argon can be added, depending on the sign’s application. Argon is much more popular, being used with the fluorescent-coated tubes. Neon is used most often in clear glass tubes, lighting up red when switched on but being clear (and so not very visible) when switched off. This characteristic makes neon signs suitable for use in ‘open’ and ‘no’ (as in ‘no vacancy’) signs.   The vacuum pump can be seen in the foreground and the 20kV, 1-amp transformer can be seen behind it. The machine has been built expressly for the purpose of making neon signs. During evacuation, a pressure as low as 0.001mm Hg can be developed. The pressure within the sign after gas filling is in the range 3-20mm Hg. Thanks to Australian Trade Neon 08 8351 7811 KING NEON SIGNS MAKING NEO  As can be seen here, the whole length of tube is now glowing brightly with the mercury mixed evenly. When the sign is switched off, the well-distributed mercury vapour will condense onto the adjacent walls. This means that all sections of the tube will glow with the same brightness when it is again switched on.  The effect of the fluorescent coating can be clearly seen here. The blue discharge that occurs in the mercury/argon mixture is visible between the electrode and the beginning of the fluorescentcoated tube, which can be seen to be glowing very brightly. Note the truncated evacuation tube on the left of the electrode. All signs are ‘run in’ on the bench. This neon-filled tube shows the characteristic red neon colour and would of course be clear when switched off. The black-painted sections of tube are simply the connecting links between the SC letters. November 1999  43