Yes I know that all these gauges cost money, but so does remaking tubes or losing customers. Eventually you should own all of them, but you do not have to purchase all of them at once. You will notice that they can be divided into two groups: those that let you monitor the tube while it is being heated, and those that let you evaluate the quality of tube and manifold vacuum. Read on and we'll go through all of them.
There are several stirrings going on in this direction: it is an upcoming subject for the NESA board and in a rare show of cooperation between some sign supply distributors.
How would this work?
Here's one rough example: a given manifold system would be inspected and awarded points for required gauges and controls. It would then be tested for it's performance qualities and awarded a second set of points. The best vacuum systems might then end up with a 5/1 rating : all five gauges/pulling and holding less than 1 micron.
Are there problems with this simple model? Sure: I don't think that performance specifications would really be one of them, but who to administer the tests (NESA, UL,?), frequency of the tests, and cost, certainly would be. This should also include "certification" of the manifold operator; you can take beautiful tubes and great equipment and put out trash with incompetent operators. (If any of you readers have opinions on this subject, please write or fax me in care of Sign Business) What would they look at? Read on.
Temperature Gauge: Glass must be heated above a certain temperature in order to release and then remove the impurities in the tube. A temperature gauge lets you know when you have reached that point. It is also important to note that some phosphors can be damaged by heating to too high a temperature, so "really burning that paper" doesn't cut it either. In other tests we have done, we have found wide variations in when different papers begin to "lightly char". This is to say that paper is not sufficient to tell when the glass has been brought up to the required temperature. Thermocrayons are much better, but in my opinion, have more drawbacks than either good clamp on thermocouples or infra red gauges (a topic for a future article).
Positive Pressure Gauge: Staining can occur from processing the tubes with too little or too much pressure in them while being heated. It is also necessary to manipulate the pressure in the tube to consistently heat the glass and electrodes to the right temperatures at the right times (see Neon Jungle article "Managing Pressure). It is possible to use a butyl oil U-gauge to monitor the pressure in the tube. It works just fine, but unfortunately too many people won't take the extra time - even though it can save them untold time to replace stained tubing and virtually eliminates sucking tubes in while bombarding. On a theoretical note, if you are using some type of finishing pump, you are probably below the vapor pressure of the butyl oil - which could end up in your tubes while filling. These pressure gauges can be either electronic or mechanical and are easily adapted to most manifolds.
Vacuum Gauge: This gauge can be used for both checking to make sure that a tube is being vacuumed out sufficiently before filling, and monitoring the condition of the manifold assembly itself. A spark tester is not good enough.
Reastat Controlled Choke: As stated earlier, current must be varied during the bombarding process to properly heat the glass and convert the emitter in the electrodes (and different electrodes require different current levels). A slide choke works fine on small bombarders, but you can't process the tube with the correct amount of pressure in the tube with a small bombarder. It is so difficult to manipulate a slide choke on a 15 or 22kV bombarder that it usually is chocked in place with blocks that may or may not be varied while bombarding. What is required is something that can be varied easily and accurately while the bombarder is on.
Pumping speed (throughput): It may be great to be able to pull below one micron, but if it takes 30 minutes it's too late; at about 175 degrees C all of the trash that is in or on glass is being released. The trick is to evacuate it before it can re-adhear to the glass while it is cooling. When we heat a tube to 225 C or so, it takes about 20 seconds for it to cool back down to 175 C. So it is very important to pump the contaminants out during this short period, otherwise these contaminates will be released over the life of the sign (with the energy from the transformer) and ruin the tube.
Leakage rate (drift rate): Any manifold after being pulled down to it's best vacuum will slowly begin to leak air back into it when the valve to the vacuum pump is closed off. Minute amounts are not a problem, but large vacuum pumps (and particularly strong finishing pumps) can mask significant leaks in the manifold. This becomes a problem when the main stopcock is closed and the tube is being filled with gas. This drift rate varies and is influenced by repeatedly exposing the manifold and vacuum gauge sensor to atmosphere but should not be greater than 1 micron per minute.
Bombarder size: large. You need lots of volts to strike and maintain an arc through long tubes at the pressures recommended by the electrode manufacturers to properly process the electrodes (see reastat controlled choke above). Think 15 kV or larger.
We should note here that we did not specify manifold material. Certainly some materials lend themselves to this application better than others, but if you can make the specifications with garden hose and and a smog pump, good for you! (And don't forget to advertise it in Sign Business after you get the patent)
Tip Of The Month: Finding old patterns I recently spent several frustrating hours one day looking for an old pattern to make a second sign for an old customers' expanding business. Several days later this brilliant tip showed up in the mail. Rather than just stuff the rolled patterns in random boxes, number the boxes and put the box number with the sign title on a Rolodex. If you're real smart you would include info like overall size for window signs, transformer sizes with mA data, repair history, original cost, and so on. This makes them easy to find, service, and great for quick quotes.
Morgan Crook is a mechanical engineer, tube bender, and president of Neon Design, a wholesale, retail and consulting firm in Columbia, S.C.