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Supplement, November 2000


 Leaking out the Facts

How To Keep Argon in your IG Units

by Jim Plavecsky

An interesting thing happened to me about ten years ago when I gave a seminar on argon retention at a window industry trade meeting. Afterward, several window manufacturers commented to me, “Jim, that was an excellent seminar, but who cares? The consumer can’t see argon, so if it does leak out of the window, who will ever know?”

Well, things have changed. Window manufacturers have seen the effects of argon gas loss. It all starts with what scientists refer to as the “Law of Partial Pressures.” The bottom line is this: argon leaks out of a window faster than oxygen, nitrogen and carbon dioxide can re-enter the insulating glass (IG) unit to replace it. This results in negative pressure inside the unit, causing glass deflection, which, in turn, causes visible distortion (see figures 1 and 2). Yes, the consumer will be able to tell that argon has leaked out of a window, because the IG unit will begin imploding, causing a distorted, blurry view. Glass deflection also leads to reduced thermal performance as the effective airspace between the two lites of glass is reduced. Not only does the consumer lose the initial thermal advantage of having argon in the unit, but also ends up having a window with a U-value worse than the same window made without argon. The glass deflection also has other adverse effects. It puts stress on the sealant/glass bondline interface, which can lead to premature unit failure. It also puts stress on the glass, which can lead to stress cracks, possibly resulting in IG failure. Having learned the hard way of these adverse effects over the years, by settling warranty claims, window manufacturers are now more than ever interested in designing and fabricating IG units that will exhibit long term argon gas retention.

For optimum argon gas retention, there are three critical areas to consider. The first area is the IG unit design, which deals with selection of spacer, desiccant and sealants. The second area, which is critical on a day-to-day basis, is adherence to proper IG unit fabrication techniques. As we will see, sound workmanship is an area which simply cannot be overlooked when it comes to ensuring argon gas retention. The third area is proper argon filling technique. It sounds basic, but we often take for granted that the unit is properly filled in the first place.

Figures 1 and 2: Argon leakage.

Proper IG Unit Design

A proper IG unit design involves proper sealant selection, corner construction and desiccant selection. A sealant must be chosen with low argon permeation rates in mind. The permeation rate or permeability of a sealant is a measure of how fast argon can work its way through the sealant’s polymer structure to exit the unit. Corner construction is also a critical area. If a conventional spacer bar is used, corner keys can often become problem areas. As the unit continuously expands and contracts in service, corner keys can work themselves loose. Therefore, butyl injection of corner keys is recommended highly. The optimum situation involves the construction of a framing system with continuous corners. This can be achieved by bending the spacer or by using one of the tape-like spacers such as Edgetech’s Super Spacer® or Tru-Seal’s Swiggle® Seal.

Desiccant selection is also important since some desiccants can adsorb argon. The 3A or 3 angstrom size is best because it will not adsorb argon, whereas 4A or 13X desiccants can allow some degree of argon to be adsorbed. Think of a desiccant particle as a cage-like structure with the 3A desiccant being a tighter cage so that it only adsorbs water vapor, where on the other hand, the 4A and 13X types have larger openings which allow enough room for argon and nitrogen to enter.   
Figure 3: A cold joint (left) is a pathway for argon to escape and should be avoided while the figure at the right shows a good seal.

 Fabrication Techniques

Glass must be clean and dry to ensure the best adhesion with sealants. Argon will slip through even the slightest gaps in the bondline. When moisture enters an IG unit through such gaps, the desiccant is there to adsorb it, which buys time. The situation is different, however, with argon. When argon escapes, it escapes for good.

As previously mentioned, corner keys can also be a problem area. Make sure these are crimped properly, which will help prevent gaps at the corners that result when corner keys work themselves loose. In addition, avoid cold joints. These are caused when hot melt is gunned incorrectly. Don’t allow one side to cool before applying sealant on the adjacent side. This can cause a cold joint and is a pathway for argon to escape (see figure 3). When fabricating dual-seal units, make sure the PIB extruder is properly bled to eliminate air entrapment. Air in the extruder can cause skips (areas where voids exist). Argon will escape the unit through these areas. Avoid starving the extruder. Keep feeding it a constant supply of PIB to avoid narrow application of PIB. When applying hot-melt butyl sealant, again, make sure the pump is properly bled—air entrapped in the system can lead to voids. Be careful not to overheat the sealant. This can cause phase separation of plasticizing agents within the butyl and lead to voids. A dense and consistent application of sealant is an absolute must when it comes to argon

Argon Filling – Intercept® Units

A two-hole method or a one-hole method may be used for argon filling. The two-hole method involves using a filling wand, which pushes argon into the unit through one of the holes, and a sniffler, which removes air through a second hole in the unit. Many Intercept fabricators prefer the one-hole method, saying it is less cumbersome and labor intensive. One may also argue that with two holes, there is twice the chance of failure. Indeed, Intercept fabricators have reported that when their units do have problems, it is usually at the swedge hole (the hole which is placed in all Intercept units to allow ventilation during the heating stage of the fabrication process). The one-hole method involves a high-speed flooding of the unit with argon while removing air at the same time using a combination wand/sniffler through the same hole. This method can be quite fast, but requires more argon to get the desired fill rate. However, argon is very inexpensive and a higher waste rate is offset by greater manufacturing productivity. Once filled, a swedge screw is drilled into the hole or holes to seal the unit. Two different sized swedge holes are employed to create a self-tapping action which firmly seats the swedge screw. It is also important to keep the lance in top condition. Bent or plugged lances can restrict proper gas flow. The gas- filling machine must be properly calibrated. FDR sells a handy in-line tester which checks argon levels to ensure units are filled to at least a 90 percent argon level. Finally, proper sealant gunning procedures must be executed to seal over the swedge holes.

Figure 4: Dual snifflers provide faster fill rates.

Argon Filling With Swiggle®

With Swiggle, a one-hole method can be employed through the open corner, prior to sealing the unit. A weighted silicone tube is dropped to the bottom of the unit through the open corner, and the proper fill rate can be achieved on the basis of time, which is calculated based upon the unit size and airspace. Alternatively, snifflers can also be employed through the same entry point. Dual snifflers can be used to facilitate faster fill rates (see figure 4). Again, make sure that fill levels are properly monitored. Once the unit is filled, the fourth corner is closed and a hand-held quartz lamp is used to heat the Swiggle tail. The tail is then folded over and sealed against the adjoining Swiggle surface.

 Super Spacer® Argon
Filling Techniques

There are several ways to gas fill a Super Spacer unit. A gas-hole punching kit is available as an add-on to Edgetech’s Super Shuttle application tool (see figure 5). This is a pneumatic punching device which makes a clean, precise and tapered hole into which a wand or sniffler can be placed. Both one-hole and two-hole methods can be employed as before. The holes are then tape-sealed using vapor barrier tape supplied in Edgetech’s kit. As an alternative, a very unique and extremely fast method has been developed by FDR involving the use of a piercing device with reusable sleeves. This unique device pierces a temporary hole through the Super Spacer. The hole is held open by the sleeve, through which a wand and/or snifflers are placed into the unit filled by either the one-hole or two-hole method. Once the unit is filled, the sleeve is removed and the hole or holes close shut. This is possible only because of the unique nature of Super Spacer—it is very resilient. After stretching, it returns to its original shape. Only a tiny nick on the backside (non-sightline side) of the Super Spacer can be seen where the mylar vapor barrier was pierced. This can be covered with a piece of vapor barrier tape for good measure, and then the sealant is applied in normal fashion.

Figure 5: The Super Shuttle application tool allows for a clean hole into which a wand or sniffler can be placed.

 Gas Retention Testing

Once we achieve what we believe is a gas-tight, argon-filled unit, how do we test units to estimate the gas retention capabilities of our IG units?

A septum or polymer plug is installed in the IG test units to enable insertion of a gas-tight syringe into the IG unit. A gas sample is withdrawn into the syringe and the sample is injected into a gas chromatograph (GC) to measure argon concentration. Once an initial reading is taken on each unit, the unit is placed into accelerated aging, removed and a second sample is taken through the septum. The difference between the initial reading and the reading taken after aging is the percent loss. The accelerated aging is said to represent five years of normal field exposure. Therefore, the percent loss per year could be estimated as the average percent loss value divided by five.

 High Humidity Results

We are looking at various IG designs tested for argon retention after high-temp/high humidity aging (see figure 6). Reported in the table are: the average result, the best result and the standard deviation. The average result is an indication of the mean gas loss after accelerated aging. The best result shows just how good that particular design did with the very best workmanship, given the accuracy limitations of the test equipment employed. The standard deviation is an indication of how consistent the results were for that given design. A low standard deviation means results were very consistent, and a high standard deviation means the results varied to a high degree.

It is important to point out that where designs exhibit a high average result, this could likely be due to workmanship issues. As discussed earlier, workmanship is critical in argon gas retention. What really concerns me is seeing units display a high average result coupled with a low standard deviation or a very poor result in the best column.

Argon Retention - NRC Study

  Average Best  Std. Deviation
Swiggle Seal 0.90 0.30 0.36
Polysulfide 6.65 0.30 13.80
Hot Melt Butyl 14.92 0.70 34.09
Silicone Dual Seal 18.07 3.10 31.03
Super Spacer® 1.07 0 0.79

Figure 6: The average result, best result and standard deviation are shown in respect to argon retention. 

Weather Cycling Results

Since the weather cycling test exposes the units to a high degree of temperature cycling coupled with high-intensity ultraviolet (UV) light exposure, it is even tougher on IG units. This stresses the bond-line of the IG unit as units are repeatedly heated and cooled. UV rays also are beaming directly upon the bond-line interface. This accelerates degradation of the chemical bonds that form the basis for adhesion. Once again, by examining the average result, the best result and the standard deviation column, we can see that workmanship is critical when it comes to argon gas retention.

Argon gas has been shown to significantly improve the thermal performance of the IG unit and overall window system, especially when combined with thermally-efficient frames, warm-edge spacer systems and low-E glass. However, because of the adverse effects that argon gas loss can have upon the durability of the IG unit, not to mention the clarity of view, it is more important than ever to design and fabricate gas-filled IG units with long-term, argon-gas retention in mind. Consumers in today’s competitive markets are looking for outstanding quality and value. Argon gas, when combined with sound IG design principles and fabrication techniques, is capable of adding long-term value to today’s modern window designs.

 Jim Plavecsky is vice president of sales and marketing for Edgetech IG Inc. in Cambridge, Ohio.


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