Why Quartz Tube Halogen Lamps Are Such Effective and Long-Lasting Infrared Emitters

Occasionally, when working with clients, they express surprise that one of the mainstays of infrared lamps is the classic “quartz tube” halogen bulb. It was invented in the 1950s, so it seems odd that such a relatively old design would still be preferred for modern infrared emitters. However, sometimes classic designs are still the best. Halogen bulbs have a remarkable longevity, and are unlikely to be surpassed any time soon, in terms of price vs. performance, for most industrial applications.

The Key to Halogen Bulbs’ Longevity

At heart, halogen infrared emitters are a variation on the classic incandescent light bulb which is still used around the world. Like incandescent bulbs, halogen bulbs utilize a filament made of tungsten which is super-heated to produce light, contained within an enclosure filled with inert gas.

Rather than glass, halogen bulbs utilize forms of quartz which are far stronger than glass – able to withstand significantly higher pressure and heat. This makes quartz casings reliable even in applications calling for several hundred degrees’ temperature.

The atmosphere within the bulb also varies. Traditional incandescent bulbs generally use a mixture of nitrogen and argon. This mixture is simply there to prevent oxidation. However, halogen bulbs use different gases like iodine or bromine, which are electronegative and held at significantly higher pressures than the gas within a traditional bulb.

This is what allows halogen infrared bulbs to often last for a thousand hours or more. When a traditional nitrogen/argon bulb burns, the tungsten filament is continuously vaporizing the outermost layers of molecules, which enter the gas and then are deposited on the inside of the glass. Therefore, when a bulb “burns out” the interior is blackened. It’s tungsten soot.

However, the gasses within a halogen bulb captures and collect these tungsten particles. Rather than depositing on the glass, they instead re-attach to the filament. In effect, the tungsten recycles itself, burning off and re-acquiring the same layers of metal repeatedly. This lengthens the lifespan of a halogen bulb by several times beyond that of a standard incandescent, while also allowing it to operate at a much higher temperature.

• Impingement Air Velocity
• Air temperature
• Humidity of the supply air
• Distance between the nozzles and the material being dried

The ability to position nozzles throughout the length and width of the dryer means that temperature can be consistently controlled, even at the edges of the web. Multiple heating zones in the machine direction, can be created using groups of nozzles that are independently controlled for temperature and velocity.

Common applications for impingement drying

Impingement dryers are typically used for drying coating on webs such as paper, films, foils, nonwoven and fabric. Impingement is a very efficient means of drying coatings on webs. In most cases, coated and non-permeable webs are the best applications for impingement drying. Permeable webs, where the  coating may “bleed” through the material or the applications where the web is saturated with coating can also be run with impingement dryers in a vertical pass configuration.   Typical end products that benefit from a higher efficiency impingement drying system include adhesive tapes, protective films, coated fabrics, architectural fabrics etc.

5 reasons to choose an impingement dryer:

1. Accurate and uniform temperature control.  Since these dryers are designed to provide uniform temperatures throughout the dryer, impingement can be used for drying various coatings on many different substrates.
2. Heat transfer is independent of web handling.  Impingement dryers can be designed to use various methods of transport through the dryer. Rolls (either idler or driven) are commonly used for webs.   Conveyors or vertical tower designs are also available depending on the material and the requirements of the process.  The adjustable control of the drying is independent of the transport method. 
3. Ease of creating multiple heat transfer zones.  In an impingement dryer, groups of independently-controlled nozzles can be arranged to create different heating zones within the dryer. As the material moves through each zone, the temperature and velocity of heated air is adjusted to the requirements of the process. As an example; depending on the thickness of the coating, the first zone may be lower on velocity so as not to disturb the coating.  As the coating dries, the velocity and temperature can be increased to improve the rate of heat transfer and reduction of the dryer length.
4. Nozzle configuration can be easily modified.  This comes in handy when you’re using the dryer for multiple products or processes that may have different requirements.
5. Ability to create recipes. Just as you have the ability to adjust the nozzle configurations, you can also adjust the velocity and temperature of each zone to create recipes for different products.

Impingement dryer limitations:

1. Higher capital costs. An impingement dryer requires a separate material handling mechanism, such as rolls or a conveyor, which adds cost, especially when driven-roll support is needed. Also, rollers and bearings require regular maintenance, and these expenses need to be taken into account.
2. Web tension issues.  Especially when a longer dryer is needed, the required tension to move the web may be a problem for some materials. Also, longer dryers may not be able to use idler rolls but may require more expensive driven-roll support.
3. Risk of marking or damage to web.  If you’re drying a material that could be damaged by contact with the conveyor or support rolls, you may want to consider a flotation dryer where the web never touches a support mechanism.
4. Possible heat transfer spikes.  For processes requiring slower line speeds, impingement drying can sometimes cause heat transfer spikes on nozzle centers

Important design considerations for an impingement dryer

If you determine that your product is a good candidate for impingement drying, remember that the dryer needs to be designed with your exact process requirements in mind. When you work with an experienced dryer manufacturer, these design options can be precisely configured according to your needs:

Source Infrared Emitters from The Experts

Anderson Thermal has over 75 years’ experience providing thermal solutions to a wide range of industries. Contact us for a full consultation on your next project.

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