As the name implies, a pre dryer sits in front of another dryer, typically a hot air oven. Infrared heaters are commonly used as pre dryers because they are very efficient and cost effective. In many cases, an IR pre dryer is added to an existing dryer to solve a problem:
- You need to increase your line speed to meet a business need.
- A solvent-based coating is being replaced with a water-based coating, which requires more drying. Rather than slow the line down, you can add a pre dryer to maintain your previous speed or even run your line faster.
- Your product line has changed and the new products require more drying.
- New coatings may require faster speeds.
- New coatings may be heavier and require more drying.
In all the above scenarios, you have two options: extend your existing hot air dryer by adding an additional zone, or add an IR pre dryer. Why would you use a separate pre dryer rather than making the hot air oven longer?
For one thing, the cost of adding an IR pre dryer is much less than adding a zone of hot air. But space is often the bigger issue. Adding a zone of hot air will require a great deal more space than adding a smaller IR pre dryer. Existing production lines usually do not have a lot of space between the coater and the dryer, so adding another large hot air zone may be impossible.
Due to IR’s significantly higher rate of energy transfer, you can achieve your target line speed increase with an IR pre dryer that’s about ¼ the size of a hot air oven extension. In this situation, an IR pre dryer becomes the obvious choice.
Of course, you aren’t limited to using pre dryers for boosting the efficiency of existing equipment. Adding an IR pre dryer to a new system can increase the line speed and efficiency of a new convection oven, while increasing energy efficiency and minimizing space.
Radiant Energy Pre Dryer Advantages
Radiant Energy Systems offers custom designed pre dryers for all kinds of applications. Typically they range in size from three to five feet long and cover the width of the web.
Combining IR and air for pre drying coatings
For most applications where pre drying a coating is needed, we use a combination of infrared and air to prevent skinning the coating with IR’s intense heat. Adding air to the process makes it gentler on the coating. Air also helps in breaking the coating’s boundary layer, which increases drying efficiency. In addition, the air helps to prevent damage to the web every time your line stops. Our smart controls turn the IR heaters off upon line stop and increase the air volume to a cooling level.
The combination infrared and air pre dryer can provide a line speed increase of 30 to 50 percent for many applications. The return on investment is unbeatable: the payback period is typically a few months, sometimes even weeks.
Choosing the right IR wavelength
For most applications, Radiant Energy uses medium wavelength IR heaters which generate most of the energy in the wavelength range of 2.5 to 3 microns. At these wavelengths, water has an excellent absorption peak making the energy transfer very efficient.
If space is very tight, we sometimes use short wavelength IR heaters (such as T3 lamps) as pre dryers. These heaters provide a higher energy density and are therefore well suited when space is an issue.
Pre Dryer Applications
Radiant Energy designs pre dryers for a wide variety of products and applications, including: