Radiant Energy has been designing and manufacturing systems for industrial drying, curing and heating applications for 30 years. Our custom designed process dryers and ovens convert gas, electricity or steam into efficient process heat. Our process dryers can heat one or both sides of the product in single or multiple-pass configurations.
Our engineers are knowledgeable about all types of hot air convection and infrared dryers, so we’ll use the right technology and create the most effective process dryer design for your needs and your application.
Hot Air Impingement Process Dryer
Impingement drying involves directing medium to high-velocity hot air onto the material to be heated or dried. The heated air can be generated using gas burners, electricity, steam or can even be recovered from other processes, such as oxidizers. Using a controlled pressure blower, hot air is forced through nozzles or slots which are precisely positioned in the dryer according to the heating requirements of the material.
Impingement dryers are typically used for drying coatings on webs such as paper, films, foils, nonwovens and fabric. Impingement is a very efficient means of drying coatings on webs. In most cases, coated webs are the best applications for impingement drying.
The high velocity of the air allows for very high heat transfer rates, and results in more moisture removal for faster, more efficient drying and curing. Processing times can be greatly reduced as compared to lower velocity convection air dryers. The increased efficiency also means that dryer lengths can be shorter than other hot air process dryers.
More impingement process dryer advantages:
1. Accurate and uniform temperature control. Since these process 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, including rolls, conveyors or vertical towers. 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 process dryer. As the material moves through each zone, the temperature and velocity of heated air is adjusted to the requirements of the process.
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.
Flotation Process Dryer
Like impingement convection dryers, flotation dryers use streams of hot air to dry a coated web. However, flotation dryers are very different in the way they move the material through the dryer.
Flotation dryers have specifically designed nozzles that support the web on a bed of air, instead of using rollers or a conveyor like an impingement dryer. Flotation supports the web normally using a controlled sinusoidal web path that keeps the web from wrinkling, and minimizing the tension needed to control it, by simulating passage over and under rolls. This unique design means that neither side of the web actually touches any surface in the dryer.
Flotation is the ideal choice when you have:
- A web coated on both sides
- A saturated or dip coated web
- A delicate substrate material that cannot be mechanically supported
- A web that can’t have any scratches on the product
Flotation process dryer advantages:
1. No need for expensive roll or conveyor web support. The flotation dryer’s built-in air support mechanism is less expensive than other options.
2. Eliminates product or coating damage from contact with supports. Since the web never touches the support system, there is no danger of marks or damage.
3. Eliminates edge curl. Edge curl is an issue seen with surface temperature differences on the top and bottom of a web. A flotation nozzle design uses a developed sinusoidal web path which simulates the effect of the web passing over rolls and minimizes or eliminates the curl.
4. Accurate and uniform temperature control. Since these process dryers are designed to provide uniform temperatures throughout the dryer, flotation can be used for drying various coatings on many different substrates.
5. No heat spikes. Unlike impingement dryers that can have heat spikes on nozzle centers when running slow line speeds, the flotation dryer’s parallel air flow component averages the heat transfer.
6. Shorter drying time. Nozzles on both sides of the web increase the heat transfer and shorten the drying time.
7. Positive web tracking through the dryer (self-centering) with minimum tension requirements. A flotation nozzle directs air across the face of the nozzles in the machine direction (rather than directly impinging on the surface of the web) which holds the web to prevent it from moving towards either side of the nozzle array.
8. Lower height. Flotation dryers are flat as opposed impingement which are arched. This is important when there is a limited height available in the plant.
Through-Air Process Dryer
Through-air dryers, as the name suggests, use a heated airflow that passes through the material to remove moisture from permeable products or to selectively melt bonding fibers. The heated air can be generated using any energy source available, such as gas, steam, thermal oil or electricity. The heated air is distributed uniformly above the product to be heated in a non-impingement fashion and then drawn through the material using a controlled suction design.
Through-air drying is typically used for drying, curing, heat setting and thermal bonding of porous materials such as nonwovens, textiles, paper and fibers. It’s also commonly used for fiberglass mat and the base material for roofing and siding shingles.
Through-air process dryer advantages:
1. Faster drying. Through-air drying produces two to three times more heat transfer than other types of convection dryers.
2. More uniform drying. The high evaporation rates from thermal and mechanical drying, along with better heat penetration through the product, result in very uniform drying though the thickness of the material.
3. Accurate temperature control. The heated air stream can be precisely controlled in machine direction and across machine direction. Flatbed designs also provide the ability to create multiple heating zones to vary temperature and air velocity as the web moves through the process dryer.
4. Enhanced texture or “hand” of non-woven materials. For certain types of nonwovens such as absorbent products used for baby diapers and sanitary napkins, through-air drying produces a desirable texture that can’t be accomplished with other types of dryers.
Radiant Energy’s through-air process dryer designs:
Rotary through-air process dryers have a rotating drum with an open-grated surface. The material to be dried covers the outside of this surface and moves with the drum.
Flatbed through-air process dryers hold the product on an open mesh conveyor belt and move it through a long, horizontal suction chamber.
Gas or Electric Infrared (IR) Process Dryer
Unlike convection dryers that transfer heat using streams of heated air, infrared dryers transfer heat by sending waves of electromagnetic energy to the object to be heated. Designed properly, IR dryers are very efficient and provide a source of high heat with an intense burst of energy. Because of higher rate of heat transfer, IR dryers are often less than half the size of an equivalent hot air dryer.
IR is usually the best choice where the process requires a high temperature. Some applications can require oven temperatures to reach as high as 800 degrees F. To build a hot air oven capable of handling this type of application, the components required (such as heavy-duty blowers and 8 inch thick oven walls) would be extremely expensive. Infrared technology can handle these temperatures easily and with lower capital expense.
IR dryers are commonly used for heat setting as well as drying and curing thinner coatings, such as pressure-sensitive adhesives on masking films for appliances and electronics. Gas IR is often the best choice for preheating or partial drying because it packs a very high energy density, so a lot of heating can be achieved with a small heater bank.
In addition to more efficient heat transfer, smaller size and energy usage, there are even more advantages to using IR dryers.
IR process dryer advantages:
1. Easy to zone in machine direction and across machine direction for uniform heating and width variations.
2. Quick start up and shut down. IR dryers get up to temperature very quickly, and cool down immediately upon shutdown, unlike other types of process dryers that have large thermal inertia. IR’s quick response can often result in faster response to changing process conditions.
3. Precise temperature control and infinite adjustability are possible with an electric IR heat source.
Combination IR and Hot Air Process Dryer
IR drying is more intense, and can provide a lot of energy for the process in a short space. Hot air ovens are gentler, but can be as much as four times longer than IR dryers. By combining the two technologies we can design systems that take advantage the best features of both.
With the right design and for the right application, a combination IR-air dryer can save space on your manufacturing floor, improve energy efficiency and increase your line speed and throughput. Here are some of the ways that IR and hot air technologies can be combined in a process dryer design:
- Adding IR as a preheater: Installing a short bank of IR heaters in front of a longer hot air convection dryer can be used to heat the coating before it enters the hot air oven, reducing the time needed to dry the coating. This design is useful for drying thicker coatings where skinning is a concern, or for temperature-sensitive substrates.
- Blowing air through holes between IR elements. In this type of design, air is pushed through the holes in between the elements, which act like the jets of an impingement dryer. This makes the drying process gentler and helps to break down the boundary layer of the coating.
- Install IR heaters in between nozzles of an impingement or flotation hot air oven to increase the drying capacity. This design works well for applications where the air temperature for the dryer may be limited and additional heat will enhance the process or increase the line speed.