Choosing the Right Process Heating Technology for Your Application
Even if you’re not an expert on process heating equipment, you probably know one thing: all heating technologies are not created equal. To get the ideal heating results at the right cost, it’s important to choose the heating technology that’s best suited for your product and your process.
It sounds simple, but there are many factors to consider and it can be tricky to determine whether you should choose an infrared (IR) dryer or a hot air convection dryer. To complicate things further, you can also choose a dryer that uses both technologies.
Here’s our process heating technology primer to help you focus your search on the most promising types of dryers for your needs.
1. Infrared Dryers
Infrared (IR) heat is commonly used for drying thinner coatings, such as pressure-sensitive adhesives on masking films for appliances and electronics. Since IR provides an intense burst of energy and high heat, it’s perfect for these coatings which can be as thin as .5 mil. IR provides an energy-efficient method for quickly drying these thin coatings where you don’t have a concern about skinning.
IR is usually the best choice where a very high temperature is needed. IR Thermal Systems is currently working with a customer that needs to anneal a Polyimide film to 400°C with oven temperatures that need to reach as high as 800°C. 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.
If you’re working with a powder-based coating application, such as laminating foam to fabric for automotive materials, IR is the best choice because of the absence of moving air. The blowing air in a hot air dryer would blow much of the powder off the product. IR heaters for such applications do not use blowers, so it’s ideal for these types of coatings.
2. Hot Air Convection Dryers
Hot air convection is a traditional heating technology that has been used in manufacturing processes for decades. The convection process in a hot air oven applies heat to the product at the same rate that the heat travels through the thickness of the material. That allows the moisture (water or solvent) to escape from the underlying layers, producing an evenly-heated and consistent product.
These ovens provide a gentler source of heat that is ideal for heavier coatings as much as 10 mils thick. These are often functional coatings such as adhesives used on Velcro or plastic wall hooks. If IR was used on such a thick coating, the intense heat would dry the top 1 or 2 mils too quickly, causing the top of the coating to skin over, trapping the moisture underneath and causing the bottom to remain wet.
Since solvents can be explosive when exposed to high temperatures, hot air convection with its more moderate heat is also the best choice when you’re dealing with solvent-based coatings.
3. IR Air Combination Dryer
With the right design and for the right application, sometimes a dryer that combines both IR and hot air technologies can be the best of both worlds. A IR air combination dryer can save space, improve energy efficiency and increase your line speed.
This is done by installing a short bank of IR heat in front of a longer hot air convection dryer. The IR bank warms up the material before it enters the hot air oven, decreasing the time needed to dry the coating. For example, let’s say a coating on plastic film won’t start to skin over until it gets to 170° to 180°F. The oven would be designed so that the IR bank heats the coating from room temperature to 130°F. The product would then enter the hot air section at a higher temperature, so it will take less time to complete the evaporation process.
If you’re looking to increase line speed by retrofitting an existing hot air oven, this can be accomplished by adding IR heaters. In many cases you can increase your line speed by as much as 50 percent by adding 3 to 5 feet of IR heaters in front of a hot air dryer.
Like IR dryers, combination IR-air is not suitable for solvent-based coatings due to the high temperatures.
4. Get expert advice before you choose
This guide is intended to give you an overview of the issues you need to consider when choosing the right heating technology for your application. At this stage of the game, it’s in your best interest to seek out the advice of industry experts who are knowledgeable in all process heating technologies. Even better, conduct your own testing in a vendor’s pilot lab that provides a wide range of equipment and heating technologies. Vendors that provide this service typically have experience with many different products and industries, and can provide guidance from lessons learned on past projects that you may not have considered on your own.
Here’s a good example. You may be considering an IR air combination dryer, but not sure if the added expense of using two technologies will pay off for your needs. An expert can help you do a cost/benefit analysis to determine if the space and energy savings will be worth the extra cost.