Process Heating: Smart Controls Prevent Overheating with IR Dryers
IR Troubleshooting: Frequent line stoppages can cause overheating
If you have a process that requires drying or heating a continuous web but also requires frequent line stoppages, you may have thought using an infrared dryer was not an option for you.
Due to the intense heat from the IR heater bank, stopping the line can cause the web to be exposed to excessive heat and result in product damage. You also might have the opposite problem: when the line stops you can’t be sure if the product got up to the desired temperature.
However, this issue can be overcome with the right dryer design and smarter controls, allowing you to take advantage of the space-saving and efficiency benefits of an IR dryer.
Problem: re-glossing and breaking down rolls of cast vinyl
Cast vinyl is used extensively in graphic arts signage and auto wrap for its longer outdoor life and ability to bend around corners.
When breaking down a large roll of cast vinyl into smaller rolls, the process requires frequent line stoppages in the manufacturing process. The concern about line stoppages and product damage became an important decision maker for a company heating vinyl webs.
The company produced large rolls of vinyl material that needed to be broken down into smaller rolls prior to being shipped to their customers. At the same time, the vinyl material was heated to restore the gloss which can diminish when the material is stored in large rolls for a period of time. The breakdown and re-glossing process for this material required line stoppages each time a new roll needed to be started.
The company had been using large hot air ovens for this process, but when the time came to replace them, they were interested in exploring the possibility of using IR ovens instead. The old hot air ovens were forgiving in terms of not overheating the product, but they were long and bulky and slow to heat up and cool down.
The advantages of using IR included a smaller footprint as well as much faster heat up and cool down, which could speed up the process. Fast heat up and cool down also has the benefit of rapid response. As the line speed changes during the process, the heater can quickly adjust to keep the web at the desired temperature.
However, there were concerns about the higher IR temperatures and residual heat causing overheating of the product in the oven during the line stoppages. Under-glossing could also occur if the web did not get up to the desired temperature due to the line stop. If the oven was 5 feet long, damaging 5 feet of product every time the line stopped would result in a great deal of waste.
The company approached Radiant Energy with the challenge of designing an IR dryer that would prevent overheating or under-glossing and the resulting wasted product.
Smart controls prevent overheating and product damage
The design process required extensive testing to prove that an IR oven with fast heat up and cool down would work for the application. Radiant’s solution to this complex problem involved sophisticated controls that would prevent damage and wasted product.
To prevent damage to the material during line stoppages, two separate control modes were set up: one to control the temperature of the IR heater banks during running conditions, and a second to control the heaters when the web is stopped.
This design required installing two separate pyrometers in the IR dryer. The first pyrometer controls the web temperature when the line is running. When the line stops, a second pyrometer takes over, measuring the temperature of the web under the heater bank through a hole in one of the heaters, and maintaining the web at the desired temperature. Once the line starts moving again, the first pyrometer resumes control and maintains the web temperature while the web is running.
An extensive amount of testing was needed to perfect the design of the controls and the process, but in the end the smart controls allowed the customer to produce a quality product with a more efficient oven.
Upgrading to infrared heaters with smart controls has not only helped the customer to improve their process by reducing start up time and increasing production capacity, but has even reduced energy usage.
If you’re considering upgrading to an infrared dryer for your process, be sure the process heating equipment vendor you choose is willing to invest the time in testing to prove the design will work for you. Not only will you be sure about what you’re getting before you sign the purchase order, but you can be more confident that the company will stand behind their product for the long term.