Convection

CONVECTION
Convection Oven systems utilize heated air to process a variety of products for drying and curing. Convection heating offers consistent, even heating throughout the oven. Convection heating can be direct or indirect with virtually any fuel from natural gas to coal. Typical convection applications include heating, drying and curing of water and solvent coatings for textiles, films, paper, fibers, and metals. Advantages Provides heat transfer and mass transfer Accurate control of temperature Uniform heating regardless of product size, color or shape Does not require contact to heat (webs can be floated with no contact) Challenges Lower rate of heat transfer Increased exposure time Slower start-up/cool down Possibility of disturbing or contaminating the product from air movement Relies on thermal conductivity of the product to heat interior of thick products Types of Convection Ovens/Dryers • Perfect Float® flotation dryers dry both sides of a web at high speeds without leaving marks or scratches. The web is supported by air bars which provide the flotation as well as a high heat transfer coefficient. Advantages of the Perfect Float® flotation dryer include high drying speeds, ability to dry on both sides, sine-wave flotation, web stability, proper exhaust removal and efficient energy use. The Perfect Float® offers several retraction options including internal, split-hood and clamshell for ease of thread up and maintenance. These dryers are used with solvent or water-based systems for paper, film or foil. Typical applications include tapes and labels, flexible packaging, magnetic media, photographic films, non-wovens and printed products. For a complete description of the process, check out Curing Coated Webs with Flotation Dryers. • Litzler OPTI-FLOW convection ovens deliver the maximum heat transfer of any hot air oven. Accurate impingement air is directed at the product through proprietary nozzle and supply systems. Spent air is recirculated between the supply nozzles to increase heat transfer and web stability. This proprietary OPTI-FLOW technique produces even side-to-side airflows which is required for consistent cross-web drying and curing. • Flow-through ovens heat webs throughout, rather than just heating the surface. They operate by pulling heated air through the web, and are particularly effective heating thick permeable webs. While flow-through ovens are generally arranged with the heated air flowing either up or down through the product, they can also be configured with the air flowing, alternately, up and down through the web. Even though this arrangement is more complex, it provides the highest and most uniform heating. • Tunnel dryers utilize air flow that is parallel to the product flow. It is common for strands and cords. Tunnel dryers provide excellent uniformity. ARTICLES
Curing Coated Webs with Flotation Dryers Improve your finished product by curing coated webs with flotation dryers, which can efficiently dry both sides simultaneously - even if the web material is sensitive to wrinkles or scratches.