Narrow Web DeCurler®
The only proven system for controlling curl on narrow web presses significantly reduces scrap.
Features/Benefits
- Ideal for all form, label and printing grades
- Compact design with multizones for profiling
- Available in manual or automatic control configurations
- Increases runnability
- Easy to install and operate for accurate control of cross machine properties
- Typically pays for itself in less than one year
The Need for a Solution
Curl has long been one of the major problems facing narrow web printers due to the extensive drying involved in this process. This impacts the bottom line by increasing scrap and reducing runnability.
Applications for Printed Paper
Curl and its Cause
Curl can be defined as the tendency for a flat piece of paper to distort in a cylindrical fashion. Typically, this is caused by the uneven expansion and contraction of fibers within the web. During the drying process, the web shrinks on the printed side causing the web to curl. Once the curl memory state is set, a change in the exhibited curl of a web can usually be attributed to a change in its moisture content. This is due to the fibers growing with an increase in moisture, usually more in the cross-machine direction (CD) than the machine-direction (MD).
Solving the Problem
When you apply steam to a printed sheet, it condenses, imparting both heat and moisture to the web. This combination of heat and moisture softens and relaxes the fibers in addition to loosening the fiber bonds. Subsequent growing of the fibers and evaporation resets the curl memory state of the restrained sheet. This means the paper will now exhibit different curl properties. The objective of curl control is to reset the memory state of the paper so the paper lies flat through a range of relative humidity conditions.
The Narrow Web Decurler Solution
Technological developments in nozzle and actuator design have lead to the development of the NWD. The NWD is designed to selectively and precisely control the amount of steam across the width of the web, providing both cross-machine direction and machine-direction curl control. At the heart of the system is the Coanda nozzle which applies steam counter and parallel to the web in the gap created between the web and the NWD. The Coanda method of applying steam maximizes the uniformity and efficiency of heat transfer by increasing the time of steam engagement and minimizing the insulating layer of entrained air traveling with the web.
Specifications
The NWD is typically positioned after the last dryer on the narrow web. Steam flow is controlled in the cross-web direction through three zones: Front, Middle, and Back. Manually adjusted control valves regulate the steam flow. The NWD is available from 6" to 40" cross-machine direction widths. The unit is compact and easy to install. If an existing steam source is not available, a compact boiler can be provided, along with a pre-assembled steam conditioning package (i.e. pressure regulator, relief valves, etc.). Constructed in 304L stainless steel, the system is designed and manufactured to withstand the harsh environment of a web press.