Web and Converting Terms
The picture above is from a project I worked on back in 2007. I haven’t worked on a web project since then, but I thought I’d share a section of my book that discusses some of the terms used in web processing. From Chapter 5:
A Web is a continuous piece of material. Paper, fabric and some extruded materials are examples of a web. Webs are usually moved through processes using rollers, which may also serve to apply tension, heating or cooling to the material. Webs may be processed directly from the manufacturing of the material or from rolls or coils. Common materials processed in web form include Nonwovens, films, textiles, foams and paper.
Because webs are moved continuously, they can be processed at higher speeds than individual sheets of material. Common uses of web processing include bonding layers of material together, cutting material into sheets or slitting it into smaller rolls, cutting or punching pieces out of it or passing the material through other heating, cooling or chemical processes.
Web handling machinery is usually composed of individual drives arranged in a linear fashion with sections performing different operations on the web sequentially. Web guiding and tensioning are important facets of controlling webs and a variety of products are manufactured to help in these areas. Web guides and steering mechanisms sense the position of the edges of the web and adjust rollers in real time to correct for misalignment. These are often placed immediately before critical sections of a line such as printing. Tension may be monitored by load cells and strain gauges, or torque feedback may be sensed by roller drives. Gaps between rollers must often be controlled and adjusted carefully for tensioning or product thickness. Pull units are drive and roller sections that have methods for these adjustments built in. They may consist of full width or “nip” rollers at the web edges.
Accumulators are used to isolate sections of web from the tension effects of other sections. They also store material while rolls are being changed. Accumulators are sometimes built with multiple festoons or may take the form of a simple take-up mechanism. Unwinders and Winders pay out rolls of material and wind them up at the ends of the process. Splicers are placed between the unwinding station and an accumulator to allow web to feed out continuously. These stations may be fully automated or operator assisted.
Slitters are used to cut webs lengthwise on a continuous basis. They may have stationary blades or rolling knives and are usually adjustable for different widths.
Some operations such as heating, cooling and slitting are continuous processes, while other operations, such as ultrasonic welding, punching or cutting across the web, may be done by starting and stopping or slowing the web between accumulators.
Converting is the process of turning raw materials, often in rolled or sheet form, into new products. Common materials used in the converting process are woven and non-wovens, paper, adhesives, rubber, foam and plastics.
Continuous rolls of material are threaded into processing machinery which then performs intermediate or final operations to produce product. An example of converting is taking a web of two layers of plastic, fusing the edges together and sealing the ends and cutting it to produce plastic bags. Common operations in the converting process include coating, application of adhesives, ultrasonic welding or other types of material bonding, sealing and patterning. Converting methods are also often used in the assembly process.