A website devoted to the  science of web handling

Web processing is unfamiliar to most people, even within the engineering Film unwind iStock 000014265814Small 300 Hprofession. But, it is used in the manufacture of a remarkable range of products. Examples are:
    • Baby diapers 
    • Paper
    • Cardboard
    • Films for LCD displays
    • Books, magazines and newspapers
    • Steel and aluminum strip
    • Carpet and plastic floor covering
    • Plastic bags and cartons (almost every container you see in a grocery store, has at one point in its manufacture, been in a web process).
    • Wall paper
    • Adhesive tape

 Anything that is flexible enough to pass over rollers as semi-continuous strips and then be wound into rolls can be considered for web processing. The attraction is always cost.

Products made with web processes  

Web handling is "the physical mechanics related to the transport of continuous flexible materials (webs) through processes and machinery." The web is almost always supported on rollers and the processes (often referred to as roll-to-roll processes) include things such as printing, coating, laminating, curing, embossing and slitting.

The field is divided into the following categories.
    • Mechanics of winding and unwinding
    • Longitudinal dynamics and tension control
    • Lateral dynamics and control; guiding and tracking
    • Out-of-plane dynamics
    • Wrinkling
    • Roller traction; air lubrication and microslip
    • Aerodynamic effects in transport
    • Measurement of tension, wound roll properties, and physical properties

My attention has been focused mostly on lateral dynamics and control, including wrinkling and roller traction.

This field has gained recognition as an engineering discipline largely through the efforts of the Web Handling Research Center at Oklahoma State University, (WHRC). Founded in 1986, the Center has created a growing body of knowledge that is used to quickly solve web process problems that once required expensive trial and error experimenting.

The key to understanding most web handling problems is knowing what the stresses in a web are doing to it. But, stress itself is very hard to see and in a thin moving web, it's very hard to measure. Like anything else that has invisible causes, it's easy to make up plausible, but completely wrong, theories (myths) about how stress produces problems. For example, before 1960 lots of web processors were completely confused about how misaligned rollers caused webs to shift laterally (and often wrinkle). One of the favorite myths was that "the web tracks to the tight side". In the middle of the twentieth century this and other mysteries began to get sorted out by small groups of researchers working in many different places.

Prior to the WHRC much of the best work in web handling stayed in desk drawers at the companies where the work was done. But, in the 1980s some enlightened engineers (friends of mine - Dr. John Shelton, and Bruce Feiertag) recognized the need to coax this knowledge out into the open, where it could be organized and extended to create a recognized branch of process technology. This was something whose time had come, because by 1986, working with Dr. Karl Reid at Oklahoma State University, they had found enough like-minded people at major corporations to meet the corporate sponsorship requirements for a federal program to create the Web Handling Research Center (WHRC) at OSU. Beginning in 1991, the Center began sponsoring bi-annual IWEB conferences where serious researchers meet, present papers and discuss their latest work. The university has also graduated a number of students who earned their PhDs with web handling research projects conducted in the center's well-equipped lab.

In addition to the difficulty caused by the invisibility of stress, the mechanics of web processes is much more complicated than one might expect. Webs will shift laterally at a misaligned roller and sometimes wrinkle. They may contract laterally when they encounter a roller that sags under the influence of tension and weight.  Air is entrained between webs and roller sufaces at even modest speeds and can cause loss of traction - even to the point of completely losing contact with rollers. Air is also entrained between the layers of winding rolls, causing a variety of problems both during and after the winding process. Slipping can mar web surfaces. 

Here is a list of the papers from the 1993 WHRC International Conference on Web Handling that gives some sense of the range and depth of problems.

Lateral Mechanics, Dynamics and Control
    • Air Support Conveyance of Uniform and Non-Uniform Webs
    • Strip Walk simulation for Continuous Processing Lines
    • Unwind and Rewind lateral Control
Longitudinal Mechanics, Dynamics and Control
    • Theory and Application of Draw Control for Elastic Webs wih Nipped Pull Rollers
    • Effects of PID Ganins for Controller with Dancer Mechanism on Web Tension
    • Control of Longitudinal Tension in Multi-span Web Transport Systems During Start-Up and Shut-Down
    • New Decentralized Control in Processing Machines with Continuous Moving Webs
    • On the Dynamics of Web Transfer in the Open Draw
    • Dynamic Behavior of Dancer Subsystems in Web Transport Systems
Web Line Developments
    • Advanced Winding Machine Development at Sandia National Labs
Nip Mechanics
    • A Study of 3-Dimensional Non-Linear Nip Mechanics
    • Instrumenting Rolling Nips for Video Recording and Strain Recording
Winding Mechanics and Air Entrainment
    • A Mathematical and Experimental Investigation of the Stack Compression of Rough Films
    • Comparing Wound Roll  Sresses Due to Web Surface Characteristics
    • Changes in Web Tension Profiles and Paper Properties during Repeated Rewinding
    • The Effect of Air Entrainment in Centerwound Rolls
    • Irreversible Reduction of Foil Tension Due to Aerodynamic Effects
    • Air Films Between a Moving Tensioned Web and a Stationary Support Cylinder
Wrinkling
    • Buckling of Webs from Lateral Compressive Forces 
    • Web Tension and Wrinkles in the Printing Press
    • Simulation of Wrinkling Patterns in Webs Due to Nonuniform Transport Conditions
Spreading
    • The Mechanics of Web Spreading 
    • Analysis of Web Spreading Induced by the Concave Roller
    • Analysis of Web Spreading induced by the Curved Axis Roller
Tension Measurement
    • Measurement of Web Tension Distribution by Point Source Pulse Excitation
    • Web Tension Profiles as Measured in a Rewinder and in a Printing Press

The WHRC has been an outstanding success. In its ten volumes of conference proceedings you will find most of what we presently know about how to "see the invisible" correctly. In fact, long-term participation in the WHRC's work (plus deep familiarity with the contents of those ten volumes of proceedings) has become the de facto credential for web handling expertise - a qualification possessed by all of the leading web handling consultants.

The success of the WHRC is demonstrated by the fact that, the Association of Metallizers, Coaters and Laminators (AIMCAL) is now offering application-oriented conferences and training programs based on its work. Several of the leading web handling consultants are now actively involved in its programs.