Digital Magazine

A Communication from the PLACE Div. of TAPPI

Providing practical information to the converting and packaging industries

The Role Of An Uneven Temperature Distribution At The Flat Die Inlet On The Die Performance
by Petra Skabrahova, Jiri Svabik, and Jiri Vlcek, Compuplast International

Application: A three dimensional analysis can examine the performance of die designs.

Flat dies have use for the extrusion of a wide range of flat products. In general, the main requirement for the die design is production of products with a good mass distribution. Common knowledge allows good die design, but its performance may be unsatisfactory due to uneven material properties at the die inlet. A three-dimensional study can examine such behavior.

This study used a 3D FEM analysis to investigate the effect of an uneven temperature distribution at the die inlet on final distribution. Modeling of temperature inhomogenity occurred in two ways. The first used a temperature profile created by the heat dissipation. The other used an L-shaped spindle (valve) to generate temperature irregularity. The spindle orientation was horizontal or vertical to the die axis. In all cases, the work studied the influence of temperature inhomogenity on final distribution at the die outlet.

The results from calculations in the study show that orientation of the spindle to the die axis has an impact on die performance. Setting the spindle orientation horizontally relative to the die results in a larger exit temperature variation, but the velocity distributions remain within acceptable limits. In the case where the spindle had vertical orientation, the backpressure (obstacle offset) significantly influenced the variation of the investigated characteristics.


Trends In Packaging—A Challenge For Adhesives Development
by Hermann Onusseit, Henkel, KgaA

Packaging protects goods and is essential for safe distribution and warehousing. Since packaging now must usually provide additional functions, packaging design today can be much more sophisticated than it was only a few years ago.

Additional packaging developments will arise in the future. Influences include the increasing automation of production processes with concomitant increase of production speed, the desire for more security including especially the protection of children and older people, and certainly the desire for more convenience. Another important factor that has substantially changed the look of packaging in recent years is the trend toward self-service. Today, the items must sell themselves through their packaging.

All these trends have led to a clear change of packaging in recent years, especially in the direction of high-quality and technically demanding structures. In response to changing food consumption habits, producers have tried to develop new packaging materials and improve processes to gain competitive advantage. For example, developing packaging for use in frozen foods is complex due to the wide range of temperatures that the package encounters throughout the supply chain from freezer temperatures as low as –40°C to ambient room temperature of approximately 23°C.

In light of rising demand for convenience food packaging, an added requirement exists for frozen meals and similar food items that undergo reheating or cooking in their packaging. In such circumstances, the packaging must withstand temperatures as high as 250°C. Besides temperature stability, the barrier properties of the packaging components require consideration. The optimum package design should prevent loss of moisture and nutrients from the foodstuff and prevent oxygen entry into the package.To make such packaging, all raw materials and additives that are necessary for the production of packaging are also subject to steady changes in additional development. Since this includes adhesives that are indispensable to the production of most packaging, recent decades have seen intensive development in packaging adhesives. As a result, tailor-made packaging adhesives exist for all kinds of applications.

A steady increase in world population and the increase of industrial production will cause additional growth of the packaging market. New packaging concepts and materials have led to increasingly sophisticated packaging in recent years. In the future, packaging will be even more complex.

Next to new materials, the main impulse for future developments will come from increase in production speed and ecological pressures. Avoiding waste by reuse and recycling will also lead to new systems. Future adhesives will continue to contribute to fulfilling the tasks of packaging in transit, during storage, and on the shelves of shops. Further improvements in cooperation in the paper chain between paper manufacturers, paper converters, adhesive manufacturers, and paper recyclers will contribute to trouble-free recycling of packaging made of paper and board in the future.

Razor, Crush, And Shear Slitting Principles: Advantages And Disadvantages For Film And Foil Applications
by Dave Rumson, Dienes Corporation

Like other web materials requiring a slitting operation, films, foil, laminates, and metalized webs have always needed specific techniques and equipment to insure a high level of finished quality and value. When slitting film or foil, razor, crush cutting, and shear slitting offer certain advantages and disadvantages. The factors of operational choice involve the material itself, the parameters of operation, the varying costs, and pertinent safety factors. The paper considers razor slitting for a material thickness of 25 microns or less, crush cutting for material thickness above 25 microns, and shear slitting for material thickness above 25 microns.

Razors have traditionally offered cleaner cuts and lower operating costs than other slitting technologies. The trade-off has been that razors are not practical for heavier materials and tend to loose their sharp edge quickly. In addition, more operator injuries also happen. The two common web path methods employed with razor slitting are a wrapped, supported web over a grooved anvil roller and an unsupported web with the blade bursting through the material.

Choice of blade material and employment methodology can extend the razor sharpness life. Standard quality razors are made from tungsten carbide and can have a ceramic coating. They can also be solid ceramic. Generally speaking, ceramic-coated blades can extend blade life by a factor of four. Solid ceramic blades have increased operational times by 50 to 100 times more than standard steel blades.

Regrinding of solid ceramic blades can provide additional life. Increased blade life is possible by installing a means to oscillate the blade during the cut. This exposes a greater length of cutting edge to the material. Small gear motors with eccentric rotation thrust and retract the blades in the web path. A blade remaining stationary to the oncoming web will dull quickly.

Another method involves having adjustable razor blade holders that provide simple manual adjustments to advance the blade edge when dulling begins. The goal of either method is to increase the time between blade replacements.

The choice of razor or shear slitting for film and foil materials should consider numerous factors. Material thickness and web speed may dictate the initial slitting choice. Although considerably more dangerous to handle, razor slitting offers economic advantages. Shear slitting of heavier gauge films allows higher speeds and longer knife life with much more sophistication in knife set-up control required.

Web Spreading
by Jeff Dammour, Converter Accessory Corp.

This presentation is a basic tutorial covering the necessity for spreader rolls and their application and operating principals. Although many types of spreader rolls are possible, the discussion covers five basic types to include crowned and concave idler rolls, grooved rolls that are either rigid or flexible, nip type, curved axis rolls and bars, and expanding surface rolls.

By definition spreader rolls are web transport rolls that are driven or idle that cause cross machine direction web movement while the web travels in the machine direction. Cross machine movement has three purposes. It will remove wrinkles, it can separate slit widths to prevent interleaving, and it can stretch web width a predetermined amount. The tutorial covers each type of spreader roll and their use in applications.

To understand why webs wrinkle and why spreader rolls work, one must understand the most important web handling principal concerning wrinkling: A web will seek to align itself perpendicular to a roll in its entry span to that roll. The web must be in traction with the roll for this web handling principal to apply and influence the web behavior. In other words, if the material slips over the roll face it can wander or remain in its current alignment with a roll not perpendicular to it.

The reason webs wrinkle is due to lateral compressive forces. This presentation will explain why lateral compressive forces occur and how to avoid them. It will cover spreader rolls that will remove wrinkles when these lateral compressive forces are unavoidable.

In a perfect world, webs would be flat without gauge band variations. Roll stock would always be wound with perfect tension from the core through the full roll diameter. Processes would always run at the perfect tension for each material and operation. All converting processes would run in a humidity-controlled environment where temperatures never varied. All rollers would be parallel from unwind to rewind and balanced perfectly. Machine vibration would not occur. Long, unsupported web lengths would be absent. Unfortunately we do not live and work in a perfect world. One or some combination of all the unavoidable circumstances listed here will cause wrinkles.

The future will find converting processes running thinner webs faster and wider. This will require more answers to solve wrinkling problems. Converters will want spreader rolls to remove wrinkles at high speeds with no web distortion.

For information about the PLACE Division of TAPPI, access the TAPPI web page at tappi.org. To obtain the complete papers whose expanded summaries appear in this section, go to the TAPPI web site at tappi.org., then click on "the PLACE" in the section designated Journals.

Telephone inquiries are welcome at the TAPPI Service Line by calling 800/332-8686 in the United States, 800/446-9431 in Canada, or +1-770-446-1400 in other countries. Send FAX to 1-770-446-6947. Address mail to TAPPI, Box 105113, Atlanta, GA, 30348-5113.

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