When Lantech engineers set out to improve the shrink-wrap process, they went right to the source. Based on interviewing over 100 users of shrink-wrap machines, they identified six specific areas to improve. By addressing each of these with design improvements in their shrink-wrap machines, Lantech has increased the runtime between maintenance and simplified the set-up and changeover for new products.
According to Jean-Louis Limousin, Lantech's Design Leader, Shrink Packaging Systems, one of the first areas to be addressed was belt tracking. The lack of consistent belt tension on existing machines dictated frequent adjustments to prevent down time. By using a system to guide the belts consistently and removing excess tension for all of the twelve rollers in the machine, they assure that all the belts are self-tracking and eliminate the adjustments.
Getting a maintenance-free cutting seal was the next area targeted for improvement. The accepted approach had been to use the same tooling for cutting and sealing. This required replacing the Teflon attached to the typical seal bar after about 8 to 10 hrs. Lantech's new Ever-Clean approach involves separating the cutting from the sealing portion and using a cutting blade made of spring steel and a clamp with rounded edges. With the heat concentrated at the edge of the blade, when the tool blade comes down on the film, it cuts very quickly and the rounded blade holder edges quickly make the seal. Using this approach reduces the temperature about 100 to 120F compared to the normal sealing approach and avoids melting the film. This reduces time for the cut and seal and reduces wear as well. By eliminating this high wear item, the time between maintenance increases from a few hours to approximately 2 million cycles providing about three to six months of uninterrupted operation.
Automate and Simplify
In a typical shrink-wrap machine, a spool system accumulates the scrap film that is disposed periodically. As the spool increases from a small to a larger diameter, the tension change can easily be sufficient to break the scrap requiring stopping the machine. The historical solution has been frequent operator adjustments to change the tension by changing the speed of the winder. By taking advantage of in-house expertise in stretch films, Lantech engineers designed a completely automatic prewinder using a load cell to measure the tension and provide soft spooling that avoids film breakage.
Simplifying the human machine interface (HMI) was another step to improve the shrink-wrap operation. The design approach uses a color touch screen LCD control with a Windows-driven system. A single starting point with pop up screens allows operators to make changes easily. The system can store up to 16 set-ups in memory for quick change over. Once the values are changed, the display automatically returns to the same starting screen. Password protection at three different levels allows different control by operator, supervisor, or other plant personnel.
The Cutting Edge—Without Melting
Side sealing was another frequent maintenance headache for users, requiring attention every four to eight hrs. Complicating the downtime aspect of the problem was the amount of rework that could be required, since detecting the need for maintenance is strictly a visual observation after producing several poor seals. Once again, separating the cutting from the sealing portion of the process proved to be the solution.
Cutting and sealing at the same time requires very high temperatures, at which the film can melt. In its molten state, the film easily attaches to, and builds up on, the cutting surface components. Lantech's answer was a separate mechanical cutting system using a sharper wheel and a heated fusing wheel on the side. By squeezing the film, the mechanical cutting system can cut cold film. On the same axis, the closely spaced (within 0.015 inch) seal wheel fuses the seam, while operating at a much lower temperature, which eliminates film build-up on the sealing surface.
This approach avoids the timing issue and variation in film width that can happen when the two processes occur in series on different axes. In addition, the forces in this process are balanced and pressure from the seal wheel to rubber wheel minimizes pressure at the metal-to-metal portions. As a result, users can expect 2 to 4 million cycles at this part of the process (depending on the film) without requiring maintenance. Again, this number of cycles can provide 3 to 6 months of uninterrupted operation. The previous industry benchmark was completing one shift without cleaning and one week before changing components, such as a silicon ring. Since determining when maintenance is required is still a visual process involving the operator or quality control person, Lantech recommends changing parts at two million cycles.
A final item that Lantech engineers addressed was simplifying the setup for the various different size products the machine could encounter in a packaging facility. The scaling process typically used in the industry required running the machine as much as one hour to establish the proper settings for a new product. Synchronized Scaling, as Lantech calls it, uses a single number to establish the scale factor. This factor is determined for the first or H1 reading and the remaining geometric aspects are scaled/calculated based on relative positioning, essentially turning a process that was considered an art into a science. The new scaling process allows completing the set up in about 2 min.
Shrink-Wrap in Action
One company that has seen the benefits from the design changes implemented in Lantech's machinery is Lakeview Farms. Lakeview packages products that include refrigerated desserts, dips, and cheesecake under various brand names. According to Lakeview Farms' Plant Manager, Peter Fink, the installed SW-1000 machines handle over 500,000 multipacks each week with dramatically reduced downtime for routine cleaning.
Running 60-gauge, 18-inch film, Lakeview Farms currently puts about 10-15,000 cycles per day on each of its three Lantech shrink-wrap machines. Fink proudly proclaims, "We're producing more, with three fewer operators on the line, less material, and virtually no rewrap."