Refining and Eliminating Wrinkles and Creases on Vertical Baggers
Varying thicknesses of film at the end seal can cause sealing problems, especially at the transition points of multiple film layers created by the fin or lap seal, gussets, wrinkles, creases, and at the corners. Applications of pressure and heat must be great enough to cause the sealant layer to flow into and seal off these voids. However, excess pressure can easily crush or split the end seal, while overheating distorts the seal and can cause poor hot tack, where the film springs back open, or “moons,” before the seal can set.
The operating window for creating quality seals can be elusive, resulting in packages that leak, are distorted, and have little appeal to consumers.
An important step in troubleshooting these issues is to eliminate unintended wrinkles and creases. This post, the second in a four-part series, will examine this process on vertical baggers; Part 1 covered these issues on horizontal flow wrappers.
Any impediment that disturbs the even flow of film can distort packages and create leakers; a combination of factors is often to blame. To find the causes of these problems and fix them we recommend a comprehensive analysis of design, condition, and adjustment, beginning with the film roll and following along sequentially as the film is unwound, formed, filled, and sealed.
Film Contact with the Forming Collar
The wing of the forming collar should completely and evenly support the film as the flat web is formed into a tube. Too much, too little, or uneven tension can cause wrinkles and creases.
When end seal issues such as leakers or splitting occur, an important initial step is to determine where, and how often, the trouble shows up. For problems that occur inconsistently—perhaps leakers on every other package, or splits only on the top or trailing end seals of the package—you need to determine if the bad seals show up randomly or according to a pattern. Do the problems occur on every package? On both ends of the package?
Start out by collecting a series of packages produced by the machine during production conditions. Number the packages sequentially and mark the machine flow direction. If you are working on a horizontal wrapper with multiple crimpers, label each pair (ex: A, B) and mark each seal according to the set of crimpers it came from. Now you can trace the problem seals back to the place they occur.
Following is a list of procedures that will help you troubleshoot intermittent seal problems. You can find additional details by clicking on the links or images in each section: Read more
Set-up procedures for knives and anvils can vary according to the make and model of the packaging machine, knife adjustment style, and other factors. There are, however, some general principles that make these adjustments more effective and efficient, reducing downtime and parts costs.
♦ Optimize Knife Design
Knives ground on a diagonal, or bias–whether they have a zig zag or a straight cutting edge–require less pressure to cut so they are easier to set up and typically last longer.
Zig zag knives with smaller (more) teeth are also easier to set up and provide longer life.
For heat seal applications, each packaging film structure has a Seal Initiation Temperature (SIT), at which the sealant layer is heated enough to flow into and seal off gaps in the end seal and provide a minimally acceptable seal, and a Maximum Temperature, beyond which the film distorts, fractures, or has inadequate hot tack (seal strength and integrity while the seal is still warm). The temperature range between the minimum and maximum is the film’s Operating Window.
For a number of reasons, regulating heat is not as straightforward as simply adjusting the temperature setting within the operating window for the film you are running.
♦ The sealing face of crimpers and sealing jaws is often hotter in the middle than at the ends, where heat dissipates more quickly. These inconsistencies are readily apparent in the thermal profile shown below:
The corporate engineering department at a large, international company commenced a project to reduce material costs for a variety of products that are individually packaged on horizontal flow wrappers. Greener Corporation was invited to participate in a series of meetings that defined the project’s initial goals:
To reduce the cut-off length for each package by reducing the overall seal width, thus allowing the product envelope to remain unchanged.
To achieve material savings without degrading seal integrity or productivity levels.
To achieve a project payback period of twelve months or less.
Greener’s latest “Tech Bites” video explains how proper clearance and pressure adjustments optimize horizontal flow wrapper performance.
Clearance and pressure settings on horizontal flow wrappers are critical for achieving quality packages, minimizing downtime, and controlling costs. We’ve noticed that the differences between clearance and pressure, and the proper occasions to adjust each of them, are not always clear to those making these adjustments. Greener’s latest “Tech Bites” video and blog post differentiate the function and adjustment of clearance and pressure. Read more
Even experienced users of forming sets can, over time, become conditioned to accept the hidden costs and preventable constraints of their packaging equipment. As with all waste, however, careful diagnosis of the root causes will lead to implementation of effective solutions.
One such root cause is forming tube misalignment. This can occur if the forming set has been accidentally mishandled and damaged or if the forming set has not been properly designed and fabricated in the first place.Read more