Knowledge Base

4.0 Root Cause of Gluing Problems

Most corrugated box plants are aware of their gluing problems by looking at their Profit and Loss statements; lost customers, returned orders, and downtime charges. While it is no secret that these problems are a common occurrence, very few box makers actually know what causes these problems and how they originate. Was it a problem with the gluing system, was it because of excess warp, or was it bad board from the corrugator? Box makers want to find the root causes of these problems and address them so they can promise their customers that the problems will not recur in the future. Armed with a lack of data, most box makers have trouble finding the fundamental causes of their gluing issues, and as a result, problems happen over and over again leading to unhappy customers and even lost business.

Over the past 4 years, ClearVision has been collecting information on gluing problems, and has analyzed the glue on over 2 billion boxes, saving a picture of every single defect. Below are samples from the data set of gluing defects box makers frequently experience.

Short Sheets, Warp, and Damaged Boxes
Short sheets coming off the corrugator pose a problem because the glue tab is not wide enough to handle the glue applicator. The result is that the glue is placed too close to the edge, squeezing out once the box is closed, and resulting in a box that is stuck shut. Furthermore, the amount of adhesive placed on the glue tab and the adhesion area has been greatly reduced, resulting in a weaker glue tab that may fail under use. Warp can present challenges for gluing systems. For one, the length of the box is effectively changed, affecting the timing and registration of the glue application point. Secondly, warp can cause inconsistent contact pressure between the board and the glue head, resulting in dabs of glue being left on the panels, as well as smeared or inconsistent glue beads.

Skewed Boxes
Boxes that are not square to the machine or that begin to skew as they pass through the gluing system can cause gluing problems such as squeeze-out or even a failed glue tab. Because the box is skewed, the distance between the glue bead and the glue tab edge changes over the length of the tab. The result is typically a gluing problem, and potentially a folding problem to follow. As with many other quality issues, skewing problems arise quite sporadically, but have a tendency to be highest with boxes that are short and wide.

Scrap on Glue Tab
As scrap pieces are being cut from the box to create the glue tab and other cuts, a few scrap pieces often randomly migrate onto the glue tab on the box. These scrap pieces can cause two fundamental issues. One problem is that they trigger the gluing system’s optical eyes, resulting in typically a major problem with the registration of glue on the box. In extreme cases, this scrap can block the optical eye resulting in there being no glue on the boxes produced. The second type of issue is that scrap can land on the glue tab, and the gluer glues right overtop of the scrap. At this point either the scrap piece will fall off of the tab resulting in a weakened glue tab with missing glue, or the scrap may end up glued in the glue tab once the box is folded resulting in other problems for the customer.

Gluer Problems
Gluer malfunctions represent about 25% of the gluing problems that customers complain about. For extrusion systems, problems include pressure issues in the airlines, nozzle blockages, dirty glue heads, contact pressures, inconsistent registration, and inconsistent volume. For glue wheels the problems include inconsistent contact pressure, dirty glue shoes and other parts that need maintenance and upkeep. Most of these problems arise without warning, and may only affect a few boxes in an entire order. Unfortunately, it may be those few bad boxes that cause the order to be returned.

Through detailed analysis of these defects with the collaboration of box plants, over 10 different types of gluing problems have been identified as frequent issues on specialty folder gluers and flexo folder gluers. These problems can be traced back to the above 4 fundamental root causes:

1. Scrap Problem
2. Defective Substrate (short sheets, delam, warp, damaged boxes, etc.)
3. Substrate Skewing/Lateral Shifting in Machine
4. Gluer Problems (missing glue lines, pressure problems, drips, etc.)

Solutions
If a perfectly consistent substrate were available and flexo folder gluers along with gluing equipment would work flawlessly, then there would be very few gluing problems. Unfortunately, we do not live in such an ideal world. With so many variables contributing to gluing problems, pinpointing specific root causes and making equipment modifications is challenging and time consuming.

Working with corrugated box plants in the US, these problems are now understood to be quite complex, completely random and such that they cannot be fixed by modifying or simply upgrading gluing equipment. The majority of these problems have nothing to do with the gluing system itself, but rather are actually caused by environmental variables, inconsistencies and malfunctions in the substrate, the converting equipment, or the converting process.

Using an automated inspection system to monitor every box is one way to catch all types of gluing problem with one simple solution. This solution effectively finds every defect regardless of the cause, or the complexity of the issue. Box plants implementing these solutions understand that “Perfect” manufacturing is not a realistic possibility, especially not in the corrugated box industry. The next best thing is to flag and remove all defects to ensure only perfect boxes that are fit-for-use make it to the customer’s door.