Knowledge Base
5.0 Glue Wheels VS Extrusion Systems: The Age Old Debate
The age old debate continues between which gluing system is better: glue extrusion or glue wheels. While some swear by the reliability and consistency of the glue wheel, others believe that the newer extrusion technology is superior. Both have their advantages and disadvantages, and in this article we will look at the merits of both gluing technologies. The data used in this article was taken from the analysis of over 3.0 Billion boxes in the past year by taking a digital photograph of every box. Various companies, shifts, operators and machinery all contributed to the data in order to average out anomalies in the statistics and isolate the raw performance of the gluing equipment. In this article, we’ll focus on how the two gluing systems differ from a quality and performance standpoint, but will also briefly touch on the differences from a maintenance, practicality and operational perspective.
Intro to Glue Wheel and Glue Extrusion: Below are images of the glue pattern applied by a glue wheel and a glue extrusion system. The glue extrusion system forces pressurized adhesive through a nozzle that typically contains 3 or 4 orifices. The beads of glue are quite thick, and are in the direction of motion of the corrugated board as in Figure 1.
Glue wheels in contrast act like a water wheel or paint roller that lays down a thin film of glue. They are typically gravity fed and leave behind hundreds of glue beads that are perpendicular to the board’s direction of motion as seen below in Figure 2.
Figure 1. Image of Glue Pattern from Glue Extrusion System
Figure 2. Image of Glue Pattern from Glue Wheel
Quality & Consistency: A gluing system has a relatively simple job in the production of corrugated boxes: Put the glue in the right spot and do it as consistently as possible. While this task sounds simple, there are a large number of variables involved which make 100% repeatability with any gluing system virtually impossible.
Over the past 5 years, our analysis has consistently found that glue wheels produce fewer overall defects than their glue extruding cousins. On average, we have found there are 2.5x more gluing defects produced with glue extrusion systems. Below is a graph showing the average difference in defect rates sampled from dozens of different machines.
Figure 3. Average Gluing Defect Rate from Glue Wheels VS Glue Extruders
The reason that glue extrusion systems produce more defects is that they are more finicky and easily affected by external variables. Analyzing pictures of the various defects has helped us understand why this is the case. For example, scrap can easily block the optical eyes on glue extrusion systems resulting in no glue on the panel as in Figure 4 below. Scrap can further trigger the optical eye too early, resulting in miss-registration of the gluing pattern on the tab or panel as in Figures 5 and 6 below.
Figure 4. No Glue Caused By Scrap Blocking Optical Eye
Figure 5. Miss-timed Glue Caused By Scrap Triggering Optical Eye Early
Figure 6. Miss-timed Glue Caused By Scrap Triggering Optical Eye Early
Glue wheels on the other hand are not so easily influenced by external factors. Because they do not “start” or “stop”, scrap problems are less severe and typically only produce a void of glue on the glue tab as in Figure 7 below. Furthermore, defects produced by scrap are typically reduced to a single problem, in contrast to extrusion systems where blocking the optical eye may produce dozens or hundreds of defects if undetected immediately.
Figure 7. Scrap Producing Void on Glue Wheel
“Squeeze-out” is another common issue where glue wheels produce fewer defects than glue extrusion systems. Because glue extrusion systems lay a thicker bead of glue, rather than a thin film, the exact placement of those beads becomes very critical. Place the glue too close to an edge and the squeeze-out will result in the box being stuck shut after the counter ejector. Figure 8 shows a short sheet or miss-feed where glue squeeze-out could result in the box not opening correctly. This same scenario is shown for a glue wheel in Figure 9, where the glue is dangerously close to the board edge. Because the glue pattern left by the glue wheel is a thin film, exact glue placement is no longer critical and squeeze-out problems are virtually eliminated.
Figure 8. Glue Extrusion and Short Sheet Result in Squeeze-out Scenario
Figure 9. Glue Wheels and Short Sheets Typically Do Not Produce Squeeze-Out
Dirt, dust, dried glue and debris cause problems for both types of gluing systems. However, similar to the squeeze-out problems discussed above, glue wheels are more robust in handling these external factors as well. With glue extrusion systems, dirty glue heads can leave unwanted glue on parts of the panel where they would cause a severe gluing problem as in Figure 10, 11 and 12 below. Furthermore, changing glue pressures, drastic speed changes, air in the glue lines or leaky valves can result in huge variations in the volume of applied adhesive as in Figure 13 below. Again, glue wheels do not suffer from these types of malfunctions.
Figure 10. Glue Extrusion Problems Caused By Dirty Glue Head
Figure 11. Glue Extrusion Problems Causde By Dirty Glue Head
Figure 12. Glue Extrusion Problems Caused By Dirty Glue Head
Figure 13. Glue Extrusion Problem Created During Drastic Speed Changes
Versatility: The glue wheel is not usable in all applications. On most specialty or complex gluing applications, the glue wheel is the wrong tool for the job. However, glue wheels work well on most flexo folder gluer applications where a single glue lap is required. Glue extrusion systems are more versatile and can be used in virtually all applications.
Maintenance: The major downside of glue wheels is the maintenance they require. Because they are larger and use several moving parts, physical part failure is more dramatic and more common than with glue extrusion systems.
Furthermore, glue wheels typically create more of a mess as the centrifugal force caused by the spinning wheel “slings” glue on the floor and machine. This increases operator clean-up time. However, proper glue formulation should be able to reduce or eliminate the effects of “slinging”.
Setup: Glue wheels do not need to be setup for each order as there are no start/stop measurements to dial in. As a result, setup times can be reduced using glue wheels.
While the glue wheel is an older system, its basic design offers greater gluing consistency and reliability. From a quality and performance standpoint, glue wheels seem to outperform glue extrusion systems by producing 2.5x fewer gluing defects on average. A change from glue extrusion to glue wheels could decrease your gluing problems by 60% at their root source. Companies running flexo folder gluers may wish to reconsider the glue wheel as a viable and more reliable way to glue their RSCs. Especially if perfect boxes are important for their customers.