Are you using the right hot melt application nozzle for your bead or dot application?

Together with the pump pressure, the hot melt application nozzle defines the amount of adhesive applied to your product. Thus the nozzle influences operating costs and whether your product is glued safely and cleanly. This blog post reveals which rules of thumb apply for choosing the right application nozzle and which mistakes you should absolutely avoid when replacing the application nozzle.

Four jetting elements with hot melt application nozzles from Robatech for bead and dot application

The adhesive application nozzle is either an integral part of the jetting element or is screwed onto a jetting element. You can easily replace screw-in nozzles yourself, which brings us to the heart of the topic of this blog post.  

Important criteria for selecting the right bead nozzle 

Each product or format sets a different demand on the quality of the adhesive application. Gluing primary packaging for pralines, for example, requires only one tiny adhesive dot placed precisely and a cut-off without stringing. With transport packaging made of corrugated cardboard, the situation is quite different. There, millimeter-thick, long beads are required to ensure that the cardboard boxes remain securely closed despite high return forces. The quality of the cut-off plays a secondary role. 

Primary packaging is used, for example, for candy, chewing gum, chocolate bars, chocolates, pasta or even six-packs. The adhesive must be applied precisely and cleanly. Primary packaging requires an application nozzle with a precise adhesive cut-off.  

When applying adhesive, the application nozzle is responsible for the following parameters:

  • Amount of adhesive per bead or dot
  • Cleanliness of adhesive cut-off

There is a complex interaction between the diameter and geometry of the application nozzle and the channel length. However, the following rules of thumb offer welcome assistance: 

The smaller the nozzle diameter, the less adhesive applied and the more precise the adhesive cut-off.

The better the heat conduction through the geometry of the nozzle and the shorter the nozzle channel, the cleaner the adhesive cut-off. 

The channel length determines the distance at which the jetting head can be positioned to the substrate. 

 

The adhesive application nozzle influences the quality of the cut-off during hot melt application. The 296 Diamond screw-in nozzle boasts improved heat conduction properties compared to the 292 and 296.  

What role does the hot melt adhesive play in the choice of nozzle?

Hot melt adhesives differ in many respects. The viscosity and temperature sensitivity of the adhesive are of particular interest when choosing the application nozzle. The following applies here:  

The higher the viscosity and/or the faster the hot melt adhesive tends to coke, the larger the nozzle diameter should be.

Larger nozzles have the advantage that they are less prone to clogging. But they also automatically apply more adhesive, which proves a favorable setup for gluing corrugated cardboard, mattresses or wood. 

Robatech’s Duero application head applying hot melt beads for gluing felt pads.Application nozzles with a large diameter are used for gluing mattresses

However, for high-end applications such as gluing primary packaging, a small nozzle diameter needs to be selected. In this case high-quality hot melts, such as metallocene-based adhesives, should be used. These have a very clean, reliable cut-off behavior. As a result, small diameter nozzles remain clean for longer, which is not the case when using less thermostable adhesives.  

The Volta application head works with 296 application nozzles of different diameters.For the adhesive application of small beads or dots, high-quality hot-melt adhesives should be used to prevent nozzle clogging.

What happens if the wrong application nozzle is installed?

This usually results in quality problems, such as stringing, too much adhesive on the substrate or too little. Obviously, too little adhesive application leads to a lack of adhesion and thus to production rejects. On the other hand, excessive adhesive application jeopardizes the safety of the bonding, as an increasing amount of adhesive prolongs the bonding time. That is the time it takes for the adhesive to develop a sufficient level of adhesion between two substrates. The nozzle diameter, adhesive application quantity, opening time, and pressing time are no longer optimally aligned. All in all, it is a scenario that has an adverse impact on operating costs because both rejects and adhesive are cost drivers.

How to avoid errors when replacing the hot melt application nozzle

Clean spare parts storage can save you hassle. Here are the most important tips:

  • Keep enough spare nozzles in stock for each type of nozzle. 
  • Keep a note of which type of nozzle is mounted on which application head. Depending on the position on the production line, different nozzles can be mounted on identical application heads. For example, different nozzle diameters are used for the side or lid gluing of corrugated cardboard boxes.
  • Do you change formats on your production line? Then make a note of which nozzle type is used for which format. 
And one final tip: Collect clogged nozzles and clean them together in one step to replenish your spare parts inventory. Find out how to properly clean nozzles here

 

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