How to avoid problems when handling hot melt adhesives

author Jan Kaše, Head of Marketing at Kaletech s.r.o.
“Hot melt likes it hot – but not too hot.” This applies to the processing of hot melt adhesives as well as to their storage. Filling the adhesive melter properly is just as important as setting the heating zones correctly or lowering the operating temperature when the adhesive application system is not in use. In this blog post, I will show you five simple rules for handling hot melt adhesives correctly to avoid problems in adhesive application. You will see: the fewer problems you have when handling hot melt, the higher your machine availability will be.


Servicetechniker an Robatech-Schmelzgerät RobaPUR 20 MOD

Rule no. 1: Filling the melter properly

Filling the adhesive tank correctly is crucial – yet mistakes are often made here. Filling too much adhesive at once is particularly problematic. This is often done in an attempt to save time. However, melted adhesive should only remain in the tank for as long as necessary, otherwise it will burn. In addition, too much adhesive can overflow and burn on the outside of the tank or – even worse – flow into the interior of the melter and damage the electronics. If the overtemperature switch fails, the adhesive melter is shut down and the entire production line may come to a standstill. What was intended to save time then ends up in costly repairs and production downtime.

Hot melt adhesive has flowed into the interior of the adhesive melter and damaged the electronics. Total failure: Melted adhesive has flowed into the interior of the melter and damaged the electronics.

Another risk associated with overfilling is the drop in temperature in the tank: if too much adhesive is added at once, the adhesive melts unevenly, leading to application errors. On the other hand, the adhesive also burns on the inside wall of the tank because that is where the temperature is highest. And burnt adhesive – as we know – causes clogging in the long term.

However, the opposite – refilling too little adhesive at a time – is also problematic. If you constantly run the tank almost empty, you have to refill more often, which costs time and interrupts the production. In addition, too small an amount of adhesive burns faster, which in turn leads to clogging in the system.

The right balance is therefore crucial to ensure smooth and reliable adhesive application.

Adhesive melter with correct fillingAdhesive melter correctly filled: Neither too much nor too little adhesive

How to optimize:

  • Train operators to fill to the correct level – and keep a photo guide at the machine.
  • Clean the tank lid and the outside of the melter regularly by wiping it with a lint-free cloth or paper.
  • Use the right adhesive format (granules, pads, or blocks).
  • Install low-level warnings or use an automatic filling system for consistent supply.

Rule no. 2: Do not increase pressure or temperature settings at random 

When the adhesive flow decreases, it’s tempting to turn up the adhesive pressure or the temperature slightly to get more adhesive out. But this is never the right move. The adhesive pressure is usually not the cause of the problem. Nor is the temperature – if it is set to the optimum, it should not be changed at random. Most often, the issue lies with clogged filters or nozzles, or mechanical wear in the solenoid valve or jetting element. Increasing the temperature above the optimum value causes the adhesive to decompose and increases the risk of clogged nozzles and poor adhesion.

How to optimize:

  • Inspect and clean the filters and nozzles in the first place. For cleaning tips, read this blog post.
  • Use metallocene adhesives, which reduce buildup and extend maintenance intervals. Remember: metallocene may cost more per kilo, but its lower density and cleaner operation deliver more usable adhesive and lower total costs.
  • If the problem persists, contact a specialist. 

SpeedStar application head with extensively burnt-in adhesiveWithout maintenance, your application head will eventually look like this – and then maintenance will become expensive.

 

Rule no. 3: Set heating zone temperatures correctly

The optimum application temperature depends – of course – on the adhesive. Always refer to the adhesive manufacturer’s data sheet! As a rule, one can say that the higher the temperature, the lower the viscosity and elasticity of the hot melt adhesive. And the lower the elasticity of the adhesive, the less stringing occurs when the adhesive is applied.

In addition, I recommend heating the adhesive gradually. This protects the adhesive and reduces wear on the system because less charring will occur. For this reason, it is important to set the temperatures of the three heating zones individually. The following heating zone temperatures serve as a reference, but they can vary depending on the amount of adhesive consumption and application. 

  • Application head: according to the adhesive data sheet
  • Heated hose: 5 to 10 °C below the application head
  • Melter: 10 to 30 °C below the heated hose

Proceed step by step when adjusting the settings, as even differences of 1 to 2 °C can change the viscosity of the adhesive. And be sure to have the heating zone temperatures confirmed by an expert!

How to optimize:

  • Do not set the same temperature in all heating zones unless glue consumption is very high.
  • Double-check your settings regularly and make sure that they are only adjusted by authorized personnel.
  • When in doubt, reach out to your Robatech representative for support.

Alpha adhesive melter: heating zone temperature settingsCorrect temperature settings in the three heating zones on the adhesive melter contribute to high-quality adhesive application.

 

Rule no. 4: Reduce operating temperature when not needed 

Every minute that the adhesive is kept at full operating temperature in the system increases the risk of problems. If the melted adhesive is heated and left standing for a long time, it begins to decompose. Stringing and discoloration of the adhesive are the first signs of this. The adhesive becomes thicker, the adhesive pressure decreases, the adhesive begins to burn, and coking clogs the heated hoses and application heads.

The good news? Robatech systems are equipped with a temperature standby function, which reduces the temperature in the adhesive melter during an interruption without switching it completely off. Restarting after an interruption therefore does not last long. 


How to optimize:

  • Train your staff to use the temperature reduction function during downtimes.
  • Automate temperature control via PLC integration.
  • Use a start-up timer to preheat the system before a shift starts — so that everything is ready when production starts.

Read more in this blog post about how to avoid charring with the temperature reduction function.

Temperature reduction function on the Vision adhesive melterThe temperature reduction function does not only save energy but it also saves your system from charring.

 

Rule no. 5: Handle and store adhesive correctly

Contaminated adhesive is a major cause of downtime. Even tiny particles – which can come from picking up spilled granules from the floor, for example – can clog filters or even destroy gear pumps.

Storage matters too: open bags in dusty environments increase the risk of contamination, and excessive temperatures or humidity can impair the adhesive’s performance. Please refer to the information on the adhesive manufacturer's data sheet. There you will also find the expiration date, after which you should no longer use the adhesive.

If you want to change the adhesive, it is very important not to mix the two different adhesives. Even different batch numbers can sometimes cause problems.

How to optimize:

  • Store glue in closed, protective containers.
  • Follow the FIFO principle (first in, first out) and use the older adhesive first.
  • Never reuse spilled glue.
  • Consult with experts before switching adhesives – and test new adhesives externally first to avoid system damage.

Adhesive in original container Adhesive stored correctly: a clean affair all round

 

Conclusion: Less problems, more uptime 

As you can see, small changes in how you handle hot melt adhesive can make a big difference. Ensuring that the rules discussed here are followed will definitely increase the uptime of your machine. Regular cleaning and proper maintenance will further enhance the availability of your systems.

Hot melt adhesive runs down the outside of an adhesive melter and burns.This adhesive melter definitely needs cleaning.

Do you need support optimizing your hot melt system? Robatech experts are available worldwide to provide training, consulting, and expertise to find solutions tailored to your operation.

 
author

Jan Kaše, Head of Marketing at Kaletech s.r.o.

Jan Kaše is Head of Marketing at Kaletech s.r.o., the Czech partner and exclusive supplier of Robatech gluing technology in the Czech Republic. For this blog post, he collected experiences from the service people in the field with the intention of sharing their knowledge and supporting Robatech customers around the world.

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