In the manufacturing industry, the original equipment effectiveness (OEE) has a significant impact on the success of a product. Downtime of vital equipment reduces the OEE, impacting productivity and leading to delays or losses. One major cause of downtime when using Hot Melt Systems (HMS) is the formation and accumulation of degraded adhesives.
What Is Adhesive Degradation?
Adhesive Degradation occurs when the hot melt adhesive is kept at high temperatures for long periods, especially when the equipment line is not running. When exposed to high temperatures for an extended period, the chemical bonds in the adhesive decay, leading to a loss of thermoplasticity: the property that makes it harden when cold and become fluid when heated. As a result, the adhesive forms into a gel which build up at the bottom of the hot melt tank and hardens in a process known as charring.
Negative Effects Of Charring – Why Degraded Adhesives Are Such A Pain
Adhesive degradation is especially a problem in hot melt tanks used for packaging, where the adhesive sits stagnant and “cooks” over time. The char that forms as a result has various negative effects on the productivity of your business:
- Reduced Efficiency: When the adhesive degrades, the increased viscosity affects the rate of flow at the dispenser, leading to the production of defective products.
- System Breakdown: The char produced by the degraded adhesive clogs the pipes and leads to the eventual breakdown of the system. Such disruptions not only affect productivity but also take up valuable resources to repair.
- Wastages: To prevent production disruption, the degraded adhesive should be removed and replaced with fresh glue. This wastage of materials increases production costs, and the time it takes to resolve is also a loss of valuable productivity.
Can Adhesive Degradation Be Eliminated?
All glues have a shelf-life. With time, most adhesives end up degrading and charring. Some adhesive types last longer than others but eventually, degradation is inevitable. You can minimise char build-up by using adhesives strictly in line with the manufacturer’s recommended usage-life and operating temperature, but some accumulation is inevitable. You can also take preventative measures and carry out regular maintenance to prevent the char build-up from affecting productivity.
Maintenance Tips To Reduce And Handle Degraded Adhesives
1) Regulate the level of adhesive in the hot melt tank
For degradation to occur, the adhesive must be subjected to high temperatures in the presence of oxygen. If the level of the adhesive drops, more oxygen enters the tank, increasing the likelihood of charring. You should, therefore, ensure that the level of adhesive in the hot melt tank is over 70%.
Another reason to keep the adhesive level high is to prevent clotting. When the level gets too low and cold adhesive is added to refill the tank, the sudden and irregular change in temperature will cause some parts of the hot glue to gel or form strings.
2) Keep the temperature regulated during downtime
Adhesive is most prone to degradation when sitting idle, which mainly occurs during downtime, or between production cycles. As a result, the temperatures should be regulated when the production line is not running. Below are some simple tips that one could apply:
- For intervals lasting 2-12 hours, reduce the temperature by 30°C.
- For 12-24 hours, reduce to 100°C.
- If it will be shut for more than 24 hours, shut the system down.
3) Keep the system clean
Impurities also in the glue increase the rate of degradation, making it important that you keep the area around the hot melt tank clean and ensure the lid is kept intact. Buying high quality adhesives also limits the percentage of admixtures and impurities in the solution.
Dealing With Adhesive Degradation
While adhesive degradation cannot be avoided, regular maintenance will help reduce the rate at which it occurs. At The Adhesive Laundry, we clean, maintain, and rebuild hot melt units to keep them free from old adhesives. Contact us today on 01480 869220 to ensure your production line is always moving.
Image source: Graco