Demands for temperature resistance and chemical durability in adhesives are increasing in many industries, including automotive and electronics. To achieve properties like electrical or thermal conductivity or adjusted expansion coefficients, adhesive manufacturers enhance their products with additional raw materials. These robust mineral or metallic fillers are used increasingly in adhesives. However, they are considered abrasive and therefore difficult to dispense. But as long-term tests have shown, this is sometimes not the case.

'Abrasive' refers to a grinding effect which can potentially wear down or damage surfaces. To assess the real-world effects of abrasive fillers on equipment and determine how adhesives with filler content affect dispensing quality, ViscoTec and DELO conducted a joint long-term study. To this end, over 6 million dispensing cycles were conducted.

To understand the research findings, it's worth taking a brief look at the setup of modern dispensing systems.

Modern dispensing systems: The rotor-stator principle

Modern dispensing systems, like progressive cavity pumps, utilize a rotor and an elastic stator to transport adhesives efficiently. This design is particularly efficient for dispensing viscous, shear-sensitive, or solid-containing fluids.

Adhesive transport: The rotor is designed to run offset to the stator surface, creating temporary seals and forming cavities. As the rotor begins to move eccentrically, new cavities form, drawing the product in and moving it along the assembly line until it is expelled through the outlet.

Furthermore, modern stators are often made from elastomeric materials. Elastomeric stators are advantageous in that they ensure constant sealing, allowing for consistent and precise dispensing. Elastomers belong to a special class of polymers known for their exceptional elasticity. These materials can change significantly in shape when stretched or bent yet afterward return to their original form. An elastomer stator can effectively absorb the rotor’s irregular movements, flexibly adapting to its shape. This leads to continual sealing, ensuring uniform and precise dispensing.
 

At regular intervals (every 20 hours), three dispensing shots were weighed to verify dispensing consistency and precision over time. An increase or decrease in the weighed dispensing shots compared to previous measurements could indicate wear in the dispensing devices. Particularly with abrasive adhesives, such changes might suggest that the material is wearing down parts of the dispensers, affecting dispensing precision.

Results showed precise and repeatable dispensing throughout all testing. DELO experts were accordingly enthusiastic:

Before and after endurance testing, rotor components made of hard-chromed stainless steel and the elastomer stators of the dispensers were measured. The result: after nearly 300,000 dispensing cycles each, no wear was detectable on the rotors, and only minimal wear was observed on the stators. Changes in the stators were so minor that the dimensions still fell within tight manufacturing tolerances.