Highly filled adhesives are easy to dose
Fillers in adhesives and casting compounds can lead to mechanical abrasion in dosing systems. Despite this potentially abrasive behaviour, they can be dosed reliably and precisely in the long term.
The demands placed on the temperature resistance and chemical resistance of adhesives are increasing in many industries, such as the automotive and electronics industries. Therefore, but also in order to achieve properties such as electrical or thermal conductivity or adapted expansion coefficients, adhesive manufacturers fill their products with additional raw materials. These robust, mostly mineral or metallic fillers are therefore used more frequently in adhesives, but are considered abrasive and therefore difficult to dose – wrongly so, as long-term tests have now shown.
Exclusion of chemical interactions
Visco Tec metering devices with two elastomer stators each were investigated. Six epoxy resins from Delo, each with different fillers, were used as adhesives. In all cases, the filler content was between 25 and 50 percent, typical for adhesives. The stators were first placed in the adhesive for 168 hours to test their basic chemical suitability for long-term contact. Subsequently, the change in mass, dimensional stability, hardness and elasticity of the elastomers were investigated. There were no abnormalities or deviations outside the narrow manufacturing tolerances. Thus, chemical interactions between the two components, which would influence the further results, could be excluded.
Precise and repeatable dosage
In the subsequent 24 long-term tests, dosing was carried out cyclically: Two seconds of dosing were followed by a second of pause to simulate a typical dosing behavior of automated manufacturing processes. This resulted in almost 300,000 dosing cycles per test series. After each 20 hours, three dosing shots were weighed and compared over time. A change in their mass would indicate wear on the dispenser due to an abrasive effect of the adhesives. In fact, according to the results of the tests, a precise and repeatable dosage was given across all test pairs.
Minimal abrasion on the stators
Before and after the endurance tests, the rotors made of hard-chrome-plated stainless steel and the elastomer stators of the dosing units were also measured. The result: After almost 300,000 dosing cycles, no signs of abrasion were visible on the rotors and only minimal signs of abrasion on the stators. The changes to the stators were so minor that the dimensions were still within the narrow manufacturing tolerances.
