Abstract
It is well known that elastomers usually possess poor dry sliding friction properties due to their highly adhesive character. In order to overcome this problematic behavior in industrial applications, interfacial materials such as oils, greases, coatings, or lacks are normally used in order to separate or to functionalize the contact surfaces of elastomers. Alternatively, the high adhesion tendency of elastomers may be explicitly reduced by modifying the elastomer composition itself or by enabling a reduction of its effective contact area through, for example, surface laser texturing. This second approach, i.e., the reduction of the adhesive character of elastomers through laser structuring, will be the main topic of the present study. For this purpose, different micro-sized grooved structures were produced on flat injection molds using an ultra-short pulsed laser. The micro-structured molds were then used to produce injection molded micro-ridged Liquid Silicone Rubber (LSR) sample pads. The investigations consisted firstly of determining the degree of replication of the mold micro-structures onto the surface of the LSR pads and secondly, to ascertain the degree of reduction of the friction force (or coefficient of friction) of these micro-ridged LSR pads in comparison to the benchmark (unstructured LSR pads) when tested under dry conditions against Aluminum alloy (Al-6082) or PA6.6-GF30 plates. For this second part of the investigation, the normal force (or contact pressure) dependency of the coefficient of friction was determined through stepwise load increasing friction tests. The results of these investigations have shown that the production of micro-ridged surfaces on LSR pads through laser structuring of the injection molds could be successfully achieved and that it enables a significant reduction of the friction force for low normal forces (or contact pressures), where the component of adhesion friction is playing an important and determining role in the overall friction behavior of the LSR elastomer.
Highlights
IntroductionTribo-systems using elastomeric sliding partners usually show characteristic properties in their friction and wear behaviors due primarily to their specific mechanical and superficial properties and this could be extensively explained for instance, through the basic concept of elastomer tribology, which is based on four mutually influencing friction force components, as previously described in the rubber friction theory elaborated by Kummer and Mayer [1] and Geyer [2]: FTotal = FAdhesion + FHysteresis + FViscosity + FCohesion (1)
Pads in comparison to the benchmark when tested under dry conditions against Aluminum alloy (Al-6082) or PA6.6-GF30 plates. For this second part of the investigation, the normal force dependency of the coefficient of friction was determined through stepwise load increasing friction tests. The results of these investigations have shown that the production of micro-ridged surfaces on Liquid Silicone Rubber (LSR) pads through laser structuring of the injection molds could be successfully achieved and that it enables a significant reduction of the friction force for low normal forces, where the component of adhesion friction is playing an important and determining role in the overall friction behavior of the LSR elastomer
Tribo-systems using elastomeric sliding partners usually show characteristic properties in their friction and wear behaviors due primarily to their specific mechanical and superficial properties and this could be extensively explained for instance, through the basic concept of elastomer tribology, which is based on four mutually influencing friction force components, as previously described in the rubber friction theory elaborated by Kummer and Mayer [1] and Geyer [2]: FTotal = FAdhesion + FHysteresis + FViscosity + FCohesion where the different enumerated friction force components of the total friction force (FTotal ) may be described as follow: Lubricants 2017, 5, 45; doi:10.3390/lubricants5040045
Summary
Tribo-systems using elastomeric sliding partners usually show characteristic properties in their friction and wear behaviors due primarily to their specific mechanical and superficial properties and this could be extensively explained for instance, through the basic concept of elastomer tribology, which is based on four mutually influencing friction force components, as previously described in the rubber friction theory elaborated by Kummer and Mayer [1] and Geyer [2]: FTotal = FAdhesion + FHysteresis + FViscosity + FCohesion (1). FAdhesion: product of the effective shear stresses and the effective contact surface. FAdhesion : product of the effective shear stresses and the effective contact surface due to constantly changing deformations of elastomer. FViscosity: shear forces of a viscous liquid layer enclosed between elastomer and surface due to constantly changing deformations of elastomer. FCohesion: intramolecular cohesive forces; forces occurring during crack formation. FViscosity : shear forces of a viscous liquid layer enclosed between elastomer and surface.
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