Bettina Winzer

Increasing flowability and bulk density of PE-HD powders by a dry particle coating process and impact on LBM processes

Purpose – The purpose of this paper is to demonstrate the processability of cohesive PE-HD particles in laser beam melting processes (LBM) of polymers. Furthermore, we present a characterization method for polymer particles, which can predict the quality of the powder deposition via LBM processes. Design/methodology/approach – This study focuses on the application of dry particle coating processes to increase flowability and bulk density of PE-HD particles. Both has been measured and afterwards validated via powder deposition of PE-HD particles in a LBM machine. Findings – For efficient coating in a dry particle coating process, the PE-HD particles and the attached nanoparticles need to show similar surface chemistry, i.e. both need to behave either hydrophobic or hydrophilic. It is demonstrated that dry particle coating is appropriate to enhance flowability and bulk density of PE-HD particles and hence considerably improves LBM processes and the resulting product quality. Originality/value – At present, ...

Correlation between shape, evaporation mode and mobility of small water droplets on nanorough fibres.

The dynamic wetting behaviour and the mobility of droplets on fibres is a very important factor in coating processes, textile fabrication, in self-cleaning processes and in the filtration of fluids. In principal, filter regeneration depends on the mobility of the droplets on the fibre surface. Mobile droplets tend to coalesce which greatly simplifies their removal from the filter. In this contribution mobility analyses of water droplets on monofilaments in air are performed. Studies of droplet evaporation on pure PET fibres and on nanorough fibres coated with SiO2 nanoparticles of diameters between 6 nm and 50 nm in a hydrophilic binder system were done. We show that the mobility of water droplets correlates with the droplet conformation which in turn is determined by the droplet-fibre interface. We demonstrate that fibre coatings can be used to tailor the conformation and mobility of water droplets. The smaller the nanoparticle diameters in the coating are, the smaller are the contact angles between water droplets and fibre and the better is the mobility of the droplets on the fibre. Our results allow a fast optimization of the fibre surface properties which are directly influencing the contact angle, the mobility and the coalescence of water droplets and thus filter regeneration.

A novel process route for the production of spherical SLS polymer powders

Currently, rapid prototyping gradually is transferred to additive manufacturing opening new applications. Especially selective laser sintering (SLS) is promising. One drawback is the limited choice of polymer materials available as optimized powders. Powders produced by cryogenic grinding show poor powder flowability resulting in poor device quality. Within this account we present a novel process route for the production of spherical polymer micron-sized particles of good flowability. The feasibility of the process chain is demonstrated for polystyrene e. In a first step polymer microparticles are produced by a wet grinding method. By this approach the mean particle size and the particle size distribution can be tuned between a few microns and several 10 microns. The applicability of this method will be discussed for different polymers and the dependencies of product particle size distribution on stressing conditions and process temperature will be outlined. The comminution products consist of micropartic...