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Causes and mechanisms for the formation of deposits and the adhesion of plastic melts on steel surfaces

(Kopie 3)

Project Leader: Prof. W. Maus-Friedrichs, Dr. F. Voigts

Funding period: 01/2012 - 12/2013
Funding body: BMWi via AiF
Funding reference: IGF 403ZN/2

Project team: M.Sc. René Gustus

Specks in moulded plastic parts due to the formation of deposits on steel surfaces in plastics processing machines and on surfaces e.g. of extrusion tools, are a widespread cause of production faults and interruptions, as well as of quality impairments. Particularly critical areas are preparation and production processes for high-quality moulded parts with exacting requirements with regard to visual properties or with high-gloss surfaces.

in the past speck problems were frequently exacerbated by insufficient technical flow design of the melt-carrying channels in machines (e.g. non-return valves) and tools. Through optimisation measures, long-term experience and the ability to perform numerical flow simulation, these causes have been largely eliminated or minimised by machine and tool manufacturers. However, in spite of these measures, problems with speck formation are still acute in certain applications.

Although the formation of deposits and the resulting speck issues has been a well-known phenomenon for several years now, the underlying causes, and in particular the early mechanisms resulting in the formation and growth of the deposits are as yet, for the most part, not understood. Granted, improvement measures have been found for individual, specific problems, e.g. by means of the selection of coatings and suitable additives in the moulding material formulae, such as certain lubricants or surfactants. However, neither raw materials manufacturers nor plastic-processing businesses have yet gained a clear idea of the mechanisms and correlations, and therefore nor do they have any systematic solution strategy to hand in order to proactively avoid deposit formation in production. Thus, for example, it has not yet in any way been explained why coatings or additives used actually have an effect or what the modes of action are.

The objective of the project is to gain an in-depth understanding of the mechanisms in the early phases of deposit formation, deposit growth and the removal of deposits. For the first time, the current standard trial-and-error procedure when selecting the steel, the coating and the moulding material formula is to be ignored, and in future targeted corrective measures are to be developed. In this project, the formation of deposits is to be expressly examined in as great detail as possible, both in relation to the changes to the metallic surface and with regard to the organic components of the boundary layer, in order to record interactions and reactions between polymer and metal material, or its passive layer. With the basic mechanisms for the formation, growth and removal of deposits in plastics processing identified in this way, as occur e.g in tools, extruders, injection moulding machines and hot runner systems, recommended courses of action must be developed for compounders, processors and machine manufacturers.

 

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