Key Engineering Materials Vol. 699

Abstract: The life time of the metallic materials exposed to marine environment is influenced by their corrosion resistance. The marine environment is considered to be very aggressive to metallic materials used in the marine industry. In order to protect metallic substrates against corrosion process, important efforts have been made to develop corrosion resistance coatings, besides the cathodic protection systems. Thus, during the last years there were developed a series of organic protective coatings that have as principal component one or more polymers. This paper present a comparative investigation regarding the corrosion resistance of: i) uncoated naval steel EN32, ii) coated naval steel EN32 with a two-component polymeric primer and iii) coated naval steel EN32 with two-component polymeric primer followed by epoxy polyurethane paint coating. All the samples have been subjected to corrosion in seawater collected from the Black Sea (Mangalia sea port). In situ electrochemical measurements as: open circuit potential (OCP), polarization resistance (R_p), potentiodynamic polarization (PD) and cyclic voltammetry polarization (CV) were performed to monitor the corrosion process. The results showed an improved corrosion resistance of polymeric coatings in marine environment compared with uncoated naval steel EN32

Abstract: Due to the global warming and diminishing petroleum oil reserves the conversion of biomass in useful biodegradable materials represent a tremendous need in terms of economic and environmental problem. During the last years, enormous effort have been sustained by the researchers who tried to develop and improve green (recyclable, biocompatible, and biodegradable) materials from renewable resources strengthening this way the global sustainability. Following this need a new material Arboform – „liquid wood“, that meets all the above conditions was developed by a team of german researchers appearing shortly on the market. This material can be processed like any other plastic material, so no need changing in terms of technological equipment. Since the injection molding is the most widely used process in manufacturing polymer products, unavoidable surface quality problems appear. In order to obtain a clear image of surface sample are analyzed the inherent properties of the used material, injection parameters and conditions using a Talysurf CLI 2000 profilometer. The equipment is able to perform high-accuracy measurements of the surface topography for Arboform L, V3 Nature (A-LW) and Arboform L, V3 Nature Reinforced with Aramid Fibers (A-LWAF) samples. The experimental research was achieved by means of the Taguchi experiment plan, with 6 input parameters (injection pressure, melt temperature, cooling time, screw displacement injection time and injection angle) each of them having two levels of variation. In case of 90 degrees angle injection (samples from 1 and 2 experiments) the dispersion roughness (Ra) measured on east-west direction is lower (26.6% for A-LW and 23.7% respectively for A-LWAF) compared with the roughness measurement on north-south direction. At 0 degrees angle injection the dispersion had the same trend (lower for east-west direction) of the A-LWAF 4 and 6 samples and higher in the east-west direction for 3 and 5 samples of A-LW material studied.

Abstract: The influence of beta radiation on the changes in the structure and selected properties (mechanical and thermal) polymers were proved. The use of low doses of beta radiation for polypropylene and its influence on the changes of micro, macro mechanical properties was thoroughly studied. The specimens of polypropylene were made by injection molding technology and irradiated by low doses of beta radiation (0, 15 and 33 kGy). The changes in the microstructure and micromechanical properties of surface layer were evaluated using WAXS and instrumented nano hardness test. The results of the measurements showed considerable increase in mechanical properties (indentation hardness, indentation elastic modulus) when the beta radiation are used.

Abstract: High performance polymers (HPP) represent a wide class of materials which is used in all the engineering sectors from automotive to domestic appliances. Thanks to their high mechanical and functional properties HPPs, have substituted metals in many applications with the result of reducing manufacturing time and costs. In such cases, this substitution also results in an improvement of part performances as in the case of tribological applications, despite of the strong sensibility of tribological polymers to manufacturing processes. However, supplying costs of high performance polymers is continuously increasing in the last years and the cheapness of this substitution is always under discussion. In this work, a comparison is made between injection moulding of glass filled polyamide and aluminum die casting in terms of process energy and production cost. The production of a motorcycle lever has been considered as case-study. The plastic lever has been also prototyped by machining to show its correct functionality.

Abstract: Rotational molding is a manufacturing method which supposes the rotation of the mold, during the solidification of the liquid phase material, so that finally a part having a hollow could be obtained. The method could be applied in manufacturing of metallic and nonmetallic parts. Usually, the equipment for rotational molding ensures slow speed rotating of the mold around two axes placed perpendicularly each other and this fact led to relatively complex equipment for achieving rotational molding. The capacity of the liquid material to entirely cover the internal walls of the mold depends essentially on the liquid material viscosity, on the rotation speed and on the movements applied to the mold. Simplified equipment including a single rotation movement could be materialized. In order to test such a solution, a preliminary experiment was designed and materialized, by using a device adapted on universal lathe. Thus, the objective of the research presented in the paper was to study if it is possible to achieve plastic parts made by rotational molding using a single rotation movement. A polyurethane resin obtained from two liquid components was used in order to obtain the liquid material that could be introduced in the mold. The research results proved the possibility to use simplified equipment for achieving a rotational molding process, at least in certain cases and with some technological limits.

Abstract: At the final step of the injection process (of a plastic product with cavities) when the part is on the point to be ejected the adhesion phenomena occurs between the core and the plastic part. The mold adhesion effect has a significant influence on the mold design ejection system and over the whole process. This paper presents a computation methodology of the demolding moment for two cases of plastic injected parts with internal trapezoidal thread. Knowing the value of this moment offer us the possibility to adopt the right design solution of the ejector system and of the entire mold. As further work the author will try to validate this method through a set of practical experiments.