Browse Articles

The paper presents some technological aspects related to a new procedure for centrifugal casting in moulds made of silicone rubber. The procedure has been enhanced by the American company Tekcast Industries Inc. and is applicable for the casting of plastics and metallic alloys of zinc and led, in the case of small production and unique items. Keywords: silicone rubber, centrifugal casting, moulds, zinc alloys

A survay on the radiothermoluminescenceof 25 polymers is presented. The RTL glow curves were recorded on the temperature range starting from 77 K up to room temperature after 60Co irradiation. The most RTL peaks occur at temperatures similar to those assigned to the onset of specific molecular motins, suggesting that the peaks are due to the liberation of electrons from traps formed by the chains of polymer. The RTL glow curves are generally in good agreement with the results reported by other researchers. This paper includes the experimental data obtained from each glow curve (temperature and intensity of maxima). The activation energies of some of the peaks were obtained using several methods. The peaks with lower activation energies generally are located at lower temperatures. Keywords: polymers, elastomers, radiothermoluminescence, characterization, activation energy

In the previous article [1], results concerning the bonding of cured non-polar elastomers supports with adhesive formulations based on non-cured non-polar elastomers have been presented. This research is dedicated to obtain additional information regarding the adhesion mechanism and to study the adhesion strength executed on cured polar elastomers supports with composition based on non-cured polar elastomers. We have used two types of polar cured elastomers basic supports, polychloroprenic rubber and nitrile rubber, and two non-cured adhesive compositions of the same elastomers type. Keywords: adhesives, elastomers, polychloroprene rubber, nitrile rubber

The paper presents the changes in chemical composition and hardness of cylindres used for grinding of rubber wastes. Based on experimental results obtained, some technical solutions can be suggested in order to determine a considerabile growth the life equipment. Keywords: rubber waste grinding

The use of Rapid Prototyping (RP) processes in manufacturing cellular solids offers the advantages of controlling the distribution, dimensions and interconnection of cells, which influence their micro and macro-structural properties. But not all RP processes are able to build cellular solids with closed cells, this article analyzing the capacity of Fused Deposition Modeling (FDM) process to manufacture this type of structures from ABS material. Using a test part containing cubic and spherical cells, it is shown that FDM can manufacture structures with completely enclosed voids, but only for a certain range of dimensions. This approach opens new study directions such as the possibility to analyze the mechanical behaviour of this type of cellular materials with closed cells and controlled geometry, or to use them as test parts for detecting voids in injection moulded parts. Keywords: fused deposition modeling, rapid prototyping, ABS polymer material, cellular solids, closed cells

In this paper the experimental results obtained at grain refining of 6082 aluminum alloy are presented, using an original method which consists in insertion of refining master alloys in two stages: in the first stage the AlTi5 elaborated at low temperature, and in stage number two AlTi5B1 classic ternary master alloy. The method ensures into the solidification process, both the elements that act by stopping the grain growth (Ti) and the nucleation centers (TiB2, AlB2, (Ti, Al)B2). Keywords: prealloys, refining

The microelectronic package continues to evolve in order to improve the performance and integrate new technology such as multidie architectures, thinner substrates, increasing integration of passive components, increasing thermal design power and lead free interconnects. Package materials must be designed to enable the electrical and thermal performance requirement and to provide high-reliability performance. Maximum heat dissipation is a requirement for today’s higher power integrated circuit devices. The maximum heat dissipation is achieved by mounting active devices directly to high thermal conductivity heat sinking substrates or packages. Direct attachment requires a compatible coefficient of thermal expansion (CTE) value of the heat sink material to avoid stress failure of the IC device. In this paper, the thermal behavior of polymers used in cooling electronics with nonlinear electrical lumped elements as a function of temperature, physical properties and sizes of a heat sink element were modeled. Keywords: high thermal conductivity polymers, heat sink, safe operating area, nonlinear thermal impedance electrical model

Rheological measurements of 3; 6; 10 and 12% INFINEUM SV 260 solutions in SAE 10W mineral oil show non-Newtonian behaviour in the temperature range 313-370 K and shear rates ranging between 3 and 1312 s-1: they follow the Bingham model at low concentrations, low shear rates and high temperatures and the Herschel-Bulkley model at high concentration, high shear rates and low temperatures. KELTAN 4200 solutions in the same solvent are more viscous than the corresponding ones given by INFINEUM SV 260 and follow the Herschel-Bulkley model onto the whole studied concentration, shear rate and temperature ranges. The slopes of the lines representing the variation of log viscosity with the reciprocal of temperature increase slightly with concentration between 3 and 10% for INFINEUM SV 260 solutions and decreases for 12%. The lowest slope is given by 3% solution, followed by 12%, and the highest one by 10% solution. KELTAN 4200 solutions present an increase of slope when passing from 3 to 6% and a decrease when the concentration exceeds the last value. The lowest slope was obtained for 12% solution, followed by 3%, while 6% solution has the highest value. This might suggest that KELTAN 4200 could be a better viscosity improver for the mineral oil SAE 10W, both at low and high concentrations. Keywords: rheological behaviour of concentrated polymer solutions, viscosity improvers, multi-grade oils

The organic coatings made with powder dyes constitute an alternative solution to liquid dyes, for thez ensure a proper equilibrium between performance, price and work protection. Depending on the utilization field, this kind of organic coatings may be realized with different degrees of shine, from dull to glossy. In practice there are preferred the dull coatings because the surface defects of the cover films (needle shots, craters, scratches) are less visible on this type of surfaces. In this paper it was analyzed the possiblity of using as a splice agent a carboxyfunctional polyester and it was emphasized the influence of this splice agent on some characteristics of the epoxy-polyesteric powder dyes of white signal type and of cover films made with them. Keywords:organic coatings, powder dyes, splice agent, cover films

This paper presents a comparative numerical simulation of an injection moulding process in the case of an acetabular cup, a basic component in a hip prosthesis, made of UHMWPE (GUR 5113, GUR EP 4224, Novatec PP BC4Y 46420) in order to determine the optimal conditions for injection process parameters. The numerical simulation was performed using fusion finite element Moldflow Plastics Insight software especially designed for injection moulding. Keywords: biocompatible materials, hip prosthesis, injection moulding, acetabular cup