The content of this paper concerns to the new tendency in industry, the concept of circular economy, based mainly on the decrease in plastic waste pollution by recovery and at source and on the significant optimization of production costs. The mechanical tests have been made on handles injected from several mixtures of grinded HDPE, with different melt flow rates and in different proportions, in order to establish the conformity of the final product to the imposed technical specifications regarding the breaking strength of this. For the industrial application, an important result is the validation of the recipes proposed for the preparation of raw material from recycled HDPE for which the final injected product preserves the physical-mechanical properties within the imposed limits. The study shows that in certain cases, for the preparation of the raw material, it could be used up to 100% recycled material, without affecting the technical specifications of mechanical resistance imposed on the final product.

The paper presents a set of experiments focused on the study of rheological behavior of a polymer flowing through a narrow section at the forming by injection of thin-walled plastic parts. The paper addresses the use of ultrasonically activated injection for fabrication of polymeric parts with thin wall features. In the experiment, a part with six different geometric features has been created. The design-of-experiments approach is applied to correlate the quality of the parts with the processing parameters. Four processing parameters are investigated using a screening factorial experimentation plan to determine their possible effect on the filling quality of the moulded parts. The experiments have been conducted on a hot runner mould with two nests in which the final (nest) nozzle has been modified to host, as the central element, the ultrasonic horn of a sonic system. It has been found that the ultrasonic activation applied on the active part of the mould does not play an important role as a stand-alone factor but could amplify or strengthen the effect of classical setting parameters (and influence factors) of the process: the melt temperature and injection pressure. Because it is easier to stimulate and to control rheological properties of the melt by setting the intensity of ultrasonic energy and, more important, the effect is forthwith, the paper recommends the runner systems with ultrasonic activation as an alternative for the hot runner with heating elements.

Low frequency ultrasounds (20÷100 kHz) at high energy (100÷1000 W), namely "macro sounds", are often employed in various industrial applications due to their effects on the processed materials. The chemical, mechanical, thermal and cavitational effects on solids and/or liquids submitted at ultrasonic activation are involved in applications such as plastics welding, ultrasonic cleaning, dimensional modelling, drilling or cutting of hard materials, other physical applications [1]. Sound propagation in solids is of substantially higher complexity than that in fluids, due to the fact that a solid body tries to maintain not only its volume but also its shape. In particular, in a solid not only longitudinal waves can be propagated as in fluids, but also transverse waves. More than that, the physical properties depend on direction and orientation and the design of an ultrasonic system becomes especially complicated, [1,2]. The conventional studies concerning the rheological behaviour at extrusion dealt with the classical assumption (convenient boundary condition) [3,4,5]:• the flow is streamline (laminar), the velocity and the stress are continue in flow section • mass and inertia forces are neglected, • at laminar flow there is no slip at the die walls due to the specific interfacial interaction solid-fluid, • in particular conditions, a stick-slip phenomenon is present, generating volume and surface faults, • a power law describes the viscosity, • hypothesis of null velocity (v = 0) of displacement at the wall of the flow section. Nevertheless, recent researches emphasize displacement through slide of the melt volume in the proximity of the extrusion die wall. The particular structure of the melted material (i.e. interpenetrated macromolecules) determines the viscous-elastically behaviour and the solidary movement of the material next to the wall generating for particular conditions (temperature, high flow velocity, wall proprieties) the "stick-slip" effectoscillating variations of the discharge and pressure at the emergence from the extrusion dies.ABSTRACT: The paper presents some experimental works that allow concluding that a new effect of the ultrasounds, "ultrasonic thermo-pellicle effect ", may be accepted. It was identified during the application of the ultrasonic energy to melted polymers in flowing state. The modifications of the properties at the interface between the melted material and the metallic die could postpone, due to ultrasonic activation, the beginning of the "stick-slip" phenomenon allowing the increase of the productivity and the product quality and the flow of the thermoplastic material through the die of the extrusion head. The concept could be extended for high dense fluids as revealed in the last part of the paper where some original application are proposed by the authors.

Each component on an industrial ultrasonic system is specifically designed from the very beginning, as part of the resonant system, for each individual application and for a present frequency and with particular working conditions. A series of factors linked to the mechanical system can significantly shift the electrical impedance and the real resonant frequency of the vibrating system. Most frequently, the capability of the ultrasonic generator to solve this problem is limited to a frequency sweeping in the limit of a 1 kHz tracking range around a fixed nominal frequency. When the range of variation exceeds 1 kHz, a more performing, but expensive, generator is needed. The paper presents a set of experiments with variable compression axial force up to 200 daN, specific situation for the ultrasonic activated drilling, and the evolution of the resonant frequency in these conditions in a range up to 3 kHz.

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