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Effect of Vibration in Viscosity of a Melt Polymer.When a vibrating force is applied to an entangled melt polymer, the van der Waals forces that connect the macromolecules become weaker, and the entanglement is relaxed; therefore, viscous force among the macromolecules decreases dramatically, resulting in the reduction of viscosity [9, 14].Viscosity Measurement. There are different techniques and apparatuses to measure the viscosity, for example, palettes, cone, capillarity, etc. However, most of the available techniques are not suitable for measuring viscosity during the injection molding process due to the process nature. Yet, a nonconventional technique developed by Clavería et al. [15], which is based on a spiral mold, is applicable to the injection molding process. Vibration Methods. Vibration actuators range from piezoelectric and ultrasonic emitters [8, 16] for high frequency and low force, up to mechanical systems for low frequency and high force [17]. In the same way, there are different techniques to excite the polymer, such as vibration induction through a vibrating wall [16], a flexible pipe, or directly through a plunger.
Manufacturing Design
Figure 1 depicts the application points of different vibration systems in the body of the machine and mold that have been afore-mentioned. It is possible to observe that the devices of Liu [9, 14], Ibar [10], and Yan et al. [12], are directly mounted on the body of the machine. Considering the advantages that the proximity to the application point offers, such as simplicity in the device, the developed apparatus in this research is positioned on the mold sprue,which does not require major modifications on the machine.
Design of the Vibrating Device. Shown schematically in Fig. 2, the vibrating apparatus consists of two systems:shaker and coupler device. The shaker provides a sinusoidal vibration signal, controlled on amplitude and frequency,and then the coupler translates the vibration into the melt polymer through the mold sprue [9, 12, 18].The main tool, designed to carry out this development, is the coupler. It is designed to operate as an accessory to the mold sprue. The coupler transfers the sinusoidal mechanical signal provided by the shaker to the inside of the sprue in which the polymer is excited. In this particular case,the perpendicular application of the vibration is selected in order to facilitate the form of the mechanism. Figure 2b depicts the coupler design.
Design of the Experimental Mold. With the purpose to quantitatively demonstrate the efficiency of the developed device, it is necessary to design a rheometer. In this work, a nonconventional method, based on a spiral mold is used. From different suitable patterns, the spiral of Archimedes is selected (Eq. (1) and Fig. 3) .because further analysis is easier than in other patterns. Noticeably, the step among threats is constant for the spiral of Archimedes, and the length R can be analytically calculated with Eq. (1) in polar coordinates, where is the angle and a is constant. At the same time, this pattern can be easily traced by using square and compass only:
R=θ*a (1)
Since the tool is only an experimental mold for short production, it was made of carbon steel AISI 1045.
Experimental setup
High-density polyethylene HDPE (grade PEAD 60120) is chosen for the experiment, because of the good physical properties and the benefit of manufacturing as low humidity absorption, low weight, flexibility, higher chemical resistance, insulating respect to electricity, among others. Both the vibration apparatus and the spiral mold are mounted on molding machine as show in Fig. 4.
The procedure of measuring the polymer-melt viscosity under vibrating is as follows.