Vibration Pressure Amplitude Research Articles

Biaxially Self-Reinforced High-Density Polyethylene Prepared by Vibration-Assisted Injection Molding. I. Processing Conditions and Physical Properties

A pulse pressure was imposed on the melt in the injection molding cavity during the injection and holding pressure stages, called vibration-assisted injection molding (VAIM) technology. With the VAIM technology, biaxially self-reinforced high-density polyethylene (HDPE) samples were prepared and the physical properties affected by the vibration processing conditions were studied. The tensile properties can be improved in both the machine direction (MD) and the transverse direction (TD) by changing the vibration frequency and vibration pressure amplitude, respectively. The elongation at break increased with increasing the vibration frequency for the VAIM sample processed at constant low vibration pressure amplitude; the yield strength increased with increasing the vibration pressure amplitude for the VAIM sample prepared at constant low vibration frequency. The softening point temperature for the VAIM sample increased by 8°C compared with a conventional injection-molded (CIM) sample.

Study on Creep Behavior of PP/CaCO3 Molded by Vibration Injection Molding at Different Vibration Frequency and Vibration Pressure

Abstract Vibration injection molding technology has achieved some good properties, such as high impact strength and high tensile strength. Although many researchers have proved that the short-time mechanical properties of the polymer could be improved by vibration-injection molding technology, the long-time mechanical properties, such as the creep behavior, have not been paid enough attention. In this paper, the creep behavior of the calcium carbonate filled polypropylene (PP/CaCO3) prepared at various vibration conditions has been observed. The influences of the vibration pressure and the frequency on the mechanical properties and creep behavior were investigated via creep test and tensile test. Firstly, the tensile fracture strain reached the maximum (11%) at 0.72 Hz. Moreover, with the increasing vibration pressure amplitude, the tensile fracture strain would decrease. The changing tendency of tensile strength is basically contrary with the change of the tensile fracture strain. Secondly, when the vibration frequency reaches the 0.72 Hz, the tensile creep is larger than that of other frequencies samples at 50 MPa; meanwhile, the tensile creep of these PP/CaCO3 parts, which has been prepared at 0.48 Hz, decreases with the increasing vibration pressure amplitude. Finally, the dynamic mechanics analysis (DMA) and the wide-angle X-ray diffraction (WAXD) were adopted to analyze the reason of the creep behavior change. The different macromolecular chains mobility caused the different creep behavior.

The Creep Behavior and Mechanical Properties of Polypropylene (pp) in Mechanical Vibration Injection Molding under Low Frequency Vibration Field

Vibration injection molding has been an advanced polymer process method. Though some researchers have investigated the universal mechanical properties of polymer prepared via vibration injection molding, the influence of the different vibration conditions on the long-time mechanical properties cannot be paid enough attention. Therefore, the creep of polymer prepared at different vibration conditions has been observed in order to attain the influence of vibration conditions on the creep property and the reason that leads to these changes. In our previous study, it has been observed that the long-time mechanical properties of polymer prepared at different vibration conditions, such as the creep, show great superiority to conventional injection molding (CIM) articles. In this paper, the influence of the vibration pressure amplitude and frequency on the mechanical properties and creep behavior of injection molded polypropylene (PP) samples was investigated. It was observed that the tensile fracture elongation reached the maximum (125mm) at 1 Hz, with the vibration frequency increasing; while with the increasing vibration pressure amplitude, the tensile fracture elongation decreased, but the tensile strength increased. Secondly, the dynamic mechanics analysis has been used to test the loss angle tangent value of the polypropylene prepared at different vibration conditions. After the dynamic mechanic analysis, the samples have been installed in the creep apparatus which applies the 4MPa to the specimens. When the vibration frequency reaches the 1Hz for PP, the creep is larger than that of other materials prepared at the same pressure amplitude (50MPa); meanwhile, the creep of these materials, which has been prepared at the same frequency (0.48Hz), decreases with the increasing vibration pressure amplitude. According to above tests, it is also very useful to improve the creep behavior by changing the condition of the vibration field.

Self-Reinforced High-Density Polyethylene Prepared by Low-Frequency, Vibration-Assisted Injection Molding. 1. Processing Conditions and Physical Properties

Using a low-frequency, vibration-assisted injection molding (VAIM) device, the effects of vibration variables (frequency and amplitude) on mechanical properties and thermal softening temperature of high-density polyethylene (HDPE) injection moldings were investigated. For VAIM-processed samples, the mechanical properties can be improved by changing vibration frequency and vibration pressure amplitude. Injected at a constant vibration pressure amplitude, a low range of frequency (below 0.7 Hz) was favorable for increasing yield strength; in the high range of frequency (0.7 Hz < f < 2.33 Hz) the yield strength remained at a plateau. Injected at a constant frequency (0.7 Hz) the yield strength increased sharply with decreased elongation when applying large vibration pressure amplitude. The maximal yield strength and Young's modulus were 60.6 MPa and 2.1 GPa for a VAIM sample compared with 39.8 MPa and 1.0 GPa for a conventional injection-molded (CIM) sample, respectively; there was also a 10°C increase in Vicat softening point temperature.

Effect of low-frequency melt vibration on HDPE morphology

BACKGROUND: A low-frequency vibration-assisted injection-molding (VAIM) device was developed to explore the morphology of high-density polyethylene (HDPE) injection moldings. Scanning electron microscopy, wide-angle X-ray diffraction and differential scanning calorimetry were used to characterize structure-property relationships of final products prepared under different VAIM processing conditions (vibration frequency and vibration pressure amplitude) with conventional injection molding for comparison. RESULTS: It was found that increasing the vibration frequency at constant vibration pressure amplitude was beneficial for obtaining ‘shish-kebab’ structures in the core region of VAIM specimens, and increasing the vibration pressure amplitude at constant vibration frequency was a prerequisite for achieving HDPE specimens with large-scale lamellas, more pronounced orientation and high crystallinity. CONCLUSION: Both preferred orientation lamellas and increased crystallinity allow one to obtain strong injection moldings with the application of the melt vibration technique. Copyright © 2009 Society of Chemical Industry

Self-Reinforced Isotactic Polypropylene Prepared by Melt Vibration Injection Molding

Polypropylene (PP) has a good combination of properties, but at low temperatures it is friable and its impact ductility is very low. To improve impact strength, a vibration injection molding (VIM) technology was used to investigate the mechanical properties of polypropylene. Yield strength is upgraded with an increment in vibration frequency and a peak stands at a special frequency for VIM; the elongation at break and impact strength are also enhanced by increased vibration frequency. The wide-angle x-ray diffraction (WAXD) curves and the scanning electronic microscopy (SEM) micrographs have shown that, in the vibration field, the enhancement of mechanical properties is attributed to the occurrence of γ-phase crystals and more pronounced spherulite deformation than those seen in conventional injection moldings (CIM), and the smaller spherulites with the existence of β-phase crystals are favored for improving toughness. With the application of vibration injection molding, the mechanical properties of isotactic PP are improved. To prepare self-reinforcing and self-toughening polypropylene molded parts it has been concluded that high vibration frequency is required. Increasing vibration pressure amplitude obviously significantly improves the yield strength and impact strength.

Melt Vibration Improved Melt Flow Behavior and Mechanical Properties of High Density Polyethylene

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.

Improving the mechanical properties of polypropylene via melt vibration

AbstractThe effect of melt vibration on the mechanical properties of polypropylene prepared by low‐frequency vibration‐assisted injection molding (VAIM) has been investigated. With the application of melt vibration technology, the mechanical properties of polypropylene are improved. The yield strength increases with the increment of the vibration frequency, and a peak stands at a special frequency for VAIM; the elongation at break decreases first and then increases with increasing vibration frequency, and a valley stands at a special frequency. The tensile properties increase sharply at an enlarged vibration pressure amplitude with sharply decreased elongation at break. The Young's modulus and impact strength also increase with the vibration frequency and pressure vibration amplitude. When it is prepared at 59.4 MPa and 0.7 Hz, the maximal yield strength is approximately 40 MPa versus 33.7 MPa for a conventional sample; an 18.7% increase in the tensile strength is produced. Self‐reinforcing and self‐toughening polypropylene molded parts have been found to be prepared at a high vibration frequency or at a large pressure vibration amplitude. Scanning electron micrographs have shown that, in the vibration field, the enhancement of the mechanical properties is attributable to more pronounced spherulite orientation and increased crystallinity in comparison with conventional injection moldings. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Improving Melt Flow Behavior via Melt Vibration

A self‐made melt vibration extrusion device was used to study the melt flow behavior in a vibration field. A pulse pressure was superimposed on the flowing melt during extrusion, called vibration assisted extrusion (VAE); conventional extrusion (CE) was studied for comparison. A die (L/D=17.5) was attached to the device to study melt flow behavior of an amorphous polymer (polystyrene) and semi‐crystalline polymers (high density and linear low polyethylene). Results show that the melt vibration technique is an effective processing tool to improve polymer melt flow behavior for both crystalline and amorphous polymers. Increasing with vibration frequency for extrusion at constant vibration pressure amplitude, the viscosity decreases sharply, and also with increasing vibration pressure amplitude at a constant vibration frequency. The effect of vibration field on melt flow behavior depends greatly on the melt temperature, with the largest change in viscosity obtained at low temperature. Increasing with vibration frequency at constant pressure vibration amplitude, the maximum decrease percentages of viscosities are 82.9, 66.7, and 48.9%, for HDPE, LLDPE, and PS, respectively; increasing with pressure vibration amplitude at a constant vibration frequency, the maximum decrease percentage of viscosities are 99.0, 94.3, and 99.0%, for HDPE, LLDPE, and PS, respectively.

Improving rheological property of polymer melt via low frequency melt vibration

AbstractA pulse pressure was superimposed on the melt flow in extrusion, called vibration extrusion. A die (L/D = 17.5) was attached to this device to study the rheological properties of an amorphous polymer (ABS) and semicrystalline polymer (PP, HDPE), prepared in the vibration field, and the conventional extrusion were studied for comparison. Results show that the melt vibration technique is an effective processing tool for improving the polymer melt flow behavior for both crystalline and amorphous polymers. The enhanced melt rheological property is also explained in terms of shear thinning criteria. Increasing with vibration frequency, extruded at constant vibration pressure amplitude, the viscosity decreases sharply, and so does when increasing vibration pressure amplitude at a constant vibrational frequency. The effect of vibrational field on melt rheological behavior depends greatly on the melt temperature, and the great decrease in viscosity is obtained at low temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5292–5296, 2006

Effect of Melt Vibration on Mechanical Properties of Injection Molding and Rheology

A pulse pressure was superimposed on the melt flow in injection molding, called vibration injection molding (VIM); the mechanical properties of the resulting samples were compared with the values of conventional injection molding (CIM). A die (L/D = 17.5) was attached to this device to study rheology. Properties of an amorphous polymer (ABS) and a semicrystalline polymer (PP), prepared in the vibration field, were compared to each other. Applying VIM, the mechanical properties can be improved whether the material is amorphous or not. Increasing with vibration frequency, the tensile strengths of PP were improved. The processing parameters to obtain self‐reinforcing and self‐toughening moldings were found at high vibration frequency Fr (Fr > 1.2 Hz). For ABS, the improvement of tensile strength is very small. For both PP and ABS, the yield strength, Young's modulus, and impact strength are all improved by increased vibration pressure amplitude. The elongation at break of PP moldings, however, decreases sharply; but the corresponding value decreases little for ABS. So long as the pulse pressure is superimposed on the melt, the average apparent viscosity decreases sharply for both crystalline and amorphous polymers, and the decreases obtained at increased vibration pressure amplitude are bigger than are those obtained at increased vibration frequency. The changes in viscosities for the amorphous material, ABS, are smaller than the are values for the semicrystalline polymer, PP. The amounts of changes in the mechanical properties and rheology depend greatly on the melt temperature. Contact grant sponsor: National Natural Science Funds of China; contract grant number: 54473053; Contact grant sponsor: Special Fund for Major State Basic Research Projects of China; contract grant number: G1999064809.

The relationship between mechanical properties and morphology of vibration‐injection‐molded polyethylene

AbstractThis paper introduces a novel melt vibration‐injection molding. The effect of mid‐frequency melt vibration on mechanical properties was introduced, and SEM, WAXD and DSC investigations had been employed to provide evidence for explaining the relationship between mechanical properties and morphology of vibration‐injection‐molded specimens. The results show that the effect of vibration frequency is very different from that of vibration pressure amplitude. At a given vibration pressure amplitude, the increase of vibration frequency is beneficial for obtaining preferential orientation, more perfect lamellae and enhanced mechanical properties. For a given vibration frequency, increase of vibration pressure amplitude is a pre‐requisite for the achievement of a large‐scale lamella, more pronounced orientation, increase of cyrstallinity and high strength of high‐density polyethylene, but part of the toughness is lost. Copyright © 2004 Society of Chemical Industry

Structure and properties of polyethylene prepared via low‐frequency vibration‐assisted injection molding

AbstractA self‐made low‐frequency vibration‐assisted injection‐molding (VAIM) device was adopted to explore the relationship between mechanical property and morphology for high‐density polyethylene injected moldings. The main processing variables for the VAIM are vibration frequency and vibration pressure amplitude, and tensile properties and morphology were investigated under different VAIM processing conditions with conventional injection molding for comparison. The moldings prepared by VAIM exhibit a very well defined laminated morphology composed of a layered structure with enhanced crystallinity. Increased with vibration frequency at constant vibration pressure amplitude, the shish‐kebab structure is exhibited in the shear layer of the specimen prepared by VAIM, whereas row nucleation lamella exists in the same layer produced by enhanced vibration pressure amplitude at a constant vibration frequency. These oriented structures and enhanced crystallinity, confirmed by scanning electron microscopy, wide‐angle X‐ray diffraction, and differential scanning calorimetry, serve to obtain stronger injection moldings. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 13–21, 2005

On Microwave-Induced Hearing Sensation

When a human subject is exposed to pulsed microwave radiation, an audible sound occurs which appears to originate from within or immediately behind the head. Laboratory studies have also indicated that evoked auditory activities may be recorded from cats, chinchillas, and guinea pigs. Using a spherical model of the head, this paper analyzes a process by which microwave energy may cause the observed effect. The problem is formulated in terms of thermoelasticity theory in which the absorbed microwave energy represents the volume heat source which depends on both space and time. The inhomogeneous thermoplastic motion equation is solved for the acoustic wave parameters under stress-free surface conditions using boundary value technique and Duhamel's theorem. Numerical results show that the predicted frequencies of vibration and threshold pressure amplitude agree reasonably well with experimental findings.

A study of surging in fan or compressor systems

An analytical study is presented which explains the cause of one type of surging in a system connected to a fan or compressor. Surging occurs in an unstable region in which the fan pressure rises with an increase in capacity. Surging does not occur in a stable region in which the fan pressure decreases with an increase in capacity. The ratio of vibration pressure amplitude to particle velocity is greater in the unstable region than in the stable region. At critical conditions the pressure wave is in phase with the velocity wave. For a given particle velocity, the pressure amplitude in the unstable region is greater than the pressure amplitude in the stable region. A criterion for no surging is given.