Cross-thickness vibration welding of polycarbonate,polyetherimide, poly(butylene terephthalate), and modified polyphenylene oxide

In vibration welding of thermoplastics, frictional heat generated by vibrating two parts under pressure, along their common interface, is used to effect welds. In the normal, well-understood mode, the vibratory motion is along the weld seam, which is at right angles to the thickness direction for straight boundaries. But in many applications, such as in the welding of closed seams of box-like parts, this vibratory motion occurs in the part-thickness direction, so that a portion of the molten layer along the seam is exposed to the ambient air during each vibratory cycle. The resulting reduction in temperature can affect weld quality. The process phenomenology and the weld strengths of such cross-thickness vibration-welded butt joints are investigated for four neat resins. Weld amplitudes and weld pressures are shown to affect the strengths of 120-Hz welds differently. It is shown that strengths on the order of the strengths of the neat resins can be achieved in 250-Hz butt welds.     

Compressional effects in the capillary flow of polycarbonate

Recently, the characteristics for pressure corrections in capillary flow have been detailed. The apparent viscosity increases with increasing capillary shear rate for polystyrene and for poly(methyl methacrylate) have been previously explained using free volume theory. These general methods have been developed further in this work and applied to the non-Newtonian flow of a new system, the polycarbonate of bisphenol A. The pressure correction for up to 2 kilobars will be shown to linearize the capillary pressure drop versus the parameter L/D, capillary length over diameter. This correction eliminates the viscosity difference due to variations in L/D ratio. It is also observed that the zero-shear viscosity obtained by the extrapolation of the corrected capillary flow curves agrees well with new and independent data on the same polycarbonate obtained using a Weissenberg rheogoniometer. The flow data have been compared with theories and with earlier published data on the same polymer. The two sets of data are not concordant. These new and corrected shear-dependent data are, however, shown to be expressed qualitatively by the theory of Graessley, using the most probable molecular weight distribution.     

Process data acquisition in vibration welding of thermoplastics

A measuring method is presented for process monitoring and process analysis of linear vibration welding of thermoplastics. The method works by recording and evaluating time-dependent signals that describe the process—such as the frequency-dependent signals of the displacement of the two parts being joined, the tangential force in the welding plane—and the nonperiodic signals of the welding process, i.e. the normal force in the welding plane and the melting or joining displacement of the parts being joined. It is possible to determine the energy input into the welding zone as a function of the selected machine parameters and the process sequence over time.     

The vibration welding of polycarbonate/acrylonitrile‐butadiene‐styrene blends to themselves and to other resins and blends

The weldabilities of two commercial blends of polycarbonate (PC) and acrylonitrile‐butadiene‐styrene (ABS) to themselves and to several other resins and blends are assessed through 120 Hz vibration welds of 6.35‐ and 3.2‐mm‐thick specimens. While the thicker specimens of both blends have relative weld strengths of 83%, the thinner specimens in one of the grades have a lower relative weld strength of 73%. Welds of thicker specimens of both grades to PC have relative strengths of 85%. Again, welds of thinner specimens of one of the grades to PC have a lower relative strengths of 68%. Welds of the thinner specimens of this grade with ABS have relative strengths of 85%. Welds of this material with poly(butylene terephthalate) (PBT), a PC/PBT blend, modified poly(phenylene oxide), and a poly(phenylene oxide)/polyamide blend, have relative weld strengths of 45%, 26%, 76%, and 20%, respectively.     

The hot-tool and vibration welding of acrylonitrile-butadiene-styrene

Thermoplastic window frames are made by hot-tool welding mitered, extruded profiles. The effects of weld process conditions on the strengths of hot-tool butt joints are investigated for a grade of acrylonitrile-butadiene-styrene that was specially developed for window-frame applications. Vibration-weld strength data, obtained on a research machine in which all the process variables can be independently controlled, are used to benchmark strengths of hot-tool welds made on a commercial welding machine. Process differences between hot-tool butt welding and the hot-tool welding of mitered, extruded profiles are discussed.     

Estimates for process conditions during the vibration welding of thermoplastics

The aim of this work is to interpret experimental findings of Stokes and Schlarb on the basis of analytical formulas and finite element calculations. In the analytical approach, some simplifications that had to be made proved to be inappropriate. Only computer calculations may reveal the details of the processes involved in vibration welding. Comparison of the computer calculations with the experiments reveals that even transient effects in viscosity have to be considered. Viscosity is dependent not only on temperature and shear rate, but also on the frequency or amplitude of vibration. After correction for these effects, the correlation between theory and experiments proved to be excellent. Based on the calculations, some recommendations are presented to improve weld quality, as ascertained by the type of fracture in a tensile test, by changing the welding parameters.     

Effects of vibration blending on the subsequent crystallization behavior of polycarbonate/polypropylene blends

The effects of blending in a novel vibration internal mixer on the subsequent multiple crystallization of 70/30 w/w polycarbonate (PC)/polypropylene (PP) were investigated by differential scanning calorimetry, wide‐angle X‐ray diffractogram, and microscopy. The vibration internal mixer was reformed from a conventional internal mixer through parallel superposition of an oscillatory shear on a steady shear. For this polypropylene‐minor phase blend, three possible crystallization peaks were observed. The crystallization behavior was sensitive to the sizes and the size distribution of the dispersed polypropylene droplets. Larger amplitude and/or higher‐frequency vibration produced more small droplets (<2 μm) and increased the number of medium droplets (2–8 μm) as a result of the spatially wider and temporally quicker variation of shear rate. The resulting subsequent low‐temperature crystallization peak became larger and shifted to lower temperature, and the intermediate‐temperature peak became obvious. On the contrary, the coalescence of small droplets, resulting from the heating treatment, weakened the low‐temperature peak but strengthened the intermediate‐temperature peak and rendered the high‐temperature peak to be wider. Mixing at the too high amplitude produced the unstable, partially cocontinuous phase morphology restricting the medium droplets and enlarging the surface area, such that the intermediate‐temperature crystallization peak did not appear. Multiple crystallization was related to phase morphology and the nucleation density as well as surface effects. Double‐fusion endotherms of the PP component were also observed, corresponding to the melting of different forms of polypropylene crystals. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 92–103, 2002     

Experimental study on gap bridging in contour laser transmission welding of polycarbonate and polyamide

Laser transmission welding (LTW) is a technique for joining thermoplastics. During contour LTW, any gaps or spaces between the two parts along the weld seam may prevent a weld from forming. This work presents an experimental study on the effects of material property (carbon black level, glass fibers, and crystallinity), process parameters (laser scan power and scan speed), and weld gap thickness on the strength and microstructure of contour welds made of polycarbonate (PC), polyamide 6 (PA6), and PA6 reinforced with 30% glass fiber. Lap specimens, with weld lines parallel to the load direction during mechanical testing, were used to assess the weld shear strength. The results indicated that low concentrations of laser absorbing pigment accompanied by high laser power improve gap bridging. The study also indicated that a novel noncontact test method can be used to search for the optimized process parameters for gap bridging. The maximum gaps bridged were 0.2, 0.4, and 0.25 mm for PC, PA6, and reinforced polyamide 6, respectively. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Vibration welding of thermoplastics. Part III: Strength of polycarbonate butt welds

In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time or weld penetration; The effects of these parameters on weld quality were systematically studied by first butt-welding polycarbonate specimens under controlled conditions over a wide range of process parameters, and by then determining the strengths and ductilities of these welds by tensile tests, A significant result is the apparent existence of a weld-penetration threshold above which high weld strengths are attained, but below which the strength drops off. Under the right conditions, the strengths of polycarbonate butt welds are shown to equal the strength of the virgin polymer.     

Comparison of orbital and linear vibration welding of thermoplastics

This work was conducted to determine if there were any benefits with orbital vibration welding compared to linear vibration welding. The experiments were conducted using standard full‐factorial designs with each process and each material. Four materials, polypropylene/polyethylene copolymer (PP/PE), polycarbonate (PC), acrylonitrile‐butadiene‐styrene (ABS) and Nylon (PA), were studied with each process. The equipment used was a modified Branson VW‐4 with an orbital head that had isolated magnets. The same machine was used to weld with both linear and orbital motions. This was achieved by modifying the controlling parameters of the drive. It was found that compared to linear vibration welding, orbital welding had a reduction of cycle time by 36% and 50% in Phase I and Phase III, respectively. It was also found that orbital welding dissipated 56% and 100% more power than linear vibration welding in Phase I and Phase III, respectively. In addition, it was seen that orbital welding was able to universally join unsupported walls with higher strengths and better consistency compared to linear welding. Other benefits included: a difference in the appearance of weld flash and small increase in weld strength. Some of the limitations of orbital welding that were identified included the effects of disengagement and residual stresses. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Pulmonary effects of combustion products from nickel-coated polycarbonate

The pulmonary effects of acute (30 min) and chronic (7, 14, or 21 days; 30 min day⁻¹) exposure to smoke from white polycarbonate structural foam, or a Ni-urethane coated version of this plastic, were analyzed by exposing groups of 4 mice in a dome chamber apparatus. The lungs of test fatalities were consistently inflamed and hemorrhagic, and characterized histologically by areas of atelectasis and hyperinflation. The Ni-coated material was more toxic than the uncoated material, and produced greater intrapulmonic hemorrhage. A histological method was developed for assessing the proliferation of type II pneumocytes as an index of damage to the alveolar epithelium. Examination of lungs from animals sacrificed at 2, 4, 8, 14, 21, or 28 days following acute exposure revealed that only the 8-day animals in the Ni-exposure group had significantly more type II pneumocytes than controls (P<0.01). Similar examination of lungs from chronically exposed animals sacrificed at 1 day following the last exposure revealed no significant differences between experimental animals and controls. The Ni content of coated samples and the ash following thermal decomposition was determined by atomic absorption spectrophotometry. The original samples were 2.5% Ni. Nickel lost during pyrolysis could account for the increased toxicity of the coated material through production of toxic Ni compounds. These results indicate that pulmonary irritants produced by these plastics affect the vascular elements of the lungs more than the alveolar epithelium, and that the pulmonary damage produced in mice under these conditions does not persist in survivors beyond 1 day post-exposure. The acute combustion toxicity of Ni-coated plastics may reflect the formation of toxic Ni compounds. © 1997 John Wiley & Sons, Ltd.     

Diluent effects on carbonate mobility in bisphenol-A polycarbonate in the solid state

The effect of miscible low molecular weight additives on the mobility of the carbonate group in bisphenol-A polycarbonate (BPAPC) has been studied using n.m.r. and dielectric relaxation experiments in the solid state. Proton-enhanced dipolar-decoupled carbon-13 n.m.r. spectra of BPAPC, isotopically enriched at the carbonate position, are obtained without magic-angle sample spinning. The resolved chemical shift anisotropy allows study of nuclear spin relaxation for the carbonate groups in the polymer that have different orientations relative to the static magnetic field in the laboratory frame. The spin-lattice relaxation time in the rotating frame (T_1?) is measured at a motional-probe frequency of 50 kHz for the undiluted polymer and for BPAPC-diluent blends containing either dibutylphthalate or dinitrobiphenyl. The T_1? exhibits some dependence on orientation in all systems studied. In the blend containing dibutylphthalate (DBP), T_1? is decreased by a factor of two for all orientations of the carbonate group. This implies that DBP substantially increases the spectral density of 50 kHz motions in the carbonate region of the polymer at ambient temperature. In contrast, dinitrobiphenyl does not significantly alter the Fourier component of thermal fluctuations at 50 kHz. Dielectric relaxation measurements at 10 kHz reveal that the primary (T_g) and secondary (β) motional processes in BPAPC are affected by low molecular weight additives. An intermediate relaxation process appears in the temperature interval between the glass transition temperature (T_g) and the sub-T_g β-relaxation (T_β) in the polymer-diluent blends. The n.m.r. spin-lattice relaxation rate in the rotating frame, T^?1_1?, correlates well with the relative magnitude of the dielectric dissipation factor (tan δ_ε) between T_g and T_β.     

The effects of stress cracking on the fracture toughness of polycarbonate

The growth of crazes from a sharp crack in extruded polycarbonate sheets immersed in ethanol was measured. Below a critical level of the stress intensity factor craze growth was controlled by solvent diffusion through the end of the notch and fracture was prevented by craze arrest. Above a critical level, growth was controlled by either end diffusion or a combination of end diffusion and diffusion through the faces of the extruded sheet, and in both cases the final result was brittle fracture. The effects of annealing and quenching was studied at various sheet thicknesses. In thin specimens annealing and/or quenching had a significant effect on crack growth rate, which was predictable in terms of the state of stress. As the specimen thickness increased, causing a transition from plane stress to plane strain conditions, the previous thermal history had a diminishing effect on craze growth rate. The effects of thermal history and thickness on the fracture toughness of polycarbonate was also investigated. It was found that thickness was the more important variable and that at a ½ in. thickness the effects of thermal history were statistically insignificant. The effect of ethanol exposure on fracture toughness was studied. It was found that exposure to solvent initially caused an increase in k_IC with time to a maximum value, followed by a substantial decrease with time which eventually led to brittle fracture. This behavior was explained as a competition between plasticization of the crack tip and coalescence of crazes to form microcracks.     

The vibration welding of poly(methyl methacrylate) to itself and to polycarbonate,poly(butylene terephthalate), and modified poly(phenylene oxide)

The weldability of poly(methyl methacrylate) (PMMA) to itself and to polycarbonate (PC), poly(butylene terephthalate) (PBT), and modified poly(phenylene oxide) (M-PPO) is assessed through 120 and 250 Hz vibration welds. Weld strengths equal to those of the base resin have been demonstrated in welds of PMMA and M-PPO to themselves. In welds of PMMA to PC and to M-PPO, weld strengths equal to those of PC and M-PPO, respectively, have been demonstrated. PMMA does not weld well to PBT; the highest weld strength obtained was 21% of the strength of PBT resin.     

The vibration and hot‐tool welding of polyamides

The weldabilities of polyamide 6 (PA‐6), polyamide 6,6 (PA‐6,6), 33 wt% glass‐filled PA‐6,6 (33‐GF‐PA‐6,6), and amorphous polyamide (PA‐A) are assessed through 120 Hz vibration welds. Weld strengths equal to those of the base resins can easily be obtained in vibration welds of both undried and dried PA‐6 and PA‐6,6. Relative weld strengths in the range of 54–57% are demonstrated for 120 Hz welds of 33‐GF‐PA‐6.6. Relative weld strengths in the range of 90–97% are demonstrated for dried PA‐A. The highest relative weld strengths obtained in hot‐tool welds of undried and dried PA‐6,6 are only 57% and 54% respectively.     

The vibration welding of poly(butylene terephthalate) and a polycarbonate/poly(butylene terephthalate) blend to each other and to other resins and blends

Vibration welding is used to assess the weldability of poly(butylene terephthalate) (PBT) and a polycarbonate/poly(butylene terephthalate) blend (PC/PBT) to each other and to other resins and blends: PBT to PC/PBT, PBT to modified poly(phenylene oxide) (M-PPO), PBT to polyetherimide (PEI) and PEI to a 65 wt% mineral-filled polyester blend (65-PF-PEB), PBT to a poly(phenylene oxide)/polyamide blend (PPO/PA), PC/PBT to M-PPO, and PC/PBT to PPO/PA. Based on the tensile strength of the weaker of the two materials in each pair, the following relative weld strengths have been demonstrated: PBT to PC/PBT,98%; PBT to PEI, 95%; 65-PF-PEB to PEI, 92%; and PC/PBT to M-PPO, 73%. PBT neither welds to M-PPO nor to PPO/PA, and PC/PBT does not weld to PPO/PA.     

Notch sensitivity of polycarbonate and toughened polycarbonate

Notch sensitivity, the effect of a notch radius on the impact behavior of polycarbonate and rubber‐toughened polycarbonate, is investigated by using a model based on the slip‐lines field theory. Impact strength, determined by the Charpy impact test, was found to increase drastically with an increasing notch radius for pure polycarbonate, whereas the increase of impact strength with increased notch radius was not as extreme for rubber‐toughened polycarbonate. These results indicate that the inclusion of rubber particles reduces notch sensitivity. An examination of fracture surfaces reveals that cracks were initiated by internal crazing at some distance from the notch tip for specimens with blunt notches. For pure polycarbonate, the impact strength is found to have a linear relationship with the square of the notch radius, which is in good agreement with that predicted by the proposed model. However, for rubber‐toughened polycarbonate, the linear relationship broke down as the notch radius increased due to the enhanced toughening effect. The proposed model can be applied to clearly explain the notch sensitivity of ductile polymers which exhibit large plastic yielding around the notch tip. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3115–3121, 2003     

A simple analytical model for estimation of melt film variables in thermoplastic vibration welding

The strength of vibration welds of thermoplastics is governed by the weld zone microstructure, which in turn, is closely tied to the welding process variables, such as the thickness of the weld melt film and the temperature profiles therein. The mathematical model described in this report is aimed at describing the role of the rheology of the melt—specifically the magnitude and shear rate dependence of the melt viscosity—in governing the melt film variables during the steady state penetration phase (Phase III) of vibration welding. The steady state momentum balance and heat transfer within the melt film are solved by using the power law model for viscosity. Closed‐form analytical expressions are obtained for estimating the melt film thickness, the shear rates, and the temperature field within the film. This model has been used to estimate weld zone variables for four different polymers displaying a wide range of viscosities and shear thinning behaviors. POLYM. ENG. SCI., 54:499–511, 2014. © 2013 Society of Plastics Engineers