Injection-molded Nylon Research Articles

Comparison of the bending fatigue performances of selective laser sintered and injection moulded nylon spur gears

This study compares the bending fatigue performance of a selective laser sintered Nylon 12 spur gear with an injection moulded Nylon 66 gear. Test gears were subjected to load-controlled, single tooth bending fatigue tests in a custom-built test setup. Cyclic pulsating loads were applied on the test gear using a steel driver gear. The bending fatigue life of selective laser sintered gears was superior compared to the injection moulded gears. In the high cycle fatigue region, the difference between the fatigue life of selective laser sintered and injection moulded gears was higher, whereas it was lower in the low cycle fatigue region. The variation in the fatigue strength of the selective laser sintered gears was due to the different thermal behaviour at low cycle fatigue and high cycle fatigue regimes. The lower surface temperature caused the higher fatigue strength of the selective laser sintered gears in the high cycle fatigue regime. On the contrary, the selective laser sintered gears’ surface temperature was higher than injection moulded gear in the low cycle fatigue regime, which reduced fatigue strength. The crack path was tortuous in selective laser sintered gears and smoother in injection moulded gears. In selective laser sintered gears, the layered structure of the part aided in impeding the propagation of crack.

No effect of cycling shoe sole stiffness on sprint performance

Most competitive and recreational road cyclists use stiff-soled shoes designed for cycling and ‘clipless’ pedals that firmly attach to the shoes. There are many unsubstantiated claims by cyclists and industry professionals about the advantages of cycling shoes and clipless pedals. Scientific research has shown that cycling shoes and clipless pedals have no significant effects on the metabolic cost of cycling during submaximal, steady-state efforts. However, a recent study demonstrated that, compared to running shoes, cycling shoes and clipless pedals do provide performance benefits relevant to sprint cycling. Here, we investigated if there was a positive relationship between longitudinal bending stiffness of cycling shoe soles and sprint performance. We measured the mechanical power outputs, velocities, and cadences of 19 healthy male recreational/competitive cyclists during maximal sprint cycling. All participants rode outdoors on a paved asphalt road with a steady, uphill grade of 4.9%. Each subject completed a total of nine 50 m cycling sprints in three (single-blinded) shoe conditions (each condition was replicated three times): identical shoe uppers with injection moulded nylon soles, carbon fibre-fibreglass blend soles, and full carbon fibre soles. The same clipless pedals were used throughout all tests. No significant differences were detected between the three shoe soles for: 50 m average and peak 1-second power, average change and peak change in velocity, average and peak cadence, maximal sprint velocity, peak acceleration, and peak crank torque (all p > 0.31). Greater longitudinal bending stiffness of cycling shoe soles had no effect on sprint performance during short uphill sprints.

Comparative evaluation of three types of denture base materials with saliva substitute before and after thermocycling: An in vitro study

Statement of problemXerostomia refers to the decrease in the quality and quantity of saliva. In denture wearers, xerostomia affects the retention of the denture because of lack of wettability of the denture base. However, which denture base resin materials are best wetted by artificial salivary substitutes is unclear. PurposeThe purpose of this in vitro study was to determine the wetting properties of 3 different commercially available denture base resin materials with artificial salivary substitute by using contact angle measurements and to compare these properties before and after thermocycling. Material and methodsA total 120 specimens were fabricated with 3 different denture base materials (n=40): heat-polymerized polymethylmethacrylate (DenTek), injection-molded nylon polyamide (Valplast), and microwave polymerized (VIPI WAVE). The advancing and receding contact angles were measured with a goniometer by using the WinDrop++ software program. The contact angle hysteresis was calculated from the advancing and receding contact angles values. The same specimens were subjected to thermocycling to measure the advancing and receding contact angles values. The comparative evaluation was carried out before and after thermocycling. ResultsThe mean ±standard deviation contact angles of the microwave-polymerized material were (62.40 ±1.21 degrees) advancing contact angle, (32.12 ±0.66 degrees) receding contact angle, and (30.28 ±1.40 degrees) contact angle of hysteresis. It was followed by the injection-molded nylon polyamide material, whose mean ±standard deviation contact angle values were (68.57 ±1.72 degrees) advancing contact angle, (43.02 ±1.39 degrees) receding contact angle, (26.27 ±2.05 degrees) contact angle hysteresis and high impact strength heat-polymerized polymethylmethacrylate material, whose mean ±standard deviation contact angle values were (69.81 ±0.16 degrees) advancing contact angle, (41.90 ±1.02 degrees) receding contact angle, and (27.91 ±0.97 degrees) contact angle hysteresis. The statistical analysis showed significant differences among contact angle values of the microwave-polymerized material as compared with the heat-polymerized polymethylmethacrylate and injection-molded nylon polyamide materials (P<.001). ConclusionsThe microwave-polymerized material showed better wettability with artificial saliva substitute than heat-polymerized polymethylmethacrylate and injection-molded nylon polyamide.

A physical investigation of wear and thermal characteristics of 3D printed nylon spur gears

Abstract The use of 3D printing to manufacture nylon polymer gears is evaluated in this paper. More specifically, Nylon spur gears were 3D printed using Nylon 618, Nylon 645, alloy 910 filaments, together with Onyx and Markforged nylon proprietary materials, with wear rate tests performed on a custom-built gear wear test rig. The results showed that Nylon 618 provided the best wear performance among the 5 different 3D printing materials tested. It is hypothesised that the different mechanical performance between nylon filaments was caused by differences in crystallinity and uniqueness of the Fused Deposition Modelling (FDM) process. SEM (Scanning Electron Microscopy) revealed dramatically different wear behaviour for the 3D printed gears when compared to literature reports of injection moulded gears. Monitoring with a thermal camera during wear tests was used to analyse the thermal performance of gears during wear tests and together with SEM was used to analyse gear failure mechanisms. The performance results showed that gears 3D printed using Nylon 618 actually performed better than injection moulded nylon 66 gears when low to medium torque was applied.

Influence of Adhesive on Shear Bond Strength Between Denture Base Materials and Self-Cured Silicon Soft Liner

Background: Soft lining materials play an important role in modern prosthodontics because of their capability of restoring health of inflamed and distorted mucosa. Gradual changes of oral tissues require that complete or partial dentures be relined to improve their adaptation to the supporting tissue. This study aimed to evaluate the shear bond strength (SBS) of heat cured acrylic and injection-molded ValplastTM denture base materials to silicone self-cure soft lining materials, with and without adhesive, after storage in two different times in artificial saliva. Materials and Methods: 40 rectangularspecimens were prepared from two types of self-cured silicone soft lining material,one with adhesive and the other without adhesive were applied to two types of denture base materials ( heat polymerized Polymethyl methacrylate and injection-molded nylon denture base materials). Shear bond strength of the specimens was measured, after immersionin artificial saliva for different periods (72 hours or 10 weeks), using Lloyd universal testing machine. Results: Acrylic denture base bonded to soft liner with adhesive at 72 hours of immersion in artificial saliva showed the highest shear bond strength. Comparing SBS values of the tested soft lining materials revealed significant differences between adhesively bonded and non-adhesively bonded types. Conclusions: This study concluded that the bond strength of the silicone soft lining materials with denture base materials increased with adhesive. Silicone soft lining materials are affected by artificial saliva storage.

English

Effects of e-beam irradiation at different doses upto 600 kGy on injection moulded nylon 66 specimens have been investigated by solution viscosity measurement and Fourier Transform Infrared (FTIR) spectroscopy. The results of gel content and viscosity indicate that e-beam irradiation generates crosslinked structure among the polymer chains. The uncrosslinked sol portion of the irradiated nylon 66 was also affected and resulted in a decrease in chain length as reflected in the results obtained from viscosity measurement. From FTIR spectra analysis, it was found that crystallinity of nylon 66 was considerably affected upon e-beam irradiation. The decrease of N-H stretch absorbance value of irradiated nylon 66 in comparison to the pristine nylon 66, indicates the loss of hydrogen bonding due to irradiation which resulted in decrease in crystallinity

Evaluation of the tensile bond strengths of heat cure acrylic and Valplast with silicone self cure soft liner

Soft lining materials have a key role in modern prosthodontics because of their capability of restoring health of inflamed and distorted mucosa. Gradual changes of oral tissues require that complete or partial dentures be relined to improve their adaptation to the supporting tissue. This study aimed to evaluate the tensile bond strength of heat cure acrylic and Valplast denture base materials to silicone self-cure soft lining material stored in artificial saliva. Materials and method: Two types of self cured silicone soft lining material (one with prime the other without prime or adhesive) applied to polymethylmet hacrylate and injection-molded nylon denture base materials for tensile bond strength testing using Instron machine. Results: The comparison between all test groups after (48) hours immersion in artificial saliva were highly significantly different from each other except for the comparison between groups PSP and VSP in which their means were non-significant. After (12) weeks, the comparison between all test groups were highly significantly different from each other when compared statistically. Conclusion: This study indicated that prime (adhesive) increase the bond strength of the silicone soft lining materials

Effect of hygrothermal ageing on morphology and indentation modulus of injection moulded nylon 6/organoclay nanocomposites

The effect of water immersion on the morphology and indentation modulus of injection moulded nylon 6 and its organoclay nanocomposites was investigated. XRD analysis showed that at 70 °C water promoted further crystallization in the nylon matrix and aided the γ- to α-crystal phase transition in the skin region. However, the presence of organoclay deterred this transformation. The combined actions of water and heat (70 °C) did not further degrade nylon 6 and its nanocomposites compared to water ageing at room temperature (25 °C). In fact, there was relative enhancement of the indentation moduli owing to the beneficial morphological changes induced in the nylon matrix. The largest improvements were found in the skin region of the injection moulded bars.

Structure and properties of polyimide-bonded magnets processed from prepolymers based on diacetyl derivatives of aromatic diamines and dianhydrides

We report a novel method of polyimide (PI) synthesis from prepolymers based on dianhydrides and diacetyl derivatives of aromatic diamines that facilitate the preparation of a melt processable mixture at 300 ± 10°C of the prepolymer and magnetic Nd-Fe-B alloy to provide PI-bonded magnets with enhanced properties. It is shown that chemical structure of the prepolymers strongly influences viscosity behavior via crystallization of the oligoimide in the melt, leading to formation of PI with rigid-rod like structure. This structural ordering of the prepolymers based on diacetyl derivative of diamine used in this study, if not controlled, leads to exponential increase of melt viscosity with time, making it practically impossible to prepare melt processable mixture of the magnetic particles and the PI prepolymers at elevated temperatures. The results obtained demonstrate that appropriate dianhydrides and diacetyl derivatives of diamines that do not lead to crystallization of oligoimides in prepolymer mixture can be used under controlled processing conditions to prepare melt-processable PI-bonded magnets containing rigid-rod like PI structure that significantly increases thermal stability of the magnets. The temperature dependencies of the magnetic properties of the PI-bonded magnets under conditions that they are likely to encounter during their service life were found to be remarkably similar to that of commercial thermoplastic magnets such as injection-molded nylon magnets. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 478–485, 2006

Structural hierarchy developed in injection molding of nylon 6/clay/carbon black nanocomposites

The influence of platelet-type clay nanoparticle (nanoplatelet) on the structural evolution in injection-molded nylon 6)/carbon composites was investigated. In the absence of nanoplatelets, the nylon 6/CB systems were found to exhibit unoriented structure with nylon 6 crystalline regions exhibiting exclusively α crystal form throughout the thickness of the samples. However, inclusion of nanoplatelets induces substantial local orientation of the nylon 6 chains in the molded parts in all processing conditions and compositions. In these clay/nylon 6/CB ternary nano systems, nylon 6 matrix was found to be exclusively in γ crystal form at the skin regions and α crystal form fraction increases towards the core of the molded parts as a result of decrease in cooling rate with depth during the solidification stage. Two nanoplatelet orientation behaviors were identified: (i) in the absence of irregular shaped CB, the nanoplatelets align parallel with one another following the local flow patterns. The latter behavior also causes enhanced orientation of the nylon 6 chains undergoing substantial shear amplification trapped in between the nanoplatelets (ii) in the CB-enriched regions, nanoplatelets though still remaining parallel to one another, are randomized by following the local contours of irregular shaped CB aggregates. These CB aggregates themselves were found to organize to form trains in larger scale as a result of flow alignment.

Wear characteristics of injection-moulded unfilled and glass-filled nylon 6 spur gears

The tribological behaviour of polymer and polymer composite gears is reported in this paper. Gear tests were conducted using a power absorption-type gear test rig. Injection-moulded nylon 6 and glass-filled nylon 6 gears were tested at different speeds and loads. Gear rotational speed influences the tooth wear of unfilled and glass-filled nylon 6 injection-moulded gears due to the change in contact period of teeth in mesh. When the polymer-based gear drives a steel gear, the difference in the elastic moduli of the mating materials causes rotational lag during gear running. When the polymer gears transmit a higher torque, a higher amount of rotational lag causes an excessive wear in the dedendum region of the polymer gear. In the cases of both unfilled and glass-filled nylon 6 gears, at higher-torque test conditions, non-uniform wear on the gear tooth surface was observed. Glass-filled nylon 6 gears showed a better wear resistance than the unfilled nylon 6 gears due to the improved compressive strength, creep resistance, and elastic modulus. A detailed wear particle analysis was carried out to understand the gear wear mechanism. The contact stress and gear material hardness affect the gear wear mechanism.

Effects of Moisture Conditioning Methods on Mechanical Properties of Injection Molded Nylon 6

The influence of various standard (ASTM, ISO) and experimental moisture conditioning methods on mechanical performance of injection molded nylon 6 is discussed as a result of an in-depth, comprehensive investigation. These methods covered a wide range for two basic process parameters for conditioning: temperature (from 23 to 100 C) and relative humidity (from 50% RH to water immersion). The variation of these parameters may result in significantly different moisture absorption rates, equilibrium levels and mechanical properties. The kinetics of mechanical performance and microstructure were evaluated prior to tests and during conditioning in this comprehensive analysis. The results from this investigation may provide comprehensive, up-to-date information and recommendations concerning accelerated nylon conditioning methods for test specimens and various molded parts, preselection of nylon based plastic for design, and prediction and optimization of mechanical performance.

Superstructural hierarchy developed in coupled high shear/high thermal gradient conditions of injection molding in nylon 6 nanocomposites

The spatial variation of the superstructure developed along and across the flow direction of injection-molded nylon 6 and its nanocomposites are presented using transmission polarized optical photomicrographs and micro-small-angle laser light scattering (SALS). At low mold temperature, 50 °C, the structure of unfilled nylon 6 is made up of steep structural gradient containing oriented threads at the surface surrounding undeformed spherulites in the interior. In nanocomposite samples, on the other hand, the development of complete spherulites is interrupted by high nucleation density caused by the presence of nanoparticles and shear amplification that occurs in small spaces between these particles. The latter phenomenon was found to be prevalent even at high mold temperatures where the cooling rates are greatly suppressed. In the structure gradient, polymer/nanocomposite samples show double shear regions near the surface surrounding the core regions that contain sheaves. The origin of complex superimposed SALS patterns is explained in terms of the short and long-range spatial correlations of these preferentially oriented sheaves and their optic axes.

Study of mouldability in gas-assisted injection moulded fibre-reinforced Nylon parts

Investigation of the characteristics of gas penetration in gas-assisted injection moulding (GAIM) of parts plays an important role in the successful application of gas-assisted injection moulding. Although these have been proposed by various investigators, quantitative rules based on well designed experiments on fibre-reinforced plastic materials have not been reported previously. Additions of glass-fibre bring about rather dramatic changes in material viscosity and heat conductivity, etc. In the present paper, spiral tube moulds with uniform diameters of 8 and 10 mm, respectively, and a plate mould of 3 mm thickness with gas channel design of semicircular crosssection were moulded using glass-fibre reinforced Nylon resin. The effects of fibre content, tube diameter, and processing parameters, including gas pressure, delay time, and injection stroke on gas penetration characteristics and mouldability for fibre-reinforced Nylon parts were investigated experimentally. It was found that the coating melt thickness decreases with increasing gas pressure, until the gas pressure reaches a critical value, when the coating melt thickness becomes relatively constant for the spiral tube. Meanwhile, using a longer delay time for gas injection will increase the skin melt thickness. The hollowed core ratio increases with increasing diameter of spiral tube. Alternatively, the hollowed core ratio of GAIM plate and spiral tube parts increases when the content of glass-fibre is increased. However, when the fibre content is over 10 wt-%, it shows less influence on the hollowed core ratio for plate parts. Furthermore, although the area of the moulding window decreases with increasing content of fibre, they all show good mouldability. From these results, one can provide an empirical formula to CAE simulation designers and part/mould designers for GAIM fibre-reinforced Nylon parts to achieve suitable mouldability and accurate CAE simulation.

Amplification effect of platelet type nanoparticles on the orientation behavior of injection molded nylon 6 composites

The effect of platelet type nanoparticles and processing conditions; mold temperature and injection speed, on the development of local microstructure in injection molded nylon 6 parts was investigated. The molded parts exhibit two crystal forms (α and γ) of nylon 6 in varying proportions from skin to core. The γ crystals preferentially grow near the surface regions and α crystal fraction increases with distance from the surface in all molded parts. However, the spatial variation of crystal phases across the thickness in nanocomposites differs from that of unfilled nylon 6. Nanoplatelets induce high levels of orientation of the polymer matrix throughout the thickness of the molded part even at high mold temperatures where nonisothermal effects are highly suppressed and confined to very close proximity of surfaces. These high chain orientation levels observed in nanoparticle filled systems is a result of the shear amplification effect that occurs in small spaces between adjacent nanoparticles of differing velocity. The local preferential crystalline orientation of nylon 6 resin and nanoparticles across the thickness of the molded parts are investigated using a series of structure characterization techniques including microbeam wide angle X-ray, SAXS and TEM.

Optimizing the Mechanical Performance in Semi-Crystalline Polymers: Roles of Melt Temperature and Skin-Core Crystalline Morphology of Nylon

Crystalline texture and mechanical (tensile and flexural) properties of injection molded nylon 6 were evaluated to understand the influence of one of the key-processing variable, the melt temperature ( Tmlt). We find that mechanical properties are sensitive to Tmlt only below ∼250°C. Rapid quenching of the surface produces a skin with lower crystallinity than the core, which cools more slowly; this difference in the rate of cooling produces γ crystalline form in the skin and α crystalline form in the core. Higher tensile strength at yield, lower elongation at break and higher flexural strength were observed in specimens molded at lower Tmlt. These characteristics are associated with thicker and less ordered skin, and a lower crystallinity core. The role of the Tmlt on micro-structure and mechanical properties of injection molded nylon 6, the development of skin and core morphologies, and the role of the residual stresses in the core are discussed.

Effect of melt temperature and skin‐core morphology on the mechanical performance of nylon 6

AbstractThe crystalline texture and mechanical (tensile and flexural) properties of injection molded nylon 6 were evaluated to understand the influence of the melt temperature (Tmlt), one of the key‐processing variables. The mechanical properties are found to be sensitive to Tmlt only below ∼ 250°C. Rapid quenching of the surface produces a skin with lower crystallinity than the core, which cools more slowly; because of this difference in the rate of cooling, the crystalline component in the skin is rich in γ and that in the core is rich in α. The thickness of this skin decreases from about 1.25 mm to 0.75 mm as Tmlt increases from 225°C to 310°C. Higher tensile strength at yield, lower elongation at break and higher flexural strength were observed in specimens molded at lower Tmlt. These characteristics are associated with thicker and less ordered skin, and a lower crystallinity core. The role of the Tmlt, on microstructure and mechanical properties of injection molded nylon 6, the development of skin‐core morphology, and the role of the residual stresses in the core are discussed.

The occurrence of surface roughness in gas assist injection molded nylon composites

AbstractGas assist injection molding has increasingly become an important industrial process because of its tremendous flexibility in the design and manufacture of plastic parts. However, there are some unsolved problems that limit the overall success of this technique. The purpose of this report was to study the surface roughness phenomenon occurring in gas assist injection molded thermoplastic composities. The materials used were 15 % and 35% glass‐fiber filled nylon‐6 composites. Experiments were carried out on an 80‐ton injection molding machine equipped with a high‐pressure nitrogen‐gas injection unit. Two “float‐shape” axisymmetric cavities were used. After molding, the surface quality of molded parts was measured by a roughness meter. Various processing variables were studied in terms of their influence on formation of surface roughness: melt temperature, mold temperature, melt filling speed, short‐shot size, gas pressure, and gas injection delay time. Scanning electronic microscopy was also employed to characterize the composites. It was found that the surface roughness results mainly from the exposure of glass fiber in the matrix. The jetting and irregular flows of the polymer melt during the filling process might be factors causing the fiber exposure.

Comparative Fatigue Resistance of Fiber Reinforced Nylon 6 Gears

The fatigue-life diagrams of injection-molded nylon 6 gears with different reinforcements are shown for various lubrication modes (dry, grease, splash oil lubrication) and for different meshing combinations (plastic/plastic and steel/plastic gears). Tests using a suitably designed back-to-back rig have been carried out, and the results compared with previous experiments, performed using unreinforced nylon 6 gears. 232 gears (70 in unreinforced and 162 in differently filled nylon) were tested. More than 700 · 106 cycles have been totalled. From test data, and from the “matrix” of the gear/pinion material combination, the capabilities of differently reinforced nylon 6 gears in terms of fatigue and wear resistance have been outlined. These capabilities are the basis for a proper material selection in plastic gear design.

Effect of moisture and orientation on the fracture of nylon 6,6 fibers

AbstractThe effect of relative humidity on the fracture of single nylon 6,6 fibers is determined using fracture mechanics. The fracture energy release rate, GIc, of these fibers is shown to be 8× that for injection‐molded nylon 6,6 at 0% RH. GIc varies from 31.3 kJ/m2 at 0% RH to 15.6 kJ/m2 at 100% RH. The dependence of GIc on RH is in agreement with previous studies indicating two types of water in nylon: a tightly bound and a loosely bound type. In addition, GIc is shown to be 10× greater for transverse fiber breaks than for axial splitting of the fiber due to the high degree of orientation in these fibers. These studies are the first of their kind for organic fibers. © 1994 John Wiley &amp; Sons, Inc.