Original Article Replacement of metallic parts for polymer composite materials in motorcycle oil pumps Sandro Donnini Mancini, Antı́dio de Oliveira Santos Neto, Maria Odila Hilário Cioffi and Eduardo Carlos Bianchi Abstract A feasibility study was conducted to determine the use of polyphthalamide/glass-fiber and polyphthalamide/glass-fiber/ polytetrafluoroethylene-based composites as substitutes for aluminum and steel, respectively, in the production of motorcycle oil pump parts (housing, shaft/inner gerotor and outer gerotor). New and used (80,000 km) oil pumps were subjected to performance tests, whose results indicated that the pressure and temperature of the used pump reached a maximum of 1.8 bar and 93�C, respectively. Thermogravimetric analysis indicated that the materials are stable at the maximum operating temperature, which is 20�C lower than the minimum glass transition temperature obtained by dynamic mechanical analysis for both materials at the analyzed frequencies (defined after calculations based on rotations in neutral, medium and high gear). The pressure value was multiplied by a safety factor of at least 1.6 (i.e., 3 bar), which was used as input for a finite element analysis of the parts, as well as the elasticity modulus at glass transition tempera- tures obtained by dynamic mechanical analysis. The finite element analysis indicated that the von Mises stresses to which the composite parts were subjected are 7 to 50 times lower than those the materials can withstand. The results suggest that it is feasible to manufacture motorcycle oil pump parts with these composites. Keywords Materials replacement, polymer composite, polyphthalamide, glass-fiber, oil pump Introduction Industries use material replacement to lower costs by reducing the weight of vehicles, and polymer materials are widely employed for this purpose. Fiber-reinforced polymer composites are attractive alternatives, even for applications that traditionally use metallic materials,1–3 such as motorcycle oil pumps. The main function of oil pumps is to inject an ade- quate flow of oil into parts that need lubrication, according to design specifications.4–6 An oil pump usu- ally consists of a housing, rotors, shaft, seal plate, hollow guide pins and screws. Internal gear pumps are considered the most suitable type for motorcycles, particularly gerotor units, whose internal gear (inner gerotor) has one tooth less than the external gear (outer gerotor).4 The inner gerotor is responsible for transmitting movement to the outer gerotor, which turns inside the housing.6–8 The purpose of this study is to analyze the feasibility of substituting metallic materials (aluminum and steel) for glass-fiber (GF)-reinforced polyphthalamide (PPA), with and without polytetrafluoroethylene (PTFE), in the production of components for motorcycle oil pumps. The choice of PPA is justified by the fact that the properties of this high-performance thermoplastic render it suitable for applications with strict require- ments.9–11 Commercial versions of PPA containing relatively large proportions of GFs generally exhibit UNESP – Universidade Estadual Paulista Sorocaba, Guaratinguetá and Bauru Campus – Brazil Corresponding author: Sandro Donnini Mancini, UNESP – Universidade Estadual Paulista, Av. Três de Março, 511, CEP: 18087-180 Sorocaba, SP, Brazil. Email: mancini@sorocaba.unesp.br Journal of Reinforced Plastics and Composites 2017, Vol. 36(2) 149–160 ! The Author(s) 2016 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0731684416673727 jrp.sagepub.com http://crossmark.crossref.org/dialog/?doi=10.1177%2F0731684416673727&domain=pdf&date_stamp=2016-10-24 superior properties and are usually of low cost.3,12,13 One of the most interesting properties of these PPA composites is their high maximum working tempera- tures,11,12,14 which are usually higher than those attained in oil pumps, and which most conventional polymers cannot withstand. PTFE incorporated into a composite is known to improve its wear properties,15–17 which is an important consideration for moving parts subjected to friction, such as oil pump shafts. Experimental Design and materials Figure 1 depicts details of a current oil pump assembly, with the identification of each component (Figure 1(a)), as well as the proposed new pump (Figure 1(b)). In addition to the materials involved, the main difference between the current and proposed oil pumps is the shaft (part 2, Figure 1(a)), which rotates the inner gerotor (part 3, Figure 1(a)), which is inte- grated in the proposed pump, as shown in Figure 1(b). Table 1 describes the materials used in the current and proposed pumps, as well as the function of each part. The tested composites are commercial versions Figure 1. Details of the (a) current and (b) proposed oil pumps. Table 1. Materials used in the current and proposed oil pumps.18–20 Current material Proposed material Component/ function DIN SINT C11 steel PPA + GF (30%) + PTFE (�14%) Outer gerotor Inner gerotor 16MnCr5 steel Shaft SAE 383 aluminum PPA + GF (35%) Housing PPA: polyphthalamide; GF: glass-fiber; PTFE: polytetrafluoroethylene. 150 Journal of Reinforced Plastics and Composites 36(2) used in the injection of parts, whose compositions were obtained from a datasheet and from previous stu- dies.18–20 The metallic materials were donated by the Schaeffler Group, while the composites were supplied by DuPont Brazil. The materials of the pins (DC04 steel) and plates (SAE 1010) in the current and pro- posed pumps were the same. Performance of the current oil pump The parameter to determine oil pump performance is dynamic behavior, which is analyzed based on a flow curve on which the pump’s rotation and flow rate are monitored.21 These curves were obtained by monitoring oil pump pressure, speed, flow rate and temperature in a 150-cc motorcycle, using the lubricat- ing oil recommended by the manufacturer. A data acquisition system based on HBM Catman/Spider 8 software was used, and the average pressure was calcu- lated during the test. Tests were conducted with the engine rotation increas- ing from zero to its maximum of about 11,200 r/min. The drive ratio of this motorcycle is produced by a gear, whose rotation is approximately 5500 r/min. Oil pressure was monitored at the pump outlet, and temperature was monitored in the crankcase. Rotation was monitored in the cylinder head, where the primary drive shaft of the engine is located. To measure the oil flow rate, the gallery immediately after the oil pump outlet was blocked and a bypass was created by con- necting a hose to the output of the cylinder head. The flowmeter was placed between these points and con- nected in series to a pressure sensor. Due to the limita- tions of the flow sensor, the data had to be analyzed with the engine idling at 1000 r/min, i.e., the flow meas- urements were validated based on this rotation. Rotation was varied by turning the motorcycle han- dles three times to accelerate the engine manually from zero to maximum speed. The test was monitored for 600 s and the engine cooling time determined during the tests was set for 2 h, using an industrial fan. Three tests were performed on a new original oil pump and another three on a pump that had operated for 80,000 km. The resulting graphs represent the average of each group of three tests. Thermal analysis of the composite materials Parameters such as temperature and frequency affect the performance of composites. A range of temperatures is usually considered in the design of several advanced struc- tures; hence, it is essential to know if and at what tempera- ture heat-related degradation occurs. It is also important to consider the frequency, in view of the influence of vibra- tion on the performance of polymers.22 Thermogravimetry is a powerful tool to analyze thermal degradations in a wide range of temperatures, and the combined influence of temperature and frequency can be determined based on dynamic mechanical analysis (DMA).23 Dynamic mechanical measurements were taken with the equipment DMS 6100 model EXSTAR 6000 of SII Nanotechnology Inc., at the Department of Materials and Technology of Guaratinguetá Engineering Faculty, UNESP. The measurements were taken in a temperature range of 25�C to 270�C (at a heating rate of 3.0�C/min), and at different frequencies, which were determined based on calculated rotations in neutral, medium and high gear (10, 50 and 100Hz, respectively). A three-point bending test with a 40.0-mm span between supports was selected as the preferred testing geometry, since clamped boundaries affect damping Table 2. Properties of the composites subjected to FEA analysis.18,20,24 Composite Property Unit Value PPA + GF Poisson ratio Non-dimensional 0.39 Parallel thermal expansion coefficient �C�1 0.15� 10�4 Normal thermal expansion coefficient �C�1 0.62� 10�4 PPA + GF + PTFE Poisson ratio Non-dimensional 0.39 Parallel thermal expansion coefficient �C�1 0.11� 10�4 Normal thermal expansion coefficient �C�1 0.65� 10�4 PPA: polyphthalamide; GF: glass-fiber; PTFE: polytetrafluoroethylene. Figure 2. Details of the bezels (shadows) locking all the degrees of freedom in the holes (housing) and in the cylindrical body (shaft). Mancini et al. 151 measurements. All the dynamic tests were carried out in sinusoidal strain-controlled mode. During the measure- ments, a strain amplitude of 10 mm was used to record the viscoelastic parameters. Composites specimens were pre-stressed with an applied force of 10N and a force track rating of 150%. Samples were obtained from molded laminated plates, and the tests were conducted on both GF/PPA–PTFE and GF/PPA composites (Table 1). Thermogravimetric analyses (TGA) were performed on a NETZSCH TGA 209 F1 Phoenix� thermobalance at the Schaeffler Brazil Group. The analyses were per- formed in the range of 20�C to 800�C, applying a heat- ing rate of 10�C/min, as described by Pini et al.,10 in a nitrogen atmosphere. This procedure consisted of heat- ing 25mg of each composite on a thermobalance and recording the change in weight resulting from heat and/ or other forms of degradation. Finite element analysis of the proposed model Among the results of the DMA, the minimum storage modulus (E0) values of each composite were used as the elastic moduli (E) in the finite element analysis (FEA). Figure 4. Oil flow rate as a function of rotation: (a) new original oil pump and (b) original pump after 80,000 km. Figure 3. Details of the pressure applied on the surface (darker) of the housing and the inner gerotor. 152 Journal of Reinforced Plastics and Composites 36(2) The minimum Tg obtained was 20�C above the highest temperature obtained in the performance test on the current oil pump, and this difference was considered to meet safety requirements. An internal pressure of 3 bar (0.3MPa) in the pump was also considered, using a safety factor of at least 1.6 times the maximum pressure obtained in the determination of the pump performance. The new components were mathematically modeled using Pro/ENGINEER Wildfire 2.0 software, based on the current geometry, whose dimensions were deter- mined using a PRISMO Navigator 7 3D measuring machine from ZEISS. The mathematically modeled new product was then analyzed by the finite element method—FEA, using PTC Pro/Mechanica software integrated with Pro/ENGINEER Wildfire 2.0. The values of the properties of some of the com- posites were taken from datasheets and are presented in Table 2. These values were entered into the software, as was the storage modulus at Tg (obtained in the DMA). Figure 2 shows the bezels in the region of the screw holes, which lock all the degrees of freedom (DoF) in the x, y and z axes, while Figure 3 illustrates the sur- faces where pressure was applied. The function of these bezels is to simulate the component under the action of the screws. In the outer gerotor, the bezel covers is its entire external diameter. All the parts that were studied to determine the feasi- bility of using substitute materials were analyzed by FEA. However, as observed during the pump perform- ance tests, the housing and inner gerotor/shaft are the most critical parts among the items studied for the use of substitute materials. All the pressure is applied on the housing, which also supports the other components, while the inner gerotor/shaft is subjected to torque and pressure and is also subject to more severe wear conditions. Only static pressure is applied to the outer Figure 5. Pressure as a function of rotation: (a) new original oil pump and (b) original pump after 80,000 km. Mancini et al. 153 gerotor (in its inner surface) and its minimal thickness is analytically calculated. The von Mises stress (given in MPa) was calculated to verify if the proposed materials can withstand the stresses to which the parts are subjected. Results and discussion Determining the performance of the current oil pump Figures 4 and 5 illustrate the results of the performance test (flow rate and pressure, respectively, as a function of rotation) of a new original oil pump (Figures 4(a) and 5(a)) and of an original pump after reaching 80,000 km (Figures 4(b) and 5(b)). Figure 6 shows the relationship between temperature and rotation for a new oil pump and a used one (80,000 km). In Figures 4 to 6, note that the highest pressure attained during the test of the new pump was about 1.6 bar (Figure 5(a)). The highest peak operating tem- perature was 88�C (Figure 6), which was reached at a working pressure of 1.5 bar (Figure 6(a)). The flow/rotation relationship approached its max- imum amplitude at 6000 r/min, reaching a maximum flow of 5.6 L/min (Figure 4(a)). Figure 7. DMA curves of the glass-fiber/polyphthalamide composite at frequencies of 10, 50 and 100 Hz. Figure 6. Temperature as a function of rotation: new original oil pump, and original pump after 80,000 km. 154 Journal of Reinforced Plastics and Composites 36(2) In Figure 4(b), note that the used oil pump showed similar flow/rotation behavior than the new pump. In both cases, this is explained by the change in the flow regime due to the gerotor profile. Nevertheless, a 5.4 -L/min flow was achieved at around 6000 r/min, con- firming that even after undergoing wear, the oil pump components showed almost no loss in efficiency. However, due to wear, the gaps were enlarged, thus redu- cing the average operating pressure. The average operating pressure in the used pump was found to be 1.35bar, which is 10% lower than that of a new pump. These values were recorded by the software at the end of the test. The operating temperature of the used pump reached 93�C (Figure 6), at which point the pressure reached the maximum of 1.8MPa (Figure 5(b)). These values represent the maximum ones reached by the two pumps during the test and will be considered in studies of the proposed substitute materials. The safety coeffi- cients used here were more than adequate to include variations shown by the standard deviations of the mean results (see item FEA for proposed model). A study similar to the presented results in Figures 4 to 6 is required for motorcycle oil pump designs, without considering the materials employed, and sub- sequent studies are useful to verify the feasibility of using substitute materials. Thermal analysis of the composite materials Figures 7 and 8 illustrate the dynamic mechanical ther- mal analysis curves of samples of composite materials chosen for the housing (PPA+35% GF) and that selected for gerotors (PPA+30% GF+14% PTFE), respectively (see Table 1). The E0 curves clearly show the limit between glassy and rubbery regions, charac- terized by the decreasing E0 values of both materials. Table 3 lists the storage modulus (E0) values at the glass transition temperature (Tg) at three frequencies (10, 50 and 100Hz), as well as the glass transition tem- peratures, considering the point at which the E0 drops as coincident with the glass transition (Tg), since it is associated with the increase in molecular chain mobility. This approach is conservative, because it gives a lower temperature than Tg obtained through tan d peak. Figures 7 and 8 show the influence of frequency on the viscoelastic parameters of both materials: at higher frequencies, the E0 and tan d are shifted to the right, indicating that the material does not have sufficient Figure 8. DMA curves of the glass-fiber/polyphthalamide/PTFE composite at frequencies of 10, 50 and 100 Hz. Table 3. DMA parameters of the glass-fiber/polyphthalamide and glass-fiber/polyphthalamide/PTFE composites at 10, 50 and 100 Hz. Material Figure Frequency (Hz) Storage module at Tg (GPa) Tg (�C) PPA + 35% GF 7 10 2.5 121 50 2.6 119 100 2.6 113 PPA + 30% GF + 14% PTFE 8 10 1.33 127 50 1.31 131 100 1.32 133 PPA: polyphthalamide; GF: glass-fiber; PTFE: polytetrafluoroethylene. Mancini et al. 155 time to relax, and that higher energy is required to trig- ger the transition event. It is evident, however, that the addition of PTFE causes variations in the behavior of the material, which is a significant phenomenon, since there is a reduction in the E0 drop point in comparison to that of the composite without PTFE. This suggests that PTFE improves chain mobility, anticipating the process of energy dissipation in the material. With regard to tan d, also plotted at 10, 50 and 100Hz along dotted lines in Figures 7 and 8, it is known that damping properties are related to the bal- ance between the elastic and viscous phases in a poly- meric structure. When fibers are used as reinforcement Figure 9. E00 curves of the glass-fiber/polyphthalamide composite at frequencies of 10, 50 and 100 Hz. Figure 10. E00 curves of the glass-fiber/polyphthalamide/PTFE composite at frequencies of 10, 50 and 100 Hz. 156 Journal of Reinforced Plastics and Composites 36(2) and adhesion is good, chain mobility restriction is observed, which is reflected in the tan d. A smaller area under the tan d peak indicates stronger interface adhesion. Therefore, although the PTFE enhanced the chain mobility, it was found to reduce adhesion at the fiber/matrix interface. As it was already commented, it was also found that, in both cases, the storage modulus values increased in response to increasing frequencies at a given tempera- ture (isothermal conditions). This is explained by the polymer chains, which absorb energy in given fre- quency ranges, a phenomenon that occurs only when the frequency is equal to the relaxation time. This relaxation time, which tends to decrease with decreasing temperature, indicates that chain mobility is related to the molecular structure of the material and to temperature. Relaxation is generally associated with conformational changes, and the effect of this condition as a consequence of the temperature and frequency relationship indicates that, at high frequencies or long relaxation times, the behavior of the polymer is glassy, with a higher storage modulus.25 PTFE influences the storage modulus, favoring polymer chain mobility. Table 3 also lists the Tg values at the point where the E0 drops at frequencies of 10, 50 and 100Hz, which were always higher (at least 20�C higher and at most 40�C higher) than the maximum working temperature reached in the oil pump performance test (93�C, Figure 6). This suggests that the composites are suitable for operating conditions at these frequencies. Figures 9 and 10 show the viscous response of the GF/PPA and GF/PPA/PTFE composites, respectively, based on their E00 curves. These curves represent energy dissipation measurements, and their height is related to the relaxation process: higher E00 values, i.e., higher peaks, indicate greater energy dissipation. In compos- ites, this is attributed to the increase in internal friction, and in this study, the composite containing PTFE pre- sented a lower value of E00, which means that lower energy was needed to cause this dissipation. Table 4 shows the main results of the thermogravi- metric tests carried out on the GF/PPA and GF/PPA/ PTFE composites. As can be seen in Table 4, the composites selected for the housing (PPA/glass) and gerotors (PPA/GF/PTFE) can be considered very stable, since the materials main- tained more than 98% of their original mass at 100�C. This negligible mass loss is likely attributable to loss of moisture. At 650�C, the GF/PPA composite contained a non- volatilized fraction (considered inorganic) of about 33%, while that of the GF/PPA/PTFE composite was 28%. These fractions are very close to the 35% and 30% GF contents reported by the manufacturer.17,18 Between 500�C and 600�C, the composite selected for the gerotors also showed an intermediate mass loss of 13.69%, probably corresponding to the PTFE. Figure 11. FEA analysis of the housing: von Mises stress (MPa). Table 4. Main results of the thermogravimetric measurements of the two composites under study. Material Loss mass at 100�C (%) Residual mass at 650�C (%) PPA + 35% GF 1.57 32.91 PPA + 30% GF + 14% PTFE 1.89 27.99 PPA: polyphthalamide; GF: glass-fiber; PTFE: polytetrafluoroethylene. Mancini et al. 157 FEA of the proposed model The maximum pressure (1.8 bar for the used pump— Figure 5(b)) determined in the performance tests of the current pump was multiplied by a safety factor of at least 1.6 to provide the value of 3 bar (or 0.3MPa), which was used in the FEA of the proposed model. The min- imum storage modulus (E0) values of each composite (2.5GPa for PPA+GF and 1.31GPa for PPA+GF +PTFE, respectively—see Table 3) were used as the elas- tic modulus (E) in the FEA. As mentioned before, the minimum Tg obtained (113�C, Table 3) was 20�C above the highest temperature obtained in the performance test (93�C, Figure 6) on the current oil pump and this differ- ence was considered to meet safety requirements. Figure 13. FEA analysis of the outer gerotor: von Mises stress (MPa). Figure 12. FEA analysis of the integrated shaft/inner gerotor: von Mises stress (MPa). 158 Journal of Reinforced Plastics and Composites 36(2) Figures 11 to 13, respectively, show the FEA results of von Mises stresses in the housing, in the shaft inte- grated with the inner gerotor and in the outer gerotor. In figures, the highest von Mises stresses are indicated by arrows. In Figures 11 to 13, note that the highest von Mises stresses (indicated by arrows) found for the housing, the shaft integrated with the inner gerotor and the outer gerotor were 12, 4 and 1.5MPa, respectively. According to the manufacturer, based on stress versus strain curves recorded at various temperatures, the composite materials withstand stresses of 80MPa at 100�C (temperature above the maximum working tem- perature considered—Figure 6).18–20,24 This means that the safety factor of the proposed substitute materials is almost 7 for the housing, while that of the integrated shaft/inner gerotor is approximately 20, and that of the outer gerotor is more than 50. The FEA analysis revealed a displacement of almost zero in the outer gerotor and in the shaft/inner gerotor: 0.00092 and 0.00813mm, respectively. The maximum dis- placement measured in the housing was 0.17664mm, which was considered acceptable. These results, albeit interesting, do not provide con- clusive evidence of the feasibility of using these com- posites for some of the oil pump parts in 150 cc motorcycles. Additional tests are needed, including tests of longer duration on the current pumps, as well as creep and aging tests of the composite materials and prototype performance tests (to obtain curves such as those shown in Figures 4 to 6). Conclusions The results of this feasibility study suggest that motorcycle oil pump parts can be manufactured with composite materials, i.e., housing made of PPA/GF composite, and outer gerotor and integrated shaft (inner gerotor and shaft) made of PPA/GF/PTFE composite. The maximum operating temperature (below 93�C) did not cause significant mass loss of the proposed materials and proved to be lower than the glass transi- tion temperature of the polymers in question deter- mined under dynamic conditions (the minimum Tg obtained was 113�C). These results suggest that the mechanical properties of the composites remain unchanged below the maximum operating temperature. 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