Automotive. Bakelite Engineering Thermosets for Durable, Lightweight Pulleys. Application Bulletin. Key Benefits

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1 Application Bulletin Automotive Bakelite Engineering Thermosets for Durable, Lightweight Pulleys As the automotive industry reduces vehicle weight and increases engine efficiency in order to comply with new CO 2 emission and fuel economy regulations, under-the-hood operating temperatures continue to increase. Bakelite engineering thermosets are cost-effective, light weight, heat resistant alternatives to heavier, conventional steel and aluminum die-cast products. Pulleys transmit motion or transfer load, and consequently demand great mechanical strength and dimensional stability under operating conditions. Bakelite engineering thermosets are the material of choice for automotive pulleys such as those used for the camshaft, power steering pump, alternator, air-conditioning compressor, water pump or deflecting rolls. Key Benefits Can weigh up to 4% less than aluminum and up to 8% less than steel. Maintain excellent dimensional stability at elevated temperatures, and can thereby meet tight design tolerances. Superior creep properties allow direct screwing, for simpler and faster assembly. Alternatively, metal parts such as bearings can be over-molded. Exhibit outstanding fatigue and wear properties, and thus produce longlived pulleys. Intrinsically chemically resistant, eliminating any additional corrosion protection coating or treatment steps. Better acoustics than aluminum. With glass fiber reinforcement, they outperform thermoplastics in abrasion and surface properties.

2 Bakelite Engineering Thermoset Grades PF 651 and PF 111 The recommended grade for multi V-pulleys is Bakelite engineering thermoset grade PF 651, and for toothed pulleys, PF 111. A number of Automotive OEMs and Tier 1s have specified these grades for pulley applications. Key product attributes can be found in the technical datasheets. Table 1: Bakelite Engineering Thermoset recommended application areas Product Bakelite PF 111 Bakelite PF 651 Application Areas Dimensionally accurate, mechanically strong motor vehicle engine attachments, toothed pulleys with very high precision and dimensional stability requirements. Dynamically and thermally highly stressed parts in the automotive field i.e. multi V-pulleys. Dimensional Stability Pulleys must operate reliably when subject to dynamic forces and temperature cycles. Internal friction and engine heat will raise the temperature of operational pulleys. Figure 1 shows the thermal expansion of Bakelite engineering thermoset grade PF 651, which ranges from / C, up to 18 C. Multi V-pulleys composed of Bakelite engineering thermoset grade PF 651 meet tolerances of up to.2% of the nominal drawing. Figure 1. Coefficient of Thermal Expansion for Bakelite PF Tg TMA [ um ] C

3 Toothed pulleys have tighter tolerances and consequently even higher dimensional stability requirements than multi V-pulleys. Toothed pulleys made from Bakelite engineering thermoset grade PF 111 meet tolerances as low as.1% of design dimensions. They behave isotropically, and have a very low coefficient of thermal expansion: 13 to / C, up to 2 C (Figure 2). Consequently, their dimensional stability is of the same order of magnitude as steel s, and outperforms aluminum and magnesium, as can be seen in Table 2. Figure 2. Coefficient of Thermal Expansion for Bakelite PF Tg [ % ] c b a a Temp 4. C 6. C 8. C 1. C 12. C 14. C 16. C 18. C 2. C CTE 9.56x1-6 /K 11.96x1-6 /K 13.16x1-6 /K 13.92x1-6 /K 14.35x1-6 /K 14.7x1-6 /K 13.66x1-6 /K 13.84x1-6 /K b Temp 4. C 6. C 8. C 1. C 12. C 14. C 16. C 18. C 2. C CTE 9.63x1-6 /K 12.49x1-6 /K 13.84x1-6 /K 14.59x1-6 /K 15.x1-6 /K 15.33x1-6 /K 15.61x1-6 /K 15.81x1-6 /K c Temp 4. C 6. C 8. C 1. C 12. C 14. C 16. C 18. C 2. C CTE 1.75x1-6 /K 12.2x1-6 /K 12.88x1-6 /K 13.47x1-6 /K 13.82x1-6 /K 14.3x1-6 /K 14.25x1-6 /K 14.39x1-6 /K Table 2: Thermal expansions of metals in comparison with Bakelite eng. thermosets Construction material Steel Aluminum A38 Magnesium AZ91 Bakelite PF 111 Bakelite PF 651 Coefficient of thermal expansion (1-6 / C)

4 Short-Term Stress Pulleys operate at elevated temperatures and need to maintain their mechanical strength. In Figures 3 and 4, the mechanical properties of Bakelite engineering thermoset PF 651 and PF 111 are shown as a function of temperature. These values provide an indication of rigidity and serve as characterization, but are also used for strength calculations and the design of molded parts. The mechanical strength of Bakelite engineering thermoset PF 651 decreases gradually with temperature, but the thermal stability can be greatly improved by post-curing of the material if needed. Bakelite engineering thermoset PF 111 maintains a high flexural modulus and excellent strength up to 2 C. As shown in Figure 5 semi-crystalline engineering thermoplastics show a significant drop in mechanical properties above Tg when the amorphous parts change from the glass to the rubbery state. Engineering thermoplastics suffer more swelling stress in response to internal friction than engineering thermosets. Figure 3. Flexural Modulus and Strength of Bakelite PF 651 as a Function of Temperature (ISO 178) Flexural Modulus [ MPa ] Flexural Strength [ MPa ] Flexural Modulus green Flexural Modulus post- Flexural Strength green Flexural Strength post- Flexural Modulus green Flexural Modulus post-cured Flexural Strength green Flexural Strength post-cured Figure 4. Flexural Modulus and Strength of Bakelite PF 111 as a Function of Temperature (ISO 178) 3 4 Flexural Modulus Flexural Modulus [ MPa ] Flexural Strength [ MPa ] Flexural Strength Flexural Modulus Flexural Strength Figure 5. Flexural Modulus of Bakelite PF 651 and 111 as a Function of Temperature vs. Competitor Materials (ISO 178) 3 25 Flexural Modulus [ MPa ] Bakelite PF 111 Bakelite PF 651 Engineering PPA Engineering PPS 65% GF Engineering PPS 4% GF

5 Long-Term Creep Behavior Creep test results provide the design engineer with a basis for calculation when designing components subject to prolonged stress loads. Figure 6 and 7 demonstrate the long-term creep behaviour of Bakelite engineering thermoset grades PF 651 and PF 111 under three different tensile loads at an elevated temperature of 12 C. These conditions were selected to represent the final application s. The tests were carried out to a time under load of 1 hours. Figure 6. Creep Strain of Bakelite PF 651 at 12 C over 1 hours (ISO 899-1) Creep Strain [ % ] log 1 time t [ hours ] Figure 7. Creep Strain of Bakelite PF 111 at 12 C over 1 hours (ISO 899-1) 12 MPa 61 MPa 41 MPa 12 MPa 61 MPa 41 MPa Creep Strain [ % ] log 1 time t [ hours ] 14 MPa 84 MPa 56 MPa Figure 8 demonstrates the superior creep resistance of Bakelite engineering thermoset PF 651 and PF 111, since even under higher loads they exhibit a lower creep strain than engineering thermoplastic PPA, PPS and Magnesium AZ91 Materials. In the case of aluminum, the pulleys must be assembled with threaded inserts to obtain sufficient creep resistance. Thanks to the excellent creep behavior of Bakelite engineering thermoset PF 651 and PF 111, these inserts can be omitted as assembly screws can be directly fastened into threaded holes; hence the numbers of required assembly steps and parts are reduced. Assembly can also be simplified by over-molding metal bearings. Figure 8. Creep Strain Comparison of Different Materials at 12 C over 1 hours (ISO 899-1) Creep Strain [ % ] log 1 time t [ hours ] Bakelite Bakelite Enginee Enginee Magnes estimat Bakelite PF 111 (56 MPa) Bakelite PF 651 (61 MPa) Engineering PPA (6 MPa) Engineering PPS (3 MPa) Magnesium AZ91 (5 MPa) estimate 5

6 Long-Term Fatigue Strength Pulleys must maintain their mechanical properties during their service lives. They are subject to long term dynamic loads imposed by the various moving masses within the engine compartment. As a result, fatigue strength is an important design driver for such components. Figure 9 shows the fatigue behavior of Bakelite engineering thermoset PF 651 in a compressor pulley application measured according to the so-called hang last test, in comparison with the technical requirements. As demonstrated, the fatigue results exceed the required levels and Bakelite engineering thermoset PF 651 fully meets the pulley specification. Figure 9. Fatigue Strength of Bakelite Engineering Thermosets and the Technical Requirement for Multi-V Pulley Applications (Wöhler Curve) 1E+9 1E+8 Bakelite Technic Load Cycle 1E+7 1E+6 1E+5 1E+4 6 N 5 N 4 N 3 N 2 N 1 N Applied Load Bakelite PF 651 Technical Requirement Figure 1 shows the fatigue behavior of Bakelite engineering thermoset grade PF 111. As one can see from the graph, the material exhibits outstanding fatigue performance with minimal strength degradation after millions of cycles. In comparison, metals and engineering thermoplastics degrade much more rapidly strength reductions of over 5% are typical for these materials after 1 million cycles, as shown in Figure 11. Parts made with Bakelite engineering thermoset grade PF 111, however, typically only lose strength in the range of 1 3% under the most demanding dynamic loads. Using Bakelite engineering thermosets such as PF 111 helps further reduce the weight of dynamically loaded parts and facilitate lifetime predictions for the design engineer. Figure 1. Fatigue Strength of Bakelite PF 111 (Wöhler Curve) (ISO 527-2) a [ log ] [ MPa ] Stress Amplitude s E+3 1.E+4 1.E+5 1.E+6 1.E+7 Load Cycles N [ log ] [ - ] Stress cycle frequency 5 Hz, R =.1 6

7 Figure 11. Wöhler Curves of Construction Materials (ISO 527-2) Percent of Fatigue Tensile [ % ] 12% 1% 8% 6% 4% 2% % 1.E+3 1.E+4 1.E+5 1.E+6 1.E+7 Load Cycles N [ - ] Stress cycle frequency 5 Hz, R =.1 Bakelite PF 111 Engineering PPS Engineering PPA Processing Engineering thermoset grades are processed by injection and compression molding machines to make molded parts. Injection molding is a versatile and economically efficient process for producing complex composite parts. Temperature has a large impact on mold processing and part quality. The mold wall temperature should be set within the upper limit range of C and can be controlled with either a water or oil heating system. This low temperature requirement is an advantage of thermosets compared with thermoplastics, which take much more energy to melt and plasticize. Internal pressure measurements are used to follow the melt flow behavior and to control finished part quality and cycle time. The internal pressure during the compression phase should be > 15 MPa. Compression molding may be a manual, semi-automatic or fully automatic process. Recommended settings are a mold temperature of C and cavity molding pressure > 15 MPa. More detailed information on processing and finishing of engineering thermosets can be found in the Bakelite engineering thermosets product guide. Further Information For further information, refer to the product guide and other automotive application bulletins to be found on the Hexion Inc. (Hexion) website. 7

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