卓越的齿轮材料 an excellent gear material for demanding a

1、DSMs Stanyl® as an excellent gear material for demanding applicationsDr. H.K. van Dijk, DSM Engineering Plastics, P.O. Box 604, 6160 AP Geleen, The Netherlands, Dr. Ir.DSM Research, Material Science Centre, P.O. Box 18, 6160 MD Geleen, The Netherlands, J. Koenen, DSM Engineering Plastics, P.O.

2、Box 604, 6160 AP Geleen, The NetherlandsAbstractDSMs Stanylâ is an excellent material for gears in demanding applications with respect to torques to be transmitted and operating temperatures.Stanyl, a polyamide 46, has a crystallinity of 70%, which results in very good wear and friction propert

3、ies and an excellent retention of mechanical properties (strength, stiffness) at elevated temperatures. The material allows for very fast cycle times with water-cooled moulds.The higher retention of mechanical properties at elevated temperatures (> 100 °C) allows smaller gears to be designed

4、 compared to PA66 or PPAs, while still transmitting the same torque.Stanyls superior mechanical properties at high T compared to PA66 and PPAs can be increased further by annealing the molded parts. Annealing is a high temperature treatment of a molded part. The result is a further 50% increase in t

5、he stiffness and strength of Stanyl at temperatures above the glass transition temperature. A secondary benefit of annealing is that the water uptake of Stanyl can be reduced to the level found with PPAs. Annealing to reduce moisture uptake is unique for Stanyl. The annealing effect is irreversible

6、and is accompanied by an increase in the materials molecular weight. Additional benefits of annealing are an increase in fatigue resistance and a further improvement of the materials wear and friction performance.DSM has extensively modeled the annealing of Stanyl. Predictions on time and temperatur

7、e needed to reach a desired effect and the effect on part shrinkage can be made and a cost model is available.An important consequence of annealing is that part tolerances for applications running at elevated temperatures become determined by CLTE value, and no longer by the dimensional changes asso

8、ciated with water uptake.Gear measurements are currently running at the University of Berlin (fully lubricated, several representative Stanyl grades and in Geleen (dry-running measurements against steel, several Stanyl grades) to provide additional supporting data for our customers.Several Stanyl ge

9、ar applications have been commercialized. Some examples : ETC gears (Hitachi, Denso), EPS gears (Honda Civic, Honda Insight), starter motor gears (outer ring gear), power window gears and seat recliner gears.1. General introduction of Stanyl PA46DSMs Stanyl is a high heat thermoplastic polyamide res

10、in. The chains are built up from adipic acid and diaminobutane, which results in a very symmetric chain structure. In fig. 1 the chain structure of Stanyl is shown in comparison to PA66 and PA6.Fig. 1. Chain structure of Stanyl in comparison to PA66 and PA6.The regularity of the chains becomes evide

11、nt from the fact that between every amide bond, always 4 CH2-moieties are present.The result of the highly regular chains is a very fast crystallizing material with a high level of crystallinity of 70%. The melting temperature of the material is at 295ºC, the glass transition temperature can be

12、 found at 80ºC. In comparison : PA66 and PA6 generally show crystallinity levels of about 50%, whereas about 30% crystallinity is generally found for PPA resins.The fast crystallization of the material allows for very short cycle time production with the use of water cooled moulds : mould tempe

13、rature is between 80-120ºC.An important consequence of the fast crystallization, resulting in a very fine spherulitic structure is the relatively high impact value of Stanyl : about 10 KJ/m2, in comparison to 5-7 KJ/m2 for PA6 and PA66 (Dry As Moulded).The most important consequence of the high

14、 level of crystallinity of Stanyl is the retention of mechanical properties (strength, stiffness) at temperatures above Tg : in fig. 2 the superior stiffness of Stanyl at elevated temperature is shown in comparison to various competitor materials.Bild 2Steifigkeit von Stanyl gegenüber Wettbewer

15、bsmaterialien in Abhängigkeit von der Temperatur (DMA-Plots)Fig. 2. High temperature stiffness comparison (DMA plots) of Stanyl vs. various competive materialsAs a result of the better high temperature mechanical properties of Stanyl, smaller gears can be designed in Stanyl (axis distance not f

16、ixed) while transmitting the same torque. This can even be more exploited after annealing of Stanyl, as will be shown later on in this paper.2. Annealing of Stanyl for further improvement of high T properties, while at the same time reducing the materials moisture uptake2A. Annealing and reduction o

17、f moisture uptakeIntermezzo : polyamides and moisture uptakeAll polyamides absorb moisture. The extent of moisture absorption is determined by 2 primary parameters :1. the materials polarity or hydrophilicity2. the materials level of crystallinityThe materials polarity can be expressed in the ratio

18、of the NHCO-groups to the CH2-groups. From fig.1 it can be concluded that this ratio is highest for Stanyl, making Stanyl the highest polarity material.The materials level of crystallinity is a second important parameter determining the water uptake level. Water absorption only takes place in the ma

19、terials amorphous phase, so the higher the materials crystallinity the lower the expected water uptake.In table 1 water uptake levels are shown for Stanyl, PA66 and PA6 at 23ºC/50% RH.Table 1. Water uptake of Stanyl, PA66 and PA6 at various % relative humidities (RH)50 % RH75% RH100% RHPA63,55,

20、511PA66359PA464713Annealed PA4623,56,5PPA2,54,26Model calculations have shown that the higher moisture absorption of Stanyl compared to competitor materials can not be explained by the differences in polarity between the various materials : in spite of Stanyl having the highest polarity, the materia

21、ls crystallinity is also highest !The main reason for the relatively high water absorption of Stanyl is the relatively low density of the amorphous phase. This is a 1-to-1 consequence of the extremely fast crystallization of Stanyl. Upon cooling down from the melt, in addition to the fast formation

22、of high levels of crystallinity, amorphous phase chain conformations are immediately frozen in, resulting in an amorphous phase with a relatively high amount of free volume. This is the main reason for the relatively high level of water absorption of Stanyl.Annealing of Stanyl results in a substanti

23、al decrease of the materials water uptake and speed of water uptake, the reason being the re-organization of the amorphous phase in a more equilibrium-like, denser structure. Annealing is accompanied by a measurable density increase of the material : for unfilled Stanyl an increase in density from 1

24、,18 gram/cm3 to 1,21 gram/cm3 was observed.A second important effect of annealing is the perfectioning of the already present crystals, as was shown by WAXS measurements. Annealing is accompanied by a big increase in DSC DH value. To an important extent this is the result of the observed crystal per

25、fectioning.Annealing is a high temperature treatment of the material. The temperature is above the materials Tg, but obviously below the melting temperature of the material. The effect is irreversible, and annealing is accompanied by solid state postcondensation, resulting in a substantial molecular

26、 weight increase. The annealing process has been modelled by DSM Research, and now a predictive model is available : for a certain anneal time and temperature combination the reduction in water uptake can be predicted fairly accurate.The lowering of the water uptake upon annealing is UNIQUE for Stan

27、yl, as is shown in fig. 3.PA46 30% GFPA66 30% GFPPA 33% GFPPA 35 % GFFig. 3. Lowering of water uptake of GF Stanyl in comparison to GF PA66 and PPAs. Annealing at several conditionsIn fig. 4 an example is shown of the reduction in moisture uptake level and speed upon annealing of unfilled Stanyl TW3

28、41 at 260°C. PA66 and cast PA6 water uptake levels (at 100% RH) are shown for comparison.Fig. 4. Reduction in water uptake of unfilled Stanyl after various annealing times at 260°C.Several of these curves were generated upon using various annealing temperatures, in orde to be able to come

29、up with a predictive model of practical use. In fig. 5 some experimental results are shown for reaching PA66 or cast PA6 water uptake levels.PA66Cast PA6Fig. 5. Some annealing experiments resulting in PA66 or cast PA6 water uptake levels for unfilled Stanyl.An important consequence of the reduction

30、in water uptake of Stanyl upon annealing is the reduction of both a parts dimensional changes upon water uptake and decrease in mechanical properties. In the following case this is illustrated. The dimensional changes upon saturation with water at 100% RH were compared for a cast PA6 gear and an unf

31、illed Stanyl gear with and without annealing. The results are summarized in the following table 2. Table 2. Annealing : 24 hours at 230°C Change without annealingChange with annealingTW341 pitch diameter change (%)2,81,2TW341 thickness change (%)4,22,1Cast PA6 pitch diameter change (%)1,2NACast

32、 PA6 thickness change (%)2,0NAIn this case the relatively high expansion in the thickness direction is due to the presence of a steel hub, preventing the expansion in the radial direction to some extent.In general it can be said that after annealing dimensional changes of parts operating at elevated

33、 temperatures are governed by the Coefficient of Linear Thermal Expansion (CLTE) rather than moisture uptake, as shown in the following scheme.99.35101.0max toleranceUF Stanyl dimensions before annealing UF Stanyl dimensions after annealingCLTE more imprtant than moisture growth !99.35100.65max tole

34、rance2B. Annealing and mechanical property changesUpon annealing of Stanyl, also important changes in mechanical properties occur. These changes are most prominent at temperatures above the glass transition temperature.In fig. 6 some DMA curves are shown, comparing unfilled Stanyl both in DAM and an

35、nealed version with PA66 and POM.Fig. 6. DMA curves of DAM and annealed Stanyl vs. PA66 and POM. Upon annealing of Stanyl a modulus increase of up to 50% can be observed at temperatures above the glass transition temperature. The same trend is observed for the tensile strength of the material. In fi

36、g. 7 the stress at 2% strain is compared for (annealed) Stanyl vs. PA66 at 120°C. From this figure it can be observed that annealing of PA66 results in an improvement of mechanical properties as well, albeit a much lower improvement than in the case of Stanyl.Fig. 7. Stress at 2% strain for var

37、ious materialsThis big difference in stress at 2% strain at 120°C can be directly translated into the possibility to design smaller gears while transmitting the same torque. This will be worked out in more detail in part 3 of this paper.As already said earlier, annealing of Stanyl is accompanie

38、d by solid state postcondensation, resulting in a substantial increase in the molecular weight of the material. Annealing of unfilled Stanyl (TW341) for 24 hours at 230°C, resulted in an increase of Viscosity Number VN of the material from 155 ml/gram to 260 ml/gram. The last level is above the

39、 VN of extrusion grade Stanyl (220 ml/gram).Upon annealing of Stanyl, also a positive effect on the fatigue performance at 140°C has been observed. This was studied for both glass fibre reinforced Stanyl TW200F6 and carbon fibre reinforced Stanyl TW200B6 (in both cases 30 w% fibre loading).The

40、results are shown in figure 8. Fig. 8. Influence of annealing (16 hours at 210°C) upon fatigue performance of glass and carbon fibre reinforced Stanyl at 140°C.In principle annealing can be carried out either in air or under nitrogen. It was observed that for reducing moisture uptake or im

41、proving mechanical properties no differences occurred between either of the 2 methods.However, for Wear and Friction (W&F) related issues, it is recommended to carry out the annealing step in a nitrogen atmosphere. Annealing in air results in the formation of an oxidized toplayer (black colour)

42、with a more brittle character. This toplayer shows an increased wear rate.Some initial studies were carried out to study the influence of annealing on the W&F performance of Stanyl. TW371 (teflon modified Stanyl for dry-running applications) was studied in this respect for a torsion dempener app

43、lication. A thrust washer set-up was used for the measurements (which were performed according to ASTM D-3702).In the table below and fig 10 the results of the weartesting are givenTW371TW371 annealed (4 hrs 240 C)Wear rate mm/hr5,32,5Figure 9 . Influence of annealing on the coefficient of friction

44、of teflon modified Stanyl TW371Annealing has a positive effect on wear and friction properties By annealing is the wear rate more than halved and also the friction coefficient is reduced from 0,22 to 0,15. Impact properties go down somewhat upon annealing of Stanyl. For TW341 a decrease in notched I

45、zod was observed from 10 KJ/m2 to 5 KJ/m2. This value is still above the value for cast PA6 (3,5 KJ/m2).Upon annealing, a certain part shrinkage has to be taken into account. The injection mould has to be compensated for that shrinkage. In several geometries the shrinkage of unfilled Stanyl was meas

46、ured. Upon annealing for 16 hours at 210ºC a shrinkage value of 0,4% generally is obtained. This value is doubled to 0,8% upon annealing for 24 hours at 230ºC.So the time,temperature combination for annealing of choice will determine the observed shrinkage value, for which a tool correctio

47、n has to be made.Currently several projects are running to study the performance of Stanyl (various grades) gears.At the University of Berlin (Prof. Blessing) a fully lubricated gear study is currently being carried out. Oil temperature is 140°C.In the US a dry-running test programm is running

48、at an ambient temperature of 100°C. Finally, at the University of Bochum (Prof. Predki) a study of injection moulded helical wormgears is being set up.In all cases the Stanyl gears run against a steel mating gear. In the last part of this paper Stanyl is positioned against competitors as a gear

49、 material. Also the value for customers upon using Stanyl as a gear material is explained.3. Positioning and application examples3.1. PositioningPolymer gears have a number of advantages over metal ones . They allow for · noise reduction due to better sound damping properties· weight reduc

50、tion due to lower density· design freedom. Injection moulding allows complex and optimised designs that can be produced on an economical way by means of injection moulding.· Lubrication free; In low torque, low sliding conditions plastic gears can be used without any additional lubrication

51、. Important properties of plastic gears are · Long Fatigue.· Good Wear properties· Good mechanical properties at operating conditionsIn chapter 2 it is explained that PA46 relative to other polymers shows clear advantages in the above aspects when used above the glass transition tempe

52、rature . An important therefore becomes at what temperature does the gear set Im designing operate.In the ISO/TR 13989-2 a method is described to calculate the temperature development in a pair of gears. The temperature calculations in this technical report are based on the flash temperature develop

53、ment of Blok.In an example below it is illustrated how important this aspect is; It is a plastic spur gear running against a steel pinion gear with module 2, centre distance of 53 mm and 12mm wide. The operating conditions are a torque of 20 Nm at 1000 rpm. The calculated root stress is 105 Mpa and

54、the Herzian stress is 229 Mpa. As a starting temperature 85 °C is chosen which represents a typical automotive interior design temperature (car in the sun in a desert).In the figure below the calculated temperature development is shown for 3 lubrication situations ; full, greased, and no lubric

55、ationFigure 10 Calculated example of temperature development in different lubrication situationsIt is clear that just considering the environmental temperature for gears can lead to unexpected errors in selecting materials. A common polymer very often used, polyacetal, has an upper use limit of 85-9

56、0 °C due to thermal stability reasons. Pa46 has an upper use limit of 180 °CComparative better mechanical properties in gears allow either higher torque levels or smaller gears. Torque (Nm) equals lever (m) x force (N). If the allowable force can be doubled the lever can be half etc. However the volume of a gear is proportional to the diameter squared This means that doubling of allowable force leads to a 4 fold decrease of the diameter . Using the stress levels from figure 7 the potential space saving are plotted in the figure 12Volume = 0,75xD2xtt= ThicknessD=DiameterFigure 11 s