杜邦VESPEL聚酰亚胺耐磨和低摩擦部件成功应用于牵引车的传动系统中
在其经济型的无极变速CVT系统中，德国变速箱专家ZF采用一款超级耐磨和低摩擦的杜邦VESPEL聚酰亚胺止推垫片。这些传动变速箱应用在全球知名的农业设备制造商，如John Deere, Claas Selbstfahrende Erntemaschinen or Same Deutz-Fahr。行星齿轮轴与这些垫片进行对磨，可以保证非常可靠使用和维护变速箱。另外，在更高要求的变速箱传动轴中采用矩形截面的止推垫片。在该系列的变速箱中含有超过20个VESPEL部件，这些部件都是有杜邦生产的。
Vespel?止推垫片：最小的磨损量
Vespel? SP零件的长期使用温度为ZF农业传动系统的开发经理Jürgen Pohlenz补充到：“Vespel?止推垫片具有非常出色的摩擦性能。在变速箱开始工作的瞬间，Vespel?垫片很快就能调节到与接触面相一致的不均匀性，这种不均匀性可能是由零件间的作用或者负载力不垂直造成的。这样的结果是，经过很少的磨合期磨损后就形成了一个良好的止推面，从而可以非常均匀地形成整个止推面来承受轴向力。在整个变速箱的使用寿命周期内，Vespel?止推垫片的摩擦力极低，这就意味着止推垫片对整个系统和润滑油的温度升高起到很小的作用。”290 °C，短期的温度可以达到480 °C。由于即使在无油润滑的环境下可以承受高达40MPa.m/s的PV值，Vespel? SP-21和SP-22非常受到变速箱制造商的青睐。“对于ZF来说，非常重要的一点是Vespel?止推垫片可以承受轴向力，并且与对磨的金属材料几乎不发生磨损”Vespel?业务欧洲传动工业市场经理Peter Bergmann，“相对金属-金属摩擦副来说，Vespel?超乎寻常的摩擦性能产生非常低的磨损量，从而更利于操控性。基于这些原因，Vespel?止推垫片多年来成功应用于小轿车、公共汽车和农业机械的传动系统中。
ZF使用的所有Vespel?止推垫片都有一个止转凸起部分，该部分锁扣在对应的铸铁行星齿轮架上。这样，只有止推垫片和行星齿轮有相对运动。由止推垫片和行星齿轮架没有相对运动，不需要对金属表面进行额外的抛光处理。
Vespel?矩形截面的密封环可以控制机油的流量
采用微切口技术的Vespel?SP-22矩形截面的密封环使用在3.5和4.5的ECCOM变速箱中，这些变速箱用于输出功率为280-385KW的发动机中。这些密封环具有良好设计的切口，可以允许密封环很地装入卡槽中，并且可以补偿热膨胀量。保留的间隙允许少量和可控的机油通过密封环。密封环两个表面的油槽可以很快就在接触面上形成油膜，利于降低摩擦，冷却摩擦面和提高零件的负载能力。通过油槽设计，在运行过程中机油超过80°C和油压超过22bar的情况下仍然可以形成稳定的油膜。
Pohlenz说到：“今天的牵引车速度可达50 km/h，对应的传动轴的速度为4200 min-1。传动轴和矩形密封环的相对速度也有那么高。在同步的压力负载下，在密封环处的PV值达22 MPa.m/s。在这样的情况下，相对于石墨铸铁件来说，Vespel?矩形密封环在耐磨方面则具有极大的优越性。在负载的压力下，相应结构的石墨铸铁会产生刮擦，从而导致在密封面出现过高的温度。而低摩擦和低磨损的Vespel?部件在这样的工况下形成稳定的润滑油膜，这样就可以在变速箱的整个使用周期内，有效地防止因摩擦而出现的密封区域的过热现象。”
无数次的试验
ZF的Eccom无级变速箱CVT经过了50,000次的试验。当前共有Eccom 1.5, 1.8, 2.0, 3.5和 4.5等5个规格，用于的发动机的输出功率为100HP到520HP（相当于75KW和385KW）。的Eccom 5.0降与2010年低上市，特别适合用于高性能的牵引车等，适合输出功率为385KW和扭矩为2300Nm的发动机。所有这些规格可以允许在启动时非常敏感和连续进行牵引工作，即使在非常苛刻的路面状况下。CVT变速箱始终一致地根据负载的变化来进行齿轮比的改变，从而可以保证发动机在的能耗下保持稳定的输出。
来自：杜邦网站，如下是英文部分。
Abrasion-resistant, low-friction DuPont? Vespel? polyimide parts for step-less tractor transmissions
The German gearbox specialist ZF Passau GmbH uses extremely abrasion-resistant and low-friction DuPont? Vespel? thrust washers for its step-less, hydrostatic power-split Eccom CVT transmissions. The transmissions are deployed in agricultural machinery from internationally renowned OEMs such as John Deere, Claas Selbstfahrende Erntemaschinen or Same Deutz-Fahr. The planet wheels rotate against the washers separating them from the planet wheel carrier, thereby ensuring the consistently reliable and low maintenance operation of the transmission. In addition, rectangular cross-section rings are used on the drive shafts of the higher-rated transmissions. Overall, Eccom transmissions may contain over 20 Vespel? parts, all of which are produced by DuPont.
Vespel? thrust washers: minimum friction – less abrasion
Vespel? SP parts are suitable for continuous use temperatures of up to 290 °C, as well as short-term peaks of up to 480 °C. Vespel? SP-21 and SP-22 parts are favored for transmission manufacture because they are able to withstand pv loads (a product of pressure and speed) of up to 40 MPa?m/s in lubricated applications. “Of critical importance to ZF was the fact that Vespel? SP-21 thrust washers were able to take up the axial forces present in the transmission almost without abrasion from other adjacent metal components,” comments Peter Bergmann, market segment leader for the European transportation industry in the Vespel? business unit. “The exceptional tribological properties of the material lead to lower friction losses than with metal-to-metal pairings, and can thus have a positive influence on start/stop performance. It is for these reasons that Vespel? thrust washers have been successfully and reliably used for decades in transmissions for cars, buses or – as in the case of ZF – for agricultural machinery.”
All the Vespel? thrust washers used by ZF, have a small stud which locks into place with a corresponding recess in the cast-iron planet-wheel carrier. As a result, relative movement only occurs between the planet wheel and thrust washer. Moreover, as there is no relative movement between the washer and the carrier, there is no need for any additional finishing of the metal surface.
Jürgen Pohlenz, development manager for agricultural transmissions at ZF adds: “The Vespel? thrust washers adopt an excellent position with regard to their tribological behavior. Immediately after start-up of the transmission, they quickly adjust to any unevenness in the contact surface that may have been caused by play in the components or load tilts. As a result, after a minimal amount of running-in wear, a thrust surface is created, which is capable of evenly transmitting axial forces across its entire area. Friction is limited to very low levels during the lifetime of the transmission, meaning that the washers make only a minimal contribution to warming of components and oil.”
Vespel? rectangular cross-section rings control oil flow
As well as thrust washers, Vespel? SP-22 rectangular cross-section rings using microcut technology are used on the Eccom transmission models 3.5 and 4.5, which are designed for engines with an output of approximately 280 to 385 kW. They come with a precisely positioned, tightly-closed joint, which allows the ring to be attached precisely on the housing bore holes and to compensate for thermal expansion. The remaining gap permits the low and controlled flow-through of hot transmission oil. Oil grooves positioned on both sides in the seal face enable the oil film between the contact surfaces to quickly build up, helping to reduce friction, cool the sliding surfaces and extend the load range. With the grooves, the oil film remains stable even when oil temperatures reach 80 °C during operation and when pulsating pressure peaks of up to 22 bar occur, as is common for such transmissions.
Pohlenz continues: “Today’s tractors can reach speeds of more than 50 km/h (approximately 30 mph), associated with transmission shaft speeds of up to 4200 min-1. The relative velocities between the shaft and the rectangular ring are correspondingly high. Under a simultaneous pressure load, pv values of over 22 MPa?m/s can occur at the seal sites. In such cases, the tribological superiority of Vespel? rectangular cross-section rings comes to the fore when compared to standard modular graphite cast iron solutions. The equivalent metal rings can abrade due to the applied load, which in turn can lead to a thermal overloading of the shaft at the seal faces. In contrast, the low-friction, low-abrasion Vespel? cross-section rings continue to retain an optimal lubricating film even under such conditions. This helps effectively avoid unwanted overheating of the seal area, caused by friction, for the entire lifetime of the transmission.”
Tried and tested thousands of times
The ZF Eccom CVT transmissions have proven themselves more than 50,000 times in practice. The five current models, the Eccom 1.5, 1.8, 2.0, 3.5 and 4.5, are designed for engine outputs of between 100 HP and 520 HP (approx. 75 kW to 385 kW). The new Eccom 5.0 will be launched before the end of 2010, a transmission that is particularly well-suited for use in high-performance standard tractors, centre-pivot steering vehicles and agricultural towing vehicles, and is capable of transmitting engine outputs of up to 385 kW and input transmission torques of up to 2,300 Nm. All models enable a sensitive and uninterrupted build-up of traction on start-up thanks to their step-less ratio changes – even on the most difficult of ground conditions and without operating a clutch or manually shifting gears. The CVT transmissions consistently respond to load variations with gear ratio changes that ensure that output is always maintained at the best engine operating point in terms of consumption.
ZF is a leading worldwide automotive supplier for driveline and chassis technology with approximately 60,000 employees at 123 production locations in 27 countries. In 2009, ZF achieved a turnover of just under EUR 9.4 billion. The company ranks amongst the 10 largest automotive suppliers worldwide. To sustain its success with innovative products, ZF invests at least 5 percent of its annual sales in research and development. In 2009, a turnover share of 14% or EUR 14.3 billion was allocated to ZF products for agricultural and construction machinery, marine, airspace, specialty and rail vehicles.
The DuPont Performance Polymers business manufactures and sells Crastin? PBT and Rynite? PET thermoplastic polyester resins, Delrin? acetal resins, Hytrel? thermoplastic polyester elastomers, DuPont? ETPV Performance thermoplastic vulcanizates, Minlon? mineral reinforced nylon resins, Neoprene polychloroprene, Tynex? filaments, Vespel? parts and shapes, Kalrez? perfluoroelastomer parts, Vamac? ethylene acrylic elastomers (AEM), Viton? fluoroelastomers, Viton? FreeFlow? processing aids, Zytel? nylon resins and Zytel? HTN high-performance polyamides. These products serve global markets in the aerospace, appliance, automotive, consumer, electrical, electronic, healthcare, industrial, sporting goods and many other diversified industries.
DuPont is a science-based products and services company. Founded in 1802, DuPont puts science to work by creating sustainable solutions essential to a better, safer, healthier life for people everywhere. Operating in more than 70 countries, DuPont offers a wide range of innovative products and services for markets including agriculture and food; building and construction; communications; and transportation.