Severe duty and IEEE 841 motors are often supplied with open bearings and provision for regreasing regardless of the motor size. However, if the grease life is shorter than the expected bearing life, the bearings need to be relubricated while the grease is still performing satisfacto- rily. This is usually the case on motors above 20 hp. When using high-performance greases, a longer relubrication interval and grease life may be possible.

ing prevent damaging electric cur- rents—sometimes seen when using a motor with a PWM (pulse width mod- ulated or inverter) ac drive—from pass- ing through the bearing. This is one of the main reasons for using hybrid bear- ings in electric motors and generators. High-speed electric motors use hybrid bearings because they provide substan- tially longer service life due to lower operating temperatures and longer grease life as well as lower friction than traditional all-steel bearings.

Conclusions

Bearing selection remains a considera- tion on larger NEMA frame motors of 125 hp and above. Different bearing

arrangements and solutions may be necessary depending on the operating conditions. Bearing load capacity, mini- mum loads, and lubrication methods all can influence the proper choice. In addition, the external loading from pulleys or sheaves can lead to additional loadings as well as misalignments within the bearing, thereby limiting life. A new toroidal roller bearing design may offer some advantages, but endplate modifications may be required. The toroidal roller bearing is a self-aligning roller bear- ing that combines the features of a cylindrical roller bearing (internally adjusts for axial movements), the nee- dle roller bearing (long rollers to maximize load capacity) and the spherical roller bearing (raceways based on spheres to accommodate misalignments). The user should evaluate the connection to the load and consult with the motor manufacturer on belted loads to achieve an optimized solution. By utilizing this new toroidal bearing, it may now be possible for mills to stock one motor that is suitable for either coupled or belted loads.

在国家电气制造商协会（NEMA）电机上规定的减摩轴承类型的选择并不都是容易或明显的。从最终用户的角度来看，如果每个电动机仅具有一个可用的轴承配置并且该轴承配置适合于直接连接和带式负载，则这将是最简单的。不幸的是，目前不是这样。这在更大的高速电机（大于125马力和快于1200转/分钟）上尤其如此。如果选择为直接连接（即深沟球轴承）为优化的轴承，并且有带式负载，则轴承可能由于机械过载状况而过早失效。另一方面，如果选择适合的轴承（即滚动轴承），并且与电动机直接连接时，轴承可能由于缺乏保持所需的最小径向载荷而过早失效。通常，如果对清洁，再润滑，对准等特别注意，则不能优化轴承选择。本文讨论这些各种因素与轴承选择之间的关系，并帮助读者了解在减摩轴承的各种应用中所涉及的权衡并提出备选解决方案。

1发展历史

在纸浆和造纸工业历史中,一个电机可以连接到负载并且驱动有两种方法:耦合和约束。有一些特殊例子,比如套筒轴插入一个变速箱或使用一个立式泵电机,需要特殊的分析;径向与轴向联合负荷这些不会在本文中加以解决。

    电机轴的耦合负载通常由柔性联轴器连接驱动负载。这种类型的负载并没有任何轴向或径向负载，除了重型电动机的转子和轴组件(但是,安装偏差可以产生径向载荷)。滚动轴承(球)或柔性联轴器(套)是常见的承受耦合负载。

    最常见类型的负载是V型带轮安装在电机轴并且连接到另一个皮带轮，驱动负载的张紧力有一个或多个。这种类型的负载可以在电机轴上生成较大的径向负载,主要产生在驱动端的轴承上，因为它是最接近外部负载的。根据径向载荷的大小,滚动轴承(球轴承或滚子轴承)用于皮带产生的负载