& U-JOINTS

o transmit rotary FLEXIBLE COUPLINGS ...... A177 tion and damping. power from one UNIVERSAL-JOINTS...... A182 • Permit adjustment of T shaft to another, FLEXIBLE SHAFTS ...... A183 torsional stiffness. where both shafts turn FLUID COUPLINGS...... A184 • Endure momentary about the same nominal COUPLINGS AND U-JOINTS ADVERTISING ...... A187 overload, overspeed, or centerline, you need posi- high vibration level. tive of the shafts. • Allow lateral shaft The coupling device can be FLEXIBLE COUPLINGS support. a rigid assembly such as two match- • Limit load and vibration pro- ing shaft-mounted flanges bolted to- An obvious function of a flexible duced by misalignment. gether, or a long rigid metal or non- coupling is connection of a driving • Provide limiting. metal sleeve fitted over and locked to shaft or flange element with an adja- Key design criteria for flexible cou- both mating shaft ends. Many rigid cent in-line driven member. The se- plings can be established with this coupling designs are available. lected coupling must transmit rated checklist: The first part of this product depart- power efficiently and meet torque, • Coupling functions from preced- ment focuses on various types of flexi- speed, acceleration-deceleration load- ing list. ble couplings, which are more popular ing, and other duty-cycle require- • Safety in operation and failure. than rigid couplings in power transmis- ments. It must flex enough while ro- • Weight and space. sion applications. Some flexible cou- tating to accommodate, within limits, • Ease of maintenance. plings can accommodate up to about 3 undesirable effects caused by axial • Aesthetic appearance. deg of angular misalignment as well as misalignment, shaft end movement, • Near constant velocity operation. limited lateral displacement between and vibration between connected • Vibration and noise isolation and two shafts. Though not covered here, members. Also, sound absorption be- damping. composite shafts are becoming popu- tween driving and driven elements is More than 80 companies manufac- lar for connecting machinery and mo- essential in many applications, such ture one or more types of flexible cou- tors that are separated by large dis- as home appliances, office machines, plings. They can be classified under tances. Cooling tower drive shafts are and computer systems. one of the following four categories: a typical use. Mechanically flexible — Cou- Universal joints, which are covered Function and design checklists plings in this category obtain their op- in the second part, are a common solu- erating flexibility from the rolling or tion to misalignment where the cen- Before selecting a coupling type, sliding of mating parts, which usually terline of one shaft relative to another tabulate desired coupling functions require lubrication. Basic types in- is expected to vary more than 3 deg. U- using the following checklist: clude spindle, gear, chain and joints can transmit power through an- • Transmit power through me- sprocket, grid, disc, metallic beam, gles as high as 30 or 40 deg even at chanical shaft joining. and bellows (Figures 1 to 7), plus uni- high speed. • Permit angu- Flexible shafts are commonly used lar, axial, parallel, to transmit rotary motion and light or combination mis- loads around obstacles. Covered in alignment. the third part, these shafts can make • Permit rapid up to 90 or 180-degree turns to con- original and subse- nect components that are not aligned. quent alignment Another type of device used to con- checks. nect a driving shaft to a driven shaft • Permit spacer- is a fluid coupling, discussed in the type or radial-type fourth part. It must be used in combi- disengagement nation with flexible couplings or U- (preferably without joints to handle any anticipated axial disturbing shafts). alignment variations or misalignment • Provide failure problems.