Power Transmission Reference Guide 2019

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POWER TRANSMISSION REFERENCE GUIDE

What are couplings for

power-transmission drive shafts?

A

s outlined in our coverage of couplings for motion control — online at couplingtips.com — couplings connect rotating shafts powered by a drive of some type — often an electric motor. All couplings serve to transmit drive torque and angular velocity. But applications for motion control (such as axes to position loads) usually use disc, slit or beam, curved-jaw, bellows, and other zero-backlash couplings capable of precise transmission of torque. In contrast, applications for power transmission (as in grinding machines, pumps, and material-handling machinery) commonly include disc, gear, chain, elastomer tire, grid, jaw, and Oldham couplings. Such PT couplings transmit more torque on average than couplings designed for motion control … even to millions of lb-in. Plus they’re more rugged to withstand challenging environments. Chain couplings — with typical maximum torques to 220,000 lb-in. at their largest — wrap lengths of chain around sprockets with clearances to impart flexibility. These powertransmission couplings excel in high-horsepower applications on axes needing correction of up to 2° and 0.01-in. angular and parallel misalignment.

ABB’s Dodge Raptor elastomeric-tire couplings use a split naturalrubber element. This element transmits torque to 340,200 lb-in.

22

DESIGN WORLD — MOTION

Couplings — Power Transmission HB 05.19.v4.indd 22

5 • 2019

This specialty double-disc coupling from R+W America is for machine-tool OEMs building designs with long spindle drives. It can send coolant directly to cutting heads via an integrated tube with interfaces at each end. These couplings operate in dynamic highspeed applications with lightweight CFRP or aluminum spacer tubes to boost performance; symmetric conical clamping ring hubs and fine balancing guarantee smooth operation. Torisonally rigid disc packs compensate for misalignment between the drive and driven shafts.

Diaphragm couplings — with typical maximum torques to 500,000 lb-in. at their largest — transmit power through a metal membrane (sometimes of varying thickness or ganged in arrays). Though often more costly than other options, diaphragm couplings mitigate and avoid problematic transmission of forces and moments to coupled equipment such as bearings. Profiles include straightspoked diaphragms; tapered diaphragms; and convoluted diaphragms assembled in arrays. These correct up to 1° and 0.1-in. angular and parallel misalignment. Elastomeric tire couplings — with typical maximum torques to 550,000 lb-in. at their largest — transmit power through a tire-shaped rubber element that bridges the coupling’s two hubs. These correct up to 1° and 0.2-in. angular and parallel misalignment. Jaw couplings — with typical maximum torques to 550,000 lb-in. at their largest — include both straight and curved variations. Much like disc couplings, the design lends itself to adaptation to both power transmission and backlash-free motion control. The coupling hubs have jaws that lock into a spider made of bronze, elastomer, or other material. Power transmission is reliable even through 1° and 0.01 in. angular and parallel misalignment. Oldham couplings — with typical maximum torques to 550,000 in. at their largest — include a metal or polymer disc with slots on each face 90° offset. Usually hub fins or tenons engage a slotted disc that’s free to slide even while transmitting torque. Oldham couplings for

motioncontroltips.com | designworldonline.com

5/14/19 12:48 PM


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