Monday, September 28, 2015

Disc Couplings - Common Terminology (Part 2)

Design Basics - Common Terminology

DI Style Disc Coupling - by Lovejoy, Inc.
DI "Drop-Out" Type Disc Coupling
The diagram of an industrial DI Type "drop-out" style disc coupling at right highlights a number of useful terms common in describing a disc couplings.

(Note that because this coupling has two disc packs, it is equipped to handle parallel in additional to angular misalignment. It is for this reason that many disc coupling designs make use of two disc packs, and not just one.)

"Hubs" are the metal element designed to attach to the two shafts of a power transmission system.

"BSE" stands for "Between Shaft Ends" and describes the specified distance between to two shafts that the coupling is design to connect.

"PW" describes the space allocated for the each disc pack.

The "Spacer Assembly" is called out specifically in this design as the whole center section of the coupling, including the two disc packs, is designed to be able to be removed from an installation with requiring the coupling hubs to be moved or removed. A drop-out spacer assembly section, as shown in the image above, is an additional feature not common to all spacer disc couplings. An example of a spacer disc coupling without a drop-out assembly section would be Lovejoy's SX Type.

In the case of Lovejoy's DI Type disc coupling, "Guard Rings" are included and hubs are piloted to ensure proper centering of the drop in spacer assembly. This piloting serves as an anti-flail feature and aids in the couplings ability to meet API 610 requirements.

SX Type Disc Coupling with SLD
While disc couplings commonly use interference fit hub-to-shaft connections, another hub-to-shaft connection feature available for disc couplings are shaft locking devices ("SLDs").  As shown in the photograph at right and the installed photograph below, shaft locking devices allow pressure to be exerted on a hub to connect the hub firmly to a shaft for torque transmission. The advantage of using shaft locking devices is that users can avoid interference fits that require significant maintenance time to remove. The disadvantage of shaft locking devices is the initial upfront cost. Additionally, watching tolerances and understanding the ratings of a shaft locking device are also critical as the shaft locking device may have ratings below the coupling and or system requirements. 

To learn more about disc couplings, please check out Part 1 of this blog series... or Lovejoy's disc coupling product pages & catalogs, the non-lubricated section of The Coupling Handbook, and/or subscribe to this blog as there will be several more blog posts on disc couplings in the immediate future.

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