Is it necessary to Align A Flexible Coupling?

          When I started my career as a maintenance engineer i got a doubt, is it necessary to align flexible coupling too?? we are using flexible coupling instead of fixed or rigid couplings because they don't have to be aligned??.

Later I read some articles and found some useful information. Today I wanna share this information with you people.

Courtecy : T B Woods Inc

For every coupling its manufacture give some common value of alignment specification:

According to T.B Woods Sureflex Coupling (with an 8je insert) 

--> Cost : about $XXX per sleeve or insert

--> Maximum  RPM : 4500

--> Parallel Misalignment : 0.020 in

--> Angular Misalignment : 0.094 in (about 0.012"/inch)

          Based on these manufactures recommendations the coupling can bear or tolerate some sort of misalignment. and also the insert (i.e rubber) is inexpensive then why we have to go precision alignment??

          Because we are aligning shafts -- we are not aligning couplings. The coupling sleeve or Insert that we use can tolerate that misalignment but the bearings on the shafts, oil seals, gears and also shafts can't tolerate.

Sometimes coupling will bend, but also it resists bending, for this it need some good amount of energy to oppose that force. That enegy is produced within itself by:

1) Increased heat due to friction

2) Increase in load on bearings, shafts, and seals.

          So finally i got to an conclusion, "is it necessary to align a flexible coupling?"- we should not worry about it but aligning the shafts to precision alignment is necessary. because, by this we will increase the machine life,  decrease vibrations, reduce energy consumption and also the couplings life. 

SHAFT ALIGNMENT

Shaft Alignment - Fundamentals

          Shaft alignment is process of positioning (or) aligning of shaft center lines of the driven and driver components (i.e., gearboxes, pumps, rolls etc.,) within a tolerated margin. Alignment is accomplished by giving shimming or moving machine components or sometimes both. The aim of shaft alignment is to maintain a common axis of rotation at operating equilibrium for two coupled shafts.

          In case of high speed equipment if the shaft alignment is not perfect we cant get maximum reliability and life through that equipment. Alignment is important in the case of direct coupled shafts and also the shafts of machines that are separated by distance even though we use flexible coupling. Shaft alignment is very important why because due to misalignment a lot of stress on shafts, vibration and noise produces. This causes excessive wear, bearing problems like heating and bearing failure, and results in the need for frequent repairs. By proper alignment we can reduce noise, vibration and also power consumption and this helps to achieve the design life of bearing, seal, shaft and coupling. 

          Alignment procedure is done by assuming a machine component is stationary, level and supported properly its base plate and foundation. Both angular and offset alignment must be performed in the vertical and horizontal planes, which is obtained by moving horizontally or by raising or lowering to align with the rotational center line of the stationary shaft. The movable components are designed as Machines To Be Moved (MTBM) or Machines To Be Shimmed (MTBS). MTBM generally refers to correction in horizontal planes and MTBS refers to corrections in vertical planes.