The Function of Couplings and Their Types

A coupling is a type of mechanical device that connects similar or dissimilar shafts in machines to transmit power and motion. Generally, a coupling is used as a temporary connection, but can be made permanent, if necessary. More than that, couplings are easy to remove for servicing and replacement, and they are typically rigid or flexible in nature.As there are a wide range of designs available on the market, there are many unique differences in the design and function of couplings. For instance, some couplings can connect to a shaft without moving the shaft itself, while others necessitate shaft movement for installation. In most cases, couplings do not change the direction of motion or angular velocity, and they cannot be connected or disconnected mid-operation.Essentially, couplings are only capable of transferring torque over short distances, whereas torque over long distances can be achieved with chain drives and belt drives. In many applications, couplings are used alongside lead screw assemblies to connect the screw shaft in-line to a motor. Moreover, couplings can withstand an array of loads and accommodate for misalignment without permitting any relative motion between shafts. 

Key Functions of Couplings

Couplings are intended to perform a few key functions other than those previously mentioned. For example, these functions include power transmission, shock and vibration absorption, misalignment accommodation, heat flow interruption, and overload protection. In the next section, we will cover each of these in detail below.

Power Transmission: consists of power and torque transmission from a driving shaft to a elements

Shock and Vibration Absorption: can smooth out any shocks or vibrations sourced from the driving element to the driven element.

Misalignment Accommodation: is needed because misalignment can occur as a result of initial mounting errors or over time due to other reasons.

Heat Flow Interruption: prevents the flow of heat between connected shafts which can later lead to damage.

Overload Protection: is featured on specialized couplings for the purpose of severing the connection between two shafts during overload conditions.

Types of Couplings

Couplings come in numerous shapes and sizes to suit a diverse set of applications. While some work for generic applications, others can be custom-designed for specific scenarios. As such, this section will outline a few of the most common couplings and their subtypes.

Rigid Couplings permit little to no relative movement between shafts. When used to connect to equipment, they act as a single shaft.

  • Sleeve or Muff Couplings: consist of cast-iron sleeves or muffs, and they usually have threaded holes that match the shaft assembly, so that axial movement can be prevented.
  • Split Muff Couplings (Compression Couplings): are sleeve couplings that have been divided into two parts, both of which are held in place using studs or bolts.
  •  Flange Couplings: have flanges that can be slipped into each one of the shafts that are going to be connected, and they are available in unprotected, protected, and marine type flange coupling variations. 

Flexible Couplings enable a certain degree of relative motion between shafts and offer vibration isolation.

  • Gear Couplings: are primarily used for non-collinear shafts and are capable of high torque transmission.
  •  Universal Joints (Hooke’s Joints): serve as good options when two shafts are not parallel or they intersect at a small angle.
  •  Oldham Couplings: are used for lateral shaft misalignment which is common where power transmission is needed between shafts at varying elevations.

Other Common Types:

1        Diaphragm Couplings

2        Jaw Couplings

3        Beam Couplings

4      Fluid Couplings


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