EMD223 Machine Component Design Dr. Mohamad Yusof Idroas Room: 3.10 (SoME) EMD223 Machine Component Design Dr. Mohamad Yusof Idroas Room: 3.10 (SoME)

Group Homework #1 To be uploaded in eLearning by today Submission Due Date: 26 Apr (Thu) 9am in class

Couplings

To understand the functionality of keys and couplings and their work mechanisms. To be able to specify suitable keys and couplings for shaft and other types of machine elements. Objectives

Function of couplings: Used to connect two shafts together at their ends to transmit torque from one to another. TWO types of couplings: 1) RIGID couplings 2) FLEXIBLE couplings Introduction

Rigid Couplings Used to connect colinear shafts Rigid shaft coupling Coupling halves can be attached to shaft ends with keys. On another halve (that transmit torque), tapered sleeves are wedged tightly by tightening the bolts connecting the two halves. The flanged portions serve as a safety function by shielding bolt heads & nuts.

Rigid Couplings Notes: Bolts in carry torque in shear. N = # of bolts

Rigid Couplings Advantages: NO relative motions between the shafts Precise alignment of the shafts Rigid coupling can forces misaligned parts such as offset on parallel shaft or axes intersect at an angle (angularly misaligned) back into alignment. Disadvantage: The force of misaligned parts by rigid coupling back into alignment may lead to early failures. The problems of small amount of shaft misalignment can be eliminated by using flexible coupling.

Flexible Couplings Advantages: Transmit torque smoothly Permit some axial, radial and angular misalignment Various types of flexible couplings: Rubber Element Flexible Couplings Metallic Element Flexible Couplings Oldham or Slider Block Couplings Universal Joints

Flexible Couplings Few designs use flexible material such as rubber & known as Rubber Element Flexible Couplings REFCs can provide appropriate elasticity and damping for control of torsional vibration & thus, control misalignment. Examples of REFCs: Sources: a, b, c Courtesy Lord Corp. d Courtesy Reliance Electric Company

Flexible Couplings Other flexible couplings use all metallic components & known as Metallic Element Flexible Couplings Examples of MEFCs (Courtesy of Reliance Electric Company) Roller chain coupling: Torque is transmitted through a double roller chain. Clearances between the chain & sprocket teeth on the two coupling halves accommodate misalignment (Source: Emerson Power Transmission Corporation, Ithaca, NY) MEFCs can sustain & have greater torque capacity

Flexible Couplings Ancient origin of flexible couplings is known as Oldham Coupling or Slider Block Coupling The sliding of the center block permits a substantial amount of shaft lateral offset. Built-in axial clearance permits some angular misalignment. Oldham or Slider Block Couplings: Both versions have a freely sliding center slider block that provides pairs of sliding surfaces at 90 o orientation. The greater the shaft misalignment, the greater the sliding. Lubrication and wear must be considered.

Flexible Couplings Universal Joints permit substantial angular misalignment of shafts having intersecting axes. Cross type U-Joints (also known as Cardan joint or Hooke’s joint) are commonly used at the end of drive shaft on rear wheel-drive automobiles to cancel speed fluctuations across the two joints & to give uniform output yoke rotation. Cross-type universal joints (Courtesy Dana Corporation)

Flexible Couplings Constant Velocity Universal Joints can transmit angular velocity uniformly across a single joint. These joints are typically applied in front-wheel-drive automobiles with short drive shafts and large shaft angles.

Design Analysis Input parameters ? Output parameters ?

Group Exercise A simply supported steel shaft in figure below is connected to an electric motor with a flexible coupling. Find the value of the critical speed of rotation for the shaft. ρ = 0.28 Ib/in. 3 for steel

Reference 1

Reference 1 (cont.)

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Reference 4

Thank You