Foundations for industrial machines handbook for practising engineers, rotary machines, reciprocating machines, impact machines, vibration isolation system d CAD publishe

FOUNDATIONS FOR INDUSTRIAL MACHINES, Handbook for Practising Engineers FOUNDATIONS FOR INDUSTRIAL MACHINES ~ ~ ~ ~ Rotary Machines Reciprocating Machines Impact Machines Vibration Isolation System Handbook for Practising Engineers K.G BHATIA DrK G Bhatia Foundations for Industrial Machines First Edition 2008 While every effort is made to publish error-free information in this handbook, the author makes no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, of the information, guidelines, methodologies or related graphics contained in the handbook, for any purpose Any reliance placed on such information is therefore strictly at one's own risk, unless that information is duly consulted and verified with the author, and subsequently confirmed in writing In no event will the author be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or 'damage whatsoever arising from loss of data or profits, arising out of, or in connection with, the use of this handbook Copyright © 2008 by D-CAD Publishers All rights reserved This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of the author The book may contain copyrighted material, trademarks and other proprietary information, including, but not limited to, text, graphics, and users shall not publish and distribute such material (in whole or in part) and/or to incorporate it in other works in any form, media or technology now known or hereafter developed ISBN 978-81-906032-0-1 www.machinefoundation.com Published by D-CAD Publishers, 158; Vardhman Grand Plaza, Mangalam Place, Sector 3, Rohini, New Delhi I 10085 Printed through Bharat Law House, New Delhi In the loving memory of My parents Late Shri Kartar Chand Bhatia & Late Smt Leelawanti Bhatia who, in spite ofsufferings on account ofpartition, struggled hard and devoted their active life in upbringing me and my siblings In expression of my gratitude to My brother Shri MG Bhatia, who sacrificed his career in support of my studies Dedicated to My wife Manjufor her constant encouragement and support throughout the tenure ofwriting of this handbook My deep Sense o/Gratitude to: Organisations of Excellencefor Wok Experience Bharat Heavy Electricals Limited New Delhi Engineers India Limited New Delhi Institutions of Excellence in Learning Indian Institute o/Technology New Delhi, India International Institute o/Seismology & Earthquake Engineering Tokyo, Japan Indian Institute o/Technology Roorkee, India Institute o/Technology BHU, Varanasi, India About the Handbook The author has been engaged in designing, testing and review of machine foundations for various industrial projects viz Petrochemicals, Refineries, Power plants etc for the last about three decades The handbook is written primarily for practising engineers as well as for students at Post Graduate level Handbook shares author's long experience on the subject and focuses on the improvements needed in the design process with the sole objective of making practising engineers physically understand and feel the dynamics of machine foundation system The handbook covers basic fundamentals necessary for understanding and evaluating dynamic response of machine foundation system The author has also conducted extensive tests on machine foundation models as well as on prototypes For over two decades, the author has been associated with Failure Analysis Studies on various types of machines Observations from all the above studies suggest need for improvement in the design o/foundationsfor better performance of machines These include: a) b) c) More comprehensive evaluation ofSite Soil Data Better understanding ofMachine Data and its use infoundation design Improvement in the Design Philosophy that suggests i) ii) Improvement in the Modeling Technique Improvement in Analysis Technique 14-10 Case Studies Action Plan: In order to fix magnetic probes on the foundation, metal washers were fixed at 1I4th, 112 & 3/4th height of all the columns as well as along top deck (both on left and right side of the machine) In addition, metal washers were also fixed at specific locations of interest at beam bottom Vibration measurements were taken at all these points in addition to bearings Bearing Vibrations are shown in Figure 14.3-2 and top deck vibrations are shown in Figure 14.3-3 Column vibration measurements along height of column are shown in Figure 14.3-4 ColA ColA Unit Unit I 10 10 Frequency in CPM 10 Horizontal Amplitudes ColI 10 ColI I!l e 3040 t) ~ 3000 10 10 Frequency in CPM 10 10 c 4) 4) M ~ t:I ~ jl., 167 ~ j 10 Figure 14.3-5 4 10 10 Frequency in CPM 10 Frequency in CPM Horizontal Amplitudes Column Amplitudes - FFT Record Unit &2 10 Case Studies 14-11 Observations: Ratio of bearing amplitudes of two units is of the order of whereas ratio of top deck amplitudes is of the order of2 It is a wild guess and a question mark whether cracking of the columns at top (close to deck bottom (soffit of beam) is responsible for such a behaviour or such high vibrations have resulted in cracking of the column? Visual examination of the column vibration and plot of amplitudes indicate that its 2nd mode frequency of some of the individual columns in transverse direction has tendency to be in resonance with operating speed Similar behaviour is also noticed for some columns in axial direction Figure 14.3-5 shows FFT analysis of column vibration records FFT analysis of records confirm to the above observation It is seen that the resonant frequency of some of the columns lie close to 50 Hz which is the machine running speed Though the amplitude levels are low, the trend is not healthy It is primarily because the analytical tools available about two decades back were not adequate to carry out such a detailed analysis and moreover the need was neither emphasized by the owner / customer nor by machine manufacturer Example 14.4 Reciprocating Compressor on Isolation pads Preamble: A reciprocating compressor on a frame foundation is to be located inside a plant building The forces developed by compressor are extremely high and supporting the foundation over the soil results in excessive amplitudes of vibration The size of the base raft also can not be increased because of restrictions imposed by other structural foundation The only options were i) either to strengthen the soil by whatsoever possible means, ii) resort to pile supported foundations or iii) use strong stiffness material underneath the base· of the foundation so as to limit the amplitudes within permissible levels This is with reference to the design problem discussed in Chapter 10 The decision by the company was to resort to isolation technique and design the foundation Machine 'iA Isolation Padsl Cork Pad 14-12 Case Studies Action Plan: A common raft was provided spanning across width of the bUilding Compressor foundation was placed over the raft with Cork as Isolation device so as to minimize transmission of forces from machine to the common foundation This system was designed by the author in 1974 Schematic arrangement is shown in Figure 14.4 -I With this arrangement Machine was installed and has run satisfactorily keeping the amplitudes within permissible limits Cork thickness of 75 mm below the frame foundation was found to be adequate Cork properties were tested at one of the national laboratory Recommended values for computation are as under: • • • • 500 kN/m2 10 MPa 15 MPa Compressive strength Elastic Modulus (Static) Elastic Modulus (Dynamic) Coefficient of Uniform Compression Cu = 20x 10 kN/m' The concept was used once again by the author, in 1979, for design of a Frame Foundation for a Gas Turbine The need arose because of slip during planning While making the layout, not adequate space was left to accommodate the GT Unlike previous case, the machine is a high rpm machine and it was rather easy to get the required frequency ratio for achieving desired isolation The success has given improved confidence level for such designs Example 14.5-1 Vibration Isolation of FD Fan Foundation Preamble: Vibration Isolation design of FD fan is discussed in Chapter 12 After machine installation, high vibrations were reported from the site M8 - Motor Bearing F.8-I - Fan Bearing - I FB2 - Fan Bearing - ' .. .FOUNDATIONS FOR INDUSTRIAL MACHINES, Handbook for Practising Engineers FOUNDATIONS FOR INDUSTRIAL MACHINES ~ ~ ~ ~ Rotary Machines Reciprocating Machines Impact Machines Vibration Isolation System. .. Undamped System - SDOF Spring Mass System 2-4 2.1.2 Damped System 2-28 Forced Vibration 2-37 2.2 2.2.1 Undamped System - Dynamic Force Externally Applied 2-38 2.2.2 Damped System - Dynamic Force... Applied 2-46 2.2.3 Damped System - Dynamic Force Internally Generated 2-55 2.2.4 Damped System - Dynamic Excitation Applied At Base 2-59 2.2.5 Undamped System - Subjected to Impact Loads 2-63