弯曲疲劳强度的工业经验

doi:10.1111/j.1460-2695.2010.01450.x

Industrial experiences of bending fatigue strength in table liner for cement mill

S.-H.BAEK,1S.-S.CHO 2and W.-S.JOO 3

1Graduate

School of Mechanical Engineering,Dong-A University,840Hadan2-dong,Busan 604-714,Korea,2Department of Vehicle Engineering,

College of Engineering,Kangwon National University,Samcheok,Gangwon-do 245-711,Korea,3Department of Mechanical Engineering,Dong-A University,840Hadan2-Dong,Busan 604-714,Korea Received in final form 17November 2009

A B S T R A C T A table liner for the vertical roller mill has been used to grind natural limestone.Un-

expected fatigue failure accidents have occurred during portland cement manufacturing process.The design life of a table liner is 4×107cycles,but the actual fatigue life of a table liner is 2×106to 8×106cycles.The fatigue crack of a table liner initiates from the outside edge of the grinding path of the limestone.When such a crack occurs,the table liner has to be replaced,and this requires 30%of the total maintenance cost of the vertical roller mill.Therefore,this study examines the fatigue failure of a table liner by plane-bending fatigue test,stress measurement test,finite element analysis and fatigue fracture analysis.

Keywords bending fatigue strength;finite element analysis;Goodman diagram;stress-life curve;vertical roller mill.

I N T R O D U C T I O N

A vertical roller mill for cement production is far supe-rior than the existing tube mill with respect to energy efficiency.However,the table liner for a roller mill un-dergoes periodic repeated loading because it is a rotary machine.A fatigue function is expressed in terms of the stress ratio and mean ually,a fatigue function uses the Goodman diagram.1–3Stress ratio R in a fatigue cycle is defined as follows.4,5R =

σmin σmax

(1)

where σmin is the minimum stress and σmax is the maximum stress in a fatigue stress cycle.

Joo et al.6,7reported that the loads applied to a turbine blade are repeated bending load,torsional load and cen-trifugal load.According to X-ray fractography and the Goodman diagram,repeated bending stress is the major cause of turbine blade fatigue failure.Mandell et al.4,8,9proposed the Goodman diagram based on 13stress ratios.This method formulated the S-N behaviour considering the effect of mean stress.

Correspondence :W.-S.Joo.E-mail:wsjoo@dau.ac.kr

Figure 1shows the photograph of the vertical roller mill analyzed in this study.The vertical roller mill consisted of two rolling tires and a table liner with eight steel plates.The table liner was made of SC450steel and had a plasma-sprayed WC-15%Co coating layer.The expected design fatigue life of the table liner was 4×107cycles,but the actual fatigue life was 2×106to 8×106cycles.The surface hardening layer of the table liner was subjected to wear and repeated bending tensile load.The prema-ture failure of the table liner can be ascertained from data on the contact fatigue.But,the surface hardening layer of the table liner was made of a big-particulate material.That is,the macrostructure of the material can relieve the stress concentration due to contact.A table liner is a rotary machine component with a very complex fail-ure pattern.Therefore,it is very difficult to simulate the in-service conditions of a table liner.In this study,the fatigue strength of a table liner is estimated by stress mea-surement,finite element analysis (FEA),bending fatigue test and the Goodman diagram.

M A T E R I A L A N D E X P R I M E N T A L P R O C E D U R E S

Material and test specimen

Figure 2shows the failure pattern of the table liner exam-ined in this study.Crack initiated from the corner of the

358c 2010Blackwell Publishing Ltd.Fatigue Fract Engng Mater Struct 33,358–364

Fatigue & Fracture of

Engineering Materials & Structures