A new way to evaluate steel sheet surfaces

Transcription

1 A new wy to evlute steel sheet surfes L. Blunt X. ing W. Zeng T. Asim Centre for Preision Tehnologies (CPT) University of Huersfiel Queensgte Huersfiel UK HD1 3DH Tel.: E-mil: x.ing@hu..uk Astrt This pper introues new ssessment tehnique to monitor the qulity of ote steel sheet surfes minly use in the onstrution inustry e.g. s ling for ommeril uilings externl surfe omposite pnels or even omesti pplitions so lerly the visul pperne is ritil. Normlly these types of steel sheets re oil ote onto steel strips. After uring the oting is soft when it hs oole to pproximte 60 C it n e emosse with pttern y pplition of pressure y roller with the ppropritely pttere surfe. After emossing n further ooling the ote strip n e oile n store. However uring the storing proess the weit of the oil (of the orer of severl tonnes) n mge the soft surfe y reting visile pressure mrks. Sometimes the surfe will relx k to the originl emosse shpe some time fter the pressure hs een relieve or with the help of het tretment. On osion however the surfe oes not reover n visul efet remins whih les to ustomer reetion. In this pper new wy to hrterize ote surfe of steel sheets whih omines wvelet filtering [1] with eompose numeril nlysis tehniques [2] is presente. The wvelet filtering is se on omplex wvelet n it hs very goo metrologil hrteristis in the sle omin n provies shift-invrine n iretions sensitive properties. In this reserh this wvelet moel is use to extrt the informtion of struture texture of ote steel surfes within the originl emoss. The eompose numeril esription is use to qulify the vrition phenomen of surfe texture uring storge n trnsporttion. The results n e feek to steel inustry to signifintly improve their oting tehniques storge n trnsporttion. Keywors: Wvelet filtering eompose numeril nlysis surfe texture 1. Introution Cote steel prouts re use wiely in the onstrution inustry ue to their eortive pperne n the ft tht the oting protets the unerlying steel from the effets of environmentl orrosion. The mnufturing proess involves oting steel sheet with polymeri mteril. During proessing the polymer is well ove its glss trnsition temperture however when the temperture rehes pproximtely 60 C texture n e roll emosse on the surfe of the oting using suitly texture roller. The oting form is efine y the roller texture n is usully of visully ppeling form. See Fig. 1. During storge n trnsporttion of the sheet flt spots n pper in the ote surfe ue to hi spot loing use y the weit of the oils whih is of the orer of severl tones n these flttens zones re esily etetle to the humn eye n n thus le to the reetion of lrge thes of ote rolle oil. This pper seek to evelop mesurement tehnique whih n etet he first signs of flt spotting n n she more lit on the origin of the prolem. Following initil rel surfe metrology n nlysis hypothesis onerning the evelopment of the mge surfe ws evelope

2 The k (or rer) sie of the sheet metl is pressing the polymer ote surfe reuing the epth of the lrge emosse pits. Aitionlly the k (or rer) sie of the sheet metl is imprting its own rouness into the existing rouness of the polymer oting surfe hene inresing the plteu rouness. To prove the hypothesis there ws nee to effetively seprte the long wvelength fetures of the surfe (the lrge pits) from the smll wvelength fetures of the surfe rouness. 2. Wvelet nlysis Disrete wvelet trnsform (DWT) n provie multi-slr nlysis whih hs een use for filtering engineering surfe t. The orthogonl wvelets use for the extrtion of rouness of engineering surfes re not liner phse filters (symmetri filter) n le to phse istortion in filtering. Biorthogonl wvelet filtering for engineering surfe nlysis is ple of otining liner phse hrteristis. To reue the omplexity of the lgorithm for iorthogonl wvelet trnsformtion n overome ounry istortions the seongenertion iorthogonl wvelet trnsforms using the lifting sheme were propose n pplie to engineering surfe nlysis. The lifting sheme of the ui spline wvelet hve een stnrise y ISO/TC213 s the stnr wvelet filter for profile nlysis. However the DWT is still hmpere for use in mny pplitions espeilly for the rel surfe nlysis ue to the lk of shift invrine whih mens smll shifts in the input signl n use mor vritions in the istriution of the energy etween DWT oeffiients t ifferent sles. Hene it the hrteriztion results re epenent on the mesurement frme [1 2]. A novel Dul-Tree Complex Wvelet Trnsform (DT-CWT) representtion ws therey previously propose for the seprtion n extrtion of ifferent omponents of engineering surfes. The DT-CWT n provie pproximte shift-invrine property n improve iretionl seletivity. Zero/liner phse property of DT-CWT ensures tht the filtering results hve no istortion n goo feture loliztion ility. The steep trnsmission urve property of the mplitue trnsmission hrteristi enles the DT-CWT to seprte n extrt ifferent frequeny omponents of surfes more urtely [1 3]. By using two prllel fully-eimte trees whih re susmple ifferently n re oth rel wvelet trnsform respetively the DT-CWT n hieve perfet reonstrution n very nerly shift invrint. The min pproh of DT-CWT opertion is to use two-hnnel filter nks in the rel n imginry prts The sle oeffiients n wvelet oeffiients (or pproximtions n etils) for the two trees re enote respetively ( ) n ( ). The filters re the sme in the two trees for level one n ifferent for other levels. For levels ove one Q-shift filter esign tehnique se on the Z-trnsform theory of liner time invrint smple systems is use to onstrut the lowpss FIR filter to stisfy linerphse n perfet reonstrution onition. For one imensionl isrete surfe profile t f x the DT-CWT n reple it with two series: 1 n 1 whih n e interprete s the rel n imginry C C prts of the omplex proess: i i (where i 1 ) After levels eomposition it n e expresse y: C C C C C C C C C W [ f ( x)] C C where enotes the orsest sle n refer to the omplex smooth oeffiients t level n the omplex etil omponents of oeffiients t the level respetively

3 For two imensions the surfe rel t f ( x y ) n lso e eompose n reorere into 4 interleve trees A B C D y using the seprle filter nk tehnique. The pproximtions n etils of the 4 trees re enote respetively ( ) ( ) ( ) ( ). Where the susript refer to the ifferent omintion of lowpss n hipss filter on the rows n olumns. At eh level the pproximtion oeffiient n e expresse y four rel oeffiients ( ). For eh sun the etils n e interprete s the rel n imginry prts of two omplex proesses n : ( ) i( ) ( ) i( ) Thus the etils of the 3 suns provie 6 omplex suns inste of 3 rel suns s in the rel se. After levels eomposition the surfe rel t f ( x y ) n e reple with: C C C C C C C C C W [ f ( x y)] where C ( ) In the present stuy the DT CWT tehnique ws pplie to the ote sheet steel prout in orer to seprte the longer wvelength fetures (the lrge pits) from the short wvelength fetures (i.e. the smll sle lol fetures of the emoss. 3. Mesure results Fig. 1. ) Optil imge of mge zone; ) zoome imge on mge region ounry. In orer to stuy the effets of the pressure spots unmge smple sheets were presse uner ontrolle onitions esigne to simulte the storge n trnsport onitions of the sheet. The pplie los use were onsistent with those oserve in storge n trnsport of the oils. The mge ws limite to smll re in orer to isolte the pressing effet. All the surfes were mesure using ontting stylus instrument operting in rel moe (Tylor Hoson Formtlysurf). Surfe mps of the unmge n mge re re shown in Fig. 2. For the purposes of nlysis eh re ws mesure fifteen times. The surfe mps plotte on the sme sle show the overll erese in feture heit s result of the epth of the lrge pits eing reue. Conversely when the rel rouness prmeters were lulte the Sr prmeter (surfe re rtio) inite tht the rel surfe re of the mge zone ws lrger thn the unmge zone. Ss (0.18 unmge region 0.24 mge region). This woul suggest tht the smll sle rouness ws inrese in the mge region

4 Fig. 2. Filtere results. In orer to verify the inrese in rouness in the mge region it ws neessry to filter the surfe t in suh s wy s to remove the long wvelength fetures of the surfe (the lrge pits) whilst preserving the fine sle rouness. This ws omplishe y using the Dul-Tree Complex Wvelet Trnsform (DT-CWT) filter. The results re shown in Fig. 3. Figure 3 shows filtere rel mp ross the ounry of the mge n unmge region. In orer to show the inrese in rouness in the mge zone 700 2D profiles were extrte from ross the filtere re n the profile rouness ompute the results re pltte ross Fig. 3. Extrte profile Fig. 3. ) DT-CWT filtere surfe of ounry zone; ) extrte profile rouness. 4. Disussion The Dul-Tree Complex Wvelet Trnsform (DT-CWT) filtering ppere to suessfully seprte the long wvelength fetures n the fine sle rouness. The 2D profile extrtion figure 3 lerly shows tht the mge region ws signifintly rouer t the fine sle thn the unmge region. Consequently it ppere tht the ksie of the sheet ppere to hve flttene the eep pits whilst imposing rou fine sle struture. The rer sie of the sheet ws mesure n ws foun to posses rouness of Sq = 0.87um whih ws omprle with the fine sle rouness of the mge region whih hs profile rouness verge of Rq = 0.92um It is this fine sle rouening tht gives rise to the poor visul pereption of the oting n ny solution to the prolem oul e se roun reuing the rouness of the ksie of the sheet

5 Fig. 4. Sheet ksie topogrphy. 5. Conlusion In this pper metho for eresing the sptil omponent of the mesurement error of the tringultion sheme hs een esrie. The metho is se on polriztion filtrtion of the rition sttere from the surfe. The experimentl investigtions performe hve given n inrese in the ury of mesurements y ftor of more thn two. It hs een shown tht using this metho for eresing the tringultion mesurement error is more vntges uner inspetion the smooth surfes of hi lss surfe proessing. The tehnil solutions esrie in this pper were use in the evelopment of unit to mesure the geometril prmeters of ylinril prouts for tomi pplitions. 6. Aknowlegements Authors woul like to thnk Prof. Yuri Chugui for vlule ontriution n helpful isussions. Referenes 1. X. ing L. Blunt. Thir genertion wvelet for the extrtion of morphologil fetures from miro n nno slr surfes. Wer pp L. Blunt X. ing (Es). Avne Tehniques for Assessment Surfe Topogrphy. 1st en Lonon Penton Press W. Zeng X. ing P. Sott. Metrologil Chrteristis of Dul Tree Complex Wvelet Trnsform for Surfe Anlysis. Mes. Si. Tehnol pp