Optimization of polypropylene pipe wall thickness measurement by pulse ultrasonic method

Transcription

1 ISSN ULTRAGARSAS (ULTRASOUND), Vol. 64, No.4, Optimization of polypropyln pip wall thicknss masurmnt by puls ultrasonic mthod S. Sajauskas, V. Markvičius, J. Savickaitė Dpartmnt of Elctronics Enginring, Kaunas Univrsity of Tchnology Studntų st. 50, 5368 Kaunas, LITHUANIA, Phon , Abstract Th analysis of optimization qustions of th pizolctric transducr for th polypropyln pip wall thicknss masurmnt is givn. Thortically and xprimntally th maximum of th transducr snsitivity is obtaind whn th protctor (acoustic dlay layr) is producd from anti-friction matrial caprolon with graphit (caprolon+c). Kywords: ultrasonic non-dstructiv tsting, plastic pips production, propyln pips Introduction Th problms of th crtification and th quality paramtrs corrspondnc to th EU's strict standards oftn aris whil implmnting th nw tchnologis in Lithuanian industry and producing th comptitivnss of th product in th EU. This work is dvotd for th largdiamtr polypropyln pip wall thicknss masurmnt tsting during th production. Th ultrasonic puls mthod is usual by for this purpos usd. In spcific cass thr is a nd for nw solutions in spit of th ultrasonic mthods dvlopmnt and high lvl of practical us. In this cas, thr is a nd to control th larg-diamtr (thicknss from 40cm to 00 cm) thin-walld (wall thicknss from 3mm to 6 mm) propyln pip manufacturing procss at th tmpratur of (40 60) C. This rquirs highprcision masurmnt of a thicknss that could b achivd by incrasing th frquncy of th usd ultrasonic signals. Howvr, polypropyln, as wll as all plastics, is charactrizd by th incrasd ultrasonic wav attnuation, xponntially incrasing with th frquncy. Th low acoustic impdanc is also charactristic to polypropyln; and it would not allow th us of th standard masuring instrumnts and stimulats th sarch for th optimal solutions. Thortical rsarch Th broadband pizolctric transducrs with th acoustic dlay layr ar usd to masur small thicknss by th puls ultrasonic mthod. Th most appropriat is to masur th product wall thicknss through pip wall from innr sid, sinc th polypropyln a pip during manufacturing procss (Fig. a) is formd on th stl cylindr (Fig. b). In this way th ultrasonic signal propagats in th tripl mchanical systm; its summarizd schm is shown in Fig. 2. Th layrs in th simplifid schm can b assumd as a flat, whras th pizolctric transducr diamtr d<<d, whr D is th diamtr of a polypropyln pip. Acoustic signal in th most common cas is dfind as a prssur function p( t) = P t cos ωt () () ( ), whr P(t) is th amplitud tim function, ω = 2πf, f is th frquncy. a b Fig.. a th sction of polypropyln pip (with a cut fragmnt), b th stl cylindr for a formd polypropyln pip. An acoustic signal is dcrasing during propagation in th carrir with th acoustic impdanc Z = ρc, whr ρ is th dnsity of th carrir, c is th vlocity of th innr sound. Whn th ultrasonic wav is flat and incidnts prpndicularly to th surfac its amplitud is givn by α x A x =, (2) 60

2 ISSN ULTRAGARSAS (ULTRASOUND), Vol. 64, No.4, whr x is th distanc, A 0 is th prssur amplitud valu on th surfac layr (x = 0), α attnuation cofficint, dscribd as Pizolmnt P ln( x ) P x α = 0 [ Np/m]. (3) Polypropyln Fig. 2. Ultrasound propagation in th tripl mchanical systm: - th acoustic dlay layr of pizotransducr, 2 - stl pip wall, 3 - th polypropyln pip wall, 4 - air. Having assssd th acoustic signal propagation through th layrs n, n + limit, th ratio as 2Z , + = n ρ = n c D n, (4) n n Zn + Zn+ ρncn + ρn+ cn+ th rlativ dcras in th signal amplitud on th road pizolmnt-third layr-bottom pizolmnt is qual to -2α d -2α 2d 2-2α 3d = D 3,2 D2,3 R3,4 D3,2 D2, (5) whr Z n and Z n+ ar th acoustic impdancs of adjacnt layrs; ρ n and ρ n+ ar thir dnsitis, c n and c n+ ar th sound phas vlocitis in thm; d, d 2, and d 3 ar th thicknsss of th st, th 2nd, and th 3rd layrs; α, α 2 and α 3 ar th sound attnuatuon cofficints in th corrsponding layrs, R = ( Zn Zn+ )/( Zn + Zn+) is th rflction cofficint from th third layr of th bottom lin. Sinc th 3rd layr from th bottom contacts air and Z n+ << Z n, so R. Thn -2 ( d 2d 3d ) D,2 D2,3 D3,2 D α + α α = + 2,. (6) Air Th calculatd thortical dpndnc (/A 0 )(Z 2 ) whn th st carrir is plxiglas (Z =0, kg/(m 2 s)) and th 3rd carrir is polypropyln (Z 3 = 0, kg/(m 2 s)) has shown that th acoustic prssur transmission cofficint of th stl pip (Z 2 = 4, kg /(m 2 s)) is 0 tims lowr (Fig. 3, point 3) than th 7 ( A x ) max = 3,3 0. Exprimntally masurd plxiglas and polypropyln attnuation cofficint valus for th frquncy f = 2,5 MHz hav bn usd for th calculation. It is clar that a polypropyln pip wall thicknss d 3 masurmnt through th stl pip wall is not optimal, so in ordr to incras th masurmnt snsitivity it is appropriat to us a spcial acoustic dlay layr with an acoustic impdanc in markd bordrs of point and 2, i.., 0,5 0 7 < Z 2 < 0,6 0 7 kg/(m 2 s). In this cas, th 2nd intrmdiat layr is also th protctor which protcts pizolmnt against mchanical war, scrolling masurd th polypropyln pip surfac through it. Thrfor, in slction of th matrial not only to th acoustic proprtis, but also to th anti-friction must b takn into considration. Fig. 4 shows th thortical acoustic signal rlativ rduction dpndnc on th intrmdiat layr thicknss d 2 for diffrnt matrials, charactrizd by a low acoustic impdanc with th rsistanc to abrasion (caprolon, caprolon + C, tflon). Fig. 4. Signals ratio dpndnc on th thicknss d 2 of th tripl acoustic systm Th low acoustic impdanc and th thicknss ar th acoustic rquirmnts for th intrmdiat scond layr (Fig. 3 and 4). So in ordr to fulfill this task it rquird to mak a hol in a stl cylindr for th mbdding of th protctor. This rquird to invstigat th doubl acoustic systm whr th first layr (protctor) has an anti-friction matrial of d layr thicknss; th scond layr is of polypropyln. Th rsults of th thortical calculations for th doubl acoustic systm ar shown in Fig. 5 and 6. Fig. 3. Signals ratio dpndnc on th acoustic impdanc of th tripl systm of th ultrasonic transducr Fig. 5. Signals ratio dpndnc on th acoustic impdanc of th doubl acoustic systm 6

3 ISSN ULTRAGARSAS (ULTRASOUND), Vol. 64, No Th tmpratur dpndnc of th polymr matrials acoustic proprtis hav bn invstigatd in ordr to valuat th ral production conditions (nvironmntal tmpratur in th masurmnt rang (T= ) 0 C) (Fig. 7). Fig. 6. Signals ratio dpndnc on th thicknss of th scond layr thicknss d 2 According to th thortical calculations, th maximum masurmnt snsitivity is obtaind using th doubl layr acoustic systm with caprolon + C. Exprimntal invstigation Th invstigations wr carrid out by th ultrasonic digital flow dtctor dscribd in [, 2]. Th acoustic proprtis of th tst matrial (polypropyln), as wll antifriction polymrs wr invstigatd thr also. Th xprimntal masurmnt rsults ar prsntd in Tabl. Exprimntally it was found that th attnuation of 5 MHz frquncy signal in polypropyln is 5 to 8 tims highr than th attnuation of 2.5 MHz signal, so all invstigations wr prformd with 2.5 MHz transducrs. Th masurmnts wr carrid out without changing th pizolctric transducr xcitation conditions. Tabl. Th xprimntally masurd and calculatd acoustic paramtrs of th polymric matrials (f =2,5 MHz) Matrial Sound vlocity c, m/s Dnsity ρ, kg/m 3 Acoustic impdanc Z, (kg/m 2 s) Plxiglas , Tflon , Caprolon , Caprolon+C , Polypropyln , Attnuation cofficint α, Np/m Fig.7. Signals ratio dpndnc on th tmpratur of th invstigatd matrials Th transducrs with th acoustic dlay lin of diffrnt thicknsss from th caprolon with carbon impurity (aprolon+c) hav bn producd. Th Gaussian shap acoustic signal of 2.5 MHz frquncy was mittd aftr th xcitation. Th pizolctric transducr acoustic dlay lin thicknss d 2 = 20 mm nsurs tmporary sparation of th rcivd signals not only from th acoustic dlay lin outr surfac, but also from th acoustic dlay lin nd from th prob xcitation signal according to th xprimntal signal imags (Fig. 8) obtaind by masuring 3.3 mm thick polypropyln pip wall by 2.5MHz transducrs. Fig. 8a shows th dlayd puls that is th signal of th scond rflction from th acoustic dlay layr and that dos not influnc th masurmnt of thin pip wall thicknss. Th optimizd structur of th spcializd pizolctric transducr adaptd to th polystyrn pip wall thicknss masurmnt has bn dvlopd according to th xprimntal rsults (Fig. 9). Th mchanical dampr of th pizolmnt is mad of th poxy rsin and th tungstn powdr mixtur by th volumtric ratio :. Th protctor is mad from th caprolon+c with its working surfac of th cylindrical profil and has a curvatur radius qual to th polypropyln pip innr diamtr radius. Conclusions Th pizolctric transducrs of th spcial dsign with anti-friction protctor, having th low acoustic impdanc, th low damping of th ultrasonic signals and a cylindrical activ surfac ar rquird for th masurmnt of th polypropyln pip thin wall thicknss during th production procss. According to th thortical calculations and xprimntal invstigation caprolon+c is th most optimal matrial for th pizolctric transducr dlay layr, which is usd as a protctor. 62

4 ISSN ULTRAGARSAS (ULTRASOUND), Vol. 64, No.4, Polypropiln Pip wall Caprolon+C Stl cylindr Cas Pizolmnt Dampr a Fig. 9. Th construction of pizolctric transducr Rfrncs. Sajauskas S. Longitudinal surfac acoustic wavs (Crping wavs). Kaunas: Tchnologija P Sajauskas S., Valinvičius A., Mižutavičiūtė L. Non-dstructiv tsting of sht product innr surfacs using longitudinal surfac acoustic wavs. Ultrasound. Kaunas: Tchnologija No.(54). P S. Sajauskas, V. Markvičius, J. Savickaitė Polipropilno vamzdžių sinlės storio matavimo ultragarsiniu impulsiniu mtodu optimizavimo tyrimai b Summary Nagrinėjamas pjzolktrinių kitiklių, skirtų polipropilno vamzdžių sinlės storiui matuoti, paramtrų optimizavimas. Toriškai ir ksprimntiškai nustatyta, kad didžiausias pjzolktrinio kitiklio jautrumas gaunamas naudojant vėlinimo (apsauginį) sluoksnį iš antifrikcinės mdžiagos kaprolono su grafito primaiša. Patikta spaudai c d Fig. 8. Ultrasonic signals of 2.5 MHz frquncy obtaind by th transducrs with th acoustic dlay lin lngth of 0 mm (a, b) and 20 mm (c, d). Th acoustic dlayr has no contact with th xplord polypropyln pip wall; only a signal rflctd from acoustic dlay lin nd is obsrvd (a and c). Fig. b and d show th signals of 3.3 mm thick polypropyln pip wall during th thicknss masurmnt. 63

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