**Improvement of The Frit Salvage Process for A Cathode Ray Tube Author(s) Chin Young Cha, Shri V. Iyer, Venn Lakshmanan, Joseph J. Rends & John Trevelyan **

**BEM MRM 44/MRM44(15-17,June2021, Valencia,spain)**

https://www.witpress.com/elibrary/wit-transactions-on-modelling-and-simulation/21/6698

**___________________________________________________________________**

**“제44차 경계요소와 그 밖의 메쉬 축소법의 세계 국제 학술대회 ( 스페인 BEM MRM 44/MRM44(15-17,June2021, Valencia,spain) 2021년 6월 15일부터 17일) 소개하는 학술지로 선택된 “음극선관의 Frit 회수 프로세스의 개선” 의 제일저자인 대한민국 차진영 공학박사”**

**영국에 있는 경계요소(BEM) 분야에서 세계에서 가장 좋은 대학인 영국에 있는 Wessex Institute Technology 주최로 개최되는 “제44차 경계요소(BEM) 와 그 밖의 메쉬 축소법(MRM)의 세계 국제 학술대회 ( 스페인 BEM MRM 44/MRM44(15-17,June2021, Valencia,spain) 2021년 6월 15일부터 17일)에 가장 좋은 학술지로 부터 선택되는 세계 국제 학술대회를 소개하는 학술지로 선택된 “음극선관의 Frit 회수 프로세스의 개선” (Improvement of the frit salvage process for a cathode ray tube)이 선택됐다. 이 학술지의 제일저자는 대한민국 차진영 공학박사”( dr.Chin Young Cha, Ph.D P.E.)다. 음극선관의 Frit 회수 프로세스의 개선의 프릿 인양 과정은 필립스 디스플레이(Phillips Display) 에서 음극선관을 재활용하는 데 사용된다. 이 프로세스에서는 인터페이스를 완전히 분리하는 균열을 만든다. frit 회수 과정의 성공률은 약 67% 이다.균열 때문에 패널로 전파되는 음극선관 중 33%는 유실되고 다시 사용할 수 없다. 이 학술지는 33% 유실되는것을 방지하기위해 방법을 찾아내는 것이다. 엔지니어링 구성 요소는 지난 10년 동안 빠르게 발전했으며 현재 두 가지 주요 대안은 유한 요소 방법(FEM)과 경계요소(BEM) 방법이다. 두 방법 모두 27인치 CRT에 대한 정적 스트레스 분석을 수행한다.경계 요소 방법은 단일 요소에 대해서도 높은 정밀도를 제공한다. 경계요소 방법은두께 방향메쉬가 필요 없으며 표면에만 메쉬하므로 아주 쉽게 아주 짧은 시간에 메쉬할수있다. 보다 정제된 메쉬로, 경계요소 방법은 또한 표면을 쉽게 재배치할 수 있게 한다. 반면에 유한 요소 방법은 “최소 8노드 벽돌 요소”가 필요한하며 스트레스 수렴 되기위해 두께방향으로 “최소 8노드 벽돌 요소” 몇개가 필요 한지 결정하는데 어려움이 있다. 또한 메쉬 하는데 경계요소(BEM) 방법은 2D 인 반면 유한 요소 방법 은 3D 이므로 유한요소 방법은 경계요소 보다 메쉬 하는데 어렵고 시간이 오래걸린다. 그러므로 경계요소 방법을 선택 하였다. 경계 요소방법을 수행에서 얻은 균열의 방향과 위치 분석은 프릿 실링 절차에서 실제로일어나는 대각선 모서리 균열과 일치한다. 학술지는음극선관 중 33% 33% 유실되는것을 방지하기위해 방법으로 필립스 디스플레이직경이 3V4인치인 유압실린더로 패널 대각선 치마에 기계적 하중을 가하였다. 따라서 대각선 모서리의 최대 기본 스트레스는 대각선으로 물개를 따라 압력을 가하는 동안 상당히 감소했다. 또한 대각선 모서리 의 패널 씰 가장자리스트레스 는 증가했다. 위의 두결과로 대각선 모서리 균열은 안일어나고 Seal Edge 를 따라서 균열이 일어나. frit 회수 과정의 성공률은 약 67% 에서 97% 로 증가 하였다. 대한민국 차진영 공학박사 는 영국 옥스포드 대학에서 열린 제22차 경계요소 국제학술대회에서 공동의장 이었으며 이때 “음극선관의 Frit 회수 프로세스의 개선” (Improvement of the frit salvage process for a cathode ray tube)을 발표했다. 차진영 공학박사는 현재 Wessex Institute Technology 의 Fellow 이다. 그는 대한민국 연세대학 기계공학과 졸업했으며, 미국의 Worcester Polytechnic Institute 공대에서 기계공학 석사, Mississippi State University 기계공학박사를 취득했다. 또한 그는 대한민국 기아 차동차회사에서 자동차 설계기사, Penn state university 에서 기계공학과 조교수 Phillips Display Company, USA 에서 Engineering Specialist 로 연구했으며 35개의 국제 학술 논문 과 2개의 미국 특허를 가지고 있다.** 전화: 1-248-320-1098 이메일: drchincha@aol.com

Improvement of the frit salvage process for a cathode ray tube

Chin Young Cha\ Shri V. Iyer\ Venn Lakshmanan’% JosephJ. Rends*” & John Trevelyan^

UniversityofDurham,Durham, UK

Abstract

The frit salvage process is used to recycle cathode ray tubes at Phillips Display. This process involvescreating a crack that will separate the interface cleanly between the panel and funnel components of the cathode ray tube. The current success rate of the frit salvage process is about 67%. Due to the crack propagatingintothepanel,33% ofthecathoderaytubesthatarelostand cannot be reused. This paper describes how a thermal stress boundary element analysis was carried out to select a mechanical device that improves the frit salvageofa27inchcathoderaytube(CRT) byredirectingthecracktothe panel funnel interface. This application isan excellent example of using the boundary element method in an industrial setting.

1 Introduction

CRTs arecommonly found intelevisionsetsand Figure 1shows its main features.The interiorofthetubecontainselectronicsthatmay failbefore

Transactions on Modelling and Simulation vol 20, © 1998 WIT Press, http://www.witpress.com, ISSN 1743-355X

638 Boundary Elements

shippingorwhileinservice. Due tothehighcostofmanufacturing the tube,PhillipswilltrytorecycleCRT bythefollowingsteps:1.Opening up the vacuum tube at the seal edge.; 2. Removing the defective electronics.;3. Replacing theelectronics.;4.Resealing thetubesothatthe interior is in a vacuum state. Step 1 is referred to as the frit salvage processandiscrucialforsuccessfullyrecyclinga CRT.

InthefritsalvageprocessthepanelandfunnelofaCRT isfritted at the seal edge. To reuse a CRT, etching and then applying a thermal shockseparatesthepanelandfunnelatthesealedgeinFigure1. A successful salvage process occurs when the crack initiates at the end of the axes and traversestowards the corner along the seal end during thermal shockasshowninFigure2(lineABC). ACRT islostwhenthecrack travelsalongthediagonalcorner(lineDE). Thecurrentsuccessrateof thefritsalvageprocessisabout67%, whichmeansthat33% ofthe components are lost and cannot be reused. Having a better understanding of the thermal shock mechanism can reduce the financial burden on PhillipsDisplay. Topromotecrackpropagatesalongthesealedge(line ABC), i.e.,increasethesuccessrateofthefritsalvageprocess,a mechanical deviceisproposedtoapplyapressuretoallcomersofthe CRT as shown in Figure 2. Numerical methods are a powerful engineering tool that can be used to obtain a better understanding of the current fritsalvage process and any modificationsthey are necessary to increasethesuccess rate.

Numerical techniques for the stress and heat transfer analyses of engineering components have developed rapidly over the past decade, and todaythetwomajoralternativesarethefiniteelementmethod(FEM) and theboundaryelementmethod(BEM). Bothtechniqueshavebeenusedto carryoutastaticstressanalysisofa27-inchCRT [1,2].Theboundary element results achieve a high degree of accuracy even for a single element in the thickness direction. Although itis found to be unnecessary to use a morerefinedmesh,BEM alsoallowsonetoremeshthesurfaceeasilyin an extremely short period of time. In contrast, the finite element results appear to require a minimum of two eight-node brick elements in the thicknessdirectionbeforetheresultsapproachconvergence. The difficulty ofremeshingaFEM volumemeshisanobstacleincarryingoutarapid convergence analysis. The simplicity of carrying out a refined boundary discretization allows a more detailed convergence study and therefore promotes confidenceinthestresses. Inconsequence,theboundaryelement model was easier and quicker to build, more accurate and also has an extremelyshortermodelingtimethanthefiniteelementmodel. Inthis

Transactions on Modelling and Simulation vol 20, © 1998 WIT Press, http://www.witpress.com, ISSN 1743-355X

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paper the boundary element method will be used to analyze the current and proposed changes to the frit salvage process.

2 Problem Statement

ThepanelandfunnelofaCRT arefrittedatsealedge.ToreuseaCRT, the panel and funnel are first separated by etching the frit along the seal edge by using Nitric acid at 130 °F. The glass isthen cooled from 130 °F to60TFwithwaterat60°Fin50seconds. Duringthermalshock,acrack has been observed to initiate at the end of the axes and traverse toward the corneralongthesealend(lineABC inFigure2).However,33% ofthe CRTs are lost due to the crack traveling along the diagonal corner (line ADEC) asshowninFigure2.Inordertopreventthecrackfromtraveling alongthediagonalcorner(lineDE) amechanicaldeviceisusedtoapplya pressureatallcornersoftheCRT asshowninFigure2.The mechanical

device will redirect the crack along the seal edge to point B by reducing the stressatthecorner(areaDE) andincreasingthestressalongthesealedge (point B).

Inordertoanalyzethemechanism,whichcausedthecrack, BEM was chosen due to its ease of use and itswell-known suitability forsolving problems involving cracks and stress concentrations [3]. A thermal stress analysis was carried out using the commercial boundary element code BEASY [4]. A steadystateheattransferanalysiswasfirstcarriedoutto determinethetemperaturevariationthroughouttheCRT duringthermal shock. A cooling rate of 84 T/min was assumed to simulate the actual

processofcoolingfrom 130°Fto60°Fin50 seconds.

A static thermal stress analysis was then carried out using the

temperature solutions from the heat transfer analysis. The maximum normal stress criteria is used to predict glass fracture; therefore, all stressesinthispaperindicatemaximumprincipaltensilestress. The thermoelasticresponseoftheCRT wasanalyzedusingBEASY.BEASY unfortunately has a limitation, which precludes the prediction of stresses, generated from distributed volumetric internal heat sources. First determining the surface temperature distribution from a heat transfer analysis, which included the volume source, and then applying that temperature portion of the solution for a thermal stress analysis an approximate solution is obtained. The assumption was made that the through thickness effects of the volume source is small, and that the term in the elasticity equations which considers the volumetric effects of the

sourcetemperatureprofileisnegligible. Thisassumptionisappropriate sincetheCRT hasacomparativelythinsection.

Transactions on Modelling and Simulation vol 20, © 1998 WIT Press, http://www.witpress.com, ISSN 1743-355X

640 Boundary Elements

A quarter symmetry three-dimensional boundary element model of the27-inchCRT showninFigure1consistsof542quadraticboundary elementsand8374nodes.TheCRT isassumedhomogenousandisotropic glass (Corning Glass code 9061) and the following information was used fortheheattransferandthermoelasticboundaryelement analyses:

Young’s modulus

Poisson’s ratio

ultimate tensilestrength ultimate compressive strength thermal conductivity coefficientofthermal expansion reference temperature

volume source

Convective heat-transfercoefficient

of water with ambient temperature

of 60 °F atouter glass surface. Convective heat-transfer coefficient

of airwith ambient temperature of 130 TF atinner glass surface.

3 RESULTS

= 10.07 x 10^ psi = 0.23

= 3600 psi

= 100,000 psi

= 1.4x 10″*BTU/in-s °F

= 5.5x 10″^in/in°F

= 68 “F

= 2.854 x 10~*BTU/in^-sec

= 1.543 x 10~*BTU/in”-sec-°F

= 2.55 x 10″*BTU/uT-sec-°F

The temperature solutionovertheouterglasssurfaceisshowninFigure3. Theentireoutersurfaceissubjectedtoatemperatureof60°F. The temperature variationovertheinnerglasssurfaceisshowninFigure4. The temperature of the inner face panel is 119 °F and gradually decreases to60°Fattheneckarea. Thistemperaturevariationisveryreasonable since the thickness of the face panel is m u c h larger than that of the neck.

The principalstresssolutionsoftheouterand innerglasssurfaces are tensile and compressive, respectively, as shown in Figures 5 and 6, respectively. The crack will always begin on the outer glass surface since thestressistensileandglassisverybrittle. Figure7showsanenlarged view of the m a x i m u m principal stresses over the outer panel surface since this isthe crack growth region. A detailed description of the outer panel shown inFigure 2 indicatesvarious locations forstudying crack growth. The panel’s stress analysis results at various outer surface locations for the salvage tube with and without a mechanical load are shown in Table 1.

The principal stress directions on the outer glass surface are shown in Figure 8 without a mechanical load (traditional frit salvage

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process). The crack starts at point A (on major axis), which has the m a x i m u m stress value (3323 psi), and proceeds along the seal edge during thermal shock. The crack then changes directiontowards point D instead ofpointB (sealedge)sincethestressofpointD is524 psigreaterthan point B. This is consistent with Figure 8 since the crack propagates perpendicular totheprincipalstressdirectionatpointD. The crackthen continues to propagate towards point E and then proceeds to the seal edge and then along the seal edge to point C. The direction and location of the crack obtained by the boundary element analysis without the mechanical load is consistent with those observed in the frit salvage procedure at

Phillips Display. The analysis determined that maximum stresses are located near the blend radius on the panel skirt at approximately 1-2 inchesoneithersideofthediagonalcorner. Also,itwasfoundthatthe stresses along the frit seal edge are uniform from the end of the major and minor axes towards thediagonal.

Table 1. Principal Stress Comparison of the Outer Panel Between the Salvage Tube with and without a Mechanical Load.

A 3¥4inchdiameterYateshydrauliccylinderisusedtoapplya mechanical pressure load of 1533 psi on the diagonal skirt to prevent thermal failure along the diagonal corner, i.e., to promote a crack along lineABC insteadoflineADECinFigure2.ThehatchedareainFigure2 designates the location of the mechanical pressure load. The principal stresses on the outer glass surface with the mechanical load are tensile with the exception of a compression area on the diagonal corner where the mechanical load isapplied as shown inFigure 9. The principal stresses on theinnerglasssurfacewiththemechanicalloadarecompressive asshown in Figure 10. The panel’s stress analysis results at various outer surface locations for the salvage tube with and without a mechanical load are shown in Table 1. The + and – signs in Table 1 indicate the amount of increased and decreased principalstress, respectively, on salvage tube with

the mechanical load.

Figure 11showstheprincipalstressvariationovertheouterpanel

642 Boundary Elements

stresses of points D and E have been reduced to 597 psi and 634 psi, respectively,asshowninTable1.The amountofthestressreductionby the pressure load is significant. The principal stress directions at points D and E are perpendicular to the seal edge as shown in Figure 12. Without themechanicalload,thedirectionsoftheprincipalstressesatpointsD and E were approximately 135° and 45°, respectively, where the inclination is with respect to the seal edge as shown in Figure 8. The direction and reduction of these principal stresses insure that the crack does not propagate through points D and E. Furthermore, the principal stress of point B has increased 335 psi due to the pressure load. This stress increase promotes crack propagation through point B. The crack will start atpointA,whichhasthemaximum stress,proceed alongthesealedgeto point B, which has 408 psi higher stress than D, and continues to follow the seal edge to point C.

4 Conclusion

The direction and location of the crack obtained by the boundary element analysiswas consistentwiththoseobservedinthefritsalvageprocedureat PhillipsDisplay. A 3V4inchdiameterYateshydrauliccylinderisusedto apply a mechanical load on the diagonal skirt to prevent thermal failure along thediagonal corner. A boundary element analysiswas carriedout withthemechanicalloadappliedasapressureonthediagonalskirt. Asa result, the maximum principal stresses on the diagonal corner have decreased significantly while the stresses along the seal at the diagonal increased. Consequently,thecrackcontinuestotransversealongthehigh stress lines at the seal edge as required for a successful frit salvage process.

References

[1] Cha, C. Y., Iyer, S. and Trevelyan J.,”Stress Failure Analysis of Neck Breakage of Cathode Ray Tube,” Proceedings of 17* International Conference on Boundary Element Methods in Engineering, Vol. 1, Computational Mechanics Publications, Southampton,UK, pp. 403-419, 1995.

[2] Cha, C. Y., Iyer, S. and Trevelyan J., “Comparison of Convergence and Modeling Times forCathode Ray Tube Stress Analysis withthe Finite Element and Boundary Element Methods/’ Boundary Element

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Communications, Computational Mechanics Publications, Southampton,UK, Vol.6,No.1,pp.1-5,January,1995.

[3] Aliabadi, M. H. and Rooke, D. P., Numerical Fracture Mechanics, Computational Mechanics Publications, Southampton, UK, and Kluwer Academics Publisher,Dordrecht, 1991.

[4]BEASY,ComputationalMechanics,Southampton,UK, andBillerica, MA.

542QuadraticElement 8374Nodes

Figure1:MainFeaturesof27VTubewith3-DBEM Model.

Figure2:CrackPath(ADEC) ObservedatPhillipsDisplay.

MechanicalPreureLoad-153psi

644 Boundary Elements

Figure 3:Temperature Solution over theOuter Glass Surface.

Figure 4: Temperature Solution over the Inner Glass Surface.

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Figure 5: Principal Stress Solution on Outer Glass Surface.

Figure6:PrincipalStressSolutionoverOuter Surface.

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Boundary Elements

Figure 7: M a x i m u m Principal Stress on Outer Panel Surface in Crack Region.

Loadset 3 Symbolicresultdisplay -HE.THERMALSTRESANALYSISOF27VSALVAGETUBE

FILENAME:BE27VS.BM

” f f *-*

<l^-Ttpr^vr, %=1-t’

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Figure 9: Principal Stresses on Outer Glass Surface with Mechanical Load.

Figure 10: Principal Stresses on Inner Glass Surface with Mechanical Load.

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