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DAVID W. AYLORNAVAL SHIP RESEARCH AND DEVELOPMENT CENTERIBetheda, Md. 20

AN EXPERIMENTAL INVESTIGATION OFBABBITT METAL BONDING

by0 Michael G. Vassilaros

4.J

4JP4.i Approved for public release; distribution unlimited.

i) MATERIALS DEPARTMENT"Annapolis

RESEARCH AN D DEVELOPMENT REPORT

May 1976Report 76-0037

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The Novel Uip Romearch and Development Center asa U. S. JNevy center lor lbierstoryeffort directed at hcievinI Improved see and aie vehicles. It was fonned in Maorh 1967 bymaerging the Dinvid Taytor Model Basin at Carderock, Maryland with the Marine KfninmetingLaboratory at Annapolsa. Maryland.

Novel Ship Research and Development C~eterBetheida, Md. 20034

MAJOR NSRDC ORGANIZATIONAL COMPONENTS

TEC"NICAL DIRECTO 1REPORT ORIGINATOR -

OFVICER.IN.CMARGE OF FICER.IN-CHARGECARDEROCK ANNAPOLIS05 04

i~~i F -AW c,, ... . .nSYSTEMSDEVELOPMENT! L DEPARTMENT

hr AVIATION AND)SHIP PERFORMANCE SURFACE EFFVCTSDEPARTMENT 15 EOPARTMENWII16S U COMPU TATIONDEPARTMENT AND MATHEMATICS

P1 D'PARTMENT

S A S PROPULSION AN D""IP !TCS, AUXILIARY SYSTEMSDE P RT EN 19 DEPARTMENT 2

MATERIALS *CENTRAL/ DEPARTMEN't INSTRUMENTATION26 DEPARTMENT 29

... .....

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UNCLASSIFIED______Sgr.UIRITY CLASSIFICATION OF THIS PAGE (Wheni Oe!a Entered)

REPORT DOCUMENTATION PAGE _ FREA INSTRUCTIONSO1. 91POPRt NUM39EP 2. 00VT ACCESSION NO. 3 ~IPI V'S CATALOG NUMBERq76-0057/___4.TITLE (and SbtIe)fo FRAk 0PRO OEE(7 ~I~;xrERIMENTA.L ;NVESTIGATIOt4 OF,,DABBITT eer vl

~ ,3TAL 'ONDING. - - -~PfM~ _ItPOTMS. CONTOR11CT ORG FIRANTNUMISRF"

Michael G./Vassilaros

6. Petr~OmMINCA ORGANIZATION NAME AND ADORES.~ 10. PAOGRAM ELEMENT. PROJtCT, TASK~AREA Q WORK UNI% NMu9111David W. Taylor Naval Ship R&D Center ak Area ZF .120Annapolis, Maryland 21402.

__________________________ Qrk. .Unixt 2814-17011. CONTROLLING OFFICE NAME AND ADDRESS 12

DaviW.Taylor Nava.l h RD Cente myia,'Bethesda, Maryland 2008U AG17ES ____lTrMN_1TORING AGENCY NAME A ADORESS0If different from ConItoIInjifffIe) 15. 5!CURITY CLASS .of this report)

Jnclassified __SeECLS~FICATIONIOOWNOfRAONo

14. DISTRIBUTION STATEMENT

Apprvedforpublic re~lease; distribujI lg iit-

17, DISTRIBUTION STATEMENT (of the r tetred In Block 20, It ffforenfrom A.,jeorf)

1S. SUFPiCMENTAiR'NOTES

1.KEY WORDS (Conti~nue on rev@ers aide It noc..esez and l~nifyneby blc-ubrBabbitt metal Bond strengthBearings CastingTinning

ABSTRACT (Ci)ntinuo on reveres tid. It nece.7eary and Identify by block numrber)ISeveral methods of casting babbitt metal to steel were evaluatedfor bond streng~th by use of tensile-type specimens. The methodsinvestigated were the use of a tin bath, torch/tin stick, and"ELectroplated nickel to insure proper babbitt-to-steel bond, aswell as no tinning. of the methods performed, only the tin-bathmethod consistently produced a bond stronger than the babbitt

____ _______ ___ ____ ____ ___(over)

DO ~ 7 1473 EDITION O0P 1 NOV 65 12 083OLIETE UNCLAZS IF lEDS/N OO2-O4~01 ISECURITi, CLASSIVICAT50ON e)F TMIS PAGE (Whom~ Veto Knisfed)

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UNCLASS IFIED-1.141T'Y CLA~SSFICA~rIOM Of TH~IS V40I(WPIWI Date Efiored)

(1+ 20. Abstract (cont)4 ,metal itself. The bond strengths developed in th e othermethods tested were erratic and always less than that obtainedwith th e tin-bath method. The torch/tin stick method gavean adequate compromise between bond strength and convenientapplication. It was found that th e oxide formed on th e tinnedsurface which precludes good bonding could be effectivelyremoved lty the use of flux during babbitt casting.

(Author)

ft

UNCLASS IFIEDSECURITY CLASSIFICATION OF THIS PAGE(no' Dots Entorod)

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ADMINISTRATIVE INFORMATIONThis report was prepared under Task Area ZF 61512001,Element Number 62766 N on Investigation of Babbitt Metal BondingWork Unit 1-28]4-170. The investigation was sponsored by NAVM AT

(MAT 03L4) as part of th e IR/IED program of the Centec underthe direction of Dr. A Powell (Code 01).SACKNOWLEDGMENT

The author wishes to express his grateful appreciation forthe assistance and guidance given by Mr. Robert F. Gustafson(Code 2r(84) throughout th e project.LIST OF ABBREVIATIONSo C - degrees Celsuis

F - degrees Fahrenheitm - metermmn - millimeterMPa - Megapascalspsi - pounds per square inch

7'

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INTRODUCT IONBACKGRO(UND

The Navy's extensive use of babbi t t bearings in surface shi"machinery requires that Navy tenders and repair ships have thecapability cf repairing babbit t metal bearings on board. Thepractice of casting babbi t t within th e limited facilities of atender 's foundry has evolved over years to a "traditional" pro-cedure passed on by crew chiefs. This method is simpler thanth e bearing manufacture's methods which are designed to optimbearing strength, and require a large, well-equipped facility.present tender practice, th e babbi t t lining of a bearing is bondto th e steel or bronze bearing shel l by means of a tin interfacelayer. Normally, th e tin is applied to th e hot bearing shell ,after which th e shell is set up in a mold and molten babbittpoured in.

The primary difference in th e methods is th e way in which thtin interface layer is applied. Manufacturers are able to use abath of molten tin in which th e hot bearing shell is immersed;however, aboard ship th e shell is heated by a flame torch, anda stick of tin is melted on th e shell , much as solder is appliedto connections. The hot tin layer oxidizes rapidly, whilecooling, and th e subsequent bond is often weak and brittle.Many turbine qear, and l ineshaft bearings are renewed annuallybecause of poor bonding. Furthermore, rebabbitting bearingsfrequently requires excessive man-hours of work because ot theunsatisfactory bonding and consequent rework.

The t radit ional method, as well as modifications, andalternatives to this method were investigated to develop andrecommend a simple, improved method of bonding babbi t t bearinglinings to metallic bearing shells. The investigation intendedto characterize the important features of a simple babbitt-bonding procedure for possible use in a tender 's foundry.Various babbitt-bonding procedures were used to make tensileof these specimens was used to evaluate th e relative efficiency.7.1c several bonding methods, as compared to the standard method(o' using a tin bath for applying the tin interface layer.

means of improving th e torch/tin stick method as well asmethods to eliminate tinning, and electroplating methods werestiai.ed.

'Superscripts refer to similarly numbered entries in th e Techni-cal References at th e end of th e text.

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MATERIALSThe babbitt metal used was a tin-based babbitt alloy number2 (Navy designation). The alloy is commercially available undera variety of trade names all with a nominal composition of 7%-

8% antimony, 3%-4% copper, and th e remainder tine (88% minimum).Commercially pure tin metal was used in th e tinning processes.The flux, when employed, was a standard solution of zincchloride made from zinc metal dissolved in concentratedhydrochloric acid. Lo w carbon steel bars (AISI IC15), 1/2 inchx 1/2 inch x 20 feet (12.7 m x 12.7 mm x 6.096 m),* were usedas th e base metal to which th e babbitt was bc.ided."DESCRIPTION OF EQUIPMENT

The babbitt was cast into a stainless steel fixture (figure1) which held th e steel bars in a gapped position during casting,so that th e steel bars and th e fixture when assembled formed themold. A stainless steel crucible in a pot of molten lead heldth e tin bath. When torch tinning was performed, an oxy-acetylenetorch adjusted to give a reducing flame was used to heat th eassembly, and th e tin was applied with a tin stick, a long thinbar of tin metal. The flux solution was applied directly with aflux brush, i.e., no flux-cored sticks were used,METHOD OF TEST

The strength of th e babbitt-to-steel bond was measured usinga tensile specimen composed of th e two 1/2-inch square (12.7 mm)steel bars whose ends were joined in a slug of cast babbittapproximately 3/4 inch (19.05 Nm) long and 1/2 inch (12.7 min)square. The specimens were pulled in a universal testing machinewhich recorded th e maximum load to fai lure. The maximum stresswas calculated from th e maximum load and th e cross-sectionalarea of th e fracture.BONDING METHODS

Five different babbitt-to--steel bonding methods wereinvestigated, and these are described briefly in th e following.

*A list of abbreviations used appears on page i."76-0037 2

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AWITW..

Method I - Standard Method (Tin Bath)This method simulated th e recommended procedure for acha strong babbi t t m etal-to-steel bond, and is used in th e manfacture of new babbi t t bearings. The steps pezforinedwere afo llows:

* Sand th e steel surface (smooth) to remove rust.e Degrease the steel surface with acetone.o 7lux th e steel with a solution of ZnCl.* Hold in a tin bath for 1 minute at 7000 F (5710e Insert tinned steel blanks into stainless steelfixture and preheat in furnace.0 Cast liquid babbit t into mold cavity.* Stir molten banbi t t and cool mold with flowingwater.

Method II - Torch TinninQThis method simulated present Navy tender foundry practThe characteristic feature of this method was th e use of aheating torch/t in stick instead of a tin bath. The steps wefollows:

o Sand and dc.grease th e steel bars with acetone.a Heat th e steel with an oxy-acetylene torch whilapplying ZnC! solution and tin from a tin stick.* Insert tinned blanks into casting fixture.o Preheat fixture assembly.o Cast liquid babbit t into mold cavity.* Stir molten babbi t t and cool mold with flowing

water.Method III-- No Tinning

This niethod simulated a bonding method which eliminatedthe tinning steps to find if flux alone might give adequatebonding. The steps are listed below:

e Sand and degrease th e steel bars with acetone.e Place cleaned steel. blank into casting fixture.

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* Preheat fixture assembly.* Pour flux into fixture just prior to casting.* Cast liquid babbitt into mold cavity.* Stir molten babbitt and cool with flowing water.

Method IV- Electroplated NickelThis method incorporated a substi tute for tinning, whereina portable electroplating rig was used to electroplate nickelonto th e steel, instead of tinning the surface with molten metal.The method was as follows:

0 Sand and degrease th e steel bars with acetone.* Electrcplate nickel with commercially available

plating kit. 3e Insert plated steel blanks into th e cast fixture.* Preheat fixture assembly.e Pour flux into mold just prior to casting.e Cast liquid babbitt into mold cavity.SStir molten babbitt and cool with water.

Method V - RebabbittingtThis method simulated th e rebabbitting of previously castbearings to determine whether th e tinnihg or nickel platingcould be reused by melting off th e old babbit t and recastingnew babbitt.

Melt off babbitt from previously babbitted speci-mens.* Insert th e steel blanks into casting fixture. Preheat fixture assembly. Pour flux into mold just prior to casting.* Cast liquid babbitt into mold cavity.e Stir molten babbit t and cool with flowing water.

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It has been found' that a tin-bath temperature of 660' F(3490 C) to 9300 F (4990 C) is necessary for good tinning ofsteel; accordingly, a temperature of 7000 F (5710 C) was chosenas th e t in-bath temperature used for method I.

The babbitt temperature in th e ladle at pouring vas 7000 F(3710 C) . Since th e mass of tha mold was approximately 190 timesthat of th e babbitt and th e mold material 's heat capacity wasover 2.5 times that of the babbitt, the cooling and solidifi-cation was controlled by th e mold preheat temperature. Thetemperatures used fo r preheating were chosen to cover th e rangeof recommended mold and babbitt temperatures, as found in th eliterature.102,4 Preheating was don~e in an electric mufflefurnace, with th e temperature measured by a type K thermocoupleon th e mold surface. The temlierature of th e mold assembly atth e time of removal from th e furnace was recorced; th e babbittwas cast in th e mold within 10 seconds after th e mold assemblywas removed from th e furnace.

RESULTS AND DISCUSSIONThe results of the tensile tests performed on th e babbitt-bonded assemblies are given in figures 2 and 5, including bothth e average and range of breaking strengths fo r each group offour specimens cast by th e method and at the temperature indi-cated.The results fo r method I, th e standard method, using a moldpreheat temperature of 6200 F (3270 C) and 7000 F (3710 C) showthat th e breaking strength varied greatly in th e eight specimenstested. only one of th e specimens, with a breaking stress of

16,200 psi (112 MPa) failed in th e babbitt rather than at th ebabbitt steel bond. The other seven specimens failed at thebond with breaking strength as low as 2,600 psi (17.9 MPa).All of th e seven specimens with bond failures had oxidescovering 30% to 90% of th e fracture surface. Theoretically,th e oxide layer on th e tinned surface should float to th e sur-face of th e babbitt arid, therefore, not degrade th e bondintegri ty. Method I was modified to alleviate th e problem ofthe tenacious oxide film. Pouring a small amov;nt of fluxsolution into th e mold prior to casting th e babbitt allowed th eflux to float on th e babbitt and remove th e oxide as th e levelof th e babbit t rose in th e mold. This method, IA, gave excellentresults , as seen in figure 2, where all of th e 20 specimenstested failed in th e babbitt. The average breaking strength ofall th e specimens was 13,500 psi (93 MPa). Hence. th e bond strengthmust have been higher than th e breaking strength. Although thismethod gave good results , th e size of th e tin bath necessary tohold a large bearing shell makes it impractical fo r shioboard use.

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Method II was th e resul t of a survey of procedures used onfour tenders (A D 19, AD 26, AD 38, and AS 36). The only surfaceconditioning used was acetone degreasing and sanding. The blankswere tinned with an oxy-acetylene torch adjusted to give areducing flame. Torch tinning dces not requ:ire a tin bath orany floor space fo r permanent equipment. The results for eightspecimens done by method II are shown in figure 2. The failuresalways occurred in th e bond. The series performed at a mold of6700 F (354" C) contained some trapped oxide on all of th efractures, and th e average breaking strength was 23% to 46%' lowerthan for method IA . To remove the trapped oxides during casting,method II was also modified to include the additional step ofpouring flux into th e mold prior to casting. The results for th e4modified method, IIA, are shown in figure 2. The averagebreaking strength of method IIA was higher than method II butlower than method IA. Of th e 20 specimens tested, four failedin th e babbit t , and th e remainder had from 10% to 50% of theirfracture in th e babbitt . The fracture surfaces indicated thatth e bond strength approximated th e strength of th e babbit t .

Method III was investigated as a possible method ofsimplification which eliminated th e tinning step entirely.Surface preparation was limited to degreasing with acetone andsanding. In all th e tests, flux was poured into th e mold justprior to casting. Although th e average bond strength in sometests of method III approach that of method IA, all of th especimens prepared by method III failed at th e bond. This mayhave been due to a brittle, copper-rich phase of babbit t formingon th e steel surface when a tin layer is not present. Thisdifference in phase distribution may be noted in comparingfigures 4 and 5, which are microprobe scan photographs of thedistribution of copper at th e interface between th e steel andth e babbitt.

Method IIIA was performed to determine th e effect of anoil residue on th e ste3el surface during preheating. Alter th esteel blanks were degreased and sanded, they were dipped inmachine oil and then placed in th e stainless steel fixture.Further preparation was as for th e other specimens prepazedby method III. The specimens were cast with th e mold preheatedto 6500 F and th e average breaking strength was reduced 16, fromth e average of th e eight specimens prepared by method III at 6500 F.The range of breaking stresses was much greater with method IIIA.A ll four specimens failed at th e bond, and three of th e four hadtrapped 3 il residue on th e fracture surface.

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Method IV utili',ed a nickel-plating process to replace th etLnning process. A nickel surface was electrochemically appliedt-o th e degreased arid sanded steel surface with a portable brushplating apparatus. 3 The results fo r th e specimens prepared bythis method, figure 3, showed th e procedure to be less effectivethan IA , IlA, and III. The breaking strengths were from 9% to[r' lower than 1A, and all of th e 16 specimens tested failed atth e babbit t - to-nickel bond.

Method VA was used to investigate th e rebabbitting ofspecimens prepared by method IA which were previously preparedand tested. The babbit t was melted off th e steel blanks, andnew babbitt was cast to th e same steel blanks with no othersurface preparation. Method VB was similar to VA, but th e steelblanks had been prepared by method III. The reduction ofaverage breaking strength varied from 22% to 77% of th e strengthof th e original value. All of th e 24 specimens rebabbitted andtested failed at th e steel-babbit t interface.

CONCLUS IONSIn comparing th e results of th e five different methods of

casting babbitt , several conclusions may be drawn:0 The best method was th e standard (t in-bath) method.* The deleterious effect of oxides on th e t innedsurfaces can be eliminated through use of flux just prior toth e babbitt casting.* The tinning of a steel surface is required for abond strength greater than that of th e babbit t metal.* Nickel plating is not a worthwhile alternative tot inning. Although a clean metal surface without a tin layer

may have a high breaking strength, th e bond will usually beweaker than th e babbitt itself.

RECOMMENDAT ION* Aboard Navy tenders and repair ships where th e torch t inningmust be used, it is recommended that procedures for these shipsbe specially documented and include th e step of applying fluxjust prior to casting th e babbitt , th e procedures describedunder method IIA of this report.

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TECHN ICAL REFERENCES1 - Prytherch, J. C., "Measurement of th e Adhesion of Tin-Base

Bearing Metals to Various Backing M ater ia ls ," Journal of th(Institute of Metals, Vol. 67, London (1942)2- "Bearing Babbitt ing Procedures," NAVSHIPS 250-644-2, Bureauof Ships, Navy Dept, Washington, D. C. (May 1961)

3 - "The Dalic Process-An Advanced Engineered System of Selecti'.Brush Plating," Sifco Matachemical, Division of SifcoIndustries Inc., Independence, Ohio (1968)4 -Bassett , H. N., Bearing Metals an d Alloys, But ler an d TannerLtd., London, U. K. (1937)

7 8

76007

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ASBESTOS TWINE

~r 71/1N ILMILD STEEL SIEELSTEEL

STAINLESS STEEL FIXTURE

Figure 1Stainless Steel Fixture and Mild Steel Blanks Assemblyof which Forms th e Mold and fo rCasting th e Babbitt

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MOI D TEMPERATURE BREAKING STRESS, KSIjMETHOD F ___ 2 4 6 101 14 94"" "C?20 40 60 80 100

I 620 327 I-----I 700 371

IA 580 304IA 600 316IA 630 3431A 66 0 349IA 700 371

.T. 560 293i.- --i] 670 354

TT A 550 288 -- --'IA 614 329[I'A 650 34 3 : 'rlA 700 3 71 I--"[IrA 750 399

L IA 9.50 510...-RANGE OF BREAKING STRESSES

AVERAGE Of FOUR TESTS

Figure 2Results of Tensile Specimen Tests Prepared byMethods I and II

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MOLD TEMPERATURE BREAKNG STRESS, KS1METHOD 100 2 14 1i'{, MPo

r' C 20 4G 60 80 100III 480 2491M1 570 29913 1 640 338TT 650 34313 1 650 343M 75 0 399

MliA 650 343 -,is[ 500 21260

650 343 -- 1-4 S66049Iz 770 410 iYA 550 288

.A 650 343YA 650 343YA 700 371YB 600 316""B 650 343 _ _....__

FigureResults of Tensile Specimen Tests Prepared byMethods III, IV, and V

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Babbitt

...Interface

Figure 4Microprobe Scan Photograph of the Babbitt-to.-Steel Interfaceof a Tinned Specimen Showing the Distribution of Copper(white dots), 50OX

-.-Babbitt

' --Interface

Figure 5Microprobe Scan Photograph of the Babbitt-to-Steel interfaceof an Untinned Specimen Showing the Concentration of Copperat the Interface (white dots), 500X

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INITIAL DISTRIBUTIONcopies CENTER DISTRIBUTION

2 NAVMAT copies Code2 (MAT 03W)1 2 075 NAVSEA11 (SEA 03)127I(SEA 035) 1 28)1 (SEA.03523) 15 28114)2 (SEA 09G32) 1 2832)30 5211.4)2 5221)5 NAVSEC 2 5222'2 SEC 6101D) 2 5231$1 SC6140)1I SEc 6148D)

1 NAVSECPHILADIV'12 DDC

*Adrsse

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