Repair & Maintenance - ESAB
A W E L D I N G R E V I E W P U B L I S H E D B Y E S A B V O L. 5 6 N O. 1 2 0 0 1Repair &Maintenance
A welding review published by ESAB AB, Sweden No. 1, 2001Articles in Svetsaren may be reproduced without permission but withan acknowledgement to ESAB.PublisherBertil PekkariEditorLennart LundbergEditorial committeeKlas Weman, Lars-Göran Eriksson, Johnny Sundin, Johan Elvander, Sten Wallin,Bob Bitzky, Stan Ferree, Ben Altemühl, Manfred Funccius, Dave MeyerAddressESAB AB, Box 8004, SE-402 77 Göteborg, SwedenInternet addresshttp://www.esab.comE-mail: info@esab.seRepair & Maintenance.Printed in Sweden by Geson Skandiatryckeriet, KungsbackaContents Vol. 56 No. 1 20013681113The repair of aluminium structuresSome of the more commonconsiderations associated withthe repair of aluminium alloys.Advanced production technology leadsto time savings of 25 %Large pistons for diesel engines arerefurbished by welding rather thanputting a totally new piston into service.Corrosion- and wear-resistant 17%Cr strip weld overlaysThe strip weld-overlay technique used forrenovating of parts in the machinerymanufacturing industry increases productivityand reduces the likelihood of defects.ESAB: your digital partner for weldingand cuttingA guide to the 21 ESAB websitesStubends & SpatterShort news2 Svetsaren nr 1 20011720Submerged-arc strip cladding ofcontinuous casting rollers using OKBand 11.82 and OK Flux 10.07Surface welding of continuous castingrollers with submerged arc welding ispreferred because of its higher depositionrate compared to MAG welding.ESAB delivers engineered automaticwelding station to Ghana in Africa forbuild-up welding of worn railway wheelsRe-building of worn parts of wheel surfacesby welding is an effective method.22Cobalarc: The future of manual hardfacingElectrodes mainly used for hardfacing inapplications where the prime factor of wearis abrasion.25Repair welding of blades for rubbermixingRe-building of the mixing equipmentused for manufacturing tyres for vehicles.
The repair of aluminiumstructuresby Tony Anderson, Technical Services Manager AlcoTec Corporation, USAWithout a doubt, aluminum is being increasingly used within the weldingfabrication industry. We are seeing a major increase in usage within theautomotive industry, where the use of aluminum continues to develop. Alsowithin other industries such as furniture, recreation and sporting equipment,shipbuilding, transportation and containers, military and aerospace we seecontinued developments with aluminum, often as a replacement for steel.As more components are produced from aluminum, theneed for reliable repair work on aluminum weldmentsis also increasing. Repair work to aluminum structuresis conducted extremely successfully on a regular basis,such items as truck body’s and boat hulls are repairedafter damage from collision or after wear and tearduring severe service conditions. This article shallexamine some of the more common considerationsassociated with the repair of aluminum alloys in anattempt to help prevent problems associated withrepair work and also to help ensure consistentlysuccessful repairs.Identification of alloy typeProbably the most important considerationencountered during the repair operation is theidentification of the aluminum base alloy type. If thebase material type of the component requiring therepair is not available through a reliable source, it canbe difficult to select a suitable welding procedure.There are some guides as to the most probable type ofaluminum used in different applications, such as, mostextruded aluminum is typically 6xxx series (AL-Mg-Si).Air-conditioning systems and heat exchangers,within the automotive industry, are typically made from3003, 5052, plate and 6061 tubing. Car wheels are oftenmade from 5454, which because of its controlledmagnesium (less than 3% Mg), is suitable fortemperature applications.Ship hulls are oftenmanufactured from 5083 (5%Mg), which is recognizedas a marine material. Unfortunately, if the basematerial type is not known, or unavailable, there is onlyone reliable way of establishing the exact type ofaluminum alloy, and that is through chemical analysis.A small sample of the base material must be sent to areliable aluminum testing laboratory, and a chemicalanalysis must be performed. Generally, the chemistrycan then be evaluated and a determination as to theThe most important consideration before repair welding isthe identifcation of aluminum base alloy type.most suitable filler alloy and welding procedure can bemade. It is very important to be aware that incorrectassumptions as to the chemistry of an aluminum alloycan result in very serious effects on the welding results.There are 7 major types of aluminum alloys whichhave a wide range of mechanical properties and,consequently, a wide range of performance andapplications. Some have very good weldability, andothers are considered to have extremely poorweldability, and are unsuitable, if welded, for structuralapplications. Some can be welded with one type offiller alloy, and others will produce unacceptable,Svetsaren nr 1 2001 3
Special care should be takenwhen welding highperformance componentssuch as car rims.extremely poor mechanical properties if welded withthat same filler alloy. Filler alloy and base alloychemistry mixture is one of the main considerationsrelating to welded joint suitability, crack sensitivity, andjoint performance. Consequently, without knowing thebase material type, you are unable to assess the correctfiller in order to prevent an unsuitable filler alloy, basealloy, mixture.I must definitely recommend that, if an aluminumcomponent is to be repair welded, and after this, usedfor any structural application, particularly, if a weldfailure, can in any way damage property and/or createinjury, do not weld it without understanding its alloytype, and being satisfied that the correct weldingprocedure is to be followed.The repair of some high performancealuminum alloysAnother problem associated with the repair of a smallgroup of aluminum structures is the temptation torepair high performance, typically high replacementprice components, made from exotic aluminum alloys.These materials are often found on aircraft, handgliders, sporting equipment and other types of highperformance, safety-critical equipment and are notusually welded on the original component. There are asmall number of high- performance aluminum alloyswhich are generally recognized as being unweldable. Itcan be very dangerous to perform welding on thesecomponents and then return them to service. Probablythe two most commonly found aluminum alloys withinthis category are 2024, which is an aluminum, copper,magnesium alloy and 7075, an aluminum, zinc, copper,magnesium alloy. Both these materials can becomesusceptible to stress corrosion cracking after welding.This phenomenon (stress corrosion cracking)isparticularly dangerous because it is generally a type ofdelayed failure, not detectable immediately afterwelding, and usually develops at a later date when the4 Svetsaren nr 1 2001Some automotive components in aluminum that have beenrepaired by welding.component is in service. The completed weld joint canappear to be of excellent quality immediately afterwelding. X-rays and ultrasonic inspection shortly afterwelding will typically find no indication of a weldingproblem. However, changes which occur within thebase material adjacent to the weld during the weldingprocess, can produce a metallurgical condition withinthese materials which can result in intergranular microcracking, which may be susceptible to propagation andeventual failure of the welded component.The probability of failure can be high, and the timeto failure is generally unpredictable and dependent onvariables such as tensile stress applied to the joint,environmental conditions, and the period of time whichthe component is subjected to these variables.It is strongly recommended that great care be takenwhen considering the repair of components made fromthese materials. Again, it must be stressed that if thereis any possibility of a weld failure becoming the causeof damage or injury to person or property, do notperform repair work by welding on these alloys andthen return them to service.
Base material strength reduction after repair welding:There are considerations relating to the effect of theheating of the base material during the repair weldingprocess. Aluminum alloys are divided into two groups:the “heat treatable” and the “non-heat treatable”alloys. We should consider the differences betweenthese two groups and the effect on each during therepair process. Typically, the non-heat treatable alloysare used in a strain-hardened condition. This being themethod used to improve their mechanical properties, asthey do not respond to heat treatment. During thewelding process, the heat introduced to the aluminumbase will generally return the base material, adjacent tothe weld, to its annealed condition. This will typicallyproduce a localized reduction in strength within thisarea and may or may not be of any design/performancesignificance.The heat treatable alloys are almost always used inone heat-treated form or another. Commonly they areused in the T4 or T6 condition (solution heat-treatedand naturally aged or solution heat-treated andartificially aged). Base materials in these heat-treatedtempers are in their optimum mechanical condition.The heat introduced to these base materials, during therepair welding process, can change their mechanicalproperties considerably within the repair area. Unlikethe non-heat treatable alloys, which are annealed andreturned to this condition when subjected briefly to aspecific temperature, the heat- treatable alloys areaffected by time and temperature. The effect from theheating during the welding repair on the heat-treatablealloy is generally a partial anneal and an over-agingeffect. Because the amount of reduction in strength isdetermined largely by overall heat input during thewelding process, there are gridlines as to how thisreduction can be minimized. Generally, minimumamounts of pre-heating and low interpass temperaturesshould be used to control this effect.However, even with the best designed weldingprocedures, considerable loss in tensile strength isalways experienced within the heat-affected zone whenarc welding these types of materials.Unfortunately, it is usually either cost restrictive or,more often, impractical to perform post weld solutionheat treatment because of the high temperaturesrequired and the distortion associated with the process.hydrocarbons which can cause porosity in the weldduring the welding operation. The other source ofhydrogen which we need to consider is moisture, oftenintroduced through the presence of hydrated aluminumoxide. For these reasons it is important to completelyclean the repair area to be welded prior to performingthe weld repair. This is typically achieved through theuse of a degreasing solvent to remove hydrocarbonsfollowed by stainless steel wire brush to remove anyhydrated aluminum oxide. More aggressive chemicalcleaning my be required for some applications.In the case were we are required to remove existingweld or base material in order to conduct the repair.We need to consider the methods available to performthis operation and their effect on the finished weld. Ifwe need to remove a crack in the surface of a weld priorto re-welding we must use a method which will notcontaminate the base material to be welded. Careshould be taken when using grinding discs, some havebeen found to contaminate the base material bydepositing particles into the surface of the aluminum.Routing and chipping with carbide tools is often foundto be a successful method of material removal. Caremust be exercised if using plasma arc cutting orgouging, particularly on the heat-treatable aluminumalloys. This can produce micro cracking of the materialsurface after cutting which is typically required to beremoved mechanically prior to welding.Conclusion: There are many considerationsassociated with the repair of aluminum alloys. Perhapsthe most important is to understand that there aremany different aluminum alloys which requireindividual consideration. The majority of the basematerials used for general structural applications canbe readily repaired using the correct weldingprocedure. The majority of aluminum structures aredesigned to be used in the as-welded condition and,therefore, with the correct consideration, repair work ofpreviously welded components can and is conductedsatisfactorily.Cleaning and material preparation prior toweldingEven when welding on new components made fromnew material we need to consider the cleanliness of thepart to be welded. Aluminum has a great attraction forhydrogen and hydrogen’s presence in the weld area isoften related to the cleanliness of the plate beingwelded. We need to be extremely aware of thepotential problems associated with used componentwhich may have been subjected to contaminationthrough their exposure to oil, paint, grease, orlubricants. These types of contaminants can provideAbout the authorTony Anderson is Technical Services Manager ofAlcoTec Wire Corporation USA, Chairman of theAmerican Aluminum Association Technical Committeefor Welding, and member of the Amerivan WeldingSociety (AWS) Committee for D1.2 Structural WeldingCode – Aluminum.Svetsaren nr 3 2000 5
Advanced production technologyleads to time savings of 25%Twin-wire submerged arc welding with flux-cored wiresby Martin Gehring, ESAB GmbH, SolingenPistons for large diesel engines like those in ships wear out during theirlifetime. Larger pistons with diameters of 700 mm are refurbished bywelding rather than putting a totally new piston into service. This isusually done by submerged arc welding using a single solid wire.Figure 1.Previously:welding inthe pistonring groovesChanging the consumables to flux-cored wires in thetwin-wire mode (two wires with the same potential inone contact tip) leads to increases in productivity ofmore than 25% without any increase in productioncosts.When the engines are working, the piston ringgrooves wear continuously because of the motion of thepiston rings. Additionally, the surface of the pistonheads wears due to the severe thermal conditionsexperienced inside the cylinder.The base materials for these pistons are 34CrMo4and 42CrMo4. A preheating temperature of 250 Cprior to welding is therefore required. Before thecustomer started a project joint venture with ESAB,circumferential welding was carried out on the edges ofthe grooves, Figure 1. A solid S2Mo wire with adiameter of 4.0 mm was welded at 620 A. Firstly, therequired number of build-up layers were welded,followed by two layers of hard-surfacing. Incombination with the silicon and manganese alloyingOK Flux 10.80, the hardness of the surface was6 Svetsaren nr 1 2001approximately 350 HB ( 37 HRC). The piston headswere also welded in the same way.Several trials finally led to the decision to weld thisapplication with flux-cord wires in the twin-wire mode.The fluxes and chemical composition of the hard-facingwire were not changed. The change that was made wasfrom solid wire to basic flux-cored wire by replacing thesingle 4.0 mm solid wire with two 2.4 mm wires. Thewire that was chosen was OK Tubrod 15.21S containing0.5% molybdenum. As it is a basic wire by nature, it hasa high degree of cracking resistance.Nowadays, the faces between the grooves aremachined away. This results in a 300 mm wide area thatis rebuilt, Figure 2. Positioning the electrodes andcontrolling the weld bead is much easier. The wires andthe set-up permit a tremendous increase in depositionrate. Additionally, the current was increased slightly. Itwas not possible to obtain a similar result with a singlesolid wire.In fact, compared with the previous method, thedeposition rate has increased by more than 50%.Welding is performed at 720 A, 29 V with a travel speedof 68 cm/min. Moreover, the change to a 300 mm widemachined area has resulted in fewer welding defectswith a more consistent bead deposit. When the weldingis completed, the grooves are machined out of the solidmaterial. The piston heads are refurbished with fewerlayers at a higher welding speed.Why flux-cored wires?The deposition rate for flux-cored wires for submergedare welding is as much as 20% higher than that of solidwires of same size welded at the same current, Figure 3.Basic flux-cored wires consist of a current-carrying,mild-steel tube with a non-conductive powder filling.Since all the current has to pass along the metal tube,the current density is much higher compared with solidwire. Consequently, the resistance heating is greater,
which leads to a higher melting rate and thereby to ahigher deposition rate. Additionally, the basic slag“cleanses” the molten weld pool, reducing the risk ofhot cracking.Why twin wire?Using two electrodes of smaller diameter results in anincrease in deposition rates of up to 20% comparedwith one single wire of a larger diameter at the samecurrent. Again, the current density is greater with twosmaller wires. The wider arc results in a wider weld beadwith less penetration. A shallow penetration bead ispreferred for the repair welding of base materials witha high carbon content because dilution and sensitivityto cracking are minimised. For twin-wire welding, onlyone power source, one control box and one feed systemwith two grooves in the rollers are used, Figure 4. Bothelectrodes are fed through the same contact tip.The customer benefitsFigure 2. Today: easy handling. An increase of more than50% in deposited weld metalPrepared cost and time calculations with realparameters revealed reductions in welding times ofmore than 25%. Although the welded area was larger,there is an additional cost saving of more than 10%.After some time in production with the modifiedwelding process, the customer confirmed the followingresults.Previously, the welding time for one particularpiston was four shifts. The same piston is now welded inthree shifts. The customer therefore saves 25% weldingtime using this advanced welding technology.Figure 3. Increased deposition rate using flux-cored wiresAbout the authorMartin Gehring works as product manager forconsumables at ESAB GmbH in Solingen in Germanysince 1994 and focuses primarily on the design ofcustomer-specific systems within SAW and on weldingusing solid wire and shielding gas.Figure 4. Twin-wire set-upConsumables for high deposition rates for twin-wire weldingBuild-up layers:OK Tubrod 15.21SHard facing:OK Tubrodur 15.40Deposition rate:0.5% MoAWS A 5.23: F7A2-EC-A4 (10.71)EN 760: SA AB 1 67 AC H5DIN 8555:UP1-GF-BCS 189-350EN 760: SA CS 1 89 AC11 kg/hDiameterFlux2 x 2.4 mmOK Flux 10.712 x 2.4 mmOK Flux 10.80Svetsaren nr 1 2001 7
Corrosion- and wear-resistant17% Cr strip weld overlaysby Martin Kubenka, ESAB VAMBERK s.r.o., and Petr Kuba, ZDAS a.s. Zdar nad SazavouMachinery manufacturers are constantly being pressurised by marketcompetitors to sharply reduce the cost of their final products. Thesale of very expensive spare parts frequently represents one way ofreversing this problematic economic situation.Figure 1. SAW strip-claddingof test pieceUsers of the above-mentioned equipment are oftenburdened by the enormous cost of equipmentmaintenance and repair due to part replacement.Welding and weld-overlay techniques have been themost frequently used procedures for the renovation ofsteel parts for equipment in virtually every industrialsector.Weld-overlay techniques are a very inexpensive andhigh-quality way of renovating the parts attacked bysome primary and secondary wear factors, such asabrasion, pressure, corrosion, wear caused by metal-tometal contact and so on.DesignationCMnSiCrCSN 13123A 406E-B 511 0.23 0.10.21.20.50.60.300.500.3016.013.0Table 1. Repaired materials8 Svetsaren nr 1 2001V0.25The strip weld-overla
A welding review published by ESAB AB, Sweden No. 1, 2001 Repair & Maintenance. 3 6 8 11 13 17 20 22 25 The repair of aluminium structures Some of the more common . failure, can in any way damage property and/or create injury, do not weld it without understanding its
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