Bucyrus Welding Ecommendations

7/24/2019 Bucyrus Welding Ecommendations

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2 114 500 en - (02)


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Published by: Bucyrus HEX GmbH

Dept. 2470 DocumentationD-44149 Dortmund, Karl-Funke-Strae 36Tel. +49 (0) 231 922-4340Fax +49 (0) 231 922-5340www.bucyrus-hex.com


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TABLE OF CONTENTS

Foreword 1..................................................................................................................................

Safety 1........................................................................................................................................

1. Fundamentals1.1 Loads on structural elements 2..............................................................................................................

1.2 Types of loading 2..................................................................................................................................

1.3 Material behaviour under different loads 4..............................................................................................

1.4 Notches in components

1.4.1 Mechanical notches 5..............................................................................................................

1.4.2 Metallurgical notches 6............................................................................................................

1.4.3 Shape-induced notches 6........................................................................................................

1.4.4 Notch effects 8........................................................................................................................

1.4.5 Practical experience 9............................................................................................................1.5 Avoiding notches

1.5.1 Grinding drag lines 10............................................................................................................

1.5.2 Grinding tools 10....................................................................................................................

1.5.3 Run-off tabs 11........................................................................................................................

1.5.4 Attaching auxiliary elements 12..............................................................................................

1.5.5 Ends of ribs 13........................................................................................................................

1.5.6 Undisturbed flow of forces 13..................................................................................................

1.5.7 Ribs and stiffeners 14..............................................................................................................

1.5.8 Welding technique 15..............................................................................................................1.5.9 Welding of "tempering beads" 16............................................................................................

1.5.10 Buffering of weld edges 16......................................................................................................

1.5.11 Welding sequence 17..............................................................................................................

2. Planning of repair and reinforcing work for steel components2.1 Causes of damage 18............................................................................................................................

2.2 Preparatory measures 18........................................................................................................................

2.3 Scope of repair work

2.3.1 Scrapping of components 19..................................................................................................

2.3.2 Temporary repair 19................................................................................................................2.3.3 Permanent repair 21................................................................................................................

2.4 Precautionary examinations 22..............................................................................................................

2.5 Detection of cracks and other defects

2.5.1 Examination for surface cracks with the dye-penetration test 22............................................

2.5.2 Examination for surface cracks with the magnetic powder test 22..........................................

2.5.3 Ultrasonic testing 22................................................................................................................

2.5.4 O&K standards for testing procedures 22................................................................................

3. Repair welding techniques3.1 Gouging out and welding of cracks 23....................................................................................................

3.2 Cracks in hub connections

3.2.1 Cracking along the center of the seam 25..............................................................................

3.2.2 Sharp, exactly radial crack along the unchamfered edge 26..................................................


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3.3 Welding on of a metal cylinder by the back-step technique 27................................................................

3.3.1 Working sequence 27..............................................................................................................

3.4 Cracks in box-type sections 29................................................................................................................

3.4.1 Opening of box-type sections 30............................................................................................

3.4.2 Removing parts of a chord plate by flame-cutting 30..............................................................

3.4.3 Backing strips 33....................................................................................................................

3.5 Recommended groove shapes for manual welding with electrodes

3.5.1 Butt joints 34............................................................................................................................

3.5.2 T-joints 35................................................................................................................................

3.6 WORKING SEQUENCE FOR WELD SEAMS

3.6.1 Butt welds 36..........................................................................................................................

3.6.1.1 V-butt weld 36........................................................................................................

3.6.1.2 Double-V butt weld 36..........................................................................................

3.6.1.3 V-butt weld with backing strip 37..........................................................................

3.6.2 T-joint 37..................................................................................................................................

3.6.2.1 T-joints (fig. 53), accessible from 2 sides 37........................................................

3.6.2.2 T-joints with backing strip (fig. 54), accessible from 1 side 37..............................

3.7 Closing of working openings, renewal of component areas

3.7.1 Closing a working opening 38................................................................................................

3.7.2 Closing a web-plate opening 39..............................................................................................

3.7.3 Replacing a chord-plate section 42........................................................................................

3.7.3.1 Salient chord plate 42............................................................................................

3.7.3.2 Recessed chord plate 45......................................................................................3.7.3.3 Possible causes of damage to chord plates 47....................................................

3.7.3.4 Repair of a boom with a salient chord 48..............................................................

4. Reinforcing of steel components4.1 Reinforcing plates

4.1.1 Dimensions 49........................................................................................................................

4.1.2 Shapes of reinforcing plates 51..............................................................................................

4.1.3 Welding slots 52......................................................................................................................

4.1.4 Fitting of reinforcing plates 53..................................................................................................

4.1.5 Weld seams of T-joints 53......................................................................................................

4.2 Shaping plates for repairs 54..................................................................................................................

4.3 Reinforcing by shape improvements

4.3.1 End of ribs 55..........................................................................................................................

4.3.2 Open sections/closed sections 55..........................................................................................

4.3.3 Reinforcing by build-up welding 56..........................................................................................

4.3.4 Improvement of curved sections in ribs 57..............................................................................

5. Materials, filler metals for welding5.1 Materials in welded components 58........................................................................................................

5.1.1 O&K component materials 59..................................................................................................

5.2 Filler metals for O&K welded components depending on partner materialsand welding techniques 62......................................................................................................................


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6. Heat treatment of materials6.1 Preheating for tacking, welding, gouging and flame-cutting 64..............................................................

6.2 Hot bending of plates 69........................................................................................................................

6.3 Hot straightening of plates 69..................................................................................................................

6.4 Stress-relief annealing of steel components 69......................................................................................

6.5 Stress-relieving of steel components

6.5.1 Warming of components 70....................................................................................................

6.5.2 Peening of weld seams 70......................................................................................................

6.5.2.1 Method of peening 70............................................................................................

6.5.2.2 Peening tools 71....................................................................................................

6.6 Treatment of filler metals 72....................................................................................................................

6.7 Temperature monitoring 72....................................................................................................................

7. Cold bending of plates 73..................................................................................................

8. Build-up welding8.1 Addition of missing / worn-out material

8.1.1 Build-up welding in drill holes 74............................................................................................

8.1.2 Build-up welding on worn-out threads 75................................................................................

8.2 Correcting of component shapes to improve the flow of forces 76..........................................................

8.3 Build-up welding as a protection against wear 76..................................................................................

9. Wear protection (hard-facing)9.1 Fundamentals 77....................................................................................................................................

9.2 Build-up welding of wear protection layers 77........................................................................................

9.2.1 Build-up welding patterns 78..................................................................................................

9.2.2 Special hints 79......................................................................................................................

9.3 Filler metals

9.3.1 For buffer layers 79................................................................................................................

9.3.2 For hard-facing layers 79........................................................................................................

9.4 Repair of build-up welds

9.4.1 State of wear 80......................................................................................................................

9.4.2 Identification of buffer and hard-facing layers 81....................................................................9.5 Repair of cracks in build-up welds 82......................................................................................................

9.6 Welding on wear-resistant steel plates or steel strips

9.6.1 Arrangement of plates/strips 83..............................................................................................

9.6.2 Bending of strips 87................................................................................................................

9.6.3 Working instructions 87..........................................................................................................

9.6.4 Filler metals 87........................................................................................................................

9.7 Welding of plates or strips with wear-resistant coatings

9.7.1 Working instructions 88..........................................................................................................

9.8 Welding of wear-resistant studs9.8.1 Working instructions 89..........................................................................................................


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9.9 Welding cutting edges onto digging tools of excavators

9.9.1 Working sequence 90..............................................................................................................

9.9.2 Welding sequence (fig. 39) and filler metals 90......................................................................

10. Repair of cast-iron components by welding10.1 Spheroidal-graphite cast iron

10.1.1 Hot welding 92........................................................................................................................

10.1.2 Cold welding 92......................................................................................................................

10.2 Flaky-graphite cast iron

10.2.1 Hot welding 93........................................................................................................................

10.2.2 Cold welding 93......................................................................................................................

10.2.3 Repair of components with the "interlock" technique 94..........................................................

11. Touching up paint coatings in repair areas 95................................................................

Appendix

Comparison: old designation - new designation 96................................................................

Part nos. for filler metals 96........................................................................................................

Conversion from foot (Fu) and inch (Zoll) to metric measure 99..........................................

Conversion for units of length 99..............................................................................................Temperature units and conversion formulas 100......................................................................

Hardness - strength comparisen 101........................................................................................


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GENERAL

Page 1

Foreword

In spite of proper design, perfect stress analysis,meticulous manufacturing, attentive maintenance andresponsible operation, damage to parts of buildingmachines and mobile industrial handling equipmentcannot always be completely avoided. Normal wear in areas subject to mecanical or abrasive action mustalways be reckoned with.

Experience in the early detection of damage and thecauses thereof, the choice of appropriate repair mea-sures and consistent, workmanlike execution contri-bute to a high availability of construction machines.

Before beginning with welding, gouging, hot and coldbending and heat treatments, the person in charge of the repair must be familiar with the material of thecomponent.

The present Technical Handbook has been compiledfrom many useful hints supplied by welding expertsas well as from experience gathered in the field of welding. They contribute to the proper planning andexecution of repair and reinforcing work. It is takenfor granted that the personnel in charge of this workpossesses the required expert knowledge. Moreover,it is important to take the particulars of the respectivecase of damage into consideration.

This latest edition of the Technical Handbook "Weld-ing for maintenance and repair" SN 2 114 500.00 is arevised and updated version and takes account of EN standards. Some sections have been supplemen-ted or added. For this reason, only the instructions inthis edition should be observed for welding work.

Safety

Always observe the accident prevention rules andsafety regulations.

Work on recipients containing or having con-tained substances

that are combustible or susceptible to stimu-late combustion,

that may be the cause of explosions and which develop noxious gases, fumes, mists or

dusts during handling

must only be carried out under expert supervi-sion and by experienced and specially qualifiedpersons.

Depressurize all circuits and components (e.g.pipelines, coolers, hydraulic oil tank, com-pressed-air receivers) before opening them.

For fitting and removing of working equipment orof components thereof, or for fitting and remov-ing of units

make sure that the machine and its equipmentare secured against unintentional and un-authorized starting. Place the working equip-ment on the ground so that it cannot move

when mechanical or hydraulical connectionsare opened or released.

make sure that equipment or components tobe fitted, removed or brought into another po-sition are secured against unintentional mov-ing, sliding or dropping by means of liftingtackle or suitable suspensions and supports.

Persons working at a considerable height mustbe equipped with a safety harness to preventthem from falling.

If - for the execution of work - helpers, such asmarshallers, are needed, it is essential to fix theresponsibilities of the individual helpers before-hand and to observe these responsibilities duringthe work in order to avoid any conflict of com-petence in safety matters.

Make sure that all tools, lifting appliances, slinggear, supports and other auxiliary devices are ina safe and reliable state of operation.

For further hints see para. 2.2 "Preparatory mea-sures".

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FUNDAMENTALS

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1. Fundamentals

1.1 Loads on structural elements

Structural elements may be subject to different loads.

Forces practically never act as individual forces butmostly in combination (fig. 1).

Fig. 1

Loads on structural elements produced by forces act-

ing simultaneously and from different directions aredifficult to assess by computation.

Modern computing methods nevertheless permit thedetermination of stress magnitudes and concentra-tions.

1.2 Types of loading

Loads (tension and compression forces) may actupon the structural element as static or mainly static(fig. 2), pulsating (fig. 3) or alternating loads (fig. 4).Pulsating and alternating loads may occur either ascontinuous or as shock loads.

Fig. 2

O+F TensionO-F Compression

Fig. 3

Fig. 4

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FUNDAMENTALS

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The following illustrations (figs. 5 and 6) give anexample of different types of loads acting on theboom of an excavator. The boom is stressed for tension.

Fig. 5

Fig. 6

During the "digging" cycle, the boom stretchesout. The lower chord plate is subject to tensionand the upper chord plate to compression.

During the "lifting" cycle, the boom is compressed.Now, the upper chord plate is subject to tensionand the lower chord plate to compression.

This means that the loads act alternately on theboom.

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FUNDAMENTALS

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1.3 Material behaviour under different loads

The mechanical stresses admissible with regard tothe operating safety of a structural element (N/mm 2)vary for the same material under static and alternat-ing loads (fig. 7).

Fig. 7

The admissible mechanical stresses are clearly belowthe values for tensile strength indicated in the stan-dards. The example shows a rolled steel EN 10025 -S355J2G3, with thicknesses _ > 3 mm _ < 100 mm.

The reason for this material behaviour lies in thegradual weakening of the cohesive forces along thegrain boundaries, and, at a later stage, in the occur-rence and increase of disturbances in the microstruc-ture (fig. 8).

Fig. 8

1 Shows an idealized material microstructure under alternating load. The material experiences elasticdeformation along the sliding planes at the grainboundaries. The sliding planes present no distur-bances.

2 Permanent elastic deformation leads to shiftingof material grains along the sliding planes wherethe first disturbances appear.

3 The disturbed areas widen as the frequency of elastic deformation increases.

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FUNDAMENTALS

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1.4 Notches in components

All areas where the ideal flow of forces in a compo-nent is disturbed are qualified as notches.

From their occurrence and their effect on the compo-nent 3 different types of notches have to be consi-dered:

- mechanical notches- metallurgical notches- shape-induced notches

1.4.1 Mechanical notches

Mechanical notches may occur during welding in theweld seam (fig. 9).

Fig. 9

1 Undercut

2 Incomplete joint penetration

3 Porosities in the weld deposit

4 Incomplete fusion

5 Grinding drag lines

6 Drop-through at the root

7 Underbead crack

These notches may, however, also have other me-chanical causes (fig. 10 and 11), such as:

steel stamping figures, chisel marks,marking tool lines, damage by lifting

chains.

Fig. 10

Fig. 11

1 Steel stamping figures

2 Chisel marks

3 Marking tool lines

4 Notches due to lifting chains

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FUNDAMENTALS

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Mechanical notches lead to stress concentrations (fig.12).

Fig. 12 2 Inadequate penetration of root

4 Incomplete fusion

These, in turn, lead to an enlargement of thenotches.This procedure may repeat itself and eventually leadto fracturing of the component.Mechanical notches are mainly produced during themanufacture, but later on also during the utilization of the machine (traces resulting from use).Mechanical notches can be detected by visual in-spection or by non-destructive testing and then be

repaired.

1.4.2 Metallurgical notches

Metallurgical notches are caused by thermal influenceon the material; i.e. always at or around weld depos-its (fig. 13).

Fig. 13

The heat applied by welding leads to zones present-ing different metallurgical and mechano-technologicalproperties depending on their distance to the heatsource.

Due to their properties, these areas, however smallthey may be, show a different behaviour under load-ing which, in turn, leads to elongation impedimentsand material constraints.The occurrence of metallurgical notches can be keptto an acceptably low level by applying optimizedwelding and heat-treatment techniques.The effect of existing metallurgical notches, e.g.those produced by improper welding, can also bemitigated by a stress-relieving and annealing proce-dure.

1.4.3 Shape-induced notches

Shape-induced notches depend on the structural de-sign and lead to stress concentrations caused by thediversion of lines of forces (fig. 14).

In many cases, shape-induced notches are moreover located in heat affected zones with metallurgicalnotches.Shape-induced notches can be largely reduced bychoosing an appropriate design. For all practical pur-poses, they have to be reduced to such an extentthat the negative influence exerted by them on theendurance strength of the structural element remainsinsignificant.

Fig. 14

1 + 2 Hardness distribution curve

Shape-induced notches can be subsequentlyeliminated by changes in shape.

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FUNDAMENTALS

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Examples (fig. 15):

a + b: inadequately executed butt-weld joints be-tween structural elements of different thicknesses.

c: better joint.

For relatively small thickness variations of the twoplates, the joint such as realized in example c) canbe sufficient.

Fig. 15

An ideal and yet cost-saving solution for the distribu-tion of forces is the butt-weld joint where the platethickness difference is reduced by chamfering in a1:4 ratio (fig. 16).

Fig. 16

The forces should be able to flow as disturbance-freeas possible through the part of the structural elementthat can be analysed.Lines of forces should not, however, traverse auxil-iary elements (fig. 17).

Fig. 17

The welds used for fastening such auxiliary elementsare mostly overestimated as they cannot absorb theforces prevailing in components

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1.4.4 Notch effects

Depending on their shape, notches have differentnotch or influencing factors.

The influence of notch factors on the fatigue strengthof a component is shown in the graph (fig. 18).

Fig. 18

Location and shape of curves W, O, 1, 2, 3 and 4refer to:

material: EN 10025: S355J2G3

no. of load cycles: 2 10 6 (2 million)i.e. of high fatigue strength

group of stress intensities: small, medium and highstresses with approx. thesame frequency

Possible notches (mechanical and metallurgical) inthe seams of butt-weld joints:

For a notch factor of "O", practically the only effectsto be expected are from metallurgical notches.

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1.4.5 Practical experience

In order to lower the weight of components, de-signers often resort to materials with higher strengthvalues and to plates of lower thicknesses with nochanges to the shape of the component.

In this respect it should not be overlooked, however,that the stability of the structural element only de-pends on the geometrical dimensions and themodulus of elasticity E of the material. E is basicallythe same for an S690Q and an S355J2G3.

This means that a component consisting of thinner plates is subject to stronger deformations and thusloses some of its service properties. Moreover, theeffects of notches on the strength of the materials are

increased.

High-strength fine-grained structural steels such asS690Q offer advantages over ordinary fine-grainedstructural steel S355J2G3 only in cases of static or predominantly static loading and reduced notching(fig. 19).

With the strength of the material increasing, the sus-ceptibility of structural steel elements to notching be-comes greater.

For machines subject to alternating loads andequipped with notched structural steel elements it istherefore recommended to use an S355J2G3.

In this context, notches resulting from marks left byusage have to be considered as well.

Fig. 19

Location and shape of curves W, O and 4 refer to:

material: S355J2G3, S690Q

no. of load cycles: _ > 2 10 6 (2 million)

group of stress intensities: small, medium and highstresses with approx. thesame frequency

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1.5 Avoiding notches

If notches in a component are avoided altogether or if their acuity (notch factor) is reduced, the admissiblestresses (N/mm 2) can be increased.In such case, the life of the component increases anddamage s can b e largely a voided.

1.5.1 Grinding drag lines

Grinding grooves transverse to the main directionof load are dangerous mechanical notches.

Grinding grooves transverse t o the direction of loading(fig. 20) should therefore be avoided during grinding.

Fig. 20

This rule cannot be observed if grinding wheels areused for the work. Under these circumstances, man-ual reworking with emery paper may be required.

It is therefore recommended to use grinding stones atleast for the finishing pass.

1.5.2 Grinding tools

Grinding wheel on angle grinder (fig. 21):

Only suitable for the rough removal of material.Not suitable for low-notch finish with controlleddirection of grinding grooves .

Fig. 21

Grinding stone (fig. 22):

Suitable for grinding of weld surfaces, weldends and plate edges. Should be used at leastfor finishing.

Fig. 22

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Grinding stone (fig. 23):

Suitable for grinding in component areas of difficult access.

Fig. 23

Steel milling cutter (fig. 24):

Suitable for rounding off small radii.

Fig. 24

1.5.3 Run-off tabs

Mechanical stresses reach their highest value at theedges of components.

Defects in the weld which are caused, for instance,by arc strikes or end-of-weld craters in edge zonesshould be avoided. The welding groove must becompletely filled along the edges of components.

Fig. 25

For this purpose, the weld seam has to be extendedby ca. 50 mm using run-off tabs (fig. 25). In thiscase, arc strikes and end-of-weld craters are locatedin the extended part of the groove.

The cross-section of the run-off tabs used dependson the shape of the welding groove.

After welding, the run-off sections are to be removedby flame-cutting and the surfaces to be finished byproper grinding.

For such work, the grinding instructions given under 1.5. 1 should be followed.

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1.5.4 Attaching auxiliary elements

For the fastening of auxiliary elements no weldingshould be carried out in the edge zones of structuralelements subject to high stresses.

The welds should end at a well-defined distance fromthe edge of the component.

Arc strikes and end-of-weld craters should be locatedas far away from the component edge as possible(figs. 26 und 27).

Fig. 26

Fig. 27

To protect the base element it may be required towork out alternative methods of fastening (fig. 28).

Fig. 28

Examples:

Fastening of pipe clamps on a very small baseelement.

Stirrups for pipes, lamps, cables and similar fix-tures fastened without welding on the highlystressed bottom chord.

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1.5.5 Ends of ribs

The ends of ribs on highly stressed structural ele-ments must taper off "gently" and be surrounded by aboxing weld.

Fig. 29

The welder must position himself and the component

in such a way that the boxing weld can be carriedout without arc strikes and end-of-weld craters.

The weld interface areas must be absolutely freefrom notches. This can only be achieved by grinding(fig. 30).

1.5.6 Undisturbed flow of forces

Auxiliary elements - in this case a crane eye - mustbe shaped in such a way that the lines of force arenot disturbed or even interrupted.

Fig. 30

Interruptions in the flow of forces produce stressconcentrations and lead to cracks (fig. 31).

Fig. 31

Recommendation: Cut off the eyes after assembly.Grind the surfaces smooth andclean.

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1.5.7 Ribs and stiffeners

Ribs, stiffeners and similar parts on components mustbe welded with endless seams if the components aresubject to pulsating or alternating loads (fig. 32).

Fig. 32

Interruptions in the weld seams are not recommend-ed, even if they facilitate the assembly of the compo-nent (fig. 33).

Tri-directional states of stresses in weld-seam cross-ings are considerably less dangerous for thestructural elements than defective or even missingboxing welds in the gaps. They represent potentialstarting points for fatigue fractures. Too large gapsmay lead to damage by "softening-up" the componentcorner, even if the weld is otherwise faultless.

Fig. 33

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1.5.8 Welding technique

The effects of metallurgical notches can be consider-ably alleviated by applying a proper handling tech-nique during welding.

When repairing components by welding, the stringer bead technique must be used (fig. 34).

Fig. 34

The advantages of the stringer bead technique are: Reduced heat input (joule/cm) per welding bead.

The heat-affected zone (HAZ) in the base materialremains very narrow, resulting in a metallurgical

notch with minimum notch action.Heat input: (J/cm) = I x U x 60

vI = current intensity (A)U = voltage (V)v = welding velocity (cm/min)

Each welding bead is tempered by the overweld-ing with the next bead.

The weld pool can be well controlled, with- good penetration at the weld edges,- avoidance of weld pool pre-flow (cold welding),- avoidance of poor fusion.

Maximum bead or pass widths:

Solid wire:

Wire Width0,8 8,01,0 10,01,2 12,01,6 16,0

Rod electrodes:

Rod Width3,2 8,04,0 10,05,5 12,0

The weld start points for multipass welding must runin terraces (fig. 35) or cascades (fig. 36). This isessential if faults due to arc strikes or end craters areto be avoided on one line in the various passes.Illustrations:

Fig. 35

Fig. 36

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1.5.9 Welding of "tempering beads"

The welding of "tempering beads" provides a sub-stantial improvement in the mechanical-technologicalcharacteristics of the weld metal both in the cover pass and in the heat-affected zone (HAZ) close tothe surface.

Fig. 37

Explanations of Fig. 37:

Beads 6 and 7 are the "tempering beads".

The welding of beads 6 and 7 re-heats the weldmetal of beads 1 and 3 / 4 and 2 respectively.The metal is tempered.

In this tempered weld metal, an ideal materialstructure with improved expansion and toughnesscharacteristics is induced with a negligible loss of strength.

If necessary, the cover pass can be ground down.

1.5.10 Buffering of weld edges

The formation of heat-affected zones (HAZ) is vital tothe durability of the weld, especially when weldingmaterials with a high carbon equivalent.The aim must be:

a narrow heat-affected zone (HAZ),

a minimum reduction in the strength of the ma-terial and of the heat-affected zone (HAZ),

a slight increase in hardness at the transitionbetween the heat-affected zone and the base ma-terial.

This aim is largely achieved by so-called buffering of the weld edges prior to weld- joining.For buffering purposes, welding is done with the low-est possible heat input (J/cm).The following details must be observed when buf-fering:

Weld the buffering with rod electrodes of the typesuited to the base material.

Diameter of rod electrodes: 3.2 mm.

Preheat the base material, depending on type.

Weld in stringer bead technique.

Check the inter-pass temperature of the materialsaccordingly.

If run-off tabs are present at the weld ends: buffer beyond the start point as far as the end of therun-off tabs.

Clean the finished buffering thoroughly beforeoverwelding. (Slag residues on the contact linefrom one bead to the next).

Start the weld-joining without intermediate coolingof the component.

When 2 separate components or fragments are to be joined by welding, buffering should be done prior toassembly in the most favourable welding position for both parts.

Assembly of the warm parts must be scheduled be-fore the heating, e.g. with an appropriate device.

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1.5.11 Welding sequence

Definition:Stipulating in which direction a joint is to be welded

and in what sequence several joints are to be weld-ed.

Explanation of drawing:

Presetting the welding sequence allows the following

to be determined:

The component must be kept as stress-relievedas possible. Delays due to the effect of weldingstresses must be accepted.

The component must be kept as dimensionallystable as possible. Intrinsic stresses in the compo-nent, resulting from the welding, must be accept-ed.

When repairing components by welding them, it willgenerally be necessary to keep the component di-mensionally stable.

When welding weld crossings, the welding sequencedrawn below must be observed (fig. 38).

Fig. 38

To avoid defects and thus to prevent mechanicalnotches, weld crossings in the edge zone of compo-nents must not have any arc strikes or end craters.

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PLANNING OF REPAIR AND REINFORCING WORK

18

2. Planning of repair and reinforcingwork for steel components

In planning the repair and reinforcement of steelcomponents, the first step should be to determine theprecise extent and the causes of damage and then tofix and to carry out the appropriate measures.Reinforcement without planning leads to new da-mage.

2.1 Causes of damage

The causes of damage may be manifold.

Dimensioning errors

Incorrect estimation of the potential stresses andload cases.Dimensioning and design errors.Unsuitable construction materials.

Manufacturing errors

Mechanical and metallurgical notches.Measuring errors.Mixing up of materials.Material defects.

Wrong operation of the machine

Wrong handling due to lack of experience.Wrong use due to an overestimation of the ma-chines capabilities.Using the machine for activities for which it is hasnot been designed.

Accidents

Accidents during transport, relocation or operation,e.g. accidents caused by falling rocks when work-ing in quarries.

2.2 Preparatory measures

To restore the machines availability independent of the cause of damage, it is essential to fix the appro-priate working procedure.

Important prerequisites for the execution of repair andreinforcing work:

Repair, reconstruction or reinforcing work onstructural steel elements of construction machinesmay be supervised only by experts with sufficientexperience in the design and construction of dy-namically stressed components.

In cases of doubt, please address the O&K after-sales service which can refer the problem to therespective specialized departments, if required.

In practice, repair, reconstruction or reinforcingwork may only be carried out by experiencedwelders. A welder holding a certificate in accor-dance with EN 287-1 135 P BW W03 t20 PC SSmk already fulfils the basic qualification require-ments.

If possible, welding is to be done in a workshopwhich is equipped with the necessary tools andlifting gear.

If welding work has to be carried out on site, thecomponent must be protected against atmospher-ic influences such as rain, snow, dew, wind, etc.This can be achieved, for example, by a tarpaulinused as a working tent.

Cleanliness at the place of work is of utmostimportance.

When dismantling the component, all built-onparts, particularly those with articulations, must beremoved from the component.

(Example: Tri-Power pin and linkage).

Hose and pipe connections opened in dismantlingthe component as well as open holes and casingsshould be closed carefully in order to prevent thepenetration of dirt.

The component to be repaired is to be cleanedproperly, particularly those parts of the componenton which work is to be carried out.

Weld grooves and surfaces for fillet welds mustbe completely cleaned down to the bare metal.

Paint coatings and priming coats must not bewelded over.

Lubricants must be completely removed frombearings in order to prevent them from liquefyingunder the effect of heat and flowing into the weldarea.

Machined surfaces, pins, bearings, piston rods,electrical components, etc. must be protectedagainst weld splashes and grinding dust by cover-

ing them with non-combustible materials. Before carrying out welding on assemblies

containing electronic components, all connectorsmust be unplugged.Example: In hydraulic excavators equipped withthe PMS system, all connectors must be un-plugged from the load-limit regulator (PMS box).

Prior to welding on components remaining on themachine, the starter batteries must be disconnect-ed. Disconnect first the negative and then thepositive terminal! After the work, reconnect firstthe positive and then the negative terminal.

Before welding, the type and the properties of thematerial involved must be determined.

Use only those weld filler metals that are suitablefor the base metal concerned.

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Page 19

2.3 Scope of repair work

The most suitable procedure to be followed in a caseof damage is shown in the diagram below.

After damage has been reported, one of the 3 follow-ing decisions is to be taken (fig. 1).

Fig. 1

2.3.1 Scrapping of components

The damage has reached such an advanced stagethat a proper repair is either technically no longer

feasible or linked with extremely high costs.

The limit for this decision is not a fixed one. Whereasat home and in most industrialized countries the de-cision to scrap is taken relatively early, it may benecessary in other countries to carry out the repair because the procurement of a new part is difficult for various reasons and sometimes even impossible. Thereasons for this situation may lie, for example, in thelack of foreign exchange, in high customs duties,long delivery periods and extended standstill periodsfor the machine. Relatively low wage costs can alsobe a reason in favour of the repair.

2.3.2 Temporary repair

The component must be repaired immediately in or-der to maintain the machines availability, e.g. be-cause the machine is used for a job with fixed timelimits (fig. 2).

In spite of being a matter of urgency, temporaryrepairs must nevertheless be performed carefully inorder to avoid new damage.

Fig. 2

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The following rules must be observed:

Cracks must be stopped by drilling when they arestill relatively short (fig. 3).

This measure ensures a reduction in the crackpropagation speed.It does not, however, constitute a repair.

Fig. 3

It is particularly important to find the actual end of thecrack.Depending on their starting point, cracks may tra-verse the component along curved lines (fig. 4).

Fig. 4

A + B correctly stopped by drilling

C incorrectly stopped by drilling

One possibility of finding the end of a crack consistsin non-destructive testing for cracks by means of oneof the well-known methods such as ultrasonic testing,dye-penetration test, magnetic powder test or X-raytesting.

After drilling, the stopper hole can be examined for persisting cracks.

Long cracks should be immediately gouged outand welded, even if the marginal conditions areunfavourable.

The area of damage must be subjected to permanentinspection. In case of a failure of the repair weld, themeasure described has to be repeated.

Do not weld reinforcing elements onto damagedareas. They not only make no sense, but more-over cover up the area of damage and makepermanent checking impossible.

Another possibility is that the area of damage maywiden and thus make proper repair at a later timeimpossible.

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Page 21

2.3.3 Permanent repair

Fig. 5

If a decision in favour of a permanent repair of thedamaged component is taken (fig. 5), the followingrules are to be observed:

The cause of damage must be determined andeliminated if it can be traced back to design or manufacturing deficiencies. To determine thecause of damage, the following simple measureswill often be sufficient:

- Personal experience and comparison withdamage patterns in similar components.

- Visual inspection of the area of damage withthe aim of finding the causes for the crackstarting point, such as mechanical notches,missing weld seams, insufficient root penetra-tion, etc.

- Visual appraisal of the fractured surfaces with

the aim of finding the crack starting point bymeans of the bench marks.Moreover, the structure of the fractured sur-face allows conclusions to be drawn with re-gard to material quality.

- A simple examination of the material consistsin comparing its hardness to that of knownmaterials.

- The wall thickness of sheets, cast-steel or

forged pieces can be controlled and comparedto the dimensions contained in the drawings.

- In case of persisting doubt, the component canbe subjected to a new analysis carried out bya neutral institution.

- In difficult cases, it is advisable to make use of the services of a laboratory if, for example,precise material analyses, hardness curvesand an appraisal of the materials microstruc-ture and surface are required.

In certain cases, the expertise of an indepen-dent laboratory may also be required in order to clear up liability matters.

A workmanlike repair giving a high fatiguestrength expectancy must be properly plannedand carefully executed on the workshop level.

In each phase of the work, all advantages at handshould be made use of.

Even so-called "trivial matters" may be of decisiveimportance for the success of a repair.

The repair work must be subject to supervisionand the phases in which inspections are to takeplace be determined beforehand.

It is advisable to explain the theoretical reasonsfor the repair measure to the craftsman carryingout the work as he will then develop a feeling of responsibility for a successful achievement of therepair.

In case of damage caused by design failures or overloading, it may be necessary to reinforce thecomponent after the repair.

Important note: The reinforcement planned mustmake sense and its positive effects be justified bymeans of an analysis.

Badly planned reinforcing measures are useless,expensive, do not offer real safety, increase theweight of the component and may impede itsfunctions.

Moreover, they do not look very nice.

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2.4 Precautionary examinations

In the field of medical treatment, precautionary ex-aminations are standard practice. Doctors teach usthat a disease, if discovered in its early stage, can becured by a simple operation, whereas in an advancedstage, help often comes too late.

The regular inspection of construction machines, for example, is also a kind of precautionary examinationand part of the VBG guideline 40.

Inspection procedure and follow-up measures:

Cleaning of the machine.

Visual inspection of critical component areas. Re-cording of all findings.

Contacting the manufacturer for a discussion of the inspection results.

Planning and execution of necessary repairs.

Stockpiling of damage-prone components.

Stockpiling of wearing parts.

2.5 Detection of cracks and other defects

Cracks and other defects in plates, forged and cast-steel parts can be detected with the help of testprocedures:

2.5.1 Examination for surface cracks with thedye-penetration test

The dye-penetration test is the simplest procedure todetect cracks in the surface of the material.

1. Carefully clean the area to be tested.

2. Spray red penetration fluid(O&K-SN 1 044 915) onto the area and allow itto take effect for 5 to 10 minutes.

3. Remove red penetration fluid with a specialcleaner (O&K-SN 552 304).

4. Spray white developer (O&K-SN 552 302) ontothe area.

Any cracks then become visible as small, redlines on a white background. The extent of "bleeding" and the waiting time allow conclusionsto be drawn as to the depth of the crack.

Wipe off the developer with a cleaning cloth.

2.5.2 Examination for surface cracks with themagnetic powder test

The magnetic powder test is suitable for the detectionof cracks on the surface of the material and for cracks not deeper than 2 mm below the surface.

The component is first magnetized and then sprayedwith a liquid containing very fine iron particles (as fineas dust). The iron particles settle along the cracksand make them visible.

2.5.3 Ultrasonic testing

The ultrasonic test can be used for the detection of defects inside materials of more then 10 mm thick-ness and in weld deposits.Ultrasonic testing can only be performed by qualifiedtesters.

Qualification: Certificates U 1 and U 2 of the"Deutsche Gesellschaft zur zer-st orungsfreien Pr ufung" (DGZFP)*.

2.5.4 O&K standards for testing procedures

Detailed information on testing procedures can befound in the following O&K standards:

07 47 04, part 1 Dye-penetration test, magneticpowder test

07 47 01, sheet 1 Ultrasonic testing of welded joints

07 47 01, sheet 2 Ultrasonic testing of cast-steeland forged parts.

The O&K standards are available from O&K Dort-mund, Standards Dept., in English or in German(please state desired language).

* (German Society for Non-Destructive Testing)

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REPAIR WELDING TECHNIQUES

Page 23

3. Repair welding techniques

The repair of a structural component by welding re-quires working methods which do not have to be

applied when the steel component is manufactured.

Many of the methods represented have been deve-loped on the basis of numerous individual exper-iences and are field-proven.

3.1 Gouging out and welding of cracks

The method best suited for gouging out of cracks isthe so-called "ARC-AIR procedure" (fig. 1).

Fig. 1

An arc is struck between a carbon electrode and thematerial to be removed, and a jet of compressed air directed towards the arc blows away the molten basemetal.

For part nos. of "ARC-AIR carbon electrodes" see Appendix.

Another gouging method consists in gouging withoxy-gas or with grooving electrodes.

It is important to start gouging at the end of the crackand to proceed towards the edge of the component.Proceeding in reverse order may enlarge the crackdue to thermal effects.

It can be taken for granted that the crack has alreadyprogressed along the grain boundaries of the materialwhere it cannot yet be detected visually or by other test procedures (fig. 2).Gouging should therefore not start at the end of thecrack but shortly before the crack begins.For gouging, preheat the cracked area (cf. 6.1).

After thermal gouging, the weld groove is to be re-worked by grinding.

The surfaces must be cleaned down to the baremetal.

Fig. 2

A Visible crackB Damage at the grain boundaries

If the crack is accessible from both sides in out-of-position work, gouging should first start on thelower side (fig. 3) with the depth of the groove beingapprox. 1/3 of the material thickness.

Fig. 3

Weld this side first.

The crack is then gouged out from the more easilyaccessible upper side down to the seam alreadywelded from the lower side.

As a final step, the weld is finished on the upper side

(fig. 4).

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Fig. 4

So-called "weld-pool backing strips" should not beused if welding from both sides is possible, as abacking strip in the root area of the weld representsa mechanical notch (shape-induced notch).

Ramified cracks

Ramified cracks should be gouged out and weldedstep by step (fig. 5).

Fig. 5

If this procedure is not respected, it may happen thatareas of material between the cracks break away andthat the gaps thus produced cannot be closed.

The same applies to long cracks where gouging outand welding should equally be done step by step.(fig. 6).

Fig. 6

During cooling of the partial welds, the surroundingcold areas prevent excessive welding shrinkage anddistortion of the component.

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3.2 Cracks in hub connections

Fig. 7 shows the connection of a hub to a box-typesection which is accessible only from one side.

Fig. 7

1 Hub

2 Web plate

3 Square-edge butt joint

4 Fillet-weld backing, welded before closing of thebox-type section.

The weld is characterized by a fillet-weld backing onthe outer edge and the chamfered web plate.

The following defects may occur:

3.2.1 Cracking along the center of the seam (fig.8)

Fig. 8

A possible cause is a broken fillet-weld backing.

Counter-measures: Gouge out the crack carefully (fig. 9).Weld the gouged joint (fig. 10).

Gouge out the web plate (2) in the area of thefillet-weld backing round the hub (1) and down to itscollar (fig. 10).Weld the gouged joint (fig. 11).

Fig. 9

Fig. 10

Fig. 11

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3.2.2 Sharp, exactly radial crack along the un-chamfered edge

A possible cause is a lack of fusion in the uncham-fered edge of the joint (see arrow in fig. 12).

Fig. 12

Counter-measures: Gouge out the crack carefully (fig. 13).Weld the gouged groove (fig. 14).

Fig. 13

Fig. 14

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3.3 Welding on of a metal cylinder by theback-step technique

The following example describes the welding of amachined cylinder onto an undercarriage.

Welding by the back-step technique can always beemployed where as distortion-free a weld as possibleis required.

This applies to circumferential seams as well as tolongitudinal seams.

Fig. 15 shows how to execute the weld between theweb plate of the cylinder and the base plate.

Fig. 15 A Outer side of cylinder

B Inner side of cylinder

Welding is carried out in the normal operating posi-tion.Welding position: horizontal

Correct positioning of the electrodes avoids defectsfrom incomplete fusion (9, fig. 16) at the web plateedges.

Fig. 16

3.3.1 Working sequence

1. Position and align the cylinder in accordancewith the drawing. Tack the cylinder solidly on theoutside and carry out a dimensional check after

tacking.

Fig. 17

2. Welding of the 1st pass from the inner side of the cylinder (fig. 17).

For this work use rod electrode 3.20 mm.

Weld in accordance with the back-step proce-dure,

step length: approx. 250 mm

Fig. 18 shows an example for the back-steptechnique.

Fig. 18

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3. Grind weld joint clean working from the cylinder outside. Remove any slag residues from the 1stpass and completely grind out any cracked tackwelds.

Do not weld over cracked tack welds!

Fig. 19

4. Weld the full seam on the cylinder outside. Theexample in fig. 19 shows a cylinder wall thick-ness of 15 mm. For other plate thicknesses, thebuild-up of the weld has to be planned andexecuted accordingly.

Rod electrode 2nd pass: 3.20 mmRod electrode 3rd and 4th pass: 4 or 5 mm

Weld all beads in the back-step procedure andstagger starting and end points of each newlayer.

Example:

5. Complete the joint on the cylinder inside (fig. 20).

Rod electrode 5th and 6th pass: 4 or 5 mm.

Weld seams as described under 4.

Fig. 20

6. Clean the weld seams and check for defects.

6.1 There must be no undercuts, weld metalpores, arc strikes, end craters, spatter par-ticles, slag, etc.

6.2 Carry out a dye-penetration test of the sur-face which must be absolutely free fromcracks.

7. Check the dimensions. Irregularities in the planeof the cylinder flange must not be levelled by theapplication of heat (danger of distortion due toweld-induced residual stresses).

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3.4 Cracks in box-type sections

Gouging and welding of cracks only from the outsidecannot be recommended.

Welding without backing strips usually leads either toan incomplete filling of the root area or to a drop-through at the root (fig. 21).

Fig. 21

In both cases, the mechanical notches in the rootarea will lead to the formation of new cracks.Welding on backing strips introduced through the jointcan equally not be recommended (fig. 22).

Fig. 22

The backing strips will not come to rest properly onthe base metal.

Flashes and slag residues on the under-side cannotbe removed.

The resulting mechanical notches will cause newdamage.

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3.4.1 Opening of box-type sections

If the crack is accessible only from one side, anaccess opening has to be created from the secondside. This can be done by opening the component in

areas not subject to high stresses (figs. 23 and 24).

Fig. 23

Fig. 24

In larger components there may also be openingsallowing access to the interior of the component. Thesize of access openings is approximately 500 mm x500 mm.

If the internal structure of the component is unknown,it is advisable to contact the design department.

A drawing showing the location of possibly existingstiffening ribs inside the box-type section should beat hand.Otherwise it may be necessary to cut out small spy-holes in order to find out the areas in which repair openings of sufficient size can be created.

Practical hint:

Ribs are often visible on the reverse side of theplates.Especially on painted surfaces they are clearly visi-

ble.

Gouge out the crack first from the inside (over 1/3 of the plate thickness) and weld. Continue on the out-side and then reclose the box-type section.

3.4.2 Removing parts of a chord plate by flame-cutting

Figures 25 to 30 show how a box-type section canbe opened in a way which does not affect theremaining parts of the component.

The section (1, fig. 25) of the top chord (2) is to beremoved.

Fig. 25

Cut a pilot hole in the chord plate (2, fig. 26) behindthe web (3) with a flame (4). Flame-cut in longitudinaldirection and as closely as possible to the web plate.

Cutting must be carried out without producing draglines in the web plate.

Fig. 26

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Sever the remaining strip of the chord plate (5, fig.27) by flame-cutting from the inside.

Fig. 27

Flame-cut the welding chamfer required for weldingthe new chord plate section (fig. 28).

Fig. 28

Make the transverse cut in the chord plate by pro-ceeding from the web plate towards the center andnot - as shown in fig. 29 - from the center towardsthe web plate (3).

Fig. 29

Cutting as in fig. 30 leads to unnecessary damage of the web plate (3, fig. 30) (5 = damaged area /flame-cut area).

Fig. 30

Welding on backing strips

Openings cut into components in order to gain ac-cess to the under-side during the welding of cracksmust be carefully reclosed in a workmanlike manner.

Welding of the component is carried out from oneside on backing strips (fig. 31).

Fig. 31

The geometry of the weld and the welding sequenceshown are to be carefully observed. Only then can awelding seam with a relatively low root notch factor be expected.

It goes without saying that the root notch factor of such a welding seam has to be compatible with theselected component area.This must be examined before opening the compo-nent.

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32

The same applies basically also to the welding of T-joints (fig. 32).

Fig. 32

The same working method can also be employed if plates of different thicknesses are welded (figs. 33and 34).

The method shown in fig. 33 is, no doubt, the better

solution.Chamfering of the thicker plate in a 1 : 4 ratio.

Fig. 33

The welding joint must in no case be too narrow, asthe planned welding sequence can otherwise not beobserved.

Fig. 34 If the joint is larger than required, welding shouldstart with a build-up weld on one of the seam edgesin order to avoid excessive transverse shrinkage.

After depositing the build-up weld, the gap betweenthe seam edges can be completely closed (fig. 35).

Fig. 35 This applies equally to the welding of T-joints with toolarge a groove.

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Page 33

3.4.3 Backing strips

Backing strips are mostly made of flat steel 30 x 6 or 25 x 4 (fig. 36).

Fig. 36

Backing strips for non-linear weld seams are flame-cut out of plates with the corresponding thickness(fig. 37) or welded together from pieces of flat steel(fig. 38). The joints (fig. 38) must be welded andground from both sides.

Fig. 37

Fig. 38

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3.5 Recommended groove shapes for manualwelding with electrodes

For repairs or welding work carried out in the field,the following weld groove configurations should bepreferred.

These groove configurations can be employed for plate thicknesses up to 30 mm. The dimensionsshown in the drawings are applicable up to this thick-ness.

For gas metal-arc welding, the weld preparation an-gle can be reduced to 45 o.

For greater plate thicknesses, the weld preparationangles must be reduced so as to leave a maximumopening width of abt. 30 mm. Except for the sharp-edge seam, all grooves should be gouged out,ground and counter-welded, if possible.

3.5.1 Butt joints

Recommended weld groove shapes:

- V-butt weld (fig. 39)- Double-V butt weld (fig. 40)- Single-bevel butt weld (fig. 41)- Double-bevel butt weld (fig. 42)- Square-edge butt weld (fig. 43)

Fig. 39

Fig. 40

Fig. 41

Fig. 42

Fig. 43

Weldingtechnique

SymbolEN 24 063

Opening angle

E 111 60

MAGM 135 45

Solid wire 136 45

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Page 35

3.5.2 T-joints

Recommended weld groove shapes:

- Single-bevel butt weld (fig. 44)- Double-bevel butt weld (fig. 45)- Square-edge butt weld (fig. 46)

Fig. 44

Fig. 45

Fig. 46

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3.6 WORKING SEQUENCE FOR WELDSEAMS

3.6.1 Butt welds

+ easily accessible side- poorly accessible side

3.6.1.1 V-butt weld (fig. 47)

Fig. 47

A Joint prepared

B Joint welded

C Root gouged out from the under-side

D Root capped

V-butt weld (fig. 48). Seam accessible from 2sides after turning of the component

Fig. 48

A Joint prepared

B Joint welded

C Plate turned, root gouged out

D Root capped

3.6.1.2 Double-V butt weld (fig. 49)Seam accessible from 2 sides

Fig. 49 A Joint prepared

B Joint welded overhead

C Root gouged out

D Seam welded

Double-V butt weld (fig. 50). Seam accessiblefrom 2 sides after turning of the component

Fig. 50

A Joint prepared

B Root welded

C Plate turned, root gouged out

D Seam welded

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3.6.1.3 V-butt weld with backing strip

V-butt weld with backing strip 25x4 (fig. 51). Seamaccessible from 1 side

Fig. 51

A Backing strip attached

B Joint prepared and 1st root bead welded

C 2nd root bead welded

D Seam welded

V-butt weld with backing strip 30x6 (fig. 52). Seamaccessible from 1 side

Fig. 52

A Weld-backing strip attached

B Joint prepared

C Joint gouged out (grinding)

D Seam welded

3.6.2 T-joints

3.6.2.1 T-joints (fig. 53), accessible from 2 sides

Fig. 53

A Web and chord plates tacked

B Single-bevel weld deposited

C Root gouged out

D Seam welded

3.6.2.2 T-joints with backing strip (fig. 54), acces-sible from 1 side

Fig. 54

A Backing strip welded

B 1st root bead welded

C 2nd root bead welded

D Seam welded

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3.7 Closing of working openings, renewal ofcomponent areas

Openings (fig. 55) should be as small as possible butas large as necessary in order to allow the unimped-ed use of tools.

Experience: Openings 300 mm long and 200 mmhigh are normally sufficient.

3.7.1 Closing a working opening

Fig. 55

The following example (fig. 55) is suitable for platethicknesses up to 25 mm.

Fig. 56 shows a backhoe stick. The diagram of mo-ments clearly shows the areas of highest loads andthus of greatest stresses. Seam [1] is therefore theseam that lies in the area of high chord stresses.

Weld seam [1] from the middle outwards to the left

and right to the midpoint of the corner curvatures.Finish upper beads or passes approximately 15 mmbefore reaching the end of the underlying bead or pass. Allow the completed weld seam to cool downto approximately + 50 oC.

Weld seams [2] and [3] alternately and use the so-called "back-step procedure" for the long seams.

Back-step welding:

Weld seam [4] in the same way as seam [1].

Fig. 56

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Page 39

3.7.2 Closing a web-plate opening

Fig. 57

1. At the web-plate (2, figs. 57 + 58), chamfer theedges to be welded with approximately 10 o.Width b of the chamfer in reldition to the platethickness can be seen in fig. 70, page 42.

Fig. 58

2. Gouge out the longitudinal seams between chordplate (1) and web plate (2) over a distance of approximately 100 mm (fig. 58).

3. Attach backing strip (3, fig. 59), but only to theweb-plate edges.

Fig. 59

Prepare backing strip (3) from flat steel 30 x 4bent on edge or burn out of 4 mm thick plate. Donot tack-weld backing strips from flat-steel barsfor lack of cover at the rounded corners.

4. Attach backing strip (3) to the web plate (2) bymeans of screw clamps (fig. 60). Do not tack-weld but rather weld with a 3 mm fillet seamrunning all around (fig. 61).

Fig. 60

After welding the fillet seam, clean the contact

surface for the cover plate by removing all tracesof weld spatter (arrow, fig. 61).

Fig. 61

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5. Prepare cover plate (5, fig. 62) for the repair opening. For this purpose, use a new plate of the same thickness and chamfer as shown.Width (b) can be seen in fig. 70, page 42.

Fig. 62

6. Attach cover plate (5, fig. 63) and check for perfect weld joints.The cover plate must be in full-face contact withthe backing strip.In case of distortions due to welding, the backingstrip has to be straightened.

Fig. 63

Press cover plate (5, fig. 64) against backingstrip by using screw clamps. In workshops, thiscan be done with box-type section widths of upto 1.5 m.

Fig. 64 If the use of screw clamps is not possible, thecover plate should be fastened by so-called"hold-down strips" (6, fig. 65). Attach the hold-down strip (6) to the web plate (2) with a filletweld. Fix the cover plate (5) by driving wedges(7) between plate and strip.

After welding of the cover plate, remove hold-down strips by flame-cutting.Grind welded areas smooth and clean.Do not knock off hold-down strips with a ham-mer.

Fig. 65

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7. Weld on cover plate (fig. 66).

Fig. 66

It is essential to observe the welding sequenceshown. The symbols used have the followingmeaning:

Weld seam [1] approximately to the midpoint of

the corner curvature. Place the first bead exactlybetween cover plate (5) and backing strip (3).The upper bead must end approximately 15 mmbefore the end of the underlying bead. After welding of seam [1], the cover plate may shrink.Proceed by welding seams [2] and [3]. Makesure that the seams interlock properly with theends of seam [1] (prepare by grinding). Weld theother ends through to the chord plate. The endof seams [2] and [3] at the chord plate are to beground as shown in fig. 66, so as to obtain thesame shape of the welding joint as the onebetween web and cover plate.

Finish the sequence by welding seam [4]. Theends of welds [2] and [3] must not come to lieagainst interruptions or starting points of seam[4]. If possible, weld seam [4] with continuousstringer beads from one end to the other.

Finish by grinding the surfaces of seams [1], [2],and [3] flush with the adjacent plates (fig. 67).

Fig. 67

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3.7.3 Replacing a chord-plate section

3.7.3.1 Salient chord plate

In a box-type section with 2 web plates (fig. 68), achord-plate section is to be replaced by a new one.

Fig. 68

Fig. 69

1. Chamfer welding bevels at 10 o. Width b (fig. 69)can be read from fig. 70 below.

PLATE THICKNESS t CHAMFER WIDTH b

8 2,010 2,012 2,515 3,020 3,525 4,530 5,535 6,540 7,045 8,050 9,0

Fig. 70

2. Work out the longitudinal seams between webplate (2, figs. 68 + 69) and chord plate (1) over alength of approximately 100 mm from the pointat which the new piece is to be fitted.

Fig. 71

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3. Attach backing strips (3, 4, figs. 72 + 73) at thetwo remaining ends of the chord plate (1). Fit theplates properly and without any gaps.

Fig. 72

Fig. 73

For the backing strips (3,4) use flat steel 25 x 4mm. Fit backing strip (3) exactly between thetwo web plates (2). Adapt external backing strips(4) to the joints of the web plates (2) and allowthem to extend outwards by approximately30 mm.

4. Tack-weld backing strips (3) between the webplates. If distortion occurs due to welding (fig.74), the backing strips have to be straightened.

Fig. 74

5. Weld the backing strips (3, fig. 75) with filletseams to the web plates (2).

Fig. 75 6. Tack-weld backing strips (4, fig. 76) to the outer

side of web and chord plates.

Fig. 76

7. Tack-weld run-off tabs (5, fig. 77) to backingstrips (4). Cf. also the section "Ends of buttwelds".

Fig. 77

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8. Fit the new piece of chord plate (6, fig. 78). Theold piece of chord plate previously removed mustnot be used again. Make sure that the new pieceof plate rests properly on its support.

Fig. 78

9. Weld the two fillet seams (fig. 79) as shown,without interruptions and without any tack points.

Fig. 79

10. Weld in the new piece of chord plate by strictlyobserving the welding sequence shown (fig. 80).The symbols have the following meaning:

Seam [1] - transverse seam in the areasubject to high chord-platestresses. Weld seam com-pletely.

Seams [2] + [3] - weld longitudinal seams inthe direction indicated bythe arrows.

Seam [4] - weld transverse seam com-pletely.

Seams [5] + [6] - weld longitudinal seams inthe direction indicated bythe arrows.

Weld seams [1] and [4] with stringer beads andcontinue the weld onto the 50 mm long run-off tabs (4). Remove the run-off tabs after weldingwith a clean cut.

The surfaces of the transverse seams must beground clean and flush with the adjacent plates.Work out properly the longitudinal seams in thearea of the transverse seams. The grinding draglines must run parallel to the longitudinal lines of force. If possible, the transverse seams shouldbe subsequently subjected to ultrasonic testing.

Practical hint:

In welding the longitudinal seams [2] [3] [5] and[6] there must be no welding starts or stops inthe area of the transverse seam (backing strip).

Fig. 80

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3.7.3.2 Recessed chord plate

The following example shows how to fit a new re-cessed piece of chord plate by welding it into abox-type section with 2 web plates (fig. 81).

Fig. 81

Working sequence:

Fig. 82

1. Chamfer welding bevel at 15 o. Width (b, fig. 82)can be taken in fig. 70, page 42.

2. Work out longitudinal seams between web plate(2, fig. 83) and chord plate (1) over a distance of approximately 100 mm beyond the cutting edgeof the chord plate.

Fig. 83

3. Attach backing strips (3, figs. 84 + 85) to the two

remaining ends of the chord plate (1).For the backing strip (3) use flat steel 25 x 4mm. Fit in backing strip (3) properly and withoutany gaps between the two web plates (2).

Fig. 84

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Fig. 85

4. Tack backing strips (3) between the web plates(fig. 85 + 86). If there is any distortion due towelding, the backing strips have to be straight-ened.

Fig. 86

5. Weld in new piece of chord plate by strictlyobserving the welding sequence shown (fig. 87).

As to the welding of the seams, cf. 10 on page44.

Fig. 87

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3.7.3.3 Possible causes of damage to chordplates

The following faults may occur in chord plates of box-type sections:

1. Transverse crackingThe chord plate may crack open transverse to thecomponent in the chord plate.

Fig. 88

Reason for the damage:Expansion of the component obstructed by non-opti-mally dimensioned or weldedcomponent elements such as bearing blocks, ribs,reinforcing plates etc.Measures:The component can almost always be repaired bywelding. For a durable repair, the component mustbe opened to allow the welds in the componentareas subject to maximum stress to be capped.

2. Plate partingThe plate may crack open almost exactly at thecentre of the plate, as shown in the diagram (fig. 89).

Fig. 89

Reason for the damage:There are non-metallic inclusions from the pool (seg-regation defects), distributed over the entire platedimension, at the centre of the plate.

Measures:The plate cannot be repaired by welding.For durable repairs, the damaged plate must be re-placed. It is to be assumed that areas of the platenot yet cracked open would eventually also crackopen as a result of the dynamic stress on the compo-nent.

3. Longitudinal crackingThe chord plate may crack open in longitudinal direc-tion of the component parallel to the edge of theplate (fig. 90).

Fig. 90

Reason for the damage:The component is not adequately stable. The chordplate is deformed under changing loads, resulting inmaterial distortions at the weld/chord plate transition.Measures:The chord plate cannot be repaired by welding.For a durable repair, the plate must be replaced in

the cracked area. The new plate must be thicker thanthe cracked one to reduce deformation to a tolerablelevel.

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3.7.3.4 Repair of a boom with a salient chord

The top chord of the boom is cracked (arrows,fig. 91).

1. Remove support eye (1, fig. 91).

Fig. 91

2. Remove top chord in the area of damage(fig. 92).

Recommendation: Remove the curved section of the top chord completely.

Fig. 92

3. Repair the damage inside the box-type sectionand in the side walls.

4. Weld on new top chord (fig. 93). Increase platethickness by 5 to 10 mm.

Fig. 93

5. Weld support eye back in place (fig. 94).

Machining of the severed parts is generally notrequired if fitting and welding are carried outcarefully.

Fig. 94

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REINFORCING OF STEEL COMPONENTS

Page 49

4. Reinforcing of steel componentsThe reinforcement of components by welding can bedone in the following ways:

Covering up a damaged area after repair by re-inforcing plates, with the aim of reducing the me-chanical stresses (N/mm 2) in the repair area.

Eliminating deficiencies caused by changes inshape, e.g. the problematic case of "open sec-tions/closed sections", shape of stiffening ribs,configuration of frame corners, etc.

Eliminating deficiencies by means of changes inshape by build-up welding, e.g. on cast-steelparts.

The necessity of a component reinforcement should,if possible, have been proved by a simple analysis.4.1 Reinforcing plates

4.1.1 Dimensions Length of reinforcing plates

The ends of reinforcing plates are places wheremetallurgical and shape-induced notches occur which may lead to damage by the concentrationof stresses (Part A, fig. 1).

Fig. 1Reinforcing plates should therefore be dimen-sioned in such a way that they end in areas withlow basic stresses (Part B, fig. 1).

Thickness of reinforcing platesThe thickness of reinforcing plates should be max.60 % of the thickness of the plate to be reinforced(fig. 2).

Fig. 2 An analysis shows that thicker reinforcing platescannot be connected to the plate to be reinforcedas the welding seams required would be toolarge.Thicker plates moreover lead to large shape-in-duced notches and make the component heavier than is really necessary.

Width of reinforcing platesIn steel components, stresses are often highestnear the edges. The reinforcing plate should

therefore be as wide as the plate to be reinforced(A, fig. 3).

Fig. 3

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For practical reasons, reinforcing plates of less than8 mm thickness can not be chamfered. In suchcases, the reinforcing plate (B, fig. 3) must be nar-rower to leave enough space for a fillet weld.The upper edges (arrow, fig. 3) of the plate to bereinforced and of the reinforcing plate should not bemelted away.

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4.1.2 Shapes of reinforcing plates

Reinforcing plates should, if possible, have simpleshapes with straight edges (figs. 4 + 5).To relieve the transverse seams of stresses, welding

slots should be provided (fig. 4).

Fig. 4

Another possibility consists in welding on strips of plate. In this case, the longitudinal seams must bewelded continuously.

Advantages:

The edge zones, where high stresses normally prevail,are reinforced. Another advantage is the reduction of weight (fig. 5).

Fig. 5

Small plate strips, flat-steel or wide flat-steel bars,can be more easily fitted and bent (fig. 5).

Fig. 6

Non-linear plate shapes (figs. 7 + 8) are difficult tomanufacture and do not offer any advantages withregard to the distribution of forces.

Fig. 7

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Fig. 8

4.1.3 Welding slots

In addition to the welding seams along the outer edges, the seams in welding slots are equallyintended to enhance the connection of reinforcingplates (figs. 9 and 10).

Fig. 9

Finish the ends of the slots by drilling stopper holes(fig. 9).

Slot width = 2 x plate thickness (fig. 9).

Fig. 10

The welding seams in the welding slots are idealthrust connections between the reinforcing plate andthe plate to be reinforced.

Circular welding holes are disadvantageous (fig. 11):

Fig. 11

The parts of the seam transverse to the lines of forces cannot bear any loads and can therefore notbe considered for analysis.

The reinforcing plates cross-section is strongly re-duced.

The hole edges are subject to stress concentrations.

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4.1.4 Fitting of reinforcing plates

Reinforcing plates should be in full-face contact withthe plate to be reinforced, i.e. they should lie asclosely as possible against the base plate. The air gap should, if possible, be nil.For relatively small components and thin plates, thereinforcing plates should be squeezed against thebase plate by means of screw clamps (fig. 12).

Fig. 12

For larger components and thicker plates, thereinforcing plates should be held in place by wedges(fig. 13).This is, however, only possible at the edges of plates.Welding and cutting of the wedge holders must be

done properly. Never knock off wedge holders with ahammer.

Fig. 13 The central area of plates can be pressed into position

by means of bolting (fig. 14).This is particularly recommended for large platesections. The studs can be favourably placed near thewelding slots.

After tack-welding, the welded-on stud may only beknocked off. The area in the base metal where the

studs have been removed must be carefully preparedby grinding before the slot is welded.

Fig. 14

4.1.5 Weld seams of T-joints

Reinforcing plates in T-joint areas should be weldedin such a way that a connection between all 3 platesis formed (fig. 15).

Fig. 15

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4.2 Shaping plates for repairsThe plates needed for repair or reinforcement pur-poses can be shaped in different ways.Problems which may arise in the different shaping

methods: Edge folding (Fig. 16):

cold shaping;observe minimum bending radius;watch for longitudinal cracking in the bendingarea.

Fig. 16

Pressing (Fig. 17):

cold or warm shaping;with cold shaping, observe minimum bending ra-dius and watch for longitudinal cracking in thebending area.

Fig. 17

Rolling (Fig. 18):

cold shaping;no problems to be expected after shaping.

Fig. 18

Multi-edge bending (Fig. 19):

cold shaping:cracking at the lines where the tools act on theplate edges is to be expected;chamfer plate edges approx. 2 x 2 mm at top andbottom after multi-edge bending.

Fig. 19

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4.3 Reinforcing by shape improvements

Bucyrus Welding Ecommendations

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