en p 01 principlesofbrazingtechnology

7/29/2019 En P 01 PrinciplesOfBrazingTechnology

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Principles of brazing technology

Umicore AG & Co. KG - BrazeTec, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangTelefon: +49 (0) 6181-59-03 Telefax: +49 (0) 6181-59-3107 Email: [email protected] Internet: www.BrazeTec.de

Brazing is a thermal process for securely joining andcoating materials, whereby a liquid phase isproduced by melting a brazing alloy (fusion-brazing)or by diffusion at the interfaces (diffusion-brazing).The solidus temperature of the base material is notreached (DIN 8505, Part 1).

1. Standards and regulations for brazing1.1 Recommendations for brazing

- Technical information sheets- Standards

Technical information sheets: Recommended

These are prepared by experts in work groups and

the information corresponds to the respective state oftechnology. It is recommended that the technicalinformation sheets be heeded as they are alsoviewed as the respective state of the technology froma legal point of view.

Examples:

- DVS-Guideline 1183: DVS-course Brazingcopper materials

- VdTV Technical Information Sheet 1160:Evaluation of processes for manufacturing

brazed joints and high temperature brazedjoints

- DVGW Work Sheet GW2

Standards: Compulsory

Any deviation from the standard must be specificallyagreed between the client and contractor. There arecurrently many national (DIN), european (EN) andinternational (ISO) standards. The existing Germanstandards are being superseded by Europeanstandards. Referral is made in particular here to DIN

EN 1044 Brazing composition of brazingalloys which replaces DIN 8513 Parts 1-5 and toDIN EN 1045 Brazing fluxes for brazing whichreplaces DIN 8511-1. Both these standardscategorise the respective materials. There are alsostandards in existence which cover the terms used inbrazing, constructional aspects, testing of brazedjoints, inspecting brazed joints, etc. which can beobtained via Beuth-Verlag (Berlin) or DVS-Verlag(Dsseldorf).

1.2 Regulations for work safety and accidentprevention, e.g.:- Accident prevention regulations, section 15:

Welding and related techniques d.BG;- VDI 2046 Safety guidelines for operating

industrial furnaces with inert gas and reactiveatmospheres

2. Wetting process and capillary forces

2.1 Distinction between welding and brazing

In welding not only is the added alloy material meltedbut the base material is also partially melted.

In brazing only the added brazing alloy melts. Thebase material is wetted in its solid state by the liquidbrazing alloy.

Usually similar materials Virtually any desired materialcombinations

Fusion welding Brazing

Virtually identical melting Brazing alloy melts attemperatures for the base lower temperaturematerial and alloy than the base material

2.2 Wetting

A prerequisite for brazing is the wetting of the base

material by the brazing alloy. Three importantconditions must be fulfilled for this to happen: the brazing surfaces and the brazing alloy must

be bare metal, the brazing surfaces and the brazing alloy must

have at least reached the working temperature, at least one component of the brazing alloy must

readily form an alloy with the base material.


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Base material

- Visible oxide layers (rust and scale), fat layers

and layers of dirt must be removed beforecarrying out brazing work. Thin oxide layers (e.g.tarnishing) may remain on the workpieces ifbrazing is carried out using a flux.

- The working temperature is the lowest surfacetemperature of a workpiece at the brazing joint at

which the brazing alloy can wet, spread and bondwith the base material. This temperature is alwayshigher than the solidus temperature of the brazingalloy. It can be above, below or the same as itsliquidus temperature.

- The wetting process involves surface alloyingbetween the brazing alloy and the base material.Next to the wetting zone there is a diffusion zonewhich is very small for brazing work and cannotbe detected by metallographic means. In order toattain optimum strength, the brazing alloy must beliquid for at least 8 to 10 seconds to give an

adequately deep diffusion zone.

There is greater interaction between the brazing alloyand base material when carrying out hightemperature brazing (flux-free brazing attemperatures above 900C in a controlledatmosphere).

2.3 Joint-brazing and gap-brazing

Joint-brazing is a brazing technique similar to gas-fusion welding from a joint preparation and working

method point of view. It is virtually always carried outmanually. The working temperature of the brazingalloy must not be exceeded when joint-brazing.

1 to 1.5 mm

The most important area of application of joint-brazing is for brazing galvanised steel pipes.

The workpieces are prepared for gap-brazing such

that the brazing joints are narrow capillary gaps.They are heated up to brazing temperature uniformlyover the whole length of the gap. The liquid brazingalloy is forced into the gap by capillary fillingpressure. This technique is easy to mechanise. Themajority of brazing work is carried out by the gap-brazing technique.

The surface forces are additive in the narrowcapillary gaps (size of the order of 0.1 mm), so thatthe brazing alloy is preferentially drawn into thenarrow gap. If brazing is being carried out with a fluxin a gas atmosphere, the brazing alloy which

penetrates into the brazing gap must be able to pushthe flux out of the gap.

In gap-brazing, the working temperature of thebrazing alloy may be exceeded by in general 20 to50C.


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ar o e we ng n erme ae sa e

Final stateII = Workpiece 1II = Workpiece 2

Both bare metal, andheated to workingtemperatureLiquid brazing alloy

Capillary filling pressure

The brazing alloy is pressed into the gap by capillaryforces. The narrower the brazing gap, the higher thecapillary filling pressure.

For a 0.1 mm parallel gap, the capillary fillingpressure reaches ca. 100 mbar, corresponding toabout 0.1 Atm. This in turn corresponds to about a 1m column of water ( = 1); assuming = 10 g/cm3(the density of a brazing alloy), the capillary heightfor low melting point brazing alloys in a 0.1 mm widegap can be calculated to be ca. 10 cm. This agreesreasonably well with experiences in practice.

(only applies forbrazing with flux)

Gap too narrow

Correct gap width

Permissible gap width for manual brazing

Gap too wide

Different gap cross-sections give different fillingpressures. An open fillet has a six times highercapillary filling pressure than a parallel flat gap.

3. Brazing alloy and flux groups

3.1 Brazing alloys

According to DIN 8505, alloys with a liquidustemperature below 450C are solders and those witha liquidus temperature above 450C are brazingalloys.

The upper and lower brazing temperature limits aredetermined by the following:

lower limit- the working temperature

upper limit

- the flux (becomes saturated with oxides attoo high temperatures), or

- the brazing alloy (individual components ofthe alloy can evaporate), or

- the economics of the process (unnecessarilyhigh temperatures cost unnecessary timeand energy), or

- the base material (structural transformation;strength loss).


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3.2 Fluxes

Fluxes are solvents for metal oxides. They have aneffective temperature range within which they areable to dissolve metal oxides. The solvating capacityof the flux is limited. About 5% of the weight of flux in

metal oxides can be dissolved. If oxides are presentin greater amounts, the flux saturates and it loses itsfunctionality.

Atmosphericoxygene Flux Oxide

More than 5 min.

The hygroscopic flux residues must be removed byscouring in water or by pickling in pickling bathssuitable for the base materials. Ultrasound aids theremoval of these flux residues.

The non-hygroscopic flux residues do not have to beremoved for fear of corrosion. If they need to beremoved for other reasons (e.g. to paint thecomponents), they are usually removed by

mechanical means (e.g. sand-blasting).Too little Sufficient

Oxide film remains Oxide film is

dissolved

The solvating capacity of modern brazing fluxes foruse at low temperatures (i.e. between 600 and800C) for common heavy metal oxides is between 1and 5%, meaning that it is limited. That means thatrelative to the oxide which is present a relativelylarge amount of flux must be available, and ultimatelyso in the molten state, otherwise sound brazing workis not achieved. Extremely narrow gaps, e.g. lessthan 0.02 mm, hence cause problems because thereis an inadequate amount of flux in the gap. This

naturally has a big effect on the soundness of thebrazed joint.

Flux

Wire of brazing alloy

For surface brazing, the high capillary filling pressurein the open fillets leads to running of the brazing alloyon the external sides. The supply of brazing alloy tothe narrow surface gap is reduced; increasedinclusion of flux hence occurs.

Brazing alloyFlux

Increased flux inclusion can be avoided by insertedbrazing alloy sheet.

Gaseous fluxes

Joints (V-seams and fillets) can be brazed usinggaseous fluxes. For brazing gaps especially forgaps having larger depths and small widths the useof gaseous fluxes is not recommended because theflame does not penetrate into the capillary gap.When using flux pastes, their working life can besignificantly prolonged by the additional use ofgaseous fluxes.

The effective temperature of gaseous fluxes extendsfrom about 750C to 1100C.


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Brazing with flux-forming brazing rods - BrazeTecSilfos brazing alloys.

OxygenFuel gas

Copper alloys, copper-tin alloys and silver can bebrazed with phosphorus-containing brazing alloyswithout the use of flux. The self-flowing properties

of these brazing alloys can be explained as follows:On melting the brazing alloy, the phosphorus in thebrazing alloy reacts with oxygen in the air to formphosphorus pentoxide. This reacts with the copperprotoxide on the copper surface to form coppermetaphosphate which acts as a flux. As coppermetaphosphate is safe from a chemical- corrosionpoint of view, the brazed joints require nosubsequent treatment.

When brazing with BrazeTec Silfos brazing alloys,the brazing time should not be longer than about 3 to

4 minutes.

4. Brazability of components

According to DIN 8514, the brazability is the propertyof a component to be manufactured in such a wayvia brazing that it meets the stipulated requirements.

A component can be brazed if the followingconditions are met (see diagram):

- the base material is suitable for brazing,- there is a brazing capability for the

manufacture, namely one or more brazingtechniques can be used,

- and the construction can be brazed such thata sound construction results, namelysatisfactory reliability of the componentunder the foreseen operating conditions.

Comment: In electrical engineering, the expressionssolderability and suitability for soldering are usedsynonymously for soldering.

Suitable base material, brazing alloy and fluxcombinations

Each of the three properties suitability for brazing,brazing capability and ability to manufacture asound brazed joint depend on the base material,manufacturing process and joint design. The degreeof dependency on these three parameters dependson the individual brazing task.

Brazabilityof the

component

Brazingcapability

Manufacture

Soundness ofthe brazed joint

Construction

Base material

Suitability forbrazing


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The suitability of base materials for brazing work isshown in Table 1.

Tables 1 and 3 give information about how theindicated materials can be brazed. This does notmean to say that components brazed in this way can

withstand all operating loads. In order to guaranteethis, the operating conditions for the brazed jointsmust be known prior to selecting theconditions/methods for carrying out the brazing work.These are workpiece-specific and differ from onecomponent to the next. More detailed information on

this matter can be found in the section entitledSelection criteria for brazing alloys and fluxes. Incertain instances where there is relatively high risk ofdamage, we recommend that you get in touch withus to enable optimum selection of the brazingparameters.

Brazing has the big advantage that virtually allmaterials which are suitable for brazing can becombined with each other. It goes without saying thatthe brazing parameters must always be selected forthe most difficult material from a brazing point ofview.

Suitability of base materials for brazing

Group 1 Group 2 Group 3

Materials which can be brazed withuniversal brazing alloys and universalfluxes and using all standardtechniques.

e.g.copper and copper alloysnickel and nickel alloysiron materialscommon steelscobalt

noble metals

Materials which require specialbrazing alloys and/or special fluxes,but which do not require specialbrazing techniques.

e.g.aluminium and aluminium alloyshard metals, stelliteschromium, molybdenum, tungsten,tantalum, niobiumsolder-like materials

Materials which can only bebrazed using special brazingalloys and special techniques.

e.g.titaniumzirconiumberylliumceramics

Table 1


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Umicore AG & Co. KG - BrazeTec, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangTelefon: +49 (0) 6181-59-03 Telefax: +49 (0) 6181-59-3107 Email: [email protected] Internet: www.Bra

Solder and brazing alloy groups (I)

Group description Soldering /brazing

temperaturerange

C

Typical solders /brazing alloys in thisgroup in accordance

with EN (DIN)

BrazeTec name Solidustemp.

C

Liquidustemp.

C

Max. permcontinuoperat

temperat

CTin-lead soldersEN 29453

145 ... 325 S-Sn60Pb40S-Pb50Sn50

183183

190215

8080

Special soldersEN 29453

145 ... 395 S-Sn97Cu 3

S-Sn96Ag4S-Sn96Ag3

S-Sn95Sb5

Soldamoll 230(BrazeTec 3)Soldamoll 220BrazeTec 4

Soldamoll 235

230

221

250

221

240

110

110

110

Cadmium-freeuniversal brazingalloys

DIN EN 1044(DIN 8513)

650 ... 1100

AG 104 (L-Ag45Sn)AG 106 (L-Ag34Sn)AG 203 (L-Ag44)AG 207 (L-Ag12)

CU 303 (L-CuZn40)

CU 102 (L-Cu)

BrazeTec 4576BrazeTec 3476BrazeTec 4404BrazeTec 1204

BrazeTec 60/40

640630675800

875

1083

680730735830

895

1083

200200300300

350

Low melting pointcadmium-containing universalbrazing alloysDIN EN 1044(DIN 8513)

610 ... 800 AG 304 (L-Ag40Cd)AG 306 (L-Ag30Cd)

BrazeTec 4003BrazeTec 3003

595600

630690

150150

Manganese-containing specialbrazing alloysDIN EN 1044(DIN 8513)

690 ... 1020 AG 502 (L-Ag49) BrazeTec 4900BrazeTec 21/68

680980

7051030

400600

1) not laid down in standards

Table 2a


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Solder and brazing alloy groups (II)

Group description Soldering /brazing

temperature

range

C

Typical solders /brazing alloys in thisgroup in accordance

with EN (DIN)

BrazeTec name Solidustemp.

C

Liquidustemp.

C

Max. pcontope

tempe

Phosphorus-containing brazingalloys for copperbase materialsDIN EN 1044(DIN 8513)

710 ... 800 CP 102 (L-Ag15P)

CP 105 (L-Ag2P)CP 203 (L-CuP6)

BrazeTec Silfos 15

BrazeTec Silfos 2BrazeTec Silfos 94

645

645710

800

825890

150

150150

Special brazingalloys for specialbrazing workDIN EN 1044

(DIN 8513)

730 ... 960 AG 403 (L-Ag56InNi) BrazeTec 5603BrazeTec 6009BrazeTec 7200

600600780

710720780

200200300

High temperaturenickel-basedbrazing alloysDIN EN 1044(DIN 8513)

900 ... 1200 Ni 107 (L-Ni7)Ni 105 (L-Ni5)Ni 102 (L-Ni2)

BrazeTec 897BrazeTec 1135BrazeTec 1002

8901080970

89011351000

Aluminium brazingalloysDIN EN 1044(DIN 8513)

560 ... 600 AL 104 (L-AlSi12) BrazeTec 88/12 575 590 200

Table 2b


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Flux groups (I) for soldering/brazing metallic materials

Flux group Flux type Information about the manufacture Most important areas of application 3.2.2.

3.1.1.

Zinc chloride and/or ammoniumchloride and free acids

Zinc chloride and/or ammoniumchloride

Chromium-containing steels;highly oxidised workpieces

Chromium-free steels and non-noble metalswashing off the residues is possible

3.1.1.

2.1.3

2.1.1

2.1.2.

Zinc chloride and ammoniumchloride in organic formulation

Organic acids

Amines, diamines, urea

Organic halogen compounds

Chromium-free steels and non-noble metalswashing off the flux residues is not possible

Fluxes forsoldering heavymetalsDIN EN 29454

1.1.2.

1.1.1.

1.1.3.

Resins with halogen-containingactivators

Resins without additives

Resins withhalogen-free additives

Copper

Fluxes forsoldering lightmetalsDIN EN 29454

3.1.1.

2.1.3.

2.1.2.

Solder-forming zinc chloridesand/or tin chlorides;also with additives

Organic compounds

Organic halogen compounds

For workpieces which can be washed

Table 3a


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Flux groups (II)

Flux group Flux type Information about themanufacture

Most important areas of application

Fluxes for brazingheavy metals

DIN EN 1045

FH10FH11

FH12

FH20FH21

FH30

FH 40

Boron compounds and fluorides

Boron compounds

Boron compounds, phosphates,silicates

Chlorides and fluorides

Silver brazing alloys with working temperaturesca. 800C

Brazing alloys with working temperatures betwe750 and ca. 1000C

Brazing alloys with working temperatures above1000C

Brazing alloys with working temperatures betwe600 and 1000C for reactor construction (boron

Fluxes for brazing

light metalsDIN EN 1045

FL10

FL20

Hygroscopic chlorides and

fluoridesNon-hygroscopic fluorides

For workpieces which can be washed (also pick

neutralised)Heat exchangers

Table 3b


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Proposals (I) for brazing alloy (solder) / flux / brazing (soldering) technique combinations (for Group 1 base ma

Base material Brazing alloy Flux Technique *) Solder Cu CP 105 (L-Ag2P)

CP 203(L-CuP6)--

Cu-alloys CP 105 (L-Ag2P)

AG 102 (L-Ag55Sn)AG 203 (L-Ag44)

FH10

FL / Ind.EL.-W / SO / VO

S-Sn97Cu3S-SnAg4

S-Pb50Sn50

3

Ni + Ni-alloysIron materials

Common steels

AG 102 (L-Ag55Sn)AG 203 (L-Ag44)

AG 304 (L-Ag40Cd)

FH10 S-Pb50Sn50S-Sn96Ag4S-Sn97Cu3

3

CU 303 (L-CuZn40)CU 305 (L-CuNi10Zn42)

FH20Cobalt

CU 102 (L-Cu) -

FL / Ind / EL.-W. / AOSO / VO

S-Cd82Zn16Ag2 3

AG 403 (L-Ag56InNi) FH12 FL / Ind. / EL.-W.Cr- and Cr/Ni-steels

NI107/NI105/NI102AG 401/CU102

- SO / VO

S-Sn96Ag4 3

Noble metals AG 102 (L-Ag55Sn)AG 202 (L-Ag60)AG 401 (L-Ag72)Gold brazing alloys

FH10 FL / Ind.EL.-W.AO

SO / VO

S-Sn96Ag4 3

*) FL = Flame; EL.-W. = Electr. Res.; SO = Inert gas furnace; K = Copper-bit; Ind. = Induction; AO = Atmosphere furnacHL = Hot air jet

Table 4a


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Proposals (II) for brazing alloy (solder) / flux / brazing (soldering) technique combinations (for Group 2 and 3 baTable 3)

Base material Brazing alloy Flux Technique *) Solder Al and Al-alloys(with Mg and/or

Si contents 2%)

AL 104 (L-AlSi12) FL10 FLAO

S-Sn96Ag4S-Cd80Zn20

3

AG 301 (L-Ag50CdNi)AG 502 (L-Ag49), possibly

as layer brazing alloy

FH12

AG 502 (L-Ag49)CU 305 (L-CuNi10Zn42)

FH12FH21

Hard metals

Stellites

CU 102 (L-Cu), possiblywith tri-metal

-

FLInd.

SO / VO

-

-

Chromium,molybdenum,

AG 502 (L-Ag49) FH12

Tungsten, tantalum,niobium

Cu87MnCo 1) FH21

FL/Ind.

AO/SO

-

ZincAntimony

- - - S-Pb60Sn40S-Sn96Ag4

3

LeadBismuth

Tin

- - -S-Sn50Pb32Cd18 3

Titanium AG 401 (L-Ag72)PD 105

- SO (Argon)VO

-

ZirconiumBeryllium

PD 105 - SO (Argon)VO

-

GraphiteMetal oxide-

ceramics

AgCuTik 1) - SO (Argon)VO

-

*) FL = Flame; EL.-W. = Electr. Res.; SO = Inert gas furnace; K = Copper-bit; Ind. = Induction; AO = Atmosphere furnac

HL = Hot air jet1

) not laid down in standards

Table 4b


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BrazeTec GmbH, Rodenbacher Chaussee 4, D-63457 Hanau-WolfgangTelefon: +49 (0) 6181-59-03 Telefax: +49 (0) 6181-59-55 50 Email: [email protected] Internet: www.BrazeTec.de

The information given about our products,equipment, plants and processes is based onextensive research work and our technicalknowledge of applications. We provide thisinformation verbally and in writing according to thebest of our knowledge, but we do not accept anyresponsibility beyond that in the individual contract.We do however reserve the right to make technicalchanges as part of our product developmentactivities. Our technical service personnel areavailable on request to provide further advice andassistance to solve manufacturing and technicalproblems.

This does however not relinquish users of theirresponsibility to check our information andrecommendations prior to carrying out their ownwork. This is also true especially for deliveriesabroad with regard to the observance of protectionrights of third parties and with regard to applicationsand procedures not expressly given in writing by us.In the event of damage, our liability is limited tocompensation to the same degree as provided for inour General Terms and Conditions of Sale andDelivery for shortcomings in quality.

en p 01 principlesofbrazingtechnology

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