bab 27b pengelasan fusi

7/23/2019 Bab 27B Pengelasan Fusi

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PengelasanPengelasan FusiFusi

((Fusion WeldingFusion Welding))Ir. Tri Prakosa, M. En .

ProsesProses ManufakturManufaktur II,II,FebruariFebruari 20112011


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Fusion WeldingFusion Welding

1. Oxyfuel Gas Welding2. Arc-Welding Processes: Consumable

Electrode3. Arc-Welding Processes: Nonconsumable

Thermit Welding Electrom Beam Welding

Laser Beam Welding


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OXYFUELOXYFUEL GAS WELDINGGAS WELDING

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OxyfuelOxyfuel gas welding /OFWgas welding /OFW

Developed in the early 1900s, this processutilizes the heat generated by the combustion ofacetylene gas (C2H2) in a mixture with oxygen.

The heat is generated in accordance with the

.combustion process, which occurs in the innercore of the flame, is

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C2H2 + O2 2CO + H2 + Heat


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OxyfuelOxyfuel gas welding /OFWgas welding /OFW

This reaction dissociates the acetylene into

carbon monoxide and hydrogen and producesabout 1/3 of the total heat generated in the flame.The second reaction is:

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which results in burning of the hydrogen andcombustion of the carbon monoxide, producingabout 2/3 of the total heat.

2CO + H2 + 1.502 2C02 + H2O + heat


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Types of flamesTypes of flames

The proportions of acetylene and oxygen in thegas mixture are an important factor in oxyfuel gas

welding.

At a ratio of 1 : 1, that is, when there is no excess

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a) Neutral Flame


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With a greater oxygen supply, it becomes anoxidizing flame. This flame is harmful, especially

for steels, because it oxidizes the steel. Only incopper and copper-base alloys is an oxidizingflame desirable because a thin protective layer of

slag forms over the molten metal.

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b) Oxidizing Flame


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If the supply of oxygen is lowered, it becomes areducing or carburizing flame. The temperature of a

reducing, or excess-acetylene, flame is lower.

Hence it is suitable for applications requiring low, , ,

hardening.

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c) Carburizing Flame


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Filler metalsFiller metals

Filler metals are used to supply additional material

to the weld zone during welding. They are available as rods or wire, and are made of

metals compatible with those to be welded.

These consumable filler rods may be bare, or theymay be coated with flux.

The purpose of the flux is to retard oxidation of thesurfaces of the parts being welded, by generating agaseous shield around the weld zone.

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Filler metalsFiller metals

The flux also helps dissolve and remove oxides and

other substances from the workpiece, resulting in astronger joint.

The slag developed protects the molten puddle of

metal against oxidation as it cools.

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Welding Torch yang digunakan padaWelding Torch yang digunakan pada

Pengelasan OxyacetylenePengelasan Oxyacetylene

(a) Gambar umum dan

(b) Penampang torch yangdigunakan padapengelasan oxyacetylene.

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Pertama kali katup acetylene dibuka; gasdinyalakan dengan korek api atau penyala;kemudian katup oksigen dibuka dan nyala diatur.


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High Pressure Gas Cylinders yangHigh Pressure Gas Cylinders yang

Digunakan pada Pengelasan OxyacetyleneDigunakan pada Pengelasan Oxyacetylene(c) Peralatan dasar yang

digunakan pada oxyfuel-

gas welding.

Untuk memastikan

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semua ulir padasambungan acetyleneadalah ulir kiri,sedangkan pada oksigenadalah ulir kanan.

Tabung oksigen

biasanya dicat merah,sedangkan tabungacetylene dicat hijau.


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ARCARC--WELDING PROCESSES:WELDING PROCESSES:CONSUMABLE ELECTRODECONSUMABLE ELECTRODE

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Shielded metalShielded metal--arc welding (SMAW)arc welding (SMAW)

(Las(Las BusurBusur ListrikListrik)) Shielded metal-arc welding (SMAW) is one of the

oldest, simplest, and most versatile joiningprocesses.

Currently, about 50% of all industrial and

maintenance welding is performed by this process. The electric arc is generated by touching the tip of a

coated electrode against the workpiece and then

withdrawing it quickly to a distance sufficient tomaintain the arc.

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LasLas BusurBusur ListrikListrik ((ShieldedShielded

MetalMetal-- Arc Welding/SMAW)Arc Welding/SMAW)Ilustrasi skematik prosespengelasan dengan elektroda

terselubung (shielded metal-arc welding). Sekitar 50%operasi di industri ukuranbesar men unaan roses ini.

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Ilustrasi skematik operasishielded metal-arc welding

(dikenal juga sebagai stickwelding, karena bentukelektroda berupa batang).


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LasLas BusurBusur RendamRendam

Submerged arc welding/SAW)Submerged arc welding/SAW) In submerged arc welding (SAW), the weld arc is

shielded by granular flux, consisting of lime, silica,manganese oxide, calcium fluoride, and otherelements.

The flux is fed into the weld zone by gravity flowthrough a nozzle. See the following figure.

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LasLas BusurBusur RendamRendam ((SubmergedSubmerged--

Arc Welding/SAW)Arc Welding/SAW)

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Ilustrasi Skematik Las Busur Rendam (submerged-arc welding)dan peralatannya. Flux yang tidak terproses, akan digunakankembali. Sumber: American Welding Society.


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Gas metalGas metal--arc weldingarc welding/GMAW/GMAW

In gas metal-arcwelding (GMAW),

the weld area isshielded by anexternal source,

such as argon,helium, carbondioxide, or variousother gas mixtures

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Ilustrasi Skematik proses pengelasan busurlogam-gas (gas metal-arc welding), dahulusering disebut dengan pengelasan MIG (metalinert gas).


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Peralatan dasar

yang digunakanpada operasigas metal- arc

The consumable bare wire is fed automaticallythrough a nozzle into the weld arc.

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.

Sumber:AmericanWelding Society.


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In spray transfer, small droplets of molten metal

from the electrode are transferred to the weld areaat rates of several hundred droplets per second.

The transfer is spatter-free and very stable.

High dc current and voltages and large diameterelectrodes are used, with argon or argon-rich gasmixtures used as the shielding gas.

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The average current required in this process can be

reduced by pulsed arcs, which are high-amplitudepulses superimposed over a low, steady current,and the process can be used in all welding

.

In globular transfer, CO2 rich gases are utilized, andglobules propelled by the forces of the electric arc

transfer the metal, resulting in considerable spatter.

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High welding currents are used, with greater weldpenetration and welding speed than in spraytransfer.

Heavier sections are commonly joined by this

method. In short circuiting, the metal is transferred in

individual droplets, at rates of more than 50 per

second, as the electrode tip touches the moltenweld metal and short circuits.

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FluxFlux--cored arc welding /FCAWcored arc welding /FCAW

The flux-cored arc welding (FCAW) process is similar togas metal-arc welding, with the exception that the

electrode is tubular in shape and is filled with flux (hencethe term flux cored).

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Iustrasi skematikproses pengelasanbusur - dengan intiflux (flux-cored arc-welding). Operasi

ini mirip dengan gasmetal-arc welding.


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Cored electrodes produce a more stable arc,improve weld contour, and improve the mechanicalproperties of the weld metal.

The flux in these electrodes is much more flexible

than the brittle coating used on SMAW electrodes. Thus the tubular electrode can be provided in long

coiled lengths.

The electrodes are usually 0.5-4 mm (0.020-0.15in.) in diameter.

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The power required is about 20 kW.

Self-shielded cored electrodes are also available. These electrodes do not require external gas

shield the weld area against the surroundingatmosphere.

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Small-diameter electrodes have made welding ofthinner materials not only possible but often

desirable.

Also, small-diameter electrodes make it relativelyy w u , ux

chemistry enables welding of many base metals.

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ElectrogasElectrogas welding /EGWwelding /EGW

Electrogas welding(EGW) is used primarilyfor welding the edges of

sections vertically inone pass with thepieces placed edge to

.

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Ilustrasi skematik proses pengelasan electrogas.Sumber:American Welding Society.

It is classified as amachine welding

process because itrequires specialequipment


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The weld metal is deposited into a weld cavitybetween the two pieces to be joined.

The space is enclosed by two water-cooled copperdams (shoes) to prevent the molten slag from

running off. Mechanical drives move the shoes upward.

Circumferential welds such as on pipes are also

possible, with the workpiece rotating.

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Single or multiple electrodes are fed through aconduit and a continuous arc is maintained, usingflux-cored electrodes at up to 750 A, or solidelectrodes at 400 A.

Power requirements are about 20 kW. Shielding is by inert gas, such as CO2, Ar, or He,

depending on the type of material being welded.

The gas may be provided from an external source,or it may be produced from a flux-cored electrode,or both.

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ElectroslagElectroslag welding /ESWwelding /ESW

Developed in the1950s,

electroslagwelding (ESW)and its

applications aresimilar toelectrogaswelding.

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Peralatan yang digunakan untuk operasi pengelasanelectroslag. Sumber: American Welding Society.


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The main difference is that the arc is startedbetween the electrode tip and the bottom of the

part to be welded. Flux is added and melted by the heat of the arc.

electrode, the arc is extinguished.

Energy is supplied continuously through the

electrical resistance of the molten slag.

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Thus because the arc is extinguished, ESW is notstrictly an arc welding process.

Single or multiple solid as well as flux-coredelectrodes may be used.

The guide may be non-consumable (conventionalmethod) or consumable.

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ARCARC--WELDING PROCESSES:WELDING PROCESSES:NONCONSUMABLENONCONSUMABLE ELECTRODEELECTRODE

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Gas tungstenGas tungsten--arc welding /GTAWarc welding /GTAW

In gas tungsten-arcwelding (GTAW),the filler metal issupplied from a

.

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Proses pengelasan busur - gas tungsten, dahulu dikenalsebagai pengelasan TIG (tungsten inert gas).


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Because the tungsten electrode is not consumed inthis operation, a constant and stable arc gap ismaintained at a constant current level.

The filler metals are similar to the metals to be

welded, and flux is not used. The shielding gas is usually Ar or He, or a mixture of

the two.

Welding with GTAW may be done without fillermetals, as in welding close-fit joints.

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The power supply is either dc at 200 A, or ac at500 A, depending on the metals to be welded.

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Perlengkapan untuk operasi pengelasan busur - gas tungsten. Sumber: American WeldingSociety.


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In general, ac is preferred for aluminum andmagnesium because the cleaning action of ac

removes oxides and improves weld quality.

Thorium or zirconium may be used in the tungsten

characteristics.

Power requirements range from 8 kW to 20 kW.

Contamination of the tungsten electrode by themolten metal can be a significant problem,particularly in critical applications, as it can cause

discontinuities in the weld.37


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Thus contact of the electrode with the molten metalpool should be avoided.

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Atomic hydrogen welding /AHWAtomic hydrogen welding /AHW

Atomic hydrogen welding (AHW) uses an arc in ashielding atmosphere of hydrogen.

The arc is between two tungsten or carbonelectrodes.

Thus the workpiece is not part of the electricalcircuit, as it is in GTAW.

The hydrogen gas also cools the electrodes.

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Atomic Hydrogen Welding TorchAtomic Hydrogen Welding Torch

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Sumber: http://www.gbwelding.com/data/welding_processes/ahw.htm


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Atomic hydrogen weldingAtomic hydrogen welding

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Sumber: http://www.gbwelding.com/data/welding_processes/ahw.htm


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PlasmaPlasma--arc welding /PAWarc welding /PAW

In plasma-arc welding (PAW), developed in the1960s, a concentrated plasma arc is produced andaimed at the weld area.

The arc is stable and reaches temperatures as high

as 33,000

C (60,000

F). A plasma is ionized hot gas, composed of nearly

equal numbers of electrons and ions.

The plasma is initiated between the tungstenelectrode and the orifice, using a low-current pilotarc.

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Unlike other processes, the plasma arc isconcentrated because it is forced through arelatively small orifice.

Operating currents are usually below 100 A, but

they can be higher for special applications. When a filler metal is used, it is fed into the arc, as

in GTAW.

Arc and weld-zone shielding is supplied through anouter shielding ring by gases such as Ar, He, ormixtures.

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ll ldi /ldi /


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There are two methods of plasma-arc welding.

In the transferred-arc method (Figure a), the

{ Transferred-arc method

{ Nontransferred method

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circuit. The arc thus transfers from the electrode to the

workpiece-hence the term transferred.

PlPl A W ldi /PAWA W ldi /PAW


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PlasmaPlasma--Arc Welding /PAWArc Welding /PAW

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Dua jenis proses pengelasan busur plasma: (a) transferred,(b) nontransferred. Lasan yang dalam dan sempit dapatdilakukan dengan proses ini, dengan kecepatan pengelasanyang tinggi.

PlPl ldi /PAWldi /PAW


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In the nontransferred method (Figure b), the arc isbetween the electrode and the nozzle, and the heatis carried to the workpiece by the plasma gas.

The thermal transfer mechanism is similar to that for

oxyfuel flame.

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THERMITTHERMIT WELDINGWELDING

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Th itTh it ldildi


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ThermitThermit weldingwelding

Thermit welding (TW) gets its name from thermite,which is based on the word therm meaning heat; the

word Thermit is a registered trademark.

The process involves exothermic (heat producing)reactions between metal oxides and metallicreducing agents.

The heat of the reaction is then utilized in welding.

This process dates back to the early 1900s.

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The most common mixture of materials used inwelding steel and cast iron is finely divided

particles of iron oxide (Fe3O4), aluminum oxide(Al203), iron, and aluminum.

Th i r i n r :

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Fe3O4 + 2Al 94Fe + Al2O3 + heat3 FeO + 2Al 3 Fe + Al2O3 + heatFe

3O

4+ 2Al 2 Fe + Al

2O

3+ heat



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This nonexplosive mixture produces a maximumtheoretical temperature of 3200 C (5800 F) within

less than a minute.

In practice, however, this temperature is only about2200-2400 C (4000-4350 F).

The mixture may also contain other materials toimpart special properties to the weld.

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The reaction is started by applying a magnesiumfuse to special compounds of peroxides,chlorates, or chromates, known as oxidizingagents, with an ignition temperature of about1200 C (2200 F).

Welding copper, brasses, and bronzes, andcopper alloys to steels, involves the followingreactions:

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3CuO + 2Al 3Cu + Al2O3 + heat3Cu2O + 2Al 6Cu + Al2O3 + heat



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Oxides of copper, nickel, chromium, andmanganese are also used in Thermit welding,

resulting in temperatures ranging up to 5000 C(9000 F).

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ELECTRONELECTRON--BEAM WELDINGBEAM WELDING

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ElectronElectron--Beam Welding /EBWBeam Welding /EBW


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In electron-beam welding (EBW), heat is generatedby high-velocity narrow-beam electrons.

The kinetic energy of the electrons is converted intoheat as they strike the workpiece.

This process requires special equipment to focusthe beam on the workpiece in a vacuum.

The higher the vacuum, the more the beam

penetrates and the greater the depth-to-width ratiois.

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Almost any metal can be welded by EBW, withworkpiece thicknesses ranging from foil to plate.

The intense energy is also capable of producingholes in the workpiece.

enera y, no s e ng gas, ux, or er meta srequired. Capacities of electron beam guns range to100 kW.

Developed in the 1960s, EBW has the capability tomake high-quality welds that are almost parallelsided, are deep and narrow, and have small HAZ(heat-affected zones).

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LASERLASER--BEAM WELDINGBEAM WELDING

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LaserLaser--Beam Welding /LBWBeam Welding /LBW


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LaserLaser Beam Welding /LBWBeam Welding /LBW

Laser-beam welding (LBW) utilizes a high-powerlaser beam as the source of heat to produce a

fusion weld.

Because the beam can be focused to a very smallarea, it has high-energy density and, therefore, hasdeep penetrating capability.

The beam can be directed, shaped, and focused

precisely on the workpiece.

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LaserLaser--Beam Welding /LBWBeam Welding /LBW


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LaserLaser Beam Welding /LBWBeam Welding /LBW

Consequently, this process is particularly suitablefor welding deep and narrow joints, with depth-to-

width ratios typically ranging from 4 to 10.

The laser beam may be pulsed (milliseconds) forapplications such as spot welding of thin materials,with power levels up to 100 kW.

Continuous multi-kW laser systems are used for

deep welds on thick sections.

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ContohContoh PengelasanPengelasan dengandengan LaserLaser


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gg gg

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Pengelasan Laserpada pisau cukur.


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bab 27b pengelasan fusi

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