305_recomendaciones para el diseÑo de maquinas_ing.pdf

7/27/2019 305_RECOMENDACIONES PARA EL DISEO DE MAQUINAS_ING.pdf

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Conveyor and processing belts

Recommendationsfor machine design

Content

1

Definitions and description 2

Drums 3

Take-up devices 5

Belt support 6

Knife edges 9

Belt tracking 10

Cleaning devices 19

Conveyor and power transmission beltsmade of modern synthetics

Worldwide leaders in technology, quality and service

Further information on machine designcan be found in our brochure no. 304Calculation methods conveyor belts.


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2

Definitions and description

With long conveyor lines and a large totalload, support rollers are often used insteadof skid plates to reduce the effective pull.

The non-driven end drum should beinstalled such that its position can be ad-

justed, enabling it to take on the functionof the tension take-up drum.

With centre distances of < 2000 mmsupport rollers should also be installed onthe return side, thereby avoiding excessivebelt sag caused by the weight of the beltitself.

In a standard conveyor in the lightmaterials handling sector, the belt runsover two end drums or terminals.

In the preferred configuration, calleda head drive, the drive drum is at the dis-charge end of the conveyor. The forcesoperating in such a configuration areutilized better than with a tail drive design(see Calculation Methods).

If the centre distance cannot be adjusted orcan only be adjusted minimally, e.g. in theevent of consecutive conveyors, tensioningunits are located on the return side.

Conveyors with troughed belts are alsoused for bulk goods conveying in the lightmaterials handling sector. In this case,two- or three-section support roller setsare installed on the upper side.

Alternatively, a skid plate of troughedconstruction can be used.


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3

Drums

Drum diameter

Drive drum

Drum diameters should always be as largeas possible. The minimum admissiblediameter is determined by

the effective pull to be transmitted(see method for calculating drivedrum diameter).

Particularly with wide conveyors, drumswith too small a diameter are subject toinadmissibly large deflection, resulting inunwanted belt creasing and mistracking.

Drum deflection should be calculated(page 17) as a counter-check.

It is recommended that the drive drumhave a cylindrical centre section withtapered edges, with the length of thecylindrical section being b/2.

For further advice on this see page 11.

Where belt width is considerably less thanthe drum length, it is the belt width whichdetermines the proportions of the drivedrum.

Guideline figures for conicity h [mm] Drum diameter [mm]bis 200 > 200 bis 500 > 500

I 1-ply belts 0.5 0.8 1.0II 2-ply belts 0.7 1.3 1.5

NOVO, E10/M, E15/M, E20/MIII 3-ply belts 1.0 1.6 2.0

The crown height figures quoted in IIand III are maximum values which shouldbe reduced in exceptional cases to matchthose quoted in I if lateral forces occurwhich the belt is no longer able to with-stand and which thus result in longitudinalcreasing.

This also applies in the case of centre

drives or for wide belts where the spacingsbetween the drive and end drums is tooshort to permit the belt tension to beequalized.

The drive drum may be cylindrical iftracking devices are installed.

the flexural properties of the belt typeused (see under dmin in product range)

the flexural properties of the lateral andlongitudinal profiles welded onto thebelt (see Belt Preparation and Finishingbrochure)


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4

Lagged surface

Bare surfaceThe faces of all drums should have asmooth finish. Any pronounced groovescaused by machining have an undesirableeffect on belt tracking.

Roughness RZ 25 (DIN 4768)

(Peak-to-valley height 25 m)

To improve the coefficient of friction of 0,

U0, A0, E0, V1, U1, UH undersides, drivedrums are frequently lagged. The laggingshould consist of an abrasion-resistantmaterial, e.g. polyurethane or rubber witha Shore (A) of 85.

Another method which can be carriedout on site is to wrap a friction laggingmaterial, e.g. Transilon with a U2 coating,spirally around the drum.


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5

Screw-operated take-up

Load-dependent tension take-up

Take-up devices

The contact pressure of the belt on the

drive drum required to transmit theeffective pull is produced by elongating thebelt with a tension take-up.

The end drum can serve as a tensioningdrum if it is installed such that it can bemoved by screw tension take-ups whileremaining parallel to the drive drum.

Such a conveyor configuration is oftenused in conjunction with Transilon whichis virtually free of any permanentelongation (therefore requiring only ashort tension take-up range) anddimensionally stable (therefore needing no

re-tensioning).

A fixed tension take-up, however, does notpermit any length compensation forvariations in elongation during start-up orwith fluctuating loads or temperatures.

On very long, heavily loaded conveyors,this tensioning unit must be located closeto the drive drum in order to compensateimmediately for elongations in the upperstrand during start-up.

Tensioning with a load-dependent systemcan be achieved, for example, with a gravitytake-up consisting of a weight suspendedfrom a cord.

Alternatively, pneumatic or spring-loadedtension take-ups can be used.

Load-dependent take-ups arerecommended for conveyors operating inhigh, fluctuating temperatures.

A load-dependent take-up is not suitablefor a reversible drive.


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6

Skid plate

Support roller design

It is important that skid plates be thor-oughly cleaned before the conveyor iscommissioned since remnants of pro-tective lacquer coatings or other types ofcontamination can cause considerabledifficulties (e.g. tracking problems, beltdamage, increase in underside coefficientof friction).

Slatted supports should be avoided ifpossible as a means of belt support sincethey often unnecessarily increase operatingnoise and wear and tear on the belt.

Support rollers are required to havelow rotational resistance and balancedrunning. For this reason, support rollersusing roller bearings with low seal frictionare almost exclusively used. In order to

maintain a low centrifugal momentum,their walls are usually made of precisionsteel tubing or steam tubing (see DIN2448).

Skid plates should be set approx. 23 mmlower than the belt and must be alignedprecisely since they have a profound effecton belt tracking as a result of slidingfriction. Their edges should be chamfered.

Materials such as sheet steel, hard plasticslaminates (Resopal, Duropal etc.) andlaminated wood panels are generally usedfor skid plates. In conjunction with thelow-friction undersides of Transilon belts,these materials ensure favourable frictionalproperties, though these can be affected bysurface finishes and operating conditions.

Tubular plastic support rollers are alsoused (because of their corrosion resistanceand low degree of soiling. N.B. Electro-static build-up is possible).

Support roller pitch is determined by the

unit length of the conveyed goods. If thesupport roller pitch is 1/2 unit length, theweight of goods will always be borne by 2rollers.

Belt support


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7

Support roller configuration

Form N 2-piece

Form N: 2-piece offset

10 mm

10 mm

Support roller configurations and dimen-sions are specified in DIN 22107/ISO 1537.Form M (as designated by DIN) is usedto support the tight and return sidesof a flat running belt and the return sideof a troughed conveyor. The tight sideof a troughed belt is supported by form Nor P support rollers.

Form P: 3-piece offset

Form M support roller2-piece forms should be offset and shouldoverlap by approx. 10 mm.

With 2-piece forms where there is nooverlap, the gap between the supportrollers should be kept as small as possibleso as to prevent creasing and wrinkling.

Form P: 3-piece, troughing angle 20 - 40

Support roller pitch for bulk goods

Support roller pitch is determined by theunit length of the conveyed goods. If the

support roller pitch is 1/2 unit length, theweight of the goods will always be borne by2 rollers.lo = upper support roller pitch in mm

lu = lower support roller pitch in mmyB = max. belt sag in mmF = effective pull at appropriate

point in N

Support roller pitch is also a function ofthe belts effective pull and the combinedmasses of belt and goods. It is calculatedaccording to the following equation:

yB . 800 . Flo =

__________ [mm]m'o + m'B

If a max. belt sag of 1% is permitted,i.e. if yB = 0,01 lo, then

Recommendation lo max 2b0

lu 2 3 lo max

8 . Flo =

________ [mm]m'o + m'B

F = % . SD . bo [N]

m'o + m'B = weight of conveyed goodsplus belt in kg/m

SD = SD value in N/mm widthbo = Belt width in mm% = Elongation at fitting


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8

Transition lengths

Snub rollers

Minimum diameterwith small arcs of contact

Is = belt width b0 c7 constant [mm]

Snub rollers are used if:

the arc of contact between the belt andthe drive drum must be increased.

the distance between the upper andreturn sides must be small for design orconstructional reasons.

If belts with a textured surface are in use,

we recommend lagging snub rollers toreduce noise.

If the arc of contact of snub, support orguide rollers is small and does not exceed15, the diameter of these rollers may beequal to 1/2 dmin (for dmin see productrange).

The upper edges of the end drum and ofthe central troughing rollers must lie in thesame plane.

In the transition area of the troughed beltfrom the drum to the belt support roller

set (and vice versa) the edges are subjectedto increased elongation.

The following nominal values for thetransition length Is should therefore beobserved:

Note:To ensure proper belt tracking it is

recommended that the end drum be oftapered/cylindrical design.

Troughing angle 15 20 30 40

c7 0,7 0,9 1,5 2


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9

Fixed knife edges

Rolling knife edges

If the knife edge belt only operates in onedirection, a gravity take-up can be installedafter the drive drum instead of the usualscrew tension take-up to ensure correctbelt tension. This movable tension rollerreduces belt tension at the knife edge andcan considerably reduce the frictional forceat the knife edge by comparison with thefixed screw tensioning system.

Energy consumption by the belt rises whenit runs over knife edges. At the same time,belts running at high speed can be sub-

jected to a substantial temperature increasebecause of friction in the knife-edge zone.

For this reason, the arc of contact shouldbe kept to a minimum (to reduce energyconsumption, heat build-up and initialtension).

Rolling knife edges, which substantiallyreduce the frictional force at the knifeedge, are finding increasing acceptance.Knife edge radii of r = 4 10 mm arecommonly used.

Knife edges


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10

Fundamentals of conveyor belt tracking

The conveyor should be as rigid as possible.It must not be distorted by the forcesexerted by the belt.

All drums and rollers, especially the drivedrum, must be clean. Removeanticorrosion coatings, oil and dirt depositsfrom skid plates, drums and rollers.Replace damaged or heavily worn parts.

Align knife edges, drive and end drums,and support rollers such that they areparallel.

To do this, first align the end drums such

that they are parallel to each other and atright angles to the conveyor frame byadjusting the drums until each centredistance 1 and each diagonal 2 are equal.

Drums whose axes are not at right angles tothe running direction of the belt will causemistracking.

Another method is first to align the drivedrum using a set square and then to adjustthe end drum until the centre distances 1are equal.

It is then possible, starting from one of theend drums, to align each support roller orskid plate section individually such that theaxes are parallel.

Goods should always be loaded onto thecentre of the belt in the direction of travel.Large drops should be avoided if at allpossible.

Attention should be paid to the surfacequality of the drums.

Straight running due to right-angledalignment of drum.

< 90 90

Belt tracking


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11

Effect of conicity and belt width

Effect of temperature

The drive drum is tapered/cylindrical.

A conveyor belt is tracked to the centre ofthe conveyor by a tapered/cylindricaldrum.

The higher the belt speed and the larger thedrum diameter, the greater the centeringeffect.

Recommendations on conicity can befound on page 4.

Excessive conicity.

Belt does not hug drum, thus losingtracking effect.

Belt is too narrow.

Solution: Match drum proportions to beltwidth.

Belt wider than drum.

To be avoided at all costs because of non-uniform tracking effects, particularly withlaterally flexible belt types.

If a tracked belt is exposed to a

considerable degree of asymmetricalheating and loading, this can lead to a non-uniform change in its inner tension state.

The result of this are tracking forces whichmay cause the belt to run off to the side.An automatic belt tracking device isrecommended.


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Effect of support rollers

Effect of negatively troughed roller sets

The tracking of troughed belts can be

controlled by angling the side rollers ofsome sets in the direction of belt travel byup to approx. 3, depending on the beltspeed.

Non-troughed belts can often be trackedsufficiently by installing some supportrollers whose position can be adjustedhorizontally and then pivoting themthrough approx. 2 4.This system is recommended for long belts.w


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13

A

End drum

B

Drive drum

Tapered/cylindrical drive drums should beadjustable in order to be able tocompensate for production tolerances inthe conveyor and belt.

With conveyor lengths of 5 m bothterminals should be tapered/cylindrical.

Initial tracking

Fit the belt and tension drums A + Bsuch that their axes are parallel untilthe required working elongation atfitting is attained.

Belt tracking can be adjusted bytensioning or slackening one end ofthe tensioning drum A. The belt willmove towards the slacker belt edge.

It may be necessary to install a belt

guidance system near the end drum(e.g. with short, wide belts).

Initial tracking

Locate all drums/rollers in theirinitial positions such that their axesare parallel.

Fit the belt and adjust the tensioningdrum B, ensuring that it remainsparallel to the other drums, until therequired working elongation atfitting is attained.

Adjust belt tracking using roller C orD, as appropriate. It may benecessary to install a belt guidancesystem using roller C or D as thetracking roller.

If tapered/cylindrical drums do notprovide sufficient belt tracking, angledrollers or automatic tracking devices canbe used.

Belt trackingwith tapered/cylindrical drums

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The greatest tracking effect is alwaysprovided by the snub roller contacted bythe belt immediately prior to the enddrum, i.e. by snub roller D when the belt isrunning in direction 1, and by roller C indirection 2.

The tracking effect is particularly markedwhen snub rollers C, D are used, especiallyif they are in contact with a coated belt face(giving a high friction coefficient).

The snub rollers should be adjustablealong the XY axis (see right - linking thepoints of contact and release).

In this way, there is scarcely any effect on

the belt edges, and major distortion of thefabric can be avoided.

Use of snub rollers


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The snub roller G and F and the tensioningdrum E are adjustable in the direction ofthe arrow. The tensioning drum can alsooperate as the drive drum.

One simple design solution is for drums G,F and E to be mounted on a plate H as asingle unit which is then adjustable in thedirection of the arrow.

Please refer to the previous and followingpages for details of the configuration,finish and tracking properties of drums A,B, C and D.

Initial tracking


Fit the belt and adjust the tensioningdrum E, ensuring that it remainsparallel to the other drums, until therequired working elongation atfitting is attained.

Adjust belt tracking using snub roller

C, and correct if necessary usingdeflection rollers G and F or plate H.It may be necessary to install a beltguidance system here too.

Tension take-up on return side

Initial tracking


Fit the belt and adjust the tensioningdrum B, ensuring that it remainsparallel to the other drums, until therequired working elongation atfitting is attained.

With reversible conveyors belttracking should be adjusted at thetapered/cylindrical terminals, not atthe snub rollers.

Reversible conveyors

It takes some time until the snub rollers arecorrectly adjusted. A belt guidance systemis recommended for very short and wideconveyors.

The important factor with conveyorswhich can reverse their direction of travelis the precision with which the conveyorand the belt have been manufactured.

Initial tracking of belts for reversibleconveyors is not entirely straightforward.Once belt tracking has been achieved inone direction, it is often found that the beltmistracks when the direction is reversed.

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Initial tracking

Locate all drums/rollers and theknife edge in their initial positionssuch that their axes are parallel.

Fit the belt and adjust the tensioningdrum C, until the required workingelongation at fitting is attained.Ensure that the operating tension isas low as possible in order to avoidunnecessarily high mechanical andthermal (as a result of friction)

loading on the knife edge.

Adjust belt tracking using rollers B,C, D and E and/or plate H. A belttracking system may beadvantageous.

Knifeedge conveyors

Belt edge sensors

Relatively short knife edge belts can betracked as shown above. The drive drum Ashould be tapered/cylindrical, whiledeflection drums B, D and E and thetensioning drum C should be cylindricaland adjustable in the direction of the arrowfor tracking purposes.

Automatic belt guidance systems aregenerally used with lengthy knife edgeconveyors (e.g. cooling tunnels).

Belt tracking ist registered by belt edgesensors.

Drums C, D and E can be mounted on anadjustable plate H, as also described onpage 14.

There are different kinds of belt edgesensor, e.g. mechanical, hydraulic,electrical, optical and pneumatic. They areactivated by deviations in the position ofthe belts edges.

Pneumatic device Photoelectric cell Mechanical sensor Electric eye


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End drum groove with1 central wedge-shaped profile

Transverse forces can be counteracted bylongitudinal profiles welded to the belt.

However, these transverse forces can onlybe absorbed in the area of the skid plate orsupport rollers.

The belt must not be subjected to trans-verse forces as it runs around the enddrums. The grooves for the longitudinalprofiles must be at least 8 10 mm widerthan the profile.

This large clearance enables the belt to betracked without it immediately running offlaterally.

Please refer to Product Preparation andFinishing brochure for details of minimumbelt lengths and information on profiledimensions, designs and minimum drumdiameters.

All means of forced guidance, such ascheck strips, rollers etc., which can damagebelt edges should be avoided.

An automatic guidance system should beused in the event of large transverse forces.

The two halves of the skid plate shouldonly be fixed in position or the guide stripsattached once the belt is running satis-factorily. A minimum clearance must beretained to allow for tolerances.

Increase the groove depth h if the system isexposed to a high degree of soiling.

If 2 longitudinal profiles are used, a suffi-ciently large value must be allowed for thedimension z.

Use of belts with longitudinal profiles

2 wedge-shaped rofiles along

belt edges z = approx. 5 10 mm

2 flat profiles along belt edges

z = approx. 5 10 mm

Plastic idler roller

Chamfer groove edgesin support rollers

1 central longitudinal profile for skidplate or support roller grooves

Plastic idler roller


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Solid drum

80 FR . I3

yTr=____________ [mm]

E . d4 . . 96

Tubular drum

80 . FR . I3yTr=

_________________ [mm]E (da

4 di4) . . 96

FR = (2 . 0.3 . 12 . 2500)2 + (9.81 . 27)2

= 18002 N

80 . 18002 . 26003

yTr = _________________________96 . 2.1 . 105 . (1504 - 1304) .

yTr1,81 > 0,35 mm = fzul

Reinforced by central brace

80 . 9001 . 13003yTr =

_________________________

96 . 2.1 . 105 . (1504 - 1304) .

yTr = 0.23 mm < 0.35 mm


17

Deflection of drums and rollers

Example

FR Active force [N](line load), resultingfrom belt pull anddead weight of drums.

FR = (2. . SD . bo)2 + (9.81 . mTr)2

I Bearing centre distance [mm]

d, da, di Drum diameters [mm]

yTr Drum deflection [mm]

mTr Drum weight [kg]

Excessive drum deflection is a frequent

cause of problems in tracking wide belts.

Reasons for deflection:

belt pull increasing in direct proportionto belt width

drum diameters are small due totechnical requirements

Please ensure that the following values arenot exceeded:

Tapered/cylindrical drums DeflectionyTr 0,5 h

With cylindrical drums

this value can be doubled

See Drive drum sectionfor h values

d

dida

A 2500 mm wide Transilon belt, type E 12/2U0/UH, runs around a steel drum of 108 mm and 4 mm wall thickness with an arc ofcontact of 180. The belt runs horizontally.

I = 2600 mmda = 150 mmdi = 130 mmSD value = 12

E 12/2 approx. 0.2 bis 0.3 % tensionedDrum weight = 27 kgE = Modulus of elasticity N/mm2

E for steel = 2.1 105 N/mm2


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Unit goods are frequently removed ordiverted laterally from the belt. In this case,too, care should be taken to ensure that thelateral forces acting on the belt are kept toa minimum. Hinged ploughs which do nottouch the belt are commonly used. Theirdesign is usually determined by the goodsconveyed.

With belt wrap configurations a higherpower input arises due to counter bendingand at low temperatures. Belt tracking canbe stabilized further by installing atapered/cylindrical drum a.

The following are recommended to

prevent impairment of the belt trackingwhen goods are loaded onto or dischargedfrom the belt:

lag the support rollers in the feed zonewith a friction lagging which willincrease the coefficient of frictionbetween the support rollers and the belt(see above)

increase the areas of belt wrap in thefeed zone by design measures as shownbelow.

Support rollers with abrasion-resistantadhesive lagging

It is the designers responsibility to providesystems which enable the product to be fedonto the belt in its direction of travel withnegligible impact and at a similar (or,ideally, the same) speed. Feed should occurcentrally to prevent the belt frommistracking. (Such systems can comprisechutes, guide plates, feed hoppers, funnelsetc.).

Hopper walls or guide strips should openin the direction of belt travel to prevent theconveyed goods clogging between thesideskirt (strip) and belt. They should onlybe as flush with the belt as is necessary forthe particular material conveyed. Sideskirtsresting on the belt lead to an increase ineffective pull. This increase should betaken into account when the belt type isselected.

Fit sideskirts at right angles to the belt

During loading operations, the conveyorbelt is subjected to both vertical (i.e. formthe impact) and tangential mechanicalstresses because of the relative speedbetween the belt and the goods carried.

Product discharge

Product feed

Sideskirts


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Scrapers

Brushes

Cleaning devices

b c

Steel scrapers (c) can be used to keepunlagged drums clean. These scrapers canbe mounted flush with the drum surface,matching the shape of the drum (e.g.trapezoidal).

When cleaning devices are used, allowancesmust be made in drive power calculations:

FA = contact force

FUR = peripheral forceof cleaning device

PR = Power requirementsfor cleaning device

FUR = FA.

FUR . VPR =

________

1000

Rotating brushes or belt cleaning systemsmay also be used for cleaning belts. If theconveyed goods are very sticky, a waterspray or a water immersion system mustbe provided to ensure that the brushes donot clog up.

Please note:

Lateral tracking forces are invoked ifcleaning devices are incorrectly fitted.

b c a

There are a number of methods ofremoving material which has stuck to aconveyor belt. The effectiveness of suchmethods, however, depends very largely onthe particular circumstances.

In many instances, one or more scraperswith plastic or rubber blades mounted in aframe made of flat or profile-section steelset at right angles to the direction of belttravel will suffice. The right blade material(not from an old conveyor belt, since thisunnecessarily increases belt wear) shouldbe carefully selected.

The belt scraper (a) should be placed asclose as possible to the belt or touch itlightly. Since the blade is subject to wear,an adjustment method (e.g. by means ofslots) must be provided.

Plough-type scrapers (b) are frequentlyinstalled close to the end drum on thereturn side to prevent any material whichhas dropped off the belt getting betweenthe drum and the belt. There should onlybe light contact with the belt.


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305

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Worldwide Siegling Service

The Siegling Group employs morethan 1600 people worldwide. Sieglingproduction facilities are located in eightcountries.Siegling has companies and agencieswith stock and workshops in more than50 countries. Siegling service centresprovide qualified assistance at morethan 300 locations throughout the world.

A member of the Forbo Group.

Because our products are used in so manyapplications and because of the individual factorsinvolved, our operating instructions, details andinformation on the suitability and use of the productsare only general guidelines and do not absolve theordering party from carrying out checks and teststhemselves. When we provide technical support onthe application, the ordering party bears the risk ofthe machinery functioning properly.

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