8/9/2019 Scrapers lectures
1/34
• A. J. Clark School of Engineering •Department of Civil and Environmental Engineering
Sixth EditionCHAPTER
7
Construction Planning, Equipment,and Methods
S R PERS R PERS
ByByDr. Ibrahim Assakkaf Dr. Ibrahim Assakkaf
ENCEENCE 420420 – – Construction Equipment and MethodsConstruction Equipment and Methods
Spring 2003Spring 2003Department of Civil and Environmental EngineeringDepartment of Civil and Environmental Engineering
University of Maryland, College ParkUniversity of Maryland, College Park
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 1
TRACTORSTRACTORS --PULLEDPULLEDSCRAPERSSCRAPERS
Tractor Tractor --pulled scrapers arepulled scrapers aredesigned to load, haul, anddesigned to load, haul, and
dump loose materials.dump loose materials.The advantage of tractor The advantage of tractor --scraper combinations is theirscraper combinations is theirversatility.versatility.
8/9/2019 Scrapers lectures
2/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 2
SCRAPERSSCRAPERS
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 3
Dozer : short haul, less than 300ft
Scraper : medium haul up to 3,000 ft
APPLICATIONSAPPLICATIONS
8/9/2019 Scrapers lectures
3/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 4
TRACTORSTRACTORS --PULLEDPULLEDSCRAPERSSCRAPERS
They can be used in a wide rangeThey can be used in a wide rangeof material types (including shotof material types (including shotrock) and are economical over arock) and are economical over awide range of haul lengths and haulwide range of haul lengths and haulconditions.conditions.To the extent that they can self To the extent that they can self --load, they are not dependent onload, they are not dependent onother equipment.other equipment.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 5
TRACTORSTRACTORS --PULLEDPULLEDSCRAPERSSCRAPERS
If one machine in the spreadIf one machine in the spreadexperience a temporary breakdownexperience a temporary breakdownit will not shut down the job, asit will not shut down the job, aswould be the case for a machinewould be the case for a machinewhich is used exclusively forwhich is used exclusively forloading. If the loader breaks down,loading. If the loader breaks down,the entire job must stop until repairsthe entire job must stop until repairscan be made.can be made.
8/9/2019 Scrapers lectures
4/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 6
TRACTORSTRACTORS --PULLEDPULLEDSCRAPERSSCRAPERS
Scrapers are available with looseScrapers are available with loose --heaped capacities up to about 44 cu yd,heaped capacities up to about 44 cu yd,although in the past a few machines asalthough in the past a few machines aslarge as 100 cu yd have been offered.large as 100 cu yd have been offered.For off For off --highway situations having haulshighway situations having haulsof less than a mile, scrapers ability bothof less than a mile, scrapers ability bothto load and haul gives them anto load and haul gives them anadvantage.advantage.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 7
TYPES OF SCRAPERSTYPES OF SCRAPERS
There are several types ofThere are several types ofscrapers, primarily classifiedscrapers, primarily classifiedaccording to the number ofaccording to the number of
powered axles or by the method ofpowered axles or by the method ofloading.loading.Scrapers are all wheelScrapers are all wheel --tractor tractor --pulled machines.pulled machines.
8/9/2019 Scrapers lectures
5/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 8
TYPES OF SCRAPERSTYPES OF SCRAPERS
Available types include:Available types include:Push-loaded (conventional)
Single-powered axleTandem-powered axles
Self-loadingPush-pull, tandem-powered axlesElevating
Auger
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 9
CONFIGURATIONSCONFIGURATIONSConventional (push-loaded)
Single engine
8/9/2019 Scrapers lectures
6/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 10
TYPES OF SCRAPERSTYPES OF SCRAPERS
Many models can achieve speeds up to 30Many models can achieve speeds up to 30mph when fully loaded. This extends themph when fully loaded. This extends theeconomic haul distance of the units.economic haul distance of the units.PushPush --loaded scrapers are at aloaded scrapers are at adisadvantage when it comes to individuallydisadvantage when it comes to individuallyproviding the highproviding the high tractivetractive effort requiredeffort requiredfor economical loading. For the singlefor economical loading. For the single --powered axle scraper only a portion, onpowered axle scraper only a portion, onthe order of 50the order of 50 --55% of the total loaded55% of the total loaded
weight, bears on the drive wheels.weight, bears on the drive wheels.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 11
TYPES OF SCRAPERSTYPES OF SCRAPERS
Conventional (push-loaded)single engine scrapers become
uneconomical when:
Haul grades > 5%
Return grades > 12%
8/9/2019 Scrapers lectures
7/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 12
CONFIGUR TIONS
Elevating
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 13
CONFIGUR TIONS
Elevating scrapers aregood for short haulsand in favorablematerial.
• Can work alone in the cut.• Cost more initially & to operate• Elevator adds weight & takes power.
8/9/2019 Scrapers lectures
8/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 14
CONFIGUR TIONS
Tandem poweredtwin engine
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 15
TYPES OF SCRAPERSTYPES OF SCRAPERS
Tandem powered ( twinengine ) scrapers are goodfor jobs having adversegrades and poor footing.
Owning and operating costare about 25% higher.
8/9/2019 Scrapers lectures
9/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 16
CONFIGUR TIONS
Push-Pull
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 17
TYPES OF SCRAPERSTYPES OF SCRAPERS
Push-Pull scrapers can workas a team or can operateindividually with a pusher.
Tire wear will increase in rockor abrasive materials becauseof more slippage from thefour-wheel drive action.
8/9/2019 Scrapers lectures
10/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 18
Auger
CONFIGUR TIONS
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 19
CONFIGUR TIONS
Auger
8/9/2019 Scrapers lectures
11/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 20
TYPES OF SCRAPERSTYPES OF SCRAPERS
Auger scrapers can self-load indifficult conditions, laminatedrock or granular materials.The auger adds weight to thescraper during travel and it ismore costly to own and operatethan a conventional scraper.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 21
VOLUME OF A SCRAPER VOLUME OF A SCRAPER
The volumetric load of a scraperThe volumetric load of a scrapermay be specified as either themay be specified as either thestruck struck oror heaped heaped capacity of thecapacity of thebowl expressed in cubic yards.bowl expressed in cubic yards.TheThe struck capacity struck capacity is the volumeis the volumethat a scraper would hold if the topthat a scraper would hold if the topof the material were struck off evenof the material were struck off evenat the top of the bowl.at the top of the bowl.
8/9/2019 Scrapers lectures
12/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 22
BOWL BOWL
ejector
The load-carrying part of a scraper.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 23
VOLUME OF A SCRAPER VOLUME OF A SCRAPER
In specifying theIn specifying the heaped capacity heaped capacity of a scraper, manufacturers usuallyof a scraper, manufacturers usuallyspecify the slope of the materialspecify the slope of the materialabove the sides of the bowl with theabove the sides of the bowl with thedesignationdesignation SAESAE . The Society of. The Society of
Automotive Engineers ( Automotive Engineers ( SAESAE ))specifies a repose slope of 1:1 forspecifies a repose slope of 1:1 forscrapers.scrapers.
8/9/2019 Scrapers lectures
13/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 24
VOLUME OF A SCRAPER VOLUME OF A SCRAPER
TheThe SAESAE standard for other haul unitsstandard for other haul unitsand loader buckets is 2:1.and loader buckets is 2:1.
Actual repose slope will vary with the Actual repose slope will vary with thetype of material handled.type of material handled.The capacity of a scraper, expressed inThe capacity of a scraper, expressed incubic yards bank measure (cubic yards bank measure ( bcybcy ), can be), can beapproximated by multiplying the looseapproximated by multiplying the loosevolume in the scraper by an appropriatevolume in the scraper by an appropriate
swell factor.swell factor.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 25
VOLUME OF A SCRAPER VOLUME OF A SCRAPER
Because of the compacting effectBecause of the compacting effecton the material in a pushon the material in a push --loadedloadedscraper, resulting from the pressurescraper, resulting from the pressure
required to force additional materialrequired to force additional materialinto the bowl, the swell is usuallyinto the bowl, the swell is usuallyless than that for material droppedless than that for material droppedinto a truck by a hoe or loader.into a truck by a hoe or loader.
8/9/2019 Scrapers lectures
14/34
8/9/2019 Scrapers lectures
15/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 28
SWELL FACTORS FORSWELL FACTORS FORDIFFERENT TYPES OF SOILDIFFERENT TYPES OF SOIL
ExampleExampleIf a pushIf a push --loaded scraper hauls aloaded scraper hauls aheaped load measuring 22.5 cu yd andheaped load measuring 22.5 cu yd andthe swell factor from the previous tablethe swell factor from the previous table(Table 1) is 0.8, the calculated bank(Table 1) is 0.8, the calculated bankmeasure volume will bemeasure volume will be
22.5 cu yd x (0.8 x 1.1) = 19.822.5 cu yd x (0.8 x 1.1) = 19.8 bcybcyNote: 10% increase in for swell factor
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 29
SCRAPER OPERATIONSCRAPER OPERATION
A scraper is loaded A scraper is loaded by lowering the frontby lowering the frontend of the bowl until the cutting edge, whichend of the bowl until the cutting edge, whichis attached to and extends across the width ofis attached to and extends across the width ofthe bowl enters the ground. At the samethe bowl enters the ground. At the sametime, the front apron is raised to provide antime, the front apron is raised to provide anopen slot through which the earth can flowopen slot through which the earth can flowinto the bowl. As the scraper moves forward,into the bowl. As the scraper moves forward,a horizontal strip of material is forced into thea horizontal strip of material is forced into thebowl. This is continued until the bowl is filled,bowl. This is continued until the bowl is filled,at which point the cutting edge is raised andat which point the cutting edge is raised andthe apron is lowered to prevent spillagethe apron is lowered to prevent spillageduring the haul.during the haul.
8/9/2019 Scrapers lectures
16/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 30
SCRAPER OPERATIONSCRAPER OPERATION
The dumping operationThe dumping operation consistsconsistsof lowering the cutting edge to theof lowering the cutting edge to thedesired height above the fill, raisingdesired height above the fill, raisingthe apron, and then forcing thethe apron, and then forcing thematerial out by means of a movablematerial out by means of a movableejector mounted at the rear of theejector mounted at the rear of thebowl.bowl.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 31
CUTTING AND LOADING
For maximum production both single- and tandem-engine scrapers need the assistance of a push tractor.
8/9/2019 Scrapers lectures
17/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 32
CUTTING AND LOADING
Dirt enters horizontally and rolls back to fill corners.Curved ejector top keeps load “boiling” to heap high.
Ejector
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 33
H ULING ULING
Apron lowered to capture the material.Keeping the bowl low enhances stability.
8/9/2019 Scrapers lectures
18/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 34
SPREADING THE LOAD
Dumping and spreading is one continuous operation.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 35
SCRAPER SELECTIONSCRAPER SELECTION
Three main factors:Three main factors:Job size, volume of material to
move and maneuver room.Scraper configuration.Job conditions, grades, rollingresistance and material type.
8/9/2019 Scrapers lectures
19/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 36
SCRAPER SELECTIONSCRAPER SELECTION
COST:Cost must consider allhourly cost for theentire pusher-scraper
fleet.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 37ECONOMIC ZONES OF
PPLIC TION
HAUL DISTANCE
S E V E R I T
Y O F
C O N D I T I O N S
8/9/2019 Scrapers lectures
20/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 38
P E R F
O R M
A N C E
C H A R
T
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 39
CYCLE TIME FOR ACYCLE TIME FOR ASCRAPER SCRAPER
The cycle time for a scraper is thetime to load, haul, dump, turn,return, and turn back into positionto pick up another load:
T s = load t + haul t + dump t + turn t + return t + turn t (1)
8/9/2019 Scrapers lectures
21/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 40
WORK CYCLE
LOAD
DUMP
HAUL
RETURN
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 41
CYCLE TIME FOR ACYCLE TIME FOR ASCRAPER SCRAPER
Average load time for push Average load time for push --loaderloaderscrapers in common earth is 0.85scrapers in common earth is 0.85min.min.BothBoth haul haul andand returnreturn timestimesdepend on the distance traveleddepend on the distance traveledand the scraper speed.and the scraper speed.
8/9/2019 Scrapers lectures
22/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 42
CYCLE TIME FOR ACYCLE TIME FOR ASCRAPER SCRAPER
DumpDump times vary with scraper sizetimes vary with scraper sizebut project conditions will affect thebut project conditions will affect theduration. Average values for dumpduration. Average values for dumptime are presented in tables.time are presented in tables.The averageThe average turnturn time in the cut istime in the cut is0.300.30 min and on the fill the averagemin and on the fill the averagetime istime is 0.210.21 min.min.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 43
CYCLE TIME FOR ACYCLE TIME FOR ASCRAPER SCRAPER
Table 2. Scraper Dump Cycle Times (U.S. Department of Transportation, FHWA)Scraper Type
Scraper Size(cu yd)
Single Engine(min)
Tandem-powered(min)
8/9/2019 Scrapers lectures
23/34
8/9/2019 Scrapers lectures
24/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 46
OPERATING EFFICIENCYOPERATING EFFICIENCYAND PRODUCTIONAND PRODUCTION
The volume of material hauled wouldThe volume of material hauled wouldequal the product of the number of tripsequal the product of the number of tripsand the average volume per load.and the average volume per load.Reality is different from this perfectReality is different from this perfectproduction. Delays occur on the job;production. Delays occur on the job;machines break down; men stop formachines break down; men stop forwater, or machines cluster causing awater, or machines cluster causing aqueue in the cut for the pusher.queue in the cut for the pusher.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 47
EFFICIENCY F CTOR
• 50 min-hrefficiency
8/9/2019 Scrapers lectures
25/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 48
OPERATING EFFICIENCYOPERATING EFFICIENCYAND PRODUCTIONAND PRODUCTION
Studies of scraper operations suggestStudies of scraper operations suggestthat thethat the average productive time is 69%average productive time is 69%of a perfect 60of a perfect 60 --min hour min hour (excluding(excludingweather delays to the job).weather delays to the job).The actual number of trips in the realThe actual number of trips in the realworld would beworld would be
10.9 X 0.69 = 7.5 trips per work hour
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 49
OPERATING EFFICIENCYOPERATING EFFICIENCYAND PRODUCTIONAND PRODUCTION
The estimator should always try toThe estimator should always try tovisualize the work site before applying avisualize the work site before applying afactor:factor:
If the pit will not be congested and if thedump area is wide open, a 55-min hour may be appropriate.If the cut involves a tight area, such asa ditch, the estimator should consider a45-min hour .
8/9/2019 Scrapers lectures
26/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 50
PUSH TRACTORSPUSH TRACTORSREQUIREDREQUIRED
If pushIf push --loaded tractor scrapers areloaded tractor scrapers areto attain their volumetric capacities,to attain their volumetric capacities,they need the assistance of a pushthey need the assistance of a pushtractor during the loading operation.tractor during the loading operation.Push tractor assistance will reducePush tractor assistance will reducethe loadingthe loading --time duration, andtime duration, andthereby will reduce the total cyclethereby will reduce the total cycletime.time.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 51
PUSH TRACTORSPUSH TRACTORSREQUIREDREQUIRED
When using push tractors, weWhen using push tractors, weshould match the number ofshould match the number ofpushers with the number ofpushers with the number ofscrapers available at a given time.scrapers available at a given time.If either the pusher or the scraperIf either the pusher or the scrapermust wait for the other, operatingmust wait for the other, operatingefficiency is lowered and productionefficiency is lowered and productioncosts are increased.costs are increased.
8/9/2019 Scrapers lectures
27/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 52
PUSHER CYCLE TIMEPUSHER CYCLE TIME
Caterpillar recommends calculatingCaterpillar recommends calculatingbacktrack pushbacktrack push --tractor cycle time,tractor cycle time,T T p p , by the formula, by the formula
T p = 1.4 Lt + 0.25
where Lt is the scraper load time (pusher contact time).
(2)
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 53
PUSHER CYCLE TIMEPUSHER CYCLE TIME
The formula is based on theThe formula is based on theconcept that pusher cycle time is aconcept that pusher cycle time is afunction of four components:function of four components:
Load time of the scraper Boost time, time assisting the scraperout of the cut, 0.15 min.Maneuver time, 40% of load time.Positioning for contact time, 0.10 min.
8/9/2019 Scrapers lectures
28/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 54
PUSHER CYCLE TIMEPUSHER CYCLE TIME
The number of scrapers that apush tractor can serve is theratio of the scraper cycle time tothe pusher cycle time:
where N is the number of scrapers per one pusher.
p
s
T
T N = (3)
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 55
ROLLING RESISTANCE ANDROLLING RESISTANCE ANDSCRAPER PRODUCTIONSCRAPER PRODUCTION
Rolling resistance varies with haulRolling resistance varies with haul --road conditions.road conditions.
A well maintained haul road permits A well maintained haul road permitsfaster travel speeds and reducesfaster travel speeds and reducesthe costs of maintenance andthe costs of maintenance andrepairs for the scrapers.repairs for the scrapers.
8/9/2019 Scrapers lectures
29/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 56
ROLLING RESISTANCE ANDROLLING RESISTANCE ANDSCRAPER PRODUCTIONSCRAPER PRODUCTION
The following figure is from fieldThe following figure is from fieldstudy of scraper haul times:study of scraper haul times:
Shaded area represents the range ofaverage travel times.Good haul roads are indicated by the
lower boundary.Poor haul roads are indicated by the
upper boundary.
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 57
ROLLING RESISTANCE ANDROLLING RESISTANCE ANDSCRAPER PRODUCTIONSCRAPER PRODUCTION
Figure 1. Average Travel Times Single-powered Axle Scrapers,Capacity < 25 cy (U.S. Department of Transportation, FHWA)
8/9/2019 Scrapers lectures
30/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 58
Example 2Example 2Based on the the scraper specified in the following figures (Figures 4-8,4-10, and 6-9 of the textbook), and for haul conditions as stated below, whatis the probable production of the scraper?Given that the total length of haul when moving from the cut to the fill is4,000 ft as follows:
1,200 +4% grade1,400 ft +2% grade1,400 ft -2% grade
Soil: Clay 3,100 lb per bcyRolling Resistance 80 lb per ton
Assumptions:average load time = 0.85 min
→
load of 96% of the capacity (Figure 2, or Figure 7.10 Textbook)
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 59
Example 2 (cont’d)Example 2 (cont’d)Figure 2 (for Example 2)
8/9/2019 Scrapers lectures
31/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 60
Example 2 (cont’d)Example 2 (cont’d)Figure 3 (for Example 2)
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 61
Figure 4
(for Example 2)
Example 2 (cont’d)Example 2 (cont’d)
8/9/2019 Scrapers lectures
32/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 62
Figure 5(for Example 2)
Example 2 (cont’d)Example 2 (cont’d)
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 63
Example 2 (cont’d)Example 2 (cont’d)
Actual Load = 0.96 X 31 = 29.8 lcy
Swell Factor = 0.74, clay (Table 1, or Table 4-1 in Textbook)
Load Volume in Bank Measure = 29.8 X (0.74 X 1.1) = 24.3 bcy
Weight of Load = 24.3 (3,100) = 75,330 lb
Weight of Scraper (empty) = 96,880 lb (see Figure 3)
Gross Weight = 172,210 lb
%42080
lb/ton20lb/toninResistanceRolling
ResistanceRolling ===
8/9/2019 Scrapers lectures
33/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 64
Example 2 (cont’d)Example 2 (cont’d)Table 3. Haul and Return Speeds
Distance (ft) Grade (%)
Total
Resistance (%) R = rr + gr
Speed (mph) Travel Time (min)
Haul (172,210 lb): 300 acceleration 4 8 5 0.68 900 4 8 10 1.021,400 2 6 15 1.061,200 -2 2 30 0.45 200 deceleration -2 2 12 0.19
Total 3.40Return (96,880 lb): 200 acceleration 2 6 10 0.231,200 2 6 21 0.651,400 -2 2 32 0.50
1,000 -4 0 32 0.36 200 deceleration -4 0 12 0.19Total 1.93
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 65
Example 2 (cont’d)Example 2 (cont’d)
Calculate the total time required for a single-engine31-cu-yd scraper to complete a 4,000-ft haul cycle.
T s = load t + haul t + dump t + turn t + return t + turn t
Load t = 0.85 min
Haul t = 3.40 min
Dump t = 0.37 31 cu yd (Table 2)
Turn t = 0.21 min @ fill
Return t = 1.93 min
Turn t = 0.30 min @ cut
Hence, Total Cycle Time = T s = 7.06 min
8/9/2019 Scrapers lectures
34/34
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 66
Example 2 (cont’d)Example 2 (cont’d)
hr bcy
843(24.3)34.7Production
contacts7.341.44
50hour min-50a perContactsPusher
scrapers59.41.447.06
RequiredScrapersof Number
min44.125.0)85.0(4.125.04.1ePusher tim
hr bcy 17224.3(7.08)hour min-50 perscraper perVolume
trips08.77.0650
hour min-50 pertripsof Number
==
==
≈===
=+=+==
==
==
p
s
t p
T
T
LT
CHAPTER 7. SCRAPERSENCE 420 ©Assakkaf
Slide No. 67
Example 2 (cont’d)Example 2 (cont’d)
estimate.wrongisthis,hr
bcy8605172Production
thencontrol,ht to been thoughadscraperthe,mistakenlyIf,
hr bcy
8434.9172Production
ely,Alternativ
=×=
=×=
Top Related