Scrapers

Mansoor Azam Qureshi
NUST
Islamabad
Scrapers
Scrapers are designed to load, haul, and dump
loose material. The greatest advantage is their
versatility. They c...
Scraper components

21 January 2014

mansoor Azam Qureshi

3
Scraper Types




Single engine: A
tractor pulling a bowl
that can operate under
its own power or be
push-assisted. This...
Scraper Types




Push–pull scraper: This type is
designed with a push block
mounted on the rear and a bail
mounted on t...
Scraper Types


Auger Scrapers This is
another completely selfcontained
loading and
haulmg scraper.
Auger
scrapers can se...
Scraper Production Cycle











A scraper is loaded by
lowering the front end of the
bowl until the cutting edge...
Estimating Production



Bowl capacity of scraper
Soil type
Empty weight of scraper
Loaded weight of scraper



Haulage ...
Loading Scraper Bowl






Loose
volume
capacity of bowl in
heaped or struck
level is specified.
Optimum load is
smalle...
Haulage/ Travel Time
Both the haul and return time depend on the
distance traveled and scraper speed. Hauling
and returnin...
Travel Time, Distance and grade
chart

21 January 2014

mansoor Azam Qureshi

11
Example
Estimate the production of a wheel tractor-scraper given the job
information below. Use the travel time curve for ...
Travel Time Curve for Scraper

21 January 2014

mansoor Azam Qureshi

13
Solution
Bucket Capacity= 31lcy  Effective Grade
◦ Haul = -4.0+100/20 = 1.0%
 Weight of material
◦ Return= 4.0+100/20=9....
Solution





Loading Time=0.6 min
Dump and maneuver
time = 0.7 min
Turning and spot=0.3
min
CycleTime
=3.2+0.6+0.7+0....
Hints for Efficient Production


Normally, the operator should
maintain a depth of cut that gives a
constant loading spee...
Hints for Efficient Production
Hauling
Maintain the haul road in
top condition; use graders
and water sprinklers as
requir...
Hints for Efficient Production
Spreading






Vary spreading procedures
according to the material
involved. Spread loo...
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Scrapers Machines

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  • Excellent report - scientifically logical!
    Feel free to assess the numbers of our corporate presentation on our efficient earthmoving equipment in using Rock Trucks as power units to pull-pan scrapers:
    http://www.slideshare.net/KtecEarthmovers/ktec-earthmovers-volvo-ce?qid=b2c9ae4b-fade-4994-a6a9-955c0e267a05&v=qf1&b=&from_search=1
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Scrapers Machines

  1. 1. Scrapers Mansoor Azam Qureshi NUST Islamabad
  2. 2. Scrapers Scrapers are designed to load, haul, and dump loose material. The greatest advantage is their versatility. They can be used for a wide variety of material types and are economical for a range of haul distances and conditions. They are a compromise between a bulldozer, and excavator, and a dump truck.  Scrapers are articulated, tractor powered, and pull a bowl that holds the soil. A blade is mounted on the bottom of the bowl that cuts into the travel surface and the disturbed soil flows into the bowl as the scraper moves forward.  Scrapers can self-load or be assisted by another scraper or a bulldozer.  21 January 2014 mansoor Azam Qureshi 2
  3. 3. Scraper components 21 January 2014 mansoor Azam Qureshi 3
  4. 4. Scraper Types   Single engine: A tractor pulling a bowl that can operate under its own power or be push-assisted. This is the most common type of scraper on large earthmoving jobs. Tandem or twin engine: This type has a second engine mounted in the rear and can develop greater power. This is ideal for steeper hauls at greater speeds 21 January 2014 mansoor Azam Qureshi 4
  5. 5. Scraper Types   Push–pull scraper: This type is designed with a push block mounted on the rear and a bail mounted on the front to assist other scrapers or be pushed by other scrapers. They are ideal for dense soil-excavating projects when a dozer is not utilized for pushing. Elevating: These are selfcontained loading and hauling units. The chain elevator serves as a loading mechanism. The extra weight of the loading mechanism is a disadvantage during the haul 21 January 2014 cycle mansoor Azam Qureshi 5
  6. 6. Scraper Types  Auger Scrapers This is another completely selfcontained loading and haulmg scraper. Auger scrapers can self-load in difficult conditions, such as laminated rock, granular materials, or frozen material. An independent hydrostatic system powers the auger that is located in the center of the bowl. The rotating auger lifts the material off the scraper cutting edge and carries it to the top of the load, creating a void that enables new material to easily enter the bowl. 21 January 2014 mansoor Azam Qureshi 6
  7. 7. Scraper Production Cycle       A scraper is loaded by lowering the front end of the bowl until the cutting edge enters the ground. At the same time, the front apron is raised to provide an open Hauling load to dump site. slot. The dumping operation consists of lowering the cutting edge to the desired height above the fill, raising the apron, and then forcing the material out· by means of the movable ejector mounted at the rear of the bowl. Turn back Return to loading site Turn to load 21 January 2014 mansoor Azam Qureshi 7
  8. 8. Estimating Production  Bowl capacity of scraper Soil type Empty weight of scraper Loaded weight of scraper  Haulage route grades and rolling resistance.    21 January 2014 mansoor Azam Qureshi 8
  9. 9. Loading Scraper Bowl    Loose volume capacity of bowl in heaped or struck level is specified. Optimum load is smaller than max capacity. Loading beyond one min may not be feasible. Loading time may remain within 0.5 to 1.0 min typically 0.8 min is taken. 21 January 2014 mansoor Azam Qureshi 9
  10. 10. Haulage/ Travel Time Both the haul and return time depend on the distance traveled and scraper speed. Hauling and returning are usually at different speed ranges.  If the haul road has multiple grade or roIling resistance conditions, a speed should be calculated for each segment of the route.  When using the charts, always consider the human element; do not blindly accept chart speeds.  Manufacturer provided average speed and grade charts may be used for calculation of travel time.  21 January 2014 mansoor Azam Qureshi 10
  11. 11. Travel Time, Distance and grade chart 21 January 2014 mansoor Azam Qureshi 11
  12. 12. Example Estimate the production of a wheel tractor-scraper given the job information below. Use the travel time curve for scraper. Scraper type: single-engine overhung Loading method: single pusher Material: sandy clay, 3,200 IblBCY 2,560 IblLCY Rolling resistance = 100 lb/ton Scraper capacity: rated payload = 72,000 lb heaped volume = 31 LCY Altitude derating factor = 4% Job efficien cy factor = 0.83 Haul route : Section 1. Level loading area. Section 2. Down a 4% grade , 2,000 ft Section 3. Level dumping area Section 4. Up a 4% grade , 2,000 ft Section 5. Level turnaround, 600 ft 21 January 2014 mansoor Azam Qureshi 12
  13. 13. Travel Time Curve for Scraper 21 January 2014 mansoor Azam Qureshi 13
  14. 14. Solution Bucket Capacity= 31lcy  Effective Grade ◦ Haul = -4.0+100/20 = 1.0%  Weight of material ◦ Return= 4.0+100/20=9.0% = 31x2560 = 79360 lcy ◦ Turnaround=0+100/20=5%  Rated payload of bucket  Travel Time = 72000 lbs ◦ Section 2 = 1.0 min  Volume of material to be carried= 72000/3200 ◦ Section 4 = 1.6 min = 22.5 bcy ◦ Section 5 = 0.45 min Load ratio=22.5/31 ◦ Total Time=3.05 min =0.73  Adjusted for altitude  =3.05x1.04 = 3.2 min 21 January 2014 mansoor Azam Qureshi 14
  15. 15. Solution     Loading Time=0.6 min Dump and maneuver time = 0.7 min Turning and spot=0.3 min CycleTime =3.2+0.6+0.7+0.3 =4.8 min  21 January 2014 Production ◦ ◦ ◦ ◦ = 22.5x60/4.8 =281.25 lcy =281.25x2560/3200 =225 bcy mansoor Azam Qureshi 15
  16. 16. Hints for Efficient Production  Normally, the operator should maintain a depth of cut that gives a constant loading speed and leaves a smooth floor.  However, pumping the bowl up and down during loading may be required when loose sand is being loaded.  The scraper should leave the cut as fast as possible, Pushers should provide an adequate boost to accelerate scrapers leaving the cut.  Adjust loading according to the encountered. Use scarifiers to loosen before loading. Maintain a loading time as close to optimum as possible and provide adequate pushers. Tandem or dual pushers may be required for adequate power.  Maintain the cut area with idle pushers Loading Hints.  Use downhill loading whenever possible.  Shuttle or chain load if possible.  Straddle loading may be used to speed up loading. In this technique.   techniques soil type rippers or hard soils 21 January 2014 mansoor Azam Qureshi 16
  17. 17. Hints for Efficient Production Hauling Maintain the haul road in top condition; use graders and water sprinklers as required .  Keep haul units uniformly spaced. Unless passing room is provided, hauling speed is limited to that of the slowest unit.  Use one-way haul roads if possible. When two-way traffic is necessary, provide grade separation on sharp curves to reduce the danger of collision.    21 January 2014 Haul from two cuts to a common fill or haul from one cut to two fills whenever possible. Either procedure reduces time lost in turning, which typically amounts to about 0.25 min per turn. Use sprinkler s to reduce dust on the haul road. Dust increases equipment wear and reduces operator visibility. Do not overwater because overwatering may cause loss of traction and be a greater hazard than dust. mansoor Azam Qureshi 17
  18. 18. Hints for Efficient Production Spreading    Vary spreading procedures according to the material involved. Spread loose sand in thin layers. wet and sticky material is best spread by moving the tailgate forward about 12 m. (305 mm) and then returning it about 6 in. (152 mm) before repeating the procedure. When using this procedure, be sure to keep the bowl high enough to allow the dumped material to pass under the scraper without clogging.  Keep the fill smooth enough to allow fast dumping and return to the haul road.  Use boosting on the fill if scrapers require extra power for fast, smooth spreading.  Spread the first load at the beginning of each fill lane and work down the fill so that the loaded scrapers compact the material spread previously. Keep the fill high on the outside for safety and to help maintain an accurate slope. However, drainage must be provided for the fill surface. Provide adequate spreading and compacting equipment and give scrapers the right-ofway on the fill. 21 January 2014 mansoor Azam Qureshi 18
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