Lecture 6 scrapers TSP-308 MPK Ferdinand Fassa

OUTLINE Introduction Types of Scrapers Scraper Production Chart

INTRODUCTION Excavating, loading, hauling, & dumping over medium distances. Can be used with pusher tractor for increased production. Some models have self loading capabilities Economical over a wide range of haul lengths Can self load and not dependent on other equipment Scraper are available with loose heaped capacities up to about 44 cy

Types of Scrapers Push-Loaded: Single Powered Axle

Types of Scrapers Push-Pull: Tandem- Powered Axle

Types of Scrapers Auger Scraper Can self-load in difficult condition (frozen material, lime-stone) More costly to own and operate than conventional single-or tandem machine

Types of Scrapers Elevating is loading and hauling scraper Used for utility work Very good in small quantity situation No pusher required

Scraper Production Chart

Average Speed Factors When machinery are required to accelerate and stop in the same section, apply the squared value from column one.

Scraper Fixed Time, min

Scraper Production Example Problem Estimate the production of a single two-axle scraper Travel time curves are shown on Figures below, Fig. 4-4 & 4-5. Max Heaped Volume = 31 LCY Max Payload = 75,000 lb Material: Sandy Clay, 3200 lb/BCY, 2650 lb/LCY, Rolling Resistance = 100 lb/ton, Operating Conditions = Average

Scraper Production Example Haul Route: Section 1. Level Loading Area Section 2. Down a 4% grade, 2000 ft Section 3. Level Dumping Area Section 4. Up a 4% grade, 2000 ft Section 5. Level Turnaround, 600 ft Turnaround Load Area 4% grade Dump Area

Scraper Production Example Loads per Cycle Heaped Cap. Wt. = 31.0 LCY x 2,650 lb/LCY = 82,150 lbs 82,150 lbs exceeds the 75,000 lbs Rated Max Payload of the Scraper. The maximum scraper volume is limited by weight to = 75,000 lbs (Rated Wt)/ 3,200 lb/BCY = 23.4 BCY/Load

Scraper Production Example

Scraper Production Example Travel Time: Section 2 ~ Down a 4% Grade, 2,000 ft. (1% Eff.) TT2=1.02 min (Figure 4-4) Section 4 ~ Up a 4% Grade, 2,000 ft. (9% Eff.) TT4=1.60 min (Figure 4-5) Section 5 ~ Level Turnaround, 600 ft. (5% Eff.) TT5=0.45 min (Figure 4-5) TT=1.02 + 1.60 = 0.45 = 3.07 min

Scraper Production Example Travel Time: Section 2 ~ Down a 4% Grade, 2,000 ft. (1% Eff.) TT2=1.02 min (Figure 4-4) Section 4 ~ Up a 4% Grade, 2,000 ft. (9% Eff.) TT4=1.60 min (Figure 4-5) Section 5 ~ Level Turnaround, 600 ft. (5% Eff.) TT5=0.45 min (Figure 4-5) TT=1.02 + 1.60 + 0.45 = 3.07 min

Scraper Production Example Travel Time: Section 2 ~ Down a 4% Grade, 2,000 ft. TT2=1.02 min (Figure 4-4) Section 4 ~ Up a 4% Grade, 2,000 ft. TT4=1.60 min (Figure 4-5) Section 5 ~ Level Turnaround, 600 ft. TT5=0.45 min (Figure 4-5) TT=1.02 + 1.60 = 0.45 = 3.07 min

Scraper Production Example Fixed Cycle (Table 4-7) – Average Conditions – Single Engine Spot = 0.3 min. Load = 0.6 min. Maneuver & Dump = 0.7 min. Total Fixed Time = 0.3 + 0.6 + 0.7 = 1.6 min Total Cycle Time = 3.07 + 1.6 = 4.67 min. Estimate Production = 23.4BCY/Load x [(50min/h)/(4.67min/Load)] = 251 BCY/h

Scraper Fixed Time, min

Scraper Production Example Fixed Cycle (Table 4-7) Load Spot = 0.3 min. Load = 0.6 min. Maneuver & Dump = 0.7 min. Total Fixed Time = 0.3 + 0.6 + 0.7 = 1.6 min Total Cycle Time = 3.07 + 1.6 = 4.67 min. Estimate Production = 23.4BCY/Load x [(50min/h)/(4.67min/Load)] = 251 BCY/h

Push-Loading

Typical Pusher Cycle Time, min

Number of Scrapers Served, Pushers Required & Production (# of scrapers that can be handled by one pusher w/o scraper delay) (# of pushers required to service a fleet of scrapers: round up to next integer)

Scraper Push-Loading Example Problem The estimated cycle time for a wheeled scraper is 6.5 min. Calculate the number of pushers required to serve a fleet of nine scrapers using pushers. Determine the result for both backtrack and chain loading methods.

Scraper Push-Loading Example Cycle Times from Table 4-8

Optimal Load Time

Optimum Load Time

Cycle Time minus Load Time = 3.0 min.

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