CONSTRUCTION EQUIPMENTS AND METHODS

SCRAPER MACHINE

PRESENTED BYVAIDIK SAKUNIAPRITHVI RAJ. P

CONSTRUCTION TECHNOLOGY AND MANAGEMENTVNIT, NAGPUR

WHAT IS A SCRAPER? Scraper is a tool or device used for scraping, to remove dirt or other

unwanted matter from a surface. In civil engineering works, scraper can be used for earthmoving

applications, mining, construction and other applications. Scrapers are articulated, tractor powered and pull a bowl that holds the

soil. The 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 bulldozer. The greatest advantage of scraper is the versatility.

Scrapers can be used to load and haul a wide range of material types and are economical over a wide range of haul lengths and haul conditions.

Scrapers are available with loose-heaped capacities up to 44 cy.

SCRAPER TYPES The scraper types are classified according to the number of

powered axles or by the method of loading. Machines that are available currently include:

Pusher-load (conventional) Single powered axle Tandem powered axles

Self loading Push-pull, tandem-powered axle Elevating Auger

PUSHER-LOADED SCRAPERS These have the potential for high travel speeds on favorable haul roads.

These can achieve speeds as high as 35mph when fully loaded that helps in extending the economic haul distance of the units.

The disadvantage is when they individually provide high tractive effort for economic loading. For a single powered axle scraper, 50 to 55% of the total loaded weight bears on the drive axle.

Tandem powered scrapers are 25% costlier than the single powered axle scraper. Hence, commonly used for working in extremely adverse grades or working in soft ground conditions.

Single powered axle wheel tractor scrapers are suited for jobs where rolling resistance is low and grades are minimal.

Tandem powered axle scrapers have two engines which produces extra power for overcoming high rolling resistance and steep grades.

SELF-LOADING SCRAPERS These are heavier and costlier than the conventional scrapers

but can be economical for stripping materials.

PUSH-PULL SCRAPERS These are tandem powered axle scrapers having a cushioned

push block and bail mounted on the front and a hook on the rear above the usual back push block.

This enables the scrapers to assist one another during loading by pushing and pulling another.

The trailing scraper pushes the lead scraper as it loads, the lead scraper pulls the trailing scraper to assist it in loading.

This enables the two scrapers to work without assistance from a push tractor.

When used in rock or abrasive materials, tire wear on these scrapers will increase because of more slippage from the four-wheel-drive action.

ELEVATING SCRAPERS A completely self contained loading and haling scraper. A chain

elevator, mounted vertically on the front of the bowl serves as the loading mechanism.

The disadvantage of the machine is that the weight of the elevator loading assembly is deadweight during the haul cycle. Such scrapers are economical in short haul distances.

These scrapers are used for utility work, dressing up behind production spreads, or shifting material during fine-grading operations.

No pusher is required, and hence there is no mismatch between pusher and the number of scrapers.

They cannot handle rock or material containing rocks due to the elevator mechanism.

AUGER SCRAPERS A self contained loading and hauling scraper, these can self-

load in difficult conditions, such as laminated rock, granular materials or frozen material.

In a soft limestone mining operation, 44 cy capacity tandem powered auger scrapers making 3 to 5 in deep cuts can be achieved.

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.

The auger adds non-load weight to the scraper during the travel cycles. These scrapers are more costly to own and operate than any other machines.

VOLUME OF A SCRAPER The volumetric load of a scraper may be specified as struck

or heaped capacity of the bowl in cubic yards. The struck capacity is the volume that a scraper would hold if

the top of the material was struck off even at the top of the bowl.

The heaped capacity of the scraper is specified by the manufacturer in respect to the slope of the material above the sides of the bowl.

Both the volumes represent loose cubic yards of material because of how a scraper loads.

The swell factor is multiplied to the loose volume in the scraper bowl to obtain the capacity in bank cubic yards.

SCRAPER OPERATION The basic operating parts of a scraper are:

Bowl. The bowl is the loading and carrying component of a scraper. It has a cutting edge that extends horizontally across its front bottom edge. The bowl is lowered for loading and raised during travel.

Apron. The apron is the front wall of the bowl. It is independent of the bowl. It is raised during the loading and dumping operations to enable the material to flow into or out of the bowl. The apron is lowered during hauling to prevent material spillage.

Ejector. The ejector is the rear vertical wall of the bowl. The ejector is in the rear position during loading and hauling. During spreading, the ejector is activated and moves forward, providing positive discharge of the material in the bowl.

SCRAPER OPERATION A scraper is loaded by lowering the front end of the bowl until the

cutting edge that is attached to and extends across the width of the bowl enters the ground.

The front apron is raised to provide an open slot through which the earth can flow into the bowl. As the scraper moves forwards, making a horizontal cut, a ribbon of material is forced into the bowl.

This is continued until the bowl is filled at which point the bowl is raised and the apron lowered to prevent spillage during the haul.

The dumping operation consists of lowering the cutting edge to desired height above the fill, raising the apron, and then forcing the material out by means of moveable ejector mounted at the rear of the bowl.

SCRAPER PRODUCTION CYCLE

The production cycle for a scraper consists of six operations Loading Haul travel Dumping and spreading Turning Return travel Turning and positioning to pick up another load.

Ts= loadt+hault+dumpt+turnt+returnt+turnt

SCRAPER PRODUCTION ESTIMATION Step 1: Weight Step 2: Rolling Resistance Step 3: Grade Resistance Step 4: Total Resistance Step 5: Travel Speed Step 6: Travel Time Step 7: Load Time Step 8: Dump Time Step 9: Turning Time Step 10: Load Cycle Time Step 11: Pusher Cycle Time Step 12: Balance Fleet Step 13: Efficiency Step 14: Production Step 15: Cost

SCRAPER SAFETY Scrapers should travel in the highest gear that is safe for haul

road conditions. Operators must always wear seat belts as uneven terrain and

ruts in haul road can cause violent pitching and bouncing. The operator should not turn the steering wheel violently. The fill should be higher on the outside edges, by keeping so

the scrapers are not prone to slide to the outside and over the edge.

Access to the fill area and haul roads should be restricted. Safety indoctination about the hazardous conditions and

proper reflective vests should be provided.

THANK YOU!