Chapter: 4 Loading and Hauling Part 3

Auger scrapers

are self-loading scrapers that use a rotating auger located in the center of the scraper bowl to help lift material into the bowl.

,,,,,,,,,,,,,,,,,,,,,,, & ,,,,,,,,,,,,,,,,,,,,,,,,,,, are the most common forms of construction hauling equipment. Trucks are also known as The heavy-duty rear-dump.

Trucks / wagons

Elevating scrapers

Utilize a ladder-type elevator to assist in cutting and lifting material into the scraper bowl. Elevating scrapers are not designed to be push-loaded.

Push-pull or twin-hitch scrapers

are all-wheel-drive scrapers equipped with coupling devices that enable two scrapers to assist each other in loading.

conveyor belts application is primarily limited by their large ,,,,,,,,,,,,,,,,,,,,,,,

capital cost.

Wagons

,,,,,,,,,,,,,,,,,,,, are tractors equipped with earthmoving semitrailers.

Scrapers types include:

- 1. Two-axle (Single-engine overhung) scrapers - 2. Three-axle scrapers - 3. Twin-engine all-wheel-drive scrapers - 4. Elevating scrapers - 5. Auger scrapers - 6. Push-pull or twin-hitch scrapers - 7. Pull-scrapers

In determining the payload per scraper cycle, it is necessary to check both:

- 1. the rated weight payload (max wt. you call haul) - 2. the heaped volume capacity The volume corresponding to the lesser of these two values will, of course, govern.

A complete pusher cycle consists of:

- Maneuver time, - Load time, - Boost time (during which the pusher assists in accelerating the scraper out of the cut), - Return time.

Some techniques for maximizing scraper production include:

- Use downhill loading whenever possible - Use chain or shuttle loading methods if possible - Use rippers or scarifies to loosen hard soils before attempting to load. - Have pushers give scrapers an adequate boost to accelerate units out of the cut.

All-wheel-drive scrapers,

- as the name implies, utilize drive wheels on both the tractor and scraper. - Normally, such units are equipped with twin engines. - The additional power and drive wheels give these units greater tractive effort than that of conventional scrapers.

There are many different types of hauling equipment available to the constructor:

- dozer, - loader, - scraper, - trucks, - wagons, - conveyor belts, and - trains.

Scrapers are capable of:

- excavating - loading - hauling - dumping material over medium to long haul distances • The scraper excavates (or cuts) by lowering the front edge of it's bowl into the soil

Scraper Variable Cycle Time include:

- haul time - return time

Scraper Fixed Cycle Time include:

- spot time - load time - maneuver and dump time

Two-axle or overhung scrapers Vs Three-axle scrapers

- utilize a tractor having only one axle. - Such an arrangement has a lower rolling resistance and greater maneuverability than does a three-axle scraper that is pulled by a conventional four-wheel tractor. - However, the additional stability of the three-axle scraper permits higher operating speeds on long, relatively flat haul roads.

Methods of push-loading scrapers:

1- The back-track method. 2- Chain loading. 3- Shuttle loading.

As a rule, haul units loaded by shovels, backhoes, and loaders should have a capacity of ,,,,,,,,, times excavator bucket capacity.

3 to 5

Because of their less precise control, clamshells and draglines require larger targets. A haul unit capacity of ,,,,,,,,,,,,,, times excavator bucket capacity is recommended for these excavators.

5 to 10

For the push-loading scrapers methods what is the most suitable method for a long, narrow cut area?

Chain loading.

Which of the three push-loading scrapers methods requires two separate fill areas for efficient operations?

Shuttle loading.

What is the the most commonly used and slowest of the three push-loading scrapers methods?

The back-track method.

The all-wheel-drive articulated dump truck is finding increasing usage because of its ability to ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,.

carry large loads over low-trafficability soils

Only the ,,,,,,,,,,,,,,,,,,,,,, is capable of achieving high efficiency in loading without the assistance of a pusher tractor or another scraper.

elevating scraper and push-pull scrapers

Wagons are available in ,,,,,,,,,,,,,,,,,, , ,,,,,,,,,,,,,,,,,,, and ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,.

end-dump / side-dump / most common bottom dump model.

The reason for using an excavator loading rate based on 100% excavator efficiency is because ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,.

excavators have been found to operate at or near 100% efficiency.

the scraper loading time which yielded maximum scraper production in a given situation was usually ,,,,,,,,,,,,,,, the loading time required to obtain the maximum scraper load

less than

If more than the theoretically required number of trucks is supplied,

no increase in system production will occur. because system output is limited to excavator output.

Spot time

represents the time required for a unit to position itself in the cut and begin loading, including any waiting for a pusher.

The result of adding together the travel times for several sections will,

yield a travel time greater than that obtained by the use of the average-speed method. because of an excessive allowance for acceleration and deceleration,