PRODUCTION TECHNIQUES

Scraper production techniques are used to achieve the most amount of work with the scrapers assigned. These techniques are as follows.

Figure 10-44.-Straddle loading.

Downhill Loading

Downhill loading uses the force of gravity on the scraper to get larger loads in less time. The added force of gravity is 20 pounds per gross ton of weight per 1 percent of downhill grade. The downhill pull adds more material per load, and the added material weight increases the total gravitational pull.

Straddle Loading

Straddle loading gains time on every third trip because the center strip loads with less resistance than a full cut. After the first scraper has made a cut, the second scraper should make a parallel cut and leave a 4- to 5-foot-wide island between the two cuts, as shown in figure 10-44. The third scraper can straddle this island of material to achieve a fast, less resistance load.

Back-track Loading

Back-track loading is the method where the cut is fairly short and loading in both directions is impractical. As shown in figure 10-45, too much time is spent back tracking and maneuvering the push cat for the next load. When the cut is wide enough, other methods should be tried.

Shuttle Loading

Shuttle loading is used for short cuts where it is possible to load in both directions, as shown in figure 10-46. The push cat pushes one scraper in one direction, then turns and push loads a second scraper in the opposite direction.

Figure 10-45.-Back-track loading.

Figure 10-46.-Shuttle loading.

Chain Loading

Chain loading is used where the cut is fairly long, making it possible for the push cat to pickup two or more scraper loads without back tracking, as shown in figure 10-47. The push cat push loads one scraper, then moves in behind another scraper, moving parallel to the first in an adjacent lane.

Optimum Loading

Optimum loading is an operation when loading time and maximum output are critical. Push-loaded scrapers should be loaded within 1 minute and within a distance of 100 feet. More time and distance may be used to obtain more material when the haul is long enough, and the added material is great enough to offset hauling fewer loads because of longer loading time.

When scrapers are backed up at the cut waiting for push cat assistance, let the scrapers cut without attaining a heaped load. When push cats are waiting for scrapers, increase loading time to achieve maximum loading. Make sure push cats use wait time to dress the cut. In some cases, it will increase production to use a dozer full time to dress the cut. At the end of a workday, take the time to shape the cut for good drainage.

NOTE: Maintaining adequate drainage throughout a cut and fill operation reduces compulsory downtime caused by bad weather.

The rule of thumb used for computing the number of push cats required for a scraper operation is to divide the scraper cycle time by the push cat cycle time. When computing cycle time for a scraper, take the total time of loading, hauling, unloading, and return; for instance,

Figure 10-47.-Chain loading.

a 5-minute scraper cycle time divided by a l-minute push cat cycle time calls for five scrapers per push cat.

Turns

When making turns, turn within the shortest radius possible and at the highest safe speed When making turns to perform cut and spread operations, use the sequence shown in figure 10-48.

Haul Roads

Haul roads should be level and laid out so time is not wasted in maneuvering the scraper. A haul road that has drastic changes in elevation reduces production. Haul roads should be kept in good condition and moist. Roads kept moist, not wet, packs into a hard smooth surface that permits higher travel speeds. The moisture also controls dust that gets into all parts of the scraper, resulting in increased lubrication problems and _{premature wear.} Additionally, controlling the dust allows better visibility.

If the haul road is a dirt road and needs grading, while returning to the cut, maintain the road occasionally with the scraper blade. This is performed by opening the apron approximately 12 inches above the cutting edges and the ejector positioned forward to within 6 inches of the cutting edge. The bowl is lowered until the cutting edges scrape about 1 to 2 inches of the road surface. By watching the road, the operator can vary the cutting action to trim small rises and carry the material to fill depressions, as the scraper travels the haul road These grading operations can be performed in second or third gear, depending upon road conditions. Grading should only be done when the road surface has ruts and rough or soft spots.

NOTE: Scrapers on the haul road should only travel in the highest gear that is safe for the road