Issue link: http://read.dmtmag.com/i/75471
EQUIPMENT MANAGEMENT ate at maximum speed and lowest cost. With the help of a push tractor, the single- engine scraper loads quickly and hauls to the fill, while carrying minimum iron and using minimum fuel. The push tractor pro- vides the primary loading power, but load- ing cost still remains lower than systems used to load trucks. If the site presents grades steeper than 5 percent on the haul and 12 percent when returning empty, tandem-powered scrapers are the answer. The higher horsepower-to-weight ratio allows twin- engine scrapers to climb grades as much as 35 percent. Also, four-wheel drive powers such scrapers through underfoot conditions that stop two-wheel-drive machines. The ability to operate in poor underfoot conditions can assure more workdays per year from the twin-engine scrapers. Tandem-powered scrapers can cut cycle times, because they have better gradeability and higher usable rimpull. Acceleration is faster out of the cut and away from the fill. Even though higher owning and operating costs partially counter the increased production, tan- dem-powered scrapers may still produce the lowest cost per yard. Push-pull arrangements allow two twin-engine scrapers to hook up and assist each other in loading. A pair of scrapers can operate as a team or they can separate and work individually with a pusher. The push-pull system offers high production and the lowest cost, because the two scrapers can load in less time than two standard scrapers working with a pusher. Elevating scrapers provide work-alone capabilities and eliminate the need for push loading. They are most economical on hauls with lower rolling resistance and in favorable material. The elevating mecha- nism breaks up chunks, which eases dump- ing and enhances compaction in the fill. Five hundred hours marks the point of several filter changes. Engine oil and filter are to be changed at that interval, as is the fuel system filter, the hydraulic oil filter, and the transmission oil filter. All wheel tractor-scrapers are built for durability and long life, and the advanced age of many scrapers still operating in fleets in North America is testimony to that. But their capabilities — loading, hauling, and spreading materials — re- quire many moving parts that must be maintained properly to ensure reliable operation and high productivity. Inspecting carefully The operation and maintenance manual for each particular model of wheel tractor- scraper should be the primary source of recommended maintenance procedures and of the frequency with which each pro- cedure must be performed. Because there are several types of scraper configurations — open bowl, elevating, auger, single engine, twin engine, push-pull — mainte- nance items vary considerably. The operator can help keep small prob- lems from becoming big ones by con- ducting a thorough pre-shift inspection of the machine (see Safty & Maintenance Checklist). In addition to regular fluid level checks, the operator should pay particular attention to the components that do the most work. The operator should check for damage, cracked welds, and distortion on the bail, ejector, ejector rollers, and cutting edge. The hitch pins and stops also should be scrutinized for any damage, and tires should be checked for damage and proper inflation. Any debris blocking airflow through the radiator or wrapping around mov- ing parts should be removed. Of course, operators should report, immediately, any damage that threatens safety or the health of the machine. Preventive maintenance Most wheel tractor-scraper models have daily service recommendations that specify components to be greased. Auger equipped scrapers and elevating scrap- ers have several additional lubrication requirements that open-bowl machines don't have. Daily maintenance procedures can be performed by properly trained and equipped operators or by service techni- cians. Similarly, the fuel system water sep- arator and fuel tank water and sediment should be drained daily. Every 50 service hours or weekly, the bowl lift cylinder bearings and the hitch should be lubricated. At 250 service hours, oil samples — engine, transmis- sion, and hydraulic — should be taken. Prompt oil analysis and reporting can help catch a developing problem before AGGREGATES MANAGER August 2012 37