Tracks are better for adverse conditions and provide a smooth ride, but tires can often offer a lower operating cost.
Titan's Arched Drawframe is said to transfer scraper load evenly to both tractor axles for maximum traction.
A scraper tractor with tires can often offer a lower operating cost compared to a tracked unit.
The High Arch Drawframe of the Titan scraper is designed to optimize weight transfer to the tractor.
Selecting the number and size of pull scrapers is part of the challenge. Calculators are available to help.
Pull scraper systems provide unmatched flexibility. “The beauty of a pull scraper system is that capacities can be adjusted by adding or subtracting scrapers from the prime mover to suit each individual project or set of conditions,” says Mark Oliver, John Deere product marketing manager, scraper systems.
This versatility has made pull scrapers popular, but selection and setup determine success. “Pairing of the tractor and scraper(s) is the most critical step,” says Oliver. “The relationships between scraper size, quantity, horsepower and ground conditions are key.”
There is an art to sizing pull scrapers. “The more volume that can be moved per load, the more you minimize repetitive trips,” says Kelly Goossen, sales manager, K-Tec Earthmovers. K-Tec takes a unique approach by offering single scrapers with a capacity of 25 to 54 cu. yds.
Ideally, you want a scraper that provides the lowest overall cost per yard for the specific job. “Factors driving the cost per yard include load carrying capability, time to load and overall cycle time, as well as fuel consumption or operating costs,” notes Walt Baty, Bult Enterprises.
Another tangible factor is versatility and the resulting utilization. “On many jobs, there are areas where using a scraper results in the lowest cost per yard. In other areas, it is more economical to top load a truck,” says Baty. “If a scraper can be top loaded, it may not be necessary to bring in additional equipment to achieve the overall lowest cost per yard.”
Both John Deere and Case IH offer scraper system productivity calculators on their websites to help compare the costs of different earthmoving solutions. This can help you identify the ideal size and quantity of scrapers to minimize the costs per cubic yard.
Dump vs. ejection scraper
Soil type is the most important factor when choosing between a dump or ejector scraper. “If your jobsite requires moving loose topsoil or land leveling, a wide format, dump-style scraper is preferred over a narrower cut ejector scraper [which is used primarily to move bulky material like clay],” says Randy Rust, president, Ashland Industries.
Dump scrapers are less costly than ejector scrapers and they can unload faster. “But ejector scrapers unload more evenly than dump scrapers,” says Rust. “This can be a benefit to meet compaction standards.”
Dump scrapers may also present problems when unloading if the material is wet or sticky.
“As material that cannot be dumped builds up in the bowl, the load carrying capacity is reduced,” says Baty. “The ejector scraper always has the ability to positively eject, or push out of the bowl, all of the loaded material. The speed of the ejector can also be adjusted to provide better control of the spreading operation at the fill site. Consistent depth of material when being spread is a benefit during the compaction process.”
Ejector scrapers do offer the ability to work in all soil conditions. “Ejector scraper design allows loading of light or heavy material, and the fast ejector scrapers are considered all-in-one scrapers,” says Goossen.
But dump scrapers can really shine in sand. “A Deere carry-all scraper approaches the cut with a slightly different angle than an ejector, making its performance in dry, loose materials superior,” Oliver asserts. “Because the carry-all relies on gravity for dumping, its cycle times are typically faster than an ejector. Its aggressive approach and front pivot design give the ejector faster blade response than a carry-all.”
Also take note of the blade configuration. “Certain blade configurations such as drop centers and teeth are better in tougher soils, while straight blades work better in sand,” says Oliver.
Tires or Tracks?
Soil type also influences the choice between wheels or tracks. “Selecting the right tires or tracks for the conditions and following the manufacturer’s recommendations for wheel slip will lead to better performance and lower costs,” says Oliver.
The advantage of a wheel tractor is the wheels slip, so you have an automatic slip clutch between the tractor and the ground. However, proper air pressures can greatly affect performance in the cut. “You must carry a little higher air pressure on a wheel tractor because of the increased weight,” says Roger Lewno, Case IH team leader of large tractor marketing.
With tracks, performance comes through the powertrain and the engine. Tracks typically perform better in loose underfoot conditions such as sand, while tires perform well in topsoil and clays. Tracks are also better suited for adverse conditions. “The Case IH Quadtrac (track tractor) will get into conditions you simply can’t get into with a self-propelled scraper,” says Lewno.
Tracks offer better ride quality, as well. But it’s important to note that they do come with a little higher operating cost.
While a scraper tractor may have the appearance of an ag tractor, critical differences exist. “The scraper tractor is factory configured to comply with most OSHA requirements,” says Rust. “A customer using an ag version tractor may risk having his/her job shut down because the tractor does not meet or exceed the OSHA requirements to be operated on the construction site.”
Scraper tractor cabs feature ROPS and FOPS. “The seat retainer meets OSHA and MSHA standards, and there is a backup alarm, wide clearance marker, strobe light and external mirror standard to improve jobsite safety,” notes Rust.
The tractors are also built to withstand the tough duty cycle. “In general, a scraper tractor should have a more robust chassis, more appropriate tire and ballast options and more horsepower than an ag tractor,” says Oliver. “Due to the high tongue weight loads of a scraper, scraper tractors should be ballasted heavily on the front in order to deliver the massive engine power to the ground.”
The John Deere Scraper Special features a short drawbar support tongue weight transfer and high-flow hydraulics for fast blade response. The most important feature, however, is the AutoLoad system. “AutoLoad allows push-button loading so that even the greenest of operators can load like a pro,” says Oliver.
Case IH also produces specifically designed scraper tractors that come with the scraper drawbar and a tow cable. “We require the heavy-duty axles with the double reduction compound planetaries,” says Lewno. “We require differential locks on the axles.” It also comes with an upgraded transmission with the default set to second gear on startups as opposed to fourth gear on the ag tractors.
If you purchase a factory produced scraper tractor, most of the configuration/setup has already been completed. “If you’re converting an ag tractor, a common mistake is purchasing a tractor without a powershift transmission,” says Rust. “This limits productivity on longer hauls.”
Proper Weight Transfer
Scraper tractors are engineered to handle the weight transfer from the scraper. “Additional front weights are required to offset the vertical weight transfer the scraper displaces onto the rear of the tractor,” says Rust. “Scraper tractor manufacturers have pre-configured weight packages and tire/wheel configurations.”
Approximately one third of the weight of the scraper is on the drawbar of the tractor. “Say an empty scraper is 18,000 lbs. You have 6,000 lbs. already on the rear of the tractor,” says Lewno. “When it fills, the dirt may weigh about 2,500 lbs. per yard. That weight is transferred to the tail of the tractor.” The nose of the tractor would be weighted to counteract this weight.
When determining ballast requirements, Oliver advises, “Try to achieve an even weight split between front and rear tractor tires under load without exceeding roughly 110 lbs. per horsepower.”
Pull scrapers utilize a special hitch. “A high-strength 1.5-in. horizontal hitch pin couples the tractor to the scraper, which allows the weight to be moved closer to the rear of the tractor,” Rust points out.
The position of the hitch requires special attention. “When hitching a scraper to a tractor, attach it as close to the rear axle and as low to the ground as possible,” says Goossen. “Ideally, the pull point needs to be as close to the center of the tractor as possible.”
The tractors have adjustable drawbars, so when you couple the scraper to the tractor, make certain the drawbar height is right for the scraper. “If the scraper is getting too high, when you lower the scraper, it will sit back on its heel and will be very difficult to load,” says Lewno.
As an alternative to conventional scraper tractors, there are tractors based on articulated dump trucks (ADTs). “You may want to consider an ADT power unit, which will greatly increase your haul road speed,” says Goossen.
For example, the Bell 4206D scraper tractor is derived from a heavy-duty articulated haul truck with specific scraper application enhancements to the drivetrain. The Terra Titan S4412 uses a high arch, or gooseneck-style, drawframe mounted to a ball hitch located near the center of the tractor.
As the S4412 scraper loads, the weight of the growing load is transferred to the center point of the tractor, which is equally distributed across both tractor axles. “This design utilizes the payload to increase traction as the scraper loads. No supplemental weights are necessary,” says Baty.
The use of grade control systems with pull scraper systems calls for special consideration.
“You need high auxiliary flow rate from the couplers,” says Rust. “Most new tractors are ‘plug and play’ and integrate with automatic machine control systems. Older tractors may require additional electric-over-hydraulic valve systems.”
Sufficient flow is needed to ensure fast, predictable hydraulic response for all functions. “Case IH requires at least 57-gpm hydraulic flow on its scraper tractors, and there is a 3/4-in. coupler option,” says Lewno. “That would minimize the restriction going back to the scrapers for increased speed.”
Plumbing a scraper setup also requires careful attention. “The industry standard quick-connection couplers may cause problems,” says Goossen. “Direct plumbing hydraulics is often the preferred choice and gives you the most hydraulic flow. When hooking up a K-Tec scraper, you will need a free-flowing hydraulic valve called a ‘CASE Drain’ to activate the automatic ride control. K-Tec’s automatic ride control allows for faster travel speed, while causing less stress to both the tractor and scraper.”