The self-propelled scraper—or in Caterpillar parlance, the “wheel tractor-scraper”—continues to be not only a viable machine in Caterpillar’s range of bulk-earthmoving equipment, but also, with the recent introduction of the 620K Series, continues to keep pace technically with the most advanced of the company’s products. The design of the new K Series models (621K, 623K, 627K), says John Gerhold, wheel tractor-scraper application specialist, is aimed at production efficiency and operator amenities, qualities that Construction Equipment recently asked a pair of seasoned professional operators to evaluate.
On a sunny but unusually cold day for late October, with wind gusts to 50 mph, Construction Equipment editors met up with a number of folks at Caterpillar’s 700-acre Edwards Demonstration & Learning Center, just west of Peoria (Ill.), for a close look at the new 627K. In attendance were Gerhold, Caterpillar demonstrator/operators Brian Cain and Nathan Myers, and from Peoria-based Operating Engineers’ Local 649, Nestor Madson and Brad Walker, professional equipment operators and long-time instructors on Local 649’s training staff.
The Caterpillar crew had parked two new 627Ks in the indoor operating arena of the Edward’s facility, and the machines easily impressed the non-Caterpillar crowd. The 627K weighs 90,000 pounds, increasing to nearly 93,000 pounds with a push-pull bail and hook. Its open bowl has a heaped capacity of 24 cubic yards and a rated payload capacity of nearly 58,000 pounds. It exceeds 51 feet in length with the bail down and develops a total of 697 net horsepower from its Cat C13 tractor engine and C9.3 scraper engine, power enough to cut more than 10 feet wide and 12 inches deep.
Gerhold began the day with a machine walk-around, noting new features and briefly explaining the 627K’s twin-engine concept, saying that the tractor engine drives an eight-speed power-shift transmission (gears 1 and 2 in torque-converter drive, 3-8 in direct drive), and the rear engine drives a four-speed power-shift that is always in torque-converter mode. The scraper power train is always pushing the tractor, he said, with the amount of push modulated by the operating situation. With the 627K’s new Fuel Economy Mode selected, the scraper engine reduces speed when both transmissions are in top gear and the machine is at full run-out speed, resulting in optimum fuel economy.
Gerhold told us that the K Series represents a technical evolution of the predecessor H Series, and that premium H Series features—such as Sequence Assist and Load Assist, which automate much of the machine’s cycle—were combined in the K Series with operator-convenience and machine-protection features, most of which, such as differential-lock protection, the result of customer input.
“The 627K tractor uses a heavy dog-clutch as a differential lock—not as technically advanced as the hydraulic-clutch lock in an articulated truck, of course, but the only type that can practically handle the power that the 627K puts to the ground. Some owners tell their operators not to use the lock, for fear of it being engaged at the wrong moment and causing damage. But we want operators to use it, because it can make a 3- or 4-second difference in cycle time. The new system takes the burden off the operator by preventing engagement until wheel speeds are equal and the clutch can be safely engaged.”
Gerhold summed up the 627K’s overall design: “With the K Series, our goals were essentially to ensure that operators can comfortably and consistently utilize the machine’s high-production capability and that owners can more effectively control operating costs, for example, by measuring and tracking material movement with the available Payload Estimator system. We think the basic platform has the structure and technology to be moving material as efficiently in 10 years as it does today.”
After the Caterpillar crew had given Madson and Walker a quick tour of the 627K’s controls, Gerhold suggested an approach to evaluating the machines: “We’d like to turn you loose for a while to get familiar with the standard controls,” he told the operators, “then we’ll introduce some of the machine’s more advanced features. That’ll give you a basis for evaluating the technology involved.”
Madson and Walker said that the Cat scrapers with which they were most familiar were older models having a basic three-lever set-up for controlling bowl, apron and ejector—so stepping into the 627K’s cabin was somewhat of a giant step forward in technology.
Basic scraper functions are now handled via a multi-axis joystick, with a thumb wheel for apron control and buttons for controlling the bail, cushion-hitch lock, transmission hold (locks in second gear for loading), and the Sequence Assist and Load Assist systems. A center monitor displays machine-operating parameters, flanked on the left by a monitor that displays input from the machine’s three cameras, and on the right by a display panel that accommodates Caterpillar’s “integrated technologies,” such grade-control.
Operator impressions
After the operators had spent a fair amount of time running the 627Ks, including single-machine loading, push-pull loading, and hauling relatively long distances at high speeds, we asked for initial reactions.
“Very comfortable to run—I like the cruise feature,” said Walker. “The throttle control is very comfortable...you’re not trying to push your foot through the bottom of the machine. It’s got plenty of power...ungodly power...good traction...it cuts smoothly and the pan loads easily.”
The “cruise” Walker noted is the 627K’s new operator-selected ground-speed control, which assists the machine in maintaining a steady speed if it encounters a rough patch on the haul road and the operator can’t keep steady pressure on the throttle. In addition, the machine’s maximum speed can be set via the monitor.
“If speed must be limited,” said Gerhold, “the machine is intelligent enough to select the highest gear possible and to bring down engine speed to save fuel. In the past, top gears were simply locked out, which caused engines to run continually at high idle and burn maximum fuel.”
Madson’s first comments were about the 627K’s cab and its overall performance: “It’s so quiet in the cab that you can’t hear the engines running. [Interior sound is 76 dB(A).] I have to admit, though, that I’m used to the old three-lever controls, and I initially had to think about everything I was doing. But the controls became more comfortable with time. The power the machine has is phenomenal: I was impressed with how easily it loaded.”
Both also were impressed with the 627K’s ride. “I have degenerative discs in my back,” said Walker, “and operating a scraper would usually be uncomfortable. But I could operate this machine all day with no problem. Being able to adjust the seat’s suspension is also a plus; I found that a firmer setting took out a lot of bounce.”
Gerhold explained that the 627K’s good ride results in part from changes in the cushion hitch, which, he noted, is designed primarily to reduce stress on pins and bushings in the hitch area, but secondarily enhances ride. New software technology, he explained, allows the system’s dual nitrogen accumulators to prevent “end-of-stroke events” (bottoming of the load-cylinder’s piston) when the machine encounters rough spots in the haul road. The result, as the operators experienced, is a much-improved ride.
“I think another big improvement is the seat’s 30-degree rotation,” said Madson. “Instead of always being forward, it can be angled to make it easier to look behind you.”
Walker also noted the machine’s visibility: “All-around visibility is excellent…especially with the cameras. When we did the push-pull, I used the rearview camera and found it very helpful…and the cutting-edge camera gives an excellent view of the loading area.” [A third camera looks along the machine’s right side.]
Madson commented on how easily the column-mounted retarder worked. The retarder (an engine-compression brake) has three settings, two of which use both the tractor and scraper engines. The machine also has a new over-speed-protection system that activates the compression brakes when it senses an imminent engine-over-speed condition.
Commenting further on the 627K’s stopping power, Walker said “the brakes work well…that’s something you usually don’t see in a scraper. The brakes did a good job of controlling speed coming into the cut. And the steering was smooth; scraper steering is usually a bit jerky, but this steered like a pickup.” (The 627K has a new high-pressure steering system designed to significantly reduce steering effort.)
Asked about the 627K’s push-pull ability, both operators were impressed with the combined power of the machines and how quickly they loaded. “For two scrapers to be able to work an area by themselves without a tractor is a big advantage,” said Madson.
Asked about any aspects of the machine that they would like to see changed, Walker noted transmission performance when the machine entered the cut: “Maybe it was just my technique,” he said, “but I noticed when going into the cut, you really had to slow down to get the machine to shift into second gear.”
Gerhold said that he’s heard that comment before: “We’d like the shift to be faster, because the machine loses some momentum going into the cut. At that point, it’s going from direct drive to torque-converter drive, and the shift takes just milliseconds, but when you’re in the seat, it seems like forever. We’ve experimented with making the shift faster, but the tradeoffs in overall performance didn’t justify the change. But as machines continue to get smarter, maybe we’ll find the perfect solution.”
Automated advantages
As a final exercise, the operators used the 627K’s available Sequence Assist and Load Assist features. Sequence Assist, Gerhold explained, uses integrated software and position-sensing cylinders to automate 14 individual implement and machine commands during the load, haul, dump and return segments.
For example, cutting-edge height and apron position can be set through the display to best suit the material being loaded, and when the machine enters the cut, pushing a single button recalls those settings, locks the cushion hitch, and holds the transmission in second gear. At the end of the cut, a second touch closes the apron, raises the bowl, and unlocks the hitch and transmission in preparation for the haul. A third touch adjusts the bowl and apron for dumping, then activates the ejector; a fourth readies the machine for the return.
Load Assist benefits the loading process by automatically controlling the position of the cutting edge based on ground speed and engine speed: “The idea is to keep the machine moving through the cut with minimum wheel spin,” said Gerhold. “Experienced operators usually outperform the system, but it does help inexperienced operators quickly become productive—and profitable. As operators learn the art of loading, they’re probably going to transition out of Load Assist, but it’s always there to assist them.” (Load Assist for the K Series has new software enhancements.)
After using the automated systems in another round of dirt moving, the operators were asked how they got along with Sequence Assist. Madson perhaps said it all with his initial comment:
“How did we get along without it?—it’s an awesome feature. When you were explaining it earlier, I was thinking, ‘I’ve been doing this for a while...I know how to do this’...but then you realize it’s just four clicks and you go.”
Walker was of like opinion: “As operators, we tend to be control freaks, and I initially wondered how Load Assist would react in terms of smoothness of the cut. But after trying it, I was impressed at how smoothly the machine cut. And Sequence Assist...I particularly like the way it sets up the machine for the haul; when you’re loaded, just push the button and go, because it’s doing everything in the back for you.”
“I can guarantee you that my cycle times were better with the automated systems than without them,” said Madson. “The whole process just becomes much more fluid. It’ll be a very useful tool for the kids coming up and doing this work now.”
Walker agreed: “The systems pretty much take out all the guesswork.”
