Pull-behind scrapers

|  June 12, 2007 |

If you’ve been using self-propelled scrapers for small site development jobs that last less than six months and involve short haul distances, you might want to consider using pull-behind scrapers.

“Most of our sales come from people who previously had been running self-propelled scrapers,” says Mark Miskin, president of Miskin Scraper Works. “When you hook them in trains, by the time you count your yardage of two or three scrapers, you’ve got more yards being hauled than in the motorized scraper.”

However, if you need to move big volumes of material for long-term projects such as construction of airports, roads or extremely large subdivisions, a motorized scraper will be more efficient. You will also need a self-propelled machine for jobsites that contain heavy clay or extremely rocky soil. If you have long haul distances, a self-propelled machine’s travel speed – 35 mph compared to about 15 mph for a pull-behind scraper – could also be an advantage.

To help contractors decide whether to use motorized or pull-behind scrapers, Scott Knoblauch, senior sales and marketing consultant for Caterpillar North American Heavy Industries, asks them five questions: What type of material are you moving? How far are you moving it? How much material are you moving? What are the underfoot conditions? How much time do you have?

The combination of answers to these questions will help you determine which machine type will give you the highest return on your investment. For example, if you are doing jobs such as site preparation for a 500-acre housing development, you might be able to use pull-behind scrapers, but self-propelled scrapers would get the job done faster and be able to handle a wider variety of material types, Knoblauch says. On the other hand, if you prepare sites for super stores, small shopping centers or small subdivisions, you are most likely be moving a low volume of material in a short amount of time, and pull-behind scrapers will get you in and out of those types of applications more economically.

Things to know before you buy
If you decide to purchase a pull-behind scraper, you’ll need to let your sales rep know a number of details about your jobsite conditions and applications.

First of all, you’ll need to know your primary soil type – whether it’s soft, sandy or contains any clay or rocks. If you have narrow tires on a scraper working in soft soil, the tires would likely sink in and the scraper wouldn’t do its job properly. “If rocks of any size or quantity are going to be encountered, a heavier blade receiver and cutting edge are a must,” says Kevin Shimp, co-owner of Port Industries.

You also need to know the type and horsepower of the tractor you’ll use to pull the scraper and the average haul lengths and number of yards of material you’ll move during current and future jobs. Your sales rep will use haul lengths and material volumes to determine the best capacity for your scraper. In general, the longer your haul lengths and the larger your volumes, the bigger your scraper should be.

The salesperson will need to know your applications – site prep or wetlands work, for example. If you will encounter exceptionally soft or soggy ground conditions on your jobsites, tracked pull-behind scrapers will give you the advantage of low ground pressure.

If your jobsites encompass steep grades over long distances, you should consider buying a machine equipped with brakes – a recent addition to pull-behind scrapers. If you have a steep grade of 6 to 8 percent, for instance, over a haul of more than 500 feet, you should have brakes on your scraper so you’re not relying solely on the tractor’s braking system, Miskin says. On the other hand, if you have a steep grade over a short distance, you probably won’t need brakes on your scraper.

“It’s just like driving a car,” Miskin says. “If you have a steep hill, but it’s short, you’re not going to warm your brakes up. But if you’ve got the same steepness of a hill and it’s a long hill, that’s when you start to worry about overheating the brakes and their performance.” See the sidebar on page 77 for information about how scraper manufacturers are working to make sure their new braking systems are compatible with tractor controls.

Steep grades might also prompt you to use single or double scraper configurations for faster transport speeds rather than doubles or triples.

TIP: Consider using a tracked pull-behind scraper if your applications involve working in wetlands or other areas where the ground is soft and soggy.

Improving efficiency
Once you have the right scraper for your applications, make sure the scraper’s hitch height matches the drawbar height of your tractor, says James Hausner, vice president of marketing for Reynolds. Because the hitch height influences the attack angle of the cutting edge, the wrong hitch height can make the scraper difficult to load. Most manufacturers provide for some adjustment of the scraper hitch so you can match it to the tractor, Shimp says.

Operation techniques can make a big difference in productivity as well.
Ken Rempel, owner of Nortec Industries and designer of that company’s scrapers, says a lot of people work the hardest trying to get the last 3 yards of material into the scraper and waste cycle time in the process. “They tend to load the machine up until they can see material running over the sides,” he says. “Really the key in moving dirt is how much you can move in a certain cycle time. And if you always try maxing that out with more dirt than your scraper is made for, then you end up wasting cycle time and your costs go up.”

When material reaches between the 3/4 and full mark, that’s a good time to pick up and go unload, Rempel says.

Operators should also place dirt where it ultimately needs to be so the same material doesn’t have to be moved a second time. This kind of forethought on the operator’s part can eliminate a lot of packing and placing dirt by another machine, Rempel says.

If your operators are transitioning from a self-propelled scraper to a pull-behind type, they may need to be retrained. Pull scrapers are designed to take a shallow cut at high speed rather than a deep cut at low speed like motorized scrapers. Miskin uses a woodworking analogy to explain the difference. “There are two ways to cut away at the wood,” he says. “One is to take a chisel and just hammer through it, making a deep cut. The other is to take a wood plane and shave it off. Pull-behind scrapers just shave the dirt off the top by taking shallow cuts.”

Another good operating technique is making sure your cut areas and fill areas remain flat and smooth. You’ll have better production because you won’t have to slow down when you cross those parts of the jobsite. “I try to get operators to take a nice even cut rather than gouging a hole and coming up and gouging another hole so that the operator behind him now has to deal with that rough ground,” Miskin says.

If you keep having to shift the transmission down as you make a cut, you are probably taking too big of a cut, says Kurt Melling, vice president of sales, earthmoving division, for Ashland Industries. “Typically you come in at fourth or fifth gear to take a cut,” he says. “If you’re going too deep, you’re going to have to start shifting down, and when you start losing ground speed, that’s when you lose your efficiency.”

If you dump your loads in thin lifts of 2 to 5 inches instead of one large pile you get the added advantage of having the weight of the scraper and trailing scrapers compact the lift. Using this method, you can often get at or close to the required compaction level, Miskin says. Dumping in thin lifts can’t always be accomplished because difficult material sometimes clogs up and won’t roll under the blade. But Miskin says he sees a lot of operators working with material they can spread out and don’t.

Other common mistakes include using a tractor with inadequate horsepower for the scraper it’s pulling and failing to adhere to manufacturer’s recommended operating speeds, Hausner says. You should also guard against over-revving the tractor to slow down a load, filling while going up an incline and using high speed with a loaded machine on a rough haul road, says Dick Carrico, marketing manager for Icon Industries.

Walk around focus of daily maintenance
Before getting in or on the scraper for service or repairs, use the safety locks provided to prevent accidental movement of the hydraulic cylinders.

Pull-behind scrapers don’t require a lot of daily maintenance, but you should always walk around the machine to inspect for damage to hydraulic hoses or lines. Also look at the shields and guards to make sure nothing is torn off or bent out of shape. Tighten loose nuts and bolts and verify the machine has the correct tire pressure and securely fastened blades in usable condition. Make sure the hitch pin is tight and in good operating condition. You should grease the scraper daily as well.

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