Equipment Focus: Shear Attachments—May/June 2004

Choosing a mobile shear attachment is no easy task, but it can be easier if you keep these points in mind as you shop.

By Jim Fowler

Since their introduction to the scrap industry some 25 years ago, mobile shear attachments have become an essential tool in many processors’ equipment lineup. 

Originally, these shears were promoted for their ability to reduce manpower and increase safety. The productivity of a medium-sized shear, for instance, could reportedly replace three to five torchcutters. That kind of cost savings coupled with improved safety led to immediate acceptance of shear attachments. Today, one industry source estimates that there are 2,000 to 3,000 shear attachments in use in North America—and that number continues to grow.

Currently, about 10 manufacturers produce shear attachments for the scrap market, all of whom are highly competitive and passionate about their products. The various shears have similarities as well as differences, so you—as a potential buyer—need to take the time and do the research to be sure you’re making valid comparisons among the different producers. Here are some points to keep in mind:

Material Matters. The first step in buying a shear is thinking through what you expect the shear to accomplish. That would include not only the material you will be cutting but the material on your “wish list” to cut as well. If you aren’t buying or accepting particular grades of scrap because you can’t handle them with your current processing equipment, be sure to mention that to the manufacturer. In short, the shearmaker needs to know the realities of your operation as well as your dreams to determine the right shear for you. As you begin your research, don’t fall for the idea that bigger is always better, advises one manufacturer. Instead, he suggests, “consider sizing your shear to handle 80 percent of the material you’re processing in your yard.”

The Machine Behind the Shear. A shear attachment can only perform as well as the excavator or material handler behind it—or, more specifically, as the hydraulics of the machine behind it. Hydraulics involve flow and pressure, with flow determining the system’s operating speed and pressure determining its hydraulic power (expressed in pounds per square inch)—and those features come from the base machine. 

Since the hydraulics on most excavators or material handlers are within 5 percent of the 5,000 psi rating common in such machines today, the shear won’t know the difference—as long as the flow and pressure are good. The critical point is to make sure you have an optimal match between the shear and the excavator/handler.

The Power Question. A shear attachment is, at root, a big lever. Hydraulic oil is pumped from the excavator/handler to the cylinder, generally at 5,000 psi. The cylinder drives an upper movable jaw, which is essentially a big lever arm. The diameter of the cylinder together with the stroke length of the cylinder rod dictates, in part, how much cutting power the shear delivers.

The other two factors that dictate a shear’s power are the length of the upper-jaw lever arm and the lever-arm ratio, which is determined by the distance from the cylinder connection on the upper jaw to the main pivot group—the center pin that holds it all together. The size of the pin can also affect leverage. There are engineering formulas to measure shearing force, and you should ask the manufacturer how its shears stack up according to the laws of physics. 

Throat force is one of the most common specs quoted regarding shearing power, though manufacturers disagree about whether it’s a meaningful indication of cutting power. Other points where cutting force is measured include the apex, where the upper primary and secondary blades come together, and the piercing tip at the end of the shear. 

Another measurement used by one manufacturer is the torque generated by the shear. As he explains, this measurement “gives an overall indication of the cutting capability of the shear, an idea of what the force is along the length of the jaw—the total force developed by the shear.” 

You also need to ask at what angle the blades are shearing. “There’s a fine line between too much angle and not enough,” says one shearmaker, adding, “I talk about what an edge can cut, not how much force it has at the blades.” 

While the formula for determining shear force is straightforward, the variables in the equation lead to pluses and minuses depending on what is expected of the shear. That’s why it’s important to look at the shear and base machine as a package, says one manufacturer who stresses the need to get the best all-around performance. That means considering the size of the cylinder, the length of the stroke, the length of the jaw, and the operating pressure of the excavator.

Power-to-Weight Ratio. Shear attachments are being built lighter to increase their power-to-weight ratio, manufacturers note. One way to accomplish this is through a larger-diameter cylinder with a shorter stroke, which moves the center of gravity back toward the excavator/handler. “This allows the operator to go to a smaller excavator—which means lower acquisition and operating costs—while maintaining the same shear force,” a shearmaker says. The objective is to get the same or more shearing power on a lighter base machine to reduce the processing cost per ton.

Another lightweighting strategy involves using new (and generally proprietary) steel alloys for the shear’s jaw and body. 

An added benefit of this trend, says one producer, is that lighter shears have greater mobility, thus reducing the static time between shear cuts. 

The heavier the shear, the more time and force it takes for the excavator or material handler to maneuver the shear between cuts. 

Processing Speed. Processing speed starts with the excavator/handler. All shear manufacturers would like to see the hydraulic oil pumps of the excavator/handler tied together—a process called “summing the pumps”—to get maximum oil flow at 5,000 psi, which is ideal for shear attachments. 

To increase cycle time—that is, processing speed—some manufacturers have added speed valves or regeneration valves that reroute the hydraulic oil so the rod-side oil flows to the bore-side. This makes the jaw close faster since the oil doesn’t circulate back through the hydraulic oil tank.

Manufacturers use various types of speed valves. As a result, you should discuss the relative merits of these valves to determine what would be best for your operation. 

One shearmaker cautions, however, that you want the cycle time fast, but not so fast that the operator can’t keep up with the shear. Otherwise, the operator could end up making cuts he did not intend to make. Also, a cycle time that’s too fast could become a safety issue.

In addition to cycle time, shearing force and blade condition affect processing speed and productivity.

Another aspect of productivity is positioning the shear for optimum cutting, which leads to the next point—rotation.

Rotation. Manufacturers have varied feelings about rotation—the ability of a shear attachment to rotate 180 or 360 degrees—and its importance in scrap processing applications. While scrap processors didn’t initially care for rotation, a shearmaker notes, more buyers are choosing it today because the rotating feature enables the shear to be positioned for optimal cutting.

Another manufacturer says he finds about a 50/50 split between those who want rotating shears and those who don’t. “Those who don’t, say they don’t want the operator spending half the day rotating the shear when he should be cutting scrap. Those who do, ask: ‘How can the operator maneuver the scrap to cut it without a rotator?’” Yet another says he finds 75 percent of shear operators use no rotation. Since you have to give up some power for rotation, most go for the power, he notes.

On the other hand, one shear producer recommends a rotator because he has found that the same operator running the same excavator/handler can increase production 10 to 15 percent in a given shift with a rotator on his shear.

As for the amount of rotation, several manufacturers claim that scrap processors don’t need 360 degrees of rotation, that 180 degrees is enough. 

Reach. Generally, manufacturers don’t view reach as an issue for the scrap industry—at least compared with the demolition business. As one shearmaker puts it, “I’ve never seen reach as a determining factor. Most of the time you bring the shear down to the ground anyway. What you do have to think about is that more reach means more weight. I don’t think reach is a real consideration in scrapyards.”

Another producer acknowledges that while reach is not critical for the scrap industry, there are some applications where it could be important, such as barge or railcar dismantling.

Visibility. Visibility refers to how well an operator can see beyond the shear attachment to view the material being cut. According to most shearmakers, visibility—which is determined by the shear’s profile—isn’t a problem issue in the scrap industry. As one veteran observes, “Some people talk about it, but it’s never been an issue in any instance I can recall. If you have a rotating shear, you can position the material almost any way you want.” Another adds, “It’s not really something to think about. Visibility is relative to how a particular shear manufacturer is spinning it.”

Safety. Shearmakers certainly agree that safety is an important consideration and that the operator should be in a cab protected by a metal cage with a polycarbonate shield. Though cutting mild steel is generally not a concern, there is the chance that hardened material such as axles, gears, and spring steel can fly back to the cab.

Such material should be avoided because it can shock-load the hydrau-lic system, potentially damage the blades, and put undo stress on the shear and excavator. Since hardened steel can end up in a scrap pile, however, one manufacturer says that every cab should be protected and that personnel in the yard should observe the safety distance from the shear specified by the manufacturer.

Maintenance. Since maintenance means downtime, less maintenance equates to more operating time and, hence, greater productivity. Not surprisingly, then, shearmakers have worked to ensure that their shears require less maintenance overall and that any maintenance is easier and faster to perform.

When weighing the maintenance features of different shears, ask how the shear is made—for instance, is it cast or fabricated? What steel is used and what is its strength-to-weight ratio? Keep in mind that a shear is made of steel and its purpose is to cut steel, so a stronger, more abrasion-resistant steel will suffer less wear. Also ask whether the shear’s wear parts are bolted or welded on? How many times can the blades be rotated—four times, eight times?

Maintenance should include greasing, checking the condition of the blades, checking for gaps between the blades, as well as making sure the fasteners are tight on the knives and rotator system. 

One manufacturer gives great importance to shimming to ensure proper cutting performance. “You can’t tolerate large gaps between the upper and lower jaws,” he states. “A gap can cause jamming problems with the shear, which is time-consuming to solve.” An anti-jam device is reportedly in the works.

Typically, when processing most grades of scrap, blades are rotated every 80 hours and shimmed so you keep your shear tolerance tight, adds another shearmaker. As the blades wear away and a larger gap develops over time, the shear isn’t as productive. “Instead of cutting, it’s trying to rip the steel,” he says. “This requires more from the excavator and shear cylinder to deliver production levels achieved when the blades were new. It puts a lot of strain and stress on the shear as well as the excavator.”

Warranties. When it comes to warranties, shearmakers offer everything from 12 months or 1,500 hours, whichever comes first, to 12 months or 2,000 hours to 18 months or 2,500 hours. 

One manufacturer says his company has always had a money-back guarantee: “If the shear isn’t 100 percent what we promised it to be, we’ll give the buyer his money back.” Another asserts, “Our reputation is to be fair regardless of the warranty.” Yet another stresses that “if a shear passes the test for a 12-month, 2,000-hour period, it won’t normally see any flaws due to a design or manufacturing deficiency. If it’s properly maintained and you’ve had it for a year, you’ll have it for a long time.”

Which begs the question: What is the expected life of a well-maintained shear attachment? The answers range from three to 18 years, with five to seven years being the average life span.

Shearing Smarts

What can you do to increase the productivity and longevity of your shear attachments? Here are some suggestions from the manufacturers:

• The excavator or material handler is the driver behind the shear—that’s where shear performance starts. As such, maintain your excavator/handler regularly and be sure its hydraulic flow and pressure are as close to new as possible. The best shear in the world won’t work properly if the base machine can’t do its part.
• Shear knives do the cutting, so keep them sharp and rotate them regularly.
• Help your operator develop a sense of ownership in the shear. After all, it’s up to him to operate and maintain the shear properly.
• Follow the instructions in the owner’s manual. Grease the shear, keep the blade tolerance close, make sure all fasteners are tight, and ensure that the shear is well-balanced with the excavator/handler.
• Establish a cutting sequence for your scrap. When the blades are sharp, for instance,
• cut the thinner, lighter material. As the blades wear, process the heavier material. Another example: Stainless steel coils can be cut better with sharp blades. As the blades wear, don’t flip them right away. Instead, move to plate-and-structural or cast—that is, other materials that don’t require as sharp a blade or as high a tolerance.