November, 2025- Maximum line speed, minimum width of edge trim, few cobbles that can be cleared rapidly, plus quick, easy knife changes. These are just some of the demands that operators of slitting and cut-to-length lines ask of the companies that build scrap choppers.
Jock Buta, president and CEO of Butech Bliss in Salem, Ohio, says there are three main styles of choppers. The lawnmower chopper features two blades, one fixed and one on a rotating drum. The cutting is “very loud, very violent. Most people don’t use them anymore,” he says. The other two are helical choppers, featuring two drums that rotate in opposite directions, in which the knives meet to trim the strip edge. A helical chopper typically has the knives at a helix angle, rather than straight, cutting across the width with less force all at once.
“If you trace that angle on the drum’s surface, it would be a three-dimensional curve. The original (and later) choppers have a 3D curved cutting edge that is very expensive and difficult to make and sharpen. What’s significant about the design my father [ John R. Buta] patented is if you use a shallow helix angle, the 3D curve can be approximated with a flat 2D curve. The cutting edge of the knife is much more simply made because it’s a flat profile from a rectilinear block of tool steel, which is just as effective” as the 3D curve.
“That was a big milestone in the development of scrap choppers 40 years ago. Operators struggled to shim, sharpen and perform other tasks to get them to cut.” The new design created a system that is easy to maintain and provides much longer knife life, Buta says.
“Another major innovation occurred 20 years ago when Butech redesigned the knife hub by reorienting the side against which the knifes are held, eliminating the need to add shims to a knife after sharpening. So we added a shimless version of the original design.”
Buta says most choppers on the market mimic the approximate helical cutting but “there are still subtleties that Butech developed that others do not capture.”
For example, Butech custom designs each entry chute to provide self-threading of the edge trim during threading and even after loss of trim.
Choppers perform a vital function in creating clean-edged strip while increasing yield.
Butech offers 25 models of choppers for a wide range of materials, strengths, widths, thicknesses and applications.
DEALING WITH CAMBER
“When you talk about yield loss, ideally a processor wants to trim as little width from the coil edges as possible. However, wider edge trim strands allow for easier guiding down the chute, but camber or varying strip-width results in loss of edge trim that restarts as a thin strip, often corkscrewing into a difficult-to-thread shape. You don’t want that to catch on anything, mess up your tooling or wrap around knife hubs,” Buta explains. “If a whole line must stop because of that cobble, you want to clear it quickly. You want an easy opening to the entry area.” Nearly every line inevitably stops due to a cobble, so even if the frequency is minimized, the chute design must guarantee a quick clearing of the cobble.
While line operators feed strip through a slitter or trimmer, camber can vary left to right. “You might lose edge trim or go from wider or thinner so companies feel they have to widen [the edge trim] due to camber. You must have an entry chute that will thread material to the knives properly at the beginning of the coil. Having self threading at the entry chute and elsewhere can be a critical aspect to the chopper in total,” says Buta.
JOCK BUTA, BUTECH BLISS
Another important factor is the speed of the chopper. If the knife drum turns more slowly than the strip is moving, material will back up, potentially creating a cobble. If the line moves slower than the chopper, when grabbing edge trim strands, it will yank it and possibly damage the prime material and the knives.
“So matching the line speed and the chopper is very important. You don’t want the knives ripping instead of cutting. Good choppers have high response drives. Some lines have high acceleration and deceleration rates, and the choppers must match that,” he says.
CHANGING KNIVES
When operations are running around the clock and maintenance is scheduled for a short period, quick-change chopper heads are a must. Butech Bliss offers designs to meet that need. Operators can lift the quick-change head out and replace it with another that’s already loaded with knives. “Some slitting and CTL lines are running so fast or cutting high-alloy super-hard material that, even with some of the latest, greatest tools, the knives won’t last long enough for a regular scheduled outage,” Buta says.
In response, Butech developed a chopper head with a wider knife so that when it dulls, the operator can shift it over a little bit and another section of knife takes over the cut. “You can index the head over a particular cutting position.”
One design approach for high-volume processing with significant uptime is a double hub. This consists of two chopper knife hubs side by side that can be indexed quickly from one position to another. “You can keep the knives going depending on the material you are running, from high hardened material on one coil to lighter gauge on another,” Buta explains.
Then, Butech Bliss can create choppers with double motors and double drives: “Flat’s more suited for 24/7 operations, or for when a knife fractures and you have to replace it right away.”
WHAT TO ASK
One of the most impactful considerations, which Buta says is under recognized, is line speed. “All processors emphasize yield but they think the impact of their scrap choppers is limited to minimizing yield loss from edge trim width,” Buta says.
However, adding ¾-inch of edge trim width on a 72-inch-wide line represents a mere 1 percent yield loss. That is dwarfed by the drop in production when running the line slower. Running a line at 20 percent reduced speed because the chopper can’t reliably guide the edge trim or cobbles due to poor speed match, represents a 20 percent drop in production. That’s why choosing the highest performing chopper is absolutely critical, says Buta.
“I was in a plant with a relatively new chopper, and the operator was grumbling about having to run at low speed. They did not have a good speed match and struggled threading the edge trim. It was alarming that they ran at two-thirds normal speed,” says Buta. “That is a lot of productivity and money they were losing. Companies should ask the operators these questions. That’s where all the subtleties of a Butech design is important.
“Our variety of chopper models, design types and custom engineering provide the broadest range of solutions to ensure maximum productivity relative to scrap chopper designs. We provide more options to both maximize uptime and minimize downtime,” he says.
SMART CHOPPER
Butech Bliss engineers are contemplating the future of metal processing. “We are looking at the integration of drive controls between the slitter and chopper; implementation of sensors to detect material fed into and processed by the chopper; a tool that performs cycle counting; using complex algorithms for different gauges, strengths and other variables; and lastly, being able to predict when the knife will fracture so that users can take a maintenance outage before it fails.”
Operators may want to consider the impact of line speed on productivity. It may be better to trim a wider edge than sacrifice output.
Customers are seeking predictive and preventive maintenance that can be incorporated into control systems, Buta says. If the company “can embed chips in the knives and arbors to keep track of the last time the tools were changed and give them a history of maintenance, to optimize knife life,” that would be useful. Then users can enter that data into AI systems to inform predictive maintenance protocols.
ENGINEERING AND SERVICE
Butech has installed more than 450 scrap choppers over the past 40 years. Buta estimates that at least 330 of those remain in operation. “We regularly upgrade, rebuild and replace components to extend the life of the ones still in service.”
What differentiates Butech from all others is its wide variety of proven chopper designs, in addition to the customization performed with every installation, paired with support services. For example, says Buta, “We spend so many engineering hours to make sure the self-threading chutes perfectly nest with each slitter, which substantially reduces the need for operator intervention.”
Butech carries a heffy supply of knives in inventory for 25 different models, including many different grades depending on what material is being processed, as well as precision sharpening. “That service is low cost and turnaround time is quick. We also have an in-house rebuild shop. Someone sends their chopper in and we will disassemble and put back together and ship it back in a weekend.” For even faster service, the company has a 24-hour field service crew available “for urgent repairs to get a broken-down chopper back into operation in a shift.”
Butech Bliss, 330-337-0000, butechbliss.com
