More Precise Bending at the Push of a Button

When structural steel needs to be shaped, it’s usually done right on the construction site. So it’s good when the bending machine is compact, quiet, and easy to operate. To achieve this, Comeco has replaced the hydraulic system with an electric drive solution featuring an integrated PLC from Nord Drivesystems. The Swedish machine manufacturer has just equipped its second machine series with this technology. And the next one is already in development. 

Fredric Hallberg demonstrates what his machine can do. He places 32-mm-thick rebar between two guide rails on the turntable and starts the motor. With a gentle whir, the turntable rotates and bends the rigid bar as if it were made of modeling clay. Hallberg had previously specified the shape the rebar was to be bent into with just a few button presses on the control panel. 

From a discovery in the warehouse to a solution partner 

Hallberg is the owner and CEO of the Swedish mechanical engineering company Comeco. What he is demonstrating here is what typically takes place directly on construction sites: Before steel bars can be woven into mesh or reinforcement cages, they must be bent into the appropriate shape. This shape can vary from one construction project to another. Construction workers therefore usually perform this precision bending on mobile, manually operated rebar benders, such as those manufactured by Comeco. 

Comeco is a small company based in Enköping, Sweden, near Stockholm and Uppsala. In 1991, the machinery manufacturer began producing radiant heaters for the construction industry. In 2009, cutting and bending machines for reinforcing steel were added to the product portfolio. Construction equipment rental companies account for 80% of their main customers. This makes it clear: Ideally, the machines should be compact, easy to transport, and simple for different users to operate. These are the features Hallberg wanted to improve on his hydraulic machines.

“Around 2015, we wanted to further develop our machines to make them more service-oriented, safer, and quieter,” he explains. “By chance, we discovered an older machine at our facility at that time that had a NORD nameplate attached to its drive.” Contact was established with the drive solutions manufacturer, and Hallberg decided to replace the hydraulics in the next Comeco machine with an electric drive system from NORD. Following an initial bending machine for 16-mm-diameter rebar, Comeco has also developed machines for 20- and 25-mm rebar. Just recently, the machine for 32-mm rebar—which Hallberg demonstrated—was completed.

Reduced to the Essentials

Two factors are crucial for rebar bending machines. First, the angle that the rebar must follow must be specified; second, the motor’s speed determines the force with which the bar is bent. “The old hydraulic solution was really very mechanical,” recalls Jonas Bergvall of the Nord sales team in Sweden. “The bending machine was adjusted using set screws. This always required a test bend to see if the angle was correct.” Furthermore, the electrical system of the hydraulic design was very complex, which made maintenance time-consuming and could only be performed by a few employees. Added to this were its bulky design and noisy operation.

The Nord solution reduced everything to the essentials. It consists of a 3-stage 2.2 kW BLOCK parallel shaft gearmotor with an encoder. With its slim design, it is particularly well-suited for space-saving installation. Its monoblock housing design guarantees a long service life and low maintenance requirements. Despite its compact size, it delivers torques of up to 3,500 Nm in the size used here. A 2.2 kW NORDAC FLEX SK 210E frequency inverter is mounted on the gearmotor; it is operated via the parameter box and offers a comprehensive functional safety package. It is NORD’s most flexible frequency inverter, which can be adapted to any application thanks to its scalable functionality and modular design. Instead of complex wiring for the hydraulic control system, the electronic drive requires only a power connection. All functions are controlled by the NORDAC FLEX’s integrated PLC, a requirement specified by the customer, Comeco.

Ease of use was a key selling point

The drive solution impressed with its ease of use. Using the control display, the user sets the speed, angle, and operating mode via arrow keys. There is no need to navigate through various menus. The integrated PLC transmits the selected angle to the motor – whose position is monitored by the encoder – as well as the required gear ratio to the gearbox. When the bending process starts, the gearmotor moves the turntable according to the setpoint values, causing the bar guides to bend the rebar into the specified shape. Six different bending settings can be selected using preprogrammed controls and saved via the PLC, allowing multiple bars to be processed in sequence. Individual specifications can also be set on the display.

“We worked intensively on how to implement the system as leanly as possible,” says Bergvall from Nord. The parameter box has reduced the number of switches required to a minimum, so that the machine can be operated with just a few buttons. Nord programs how these buttons are assigned and what the display shows in each case according to customer specifications. “The number of digital inputs in the frequency converter is limited,” explains Bergvall. “We’ve carried out extensive programming here and can now offer the same functionality while using fewer digital inputs.”

Complete Drive Solution from a Single Source

Comeco relies on Nord as its system supplier and sources the complete drive solution from a single source. This has cut assembly times for the bending machines by nearly half. The drive solution itself has proven to be a key success factor for Comeco. “We are currently the only manufacturer of this type of machine. We operate in a very narrow niche,” says Fredric Hallberg. And Comeco intends to expand further in this niche. Currently, the company sells the bending machines primarily in Sweden, Norway, and Finland. Hallberg’s goal is to also place the machines in other European countries.

He intends to continue this journey with Nord. “Nord responds very quickly to our needs and develops the drives we require,” he says. “Our collaboration so far has been exemplary and will continue.” Thanks to the scalable PLC, a bending machine for the next size of rebar will soon be launched on the market. It will be capable of bending steel bars with a diameter of 40 mm. In addition, the entrepreneur plans to integrate Nord solutions into his rebar-cutting machines in the future.

Bilder: NORD Drivesystems