A move to larger machine sizes and the introduction of an electric/ hydraulic hybrid series were announced recently by injection machine builder Arburg, Inc. For the first time, the company is moving to hydraulic press sizes larger than 300 tons. It is also planning larger models in its new all-electric line.
Arburg decided to go into larger-size machines because customers requested it, says Herbert Kraibuhler, managing director of technology and engineering at Arburg’s parent company in Germany. His colleague, Michael Grandt, managing director for commercial and financial activities at Arburg GmbH, notes that other machinery suppliers have become more competitive with Arburg by introducing smaller machine models. Arburg’s response was to develop larger presses.
Arburg is expanding its Allrounder S line of fully hydraulic machines with a new 350-ton model 720 S. Previously, Arburg’s biggest machine was the 275-ton 630 S model. The new unit has tiebar spacing of 28.35 in. square, and it sports a new injection unit with a shot capacity of 45.4 oz, injection pressures up to 36,250 psi, and a choice of two screw sizes. Arburg plans to introduce a 440-ton unit by the end of the year. One 440-tonner has already been sold to a U.S. customer.
Highlight on hybrids
Arburg unveiled the Allrounder C Advance, a new line of hybrid machines that feature servo-controlled plastication and a variable-speed main pump motor for energy savings, combined with hydraulic clamping and hydraulic servo-controlled injection for accuracy and repeatability.
The new six-model line from 33 to 220 tons is based on Arburg’s fully hydraulic Allrounder C press. However, special Advance models will also extend to the Allrounder S range in the near future. The Advance package features an electric screw drive (dubbed Eldos), the new Arburg Energy-Saving System, and a position-regulated screw. Together, these features are said to deliver faster cycles and lower energy use plus accurate, quiet operation. The machines also have Selogica controls.
Eldos is a servo-electric direct screw-drive system that reduces hydraulic oil requirements, since none is used in this function. Plasticating functions, now independent of the other process movements, can be overlapped with mold movements or part ejection, saving cycle time. Eldos can reduce energy requirements up to 20%, says Tony Firth, U.S. sales director.
Arburg also developed a special electronic system that regulates the hydraulics. The new Arburg Energy-Saving System (AES) anticipates oil volume and pressure demands and adjusts the speed of the pump motor through use of a variable-frequency drive. Some other systems have variable-speed pumps to control oil flow, but the motor for the pump runs continuously at full throttle, even when the pump is idle. In contrast, the AES can reduce the speed of the motor to optimize energy efficiency.
AES regulates the speed of the variable-displacement pump so that oil flows only when it is needed, and that flow is continuously monitored for operating efficiency, says Firth. The speed of the pump motor is infinitely adjusted to meet the power requirement using a frequency converter.
The new Advance line also uses a position-regulated screw (PRS) to achieve accurate and repeatable shot size. Offered as an option on its C and S series hydraulic machines, PRS monitors injection pressure using pressure transducers. The transducers trigger valves on the twin injection cylinders. PRS also has a stroke-measurement system to determine screw position. Any injection-speed profile and/or holding-pressure profile can be attained by regulating the pressure on the injection pistons. The PRS system is significantly more accurate than a conventional closed-loop system, says Firth.
Bigger electric machines
Larger sizes of Arburg’s new modular electric line are coming in the next 12 to 18 months. “In the U.S. market, some purchasers of machines up to 300 tons have a preference for electric models,” Firth explains. The Allrounder Alldrive line, which made its debut in an 88-ton model at last year’s K 2001 show in Germany, will range from 17 to 485 tons. These modular machines have water-cooled servo-electric motors for plasticating, injection, and clamping, plus a choice of hydraulic or electric operation for the auxiliary axes such as core pull or ejection. The clamp has a five-point toggle design.
“All-electric and hybrid technologies will gain more and more market share in the next five to 10 years,” says Kraibuhler. Although the Alldrive is more expensive than the new Advance line, Arburg officials suggest that high-end applications requiring a clean- room (no-oil) environment could be one area where users might choose the all-electric design. The weaker points in an all-electric model may be nozzle contact force as well as core-pull and ejector force, says Arburg Inc. president Friedrich Kanz. The Advance model may provide the same performance as the Alldrive at a lower price, he adds.
“It is not our job to convince a customer that a hydraulic, hybrid, or all-electric is the solution. We will offer all three lines, then help customers make a decision as to which machine type is best for their operations,” says Firth.