New fully closed-loop injection machine series.

A new "C" series of fully closed-loop, hydraulic-clamp injection machines is being introduced to the North American market by Arburg, Inc., Berlin, Conn. The Allrounder C series has been offered in Europe for about a year and consists of eight machines from 33 to 110 tons, with tiebar clearances of 10.63 in. and 14.57 in. square, and five screw diameters ranging from 20 to 40 mm.

The Allrounder C design combines many Arburg standard features and flexibility of machine configurations. The four Allrounder 270 C machines with a tiebar clearance of 10.63 in. square accommodate clamping forces of 33, 44, or 55 tons; four Allrounder 370 C machines with tiebar clearance of 14.57 in. square are available in clamp forces of 66, 88, or 110 tons. The 270 C and 370 C versions accept two injection-unit sizes, and each of the eight C series machines is available with three possible screw diameters.

The possibility for many configurations is said to provide an exact solution to specific production requirements, says the company. For example, the 66-ton 370 C machine can be configured to combine large tiebar spacing with a small injection unit and 20-mm screw--important in the U.S., where the tendency is to mold smaller parts in larger mold bases.

CENTRAL OR ECCENTRIC INJECTION

The same flexibility is evident in the machines' operating features. C-Series machines are available in two versions: fixed central injection and horizontally displaceable injection unit. Both configurations are available for the same price. In the horizontal displacement mode, or so-called "Vario Principle," the injection unit can be repositioned horizontally at any point along a 120-mm path on the 270 C or 170-mm path on the 370 C. In both fixed central and horizontally displaceable versions, the injection unit is contained in a modular assembly that is capable of vertical parting-line injection when equipped with the proper adaptation.

One advantage of the Vario Principle is that it can be used as alternative to vertical parting-line injection, which can be impractical on larger machine sizes. Instead, the injection unit can be displaced horizontally to inject at the optimal point for the mold design. This permits, for example, injecting at the end of a part to permit a straight linear filling pattern along the length of the cavity, without requiring a long runner or offset mold mounting on the platens (see diagram). The Vario approach can accommodate a hot-runner system, and central mold-clamping force is maintained even when the injection unit is eccentrically positioned because the mold is centered with respect to the platens.

The C machines are also designed for relatively easy changeover of the plasticating cylinder. The barrel and screw are equipped for quick central coupling. Connections for heater bands and thermocouples are located in a central manifold and are automatically connected during cylinder installation. The barrel length is consistent for any size of injection unit, simplifying changeover.

The two-stage backpressure profile is capable of both positive and negative backpressure control. Negative backpressure relieves the pressure in front of the screw during recovery and minimizes the frictional shear developed by the screw. By decompressing the material after dosage, injection units on the C machines are able to operate with an open nozzle, providing advantageous flow characteristics.

PRECISE CLAMPING ACTION

The clamp is said to be operated with a high degree of precision. For extra stability, the moveable platen is supported on horizontal and vertical rails mounted on the machine base, as well as guided along four individually removable tiebars. The hydraulic clamping system consists of two internally combined cylinders responsible for mold movement and clamping pressure.

Employing a second cylinder for movement is said to allow precise velocity control, eliminating the "slipstick" effect at low speeds.

A patented ring piston system exchanges oil over the shortest possible path to open and close the mold, Arburg says. Oil travels between the piston's forward and rear chambers rather than to and from the main tank, saving energy and minimizing pressure and speed losses.

The hydraulic ejector is integrated into the clamping system. During mold opening and closing, simultaneous movement of the nozzle and ejector is possible, helping to minimize overall cycle time.

SEPARATE HYDRAULIC MANIFOLDS 

Clamping and injection units operate from separate hydraulic manifolds, said to provide faster reaction times and more precise control. Oil is piped to the manifold, and hoses are kept to a minimum. The manifolds are surrounded by a protective frame that, when removed, gives free access to the valves.

The hydraulic system consists of two regulating pumps, a main pump for movement and a separate pump to maintain pressure. Servo-electric valves regulate speed and pressure. Performance switches have been integrated directly into the electrical connections at the valve, which is said to provide fast valve actuation with only slight energy losses.

The temperatures of the control cabinet, oil, and feed yoke are closed-loop regulated by a cooling-water distributor. Additional hand-adjustable cooling circuits provide mold cooling. In addition, a water-saver valve permits limiting water flow to applications in which it is needed.

CONTROL FEATURES

The machines are equipped with Arburg's Dialogica 16 CRT controller and are capable of storing 100 set-ups per memory diskette. Two-stage screw speed, five-stage injection speed, and 10-stage holding pressure profiles are standard closed-loop functions. Linear transducers measure speed directly at the screw and feed that information back to the control unit.

The C machines include a computer-controlled, four-stage ramping function when changing to a lower speed and at stop. An oil preheat program reduces machine start-up time. Up to eight control parameters out of a total of 50 may be selected by the user for quality monitoring.

Mold and barrel heating are programmable on the CRT. Adaptive heating regulation is said to achieve perfect PID automatically, without calibration, optimizing temperature regulation for each application.

Besides the main control station mounted on a swivel hinge at the rear of the machine, a smaller keypad with start/stop buttons and manual control functions is mounted on the fixed platen for operator convenience.

COMPACT DESIGN

The Allrounder C machine base, which incorporates the oil tank, is freestanding and mounted on anti-vibration pads. Openings on three sides allow for easy part removal and installation of an optional conveyor. The machine itself has a small footprint, Arburg says.

Arburg has installed a C machine for demonstrations at its Berlin, Conn., facility, and will display it at the Plast-Ex exhibition in Toronto this month. Base prices range from $54,500 to $65,910 for the 270 C and from $74,275 to $87,320 for the 370 C. (CIRCLE 3)