Günther Heisskanaltechnik Hot runner engineering for all-electric injection moulding

Editor: Eric Culp

Günther’s complete hot runner solutions promote energy efficiency and provide a technological basis for cleanroom applications.

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An important element of mould design, hot runner engineering influences the construction, efficiency and cost of heavy-duty injection moulding tools. It can also promote energy efficiency and support cleanroom moulding. Hot runner technology specialist Günther Heisskanaltechnik GmbH, working with partners Arburg and Ernst Rittinghaus, developed an efficient hot runner system that met stringent cleanroom requirements and exhibited it at the 2012 Medtec trade fair for medical technology.

The clean, efficient 16-drop Günther hot runner with electrically driven NTT valve gate nozzles ran on Arburg’s electric 520 A Allrounder injection moulding machine with a 16-cavity mould produced by Rittinghaus. The application demonstrated was the production of 1.06-g polypropylene collecting tubes—metering chambers for laboratory analysis—in 5.8-second direct-injection cycles. This all-electric system was able to deliver higher precision and use less energy than a pneumatically designed system.

For the Medtec demonstration, Günther’s design department developed a complete mould half that was then built by Rittinghaus in close consultation with Günther.

Electric valve gate

The NTT type of valve gate nozzle is installed from the parting line and can therefore remain on the machine while maintenance work is performed. Another distinguishing feature of this nozzle is that it has two fits. These not only ensure exact positioning on the pitch spacing, but also provide optimum protection for the nozzles and cabling against any leakage that might occur between the manifold and the nozzle. The manifold area is sealed off from the cable ducts by means of the fits.

The 16-cavity valve gate mould for the collecting tubes is equipped with a powerful servomotor (a linear actuator) to drive the sliding-plate mechanism. Thanks to a finely graduated gear, this drive closes and opens the valve gate needles in less than 0.2 seconds, an actuation speed that is necessary to ensure the desired short cycle times. Another advantage of the drive is that it requires little installation space.

The motor is controlled by a modular servo controller. The system designer has the option of integrating it into the moulding machine’s control cabinet or into a separate controller enclosure with a multifunctional control panel. The needles can be moved into any position, and reference runs are not necessary, because the servo drives have absolute encoders.

The sliding mechanism’s precise transmission and the actuator’s exact repetition accuracy make possible a valve gate needle positioning precision of better than 5 µm.

Valve gate technology

The Günther valve gate nozzle series fitted in the mould features optimum thermal separation between the two components of its shaft. This ensures very good insulation in the front area of the shaft and, accordingly, holds the loss of heat between the hot runner nozzle and the mould cavity to an extremely low level.

Another advantage derives from the innovative design of the contouring needle guide, which is made of powder-metallurgical steel.

The optimised valve gate allows noncontact, low-wear operation. During the closing movement, the needle is centred in a conical guide until it moves down precisely into the cylindrical guide. The needle guide can easily be changed if necessary, without the inserts having to be reworked.

The needles are driven and controlled by the servomotor-powered sliding-plate mechanism. The preferred drive for close nest pitches, it enables all needles to be opened and closed precisely.

Special openings in the mould clamping plate allow the valve gate needles’ downstroke depth to be individually adjusted from the outside while the needles are still mounted. In addition to this mechanical option, the controller in the servo drive provides a convenient way to set the downstroke depth automatically; depths can be set in steps of 0.01 mm without any need to take the mould off the machine.

As this technology does not require utility supply bores in the clamping plate, it supports the design of highly compact moulds even for complex parts.

Cost savings

Günther’s high-efficiency complete hot runner solutions offer maximum cost-cutting potential for injection moulding. Unlike selective, local system optimisations, they are equally effective in helping reduce energy costs, ensure reliable process control and eliminate mould making problems.

Günther Heisskanaltechnik GmbH

Frankenberg/Eder, Germany