Today, sustainability is also a top priority in the plastics industry. An important step in this direction is therefore the recycling and processing of recyclable plastic packaging materials. Extrusion lines have to meet particularly demanding requirements in this environment. For the reliable drive of the screw, Diamat Maschinenbau GmbH therefore relies on air- and water-cooled vector frequency inverters from Gefran, as these are particularly robust, durable, compact and precisely tailored to this area of application.
Diamat Maschinenbau GmbH was founded in 1976. The company, based in Dinkelsbühl in Middle Franconia, builds machines, equipment and tools for the production, processing and recycling of plastics. "Our goal is to make many of our machines fit for the circular economy," reports Uwe Stark, Managing Director of diamat Maschinenbau GmbH. Especially in the field of flat film extrusion, the company has a wealth of experience and numerous references worldwide. The films produced with the manufacturer's machines impress with their clarity, stiffness, transparency, strength and suitability for further processing. These flat films are then processed into food packaging, for example," says Stark.
In order to generate as high a recycling share as possible here, the company gears its machines accordingly so that packaging materials can be reused several times and offers turnkey solutions for processing PET waste into high-quality films such as A-PET, C-PET and PET-G. However, single-screw extrusion can process not only high-quality bottle regrind, but even large quantities of film and die-cutting grid material without any major impact on film quality. The company guarantees a drying value of ~ 50 ppm and thus a low IV loss, i.e. an intrinsic viscosity that is as constant as possible.
With energy-saving and highly flexible friction, crystallisation and pre-drying systems, the company covers a broad spectrum from ground material to finished film. With an automatic filter system, lower-quality materials can be transformed back into high-quality products. This is a demanding task, because when processing post-consumer waste, more contamination and greater wear due to more abrasion on the machine parts must be expected. This is why the manufacturer's extrusion lines for melting plastics are designed to be particularly robust and durable in order to cope with demanding tasks in harsh environments.
Gefran frequency inverters provide the right drive concept
"The drive is the heart of every machine, so when we select our drive components, we pay particular attention to ensuring that they are reliable, durable and user-friendly," Stark tells us. "For our extrusion lines, we're talking about a power range of up to 400 KW, so our main concern is to use powerful frequency converters that, moreover, meet these high requirements."
Since the machine manufacturer needed a solution tailored to its requirements, which many competitor products did not meet, it has been working with Gefran since 2012. The innovative drive components of the ADV200 series convinced him on the one hand in terms of robustness, and on the other hand they are not overloaded with unnecessary features and setting parameters that only complicate operation or commissioning unnecessarily. "The units are therefore tailored exactly to the core competence required at our company," explains Stark. Another important point was electromagnetic compatibility - EMC - i.e. the reduction of disturbing harmonics for the electrical network. "In order to comply with certain limit values, it is important that the enclosure can be designed accordingly," Stark continues. "Gefran provides us with optimum support here. Even if several inverters are used on one machine, the legally prescribed EMC guidelines can be complied with."
ADV200 - especially suitable for plastics extrusion
Diamat Maschinenbau GmbH has been using the vector frequency inverters with field-oriented control of the ADV200 series with air cooling as the main drive for the screw in the extruders of film stretching lines for several years now. "Very high forces have to be applied when the screw rotates, because this compresses and melts the plastic," explains Stark. "This in turn requires high currents and optimum control for constant motor speed so that the screw rotates evenly - Gefran converters are ideal for this task."
Specifically for the plastic extrusion sector, Gefran offers the ADV200 series of scalable frequency inverters with power ranges from 0.75 KW to 1800 KW and a supply voltage from 400 VAC to 690 VAC. They can be used with asynchronous and synchronous motors with or without encoders. With encoderless synchronous control, they achieve a torque accuracy of < 3% absolute to the setpoint. This saves energy without reducing the material quality.
Considerable space savings thanks to innovative water cooling system
In addition to the air-cooled ADV200 variant, the compact ADV200 LC is particularly suitable as the main drive for the extruder screw. The product designation LC stands for liquid cooled and describes an innovative cooling system with water or oil for electrical and mechanical units, which drastically reduces the size of the frequency converter. "On the one hand, we offer the liquid-cooled version as an integrated control cabinet version with heat exchanger - or if the user does not want to have water connections in the control cabinet, with the option for through-hole mounting," reports Giuseppe Savoca, sales manager at Gefran. "The use of anti-condensation sensors and humidity sensors can also effectively prevent condensation in the inverter."
The vector frequency converter with field-oriented control from 30 KW to 400 KW with integrated mains filter and choke can be easily integrated into existing systems and is often used when extrusion or injection moulding lines are already equipped with water cooling. A sophisticated cooling system of aluminium tubes and stainless steel connectors with internal separation between electronics and water cooling provides excellent corrosion protection. For sizes up to 55 KW, the braking resistor can be mounted directly on the heat sink. An integrated coolant temperature control function is used to control an external valve for the drive and motor.
Although the units with water cooling are much more compact than the air-cooled version, they still offer comparable performance. The control structure, operation and programming are also the same as the ADV200 series and the same options are available to the user with the ADV200 LC. Incidentally, Gefran's vector-controlled frequency inverters with DC bus power supply are extremely energy-efficient.
Since diamat Maschinenbau GmbH is primarily committed to topics such as sustainability, recycling, future viability and energy efficiency, the company has been integrating Gefran's ADV200 LC water-cooled systems in its extrusion lines since 2019, in addition to the air-cooled frequency inverter - with the aim of convincing an ever larger customer base of the water-cooled variant over time.
Service is a top priority
Overall, the machine manufacturer from Dinkelsbühl is very satisfied with the service. "Gefran is always a reliable partner for us and offers top support at all times," concludes Stark. "We appreciate that and would like our users in plastics processing to continue to benefit from the advantages of the air- and water-cooled vector frequency converters with field-oriented control in our extrusion lines in the future."