Customers expect modern plants to have increased environmental protection. Consequently, WMV Apparatebau deploys modular constructed frequency converters with integrated energy recovery for driving their centrifuges. This makes it easy to benefit from a major saving potential.
WMV Apparatebau GmbH is based in Windeck, Germany, their patented Vario-Cent system for centrifuges still forms the foundation of the company's success, even today, almost four decades later. The company with approx. 80 employees offers individualized large plants based on customer specifications for the cleaning and coating of parts, but also builds standard machines in various sizes for the manual placement and operation.
Such customized machines are required in many production operations, for example the removal of oil from bulk mass-produced parts, the drying of small parts, as well as the centrifugation of coating residues and similar. Frequency converters perform the associated speed up to 750rpm. Alternating-current asynchronous motors are used to produce the rotary movements.
Recently, another complete plant for corrosion-protection handling was supplied for a coating subcontracting operation in Italy. With a footprint of approx. 70 x 40 m, it is suited, for example for, the fast throughput of tons of screws deployed in sectors such as the automotive industry. Since 2009, Siemens Sinamics G120 and G120D frequency converters have been used for the rotary movements in this plant.
Integrated energy recovery
Dipl.-Ing. Lothar Peukert, WMV sales manager, explained the technical finesses of these products as being the reason: "Even the energy recovery integrated in these devices saves a significant amount of energy for our customers; our estimates indicate that such a saving can be as high as 20%." A major advantage of these devices is also their modular construction. The devices consist of a control unit (CU) and an appropriate power module (PM) that can be individually combined with each other.
Fourteen Sinamics G120D converters supply the centrifuges in the pre-treatment areas of the plant. These units include oil-removing devices, washing stations and drying devices. Because these centrifuges have a relatively small moment of inertia, drive powers up to 5.5kW suffice. "For this reason, we have decided on the distributed Siemens Sinamics G120D frequency converters", reported Lothar Peukert, who added: "Their placement near the drives means we no longer need the switchbox and so save a significant amount of space in the plant."
In addition, a further seven Sinamics G120D converters are used for controlling the lift drives for the devices that transport the goods within the plant.
Via Profibus to the plant control
These modular devices consist of the CU240D DP control unit and the PM250 power module for the energy recovery. Because these devices can be integrated very easily NAMUR-conform via the Profibus in the plant control, the installation work is optimized and the commissioning times reduced. "We are very satisfied with the capability and the product quality of these frequency converters", summarized Lothar Peukert.
The compact F3E (Fundamental Frequency Front End) technology keeps the system-perturbation effects significantly smaller than for a standard converter. To achieve similarly good values with a standard converter, it would need to be operated with a choke with at least 6% impedance, something that is not economically feasible. The power modules with a bidirectional input-current converter permit the regeneration of process energy to the supply system without requiring either a brake chopper or a brake resistor.
The described Italian plant for the corrosion-protection coating of screws consists of eight coating centrifuges of the TULZ900 type in a line. The goods weighing up to 250kg are immersed, centrifuged and tipped in a bucket with 900mm diameter and 650mm height. The centrifuges are driven by a 15kW asynchronous motor fed by a Siemens Sinamics G120 converter.
The heavy moved weights supply a large amount of power to the supply system
Every two minutes, a new bucket enters the plant while a completed bucket exits; this results in a throughput of approx. 7.5 tons/hour. The containers are accelerated and brought to a stop as many as six times per cycle. This is done after the immersion of the buckets in the corrosion-protection liquid contained in the zinc laminates. The centrifuges separate any excessive liquid and prepare the workpieces for drying in the oven and the next immersion action.
The total weight to be decelerated each time for each coating centrifuge consists approximately of 250kg for the workpieces, 70 kg bucket weight and around 500 kg weight to be moved, such as for the bucket acceptance. Lothar Peukert commented: "This shows that the energy recovery, easily implemented with the Siemens Sinamics frequency converters, makes a major contribution to the energy saving and thus for the conscious use of resources."
Small system perturbations
The Sinamics G120 and G120D converters cause only small system perturbations. The power consumed from the power supply system is also up to 20% less than for comparable devices. The advantages for the user include the absence for the need of a line reactor and also the connection cross-section can be kept relatively small.
The modular construction means that should service be required, the module can be replaced individually, a feature that highlights the ease of servicing the devices. The new cooling concept makes the Sinamics devices very robust, something particularly advantageous in working areas subject to contamination because the heat produced is dissipated exclusively as convection cooling at the external device heat sinks. If extremely high ambient temperatures mean this does not suffice, the remotely mounted Sinamics G120D frequency converters can be equipped with an external cooling system above 4KW that is automatically activated until the device temperature returns to the normal range. This means any possibly disturbing fan noise occurs only for a limited time.
Ecological and economic
WMV Apparatebau GmbH in Windeck proves that the upgrade to and the deployment of modern frequency converters with integrated energy recovery pays for itself. It allows its customers to save not only much energy for the cleaning but even more for the corrosion-protection coating of workpieces. The modular design of the Siemens Sinamics G120 and G120D frequency converters makes them an interesting and capable drive solution for centrifuges. For Lothar Peukert, they represent an important step for achieving an ecological and economically useful drive technology: "Nowadays, everything concerns environmental protection, something we obviously happily follow with our plant engineering – literally and also unbelievably economically."