Flexibility is key: Screw pumps in oil-supply systems

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Courtesy of ALLWEILER GmbH

Flender AG, a subsidiary of Siemens AG, has been using screw pumps from Allweiler AG for more than 25 years. Flender’s plant in Voerde, Germany (in the industrialized Ruhr region) manufactures gear units for extruder systems and vertical mills. The pumps supply the gear units with oil that is needed both for lubrication and for cooling. Large vertical mills require as much as 2000 l/min in order to achieve the required cooling capacity of 400 to 500 kW. In extruder gear units, pump capacity is usually 1200 l/min and cooling capacity is approximately 600 kW. Because gear pumps are unable to achieve the high capacities required, they are generally unsuitable for use with these systems. The trend towards ever-larger systems with elevated capacity requirements is another reason for the popularity of screw pumps. Flender is also examining the feasibility of using screw pumps with ball mills in the cement industry, since they are better suited to this application as well. In this case, vertically immersed screw pumps of the “RUV” series are under consideration.

Individual solutions
In decades of use, Allweiler’s “SN”, “SNS”, and “SNF” series have proven to be ideal for use with extruder systems. According to Jens Jürgensen, the director or product management for oil supply systems, Allweiler’s flexibility is a major advantage. “Every customer has different requirements for extruder systems, so we depend on suppliers who are highly flexible and can fulfill even special wishes quickly.' For example, some operators must meet a variety of materials guidelines or they may have specific preferences for the motor coupling and piping connections. In fact, one major benefit of the “SNS” series is its vertical, space-saving installation.

In addition, Allweiler pumps effectively resolve the problem of air dissolved in the oil through design details and special dimensioning that guides air bubbles contained in the oil into the rear-mounted screw chamber. There the air bubbles are re-incorporated into the solution. This design avoids generation of noise and prevents premature wear to the pump. Even the flow rate and oil volume are selected for each system so that most of the unavoidable quantities of air can escape. The pumps are driven by three-phase motors running at a speed of 1200 1/min. (60 Hz) and 1500 1/min. (50 Hz).

Wide viscosity range
Chamfering of the spindles is carefully matched to the oil quality being used. Oil of the “VG320” quality has an ideal viscosity and has proven to work effectively. When the machine starts, oil temperature is 15 °C with viscosity of about 2400 mm²/s; in continuous operation, oil temperature hits 60 °C with viscosity of approximately 100 mm²/s. Temperature can reach as high as 70 °C in extruder gear units. Allweiler screw pumps cover these temperature and viscosity ranges without limitations.

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