Thorsten Wagener/Ute WatermannSince 1922, Oerlikon Barmag's gear pumps have been used worldwide as process engineering components in applications involving chemicals, plastics, colours and dyes as well as PUR.
Gear pumps operate on the principle of rotating displacement. The drive shaft turns the gears. This transports the medium enclosed in the tooth spaces between the gears from the pump inlet to the pump outlet, displacing it to the outlet by the meshing of the gears. As a result of the transport of the medium, the pressure drop at the pump inlet is compensated by the flow of medium, maintaining the conveyance of flow (Fig. 1).
The GM Series
Components capable of withstanding extreme loads - in the automobile and automobile-supply industry, for instance - play a major role in more and more applications today. Particular attention is devoted to the seals that protect these components from penetration by dirt. Here, a new process has been developed with which a special high-pressure technology for small throughput volumes enables considerably more economical application of seals with the same high manufacturing quality. For these and other demanding engineering processes, Oerlikon Barmag has the right components with its gear metering pumps programme.
Wherever high-precision metering of liquids and chemical fluids are indispensable to process stability, Oerlikon Barmag gear metering pumps are there to provide precise flows of material.
Particularly for use in the high-pressure technology described above, with small throughputs, the GM series has been expanded through addition of an option in regard to pressure build-up capacity. Thanks to the improved capacity for pressure build-up at low viscosities (e.g. 250 bar, 100 mPas), higher levels of volumetric efficiency can be achieved, along with a greater usable rpm range. The cost-intensive systems in use up until now are thus joined by a low-priced and robust gear metering pump. For makers of PUR moulded parts, block foam, refrigeration equipment insulation or sandwich panels, this means constant process stability at low investment cost.
The GT Series
Oerlikon Barmag has taken the durability and reliability characteristic of the GM series and incorporated it into the development of its new GT series of metering pumps. Installed up-stream of the GM-series gear metering pumps, these pumps are primarily used for the supply of the various media.
At throughputs ranging between 6 and 4500 litres per hour in the range of up to 25 bar, they operate in the accustomed Oerlikon Barmag process quality. Their main areas of application are the PUR-manufacturing and processing industry as well as the area of fibre-reinforced composite component production. Typical other areas of application can be found in mechanical engineering, in oil tank farm construction, and in chemicals plant construction. The possible media also span an entire range - from the raw materials used to produce polyurethane to paints, oils, adhesives and even waxes and the raw materials used in composites. They are deliverable in throughput volumes ranging from 0.65-3 cm³/revolution and in a second category from 8-50 cm³/revolution and are liquid- or electrically heatable. To accommodate this, the pump is equipped with a temperature sensor bore for a PT 100 temperature sensor.
The main connection measurements within the available sizes are the same; this makes it easy to replace the pumps. This is how the modular design permits quick and efficient, process-specific operational adjustment of the pumps. The pumps are designed to enable both flange and foot bolt connections. The mould plate package sealed with O-rings prevents leakage to the outside - particularly for heavily creeping media. The pump plates are mounted to one another with centre pins. This simplifies the customer's work of assembly and disassembly. The seal casing centred towards the drive shaft considerably reduces the sealing rings' susceptibility to wear. The short, straight flow channel duct provides good intake behaviour and quiet running. The pumps' nominal connection widths are designed so that the standard values can be used for the dimensions of the intake. The product connection can be designed as a threaded connection or with a standard flange. This way, the pump can be flexibly adapted to the customer's production conditions. GT metering pumps can be delivered with or without drive as needed, and a frequency-controlled AC motor with integrated converter is available as a standard solution.
Transfer pump design and operation
Figure 2 illustrates the simple and robust design of the new GT transfer pump. In its standard design, the pump consists of the front plate (1), centre plate with wheels (2), drive shaft (3), plug (4), rear plate (5), seal casing (6), bearing bushings (7), optional flange connection (8), O-ring seal (9), foot bolt connection (10) and flange bolt connection (11). Oerlikon Barmag transfer pumps have a pump housing into which the friction bearings for the pinions and the pinion shaft are inserted. In these cases, bearing lubrication is provided through the medium itself. When the pump is started, adequate lubrication is supplied through runners that extend from the inflow to the four bearings. During operation, the pressure difference between outlet (e.g. 5 bar) and inlet (e.g. 1 bar) creates circulating lubrication of the bearings. The positive effect here is that the medium provides a constant source of cooling for the bearings. This also ensures that the bearings are always bathed in fresh material; this prevents undesirable reactions in the medium.
Bearing and axial clearances are designed to provide sufficient bearing lubrication even at high speeds (1500 rpm). To compensate for lubrication shortages, friction bearings with good flat running properties can be used. This extends service life considerably, particularly where poorly lubricating media are in use. Dry operation often results upon commissioning or during production - in the event of interruptions to the follow-up supply of medium, for instance. Pumps still wet inside with the residue of media previously put through can be operated for up to an additional 20 minutes in this condition.
Where abrasive media are in use, the pump can be fitted with wear-resistant steel bushings. Depending on the filling level of the medium with abrasive fillers, these steel bushings can be coated with additional anti-wear protection (DLC).
Where wear and corrosion-resistance requirements for the friction bushings are particularly high, the bushings can be produced of silicon carbide or zirconium.
As a standard, the shaft seal is delivered with gland packing (PTFE) that is very robust in its resistance to abrasive particles and can be retightened if necessary. Alternatively, the shaft seal can be provided with a low-maintenance radial sealing ring for unfilled media. This ring does not require retightening. Where the shaft seal is subject to high demands, there are low-wearing and maintenance-free, single- and double-action sliding ring seals available. All of the seal variants mentioned are prepared for use with a locking template. Sealing liquid is a liquid seal on the drive shaft that prevents the entry of humidity into the product chamber. This can prevent undesirable reactions (crystallisation) in the product chamber.
The optionally available relief valve in the rear plate of the pump is a spring-loaded design. It may only be activated occasionally as a valve to limit pressure. If larger portions of the flow are dissipated over longer periods of time, a separate valve with return feed to the suction container can be added to the pipeline.
The new transfer pump by Oerlikon Barmag was designed especially for use in coping with high throughputs. Given the extensive development expertise at Oerlikon Barmag for high-performance gear metering pumps, this pump is a guarantee for extended and reliable process control.
(Displacement) - Fig. 1: How the transfer process works